Modification Of Surface, Physical And Chemical Properties Of Activated Carbons For Water Purification
The title “Modification of Surface, Physical, and Chemical Properties of Activated Carbons for Water Purification” encompasses a comprehensive exploration of enhancing the efficacy of activated carbons in treating water. Activated carbons, derived from various carbonaceous precursors, undergo alterations aimed at improving their surface characteristics and chemical reactivity for enhanced water purification. This involves strategic adjustments in pore size distribution, surface functional groups, and overall morphology. By tailoring these properties, researchers seek to optimize the adsorption capacity, selectivity, and kinetic performance of activated carbons in the removal of diverse contaminants from water sources. The synergy of physical and chemical modifications contributes to the development of advanced materials capable of addressing specific challenges in water treatment, thereby presenting a significant advancement in the field of environmental remediation.
The purpose of this work was to study the effect of chemical surface properties of
activated carbons for their use in water purification. To achieve this objective,
activated carbon in both granular and powdered forms namely: as received and
devolatilized carbons were prepared. Proximate analysis of the carbon materials
was performed. Mass titration experiments were carried out to determine the point
of zero charge of the activated carbon materials. Again, using an ultraviolet
spectrophotometer, the adsorption of phenol on as-received and devolatilized
activated carbon was investigated. Adsorption isotherms were acquired from which
the monolayer adsorption capacities were calculated.
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Title page
Approval page
Dedication
Acknowledgement
Abstract
Table of contents
List of Tables
List of Figures
CHAPTER ONE:
INTRODUCTION 1
1.1 Origin and nature of activated 1
1.2 Methods of manufacture of activated carbon 2
1.3 Need for present investigation 3
1.4 Objectives and Scope of the study 4
CHAPTER TWO:
LITERATURE REVIEW 6
CHE/2007/063 7
2.1 Preamble 6
2.2 The adsorption process 6
2.3 Historical background of activated carbon 7
2.4 Raw materials for the production of activated carbon 9
2.5 Activated carbon manufacturing process 9
2.5.1 Thermal processing technique 10
2.5.2 Chemical activation technique 13
2.5.3 Steam activation technique 13
2.6 Properties of activated carbon 14
2.6.1 Physical properties 15
2.6.2 Chemical properties 15
2.7 Structure of activated carbon 17
2.8 Applications of activated carbons 19
CHAPTER THREE:
EXPERIMENTAL 22
3.1 Selection of materials 22
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3.1.1 Selection of activated carbon material 22
3.1.2 Selection of adsorbate 22
3.2 Apparatus used 22
3.3 Reagents used 23
3.4 Modification of the activated carbon 24
3.4.1 Devolatilization of the coconut shell based activated carbon 24
3.4.2 Treatment of the activated carbon with nitric acid 24
3.5 Mass titration 25
3.6 Proximate analysis of the activated carbon material 26
3.6.1 Moisture content 26
3. 6.2 Volatile matter content 26
3.6.3 Ash content 26
3.6.4 Fixed carbon 27
3.7 Adsorption experiment 27
CHAPTER FOUR:
RESULTS AND DISCUSSION 28
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4.1 Mass titration 28
4.2 Proximate analysis 36
4.3 Adsorption isotherms 37
4.4 Surface coverage 45
4.5 Discussion of results 46
4.5.1 Mass titration 46
4.5.2 Proximate analysis 46
4.5.3 Adsorption isotherms and surface coverage 47
CHAPTER FIVE:
CONCLUSION AND RECOMMENDATIONS 49
5.1 Conclusion 49
5.2 Recommendations 50
References 51
Appendix A 53
Appendix B 55
Appendix C 60
INTRODUCTION
1.1 ORIGIN AND NATURE OF ACTIVATED CARBON
Carbon is the fifteenth most abundant element in the earth’s crust and the fourth
most abundant element in the universe by mass after hydrogen, helium and
oxygen. Scientists, industries, and consumers use different forms of carbon and
carbon containing compounds in many ways such as activated carbon or carbon in
its active form which can be used to purify water, among others.
Activated carbon is a form of carbon that has been produced to make it extremely
porous and thus have a very large surface area available for adsorption or chemical
reactions.
It can be defined as a microcrystalline non-graphitic amorphous form of carbon
which has been processed to develop a high internal porosity due to its network of
inter-connecting pores.
The history of activated carbon is dated since the fifteenth century, during the
time of Columbus when sailors used to blacken the inside of wooden water barrels
with fire, since they observed that the water would stay fresh much longer. It is
likely that people at that time proceeded by intuition only without having any
insight into the mechanism of the effect. The mechanism was recognized
beginning from the eighteenth century.
In 1862, Lipscombe prepared a carbon material for purifying portable water. This
development paved the way for the commercial application of activated carbon
first for portable water and then in waste water sector.
1.2 METHODS OF MANUFACTURE OF ACTIVATED CARBON
The methods employed in the industrial manufacture of activated carbons are
numerous but consist of three main methods namely; Chemical activation, Steam
activation and thermal processing techniques.
The raw materials or precursors used in the manufacture of activated carbon are as
follows; Softwood, coconut shell, lignite, hardwood, grain and agro products,
bituminous coal, anthracite, etc.
Chemical activation is generally used for the production of activated carbon from
sawdust, wood or peat and uses chemicals for activation. Chemical activation
technique involves mixing an inorganic chemical compound with the carbonaceous
raw materials and the most widely used activating agents are Phosphoric acid and
Zinc Chloride.
Steam activation technique is generally used for coal-based, coconut shell and
grain-based activated carbons and uses gases, vapors or a mixture of both for its
activation.
Thermal processing technique is a separation process that removes unwanted
materials from the carbonaceous precursor used under varying heat applications.
This technique is at a lower cost compared to the two techniques above and meets
all environmental standards, while others need expensive solutions to achieve the
same results.
1.3 NEED FOR PRESENT INVESTIGATION
The need for present investigation of this material cannot be over emphasized. This
is as a result of the pressing need for treatment of waste water emanating from
domestic and industrial concerns.
Activated carbon plays an important role in the purification of fluids (water),
including vegetable oils used in domestic cooking and as a precursor in industrial
manufacture of food products. The slow pace of technological development in the
country has resulted to the expenditure of the nation’s resources on importation of
activated carbons to meet the demand for local chemical and process industries, as
well as the demand for municipal and industrial water treatment plants.
Rapid industrialization, together with the increase in modern methods of
agriculture and the increase in population, has contributed to the pollution of the
ecosystem. Most of the pollutants are toxic to living organisms. It is therefore
imperative that waste water has to be treated to remove the toxic materials before
disposal to the environment. Most methods of treating water have some inherent
shortfalls. Activated carbon treatment was therefore developed because of its
effectiveness in pollutants removal, especially in water purification.
1.4 OBJECTIVES AND SCOPE OF THE STUDY
The primary objectives and scope of the present investigation include the
following:
i. Acquisition of the different types of activated carbons available to the nation’s
chemical industry.
ii. Modification of the surface physical and chemical properties of the carbon
material, for their use in liquid phase applications.
iii. Determination of the physical properties of the as-received and modified
activated carbon materials.
iv. Testing the adsorption capacity of the carbon materials in adsorption processes.
v. Evaluation of the fractional surface coverage for each carbon material.
vi. Proposal of a scheme for the optimal modification of activated carbon material
for optimal application in liquid phase adsorption.
Modification Of Surface, Physical And Chemical Properties Of Activated Carbons For Water Purification:
Activated carbon is a versatile adsorbent widely used for water purification due to its ability to remove a variety of contaminants, including organic compounds, volatile organic compounds (VOCs), chlorine, heavy metals, and more. Modifying the surface, physical, and chemical properties of activated carbon can enhance its effectiveness for water purification. Here are some common modifications:
Chemical Surface Modification:
Acid Treatment: Treatment with strong acids like sulfuric acid or nitric acid can introduce oxygen-containing functional groups (e.g., carboxyl, hydroxyl) on the surface, increasing the adsorption of polar contaminants.
Alkaline Treatment: Treating with strong bases like sodium hydroxide can increase the number of basic functional groups on the surface, enhancing the removal of acidic contaminants.
Oxidation: Oxidizing agents like ozone or hydrogen peroxide can be used to create reactive oxygen species on the carbon surface, improving its adsorption capacity for various pollutants.
Physical Modification:
Particle Size Reduction: Reducing the particle size of activated carbon can increase the surface area and accessibility of active sites for adsorption.
Micropore Enlargement: Activated carbon can be thermally or chemically treated to open up and enlarge micropores, increasing its capacity for adsorbing smaller molecules.
Impregnation: Impregnating activated carbon with metal nanoparticles (e.g., silver, iron) or other materials can enhance its catalytic and adsorption properties for specific contaminants.
Surface Functionalization:
Silanization: Coating activated carbon with silanes can modify its surface properties, making it more hydrophobic or hydrophilic depending on the silane used.
Polymer Coating: Applying a polymer coating can alter the surface chemistry and enhance the selective removal of certain contaminants.
Composite Materials:
Hybrid Composites: Combining activated carbon with other materials like zeolites, clay, or graphene can create composite materials with improved adsorption capacities and selectivity.
Mixed Bed Systems: Using multiple types of activated carbon with different properties in a single treatment system can target a wider range of contaminants.
Regeneration and Reuse:
Activated carbon can be regenerated by thermal or chemical methods, extending its lifespan and reducing operational costs.
Surface Area Enhancement:
Activated carbon can be physically activated through steam or CO2 activation to increase its surface area and pore volume, improving adsorption capacity.
Tailored Adsorbents: Designing activated carbons with specific characteristics (e.g., high mesopore content for larger molecules) based on the target contaminants can optimize performance.
Functional Group Addition: Introducing specific functional groups through chemical modification can enhance the carbon’s affinity for specific contaminants.
Testing and Characterization: Characterizing the modified activated carbon using techniques like BET surface area analysis, X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) helps ensure the desired properties have been achieved.
It’s important to note that the choice of modification method depends on the contaminants present in the water and the desired treatment outcomes. Careful consideration of the water quality, treatment objectives, and cost-effectiveness is essential when selecting and implementing modifications to activated carbon for water purification applications. Additionally, regular monitoring and maintenance are crucial to ensure the continued efficiency of the modified carbon.