Mechanical Seminar (The 57th Hiroshima University ACE Seminar)
Lecture： Velayutham MURUGESAN, Annamalai University (India)
Title: Nano semiconducting Materials for Wastewater Remediation
Date： 9/20, 11:00-12:00
Place： Engineering A3-131 Lecture Room, Higashi-Hiroshima Campus, Hiroshima University
Contamination of water resources by man-made industrial chemicals and pesticides interfere with the normal functioning of human and wildlife endocrine systems. A wide range of substances including pesticides, surfactants, plasticizers and organohalogens are collectively referred to as endocrine disruptors. The removal of endocrine disrupting chemicals (EDCs) from wastewater is a complex problem, and this cannot be resolved by conventional treatment methods. Photocatalytic degradation is a promising technique for mineralisation of various organic pollutants in wastewater including EDCs. Among the semiconductors employed, bulk TiO2 is a good photocatalyst because of its high photosensitivity, non-toxicity, easy availability, strong oxidising power and long-term stability. Several attempts have been made to improve the efficiency of bulk TiO2. Nanocrystalline TiO2 is expected to offer better solution as it exhibits unique properties such as quantum size effect, high surface area, tunable surface properties and short interface migration distances, all of which enhance photocatalytic performance.
This presentation highlights the preparation, characterisation and photocatalytic performance of nano TiO2, La3+, Gd3+ and Zr4+ doped nano TiO2. The materials were prepared by sol-gel process and characterised using XRD, BET, FT-IR, TGA, UV-Vis, SEM, XPS and TEM. The band gap values of doped nano TiO2 were higher than the pure nano TiO2. The entry of dopant ion into the lattice of nano TiO2 created charge compensating anion vacancy in the lattice points of nano TiO2 which enhanced adsorption of pollutants. Further, the dopant ion like Zr4+ with ionic radius (0.79 Å) larger than Ti4+(0.75 Å) but smaller than O2-(1.31 Å) can either isomorphously substituted or interstitially introduced into the matrix of nano TiO2, thus producing oxygen vacancies which accelerate the transition and nanocrystallite growth of anatase form of nano TiO2. The photocatalytic activity in the degradation of selected EDCs like monocrotophos, bisphenol-A, carbofuran and 2,4,6-trichlorophenol were found to be higher for doped nano TiO2 than pure nano TiO2 and commercial TiO2 (Degussa P-25). The influence of various parameters such as initial concentration of pollutants, catalyst loading, pH and light intensity were optimised for maximum degradation efficiency. The detailed results will be discussed in this presentation.