Project PDF

THERMODYNAMICS OF ADSORPTION OF
4-CHLOROPHENOL ONTO ACTIVATED CARBON
BY
JAMES, DAVID OMEIZA
MATRIC NUMBER: 100804045
THE DEPARTMENT OF CHEMISTRY FACULTY OF
SCIENCE UNIVERSITY OF LAGOS, AKOKA, YABA
IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR
THE AWARD OF BACHELOR OF SCIENCE DEGREE
(B.Sc Hons), IN CHEMISTRY.
NOVEMBER 2014

CERTIFICATION
This is to certify that this research project was carried out by JAMES DAVID OMEIZA under the
DIRECT supervision of DR. I.A. AKINBULU for the award of B.Sc. Degree in the department of
chemistry (pure and applied), University of Lagos, Akoka.
JAMES DAVID OMEIZA
Project student
Date: _ _ _ _ _ _ _ _ _ _
DR. I.A. AKINBULU
Project supervisor
Signature: _ _ _ _ _ _ _ _ _ _
Date: _ _ _ _ _ _ _ _ _ _
DR. (MRS) O.T. ASEKUN
Head of Department department of Chemistry
Signature: _ _ _ _ _ _ _ _ _ _
Date: _ _ _ _ _ _ _ _ _ _

ACKNOWLEDGEMENT
I like to seize this opportunity to express my deep sense of gratitude to everyone that have in one way or
the other assisted and encouraged me during the course of my project.
I would like to first and foremost offer my sincere gratitude to God Almighty for the will to continue and
never to give up and to my project supervisor Dr. I.A. Akinbulu for his guidance and assistance in this
research work, to the Head Of Department Dr (Mrs) O.T Asekun and the entire lecturers of the
department of Chemistry, University of Lagos.
I am also thankful to Mr Ahmed for his assistance and to the Chemistry department for providing reagents,
apparatus, facilities and instruments used during my project work.
Lastly, I want to say a big thank you to my guardians Pastor and pastor Mrs Tokunbo and Funmi Johnson
for their support, encouragement and well wishes and also to my parents and coursemates without which
this project work would not have been a success.

ABSTRACT
In this research work, powdered activated carbon was used to remove 4-Chlorophenol from its aqueous
solution. For batch adsorption procedure, operational parameters such as adsorbent dose, contact time,
initial concentration and temperature were studied. The experimental result showed that at an optimal dose
of 0.3 g, the adsorbent capacity increased as the time increase until if became fairly constant at 120
minutes, it also became fairly constant at initial concentration of 150 ppm and generally increased as the
temperature increased. The adsorption equilibrium data was studied using the Langmuir isotherm model
at five different temperatures (298 K, 308 K, 318 K, 328 K and 338 K) to determine the Langmuir
parameters Ka (Langmuir constant) and qm (maximum adsorption capacity) in each case. The isotherm
parameters was then used to obtain the thermodynamics parameters such as ΔH0
, ΔS0
and ΔG0
. The value
of ΔH0
was found to be positive, indicating that the adsorption of 4-Chlorophenol by activated carbon is
endothermic in nature. Negative values of ΔG0
were also obtained. This showed that the reaction was
feasible
The value of ΔH0
was found to be positive, indicating that 4-Chlorophenol adsorption onto powdered
activated carbon is endothermic in nature.

CONTENT
Pages
Title page Certification
i
Acknowledgement ii
Abstract iii
Content iv - vii
List of figures and tables viii - x
Nomenclature xi
Chapter 1.0 Introduction 1 - 35
1.1.0 Activated carbon 1
1.1.1 Structure of activated carbon 3
1.1.1.1 Physical structure 3 - 7
1.1.1.2 Chemical structure 7 - 9
1.1.2 Manufacturing process of activated carbon 9
1.1.2.1 Steam activation 9 - 10
1.1.2.2 Chemical activation 10 - 12
1.1.3 Uses of activated carbon 12 - 13

1.2 Phenolic derivatives 13 - 16
1.2.1 Uses of 4-Chlorophenol 16 - 17
1.2.2 Methods of treatment 18 - 20
1.3 Uv-Visible spectrophotometry 21 - 22
1.4 Adsorption process 22 - 25
1.4.1 Mechanism of adsorption 25
1. Physisorption 25
2. Chemisorption 25-27
1.4.2 Adsorption Isotherms 27
1.4.3 Langmuir adsorption Isotherm 27 - 29
1.5 What is thermodynamics 29
1.5.1 Thermodynamics parameters and their uses 30
1.5.1.1 Enthalpy 31
1.5.1.2 Entropy 31 - 32
1.5.1.3 Gibbs Free Energy 32 - 33
1.5.2 Determine of the Gibbs free energy of an adsorption process 34
1.5.3 Relevance of Free Energy 35
1.6. Aim of the project 35

Chapter 2.0 : Materials and method 37 - 38
2.1. Materials 37
2.2 Equipments and apparatus 37
2.3 Preparation of solution 37
2.3.1 Preparation of test solution of 4-Chlorophenol 37
2.4 Analytical measurement of 4-Chlorophenol 37
2.5 Batch adsorption isotherm 38
2.6 Langmuir adsorption isotherm study 38
Chapter 3.0 : Results and discussions 40 - 59
3.1 Calibration curve 40
3.2 Study of the effect of various parameters on 4-Chlorophenol adsorption41
3.2.1 Effect of adsorbent dose 41 - 43
3.2.2 Effect of contact time 43 - 45
3.2.3 Effect of initial concentration 45 - 48
3.2.4 Effect of temperature 48 - 49
3.3 Adsorption equilibrium study 49 - 50
3.3.1 Langmuir isotherm 50 - 51
3.3.2 Adsorption equilibrium study at different temperatures 51

3.3.2.1 Adsorption equilibrium study at 298 K 51 - 53
3.4 Thermodynamics parameters for the adsorption of 4-Chlorophenol 61 - 63
Chapter 4.0 : Conclusions and References 64 - 67
4.1 Conclusions and future studies 64
4.2 References 65 - 67

LIST OF FIGURES AND TABLES
FIGURES
No. Topic
Fig. 1.0 Granular activated carbon
Fig. 1.1 Powdered activated carbon
Fig. 1.3 Scanning electron micrograph of activated carbon
Fig. 1.4 Flow sheet representation of methods of carbonization process
Fig. 1.5 Structure of 4-Chlorophenol
Fig. 1.6 Uv-Visible Spectrophotometer
Fig. 3.1 Calibration curve
Fig. 3.2 Effect of dosage
Fig. 3.3 Effect of contact time
Fig. 3.4 Effect of initial concentration
Fig. 3.5 Effect of temperature
Fig. 3.6 Langmuir isotherm plot of 4-Chlorophenol adsorption by Activated carbon at
298K
308K
Fig.3.8 Langmuir isotherm plot of 4-Chlorophenol adsorption by Activated carbon at
318K
328K

338K
Fig. 3.11 Plot of RInKa vs 1/T
TABLES
No. Topic
1.0 Amount of Chlorophenols present in industrial effluents
1.1 Health hazards caused by 4-Chlorophenol
1.2 Comparism between physisorption and chemisorption
3.1 Effect of dosage on adsorption of 4-chlorophenol
3.2 Effect of contact time on adsorption of 4-Chlorophenol
3.3 Effect of concentration on adsorption of 4-Chlorophenol
3.4 Effect of temperature on adsorption of 4-Chlorophenol
3.5 Langmuir adsorption study for 4-Chlorophenol at 298K
3.10 Langmuir Isotherm parameters of 4-Chlorophenol-Powdered activated carbon
system
3.11 RInKa and 1/T values

3.12 Free energy of adsorption of 4-Chlorophenol by activated carbon at different
temperatures
NOMENCLATURES
M Mass of activated carbon
V Volume of 4-Chlorophneol solution
Co Initial concentration of 4-Chlorophenol solution
Ce Equillibrium concentration of 4-Chlorophenol solution
qe Amount of 4-Chlorophenol adsorbed per unit mass of the adsorbent
Ka Langmuir isotherm constant L/mg related to free energy of adsorption (Langmuir parameter)
qm Maximum adsorption capacity (Langmuir parameter)
%R Percentage removal
ΔH0 Standard Change in enthalpy of adsorption (J/mol)
ΔS0 Standard change in entropy of adsorption (J/mol)
ΔGo Standard free energy of adsorption
Ppm parts per million
Nm Nanometer

CHAPTER ONE
INTRODUCTION
1.1 ACTIVATED CARBON
Activated carbon also known as active carbon or activated charcoal refer to a wide range of carbonaceous
materials with a high degree of porosity and an extended inter-particulate surface area and widely used
adsorbent in wastewater treatment throughout the world
Activated carbon is a unique material because of the way it is filled with holes of the size of molecules.
One thing that is distinct about these holes is that although they do not contain electrons, they possess
intensive Van-der Waals forces and these are responsible for their adsorption properties.
They are obtained by combustion, partial combustion or thermal decomposition of a variety of
carbonaceous substances such as wood, peat, coal, coconut shell, waste of vegetable origin (e.g nutshell,
fruits) (Amit Bhatnagar and A.K Minocha). The process consist of dehydration of the raw material and
carbonization followed by activation. Active carbon have been obtained as granular activated carbon (Fig.
1.1) and as powdered Activated Carbon (Fig.1.2) shown below
Figure 1.1 Granular activated carbon

Figure 1.2 Powdered activated carbon (PAC)
The granular form of activated carbon shown in Figure 1.1 above has a large internal surface area and
small pore size while the finely divided powdered form in Figure 1.2 is associated with layer pore
diameters and a small internal surface area. In the recent, although activated carbon have been extensively
used as adsorbent, catalyst and catalyst support and in environmental application, their adsorption ability
and catalytic activity are largely controlled by their surface characteristics.
The existing relationship between the surface properties of activated carbon and its effectiveness as an
adsorbent or catalyst emphasizes the importance of developing methodologies to produce activated carbon
with specific properties.
Activated carbon are unique and versatile adsorbents and they are used extensively for the removal of
undesirable odor, color, taste and other organic and inorganic impurities (generally referred to as
adsorbates) from domestic and industrial wastes, for air purification in inhabited places, restaurants, food
processing, removal of color from various syrups and pharmaceutical products, in air pollution control
from industrial and automobile exhausts and in a variety of gas phase applications. They are also well
known for their applications in medicine for the removal of toxins and bacterial infections in certain
ailments.

Adsorption by activated carbons is one of the most frequently used methods to remove organic compounds
from water, because Activated carbon possesses perfect adsorption ability for chlorophenols.
In this project, the objective is to investigate how the adsorption capacity of activated carbon is influenced
by elevated temperatures using different concentrations of parachorophenol as the adsorbate.
1.1.1 STRUCTURE OF ACTIVATED CARBON
Adsorption takes place at the surface of activated carbon. The surface characteristics of activated carbon
play a crucial role in adsorption from aqueous solutions and catalytic properties of carbon. The structure
of activated carbon is classified based on the activities that occur at the surface of the carbon. The structure
of activated carbon surface can therefore be viewed in two dimensions namely: physical structure and
chemical structure
1.1.1.1 Physical Structure of Activated Carbon
This refers to how the atoms of activated carbon are linked together and how this arrangement actually
give rise to the adsorption ability of activated carbon. It also describe the various pore sizes available on
the surface of activated carbon which is responsible for its wide range of applicability in the sense that the
pore size of any particular activated carbon determines to a large extent what it is used for.
The physical structure of activated carbon is further divided into:
• Crystalline structure
The micro-crystalline structure of activated carbon starts to build up during the carbonization process. Its
crystalline structure interlayer spacing ranges between 0.34nm and 0.35nm with a less ordered layer

orientation. The presence of heteroatoms such as oxygen and hydrogen on the surface of carbon is
responsible for the disorder in the layer orientation. R.E Franklin classified activated carbon into two types
based on its graphitizing ability using x-ray studies. He observed that for a graphitizing carbon such as
PVC (poly vinyl chloride) charcoal, the crystallites were mobile and had weak cross-linking from the
beginning of the carbonization. The charcoal obtained was weak and had a less developed porous structure
but its crystallite has a large number of graphitic layer oriented parallel to each other.
As for the non-graphitizing carbon, Franklin observed that during carbonization, strong cross-linking
between the neighboring oriented crystallites were developed resulting in the formation of a rigid
immobile mass. The obtained charcoal are hard and show a well-developed micro-porous structure (R.E
Franklin 1951)
• Porous structure
Non-graphitizing carbon (i.e active carbon with a random arrangement of micro-crystallites, strong cross-
linking between neighboring crystallites and well developed porous structure) was found to have relatively
low density (less than 2g/cm3
).The porous structure formed during carbonization process is further
developed during activation process. Activation process is a process through which small, low volume
pores which increase the surface area of carbon are created within its structure by either heating carbon at
temperature ranges between 600 – 12000
C in the absence of Oxygen or by impregnating carbon with
certain chemicals such as acids, strong bases or salt followed by heating at low temperatures of about 400
– 7000
C. This process enlarges the diameter of the pores and improve their volume. The nature of the raw
material used for carbonization determines the structure of the pores generated and the pore size
distribution.

Activated carbon pores are categorized based on their size and their function. Based on their function, we
have
Pores for adsorption: They are the smallest pores within the carbon particles consisting of gaps between
carbon plates of about 1 – 5 molecular diameter in size
Pores for transport: These are the largest pores within the particle. They vary from pores greater than 5
molecular diameter to visible cracks. They consist of a variety of different sizes and shapes.
Based on their sizes, three groups of pores can be distinguished and they are:
 Micro-pores ( < 2nm diameter)
 Meso-pores ( 2-50nm diameter)
 Macro-pores (> 50nm diameter)
Micro-pores generally contribute to the bulk part of the internal surface area while meso-pores and macro-
pores are generally regarded as highways into the carbon particles and are crucial for kinetics.
According to Dubinin and Zaverina, a micro-porous active carbon is produced when the degree of burn-
off is less than 50%, macro-porous active carbon is produced when the extent of burn-off is between 50%
and 75%, the product will contain a mixture of all types of pores
The classification of pores by Dubinin is based on their width which represents the distance between the
walls of a slit shaped pore. This classification has now been adopted by the International Union for Pure
and Applied Chemistry.
Adsorption in micro-pores whose effective radii is less than 2nm occur through volume filling with no
capillary condensation taking place. The adsorption energy in micro-pores is much larger compared to
other pore types. Their volume range between 0.15 – 0.70cm3
/g.

The dimension of meso-pores range from 2-50nm and their volume varies from 0.1 - 0.2cm3
/g. The surface
area of these pores is about 5% of the surface area of the carbon. They are characterized by capillary
condensation of the adsorbent with the formation of meniscus of liquefied adsorbate. Macro-pores do not
contribute much to the adsorption process in activated carbon due to their effective area which is larger
than 50nm ( 50 – 2000nm range) with a pore volume of between 0.2 – 0.4cm3
/g. They mainly act as
transport channels for the adsorbate to get into the micro-pore and meso-pores. To this effect, each type
of pore plays specific role in the adsorption process.
The porous structure in activated carbon is such that the macro-pores being the pores with the widest
diameter is directly opened to the external surface with the meso-pore linked to it directly and then the
micro-pore branching off from the meso-pores. Two types of surfaces exist and they are internal surface
(Sint) and external surface (Sext). The internal surface of activated carbon is observed to increase as the
temperature increases to 8000
C during carbonization process due to an enlargement of porosity but
decreases as the temperature gets to 9000
C and beyond. At such high temperatures, overheating occurs
and the walls of the carbon begins to fall. This may lead to the closure of pores within the carbon structure.
The internal surface area is given by
(Sint) =
2 × 103
W
L
- - - - - - - - - - - - - - - - - - - - - - - - - (1)
Where (Sint) is the internal surface area in m2
/g, W is the volume in cm3
/g and L is the width in nanometers.
From equation (1) above, the relationship between the internal surface and the pore width is inverse. This
is why the small pore width in micro-pores results in a much larger area than the area of meso-pores and
macro-pores.

The external surface area which can either be the walls of the meso-pores or micro-pore i.e the edge on
the outer facing sheets varies between 10 and 200m2
/g for many active carbon. The difference between
the two surfaces is dependent on the volume of adsorption energy which is very high for micro-pores.
Figure 1.3 below shows the heterogeneous distribution of pores and rough texture on the surface of
activated carbon.
Figure 1.3 scanning electron micrograph of activated carbon
1.1.1.2 Chemical Structure of Activated Carbon
Besides the crystalline and porous structure, an activated carbon surface has a chemical structure as well.
Even though the adsorption capacity of active carbon is determined by their physical or porous structure
it is strongly influenced by its chemical structure. The surface characteristics of the activated carbons are
mainly due to the presence of different functional groups which can either be acidic or basic. The acidic
functional groups can be created by oxidation with oxygen at elevated temperatures or with liquid
oxidants, typically nitric acid. The acidic surface shows cation exchange properties in aqueous solutions.
However if the carbon is de-gassed at a high temperature e.g. 9500
C in vacuum or under an inert
atmosphere and subsequently oxidized at room temperature after cooling, it exhibits basic character and
hence acquires an anion exchange capacity (Bansal R.C., Goyal M 2005).

The component adsorption forces on a highly ordered carbon surface is the dispersive component of Van
der Waals forces. For active carbon, the disturbances in the micro-crystalline structure due to the presence
of partially burnt layer in the crystallite causes a variation in the arrangement of electron clouds in the
carbon skeleton and results in the creation of unpaired electrons and incompletely saturated valencies.
This influences adsorption properties of active carbon especially for polarizable and polar compounds.
Active carbon is associated with heteroatoms such as Oxygen, hydrogen, sulphur, nitrogen and halogens.
These atoms become chemically bonded to the surface of carbon during activation or subsequent
treatment. They are derived from the starting material and may become a part of the chemical structure of
the activated carbon due to partial or imperfect carbonization to form groups like C=O, C=C, C-O-H, C-
H. Activated carbon can also adsorb molecular species such as phenols, Nitrobenzene, chlorophenols,
Nitrophenols, amines and several others. These molecules and heteroatoms are bonded to carbon atoms at
defect positions and give rise to carbon-heteroatom compounds. These compounds formed by the carbon-
heteroatom association are known as surface groups or surface complexes. The presence of these surface
compounds changes or influences the surface properties and the characteristics of activated carbon.
1.1.2 THE MANUFACTURING PROCESS OF ACTIVATION CARBON
Activated carbon preparation is popularly known as activation. However activated carbons are not cost
effective for use as adsorbents in the process of adsorption because of the difficulty in their regeneration
and disposal which made the scientists to rethink about the raw materials which will lead to cut down the
cost of activated carbons considerably. Among the raw materials are animal waste products, plants and
agricultural wastes, industrial wastes etc are the potential materials for the preparation of very low-cost
activated carbons as all materials containing a high fixed carbon content can be activated. The most

common raw material used in the manufacture of activated carbon include: coconut shell, both soft and
hard wood, cow bones, coal (bituminous, lignite and anthracite), peat and petroleum based residues. Other
raw materials from which activated carbon has also been generated are palm kernel, walnut shell, rice
hulls etc. However some of these latter raw materials are not readily available and so their use is limited.
Most of the carbonaceous materials earlier mentioned do have a certain degree of porosity and an internal
surface area of between 10 – 15m2
/g. When activated, their internal surface area becomes more highly
developed by controlled oxidation of the carbon atoms usually achieved through one of the following two
methods of activation stated below
1.1.2.1 Physical or Steam Activation: This process is the most widely used method for activation of
carbonaceous materials. It involves three stages as shown in the flow chart in fig. 1.4 below Firstly, the
carbonaceous raw material is heated in an inert atmosphere in order to dehydrate and devolatilize it at 400
– 5000
C (pre-carbonization). In the second stage, steam is introduced into the reaction chamber and the
carbonized product is activated at very high temperature of 8000
C -10000
C to develop the porosity and
surface area. The chemical reaction that takes place here removes carbon from the pore walls of the
internal surface of carbon and thereby enlarges the pore. Air is then blown into the furnace to convert the
produced gases: CO and H2 into CO2 and steam (partial gasification).
C (s) + H2O (g) → CO (g) + H2 (g) 1.1
2C (s) + O2 (g) → 2CO (g) 1.2
2CO (g) + O2 (g) → 2CO2 (g) 1.3
H2 (g) + 1
/2O(g) → H2O (g) 1.4

1.1.2.2 Chemical Activation: The raw material is impregnated with certain chemicals (activators)
typically acids, strong bases or salt to activate the carbon material. This is the first stage in chemical
activation as shown in fig. 1.4. Examples of such chemicals are phosphoric acid, sodium hydroxide,
potassium hydroxide, zinc chloride e.t.c (most of these are dehydrating agents). This method is used
mostly for production of activated carbon from raw materials such as wood or saw dust. The most
popularly used activating agent is phosphoric acid. The raw material and activator are mixed together to
form a paste/slurry (chemical blending). This is then carbonized in a kiln at about 400 - 6000
C to open up
the cellulose structure thereby creating a porous structure and an extended surface area. Carbon With the
highest surface area will be obtained when the temperature gets to 8000
C (carbonization).
(http://www.iosrjournals.org/)
If the carbonized product is further heated to temperatures of about 9000
C, at this temperature, the walls
of the structure is likely to collapse, leading to a decrease in the surface area of the carbon structure. Lastly,
the activated carbon obtained is then washed with water and dried as shown in Figure. 1.4 below
Figure. 1.4 Flow sheet representation of methods of Carbonization process
CHEMICAL BLENDING
RAW MATERIALS
CARBONIZATION
PHYSICAL ACTIVATION
PARTIAL
PRE-CARBONIZATION
CHEMICAL
WASHING AND DRYING

Raw materials + Activator → Product washed and dried → Activated carbon
Increasing the concentration of the activating agent or altering the furnace temperature (by ensuring that
it does not exceed 8000
C) and controlling residence time can lead to increase in the activity of the activated
carbon.
Chemical activation process normally yield powdered activated carbon but if granular product is desirable,
granular raw materials are used with the activating agent and the same method is followed. This method
needs a stream of mild oxidizing gases for ensuring uniform pore development during oxidation. Activated
carbons produced by this mode is primarily used for gas and vapor adsorption (Yang R.T 2003).
1.1.3 USES OF ACTIVATED CHARCOAL
The use of activated carbon is very diverse and it range from domestic use, pharmaceutical use to food
industry, water purification
1. In the olden days, a suspension of activated carbon is usually given to poisoned patients to relieve them
due to its adsorption ability.
2. Activated carbon is used for purification of liquid sugar by decolorizing the sugar solution before they
are used in production of soft drinks or alcoholic drinks etc. It is also used to remove congeners that affect
the taste and odor of these beverages.
3. It is used in refining of cane sugar by de-colorization of the sugar syrup before being crystallized to
make granulated sugar that is white in color and also to adsorb plant pigments during sugar manufacturing
from sugar cane.

4. Activated carbon is present in carbon filters which is usually used in water treatment plants to remove
taste, odor and colored compounds from drinking water.
5. 50% w/w combination with celite is used in analytical chemistry as stationary phase in low-pressure
chromatographic separation technique of carbohydrates (mono, di, and tri-saccharides) using ethanol
solution (5-50%) as mobile phase.
6. It is also used in filters in compressed air and gas purification to remove oil vapors, odor and other
hydrocarbons from the air.
7. In alcoholic beverage purification, it is used to filter vodka and whiskey of organic impurities which
can affect its color, odor and taste by passing organically impure vodka/whiskey through activated carbon
filter at the proper flow rate.
1.2 Phenolic derivatives
Fresh water crisis, among others, is one of several crucial global issues that is facing man in recent times.
It is a challenge due to the fact that in our day to day life, we make use of water for cooking, drinking,
washing, manufacturing etc.
Many domestic and industrial activities have polluted the surface water and underground water to a large
extent through the discharge of organic and inorganic pollutants into the various water bodies. One of the
most common sets of organic pollutants is Phenol and its derivatives (one of which is Para-chlorophenol).
Phenol is an important industrial chemical used as a precursor or starting material for the manufacture of
many organic compounds. It is used as a chemical intermediate in the production of alkylphenols, phenolic
resins (used as a coating for plywood in the housing industry), aniline, 2-6 xylenol and mainly caprolactam
which is in turn used in plastics making, carpet and textile industries (http://www.honeywell.pmt.com).
Phenol and its derivatives (compounds derived from phenol such as Nitro-phenols and Chloro-phenols)

are used in making detergents, as preservative agents for woods, paints, vegetable fibres, leather, nylon,
fertilizers, fungicides, insecticides, herbicides and as chemical intermediate in the production of
pharmaceutical drugs and dyes.
Phenol and its chemical derivatives find their way into our environment through the effluents of these
chemical industries thereby polluting the environment (Weber, Manfred et al 2004).
Phenolic derivatives such as chlorophenols (which are the largest groups of phenolic derivative)
are classified to be extremely toxic for human beings and for animals. Chlorophenols are a large category
of chemicals with chlorine atoms (between one to five) attached to the phenolic structure. They are
normally used in herbicides (Tsyganok, A.J,Yamanaka et al 1999), Insecticides (Dabo, P.,Cyr, A.,
Laplante et al 2000), wood preservatives and industries as synthetic intermediates or as raw materials in
the manufacturing of pharmaceuticals and dyes (Pera-Titus, M. and Garcia-Molina 2004). According to
Pera-Titus et al, the world market of chlorophenols is about ca. 100
kilo-tones per year out of which heavy chlorophenols is about ca. 25-30 kilo-tones and light chlorophenols
account for 60 kilo-tones yearly. Apart from the taste and odor chlorophenols add
to water even at very low concentrations of 100mgL-1
(Verschueren, K. 2001)., they also cause the
degradation of the water quality for both industrial and domestic use.
This problem has become very significant due to lack of proper water treatment systems that can reduce
the concentrations of these chemical substances that pose a great chemical risk to both human and aquatic
life even at very low concentrations. The presence of chlorophenols has been detected in both surface and
underground waters (Howard, P.H 1989).Toxic reference values was put at 13.0ppb and maximum
average values not exceeding 0.055ppm in surface water (EPA, 1992 Jones, A.P. and R.J. Watts, 1997).

In drinking water, it should not exceed 10ppm. Apart from the taste and odor chlorophenols add to water
even at very low concentrations, chlorophenols also cause severe adverse effects such as carcinogenicity
(Huff. J 2001).. Table 1.0 below shows the various amounts of chlorophenols present in effluents produced
by various industries where they are being used (Busca Guido, Berardinelli Silvia et al 2008).
Table 1.1 Amount of chlorophenols present in industrial effluents
Industry Amount of chlorophenol (ppm)
Coal processing
Oil refineries
Petrochemical manufacturing
Coking plants
Fungicides and Herbicides manufacturers
9 – 6800
6 - 500
2.8 - 1220
28 - 3900
33 – 5400
Due to the toxic nature of chlorophenols, several regulatory bodies all over the globe like the
Ministry of Environment and Forests (MOEF), Government of India and EPA, USEPA have listed one of
them (4-chlorophenol) on the priority-pollutants list. (Hayward , K 1999).
Para-chlorophenol : 4-Chlorophenol also known as 4-chlorophenol is an organic compound with
chemical formula C6H4ClOH. It is a colorless or white crystalline solid when pure, straw colored or pink
when impure with an unpleasant medicinal odor. Chemically, 4-Chlorophenol is acidic because of the
electron withdrawing effect of the phenyl group which makes the OH bond more polar. The presence of
Cl (a strongly electronegative element at the para position of the chlorophenol makes the OH bond even
more polar than we have in phenol and hence enhances its ionization. This accounts for the greater acidity

of 4-chlorophenol than phenols. It is however less acidic than carboxylic acids. It is moderately soluble in
water. The physical properties and structure of 4-Chlorophenol (figure 1.5) is given below
PHYSICAL PROPERTIES
Molecular weight : 128.556305g/mol
Melting Point : 41.440
C
Boiling Point : 2200
C
Water Solubility : 27g/L
Vapor pressure : 0.078 (250
C)
Vapor density : 4.4 (250
C)
Density : 1.31g/cm3
(200
C)
pKa : 9.26
Figure 1.5 Structure of 4-Chlorophenol

1.2.1 Uses of 4-Chlorophenol
1. It is used as an antiseptic to prevent infection
2. It can be used as a disinfectant for homes, hospitals and farmlands
3. 4-Chlorophenol is used in pulp and paper manufacturing
4. It serves as an intermediate in organic synthesis of dyes and drugs
5. It is used for wood preservation, production of herbicides and germicides.
6. It can be used as a solvent in the refining of mineral oil
4-Chlorophenol is one of the very important chlorophenols used in many chemical manufacturing
industries because of its use as a precursor for many organic synthesis, oil refineries, pulp and paper
industries, production of herbicides, use as an antiseptic, disinfection of homes and farmlands. Hence they
are found in our environment from industrial effluents of pulp and paper manufacturing industrial wastes,
run-offs from farmlands where herbicides are being used and wastes from oil refineries. As a result of
these numerous uses, 4-chlorophenol easily finds its way into our environment through wastes from these
industries which most times enters into our water ways since it is quite soluble in water (27g/l) and
therefore pollutes it with taste and odor which makes the water undrinkable because many of these
industries are situated within communities where many people live. When 4-Chlorophenol is discharged
into the environment, due to its toxicity and harmful nature, it poses a variety of danger to both human
and animal life. Below is a table (Table 1.2) that shows health hazards that may occur due to exposure to
4-Chlorophenol

Table 1.2 Health Hazards Caused By 4-Chlorophenol
Exposure type Effect due to exposure
Inhalation Causes headache, dizziness, weak pulse
Ingestion Irritation of mouth and stomach, headache,
dizziness.
Contact with eye and skin Severe irritation and burning
It is therefore very imperative to device means of removing it from our environment (especially waste
water) due to its toxicity and health hazards.
1.2.2 Methods of treatment: Several methods are available for treating the chlorophenolic waste water
like granular activated carbon based adsorption, reverse osmosis, stripping-oxidation and distillation
processes etc. All of these are used for treating organic and inorganic waste. Most of these methods suffer
from some drawbacks such as high capital and operational cost, regeneration cost and problem of residual
disposal. Liquid phase adsorption has been shown to be a highly efficient, well-established technique for
the removal of organic compounds due to its simplicity, adsorbent cost, effectiveness and the availability
of a wide range of adsorbents (Salame I.I Bandosz T.J 2003).
Therefore in this project, I shall demonstrate how to use a low cost adsorbent (powdered activated carbon)
to adsorb 4-Chlorophenol from its aqeous solution. The next paragraph gives a review of the adsorption
of some phenolic derivatives using activated carbon by Song Liu et al., (2010), Lin and Juang (2009) and
Ghatbhande et al

Song Liu et al., (2010) had investigated adsorption of phenolic compounds like phenol, 2-chlorophenol,
4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 4-Chlorophenol and 2,4-dinitrophenol onto
Activated carbon fibers from aqueous solutions. The adsorption capacities followed the order of TCP
>DNP≈DCP > 4-NP > 4-CP > 2-CP > phenol. Adsorption isotherms at different temperatures were
determined and modelled with Langmuir, Freundlich and Redlich –Peterson equations. Thermodynamic
parameters were calculated and correlated with the adsorption behaviours. The effects of solution pH on
the adsorption were also studied. The adsorption mechanism was discussed based on the experimental
results, and the π-π interactions, solvent effects, hydrophobic interactions and molecular dimensions were
considered to be important in the adsorption. Kinetic studies showed rapid adsorption kinetics of the
phenols, due to the open pore structure of the activated Carbon Fiber. The relationship between the steric
effects and the molecular dimension was also proposed.
Lin and Juang (2009) had reviewed the technical feasibility of the use of activated carbon, synthetic
resins, and various low-cost natural adsorbents for the removal of phenol and its derivatives from
contaminated water. They basically involved those research works in their
study in which researchers have worked on inexpensive materials such as coal fly ash, sludge, biomass,
zeolites, and other adsorbents, which have high adsorption capacity and are locally available. Apart from
that they have also made a comparison of their removal performance with that of activated carbon and
synthetic resins and found that adsorbents that stand out for high adsorption capacities are coal-reject,
residual coal treated with H3PO4, dried activated sludge, red mud among those of synthetic resins, HiSiv
1000 and IRA-420 displayed high adsorption capacity of phenol and XAD-4 had shown good adsorption
capability for 2-nitrophenol. These polymeric adsorbents were found suitable for treating industrial
effluents containing phenol and its derivatives.

Ghatbhande et al (2009) Studied the equilibrium kinetics and thermodynamics of the adsorption of 4-
Chlorophenol from its aqueous solution using activated carbon made from bituminous coal in a batch
adsorption system with respect to temperature. Langmuir adsorption isotherm model was used to describe
the equilibrium data they obtained from the adsorption process which lasted for 5hours. They carried out
the batch process at different temperatures to evaluate the effect of temperature rise on the adsorption
capacity of the adsorbate and they found out that the uptake of 4-Chlorophenol increased as the
temperature increases which showed that the adsorption process was endothermic. This rise in the uptake
of PCP was attributed to the enhanced mobility of 4-Chlorophenol ions from the solution towards the
surface of the adsorbent which led to intraparticle diffusion within the activated carbon structure. The
energy of activation and the thermodynamics parameters (Gibbs free energy, entropy and enthalpy) were
determined using the Langmuir constants qm and equilibrium constant Ka. The results they obtained
further confirmed the endothermic nature of the adsorption process.
Phenol and its derivatives are formed when one or more hydrogen atom(s) are replaced on the benzene
molecule. This substitution does not affect the conjugated double bond system of the benzene molecule
which is very stable. When a beam of electromagnetic radiation is passed through a solution of such a
compound with conjugated pi-electron system ( e.g phenol and its derivatives), much of the radiation is
transmitted without loss in intensity but at certain wavelengths, some of it is absorbed. This process is
called absorption and the wavelength at which there is maximum absorption (i.e the wavelength at which
the intensity of the radiation is attenuated most) is called the maximum or peak wavelength or lambda
max. The absorbed radiation is in form of energy that is used to promote pi-electrons from lower energy
levels to higher energy levels or from ground states to excited states. It has been established by Beer and
Lambert that the concentration of the solution of the compound through which the radiation passes is

directly proportional to the decrease in the intensity of the radiation. This is referred to as the Beer-
Lambert’s law. A spectroscopic method has been designed to apply the Beer-Lambert’s law in measuring
the absorbance of solutions of compounds with conjugated double bond systems. This method is called
the UV-Visible spectrophotometry.
1.3 UV-Visible Spectrophotometry
This is a spectroscopic method that measures the extent of interaction between matter (analyte) and
electromagnetic radiation. It is a simple technique in which a beam of electromagnetic radiation is passed
through a solution of an analyte in order to determine the concentration of the analyte. Part of this radiation
is absorbed by the analyte in the form of energy and the energy absorbed is used to promote or excite
electrons from the highest occupied molecular orbital (low energy level) to the lowest unoccupied
molecular orbital (higher energy level). An instrument called the Uv-Visible spectrometer shown below
(Fig.1.6) whose operation is based on Beer-lambert’s law records the wavelengths at which absorptions
occur together with the degree of absorption at each wavelength (absorbance) and then displays the results
on a graph of absorbance versus wavelength.
Figure 1.6 Uv-Visible Spectrophotometer

Beer-Lambert’s law states that the amount of radiation absorbed by a sample solution is proportional to
the concentration of the sample in the solution and the path length of the container of the solution
Mathematically,
A ᾳ Cl
A=ԑCl ---------------------------------- 1.5
where ԑ = Molar absorptivity ( dm3
mol-1
cm-1
)
C = concentration ( mol/dm3
),
l = Path length (cm)
A= Absorbance)
A spectrum of these absorption is displayed on a monitor as a graph of absorbance (A) versus wavelength
(λ). Once the molar absorptivity and path length which are usually constant is known, the concentration
of the analyte can then be obtained by applying the Beer-Lambert’s law. The wavelength at which
maximum absorption takes place is usually referred to as the peak wavelength or Lambda max (λmax).
Absorption of the radiation is highest at the λmax wavelength. A common feature displayed by such
compounds that can undergo this kind of absorption is the presence of a system of extensive conjugated
pi-electrons as seen in 4-Chlorophenol.
Therefore a Uv-Visible spectrophotometer (Figure 1.6) was employed in determining the initial and
equilibrium concentrations of 4-Chlorophenol at λmax = 270nm – 300nm (A.S. Ghatbandhe 2009) and
also to prepare the calibration curve.

1.4 Adsorption process
Adsorption process refers to the series of events that lead to a steady-state adsorption conditions where
there is a physical equilibrium between the concentration of adsorbate in the liquid phase and the adsorbent
phase as a result of forces active within the phase boundaries or surface boundaries.
Adsorption of a solute on to activated carbon may be as a result of high affinity of the solute for carbon
surface or its solubility in a solvent (hydrophobicity in the case of water). The more soluble in the solvent
the adsorbate is, the less likely it is to be adsorbed.
Speaking about the affinity of the solute for the adsorbent, two type of adsorption can be identified. Their
affinity may be due to
i. Van-der Waals attraction ( Physisorption or ideal adsorption)
ii. Chemical reaction ( Chemisorption or chemical adsorption)
Many organic compounds are adsorbed by activated carbon as a result of specific interactions between the
functional groups on the adsorbate and the surface of the adsorbent (activated carbon). This adsorption
shows large range of binding energies from lower energy values commonly associated with physical
adsorption to higher energy values associated with chemisorption.
As earlier stated, adsorption results in the removal of solute from solution and their concentration at the
surface of the adsorbent until an equilibrium is reached between the amount of solute remaining in the
solution and the amount of solute at the adsorbent surface.
This equilibrium can be shown by expressing the amount of solute adsorbed per unit weight of adsorbent
say qe, given by

qe =
(C0 ̶ Ce)V
M
1.6
The above expression is referred to as Adsorption Isotherm equation, Where
qe = amount of adsorbate adsorbed per unit weight of solid at equilibrium (mg/g)
C0 = initial concentration of adsorbate (mg/dm3
)
Ce = equilibrium concentration of adsorbate (mg/dm3
)
V = volume of the solution (dm3
)
M= Mass of adsorbent (g)
The adsorption isotherm is useful for representing the capacity of activated carbon for adsorbing 4-
chlorophenol from aqueous solution. Langmuir and Freundlich equations are common isotherms that
describe adsorption isotherms for various gas-solid, gas-liquid and liquid-solid phases. There are many
other isotherm equations.
There are three main steps involved in the adsorption process of materials from solution by adsorbents.
They include
• The transportation of the adsorbate through a surface film to the exterior of the adsorbent i.e film
diffusion
• Diffusion of the adsorbate within the pores of the adsorbent termed as pore diffusion
• Adsorption of the solute on the interior surface bonding pore and capillary spaces.

Several factors affect the adsorption of 4-chlorophenol by activated carbon. These factors include:
1. The surface area of activated carbon.
2. Pore structure and functional group present at the surface of the adsorbent.
3. Nature of the adsorbate (4-chlorophenol)
4. pH of the solution
5. Activated process to which the carbon was subjected to during activation
6. Viscosity of solution
7. The temperature of the liquid phase and the contact time of the adsorbent with the solution
8. Experimental conditions such as temperature, pressure etc.
1.4.1 Mechanism of adsorption
Activated carbon is a material with surface area made up of millions of pores like a molecular sponge and
the process by which surfaces such as this concentrates fluid molecules by physical or chemical forces is
known as adsorption.
There are two types of adsorption based on the nature of interaction between the adsorbate and the
adsorbent as early stated and they are:
1. Physical adsorption or Physisorption : In the physical adsorption process, molecules are held by
intermolecular forces known as Van-der Waals forces. Thus there is no chemical change or chemical
reaction between carbon and adsorbate. This interaction can be easily reversed by heating or by decreasing
the pressure (gas) because the forces are weak.

2. Chemical adsorption or chemisorption : In chemical adsorption, molecules of the adsorbate reacts with
the carbon surface chemically and are held by much stronger chemical bond. This interaction cannot be
easily reversed.
In order to achieve adsorption, one must ensure that the molecule to be adsorbed has a size close to the
size of the available pore. A plot of adsorption capacity against concentration (for liquids) or pressure (for
gases) at constant temperature gives the adsorption isotherm. Adsorption increases with increase in
pressure for gases and with increase in concentration for liquids and also with increasing molecular weight
within a series of chemical family. This is useful when a particular system has more than one component
to be adsorbed (Marsh, H. and Rand B. J., et al ).
At equilibrium and thereafter, it is observed generally that the higher molecular weight specie of a multi-
component system are adsorbed in preference to the lower molecular weights. This is known as
preferential or competitive adsorption. This usually occurs due to but not limited to the differences in
molecular size and also due to differences in molecular charge and molecular shape.
In general, highly charged species are less preferred by activated carbon surfaces for adsorption. This is
why organic molecules in water are readily adsorbed because they carry less charge relative to water
molecules therefore highly charged molecules are less readily adsorbed compared to molecules with less
charge i.e the specie with the lowest charge is adsorbed first in preference to highly charged species.
In certain cases, some species are adsorbed physically to a low level irrespective of variations in the
operating conditions. In such instances, the method employed is to improve the carbon’s capability by
impregnating it with a particular compound that is chemically reactive towards the specie that is required
to be adsorbed. Since a chemical bond is then going to be formed between the adsorbate and the reaction
sites on the surface of the adsorbent, the resulting adsorption becomes chemisorption. This principle is

applied in many industries particularly in catalysis where the efficiency of a catalyst can be enhanced by
spreading it over activated carbon surface.
Below is a table (Table 1.2.1) that gives the general comparism between physisorption and chemisorption
Table 1.3. Comparism between physisorption and chemisorption
Physisorption Chemisorption
1. Involves low heat of adsorption usually in
the range of 20 – 40KJ/mol
High heat of adsorption in the range of 40 –
400KJ/mol
2.Force of attraction is due to weak Van-der
Waals forces and it is easily reversible
Force of attraction is due to chemical bond
forces and it is not easily reversible
3. It usually decrease with increase in
temperature
Takes place at high temperatures
4. It is related to the ease of liquefaction of
gases
The extent of adsorption is not related to the
liquefaction of gases
5. It forms multi-molecular layer
6. It does not require any activation energy
Forms mono-molecular layer
It requires activation energy

1.4.2 Adsorption isotherms
Adsorption isotherm is a functional expression that correlates the amount of solute adsorbed per unit
amount of the adsorbent and the concentration of the adsorbate left in solution at a given temperature
under equilibrium conditions. Simply put, adsorption isotherm may be described as an equation relating
the amount of solute adsorbed onto the adsorbent and the equilibrium concentration of the solute in
solution at a given temperature.
It is a graph that shows the amount of adsorbate (X) adsorbed onto the surface of adsorbent of mass (m)
and concentration or pressure at constant temperature.
The quantity of adsorbate adsorbed is nearly always normalized by the mass of the adsorbent to allow
comparison of different materials.
It was observed that after the saturated concentration, adsorption does not occur anymore and the graph
becomes flat gradually. At this point, there is limited number of adsorption sites unoccupied on the surface
of the adsorbent and finally it becomes flat completely at which point further increase in the concentration
of the adsorbate does not cause any difference in the adsorption process.
There are several isotherm models for predicting the equilibrium distribution of an adsorbate. Examples
of such models include: Langmuir isotherm, Freundlich isotherm, Temkin and Dubinin isotherm, Gibbs
isotherm, Brunauer Emmet Teller isotherm etc. Gibbs and Langmuir adsorption isotherm are the most
commonly used isotherms in the study of liquid phase adsorption using activated carbon. For this research
work, Langmuir adsorption isotherm was to study the equilibrium.

1.4.3 Langmuir Adsorption Isotherms
Langmuir Isotherm assumes monolayer adsorption onto the surface containing a number of adsorption
site with no transmigration of adsorbate in the plane of surface. This describe quantitatively the formation
of a mono-layer adsorbate on the outer surface of the adsorbent and after that no further adsorption takes
place. The Langmuir isotherm is valid for monolayer adsorption onto a surface containing a finite number
of identical sites. The model assumes uniform energies of adsorption onto the surface and no
transmigration of adsorbate in the plane of the surface. Based upon these assumptions, Langmuir
adsorption isotherm is represented by the following linear equation
1
qe
=
1
qm
+
1
qmKaCe
----------------------- 1.7
Where
Ce = The equilibrium concentration of adsorbate (mg/dm3
)
qe = Amount of adsorbate adsorbed per gram of the adsorbent at equilibrium (mg/g)
qm = Maximum adsorption capacity for forming single layer (mg/g)
Ka = Langmuir isotherm constant (L/mg) related to free energy of adsorption
The values of qm and Ka can be calculated by plotting a graph of
1
qe
against
1
Ce
The Langmuir adsorption requires three basic assumptions and they are that:
1. The surface of the adsorbent is in contact with a solution containing an adsorbate which is strongly
attracted to the surface.
2. The surface has a specific number of sites where the solute molecules can be adsorbed.

3. The adsorption involves the attachment of only one layer of molecules to the surface, i.e monolayer
adsorption.
1.5 What is thermodynamics
Thermodynamics is the branch of science that describes the behavior of matter and the transformation
between different forms of energy on a macroscopic scale. It is concerned with heat and temperature and
other macroscopic variables such as internal energy, enthalpy and entropy that partially describes a body
of matter.
Thermodynamics look into the constraints of behavior of these variables which are common to all
materials. These constraints are expressed in the four laws of thermodynamics.
Thermodynamics arose from the study of two kinds of energy transfer: as heat and as work and their
relationship with the system’s macroscopic variables of volume, pressure and temperature.
A thermodynamic system consist of all the materials involved in the process under study, while the rest
of the universe is referred to as the surroundings. Any system that can exchange energy with the
surroundings is called an open system, if not it is called a closed system. An isolated system is a system
that do not exchange either matter or energy with its surroundings. The interface between the system and
the surroundings is called the boundary. This boundary determines if energy and mass can be transferred
between the system and the surroundings.
Thermodynamic equilibrium refers to a condition in which equilibrium exists with respect to pressure (gas
systems), temperature and concentration (liquid system). A system can be in equilibrium with respect to
any one of the given variables.

The thermodynamics of an adsorption process was used to study the effect of temperature on the process.
Since adsorption is a kinetic process, the rate of removal of the adsorbate can be increased or decreased
by increase or decrease in system temperature.
1.5.1 Thermodynamics parameters and their uses.
The thermodynamics parameters of major concern during the adsorption process of 4-Chlorophenol by
activated carbon are as stated below
1.5.1.1 Enthalpy (H,ΔH): Enthalpy is the amount of heat content used or released in a system at constant
pressure. Enthalpy is usually expressed as the change in enthalpy. The change in enthalpy is related to a
change in internal energy (ΔU) and a change in the volume (ΔV), which is multiplied by the constant
pressure of the system as shown in equation 1.8 below
ΔH=ΔU+PΔV ---------------------- 1.8
The enthalpy value of a reaction helps us to know if heat was released or absorbed in the course of a
chemical reaction. A positive enthalpy value shows that heat was absorbed during a reaction (endothermic)
while a negative enthalpy value indicates that heat was released in the course of a chemical reaction
(exothermic).
Enthalpy is also used to estimate the strength of a chemical bond. Bonds with high positive enthalpy value
requires high energy to be broken and thus are stable while chemical bonds with low or negative values
require less energy to be broken and are relatively less stable.
In an adsorption process, a low positive value of enthalpy indicates that very little heat was required for
the adsorption to take place meaning that the adsorption is physisorption but if the value of enthalpy is

very high, it means a lot of energy is required for the adsorption to take place which makes the process
chemisorption. In summary, enthalpy helps us to know if an adsorption process is due to physisorption or
chemisorption.
1.5.1.2 Entropy (S,ΔS): Entropy is a measure of the disorder of a thermodynamic system. By disorder It
means the number of different microscopic states the particular system can exist in, provided that the
system has a fixed composition, volume, energy, temperature and pressure.
For a reversible process, the change in entropy is given by equation 1.9 below
dS =
dqreversible
T
----------------------- 1.9
The above equation can be regarded as the mathematical statement of the second law of thermodynamics
which states that a closed system has entropy which may either increase or remain constant. Entropy has
the dimension of energy divided by temperature which has a unit of Joules per kelvin (J/K). Entropy
cannot be directly observed but must be calculated.
The entropy of a system depends on its internal energy and external parameters such as volume,
temperature and pressure. This relationship is known as the fundamental thermodynamics relationship
given by equation 1.10
dU = TdS – PdV ---------------------- 1.10
Entropy change is used to describe the direction and quantify the magnitude of simple change such as heat
transfer between systems. It can also be used to predict the outcome of a reaction. Entropy measures the
mixing of substances as a summation of their relative quantities in the final mixture

1.5.1.3 Gibbs free energy
The Gibbs free energy can be defined as the energy available for a chemical reaction that can be used to
do work. It measures the process initiating work obtainable from a thermodynamic system at a constant
temperature and pressure or simply put a system’s capacity to do work. The Gibbs free energy of a system
at constant temperature and pressure is given by equation 1.11 below
G = H – TS -------------------- 1.11
Gibbs free energy is a state function because it is defined in terms of thermodynamic properties that are
state functions as well. Therefore a change in Gibbs free energy of a system that occurs during a reaction
is a change in the difference between the change in enthalpy of the system and the product of the
temperature and change in entropy of the system.
The standard state free energy of a reaction ΔG0
is the free energy change of the reaction at standard state
conditions and is given by
ΔG0
= ΔH0
– TΔS0
---------------- 1.12
The standard state conditions must be such that the partial pressure of any gases involved in the reaction
must be 0.1 MPa while the concentration of all aqueous solution are 1M at a temperature of 250
C (298
K). The following equation (equation 1.13) relates the standard state free energy of a reaction with the
free energy of the reaction at any moment in time during a reaction (not necessarily at standard state
conditions)
ΔG = ΔG0
+ RT InKa ------------------ 1.13

Where ΔG = free energy change at temperature T (K)
ΔG0
= standard state free energy
R = Ideal gas constant
T = Temperature (Kelvin)
InKa = Natural logarithm of the reaction quotient
1.5.2 Determination of free energy in an adsorption process
The Gibbs free energy change (ΔG) of the adsorption process is related to the equilibrium constant by the
classic Van’t Hoff equation (ΔG = 0 at equilibrium)
ΔG = ̶ RT InKa ----------------------- 1.14
According to thermodynamics, the Gibbs free energy change is related to entropy change and heat of
sorption (enthalpy change) at constant temperature by equation 1.12 below
ΔG0
= ΔH0
– TΔS0
Dividing equations (1.14) and (1.12) through by T and equating them, we get
ΔG0
T
=
̶ RTInKa
T
=
ΔH0
T
̶
TΔS0
T
---------------------- 1.15
ΔG0
T
= ̶ R InKa =
ΔH0
T
̶ ΔS0
---------------------- 1.16

Multiplying equation 12 through by a negative sign, we get
̶ ΔG0
T
= R InKa =
̶ ΔH0
T
+ ΔS0
---------------------- 1.17
where, Ka is the Langmuir Isotherm constant, ΔH is the enthalpy change (kJ/mol), ΔS is the entropy
change (J/K mol), R is the molar gas constant (8.314 J/mol K) and T is the temperature in Kelvin.
Gibbs free energy of specific adsorption was calculated from the well-known equation 1.14. The
thermodynamic parameters ΔS0
and ΔH0
were obtained from the slope and intercept of the linear Van’t
Hoff plot of (RlnKa vs 1/T) respectively using equation 1.17
1.5.3 Relevance of free energy
Gibbs free energy is used to determine if a reaction is favorable (spontaneous) or not. Negative value of
ΔG0
indicates that a reaction is spontaneous while positive value of ΔG indicates that the reaction is not
spontaneous or favorable.
1.6 AIM OF THE PROJECT.
1. To demonstrate the phenomena of the adsorption of 4-Chlorophenol on activated carbon and to
determine the adsorption capacity of activated carbon.
2. To study the effect of various parameters such as dose, concentration, contact time and temperature on
the adsorption of 4-Chlorophenol using activated carbon.

3. To determine the maximum uptake of 4-Chlorophenol by activated carbon and to show how the
adsorption capacity of activated carbon varies with changes in temperature.
4. To know if the adsorption process of 4-Chlorophenol by activated carbon is endothermic or exothermic
5. To know if the adsorption process is spontaneous or not by determining the value of Gibbs free energy
ΔG0
using a suitable adsorption isotherm and Van’t Hoff’s equation.

CHAPTER TWO
MATERIALS AND METHODS
2.1 Materials
4-Chlorophenol was obtained from the chemistry department laboratory of the University of Lagos.
Commercial powdered activated carbon was obtained from a local pharmaceutical store.
2.2 Equipments and apparatus
Thermostatic water bath, UV-Visible spectrometer, Analytical weighing balance, shaker, centrifuge
machine, volumetric flasks, glass rod, beakers, conical flasks, Filter paper and measuring cylinders
2.3 preparation of solutions
2.3.1 Preparation of test solution of 4-Chlorophenol
A stock solution of 4-Chlorophenol was prepared by dissolving exactly 1.0 g of 4-Chlorophenol in
distilled water and diluted to 1000 ml. This gave 1000 ml of 1000 ppm 4-Chlorophenol solution. Several
dilutions of stock solution were made to obtain concentrations of 50 ppm, 100 ppm 150 ppm, 200 ppm
and 250 ppm which were required for the adsorption study using the serial dilution formular
C1V1 = C2V2 -------------------------------------------- 2.1
2.4 Analytrical measurement of 4-Chlorophenol
The standard calibration curve of 4-Chlorophenol was plotted by taking the absorbances of several known
concentrations (20 ppm, 60 ppm, 100 ppm, 140 ppm, 180 ppm, 220 ppm, 260 ppm) at the wavelength of
λmax = 272 nm against the concentrations in ppm and a straight line graph was obtained, whose origin is
from zero. A spectrophotometer was used for absorbance measurement.

2.5 Batch adsorption isotherm.
Batch adsorption experiments were performed using an electrical shaker at the speed of 120 rpm and a
thermostatic water bath using a 250 ml conical flask containing 30ml of the 4-Chlorophenol solutions of
100 ppm concentration. The experiment were performed at 250
C throughout the experiment. Other
parameters such as adsorbent dose, temperature, concentration, contact time were either kept constant or
varied as required during the course of the experiment. All the samples were filtered twice after adsorption
and the concentration of 4-Chlorophenol in the filterate were determined by a UV-visible
spectrophotometer.
2.6 Langmuir adsorption isotherm study
The Langmuir adsorption isotherm study is characterized by certain constant values which expresses the
surface properties and the affinity of the adsorbent and can also be used to compare the adsorptive
capacities of the adsorbent for different pollutants. The equilibrium data were analysed using Langmuir
adsorption isotherm. The amount of 4-Chlorophenol adsorbed per unit mass of the adsorbent qe was
determined using the equation below
qe =
(C0 ̶ Ce)V
M
-----------------------2.2
Where
C0 = Initial concentration (ppm)
Ce = Equillibrium concentration (ppm)
M = Mass of adsorbent (g)
V= Volume of adsorbate solution used (dm3
)
The percentage removal of 4-Chlorophenol was calculated by the following equation

%R =
(C0 ̶ Ct)
C0
× 100--------------------------------2.3
Langmuir adsorption isotherm is the most widely used isotherm equation for the presentation of adsorption
data and is valid for monolayer adsorption onto a surface that contains finite number of identical sites and
the linear form of the equation is given below
1
qe
=
1
qm
+
1
qmKeCe
------------------------------2.4
The Langmuir constants were obtained from a plot of
1
qe
against
1
Ce
Where
1
qm
= Intercept and
1
qmKe
= Slope
The thermodynamics of the adsorption process was investigated at temperatures of 298K, 308K, 318K,
328K and 338K. Hence, by plotting a graph of RlnKa vs
1
T
, the values of the thermodynamic parameters
ΔH0
and ΔS0
were obtained from the slope and intercept of the graph respectively.

CHAPTER THREE
RESULTS AND DISCUSSIONS
3.1 Calibration curve
In Analytical chemistry, calibration curve is a plot that shows how the analytical signal of an analytical
instrument changes with the concentration of an analyte. It is a general method used to determine the
concentration of an unknown sample solution by comparing its absorbance to a set of standard samples of
known concentrations.
A series of concentrations in the range of expected concentrations of the analyte in the unknown solutions
were prepared and their concentrations noted. Their absorbance were taken with the aid of a UV-Vis
spectrophotometer and recorded. A plot of their absorbance was plotted against their concentrations which
showed a linear relationship as shown in the graph below.
Fig. 3.1 Calibration curve
A = 0.009C + 0.0761
R² = 0.9981
0
0.5
1
1.5
2
2.5
3
0 50 100 150 200 250 300
Absorbance
Concentration (ppm)

Using the calibration curve, the concentrations of the unknown solutions were extrapolated from the
calibration curve after their response (absorbances) has been taken.
3.2 Study of the effect of various parameters on the adsorption of 4-Chlorophenol by activated
carbon
In this section, the effect of various operational variables such as dose of adsorbent, agitation time, pH,
initial concentration of 4-Chlorophenol and temperature on the adsorption of 4-Chlorophenol by
commercial activated carbon was examined.
3.2.1 Effect of adsorbent dose on the adsorption of 4-Chlorophenol
The effect of adsorbent dose is an important parameter that must be studied during an adsorption process
in order to determine the minimum amount of adsorbent that will effectively remove the 4-chlorophenol
present in the solution without using excess of the adsorbent. This helps to prevent the use of excess
adsorbent dose.
This effect was studied by weighing masses of 0.05 g, 0.10 g, 0.15 g, 0.20 g, 0.25 g, 0.30 g, 0.50 g, 0.70
g, and 1.0 g into 9 different 250ml conical flasks. 25 ml of 100 ppm 4-Chlorophenol solution was added
to the activated carbon present in each of the conical flasks and then agitated for 1 hour at the solution’s
natural pH. The solutions were left for 30 minutes more in order to attain equilibrium and then filtered
twice afterwards using whatman filter paper 1. The clear filterate was centrifuged for 15 minutes and then
analyzed using the Uv-Spectrophotometer. The results obtained are shown in the table below.
Table 3.1 Effect of adsorbent dose on adsorption of 4-Chlorophenol

Mass of P.A.C
(g)
Initial
concentration
(ppm)
Final
concentration
(ppm)
Amount
adsorbed (ppm)
0.05 100 34.32 65.68
0.10 100 24.32 75.68
0.15 100 20.99 79.01
0.20 100 20.43 79.57
0.25 100 17.54 82.46
0.30 100 14.66 85.34
0.50 100 14.10 85.90
0.70 100 14.08 85.92
1.0 100 14.04 85.96
From the table above, it was noticed that as the adsorbent dose increases, the amount of 4-Chlorophenol
adsorbed also increased due to an increase in the number of adsorption sites available on the activated
charcoal. The optimal dose was found to be 0.3g

Figure 3.2 Effect of adsorbent dose on adsorption of 4-Chlorophenol
Amount of 4-Chlorophenol increases as mass of adsorbent increases. However, at adsorbent dose of 0.3
g, the amount of 4-Chlorophenol adsorbed remained fairly constant because as more and more of the
adsorbent is introduced into the solution, the adsorbent particles begin to accumulate at the vacant sites
thereby blocking some of the adsorption sites (Singh K. P., Malik A et al 2008). The dose at the point on
the x-axis where the graph became flat was taken as the optimal dose for the activated carbon which was
0.3 g/25 ml.
3.2.2 Effect of Contact time for adsorption of 4-Chlorophenol onto Powdered activated carbon
The effect of contact time on the adsorption of 4-Chlorophenol was studied in order to know how long it
takes for the adsorption process to reach equilibrium. The experiments were carried out with a constant
dose of 0.3g in about 7 conical flasks containing 25 ml 100 ppm of the adsorbent solution for about 2
hours. The samples were withdrawn at intervals of 20 minutes, filtered and then centrifuged for 14
60
65
70
75
80
85
90
0 0.2 0.4 0.6 0.8 1 1.2
AmountAdsorbed(ppm)
Adsorbent dose (g)

minutes. The concentration of 4-Chlorophenol present in the filterate was determined for all the samples.
Below is a table that shows the results obtained after 2 hours.
Table 3.2.2 Effect of contact time on adsorption of 4-Chlorophenol
Time (mins) Initial conc.
Co (ppm)
Equilibrium conc.
Ce (ppm)
Amount
adsorbed
(ppm)
Amount adsorbed
Per unit weight
qe
20 100 33.66 66.34 5.53
40 100 32.99 67.01 5.58
60 100 31.66 68.34 5.69
80 100 30.21 69.79 5.82
100 100 27.43 72.57 6.05
120 100 24.10 75.9 6.33
The amount of 4-Chlorophenol adsorbed for all the time interval was determined and the amount per unit
weight of the adsorbent qe was plotted against time as shown in Figure. 3.3

Figure. 3.3: Effect of Contact time for adsorption of 4-Chlorophenol onto powdered activated carbon
From the graph above (figure. 3.3), it was observed that the adsorption rate at the first 20 minutes was
very high. This may be due to the presence of large number of vacant sites available on the adsorbent at
the beginning which has led to the rapid adsorption of the adsorbate on the adsorbent surface (Terzyk A.
P 2003.) As the time continues to increase towards equilibrium, there was a drop in the rate of adsorption
at the later stages due to the accumulation of 4-Chlorophenol particles on the adsorption sites present on
the surface of the activated carbon.
3.2.3 Effect of initial concentration on adsorption of 4-Chlorophenol
To study the effect of initial 4-Chlorophenol concentration on the adsorbent, batch experiments were
carried out by placing a fixed adsorbent dose of 0.3 g in five different labelled 100ml conical flasks each
containing various 4-Chlorophenol concentrations of 50 ppm, 100 ppm, 150 ppm, 200 ppm and 250 ppm.
These flasks were agitated for 11
/2 hour and left to stand for 30 minutes in order to attain equilibrium.
Afterwards, the samples were filtered using whatman filter paper and subsequently centrifuged for 15

minutes. The centrifuged samples were then taken to the UV-Visible spectrophotometer and their
absorbances taken as shown in table 3.3
Table 3.3: Effect of initial concentration on adsorption of 4-Chlorophenol
Initial
conc. (ppm)
absorbance Final
conc.
(ppm)
Amount
adsorbed,
(ppm)
Percentage
adsorbed %
50 0.3524 30.7 19.3 38.60
100 0.3800 33.77 66.23 66.23
150 0.3914 35.03 114.97 76.64
200 0.4085 36.93 163.07 81.5
250 0.4569 42.32 207.68 83.07
A graph of the amount of 4-chlorophenol adsorbed was plotted against different concentrations as shown
in the fig. 3.4

Figure3.4: Effect of initial concentration on adsorption of 4-Chlorophenol
It can be observed from figure. 3.4 above that increase in the concentration of 4-Chlorophenol solution
results in an increase in the amount of 4-Chlorophenol uptake by the adsorbent. This was as a result of an
increase in the number of 4-Chlorophenol molecules accessible to each binding sites on the surface of the
adsorbent. Expectedly, an increase in the concentration of reactants leads to increase in the rate of reaction
(in this case rate of adsorption). The rate of adsorption remained fairly constant at an initial concentration
of 150 ppm and above. This may be due to the fact that for the same dose of the adsorbent, more and more
of the adsorbate molecule is being supplied and so the binding sites are becoming saturated with limited
sites left to accommodate more of the available 4-Chlorophenol molecules being introduced into the
system as the concentration increases. . (Uddin M. T., Islam M. S., and Abedin M. Z., 2007)

3.2.4: Effect of temperature on adsorption of 4-Chlorophenol onto activated carbon
In order to determine the effect of temperature on the adsorption of 4-Chlorophenol onto activated carbon,
0.3 g of the powdered activated carbon was weighed into 5 different conical flasks and 25 ml of 100 ppm
4-Chlorophenol solution was transferred into each of them. The samples were then agitated in a water bath
for 2 hours at different temperatures of 35o
C, 45o
C,55o
C and 65o
C. These solutions were then filtered
and centrifuged for 15 minutes and their absorbances determined using the UV Spectrophotometer. The
results obtained is shown in table 3.4
Table 3.4: Effect of temperature on adsorption of 4-Chlorophenol
Temperature ( K ) Initial
conc. (ppm)
Final
conc.
(ppm)
Amount
adsorbed
(ppm)
298 100 21.66 78.34
308 100 13.54 86.46
318 100 12.99 87.01
328 100 12.65 87.35
338 100 10.43 89.57
Below is a graph that shows the effect of increase in temperature on the adsorption process.

Fig 3.5: Effect of temperature on adsorption of 4-Chlorophenol by powdered activated carbon
From the graph above (figure. 3.5) it was observed that the adsorption rate of 4-Chlorophenol was affected
by temperature and it increases as the temperature rises. This could be due to an increase in the average
kinetic energies of the 4-Chlorophenol ions in the solution which means that the individual ions now have
enough energy to penetrate deeper into the pores present on the surface of the adsorbent. Thus further
enhancing the intra-particle pore diffusion. (Celis, R., M.C Hermosin, L. Cox.et al 1999). Therefore, this
suggests that the adsorption of 4-Chlorophenol onto powdered activated carbon is endothermic. This result
is similar to the one reported by Ghatbandhe et al in 2009
3.3: Adsorption equilibrium study
The capacity of adsorbent dose is usually determined with the aid of equilibrium study of any adsorption
process. The most frequently used isotherms are Langmuir, Freudlich and BET . They describe the
equilibrium of the adsorption of materials at a surface boundary at constant temperatures (which is why
they are referred to as isotherms). These isotherms provides certain constant values from which the
76
78
80
82
84
86
88
90
92
295 300 305 310 315 320 325 330 335 340
Amountadsorbed(ppm)
Temperature (Kelvin)

number of adsorption sites present on the adsorbent and can be determined. They are also used to compare
the adsorption capacities of various adsorbents on different organic pollutants.
Langmuir isotherm model was applied to the experimental equilibrium data of 4-Chlorophenol adsorption
in this research work.
3.3.1 Langmuir isotherm
The Langmuir adsorption isotherm is applicable to monolayer adsorption processes taking place at liquid-
liquid or liquid-solid interface. It is the most widely used adsorption isotherm and it is based on the mass
action approach. The linearized form of the isotherm is given in the equation below
1
qe
=
1
qm
+
1
qmKaCe
-----------------------------3.1
Where
Ce is the equilibrium concentration of adsorbate (mg/dm3
)
qe is the amount of adsorbate adsorbed per gram of the adsorbent at equilibrium (mg/g)
qm represents the maximum adsorption capacity for forming single layer (mg/g)
Ka is the Langmuir isotherm constant (L/mg) related to free energy of adsorption
The values of qm and Ka were calculated by plotting a graph of
1
qe
against
1
Ce

3.3.2 Adsorption equilibrium study for 4-Chlorophenol adsorption at different temperatures
Equilibrium studies was carried out for the adsorption process at several temperatures
3.3.2.1 Adsorption equilibrium study for 4-Chlorophenol adsorption at 298K
Table 3.5 presents the experimental equilibrium data obtained for different concentrations of 4-
Chlorophenol solutions at different temperatures
Table 3.5 Langmuir adsorption study for the adsorption of 4-Chlorophenol at 298K
Initial
conc. Ppm
Final
conc.
ppm
Amount
Adsorbed/g
qe (mg/g)
ppm
1/ qe
(g/mg)
1/Ce
(ppm-1)
50 30.7 1.61 0.62 0.0348
100 33.77 5.52 0.18 0.0296
150 35.03 9.58 0.104 0.0285
200 36.93 13.59 0.073 0.0271
250 42.32 17.31 0.058 0.0253

Figure. 3.6 Langmuir isotherm plot of 4-chlorophenol adsorption by powdered activated carbon at
298K
From the above plot, the maximum Langmuir adsorption capacity for forming single layer can be
obtained using the Langmuir isotherm formula below
1
qe
=
1
qm
+
1
qmKaCe
Intercept on the graph = ̶ 1.6182
But
1
qm
= intercept on the graph
1
qm
= ̶ 1.6182
IqmI = 0.62ppm
1
qmKa
= slope
From the graph,
Slope = 62.8
1/qe = 62.808 1/Ce - 1.6182
R² = 0.9154
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.024 0.026 0.028 0.03 0.032 0.034 0.036
1/qe
1/Ce

62.8 =
1
qmKa
Ka =
1
62.8×0.62
Ka = 0.0257ppm-1
Initial
conc. Co (ppm
Final
conc. Ce
(ppm)
Amount
Adsorbed/g
qe (mg/g)
1/ qe
(g/mg)
1/Ce
(ppm-1)
50 27.26 1.90 0.53 0.0490
100 32.17 5.65 0.18 0.0311
150 41.03 9.08 0.11 0.0244
200 56.93 11.92 0.084 0.0175
250 70.32 14.97 0.067 0.0142
Below is a graph that represents the data presented in table 3.6 above

Figure 3.7 Langmuir isotherm plot of 4-chlorophenol adsorption by powdered activated carbon at 308K
From the above plot, the maximum Langmuir adsorption capacity for forming single layer can be
obtained using the Langmuir isotherm formula below
1
qe
=
1
qm
+
1
qmKaCe
But
1
qm
1
qm
= ̶ 0.1716
IqmI = 5.83ppm
1
qmKa
= slope
From the graph,
Slope = 13.4
13.4 =
1
qmKa
1/qe = 13.428 1/Ce - 0.1716
R² = 0.9252
0
0.1
0.2
0.3
0.4
0.5
0.6
0 0.01 0.02 0.03 0.04 0.05 0.06
1/qe
1/Ce

Ka =
1
13.4×5.83
Ka = 0.0128ppm-1
Initial
conc. Co (ppm)
Final
conc. Ce
(ppm)
Amount
Adsorbed/g
qe (mg/g)
1/ qe
(g/mg)
1/Ce
(ppm-1)
50 23.31 2.224 0.4496 0.0429
100 31.75 5.688 0.176 0.0250
150 55.03 7.914 0.126 0.0182
200 67.77 11.01 0.091 0.0148
250 81.16 14.07 0.071 0.0123
1/qe = 12.443 1/Ce - 0.099
R² = 0.9807
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045
1/qe
1/Ce

318K
1
qe
=
1
qm
+
1
qmKaCe
But
1
qm
1
qm
= ̶ 0.099
IqmI = 10.10ppm
1
qmKa
= slope
From the graph,
Slope = 12.44
10.10 =
1
qmKa
Ka =
1
10.10×12.44
Ka = 0.00795ppm-1

Initial
conc. Co (ppm
Final
conc. Ce
(ppm)
Amount
Adsorbed/g
qe (mg/g)
1/ qe
(g/mg)
1/Ce
(ppm-1)
50 21.22 2.398 0.4170 0.0471
100 27.36 6.05 0.165 0.0305
150 48.60 8.45 0.1183 0.0210
200 66.02 11.165 0.0896 0.0151
250 75.14 14.57 0.0686 0.0133
Fig. 3.9 Langmuir isotherm plot of 4-chlorophenol adsorption by powdered activated carbon at 328K
1
qe
=
1
qm
+
1
qmKaCe
1/qe = 9.9321 1/Ce - 0.0804
R² = 0.9375
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05
1/Ce
1/qe

But
1
qm
1
qm
= ̶ 0.804
IqmI = 12.44ppm
1
qmKa
= slope
9.932 =
1
qmKa
Ka =
1
12.44×9.932
Ka = 0.00809ppm-1
3.3.2.5 Adsorption equilibrium study for 4-Chlorophenol adsorption at 338
Initial
conc. Co (ppm
Final
conc. Ce
(ppm)
Amount
Adsorbed/g
qe (mg/g)
1/ qe
(g/mg)
1/Ce
(ppm-1)
50 15.59 2.8675 0.3487 0.0641
100 25.09 6.243 0.160 0.0399
150 37.01 9.42 0.106 0.0270
200 53.23 12.23 0.0818 0.0188
250 70.74 14.938 0.0669 0.0141

-
338K
1
qe
=
1
qm
+
1
qmKaCe
But
1
qm
1
qm
= ̶ 0.0317
IqmI = 31.55ppm
1
qmKa
= slope
Slope = 5.6259
5.6259 =
1
qmKa
Ka =
1
5.6259×31.55
Ka = 0.00565ppm-
1/qe = 5.6259 1/Ce
̶ 0.0317
R² = 0.9604
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.01 0.02 0.03 0.04 0.05 0.06 0.07
1/qe
1/Ce

Table 3.10 gives a summary of the values of the maximum adsorption capacity per unit dose of the
adsorbent qm and the Langmuir constant Ka obtained at different temperatures
Table 3.10 Langmuir isotherm parameters of 4-Chlorophenol-Powdered activated carbon system
Temperature (K) qm(mg/g) Ka(L/mg) r2
298 0.62 0.0257 0.9154
308 5.83 0.0128 0.9252
318 10.10 0.00795 0.9807
328 12.44 0.00809 0.9375
338 31.55 0.00565 0.9604
The table above shows a summary of the values of the maximum adsorption capacity for monolayer
adsorption qe (mg/g) and the Langmuir isotherm constant Ka (L/mg) that are related to free energy of
adsorption at the various temperatures
3.4 Thermodynamics parameters for the adsorption of 4-Chlorophenol onto powdered activated
carbon
The thermodynamic parameters ΔS0
, ΔH0
and ΔG0
can be evaluated from the slope and intercept of the
linear Van’t Hoff plot of RlnKa vs 1/T respectively (R=8.314 J/mol K)

Table 3.11 RInKa and 1/T
Ka (L/mg) RInKa T (K) 1/T (K-1
)
0.0292 29.38 298 0.00336
0.0137 35.67 308 0.00325
0.0072 41.01 318 0.00315
0.00715 41.01 328 0.00305
0.00565 43.03 338 0.00296
Below is a plot of RInKa against 1/T
Figure. 3.11: Plot of RInKa against 1/T
The values of ΔH0
and ΔS0
can then be determined from the slope and intercept of the graph above
Where ΔS0
is the intercept and ΔH0
= ̶ slope
ΔH0
= + 29.22J/mol
RInKa = -29.216 1/T + 130.13
R² = 0.9035
0
5
10
15
20
25
30
35
40
45
50
2.9 3 3.1 3.2 3.3 3.4
RInKa
1/T × 10-3 K-1

ΔS0
= + 130.13 J/K
The standard Gibbs free energy change (ΔG0
) of the adsorption process at the different temperatures can
then be obtained using the following equation
ΔG0
= ΔH0
̶ TΔS0
The following table shows the standard free energy change of 4-Chlorophenol adsorption by activated
carbon at different temperatures
Table 3.12 Free energy of adsorption of 4-chlorophenol by powdered activated carbon at different
temperatures
Temperature (K) ΔG0
(KJ/mol)
298 ̶ 38.75
308 ̶ 40.05
318 ̶ 41.36
328 ̶ 42.65
338 ̶ 43.95
From the values tabulated above, it can be concluded that the adsorption of 4-Chlorophenol onto powdered activated
carbon is endothermic and is therefore favoured at high temperatures. Negative values of ΔG0
also indicates that
adsorption of 4-Chlorophenol onto activated carbon is spontaneous or feasible.

CHAPTER FOUR
CONCLUSIONS AND REFERENCES
CONCLUSIONS
The following conclusions was made from this research work
 The optimum conditions for the adsorption of 4-Chlorophenol adsorption are dose = 0.3 g/L, Co =
150 ppm, Time = 120 minutes, Temperature = 308 K (350
C)
 The equilibrium study of the adsorption of 4-Chlorophenol onto powdered activated carbon
showed that the adsorption process can be described by Langmuir isotherm
 The capacity of powdered activated carbon adsorption of 4-Chlorophenol (qm) was found to
increase as the temperature increases.
 Adsorption is endothermic as ΔH0
value is positive and the positive value of ΔS0
shows that there
was an increase in the degree of disorder of 4-Chlorophenol adsorption. As more energy (heat) is
supplied to the ions in the solution when the temperature increases, their average kinetic energy
also increased hence the increase in their disorder.
 The negative values of ΔG0
showed that the adsorption of 4-Chlorophenol onto powdered
activated carbon is spontaneous and feasible.
FUTURE STUDIES
In the future, the following studies can still be done
 Kinetic studies and desorption of 4-Chlorophenol from activated carbon surface and the
regeneration of activated carbon to determine its reuseability.
 Determination of the number of adsorption sites present on the surface of activated carbon and
the effect of molecular size on activated carbon adsorption

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