(405g) Visible Light Induced Degradation and Disinfection Using Multifunctional Ag/AgCl – Activated Carbon Composite Photocatalysts

In this study, novel Ag/AgCl – activated carbon (AC) composite photocatalysts were prepared and their activity tested for visible light induced photocatalysis. These composites combine the high visible light activity of Ag/AgCl, which arises due to its surface plasmon resonance and charge separating effects, with the improved mass transfer and adsorption characteristics of activated carbon. The composites were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, N₂ adsorption-desorption porosimetry  and UV-visible light diffuse reflectance spectroscopy, and the properties of the composites and the effect of the incorporated catalyst on the AC matrix were elucidated. The composites were found to possess good adsorption capabilities, and the sorption kinetics, isotherms, and mechanism were investigated using methyl orange (MO) as a model organic pollutant.  The photocatalytic degradation of MO was studied under visible light, and was modelled using Langmuir-Hinshelwood kinetics. The effects of solution concentration, pH, and radical quenchers on the overall reaction rate were also studied, and a mechanism of photocatalysis proposed where the silver acts as the electron/hole generator, and polarization of the photoinduced charge relative to the AgCl facilitates electron-hole separation, while the AC works to concentrate the MO around the active sites. The prepared Ag/AgCl – AC was also investigated for use as an antibacterial and photocatalytic inactivation agent against a model microorganism, Escherichia coli K-12. The antibacterial and photocatalytic effects were confirmed, and their relative contributions to inactivation were compared via zone of inhibition, multiple-blot, and standard plate count assays. The photocatalyst was found to inactivate up to 99.5% of bacteria under irradiation for sixty minutes in a 5 g/L slurry. The composite also possessed some antibacterial action due to the incorporated nanosilver; however, the action of the photo-induced radical species on the bacteria was thought to dominate the process in the presence of irradiation. The mechanism for photocatalytic cell death was probed using selective plate assays, measurements of potassium ion leakage from the cells during treatment, and Fourier Transform Infrared spectroscopy (FTIR) to investigate structural changes which occurred. From these studies, inactivation was thought to be initiated by the action of photo-induced radical species on the cell wall. Due to its activity for visible light induced degradation and disinfection, the novel Ag/AgCl - AC prepared provides interesting potential for use as visible light active photocatalysts in applications such as solar photocatalytic water treatment.