Plant extract aided synthesis of iron sulphide/nickel sulphide type-II heterostructure for photochemical CO2 reduction and simultaneous degradation of dyes

Abstract

The green synthetic route, solving issues in the energy sector and the removal of wastes for a clean environment are the major concerns across the globe for a sustainable future. The current work involves the synthesis of iron sulphide (FeS), nickel sulphide (NiS) and FeS/NiS heterostructure using a Calotropis procera leaf and flower extract as a reducing agent without any additional sulphur source. Structural optical, photo/electrochemical and morphological characterizations suggest the formation of a heterostructure between FeS and NiS of type II with tuned edge potentials. Due to which FeS/NiS showed enhanced activity in evolving CO and CH₄ through photoctalytic CO2 reduction reaction (CRR) and was found to be 2.5 and 2 times higher than FeS and NiS, respectively. Further, all three materials were studied for photocatalytic degradation of two cationic dyes (methylene blue: MB and safranin O: SO) under different light sources. The % degradation of dyes MB and SO was found to be 98 and 96 %, respectively, in the presence of FeS/NiS heterostructure under sunlight. The factors affecting the dye degradation (pH, initial concentration, catalyst dosage) were optimized to achieve maximum efficiency. The degradation study using FeS/NiS was additionally examined in industrial effluent and the simultaneous degradation of MB and SO and the results are satisfactory. Photocatalytic mechanism was predicted based on the degradation results using liquid chromatography mass spectrophotometry (LCMS). The decreased charge transfer resistance, superior photocurrent response, bandgap tuning, shift in edge potentials, and formation of heterostructure and effective charge separation could be attributed to the appreciable efficiency of FeS/NiS. This work may lead to further research on the formation of metal sulfide-based heterostructures using a green approach and their application towards waste reduction and converting them to wealth towards energy and environmental remediation.