Ti doped ZnO nanoparticles for photocatalytic hydroxyl radical generation under UV light for improved dye degradation and antimicrobial activity

Abstract

Photocatalysts are emerging as promising material for various light driven chemical reactions for the applications ranging from fuel generation to pollutant degradation. In this study, we synthesized ZnO and Ti doped ZnO (Ti:ZnO) nanoparticles inpropanol using sol-gel method with 2 -12.8atomic percents (at.%) of Ti doping in Ti:ZnO.The composition and optical response of the nanoparticleswere studied using energy dispersive spectroscopy (EDS) and diffuse reflectance spectroscopy respectively.The morphological and crystalline quality of the nanoparticles were reported using high resolution scanning electron microscopy (HRSEM) andX-ray diffraction (XRD) respectively.The role of Ti doping on crystallinity, photocatalytic response and anti-microbialactivityis addressed. Using ZnO nanoparticles, degradation of methylene blue occurred with rate constant of about 4.6x10^-2 min^-1 which was found to increase by 20% for 12.8% Ti in Ti:ZnO photocatalyst.For other Ti dopant concentrations the degradation rate constant decreased attributing to lower crystallite size with higher grain boundaries leading to charge carrier recombination and suppressed formation of reactive oxygen species.By addition of varying concentration of iso-propyl alcohol, the suppressed degradation process revealed the role of hydroxyl radicals in this low power UV light assisted photocatalysis. This was further supported with controlled experiments through generation of photoluminescence in terephthalic acid induced by the hydroxyl radicals. Ti:ZnO nanoparticles also showed significant anti-bacterial activity towards the gram positive (Staphylococcus aureus, Streptococcus mutans) andgram negative (Pseudomonas aeruginosa, Klebsella pneumonia) organisms. In addition to that, these nanoparticles also showed remarkable activity against fungi Candida albicans and Aspergillus flavus due to their greater surface area leading to generation of hydrogen peroxide. This study reveals importance of crystallite size in dye degradation process and anti-bacterial activity. The grown Ti:ZnO nanoparticles using a simple and scalable synthesis route are highly efficient photocatalyst material and anti-microbial agent for application of waste water treatment in industrial effluents and bacterial killing.