Photocatalytic wastewater purification with simultaneous hydrogen production using MoS2 QD-decorated hierarchical assembly of ZnIn2S4 on reduced graphene oxide photocatalyst

Abstract

It is attractive to photocatalytically purify wastewater and simultaneously convert solar energy into clean hydrogen energy. However, it is still a challenge owing to the relatively low photocatalytic efficiency of photocatalysts. In this study, we synthesized a molybdenum disulfide (MoS₂) quantum dot-decorated 3D nanoarchitecture (MoS₂QDs) of indium zinc sulfide (ZnIn₂S₄) and reduced grapheme oxide (MoS₂QDs@ZnIn₂S₄@RGO) photocatalyst using a simple solvothermal method. The RGO promotes the electron transfer, and the highly dispersed MoS₂QDs provides numerous catalytic sites. The photocatalytic purification of rhodamine B (RhB), eosin Y (EY), fulvic acid (FA), methylene blue (MB) and p-nitrophenol (PNP) in simulated wastewaters were further tested. The degradation efficiencies and TOC removal were 91% and 75% for PNP, 92.2% and 72% for FA, 98.5% and 80% for MB, 98.6% and 84% for EY, and 98.8% and 88% for RhB, respectively (C_organics = 20 mg/L, C_catalyst = 1.25 g/L, t = 12 h, I_light = 3.36 × 10^-5 E L^-1 s^-1). Among these tests, the highest hydrogen production was achieved (45 μmol) during RhB degradation. Both experimental and calculational results prove that lower LUMO (lowest unoccupied molecular orbit) level of organic molecules was available for transferring electrons to catalysts, resulting in more efficient hydrogen production. Significantly, the removal efficiencies of natural organic substances in actual river water reached 76.3-98.4%, and COD reduced from 32 to 16 mg/L with 13.8 μmol H₂ production after 12 h.

Keywords: Hydrogen production; Photocatalysis; Wastewater purification.