Titanium Dioxide Coupled with Tungsten Trioxide and Titanium Dioxide Coupled with Molybdenum Trioxide Nanocomposite-Assisted Photocatalytic Inactivation of Escherichia coli in Direct Sunlight, Solar Simulator, and Visible Light

Florence Masese; Shem Wandiga; Vincent Madadi; Damaris Mbui; Stephen Ojwach

Florence Masese Department of Chemistry, University of Nairobi
Shem Wandiga Department of Chemistry, University of Nairobi
Vincent Madadi Department of Chemistry, University of Nairobi
Damaris Mbui Department of Chemistry, University of Nairobi
Stephen Ojwach University of KwaZulu-Natal, School of Chemistry and Physics

Keywords: Photocatalysis, semi-conductors, Reactive oxygen species, Escherichia coli

Abstract

Photocatalysis may be considered as a possible alternative method in the elimination of Escherichia coli from domestic water. It has several advantages when compared with conventional methods, as it is non-toxic, utilizes energy from the sun and offers a green route that could be used to purify water polluted with Escherichia coli. The aim of the study was to investigate the effectiveness of the synthesized modified titanium dioxide photocatalyst in disinfecting Escherichia coli in domestic water under varied light intensities. Escherichia coli concentrations between 400 and 800 colony forming units per milliliter were used to investigate photocatalytic disinfection of the water containing Escherichia coli, under three different sources of light; visible light, natural sunlight and illumination from a solar simulator.
The two linked photocatalysts, titanium dioxide coupled with tungsten trioxide and titanium dioxide coupled with molybdenum trioxide were compared in disinfection studies to examine the impact of catalyst loading on disinfection rate. The synthesised photocatalysts were also characterised using the Energy Dispersive X-ray, Transmission Electron Microscopy, and Scanning Electron Microscope. The results showed that titanium dioxide coupled with tungsten trioxide was more successful in killing Escherichia coli bacteria compared to titanium dioxide coupled with molybdenum trioxide across all tested light sources: natural sunlight, visible light, and light from a solar simulator. After 120 minutes of irradiation using 1g/L of each catalyst, the results showed significant differences in inactivation efficiencies. Under natural sunlight, titanium dioxide coupled with tungsten trioxide achieved a high disinfection rate of 96%, whereas titanium dioxide coupled with molybdenum trioxide achieved 89%. A similar trend was observed under visible light, with efficiencies of 95% and 88% for titanium dioxide coupled with tungsten trioxide and titanium dioxide coupled with molybdenum trioxide respectively. When exposed to irradiation from a solar simulator, titanium dioxide coupled with tungsten trioxide performed better, with an efficiency of 92%, compared to 83% for titanium dioxide coupled with molybdenum trioxide. Experiments carried out without catalysts, served as blanks. These experimental results confirm that coupled titanium dioxide nanoparticles are effective and may be used in treating domestic water contaminated with Escherichia coli.