Environment Friendly Development of Modified Oxide-based Nanostructures for Removal of Water Contaminants

Abstract

Oxide-based nanostructures with their unique qualities like simple processability, high surface activity, reproducibility, and superior conductivity with controllable band gaps have become promising materials for wide range of environmental restoration applications. Furthermore, these oxide nanostructures allow structural modifications which offer the ability to alter their activity, surface stability and selectivity during any reaction. From a green synthesis strategy the use of environmentally benign solvents, non toxic chemicals, and renewable resources are some of the major problems that require important consideration. Among all available nanostructured oxides, SiO2 and Al2O3 have been preferred materials for adsorption applications. Similarly, CeO2 and WO3 are known as a special class of oxides with unique light harvesting capacity for photocatalytic applications. Keeping this in mind, this thesis is broadly divided into two major types; (1) environment friendly synthesis and modification of oxide nanostructures such as SiO2 and Al2O3 for adsorptive removal of inorganic pollutants from water and (2) environment friendly synthesis and modification of oxide nanostructures such as CeO2 and WO3 for photocatalytic degradation of organic pollutants from water. All the oxide based nanocomposites [SiO2-Graphene Oxide (GO), Al2O3–Hydroxy Propyl Methyl Cellulose (HPMC)-Chitosan, CeO2-ZnFe2O4-Bioreduced Graphene Oxide (BRGO), WO3-ZnWO4- Polyaniline (PANI), and WO3-CoFe2O4-PANI] depicted in this thesis have been utilized for water remediation applications via adsorption and photocatalysis process. In the initial stage of research, very few literatures reported about the environment friendly synthesis of modified oxide based nanostructures for removal of inorganic contaminants from water. In the first project, the objective was to remove the cationic inorganic contaminants like Pb (II) and As (III) from wastewater. In this direction, a graphene oxide modified SiO2 (SiO2-GO) nanocomposite was designed to enhance the adsorption power of bare SiO2. After successful removal of cationic inorganic contaminants, focus was on the removal of anionic species like F􀀀 ion from wastewater. Al2O3 is considered to be an excellent adsorbent for fluoride removal from polluted water. To improve its adsorption capacity, the alumina nanostructures were modified with cross-linked chitosan-HPMC biocomposite film (CgHA) for superior fluoride removal capacity from water/wastewater. Another major part of this PhD thesis is to use modified oxide-based nanostructures for organic contaminant removal from water by photodegradation process. CeO2 has been a prominent photoharvesting oxide nanostructure with improved photcatalytic efficiency. Keeping an eye on this, a direct Z-scheme CeO2-ZnFe2O4-BRGO (BRZC) nanocomposite was designed via in situ reflux method with leaf extract as green solvent. Here, the BRZC photocatalyst showed excellent photodegradation efficiency towards chloropyrifos pesticide. In the fourth project, visible light active WO3 nanostructures were modified with a conducting polymer PANI and ZnWO4 nanostructures and synthesized a WO3-ZnWO4-PANI (PZW) ternary nanocomposite following an ionic liquid (IL) assisted in situ oxidative polymerization method. The ternary nanocomposite was utilized for enhanced photocatalytic degradation of glyphosate herbicide. Motivated by the potential results of WO3 in photocatalysis, the final project involved the modification of WO3 nanostructures with PANI and magnetic spinel nanostructures CoFe2O4. The WO3-CoFe2O4-PANI (PCFW) nanocomposite, synthesized by microwave assisted ionic liquid method was found to be an excellent photocatalyst for visible light mediated degradation of tetracycline anti-biotic. All the oxide based nanocomposites demonstrated in this PhD thesis are stable, efficient, and recyclable for adsorptive and photocatalytic water purification applications.