Mechanistic investigation of photocatalytic degradation of Bisphenol-A using MIL-88A(Fe)/MoS₂ Z-scheme heterojunction composite assisted peroxymonosulfate activation

Abstract

In this study, a green synthesis method was employed to synthesize MoS₂ incorporated MIL-88A(Fe) composite photocatalyst, MIL-88A(Fe)/MoS₂ (MSMIL). Its catalytic property was utilized to degrade Bisphenol-A (BPA) in aqueous solution, using peroxymonosulfate (PMS) as oxidant under UV irradiation (intensity: 48 W). Doping of 20 wt% MoS₂ was found to produce heterojunction with optimal activity, increased surface area (15.8 m²/g for MIL-88A(Fe) to 78.2 m²/g for MSMIL20) and abundant number of active sites. Insitu formation of intimate heterojunction, coupled with hierarchical porosity, conductive network, and abundant exposed active sites results efficient charge carrier migration to the catalyst surface and accelerates PMS activation to yield highly active radicals. X-ray photoelectron spectroscopy indicates that surface bound Fe³⁺/Fe²⁺ and Mo⁴⁺/Mo⁶⁺ redox interconversions play significant roles in surface adsorbed PMS activation. Scavenging experiments established that both radical (OH , SO₄^- , O₂^-) and non-radical (O½,h⁺ based degradation pathways were responsible for BPA degradation. The excellent photocatalytic activity was due to the formation of suitable heterojunction which resists e^-/h⁺ recombination, along with formation of an efficient Z-scheme heterojunction. LCMS/MS analysis was employed to determine the intermittent intermediates during BPA degradation and plausible pathways were designed. The apparent degradation rate constant of MSMIL(20)/PMS system was 0.083 min^-1 which was 16.6 times and 25.4 times that of PMS alone and MSMIL(20) alone, in presence of UV irradiation. This work elicits critical insights towards synthesizing highly efficient and stable MOF based heterojunction photocatalyst and corresponding mechanistic elucidation of the catalytic activity towards degradative removal of refractory contaminants.