Enhanced visible-light photocatalytic decomposition of malachite green over squaraines sensitized SnIn4S8 composites and effect of dye structure on photocatalytic behaviors

A series of indole squaraines (SQs) sensitized SnIn4S8 particles with the mass ratio of 1:10 were fabricated by a facile ultrasonic method. The obtained samples have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, diffuse reflection spectroscopy, Fourier transforms infrared spectroscopy and Raman spectroscopy. The as-prepared squaraines/SnIn4S8 composites exhibited the excellent thermal stability. The efficient charge-transfer ability of squaraines was calculated by Gaussian 98 at the B3YP/6-311 + G(d,p) level. The highest occupied molecular orbital and the lowest unoccupied molecular orbital states had been obtained to match the band gap of pure SnIn4S8. The malachite green (MG) was used as the degradation dye to measure the photocatalytic performance of different SQs sensitized SnIn4S8 composites. The results showed that the sensitized composites exhibited significantly enhanced photocatalytic activities. Among them, The BSQ/SnIn4S8 composites showed the best photocatalytic performance whose degradation rate reached 97.91% under 40 min visible-light irradiation. The k(app) value of BSQ/SnIn4S8 composites (0.0962 min(-1)) was 4.20 times larger than that of bare SnIn4S8 (0.0229 min(-1)). The k(app) value of ISQ/SnIn4S8, MSQ/SnIn4S8, FSQ/SnIn4S8 and CSQ/SnIn4S8 was evaluated to be 0.0328, 0.0358, 0.0526 and 0.0192 min(-1), respectively. According to the fluorescence spectra, BSQ/SnIn4S8 possessed the highest fluorescence quantum yield of 0.4621 within all nanocomposites. Furthermore, the photocatalytic mechanism of squaraines/SnIn4S8 composites was also proposed.