Fig. 4.

Proposed charge separation and transfer pathways for d-OR, a-OR, and s-OR photocatalysts under light irradiation and corresponding evidence from total densities of state (TDOSs) and partial densities of state (PDOSs). (A–C) According to the calculated band structure and the results of XPS and in situ XPS analysis, the photogenerated charges of d-OR can migrate from PMo₁₂ to Ni₅ under light irradiation. When d-OR extends to the infinite one-dimensional structure of a-OR, the photogenerated electrons can further transfer to the next cluster, which fundamentally weakens the reducing capacity. While d-OR changes into s-OR, presenting a mirror-symmetric O-R-R-O pattern, the symmetric charge-transfer pathway can extremely inhibit the recombination of photogenerated electron hole pairs, thus achieving the best photocatalytic performance. (D) TDOS and PDOS of isolated PMo₁₂, isolated Ni₅, and Pmo₁₂ and Ni₅ moieties of d-OR, a-OR, and s-OR clusters. For the isolated Ni₅ and PMo₁₂, there is almost no orbital overlap and hybridization, and the probability of charge transfer is slight. For the d-OR, a-OR, and s-OR clusters, the unoccupied states’ energy levels of Ni₅ moieties of d-OR and s-OR exhibit a significant decline. (E) PDOS of isolated Ni₅ and Ni₅ moiety of d-OR, a-OR, and s-OR clusters. Ni stands for the Ni moiety, L-host stands for the benzotriazole moiety, and L-vertex stands for the piperazine, H₂O, and NO₃ moieties.