Doped Titanium Dioxide Nanostructures for Environmental Applications

Abstract

Titanium dioxide (TiO2) nanostructures have enormous application in various fields such as sensors, water splitting, super capacitors and, photovoltaic devices, etc. And they are extensively exploited for number of other energy and environmental applications now-a-days. As, the rapid urbanization and industrialization is polluting both water, air and existing developed technologies do not have adequate potential to overwhelm this environmental dilemma. Photocatalysis based on TiO2 nanostructures have procured significant attention in current era for the complete decomposition of hazardous compounds from water and purification of air due to low cost, thermal stability, chemical stability, huge surface area, non toxicity. This thesis is mainly focused on the use of doped nanostructure titanium dioxide as photocatalyst for environmental application specifically mineralization of dyes (alizarin red S, procion blue MXR, malachite green) and phenol, and photoreduction of carbon dioxide using un-doped and co- doped titanium dioxide nanostructures with anion i.e., sulfur (1 wt%) and transition metal ions (copper, cobalt, ruthenium, iron and chromium with varying the concentration from 1-5 wt %) having excellent chemical and photostability, good crystallite size, homogenous distribution, superior structural properties and excellent surface area and pore volume were synthesized by singe-step sol-gel reaction. The structural and morphological properties of prepared nanostructures were exploited by X-Ray Diffraction (XRD), Diffuse Reflectance Spectroscopy (DRS), Scanning Electron Microscopy coupled with Energy Dispersive Spectroscope (FESEM- EDX), High Resolution Transmission Electron Microscopy (HRTEM), Raman Spectroscopy, Thermal Analysis (TGA/DSC), Brunauer–Emmett–Teller (BET) surface analysis, Rutherford Back Scattering (RBS) and Fourier Transform Infra Red Spectroscopy (FTIR). The synergetic effect of anion and metal ion doping on titanium dioxide tailored the morphological and bulk superficial properties of the samples. Doping induced structural changes, enhancement of the visible light absorption capability, surface area, stability and photocatalytic activity. However, 5% metal ion co-doped titanium dioxide nanostructures demonstrated efficient band gap, thermal stability, good particle size, higher surface area and remarkably higher photocatalytic activity for photodegradation of dyes and phenol and CO2 photoreduction as compared to un-doped, S-doped and co-doped TiO2 with lower amount of metal ion. The parameters that affect the photocatalytic activity of TiO2 nanostructure powders for degradation of pollutants, namely concentration of dyes, catalyst loading, pH, irradiation source, and recyclability were optimized. The CO2 reduction and recycling of CO2 into value added products such as methane, methanol, ethanol, etc. was carried out under both UV and visible range and hydrogen was obtained from water in- situ. TiO2 nanostructures were found to be feasible and attractive for CO2 environment management and waste water treatment due to rapidness, cost effectiveness, catalyst inert nature, photostability and competent reusability. Hence, the activity of titanium dioxide nanostructure in visible range suggested that solar energy can be an alternative cost effective light source to resolve the environmental problems in future and this single step process can useful for industries.