| dc.description.abstract | Photochemistry is a process based on transforming the energy of absorbed photons into chemical bonds. Here, sunlight-induced charge generation in a semiconductor material can facilitate the conversion of various (waste) materials into value-added chemicals via reduction or oxidation. To achieve high conversion efficiencies, the semiconductor requires a bandgap with an energy matching the reduction or oxidation potential of the respective species. In addition, the absorption of the semiconductor should overlap with the emission of sunlight to minimize absorption losses. Photochemistry is a promising way to tackle some of the global issues faced today. Due to the ever-growing CO2 pollution in the atmosphere, the photoinduced reduction of CO2 into useful chemical building blocks, such as CO and CH4, can play a paramount role in reversing the devasting effects of CO2 on the global climate. In this work we continue on this virtue and focus on using elpasolite-structured Cs2AgBiBr6 (CABB) for photochemical reactions. This photoactive material is better known as a double perovskite (DP) and has a high stability under ambient conditions. However, CABB shows moderate absorption of visible light, especially at higher wavelengths. We aim to increase the visible light absorption of CABB by substituting the Bi3+ cation with another cation, lowering the bandgap energy and shifting the absorption towards higher wavelengths. This way we seek to increase the photochemical activity of CABB without compromising the chemical stability. We have first incorporated Sb3+ at the sites of Bi3+ at known ratios of Sb3+:Bi3+ and synthesized crystalline DP thin films. We assessed the photochemical activity of these thin films for photochemical CO2 reduction and monitored the production of CO and CH4 via gas chromatography. These measurements indicated that the low performance of our DP thin films makes it challenging to observe the effect of bandgap manipulation on the photoactivity. Hence, we directed our research to another photochemical process, namely dye degradation, which is often used as a model system to study changes in photochemical activity. In this part of the work, we are interested in evaluating the effect of DP alloying on the photochemical activity towards rhodamine B (RhB) and methylene blue (MB) degradation. A solid-state mechanochemical synthesis approach is used to produce an extensive inventory of different alloyed DPs, (partially) replacing the Bi3+ with Sb3+, In3+, Fe3+, Al3+, Sn2+, and Ti4+, respectively. Crystallography analysis reveals that, using a ball mill setup, each of the cations mentioned above could be incorporated into the CABB crystal structure forming a crystalline composite. In addition, UV-Vis diffuse reflectance spectroscopy shows a favorable redshift of the absorption for some of these composites (i.e., Sb, Fe, Sn, and Ti-based DPs). Several dye degradation experiments are recorded under irradiation of various light sources. The results of these experiments indicate that the addition of up to at least 10% Fe3+ as replacement of Bi3+ improves the light absorption and enhances the degradation rate of MB under irradiation of blue and green light. These results highlight the promising endeavor towards improving photochemical reaction activities of DP materials. | |
