Fabrication of visible-light-active MR/NH2-MIL-125(Ti) homojunction with boosted photocatalytic performance

Visible-light-active MR/NH2-MIL-125(Ti) homojunction was successfully synthesized via post-synthetic modification of NH2-MIL-125(Ti). A chromophore group (–MR) similar to the structure of methyl red, was introduced to partially replace the –NH2 group. Using pure NH2-MIL-125(Ti) and MR-MIL-125(Ti) as control samples, the possible structural and optical changes were carefully studied. It was found that the lattice structure remained unchanged, while the specific surface area and band gap were in the order of NH2-MIL-125(Ti) > MR/NH2-MIL-125(Ti) > MR-MIL-125(Ti). Despite of these, MR/NH2-MIL-125(Ti) exhibited highest photocurrent response and lowest charge transfer resistance, which were associated with optimal photocatalytic performance. For the photocatalytic reduction of Cr(VI), the estimated rate constant on MR/NH2-MIL-125(Ti) was ca. 9 times and 3 times relative to that on NH2-MIL-125(Ti) and MR-MIL-125(Ti), respectively. Besides, 4.6 times rate enhancement can also be observed on the homojunction relative to physical mixture (MR/NH2-MIL-125(Ti)-PM). The boosted photocatalytic performance may be ascribed to promoted separation and transfer of photogenerated electron-hole pairs. The operating factors was optimized at acidic pH (2.0), lower catalyst dosage (0.1 g/L) and appropriate concentration of coexisting organics (2.0 mM) within the tested range. Furthermore, good stability both in photocatalytic performance and structure were also observed after 5 cyclic runs. Thus, this study report a facile way for the construction of visible-light-active MOFs, and provided a stable photocatalytic candidate for the disposal of Cr(VI)-containing wastewaters.