Mixed perovskite- and mullite-type bandgap tailored visible light photocatalysts for wastewater purification

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The proposed project optimizes narrow bandgap materials for enhanced photocatalytic activity by using a combination of perovskite- and mullite-type compounds. Perovskite-type BiFeO3 and mullite-type Bi2Fe4O9 structures exhibit both high photocatalytic activities and oxidize organic pollutants, as in wastewater, into carbon dioxide and mineral acids under visible light irradiation. It is possible to substitute Fe3+ with other cations like Al3+, Ga3+ and Mn3+, also showing photocatalytic activity. Therefore, it bears a critical importance to investigate the rich set of solid solutions, by replacing the M-cations (M = Al3+, Ga3+, Mn3+) systematically, to establish a relation between composition, bandgap and the highest possible photocatalytic activity. The materials to be investigated are mainly Bi2M4O9 structures but explorative work on the Bi2Mn4O10 structure and related structures/compositions are as well planned. Our recent experiments showed that designing quantum-sized crystallites led to a co-crystallization of metastable (Bi1-xFex)FeO3 and Bi2Fe4O9. This finding offers the possibility to form two different photocatalytic active structures within one matrix leading to pseudo-single exciton stabilization analogous to that of well-known TiO2 rutile/anatase mixture. Using different synthesis routes such as the glycerin method, polyol method, PVA method and the flame spray pyrolysis different particle sizes, crystallite sizes as well as morphologies and perovskite-/mullite-type ratios could be produced. The materials will be characterized by diffuse reflectance UV/Vis spectroscopy, X-ray powder diffraction (XRPD), infrared (IR) and Raman spectroscopy, dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and microscopic methods (TEM, SEM and EDX). For selected samples of good quality, the photocatalytic activity will be determined. For selected samples of good quality, the photocatalytic activity is determined, for which a corresponding flow cell is built and used as a test system. The resulting decomposition products are examined for their toxicity as well as by potential material abrasion.