Tuning band structures at metal sulfides/Zr-MOF heterojunctions: modulate optical-electronic properties to boost photocatalytic detoxification of Cr(VI) and degradation of reactive dyes

Assembly of advanced MOFs based heterojunctions is an effective avenue to facilitate light utility and photo-generated electron-hole separation for photochemical detoxification of Cr(VI) and degradation of reactive dyes. Systematically polishing the band states of photocatalysts is the crucial point but still requires further study. Herein, a band structure tuning strategy was designed by depositing carefully selected metal sulfides on a 2D Zr-MOF to assemble six metal sulfides/Zr-MOF heterojunctions. Fortunately, In2S3/Zr-MOF presents prominent optical-electronic properties and photocatalytic performances since the highly matched band structure. And its UV-Visible light utility, carriers migration rate, electron-hole separation efficiency and recombination inhibition ability have been greatly optimized. Ingeniously, In2S3/Zr-MOF (M5) exhibits best photochemical purification abilities towards ultra-stubborn reactive dyes RR11, RB21 and highly toxic Cr(VI) ions, under 500 W xenon lamp, with degradation/reduction efficiencies of 91.8, 93.3 % and 97.9 % within 5, 13 h and 70 min, respectively. Compared with pure In2S3 and Zr-MOF, the photocatalytic degradation kinetics towards RR11 have been increased 27.18 and 38.50 times, respectively, providing the recyclability of more than 4 times. Mechanism studies confirm that center dot O-2(-) species play dominant roles in removal of reactive dyes, and the powerful electrons transfer from the conduction band (CB) of In2S3 to Zr-MOF's relatively positive CB further reinforce their ability to combine with dissolved O-2 in water to provide more center dot O-2. While the cooperation of electrons in CB of Zr-MOF with O-2/center dot O-2 has been suggested as the mechanism for photocatalytic detoxification of Cr(VI) to Cr(III). This study provides a feasible strategy for boosting the photochemical purification capacities of Zr-MOFs based heterojunction platforms.