Organic Moiety-Regulated Photocatalytic Performance of Phosphomolybdate Hybrids for Hexavalent Chromium Reduction

Visible-light-driven photocatalytic Cr(VI) reduction is a promising pathway to moderate environmental pollution, in which the development of photocatalysts is pivotal. Herein, three hourglass-type phosphomolybdate-based hybrids with the formula of: (H₂ bpe)₃ [Zn(H₂ PO₄ )][Zn(bpe)(H₂ O)₂ ]H{Zn[P₄ Mo₆ O₃₁ H₆ ]₂ } ⋅ 6H₂ O (1) Na₆ [H₂ bz]₂ [ZnNa₄ (H₂ O)₅ ]{Zn [P₄ Mo₆ O₃₁ H₃ ]₂ } ⋅ 2H₂ O (2) and (H₂ mbpy) {[Zn(mbpy)(H₂ O)]₂ [Zn(H₂ O)]₂ }{Zn[P₄ Mo₆ O₃₁ H₆ ]₂ } ⋅ 10H₂ O (3) (bpe=trans-1,2-bi(4-pyridyl)-ethylene; bz=4,4'-diaminobiphenyl; mbpy=4,4'-dimethyl-2,2'bipyridine) were synthesized under the guidance of the functional organic moiety modification strategy. Structural analysis showed that hybrids 1-3 have similar 2D layer-like spatial arrangements constructed by {Zn[P₄ Mo₆ ]₂ } clusters and organic components with different conjugated degree. With excellent redox properties and wide visible-light absorption capacities, hybrids 1-3 display favourable photocatalytic activity for Cr(VI) reduction with 79%, 70% and 64% reduction rates, which are superior to that of only inorganic {Zn[P₄ Mo₆ ]₂ } itself (21%). The investigation of organic components on photocatalytic performance of hybrids 1-3 suggested that the organic counter cations (bpe, bz and mbpy) can effectively affect the visible-light absorption, as well as the recombination of photogenerated carriers stemmed from {Zn[P₄ Mo₆ ]₂ } clusters, further promoting their photocatalytic performances towards Cr(VI) reduction. This work provides an experimental basis for the design of functionalized photocatalysts via the modification of organic species.