ABSTRACT
Nanocomposites adsorbents were fabricated from different types of plant biomass and functionalized multiwalled carbon nanotubes decorated with silver nanoparticles (Ag/f-MWCNTs). A set of adsorption experiments were performed to determine the effect of solution pH, agitation time, adsorbate temperature, adsorbent dose, initial dye concentration, and desorption of the dyes in order to validate the efficiency of these nanocomposites to eliminate rhodamine B (RhB) and malachite green oxalate (MGO) from aqueous solution. The results obtained showed an increase in RhB and MGO uptake with increased contact time, adsorbent dose, and initial concentration of RhB or MGO. The optimum uptake was observed at pH 3 for RhB and pH 7 for MGO. Kinetics studies showed that the adsorption of MGO and RhB proceeded according to the pseudo-second order and Elovich models, respectively. Equilibrium data obtained from the uptake of RhB and MGO were best described by the Langmuir and Sips isotherm models. The thermodynamic parameters (ΔG°, ΔH° and ΔS°) of the adsorption process revealed that the uptake of RhB and MGO by the adsorbents was entropy-driven, feasible, and spontaneous. The composites demonstrated higher uptake capacities than Ag/f-MWCNTs for the removal of MGO. Meanwhile, the reverse was the case in the elimination of RhB. The nanocomposite materials demonstrated good capacity to eliminate MGO and RhB from aqueous systems, and have shown the ability to be reused. Hence, these nanomaterials are suitable for wastewater treatment at the industrial scale.
TABLE OF CONTENTS
Title Page
i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Abstract vi
Table of content vii
List of Tables viii
List of Figures ix
Abstract x
CHAPTER
1
INTRODUCTION
1.1 Background of the Study 1
1.2 Statement of the Problem 2
1.3 Aim and Objectives 4
1.4 Justification of the
Study 5
1.5 Scope of the Study 5
CHAPTER 2
LITERATURE REVIEW
2.1 General Outline of Dyes 6
2.1. Organic Dyes in Water 6
2.1.1. Rhodamine
B 6
2.1.2. Malachite
green oxalate 7
2.2. Conventional Methods of Removing Organic
Dyes 8
2.2.1. Photodegradation 8
2.2.2. Chemical
oxidation 9
2.2.3. Biological
treatment of organic dyes 9
2.3. Adsorption 10
2.3.1. Types of
adsorption 10
2.3.1.1. Physical adsorption (Physisorption) 10
2.3.1.2. Chemical adsorption (Chemisorption) 11
CHAPTER 3
MATERIALS AND METHODS
3.1. Materials 13
3.1.2 Chemicals 13
3.2. Preparation
of Composite Samples (Biomass-Ag/f-MWCNTs) 13
3.3. Characterization
of Adsorbent 14
3.4 Adsorbate
Preparation 14
3.5 Determination
of Dye Concentrations 14
3.6 Batch
Adsorption Experiments 14
3.6.1. Kinetics studies 15
3.6.2. Adsorption isotherms 16
3.6.3.
3.7.
CHAPTER 4
RESULTS AND DISCUSSION
4.1. Characterization of
Pristine and Dye-loaded Adsorbents 19
4.2. Batch
Adsorption Experiments 32
4.2.1. Effect
of PH 32
4.2.2. Effect of adsorbent
dose 35
4.2.3. Effect of contacts time 37
4.2.4. Adsorption kinetics 39
4.2.5. Effect of initial concentration of RhB or MGO 47
4.2.6. Effect of solution temperature 47
4.2.7. Adsorption
isotherm 48
4.2.8. Thermodynamic parameters of adsorption 59
4.2.9. Desorption studies 63
CHAPTER 5
CONLUSION AND RECOMMENDATIONS
5.1 Conclusion 64
5.2 Recommendations 64
REFERENCES
LIST OF TABLES
2.1:
Distinctions between physisorption and chemisorption 10
3.1: Kinetics models investigated for the adsorption
of RhB and MGO 15
3.2: Isotherm models used to
describe the uptake of RhB or MGO by AMC, FEC, AXC,
AMB, FEB, AXB, and Ag/f-MWCNTs. 17
4.1: Kinetics parameters for the
adsorption of MGO onto AMC, AMB, FEC, FEB, AXC, AXB and Ag/f-MWCNTs adsorbents 42
4.2 Kinetics parameters for
the adsorption of RhB onto the adsorbents AMC, AMB, FEC, FEB, AXC, AXB and Ag/f-MWCNTs. 43
4.5 Comparison
of the Langmuir maximum adsorption capacities for RhB and MGO onto AMC, AMB,
FEC, FEB, AXC, AXB and Ag/f-MWCNTs
with those of other sorbents. 50
4.6: Isotherm parameters for the adsorption MGO onto the adsorbent AMC,
AMB, FEC,FEB,AXC,AXBandAg/f-MWCNTs. 53
4.7: Isotherm parameters for the adsorption RhB
onto the adsorbents AMC, AMB, FEC, FEB, AXC, AXB and Ag/f-MWCNTs 56
4.8:
Thermodynamic parameters for the adsorption of RhB and MGO onto AMC, AMB, FEC,
FEB, AXC, AXB and Ag/f-MWCNTs. 61
4.9 Percentage desorption of RhB and
MGO by using ethanol or acetone [Experimental conditions: 10 cm3 of
either acetone or ethanol, 50 mg of (RhB or MGO)-loaded absorbent, agitation speed 120 rpm, contact time 30 min, and
solution temperature 22 °C]. 63
LIST OF FIGURES
2.1: Structure
of rhodamine B [molar mass: 479.02 g mol-1; acid dissociation
constant (pKa):
3.71; solubility in water: 15 g dm-3; density: 1.31 g cm-3
(20 °C); melting point:210-211°C](33) 6
2.2: Malachite
green oxalate (MGO) [molar mass: 927.02 g mol-1; acid dissociation constant
(pKa): 6.9;
solubility in water: 60 g dm-3; melting point: 164 °C]
4.1 Raman spectra of pristine
adsorbent and RhB-loaded adsorbent 20
4.2 Raman spectra of pristine adsorbent
and MGO-loaded adsorbent 22
4.3 FTIR spectra of
unloaded adsorbents compared with the spectra of RhB and MGO-loaded adsorbents 23
4.4 (a) FESEM micrographs
of RhB-loaded absorbents compared with the pristine adsorbents 26
4.4 (b) FESEM micrographs of RhB-loaded absorbents compared
with the pristine adsorbents. 26
4.5 (a) FESEM micrographs of MGO-loaded absorbents compared
with the pristine adsorbents 27
4.5 (b) FESEM micrographs of MGO-loaded absorbents compared
with the pristine adsorbents 28
4.6 FTIR spectra of AMC, AMB,
FEC, FEB, AXC, AXB, Ag/f-MWCNTs and Funtumia
elastica plant extract. 31
4.7 Effect of pH on
the adsorption of (a) MGO and (b) RhB onto
AMC, AMB, FEC, FEB, AXC, AXB and Ag/f-MWCNTs
[conditions: 25 cm3 of 100 mg dm-3 RhB or MGO, 24 h
equilibration time, 50 mg adsorbent dose, agitation speed 120 rpm, temperature
22 °C]. 34
4.8 Effect of
adsorbent dose on the adsorption (a) MGO and (b) RhB by AMC, AMB, FEC, FEB, AXC, AXB and Ag/f-MWCNTs [conditions: 25 cm3 of 100 mg dm-3
MGO/RhB, 24 h equilibration time, pH 7
(MGO) and pH 3 (RhB), agitation speed 120 rpm, temperature 22 °C]. 36
4.9
Effect of contact time on the adsorption of (a) MGO
and (b) RhB by AMC, AMB, FEC, FEB, AXC, AXB and Ag/f-MWCNTs [conditions: 25 cm3
of 100 mg dm-3, equilibration time, pH 7 (MGO) and pH 3 (RhB),
agitation speed 120 rpm, temperature 22 °C].
38
4.10 Comparison of the various kinetics models fitted to the
experimental data of MGO onto (a)
AMC, (b) AMB, (c) FEC, (d) FEB, (e) AXC, (f) AXB and (g) Ag/f-MWCNTs and (pseudo-first order,
pseudo-second orde, intraparticle diffusion, Elovich ). 45
4.11 Comparison of the various kinetics models fitted to the
experimental data of RhB onto (a) AMC, (b) AMB, (c) FEC, (d) FEB, (e) AXC, (f)
AXB and (g) Ag/f-MWCNTs (pseudo-first
order, pseudo-second order, intraparticle diffusion, Elovich). 46
4.12 Effect of
temperature on the adsorption of RhB onto (a) AMC, (b) AMB, (c) FEC, (d) FEB,
(e) AXC, (f) AXB and (g) Ag/f-MWCNTs
[Conditions: 25 cm3 of 10 to 100 mg dm-3, 24 h contact
time, 20 mg adsorbent dose, pH 3, agitation speed 120 rpm] 51
4.13 Effect of
temperature on the adsorption of MGO onto (a) AMC, (b) AMB,(c) FEC, (d) FEB,
(e) AXC, (f) AXB and (g) Ag/f-MWCNTs
[Conditions: 25 cm3 of 10 to 100 mg dm-3, 24 h contact
time, 20 mg adsorbent dose, pH 7, agitation speed 120 rpm] 52
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
The discharge of
coloured effluents produced from textile, leather, paper making, plastics, food, rubber,
cosmetics, and dye manufacturing industries,
into the aquatic body has posed a high degree of threat to man, plants and
aquatic biota (fauna and flora) (
Hayeeye et al., 2017). This is due
to the non-biodegradable nature of some of the pollutants and their stability to light, heat, and oxidizing agents (
Wang et al., 2006). Effluents are composed of different kinds of
pollutants ranging from dyes to heavy metal ions. These pollutants bio-accumulate in plants and
in most cases lead to phytotoxicity of
the plants. However, the food chain creates a link through which man ingests these
pollutants, and hence, health challenges such as pain, vomiting, skin
irritations, severe headaches, and acute diarrhoea
are inevitable (
Baek, et al., 2010).
Most dyes used in the industries are designed to be
very reactive and are known to have good properties that make their demand and application high. Meanwhile,
these dyes are very problematic due to their high solubility. About 20-40% of the widely used cationic dyes
are often discharged alongside with
industrial effluents; acid dyes are also very difficult to remove from wastewater, these challenges are often blamed on the high solubility of
these dyes (
Konstantinou and Albanis, 2004, Choy et
al.,
2004). Basic dyes
are not exempted, as they are the brightest class of dyes with high tinctorial
values (
Inbaraj and Sulochana, 2006). The colour impact of dyes on water bodies reduces
the penetration of light into the water bodies, hence the dissolved oxygen and
photosynthetic processes are negatively affected, and this affects the growth of aquatic organisms (
Huang et al.,2008). Hence, this study seeks
to fabricate nanocomposite materials as potential agents for decontamination. To accomplish this, acid-functionalized
multiwalled carbon nanotubes decorated with metallic silver nanoparticles were
sandwiched and modified with plant biomass to enhance the binding affinity of
the adsorbents as well as the antimicrobial potential of the nanocomposites.
1.2 STATEMENT OF THE PROBLEM
In the aquatic
ecosystem, bioaccumulation
and bio-magnification aid the stability
of these hazardous materials in the food web (Gupta
et al.,1990, Halliday and Beszedits,
2006). In humans,
the toxicological implication of these substances when ingested include, but
are not limited to, biochemical, physiological
or behavioural defects (Patil and Shinde, 1988 ;
Lian et al., 2009). Meanwhile, above the threshold limits of these contaminants, disastrous environmental
and ecological problems are also inevitable (
Tsai et al., 2013). The water
body receives a vast amount of dyes and heavy metals from industrial activities
such as printing, mining, smelting, electroplating, steel smelting and the
manufacturing of fertilizers, pesticides, herbicides, alloys, pulp, ceramics,
glass, textiles, and leather, amongst others (Wahi
et al, 2005, Mittal et al.,2009, Asfour et al., 1985).
In this work two cationic dyes were of interest. Considerable research has been carried out on
the effect of exposure to high
concentrations of RhB or MGO. These
studies have demonstrated the high potential of RhB or MGO to cause cancer,
neurotoxicity, and reproductive and developmental diseases in man (
Dawood and Sen, 2012). The intravenous median lethal dose (LD50) of RhB and MGO are
very small, this indicates how toxic both
dyes can be. Hence, the need for
necessary safety measures for the usage of MGO and RhB is important (
Mittal and Mishra 2014). Several
methods, which include chemical oxidation (
Neamtu et al., 2004), reverse osmosis (
Gupta et al.,1990), coagulation and flocculation (
Halliday and Beszedits 1986), biological treatments (
Patil and Shinde 1988), and photo-degradation (
Lian et al 2009, Baek et
al, 2010, Tsai et al, 2013, Wahi
et al., 2005), have been developed for the removal and recovery of
dyes from wastewater. Some of these
methods are known to have limitations such as high cost of maintenance, high
energy consumption, longer retention time, ineffective at low dye concentrations
and generation of secondary waste.
Hence, there is an urgent need for the development
of effective and economically viable technologies for the removal of dyes from wastewater. Adsorption is quite popular due to its
user-friendly nature and high efficiency, as well as the accessibility of a
wide range of adsorbents. It is worth
mentioning that activated carbon has demonstrated high competence for the
removal of dyes from contaminated water (Mittal
et al.,2009), however, this is due to the high porosity and large
surface area of activated carbon. Meanwhile, the drawback to the application of activated carbon in adsorption
processes includes high cost and low
regeneration efficiency. Intensified
efforts have therefore been geared towards the development of inexpensive and
effective alternatives to activated carbon.
Materials such as wood (
Asfour et al., 1985), Fullers earth
and fired clay (
McKay et al.,1987), fly ash (
Khare et al, 1987), biogas waste slurry (
Namasivayam and Yamuna, 1992, Namasivayam and Yamuna (1992), waste orange peel (
Namasivayam et al., 1996 ), banana pith (
Namasivayam,and Kanchana 1992), peat (
Ramakrishna and Viraraghavan, 1997), chitin (
Mc Kay et al, 1983), chitosan (
Juang et al, 1997), silica (McKay,1984), jute stick powder (
Panda et al., 2009), peanut hull (
Gong et al., 2005), jute processing wastes (.Banerjee and Dastidar, 2005), soy meal hull (
Arami, et al., 2006), rice husks (
Mckay et al., 1987), maize stalks (
Meye et al., 1992), hazelnut shells (
Doğan et al., 2006), bottom ash and de-oiled Soya (
Gupta et al., 2009, Gupta et al.,2006), wheat bran and rice bran (.
Wang and Chen, 2009), jackfruit peel (
Hameed,
2009), spent brewery grains (
Jaikumar, 2009), sunflower seed hull (
Thinakaran, 2008) and papaya seeds (Hameed,
2009), Guava (Psidium guajava) leaf powder (
Ponnusami et al.., 2008), Posidonia oceanica (L.) fibers .
(Ncibi et al., 2008). pumpkin seed hull (
Hameed and El-Khaiary, 2008), amongst many other examples, have been applied as
adsorbents for the removal of dyes from aqueous solutions. However, there are scarce or no report on the application of agro-waste materials
as adsorbent modifiers.
Since Iijima re-discovered carbon nanotubes (CNTs) in
1991, CNTs have been intensively studied.
Due to their unique physical and chemical properties, CNTs have been
used in different fields for a variety of
applications (
Fagan et al., 2004, Ajayan, 1993). The
effectiveness of CNTs for the uptake of organic and inorganic pollutants have
been studied and the results obtained were comparable to carbon-based adsorbents
that are used for commercial applications (
Kerdnawee et al., 2017). Metal doped multiwalled carbon nanotubes (M/MWCNTs),
commonly described as nanohybrids, have found extensive
application in the medical field as the MWCNTs play the role of a delivery
agent for the zero-valent metal, which turns ionic
in the cytoplasm of a bacteria cell. Of the various metals, silver nanoparticles,
in particular have been extensively employed in diverse areas such as,
biological labelling, surface enhanced Raman scattering (SERS), photography
optoelectronics, catalysis, photonics, antimicrobial agents, and water
remediation practices (
Sun and Xia, 2002, Taheri et al.,
2014). Metallic silver-decorated multiwalled carbon
nanotubes (Ag/f-MWCNTs) may find good
environmental application as adsorbents for water decontamination and as water
disinfectant.
Treatment of wastewater before discharge is the only
way to ensure a comprehensive healthy ecological environment. To achieve
this, Annona muricata petals (AMB), Funtumia elastica
husk (FEB), and Acacia xanthophloea stem
bark (AXB) were used to modify the nanohybrid, Ag/f-MWCNTs, and form nanocomposite, materials, namely, Annona muricata petal composite (AMC), Funtumia elastica
husk composite (FEC) and Acacia
xanthophloea stem bark composite (AXC) respectively. These nanocomposite materials (AMC, FEC, and AXC) were investigated as low-cost adsorbents
for the removal of RhB and GMO from aqueous solution. The effects of influential parameters, such
as agitation time, adsorbent dose, initial adsorbate concentration, solution
pH, and solution temperature were studied.
To the best of our knowledge, the application of agro-waste as
adsorbents modifier has not been exhaustively researched and hence this
investigation pursues and discusses the potential of low-cost adsorbents
fabricated from silver nanoparticles, MWCNTs and agro-waste (modifiers) for the removal of RhB and MGO from
simulated wastewater.
1.3 AIM AND OBJECTIVES
This study aims to synthesize novel nanocomposites with good polarity and excellent dispersion in the
aqueous phase that also possess decontamination properties. This is hoped to be achieved by
carrying out the following objectives.
(1) To functionalize commercially obtained
pristine-MWCNTs with a mixture of concentrated nitric and sulphuric acids,
(2) To
synthesize metallic silver nanoparticle decorated functionalized multiwalled carbon nanotubes by making use of the extract from the husk of the Funtumia elastica
plant (nanohybrid (Ag/f-MWCNTs)),
(3) To modify the metallic silver nanoparticle decorated multiwalled
carbon nanotubes with Funtumia
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,
(4) To characterize the composites by making use
of techniques such as transmission and scanning electron microscopy, and Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy,
(5) To
evaluate the adsorption potential of the composites, modifiers, and Ag/f-MWCNTs for the removal of rhodamine B
(RhB), and malachite green oxalate (MGO) from aqueous solution, considering the
influence of pH, contact time, adsorbent dose, initial adsorbate concentration
and temperature on the adsorption process,
1.4 JUSTIFICATION OF THE STUDY
Anthropogenic activities involving the introduction of
chemical, physical, microbial and radioactive substances into aqueous media are
responsible for increased pollution, hence, exacerbating the scarcity of clean
water. Wastewaters containing several toxic pollutants are regularly generated
by industries, and are taken through little or no further treatment before
their disposal into the environment. Unfortunately, most pollutants are water
soluble and eventually end up in groundwater, rivers, streams and oceans
through various natural processes. Water pollution before limits the
availability of water, posing serious environmental and health challenges to
its dependents and can lead to death and the spread of diseases. To avert this
problem, a crucial need exists for the remediation of wastewater produced by
industries in order alleviate water scarcity and generate freshwater to cater
for human needs.
1.5 SCOPE OF THE STUDY
This concept was
adopted to produce AMC, FEC, AXC, AMB,M FEB, AXB and -Ag/fMWCNTs for the
removal of the RhB and MGO from aqueous solutions.
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