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

Abstract：

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 O^2-(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.