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

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. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

This work systematically investigates the doping of sulfide ions (S2-) on photoactive MIL-53(Fe) and evaluates its performance. The study found that doping can influence the optical band-gap energy of materials, but this does not always lead to improved performance in photocatalytic reactions, especially for hybrid materials like Metal Organic Frameworks (MOFs). By varying the percentage of dopant in the reaction mixture, the study explored the effects of doping on the structural conformations and optical properties of MIL-53(Fe), demonstrating changes in band-gap energy and electron cloud expansion. The best performance in terms of MB degradation was observed for 1% S doped MIL-53(Fe) and the material showed stability even after multiple cycles, indicating potential for practical applications.