Enhanced photocatalytic performance of novel S2− doped MIL-53(Fe) under visible light

Abstract

This work highlights a systematic investigation on doping (S2−) on photoactive MIL-53(Fe) and its performance evaluation. Doping (structural/interstitial), leading to tailoring of optical band-gap energies of the parent materials to maximize their performances is well known. However, alteration or tuning of band-gap energy may not essentially always lead to a better performance in photocatalytic reactions and this aspect becomes more pertinent for hybrid materials like Metal Organic Frameworks (MOFs). Since, doping might lead to wider variations in structural conformations in a hybrid MOF like material, underlines the importance of the extent. A microwave synthesis route was proposed to effectively synthesize the products where dopant (S2−) percentages were varied from 1 to 10% stoichiometrically in the reaction mixture. Different spectroscopic techniques like UV–vis DRS, FT-IR, micro Raman, Photoluminescence (PL), Electrochemical Impedance Spectroscopy (EIS) and Electron Spin Resonance spectroscopy (ESR) were used to understand the extent of doping on structural conformations of MIL-53(Fe). The influence of doping showed an increase in optical-band gap energy w.r.t to parent MIL-53(Fe) (1.996 eV): 1% S (2.224 eV); 4% S (2.376 eV), 7% S (2.448 eV) and 10% S (2.579 eV). The coordination of metal oxo cluster from calculated Nephelauxetic factor values in synthesized materials showed electron cloud expansion from 6.51% (1% S) to 16.36% (10% S). The IVCT band intensity was highest for 1%S and accordingly Methylene blue (MB) degradation yielded best performance for 1%S doped MIL-53(Fe) (ca. 97.14%) and repeatability study showed the material to be stable even after 5 cycles. The overall reaction mechanism was hypothesized based on DPBF assay and standard reaction kinetic trap analyses.