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.
Click “DOWNLOAD NOW” below to get the complete Projects
FOR QUICK HELP CHAT WITH US NOW!
+(234) 0814 780 1594
Login To Comment