Metal-Regulated Different TeMo 6 O 24 6 – -Based MOCs with Viologen Ligand for Catalytic Reduction of Cr(VI) and Oxidation of CEES under Multi-Wavelength Irradiation

Three new dual-functional polyoxometalate (POM) -based metal-organic complexes (POMOCs): H2Zn2 (bcbpy) 2 (H2O) 8 (TeMo6O24) ·10H2O (BHU-10, HbcbpyCl = 1- (4-carboxybenzyl) -4, 4'-bipyridinium), H2Cu2 (bcbpy) 2 (H2O) 8 (TeMo6O24) ·10H2O (BHU-11), and H2Co2 (bcbpy) 2 (TeMo6O24) (H2O) 6·6H2O (BHU-12) were successfully synthesized. The central metal ion significantly modulates the structure: BHU-10 (Zn) and BHU-11 (Cu) adopt identical "sandwiched" structures comprising two M2 (bcbpy) 2 (H2O) 84+ units and a free TeMo6O246- cluster, whereas the Co-based BHU-12 exhibits a distinct "zig-zag" structure with two Co (bcbpy) (H2O) 32+ units bridged by TeMo6O246- cluster. In photocatalytic Cr (VI) reduction and CEES oxidation under multiwavelength irradiation, BHU-12 significantly outperformed both BHU-10 and BHU-11. Under visible light, BHU-12 reduced 96% of Cr (VI) to Cr (III) within 90 min and oxidized CEES with 99% conversion and 99% selectivity in just 1 h. Furthermore, BHU-12 maintained stable catalytic activity after three cycles, demonstrating excellent structural stability and recyclability. The superior performance originates from BHU-12's unique "zig-zag"-type architecture. Compared to the "sandwiched" structure of BHU-10/11, the open-ring "zig-zag" configuration of BHU-12 facilitates better exposure of catalytic active sites. Additionally, the intrinsic properties of the central cobalt metal may contribute positively to the catalytic ability of BHU-12. A series of characterizations consistently confirmed that BHU-12 possesses superior photogenerated carrier separation and migration efficiency. The detailed mechanisms of the photocatalytic Cr (VI) reduction and CEES oxidation were studied.