Abstract

Composite photocatalysts that consist of TiO2and noble metal nanostructures have been considered tobe the promising and pivotal material for accessible enhancement of the efficiency in the photocatalyticprocess carried out in the aqueous and gas phases. In this work we fabricated porous TiO2microspheresthrough a hydrothermal process followed by photochemical reduction of noble metal nanoparticles atthe TiO2surface. The morphology and structure of M-TiO2spheres (M = Ag, Au, Pt and Pd) were studiedwith the use of various techniques, including transmission electron microscopy (TEM), X-ray powderdiffraction analysis (XRD), photoluminescence (PL) and UV–vis diffuse-reflectance spectroscopy (DRS).The effect of metal amount (from 0.1 to 1 wt.%.) on the photocatalytic activity during toluene degradationin gas phase and phenol degradation in aqueous phase was investigated. Additionally, the photocatalyticactivity of the M-TiO2samples was evaluated by measuring the formation rate of photo-induced hydroxylradicals (•OH) under UV–vis light irradiation using coumarin as a probe. The obtained results indicatedthat toluene could be mostly removed from the air over TiO2microspheres modified with Ag, Au, Pt, andPd nanoparticles. UV-mediated photoreactivity was almost similar for all samples obtained by loadingmetals from solutions consisting of 0.1 and 1 wt.% of metal precursors. Under visible light, except for Au, ingas phase toluene oxidation, the optimized loading of the metals was 0.1 wt.-% (photoreactivity changedin order: Ag-TiO2≈ Pd-TiO2> Pt-TiO2» Au-TiO2). In case of phenol degradation in the aqueous phase, inthe presence of UV irradiation the highest amount of metal (1.5 wt.%) was profitable, while under the Vislight reaction the medium amount of metal (0.5 wt.%) was beneficial. Additionally, it was noticed thatphenol was degraded not only via oxidation by•OH radicals but probably also in direct reaction withthe photogenerated carriers (e−/h+), particulary in the presence of TiO2spheres loaded with Au and Agnanoparticles.

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Authors (5)