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

Abstract

Assembly of advanced MOFs based heterojunctions is an effective avenue to facilitate light utility and photogenerated 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 ·O2− 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 O2 in water to provide more ·O2−. While the cooperation of electrons in CB of Zr-MOF with O2/·O2− 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.