Dark catalysis under ambient conditions using mechanochemically synthesized SnS nanoparticles for the degradation of methylene blue

Abstract The development of cost-effective materials that are catalytically efficient under both dark and light conditions remains a challenging goal in the field of water remediation. In this work, mesoporous SnS nanoparticles, synthesized using the ball-milling method, are demonstrated as a suitable and reusable candidate for the catalytic degradation of methylene blue under both dark and light conditions. A more detailed analysis is carried out on the dark activity which has been less explored. The prepared SnS particles are characterized using XRD, XPS, TEM, BET, UV–vis spectrophotometer, cyclic voltammetry and DLS techniques. Preliminary studies on the catalytic performance of various sizes of SnS nanoparticles are conducted under visible light, with 15 nm particles showing the best efficiency. Further studies are carried out with different quantities of 15 nm sized SnS catalyst under dark and degradation rate increased to as high as 0.1 min −1 . The surface electron transfer mechanism is identified as the driving force behind the dark catalysis, which is validated by the HOMO–LUMO alignment between the dye and the SnS nanoparticle. Moreover, the negative surface charge of SnS nanoparticles is expected to increase the electrostatic attraction and thereby the adsorption to the cationic dye molecules. The reusability of the catalyst is analysed using the repeatability studies and the structural stability is confirmed using x-ray diffraction and FTIR spectroscopy.