Eco-Friendly Synthesis of Metal Doped TiO2 Nanoparticles for Photocatalytic Application in Water Treatment

Abstract

In this thesis, Nano-porous TiO2 anatase as well as metal (In & Ga) doped TiO2 anatase were Environment-Friendly prepared using Coffee Husk Extract (CHE) as bio-template instead of hazardous chemicals and solvents and ultrasonic waves. Caffeine and Caffeic acid were found to be the main compounds in CHE to modify the morphology of TiO2. The properties of as-prepared Titanium Dioxide particles were determined by different characterization techniques. The results demonstrate the formation of meso/macro-porous channel consisting of small TiO2 particles (8-10 nm). The as prepared green nanoparticles exhibited improved photocatalytic activity for the degradation of organic water pollutants with good recyclability. The enhancement in efficiency of green Nanoporous TiO2 can be attributed to higher surface area and the presence of more active adsorption sites inside the pores. In addition, the antimicrobial activity of the green TiO2 nanoparticles has been evaluated for disinfection of E-coli. The as prepared green Nanoporous TiO2 has shown 99.1 % efficiency for E-Coli disinfection.Upon Indium and Gallium doping of TiO2 nanoparticles, the photocatalytic activity for degradation of MB, phenol and Pb2+ ions reduction was further improved. This improvement has been readily linked to the fact that, upon doping new trapping locations are added that affect the durability of the charging carriers by separating the time of arrival of the photogenerated electrons and holes entering the layer of the photocatalyst, thus reducing the recombination of electron – hole pair.Interestingly, photocatalytic behavior was dramatically enhanced by adding a small portion of 0.5 % of dopants. A further increase in the doped concentration decreases the photocatalytic activity. An improvement in photocatalytic activity of 0.5 % can be attributed to the absorption the photoexcited electrons by dopant species leading to division of charge carrier, thereby helping to improve photocatalytic operation. By increasing dopant amount, the accumulation of the dopant can cover part of the TiO2 surface, reducing the number of surface-active sites and thus the photocatalytic activity.Moreover, the antibacterial activity of In and Ga doped TiO2 nanoparticles reached 100 %. The enhancement of the antibacterial activity against the gram-negative Bacteria E-Coli is readily attributed to the fact that, In and Ga doped TiO2 samples are associated with increasing negative zeta potential up to -29.3 mV compared with less negative value of the undoped TiO2 nanoparticles (-9.85 mV), due to increasing surface hydroxyl group. Since the6bacterial disinfection mechanism in the presence of nanoparticles based on the interaction of the TiO2 surface ions with the bacterial cell walls cause the damage the cell walls, followed by increasing membrane permeability leading to loss of the proton motive force and outflow of intracellular components. Thus, increasing surface hydroxyl group upon doping leading to increasing bacterial disinfection. It is believed that, the current research provides low cost and safe and eco-friendly way to produce efficient photocatalyst and antimicrobial agent for remediation of polluted water