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Carbon-containing SiO 2-based photocatalysts were prepared by the solvothermal treatment of rice husk as biogenic precursor in the presence and absence of TiO 2 and used for the photocatalytic degradation of rhodamine-B under simulated solar light. Data showed that the prepared catalysts are mainly composed of biogenic silica and displayed mesoporous character with surface areas ranging from 65 to 174 m 2 g-1. The obtained materials showed photocatalytic activity comparable to that of commercial TiO 2-P25 powders for the degradation of rhodamine-B under sunlight. The calcination at 350 ºC improved the photocatalytic activity of the biogenic precursor by three times in the absence of TiO 2. At converse, calcination of sample SiO 2-TiO 2 decreased the photoactivity due to the appearance of non-photoactive TiSiO 4 crystalline phases in the catalyst, as inferred by XRD and XPS. A reaction mechanism for rhodamine-B degradation excluding the deethylation pathway has been proposed, based on the evolution of the absorbance spectra of rhodamine-B upon the photocatalytic tests.

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Photodegradation of methylene blue (MB) was studied on TiO2 in the presence of activated carbon (AC) prepared from the sawdust of a soft wood by physical activation under CO2 flow, by pyrolysis under N2 flow, and by chemical activation with ZnCl2 and H3PO4 under N2 flow. MB photodegradation was performed under UV and UV-visible irradiation to verify the scaling-up of the present TiO2-AC binary materials. It was verified that oxygenated surface groups on carbon were intrinsically photoactive, and a synergy effect between both solids has been estimated from the first-order apparent rate constants in the photodegradation of MB. This effect enhances the photoactivity of TiO2 up to a factor of about 9 under visible irradiation, and it was associated to the surface properties of AC.

<span>Photodegradation of methylene blue (MB) was studied on ZnO in presence of home-made biochars </span><span>prepared by different methods. MB photodegradation was performed under UV-visible irradiation to verify </span><span>the scaling-up of ZnO-AC hybrid materials. It was verified that oxygenated surface groups on carbon were </span><span>photochemically active in the photodegradation of MB and a synergy effect between both solids has been </span><span>estimated from the first-order apparent rate-constants. This effect enhances the photoactivity of ZnO up to </span><span>a factor about 2.5 and the difference in photoactivity in the binary materials was associated to the surface </span><span>properties of AC.</span>