Flower globose AgIn5S8/AgInS2-SnIn4S8 heterojunction composites constructed by microwave-assisted hydrothermal synthesis for enhanced photocatalytic efficiency toward methyl orange

Ternary metal sulfides normally have narrow band gap energy levels, leading to fast recombination of photogenerated electron pairs. Design and construction of composites with heterojunctions is one of the effective ways to improve this disadvantage. In this paper, different ratios of AgInS2-SnIn4S8 composites were synthesized by a microwave-assisted hydrothermal method, and the molar ratio of SnIn4S8:AgInS2=0.5:1 was determined as the optimal ratio based on the experimental results of visible photocatalytic degradation of methyl orange (MO). Furthermore, AgIn5S8/AgInS2-SnIn4S8 composites were successfully prepared by changing the feeding ratio of In and S elements. The constitution, structural morphology and surface physicochemical properties of the composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), ultraviolet–visible diffuse reflectance absorption spectroscopy (UV–vis/DRS) and nitrogen adsorption–desorption tests. The results show that AgIn5S8/AgInS2-SnIn4S8 composites have a flower globose structure with uniform size distribution, and AgInS2 and AgIn5S8 are compounded with SnIn4S8 to form a heterogeneous structure. After recombination, light absorption properties are changed and light absorption range is broadened due to stronger light absorption capacity in AgInS2 and AgIn5S8. As they have matched energy band structures, the electron transfer paths are increased and the e-–h+ lifetime is prolonged, which leads to enhanced photocatalytic performance of AgIn5S8/AgInS2-SnIn4S8 composites. Moreover, the formation of regular and homogeneous flower globose structure under the effect of microwave polarization also has an important contribution to the improvement of their photocatalytic performance. AgIn5S8/AgInS2-SnIn4S8 composites exhibit a certain degradation ability towards MO, and the degradation is almost complete within 180 min under UV light. Finally, through trapping experiments with the addition of different radical trapping agents, photocatalytic active species are identified, and thus the possible photocatalytic reaction mechanism of AgIn5S8/AgInS2-SnIn4S8 composites was inferred.