PREPARATION AND CHARACTERISATION OF PLANTAIN WASTE BASED CELLULOSIC NANOCOMPOSITES FOR THE REMOVAL OF SELECTED HEAVY METALS FROM BATTERY EFFLUENT

ABSTRACT

In this study, Ag NPs and Ag-CNCs impregnated on CNTs nano adsorbents were developed using a combination of green chemistry protocol and chemical vapor deposition techniques and subsequently characterized using, HRTEM, HRSEM, XRD, EDS and SAED. The adsorption capability of silver-carbon nanotubes (Ag-CNTs) and silver-cellulose nanocrystals are modified multiwalled carbon nanotube (Ag-CNTs- CNCs), the nanocomposites are for rapid and efficient removal of selected heavy metals (Fe, Cu, Ni, Zn and Pb) as well as analysis of physico-chemical parameters such as, pH, total dissolved solids (TDS), chemical oxygen demand (COD), biochemical oxygen demand (BOD), nitrates, sulphates, and chlorides from battery effluent using a batch process. The aim of the study is the preparation and characterization of plantain waste based cellulosic nanocomposites for the removal of selected heavy metals from battery effluent. The result showed successful deposition of Ag and the grafting of CNCs into the matrix of CNTs as confirmed by the microstructures, morphology, crystalline nature, and elemental characteristics of the Ag-CNTs-CNCs. Optimum batch adsorption parameters include; contact time (90 min) and adsorbent dosage (0.03 g) for Ag-CNTs and contact time (90 min), adsorbent dosage of (0.02 g) for Ag-CNTs-CNCs. The adsorption capacities were obtained as follows; Fe2+  (105.263 mg/g), Cu2+ (238.095 mg/g) Ni2+ (166.667 mg/g), Zn2+ (121.951 mg/g) and Pb2+ (119.048 mg/g), for Ag-CNTs. Langmuir isotherm and pseudo-second order kinetic model best described the experimental data in the batch adsorption with Ag-CNTs adsorbent. The adsorption capacities using the Ag- CNTs-CNCs adsorbent were obtained as follows; Fe2+  (200.000 mg/g), Cu2+ (263.158 mg/g) Ni2+  (238.095 mg/g), Zn2+  (169.492) and Pb2+  (181.818mg/g), with a higher adsorption capacity following more physical adsorption, electrostatic interactions and surface complexation. On the contrary, the Freundlich isotherm and pseudo-second order kinetic model best described the experimental data in batch adsorption for Ag-CNTs- CNCs, which validated the chemisorption and multilayered nature of the adsorption process. The high physico-chemical parameters in the effluent were successfully analyzed in the batch systems to fall within WHO permissible concentrations. This study establishes that Ag-CNTs-CNCs is efficient for the treatment of industrial effluent when compared to Ag-CNTs.

CHAPTER ONE

1.0     INTRODUCTION

1.1       Background to the Study

Water is a universal liquid in the world and vital for domestic purposes such as drinking, cooking, washing, bathing among others, with 75% of the human body made up of water because of its specific gravity (Seiyaboh and Izah, 2017). Nevertheless, environmental pollution is currently one of the most important issues faced by humanity and has increased exponentially to alarming levels in terms of its effects on living creatures (Renge et al., 2012). Increased industrial and agricultural activities have resulted in the generation of various types of toxic pollutants, which are the main cause of environmental water pollution on a global scale. However, years of increased industrial, agricultural and domestic activities have resulted in the generation of large amount of effluent containing a number of toxic pollutants which are polluting the available fresh water continuously (Bhatnagar and Sillanp, 2010).

With a swift increase in the population of the world, demand for drinking water has been on the increase and it is expected that there would be a corresponding upsurge in domestic, agriculture and industrial water sources, especially in developing countries where the need of water is greater as compared to its economic status and population (Zahid et al., 2018). Rapid industrialization in developed and developing countries has led to a substantial increase in the generation of industrial effluents. These effluents are a great concern to health scientists all over the world as they constantly pollute water bodies when discharged without adequate treatment (Sweetly et al., 2015).

Effluents from numerous industries such as paints and pigments, glass production, mining operations, metal plating, and battery manufacturing processes are known to contain contaminants such as heavy metal, chlorides, sulphides, and pathogens to mention but a few (Manjuladevi and Sri, 2017). Most of these pollutants present in industrial effluents, are not biodegradable and their existence in receiving lakes and streams cause bioaccumulation in living organisms, which leads to several health problems in animals, plants and human beings such as cancer, kidney failure, metabolic acidosis, oral ulcer, renal failure and damage in the stomach of the rodents (Mehmet et al., 2006).

Batteries may be hazardous wastes because they contain heavy metals and corrosive electrolyte solutions that are the sources of their energy (Sweetly et al., 2015). Battery industries discharge mostly inorganic pollutants containing heavy metals such as, lead, zinc, lithium, cadmium as well as sulfuric acid (Iloms et al., 2020). It is, therefore, essential to remove or reduce the presence of these inorganic contaminants in order to diminish the possibility of uptake by animals, plants, humans and eventual accumulation in the food chain to prevent them from contaminating surface and groundwater by dissolution or dispersion (Ibigbami et al., 2016).

To address the undeniable need of alleviating water pollution from industrial activities, various water treatment technologies have been proposed and applied at experimental and field levels. These technologies commonly fall into primary (screening, filtration, centrifugation, separation, sedimentation, coagulation and flocculation); secondary (aerobic and anaerobic treatments); and tertiary (distillation, crystallization, evaporation, solvent extraction, oxidation, precipitation, ion exchange, reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), microfiltration (MF), electrolysis and electrodialysis) level water treatment technologies (Gupta et al., 2012). However, the most used of these technologies are not capable of fixing water pollutants present in battery effluents in an effective way. Some of the mentioned methods are energy and operationally intensive and thus are not affordable on a commercial scale. Adsorption techniques are easy and simple and can be carried out with polymeric materials or membranes.

Polymer nano-composite membranes are basically modified type of polymeric membranes with nano-materials dispersed in their matrices (Qalyoubi et al., 2021). Polymer nano-composite membranes are applied in organic solvent nanofiltration, pervaporation, effluent treatment, direct methanol fuel cells, sensor applications, gas separation and proton exchange membrane fuel cells (Rasheed et al., 2020). Polymeric membranes have been widely used for water treatment. These include; waste streams from agro-food (Castro-Muñoz et al., 2016), textile (Van der Bruggen et al., 2004), and petroleum industries (Alzahrani, and Wahab et al., 2014) or removal of pollutants from drinking water (Kim and van der Bruggen, 2010) enabling the concentrate to be treated or discharged and, thereby, reducing the contaminants directly or indirectly discharged into wastewater (Castro-Muñoz et al., 2016). However, the basic setback associated with polymeric membrane in the industrial scale includes high cost of maintenance and membrane fouling (Ursino et al., 2018).

Over the past decade, numerous trials have been devoted to make use of agricultural wastes from fruits such as, plantain and pineapple peels which contains appreciable amount  of natural  cellulose  for the manufacture of nanocomposites  with  particular applications having appropriate features such as permeability, selectivity, and specific chemical and physical properties. Cellulose is the most abundant polysaccharide in the world and it is widely considered to be a long-term renewable alternative to synthetic plastics. Cellulose is a long chain linear homo-polymer comprising anhydro-β-D- glucopyranose units linked by (1→4) glycosidic bonds (Spinella et al., 2016; Yadav et al., 2017). Cellulose has received increasing research interest owing to its environmental friendly   advantages   and   attractive   features,   such   as   nontoxicity,   biological biodegradation, biocompatibility, excellent thermal and mechanical properties, renewability and easy modification (Dai & Huang 2016, 2017a, b; Khawas & Deka 2016; Zhang et al., 2017). Recently, highly crystalline nanoscale materials, namely cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) have be produced from cellulose and combined with other nanomaterials via techniques such as, track-etching, stretching, sintering, phase inversion, electrospinning and interfacial polymerization with superior properties (Lalia et al., 2013). Likewise, nanoparticles (NPs)-based membranes have demonstrated low-fouling process through adding the inorganic particles (Kim and van der Bruggen, 2010). Dispersing the NPs into the natural polymer generally forms nanocomposite membranes, which are also a suitable tool to improve the performances, such as permeability and selectivity (Madaeni et al., 2015). The unique features exhibited by natural polymeric membranes such as, nanocellulosic crystals when reinforced with silver (Ag) nanoparticles and carbon nanotubes (CNTs) to form nanocomposites is what this research intends to utilize for effluent treatment in a battery manufacturing factory at industrial scale.

1.2       Statement of the Research Problem

Noxious and hazardous electrolytes and materials are widely used in the battery industry (Fedorov, et al., 2017). The problems of low pH and high concentration of lead are often associated with battery effluent (Vu et al., 2019). Consumption and exposure of aquatic species and humans to battery effluent have caused challenges which has led to several health problems in animals, plants and human beings such as cancer, kidney failure, metabolic acidosis, oral ulcer, renal failure and damage in the stomach of the rodents (Mehmet et al., 2006). Besides, the effluents have offensive odour and contains a lot of contaminants.

In addition, accidental discharge of such battery effluent into water bodies will deteriorate and degrade the quality of limited clean water. Many traditional methods such as chemical precipitation, electrochemical reduction, ion exchange, activated carbon and biosorption to mention a few, has been used for the removal of one of the major constituent of battery effluent (Pb2+). This method can only be used effectively for heavy metal extraction when the concentration of the heavy metal is less than 100 mg/L (Inbaraj  et al., 2009). Furthermore, the use of polymeric materials alone for the treatment of industrial effluent can be prone to fouling. Likewise, pristine CNTs alone often forms aggregates when put to use over time which significantly decreases water flux and pollutant rejection capacities of the membranes. CNTs are generally contaminated with metal catalysts, impurities and physical heterogeneities (Madaeni, 2007). Also, reinforcement of CNTs into metal matrix or natural polymer remains a challenge due to their entangled structure. The CNTs are held together by weak, non-covalent interactions. These interactions are π- π attractive bonding, electrostatic and van der Waal forces which is the main reason CNTs have tendencies to agglomerate. Plantain is an important plant whose fruits are consumed on daily basis. However, the peel and trunk fiber of this fruits are underutilized and are usually discarded after consumption and left to decompose in this part of the world. This plantain tree waste can cause serious environmental threat if not properly managed, and can produce greenhouse gas such as (methane) if dumped in wet condition.

1.3       Justification for the Study

In order to avoid some disadvantages of conventional adsorbents based on synthetic polymers (high prices, difficulties in production, pollution produced during their synthesis), unconventional materials are increasingly being used for effluents analysis and  treatment  (Suteu  et  al.,  2007).  The  abundant  availability  of  natural  polymeric absorbents such as clay, kaolin and several agricultural wastes which includes plantain trunk and stalks makes them to be considered as alternative sources of effective and eco- friendly adsorbents for removal of pollutants from effluents in battery manufacturing factories. Modification of this polymeric materials or membrane both enhance the surface area and adsorption capacity.

Carbon nanotubes (CNTs) have recently attracted the attention of researchers due to their extraordinary electrical, mechanical, and thermal properties and antibacterial activity. Indeed, they alter the physico-chemical properties of polymer membranes, which encourage their potentiality for several applications. Typically, the inner pores of CNTs tend to act as selective nanopores. Therefore, the CNT-filled membranes show an enhanced permeability without a decrease in selectivity, coupled with enhancements in mechanical and thermal properties (Fontananova et al., 2017). Silver (Ag)-based NPs when present in polymer membranes, generally offer antimicrobial properties that give them potential for several applications including water treatment and disinfection of medical devices (Ursino et al., 2018). Therefore, since silver nanoparticles is among the most often used nanoparticles for antimicrobial applications with less health and environmental consequences. A synergistic nanocomposition of Ag NPs, CNTs and CNCs would improve the performance of the base cellulosic natural polymeric with several attractive features including surface hydrophilicity, thermal and mechanical stability, antimicrobial and anti-fouling properties which are relevant in water treatment or industrial effluents remediation.

1.4       Aim and Objectives of the Study

The aim of this study is to prepare cellulose nanocrystals from plantain waste (pseudo- stem/trunk) and modify them with carbon nanotubes and biosynthesized silver nanoparticles for the sequestration of selected heavy metals from battery effluents.

The aim was achieved through the following objectives;

i.      Biosynthesis of Ag nanoparticles (AgNPs) using AgNO3 as a precursor and tea leaves extract.

ii.      Synthesis of CNTs via catalytic chemical vapor deposition method. iii.     Preparation of Ag-CNTs nanocomposite

iv.      Preparation of cellulose nanocrystals (CNCs) using dried plantain trunk (DPT) and  to  modify it  with  the  prepared  Ag-CNTs  nanocomposite  via  ultrasonic cavitation to obtain Ag-CNTs-CNCs.

v.      Characterisation  of the  Ag NPs,  CNTs  and  Ag-CNTs,  and  Ag-CNTs-CNCs nanomaterials produced to determine the morphologies, microstructures and crystallinities using High Resolution Scanning Electron microscopy (HRSEM- EDS), High Resolution Transmission Electron Microscopy (HRTEM-SAED) and X-ray Diffraction (XRD) respectively.

vi.      Evaluation of the adsorption potentials of the developed Ag-CNTs & Ag-CNTs- CNCs for the removal of the selected heavy metals from battery effluent by varying the contact time and dosage of the nanosorbents via batch adsorption process.

vii.      Evaluation of the adsorption kinetics of the developed Ag-CNTs and Ag-CNTs- CNCs using pseudo-first order, pseudo second order and Elovich models, as well as to investigate the adsorption isotherms using Freundlich, Langmuir and Temkin isotherms.

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