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.

We have explored the simultaneous degradation of cyanides and thiocyanate present in wastewaters from a cokemaking factory using photoassisted methods under varied illumination conditions (from simulated solar light to UV light). Overall, the photochemical degradation of cyanides was more efficient than that of thiocyanates, regardless of the illumination conditions, the effect being more pronounced in the absence of a photocatalyst. This is due to their different degradation mechanism that in the case of thiocyanates is dominated by fast recombination reactions and/or charge transfer reactions to electron scavengers. In all cases, cyanate, ammonia, nitrates, and nitrites were formed at different amounts depending on the illumination conditions. The conversion yield under simulated solar light was almost complete for cyanides and quite high for thiocyanates after 6 h of illumination. Regarding toxicity, photochemical oxidation at 254 nm and under simulated solar light decreased significantly the toxicity of the pristine wastewater, showing a correlation with the intensity of the irradiation source. This indicate that simulated light can be effectively used to reduce the toxicity of industrial effluents, opening an interesting perspective for optimizing cyanide detoxification systems based on natural light.