Search

Photoreduction/removal of cadmium was studied at pH 7 using TiO2 Degussa as photocatalyst, and either formate or methanol as hole scavengers. In the absence of organic additives, approximately 60% of 30 ppm cadmium was found to be removed from the solution by adsorption. Addition of formate resulted in the photoreduction of cadmium to its metallic form. No cadmium reduction was observed when methanol was added as the hole scavenger. Zeta potential measurements of the catalyst suspensions and studies on the extent of organic additive adsorption and mineralisation were used to prove the photoreduction process. It was found that the adsorption of both cadmium and the organic hole scavenger is crucial for the photoreduction of cadmium. It is postulated that to be an effective hole scavenger the organic additive needs to be easily photooxidised under an anoxic environment. In addition, the presence of formate radicals could be responsible for the Cd photoreduction. [Copyright &y& Elsevier]

Abstract: Natural zeolite coated with titanium dioxide (TiO2) was used as an adsorbent to rapidly remove humic acid (HA) from an aqueous solution. Coating TiO2 onto zeolite markedly improved its efficiency in adsorbing HA: most of the bulk organic matter (80%) could be removed within 5min of adsorption by the zeolite/TiO2 particles at neutral pH, whereas less than 20% was removed by bare zeolite alone. In addition, immobilisation of TiO2 onto zeolite permitted easier separation of the adsorbent from the treated water. Photocatalytic properties of TiO2 were exploited for the regeneration of the adsorbent. The adsorbent was shown to be readily regenerated by photocatalytic oxidation and was still effective in removing HA after 5 adsorption/regeneration cycles. These results indicate that TiO2-coated zeolite can be a very attractive adsorbent for the rapid removal of HA from aqueous solutions. [Copyright &y& Elsevier]

Abstract: The photocatalytic activity of sodium titanate (Na1.48H0.52Ti3O7), sodium hexatitanate (Na2Ti6O13), and hydrogen titanate (H2Ti3O7) nanoribbons and anatase TiO2 nanorods were compared for water splitting, oxalic acid photodegradation and H2 and O2 generation using sacrificial agents. The intrinsic properties of the materials were found to affect their performance depending on the particular reaction system. The Na2Ti6O13 nanoribbons, in the presence of RuO2 co-catalyst, outperformed the anatase nanorods, for the water splitting reaction, generating over 10 times more H2/O2. This was thought to derive from their tunnel-like structure which provided better electron/hole separation when compared with TiO2. However, the efficient holes and electrons scavenging in the presence of sacrificial agents, methanol or AgNO3, to generate H2 or O2, respectively, overwhelmed the tunnel-like structure effect. In this case photoactivity was governed by the crystal structure, with observed decreasing activity in the order TiO2>Na2Ti6O13>H2Ti3O7∼Na1.48H0.52Ti3O7, and by the band gap of the semiconductor which determined its capacity to absorb photons in producing electron/hole pairs. [Copyright &y& Elsevier]

Abstract: A photoreactor comprising a bundle of TiO2-coated quartz tubes was studied by varying its tube wall thickness and tube configuration as well as introducing a mesoporous SiO2 intermediate layer between the TiO2 coating and quartz tube. The bundled tube photoreactor (BTP) performance was assessed based on tube light propagation and photocatalytic degradation rate of ethylene. Increasing the tube wall thickness improved the tube light propagation and the degradation rate of ethylene. An array of eight 6-mm tubes was found to be the best BTP configuration in this work. The findings from varying the tube configuration suggested an effectively illuminated surface area as a second important parameter to consider when comparing different BTP performances. Introducing a mesoporous SiO2 intermediate layer with a thickness between 210 and 400nm between the TiO2 coating and quartz tube improved not only the tube light propagation but also the ethylene photocatalytic degradation rate by up to 70%. This improvement was attributed to controlled light refraction from the quartz tube, which can be achieved under the conditions of frustrated total internal reflection. [Copyright &y& Elsevier]

Abstract: A dopant-free aerosol synthesis of highly crystalline TiO2 nanoparticles (20–35nm) with tunable polymorphic content is demonstrated by rapid flame spray pyrolysis. By controlling precisely the total ambient oxygen partial pressure of the combustion in a quartz tube enclosure, anatase content as high as 96wt% (4wt% rutile) was obtained at high oxic flame conditions, while rutile content as high as 94wt% (6wt% anatase) was obtained under anoxic flames. The polymorphic variability lies within a narrow range of combustion equivalence ratios, that is, 1.0<Φ<1.5. Unlike any other flame aerosol syntheses, the anatase and rutile crystallite sizes were similar within each sample. Under highly oxic flame conditions (Φ<1.0), twinnings between anatase {011} planes could be observed, inferring oriented attachment taking place. Such mechanism could not, however, be seen under anoxic flame (Φ>1.0) possibly due to physical hindrance by surface carbonaceous content (typically <2wt%). The carbon content can be easily removed by short calcination without significantly affecting the surface areas and crystallite properties of the original TiO2 nanocrystals, preserving hence its pristine state. [Copyright &y& Elsevier]