Facile fabrication of Fe-BDC/Fe-2MI heterojunction with boosted photocatalytic activity for Cr(VI) reduction

Novel Fe-BDC/Fe-2MI heterojunction (H2BDC: terephthalic acid, 2MI: 2-methylimidazole) was prepared via a one-pot solvothermal method. Herein, mixed ligands (H2BDC and 2MI) was applied to form complex with Fe(III). Interestingly, the presence of 2MI can regulate the structure of Fe-BDC. Spindle-like MIL-88B(Fe) was observed in Fe-BDC/Fe-2MI composite, while MIL-53(Fe) was identified in naked Fe-BDC. By employing photoelectrochemical characterizations, Fe-BDC/Fe-2MI was optimized at an initial molar ratio of 1:0.5:10 for Fe(III):H2BDC:2MI, which exhibited the highest photocurrent response, lowest charge transfer resistance, and fastest surface reaction kinetics as compared to the individual Fe-BDC and Fe-2MI. Due to the formation of the heterojunction which lead to beneficial photoelectrochemical properties, the as-prepared samples exhibited boosted photocatalytic activity for Cr(VI) reduction. The calculated pseudo-first-order rate constant (k) was 0.046 min−1 for Fe-BDC/Fe-2MI, which was 15.3 and 6.6 times that of Fe-BDC (0.003 min−1) and Fe-2MI (0.007 min−1), respectively. Moreover, the optimized Fe-BDC/Fe-2MI demonstrated superior performance with negligible loss in activity after 4 cyclic runs.