KINETIC, ISOTHERM AND THEMODYNAMIC STUDIES OF THE REMOVAL OF PB(II) AND CD(II) FROM AQUEOUS SOLUTION

                                                                   ABSTRACT

This study assessed the capacity of four adsorbents, namely, Annonamuricata petal composite (AMC), Acacia xanthophloea stem bark composite (AXC), Funtumiaelastica husk composite (FEC) and nanohybrid (Ag/f-MWCNTs), to remove Cd(II) and Pb(II) ions from aqueous solution.  The nanocomposite materials were fabricated via the agro-waste (Annona muricata petal (AMB), Funtumia elastica husk (FEB), or Acacia xanthophloea stem bark (AXB)) modification of Ag/f-MWCNTs.  The kinetics study showed that the uptake of Cd(II) or Pb(II) ions by AMC, FEC, AXC, AMB, FEB, AXB and Ag/f-MWCNTs was best described by the pseudo-second order kinetics model.  It emerged that the equilibrium data obtained for the uptake of Cd(II) ions by the AMB, AMC, FEC, FEB, AXC and AXB adsorbents fitted the Langmuir and Sips isotherm models while Ag/f-MWCNTs were best described by the Freundlich isotherm model.  However, the adsorption equilibrium data obtained for the removal of Pb(II) ions by the adsorbents AXC, AXB, FEC and FEB were found to fit the Freundlich isotherm model, while the uptake of Pb(II) ions by AMC, AMB and Ag/f-MWCNTs was best described by the Langmuir isotherm.  Among the three-parameter isotherm models used, the Sips isotherm model best described the uptake of Pb(II) ions.  Variables controlling the adsorption process, including contacts time, adsorbents dose and initial concentrations of Cd(II) or Pb(II) ions, were found to have a common trend, as these variables increase, the uptake capacity of the adsorbents increased.  The nanocomposite materials demonstrated enhanced uptake potentials, as their uptake capacities were observed to be greater than the adsorption capacity of Ag/f-MWCNTs.  The estimated Gibbs energy of adsorption for the removal Cd(II) and Pb(II) ions indicates that the adsorbate-adsorbent interactions within the range of temperatures studied was feasible and spontaneous.  A desorption efficiency greater than 70% was reported for all nanocomposites, hence effective adsorption-desorption activities were observed, suggesting that these nanocomposite materials will be effective in treating real wastewaters contaminated with toxic Cd(II) or Pb(II) ions.  

TABLE OF CONTENTS

Title page        i          

Declaration      ii         

Certification    iii

Dedication      iv

Acknowledgement      v         

Abstract          vi

Table of contents        v          ii

CHAPTER 1

INTRODUCTION

1.1  Background of the Study                        1

1.2  Aim and objectives                        4

1.3  Justification of the Study                6

1.4  Scope of the Study                                    6

CHAPTER 2

LITERATURE

2.0 General Outline of Heavy Metals 7

2.1Lead           7

2.2 Cadmium  8

2.3 Heavy metal removal: conventional and emerging methods        8

2.3. Ion exchange        9

2.3.2 Precipitation       10

2.3.3. Solvent extraction         10

2.3.4. Membrane Filtration     11

2.3.4.1. Reverse osmosis         11

2.3.4.2. Electrodialysis            12

2.3.4.3. Nanofiltration 12

2.3.4.4. Ultrafiltration 13

2.4. Adsorption           14

2.4.1. Types of adsorption      14

2.4.1.1. Physical adsorption (Physisorption)   14

2.4.1.2. Chemical adsorption (Chemisorption)           15

2.5. Adsorbents           15

2.5.1. Biosorbents       15

2.6. Nanotechnology in water treatment        20

2.6.1. Silver nanoparticles       21

2.6.2. Carbon nanotubes         22

CHAPTER 3

MATERIALS AND METHODS

3.1. Materials  25

3.2.1. Fabrication of nanohybrid (Ag/f-MWCNTs)    25

3.2.2. Preparation of composites (modified-Ag/MWCNTs)  26

3.3. Adsorbate preparation     26

3.4. Metal analysis procedure 26

3.5.0. Batch adsorption experiments  26

3.5.1. Adsorption kinetics       27

3.5.2. Adsorption isotherms    28

3.6. Desorption studies           29

3.7. Data analysis        30

CHAPTER 4

RESULTS AND DISCUSSION

4.1. Surface chemistry (acidic and basic functional groups)  31

4.2. Point of zero charge         32

4.3. Surface area analysis        33

4.4. Crystallinity         34

4.5. Raman spectroscopy        36

4.6. Comparison of pristine and used adsorbents       37

4.7. Batch adsorption experiments     44

4.7.1. Effect of pH     45

4.7.2. Effect of contact time   47

4.7.3. Adsorption kinetics       48

4.7.4. Effect of adsorbent dose          55

4.7.5. Effect of initial concentration of Cd(II) and Pb(II) ions removal        56

4.7.6. Effect of temperature   57

4.7.7. Adsorption isotherms    60

4.7.8.Thermodynamics            70

4.8. Desorption           73

CHAPTER 5

Conclusion  and Recommendations  74

References

Appendix

CHAPTER 1

INTRODUCTION

1.1       BACKGROUND OF THE STUDY

Water pollution by heavy metals is a big serious challenge to mankind, as the scarcity of clean water sources increases Ort et al. (2010).  Anthropogenic activities, such as the indiscriminate discharge of industrial wastewaters into the water streams, wash-off of agrochemicals from farmlands into the water bodies, mining activities, urbanization and mechanization, have posed a serious health hazard to the ecosystem and man Cantu et al. (2014).  Most heavy   metals used in industrial products end up as environmental pollutants after their useful life Gardea-Torresdey et al. (2002).  These heavy metals are known to cause serious health hazards such as cancer, organ damage, disorders of the nervous system, and in extreme cases, death Vetriselvi and Santhi (2015).  Among these heavy metals, Cd(II) and Pb(II) ions have been rated the most toxic Hlihor et al. (2017).  Because of their undesirable properties, there is a need to remove them from aqueous systems.

Cadmium and lead ions are commonly released into water bodies via fertilizer runoff from farmlands, waste batteries, paints, alloys, coal combustion, printing, pulp, refineries, steel smelting and electroplating industries. Garg et al. (2008).  Different ailments caused by acute cadmium exposure include hypertension, liver and kidney damage, renal damage, lung inefficiency, initiation of cancer growth, and calcium depletion in bone Bernard (2008),   Jain  et al (2015).  Meanwhile lead toxicity might pose a minor or major health challenge as it has been reported to cause learning and behavioural difficulty in children, malaise, loss of appetite, anaemia and organ failure Jain et al. (2016), Salman et al. (2015) Sreejalekshmi et al. (2009).  The danger of these toxic ions is due to their ability to bio-accumulate in the food chain which may lead to a biological effect due to the fact that they are non-biodegradable in nature Volesky and Holan (1995), El-Nady. and Atta (1996), Igwe and Abia (2006). The outbreak of cadmium poison in Japan in the 1950s, popularly known as “Itai-Itai disease” indicates how devastating the effects of cadmium pollution will be if not checked.Salman et al. (2015) Meanwhile, a considerable impetus has been given to the permissible limit of Cd(II) and Pb(II) ions in domestic water by the World Health Organization (WHO) as 0.05 mg dm^-3 Sarma et al. (2015).  Phytotoxicity induced by metal ions alters the morphology and physiology of plants via oxygen free-radical-mediated oxidative stress and peroxidation of membrane lipids Anitha et al. (2016).

Extensive investigations have been carried out on heavy metal detoxification of soils by using methods such as metal complex formation with various ligands, metal pumping out, and sub cellular compartmentation Ruckart et al. (2019).  This is to enhance heavy metal cleanup from the environment, but the equilibrium state of the ecosystem remains unaffected due to the adsorptive ability of the biological materials as evident from the studies on metal adsorption by bacteria Cui et al (2008), and fungi Järup (2003) Rahman et al. (2016).  Materials of animal origin are also effective for these cleanup operation, some examples include crab shell biomass Vijayaraghavan et al. (2006) and bivalve shell Liu et al (2009). The removal of toxic heavy metals has received immense attention from researchers across the world.  This has been geared towards developing cost-effective and environmentally friendly methods for aqueous metal ion removal Krika et al. (2015). Several methods such as chemical precipitation Barka et al. (2012), chemical oxidation or reduction Safdar et al. (2011), filtration Ding et al. (2014), electrochemical treatment Sulaymon et al. (2011), application of membrane technology Peterskova et al.(2012), solvent extraction, and ion-exchange processes Wong et al.(2014) are, the conventional methods employed for heavy metal removal from industrial wastewaters.  These conventional methods are inefficient at low concentrations of metal ions, very expensive and, in some cases, generate secondary pollutants.

In recent times, the search for eco-friendly and cheap technologies for heavy metal remediation has been at the forefront.  One avenue of research has been the application of agro-waste and by-products as adsorbents for heavy metal ion removal.  The uptake of the metal ions by agro-waste is based on the interactions of the metal ions with the functional groups at the surface of the adsorbents, and the mechanisms are associated with electrostatic interactions, surface complexation, ion-exchange, and precipitation, which can occur independently or simultaneously Oliveiran et al.(2014). However, there are few or no reports on the application of agro-waste as adsorbents modifiers.

Annona muricata plants have their origin traced back to the south-northern tropical part of America.  These plants have widely spread to other continents and are dominant in tropical and subtropical parts of the world.  This plant belongs to the family Annnona ceace, commonly called sour-sop.  The flowers are stalked, 4-5 cm long, flabby, and three-sided and within the three fleshy fairly spreading outer petals are the centrally placed petals George, et al.(2012), Morton (1996).  Different parts of this plant have been reported to possess strong antimicrobial activity, and are extensively used in human herbal therapy Abubacker and Deepalakshmi (2012), Viera et al. (2010).  On the other hand, Funtumia elastica husk is commonly called silk rubber husk.  This plant is about 30 metres tall, is a good source of quality latex and can be used in charcoal production.  The ethanolic extract of the Funtumia elastica plant (leaf) have demonstrated good antimicrobial activity besides its therapeutic values Agyare et al. (2013). The husk of Funtumia elastica is brownish on the outer part and beige in the interior, and may house vital phytochemicals with rare chemical moieties for aqueous pollutant removal.  The Acacia xanthophloea tree plant, otherwise known as the yellow fever tree, is about 10 to 15 m tall with a greenish-yellow bark.  This tree plant is a good nitrogen-fixing agent (to the soil) and is known to store unwanted nutrients in its sacrificial limb.  The characteristics of its stem bark suggest that the stem bark of this tree may house active chemicals containing functional groups with potential for the removal of metal ions from wastewater.  A recent study showed that the physical and chemical properties of adsorbents can be enhanced by pretreating the adsorbents before use; this prevents organic leaching Ngah and Hanafiah (2008).  On the other hand, the introduction of new adsorption sites and improved adsorbents mechanical strength can be achieved via chemical modification of the adsorbents.   A major drawback to the application of agro-waste is the generation of large volume of solid biomass after use; however, this can be controlled by regenerating the adsorbents.  To achieve this, an effective eluting solvent must be used.  Mineral or organic acids are good eluting agents for heavy metals but the effectiveness of the eluting agent is a function of its ability to completely elute the metal ions and at the same time keep the structure of the functional groups on the surface of the adsorbents undamaged Mata .et al. (2009).

In 1991 Iijima reported the discovery of carbon nanotubes (CNTs), and ever since then, great efforts have been made to improve the property of CNTs.  Properties such as physical, chemical, magnetic, mechanical and thermal conductivity are known to be the cardinal properties of interest.  Among these properties, a good mechanical strength and high aspect ratio of CNTs are important properties which have made them very valuable in the fabrication of nanocomposites Salman et al. (2011).  Carbon nanotubes are nanomaterials with a high surface area possessing a high degree of agglomeration, resulting from strong van der Waals forces.  This is a demerit to the unique and admirable properties of CNTs as it leads to site defects via clustering.  To enhance the dispersion of CNTs, chemical modification of the surfaces must be carried out, these modifications sometimes cause defects on the properties of CNTs such as loss of mechanical strength and electrical characteristics Balasubramanian and Burghard (2005). The typical chemical modification carried out is an oxidative process which introduces –COOH and –OH functional groups to the surfaces of the CNTs.  These groups enhance the electrostatic behaviour of the CNTs, and enhance the metal in uptake ability Saito et al. (2002).  In this work besides functionalising the surfaces of the CNTs, we have also decorated their surfaces with silver nanoparticles to enhance their antimicrobial properties for water disinfection.  Further, we have enhanced their metal bing sites by combining them with plant biomass that possesses a large number of active sites.  Hence we report the ability of these composites to remove Cd(II) and Pb(II) ions from aqueous systems.  In the adsorption study, the effect of pH, contact time, adsorbent dose, initial concentration and solution temperature were examined.  Similar experiments were carried out on the plants modifiers (AMB, FEB, and AXB) and the nanohybrid (Ag/f-MWCNTs) for comparison purpose.  Experimental data obtained from the contact time and initial metal ion concentration experiments were fitted into kinetics and adsorption isotherm models respectively.  Toxic Lead(II) ion and cadmium(II) ion recovery and reusability of the composites were also investigated.

1.2       AIM AND OBJECTIVES

 This study aims to synthesize novel nanocomposites with good polarity and excellent dispersion in the aqueous phase that also possess disinfection properties.  The nanocomposite materials were used for the elimination of heavy metals from contaminated water.  This was achieved by carrying out the following specific objectives.

(1)       To synthesize metallic silver nanoparticle decorated functionalized multi walled carbon nanotubes by making use of the extract from the husk of the Funtumia elastica plant (nanohybrid (Ag/f-MWCNTs)),

(2)       To modify the metallic silver nanoparticle decorated multiwalled carbon nanotubes withFuntumia elastica husk (FEB), Annona muricata petals (AMB), or Acacia xanthophloea stem bark (AXB) so as to enhance the polarity and water dispersibility of the composites,

(3)       To characterise the composites by making use of techniques such as transmission and scanning electron microscopy, thermogravimetric analysis (TGA), Brunauer-Emmett and Teller (BET) surface area analysis, and Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy,

(4)       To evaluate the adsorption potential of the composites, modifiers, and Ag/f-MWCNTs for the removal of Pb²⁺ and Cd²⁺, considering the influence of pH, contact time, adsorbent dose, initial adsorbate concentration and temperature on the adsorption process,

(5)       To assess the mechanisms of the adsorption process by considering kinetics models such as the pseudo-first order, pseudo-second order, intraparticle diffusion and Elovich models,

(6)       To fit the experimental adsorption data to the Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Toth, Redlich-Peterson, Khan and Sips isotherms,

(7)       To validate the mechanism of adsorption responsible for the uptake of Pb²⁺ and Cd²⁺ for all the adsorbents by estimating the thermodynamic parameters of adsorption, namely, the change in Gibbs energy, ∆G° the change in enthalpy, ΔH° and the change in entropy, ∆S°

(8)       To perform desorption studies for all adsorbents to assess the possibility of regenerating the adsorbents and the recovering of the adsorbates for reuse

1.4       JUSTIFICATION OF THE STUDY

Heavy metals exist in a wide range of environmental systems such as soils, plants, air and aquatic ecosystems. Many industries and products require heavy metals. Waste products containing heavy metals from these activites are discharged into the environment and transported by natural factors into aquatic systems thereby causing contamination. Heavy metals are of serious concern because of their potential toxicity, and because they can be accumulated in the food chain and cause various carcinogenic  effects to humans.

This therefore calls for remediation studies to ensure that the water does not contain unacceptable pollutant contaminations. This chapter contains a general introduction and describes the impact of heavy metals in the environment.it describes the problems and the significance of this work. It also includes the aims and objectives of this research. Besides, it introduces the techniques involved in this study, and the use of Annona muricata petal composite, Acacia xanthophloea stem bark composite Funtumia elastica husk composite and Agf-MWCNTs as adsorbents for heavy metal removal from aqueous solution.

1.5       SCOPE OF THE STUDY

The concept was adopted to produce AMC, FEC, AXC, AMB, AXB, and Agf-MWCNTs for the removal of Pb²⁺ and Cd²⁺ (heavy metals) from aqueous solution.

Buyers has the right to create dispute within seven (7) days of purchase for 100% refund request when you experience issue with the file received. 

Dispute can only be created when you receive a corrupt file, a wrong file or irregularities in the table of contents and content of the file you received. 

ProjectShelve.com shall either provide the appropriate file within 48hrs or send refund excluding your bank transaction charges. Term and Conditions are applied.

Buyers are expected to confirm that the material you are paying for is available on our website ProjectShelve.com and you have selected the right material, you have also gone through the preliminary pages and it interests you before payment. DO NOT MAKE BANK PAYMENT IF YOUR TOPIC IS NOT ON THE WEBSITE.

In case of payment for a material not available on ProjectShelve.com, the management of ProjectShelve.com has the right to keep your money until you send a topic that is available on our website within 48 hours.

You cannot change topic after receiving material of the topic you ordered and paid for.