Ultra-thin SiO2 layers on TiO2: improved photocatalysis by enhancing products' desorption

Abstract

A study on the photocatalytic degradation of contaminants (salicylic acid and stearic acid) on titanium dioxide films overcoated with a few monolayers of silica is presented herein. A rather uncommon situation was observed, where the presence of the thin silica layers decreased the degradation rate of stearic acid while increasing that of salicylic acid. The results were explained by addressing the effect in the presence of silica films on the desorption of the intermediate products formed in the degradation of salicylic acid. This finding, which may apply also to other aromatic compounds, may have implications on the design and operation of photocatalytic devices for indoor applications, since ultrathin layers of silica are known to be formed over time on the photocatalyst. An interesting effect of the thickness of the silica sub-nanometre layer on the degradation rate of salicylic acid was explained in terms of gradual changes in the isoelectric point. If optimized, this effect can be utilized to precisely control adsorption or desorption and accordingly to induce specificity in the photocatalytic degradation of contaminants. A methodology for preparing a molecularly imprinting photocatalyst with an inert ultrathin layer in between the imprinted sites was presented. It was found that overcoating the area in between the imprinted sites preserved the benevolent effect of imprinting. While at present the imprinting effect was moderate, there is a reason to believe that this effect can be improved considerably by controlling the type of inert overlayer.

Interactions of titania based nanoparticles with silica and green-tea: Photo-degradation and -luminescence

“…2 (a2) and (b2). So, the peak at 1076 cm À1 corresponds to m(SiAOASi) and the two peaks at 1096 and 1180 cm À1 are associated with SiAOATi bond [45,46]. The peak at 953 cm À1 corresponds to SiAOH peak and the carbonyl group peak can be assigned at 1716 cm À1 .…”

Chapter Green Nanotechnology: Development of Nanomaterials for Environmental and Energy Applications

“…Selection of the second material might have been based on the easiness of processing and controlling its porous structure. This can be explained by the 218 wide use of silicates in many applications (147,154). Meanwhile, there has been no attempt to use porous TiO 2 photocatalysts for the size exclusion.…”

“…Photocatalysts can also be specially designed for selectivity. This includes doping with noble metals, coating with a specific material, impregnation onto inert organic/inorganic domains, and chemical imprinting (138,(144)(145)(146)(147). Mixing activated carbon and TiO 2 particles was found to increase the degradation rate of phenol (148).…”

“…Selection by size has been researched by developing innovative photocatalytic materials with well-defined specific porous structures (147,(152)(153)(154). As an example, incorporation of TiO 2 particles into sheet silicates of clay was suggested (152).…”

“…Prevention of the nonspecific sorption and oxidation of coexisting organic chemicals at the TiO 2 surface (e.g., NOM, organic interferents, proteins, microorganisms, and any organic chemicals other than target chemicals) is of interest (141)(142)(143)(144)(145)(146)(147). Operational parameters, including temperature, pH, residence time, solvent, and UV wavelength, can change the degradation ratio of more than two competing chemicals (138).…”