Simultaneous H2 Production and Bleaching via Solar Photoreforming of Model Dye‐polluted Wastewaters on Metal/Titania

Dyestuff substances in textile wastewaters are harmful pollutants which pose serious disposal challenges. A solar photocatalytic treatment combining degradation of structurally diverse dyes (Rhodamine B, Reactive Orange 16 or Auramine O) and energetic valorisation by H2 production on systematically varied M/TiO2 (M=Au, Ag, Cu or Pt) is herein explored. Bleaching was efficient in all cases, and especially rapid for azo (>98 % after 2 h) as compared to poly‐heterocyclic chromophores. Interestingly, dye degradation rates were similar to literature results under aerobic conditions, whereby no energy recovery is possible. Due to the recalcitrant dye structures, H2 production becomes markedly sensitive to metal co‐catalyst chemistry and morphology. The occurrence of active metallic, i. e. M(0), surfaces in sufficiently large nanoparticles are key to ensurie initial H2 evolution. An increase in Au domain sizes from 101 up to 102 nm ranges resulted in 10‐fold site‐specific catalytic activity (TOF) enhancement, whereas growth of Pt nanoparticles well above the sub‐nanometric regime was essential for efficient H2 production. In quest of using affordable metallic elements, bleaching and sustained H2 evolution was proven after prolonged irradiation using Cu/TiO2, owing to the in situ reduction of the copper co‐catalyst. In summary, anaerobic photoreforming can be as efficient as the more common aerobic approach, also allowing energy recovery in the form of waste‐derived hydrogen.