Influence of Titanium on Photodegradation and Antimicrobial Properties of ZnO

Abstract

Photocatalysts are emerging as promising materials for various photolytic 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 using sol-gel method with 2–12.8 at % in ZnO. The chemical composition and optical response of the nanoparticles were studied using energy dispersive spectroscopy (EDS) and diffuse reflectance spectroscopy (DRS) respectively. The morphological and crystalline properties of the nanoparticles were characterised using high resolution scanning electron microscopy (HRSEM) and X-ray diffraction (XRD) respectively. The role of Ti doping on crystallinity, photocatalytic response and anti-microbial activity is addressed. Using ZnO nanoparticles, degradation rate constant of Methylene Blue (MB) about 4.6 × 10^–2 min^–1 occurred 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 due 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 isopropyl alcohol, the suppressed degradation process revealed the role of hydroxyl radicals in this low power UV light assisted photocatalysis. This was further confirmed 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) and Gram-negative (Pseudomonas aeruginosa, Klebsella pneumonia) organisms. In addition, 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 the role of grain size in dye degradation process and anti-bacterial activity. The Ti:ZnO nanoparticles obtained 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.