Combining photocatalytic water treatment and fuel synthesis: improving the activity of TiO2 by cobalt - doping and Ag/Ag2O - deposition
- [published Version]
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Description:
Water treatment and solar fuel synthesis are nowadays considered to be the two major concerns for achieving a sustainable living environment. With the growing demand for advanced environmental remediation of polluted water and as the cost of fossil fuels increases, photocatalysis has received increasing attention in recent years. In the present work, modified TiO2 photocatalysts are used for both photocatalytic processes. Initially, TiO2 (P25) is modified with different mass ratios of self-prepared Ag/Ag2O employing two synthetic methods, namely, a mechanical mixture and a precipitation method. After the characterization, the photocatalytic activity of the seven prepared materials including Ag/Ag2O, Ag/Ag2O ⁄⁄ TiO2 mixtures (TM), and Ag/Ag2O ⁄⁄ TiO2 composites (TC) is evaluated by methylene blue (MB) bleaching under UV-vis and only visible light illumination. The results reveal that the light-induced bleaching of aqueous MB in the presence of TM and TC under both UV-vis and visible illumination is enhanced. Interestingly, Ag/Ag2O shows the best photocatalytic activity under both illumination conditions. However, the observed photobleaching of MB is found to be rather initiated by an interfacial electron transfer from the photo-excited MB adsorbed at the surface of Ag2O to the latter′s conduction band. Moreover, XRD and XPS data confirm that Ag2O performs as an electron acceptor in the light-induced reaction of MB, and Ag+ is reduced to Ag(0). On the other hand, photocatalytic H2 generation from methanol reforming under solar light using all-synthesized photocatalysts is also studied. The experimental results indicate that bare Ag/Ag2O is not able to transfer an electron to H+, which is also confirmed by the flatband potentials measurements. Nevertheless, with increasing the mass fraction of TiO_2 in the TC and TM, the evolved amounts of H2 are observed to increase implying that the fraction of photons absorbed by Ag2O being inactive decreases. Hence, it is concluded that Ag/Ag2O is not a (photo)stable material ...