Evaluation of the photocatalytic activity of photocatalysts
Photodegradation experiments were performed using a custom-made photocatalytic reactor to evaluate the effect of contact time on the photodegradation process. The kinetics of the photodegradation of MO were studied using F-doped photocatalysts owing to their superior photocatalytic properties. The photodegradation studies were carried out using 100 mL of synthetic wastewater at 25 °C, at pH 7.2, a photocatalyst dosage of 500 mg, a dye concentration of 2 mg/L, and contact time of -60, 0, 60, and 120 min in a 150 mL beaker, following a variation of the method reported by Mukonza et al.25 To eliminate the interference of leftover photocatalyst in absorbance readings, a blank experiment of distilled water and photocatalyst was set up. All samples were stirred in the dark for 1 h under room temperature (25±1 °C) to attain absorption equilibria before being irradiated with visible light in the photocatalytic reactor.
The concentrations of MO before (C0) and after (Ct) photodegradation experiments were determined based on UV-Vis absorbance spectra. Samples (4 mL) were drawn at 1 h intervals using a 10-mL syringe and filtered through a 0.45-µm filter. The aliquots were centrifuged and the residual concentration of MO “in the supernatant was measured at 460 nm using a UV-Vis spectrophotometer (Spectroquant® Pharo 300). The dye removal (r) was computed using Equation 3.
“The order of reaction for the photocatalytic degradation of MO was confirmed using the linearised Langmuir–Hinshelwood model (Equation 4). where kapp is the apparent reaction rate constant.
Article TitleVisible light photodegradation of methyl orange and Escherichia coli O157:H7 in wastewater
Water pollution due to dyes and pathogens is problematic worldwide, and the disease burden is higher in low-income countries where water treatment facilities are usually inadequate. Thus the development of low-cost techniques for the removal of dyes and pathogens in aquatic systems is critical for safeguarding human and ecological health. In this work, we report the fabrication and use of a photocatalyst derived from waste from coal combustion in removing dyes and pathogens from wastewater. Higher TiO2 loading of the photocatalyst increased the removal efficiency for methyl orange (95.5%), and fluorine-doping improved the disinfection efficacy from 76% to 95% relative to unmodified material. Overall, the work effectively converted hazardous waste into a value-added product that has potential in point-of-use water treatment. Future research should focus on upscaling the technique, investigating the fate of the potential of the photocatalysts for multiple reuse, and the recovery of TiO2 in treated water.