Hybridization of adsorptivity with photocatalytic activity—carbon-coated anatase

Carbon-coated anatase catalysts were prepared from poly(vinyl alcohol) (PVA) and TiO2 of anatase structure. Powders of PVA and commercial TiO2 (ST-01) were mixed with different mass ratios and were heated at 700 and 900 °C under nitrogen. Such prepared catalysts were tested for adsorption and decomposition of two different dyes: methylene blue (MB) and Reactive Black 5 (RB5). Photoactivities of carbon-coated anatase catalysts were compared with ST-01. Carbon coating anatase suppressed anatase transformation to rutile at high temperatures. It was experimentally proved that this suppression appeared in samples with carbon content above 5 mass%. The crystalline structure of anatase was improved in catalysts heated at 900 °C. Although the sintering of anatase crystals was depressed by the carbon layer, the BET surface area of catalysts decreased, but not so much as it was observed in ST-01 heated at 700 °C. Adsorption of both dyes, MB and RB5 on carbon-coated samples was much more higher than on the original ST-01 and that heated at 700 °C. MB photodecomposition was much more higher on carbon-coated TiO2 catalysts than on ST-01. But Reactive Black 5 was decomposed faster on ST-01 than on carbon-coated TiO2. It can be explained by different mechanism of photodecomposition. Surface diffusion of adsorbed species through the carbon layer slowed down the rate of decomposition. High crystalline structure of anatase seems to be important in the photodecomposition process.