Heterostructured TiO2@OC core@shell photocatalysts for highly efficient waste water treatment

Abstract

In this exemplary study, commercial titanium dioxide (TiO₂) particles (∼100–250 nm) were coated with a thin organic layer (OC) hydrothermally using different weight ratios of the TiO₂ particles and glucose. The obtained heterostructured TiO₂@OC core@shell particles were characterized using scanning electron microscopy, X-ray diffraction, and Raman spectroscopic analysis. Their photodegradation activity on the exemplary cationic methylene blue (MB) dye increased with certain starting weight ratios of TiO₂ particles and glucose as measured under UV light at a wavelength of 365 nm. The possible reason for the increased photocatalytic activity (from hours to minutes) is that the organic coating layer allows fast adsorption and activation of the organic pollutant compound. Furthermore, adsorption kinetic studies demonstrated that the heterostructured TiO₂@OC core@shell particles follow a pseudo-second-order rate model indicating a chemisorption process while the pristine TiO₂ particles follow a pseudo-first-order rate model showing a physisorption process. Equilibrium studies showed that both pristine TiO₂ and heterostructured TiO₂@OC particles undergo a monolayer adsorption of the MB molecules by following the Langmuir–Hinshelwood mechanism. The thermodynamic properties of the reaction classified the degradation of the pollutant as an exothermic spontaneous reaction at 25 °C with decreasing entropy at higher temperature. Additional degradation analysis was effectuated using Red MX-5B as an example of anionic dyes. Based on the obtained results, it can be concluded that this facile coating of photocatalytic TiO₂ particles with a thin organic layer is a promising method to increase their photocatalytic efficiency for water purification of both cationic and anionic contaminants. It is expected that this simple, scalable and cost-effective organic coating procedure could be applied for other photocatalysts.