Insight into the growth mechanism of AgIn5S8 nanoparticles in a low temperature co-precipitation process and their visible-light-driven photocatalytic activities

AgIn5S8 (AIS) nanoparticles with excellent photocatalytic performance were synthesized by a convenient low temperature co-precipitation process. The growth mechanism of AIS in the reaction system was studied in terms of reaction time, which had obvious effect on the composition, morphology, and photoelectrochemical properties of the resulting samples. During the co-precipitation process, the initially formed Ag2S precipitate gradually transformed to AIS, which was obtained after reacting for 2 h. Although AIS with better crystallization can be obtained by further extending the reaction time to 12 h, the sample S-2 obtained at 2 h showed the best photocatalytic degradation performance towards several organic pollutants, including methyl orange (MO), malachite green (MG), o-nitrophenol (2-NP), p-nitrophenol (4-NP), p-fluorophenol (PFP) and bisphenol A (BPA). In addition, the photocatalytic reduction efficiency of S-2 towards 40 mg/L Cr(VI) reached 98.5% in 80 min. The possible presence of defects in S-2 caused by the phase transition process contribute to the enhancement of photocatalytic performance. Several characterization methods, including UV–vis DRS, photoluminescence (PL), and photoelectrochemical analysis demonstrated that S-2 had the fastest separation efficiency of photoinduced charge carries and the narrowest bandgap among all the synthesized samples, resulting the improvement of photocatalytic activity. A possible visible-right-driven photocatalytic mechanism was proposed in combination with the bandgap (Eg), conduction band (CB) and valence band (VB) position of AgIn5S8. The radical trapping experiments and electron spin resonance (ESR) results revealed that •O2−, h+ and •OH were involved in the photocatalytic process.