Incorporating nickel-substituted polyoxometalate into a photoactive metal-organic framework for efficient...

Hydrogen bonding enhances the interactions between host and guest molecules and facilitates electron transfer between them. In this study, a series of hydrogen-bonded Z-scheme photocatalysts were prepared via impregnation. Nickel (Ni)-substituted polyoxometalate (POM) Na₆K₄[Ni₄(H₂O)₂(PW₉O₃₄)₂]∙32H₂O (Ni₄P₂) was anchored within the pores of Zr₆(μ₃-OH)₈(-OH)₈(TBAPy)₂ (NU-1000) via hydrogen bonding interactions (H₄TBAPy = 1,3,6,8-tetrakis(p-benzoic acid)pyrene). Hydrogen bonding not only effectively prevented the leakage of Ni₄P₂ from NU-1000 pores but also facilitated electron transfer from Ni₄P₂ to NU-1000. The optimized 0.3-Ni₄P₂@NU-1000 photocatalyst delivered remarkable performance toward thiamethoxam (TMX) photodegradation, achieving a degradation efficiency of 75.1 % after 120 min. The effects of the photocatalyst dose, pH, coexisting ions, and water sample on TMX degradation were investigated. Radical scavenging experiments and electron spin resonance data revealed that superoxide radicals and holes are the primary species responsible for photodegradation. Moreover, the reaction mechanism and degradation pathways of TMX were thoroughly investigated. Density functional theory calculations confirmed that TMX is adsorbed onto Ni₄P₂ via hydrogen bonding, structurally changing TMX and increasing its susceptibility to degradation. Chia seed growth experiments and Toxicity Estimation Software Tool analysis indicated that the aquatic toxicities of TMX intermediates and final products are lower than that of the undegraded TMX. This study advances the application of substituted POM-modified NU-1000 for treating TMX-contaminated wastewater.