Combination Mechanism and Enhanced Visible-Light Photocatalytic Activity and Stability of CdS/g-C3N4 Heterojunctions

In this study, CdS/g-C3N4 (CSCN) heterojunctions were in situ fabricated with a large amount of CdS nanoparticles anchored on g-C3N4 nanosheets. A wet chemical method was developed for the first time to determine the actual content of CdS in CSCN composites. X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), high-resolution transmission electron microscopy (HRTEM) and UV-vis diffuse reflectance spectra (DRS) were employed to characterize the composition, structure and optical property of CSCN composites. Based on the isoelectric point (IEP) analysis of g-C3N4, a conclusion was obtained on the combination mechanism between CdS nanoparticles and g-C3N4 nanosheets. The photocatalytic activity of CSCN composites was much better than those of individual CdS and g-C3N4 for the degradation of azo dye Methyl Orange (MO) by 40 min adsorption in the dark followed by 15 min photocatalysis under visible light irradiation. After 5 cycles, CSCN composites still maintained high reactive activity with the MO degradation efficiency of 93.8%, exhibiting good photocatalytic stability. The Cd2+ concentration dissolved in the supernatant detected by atomic absorption spectroscopy (AAS) of CSCN composites was lower than that of pure CdS, implying that the photocorrosion of CdS could be suppressed via the combination with g-C3N4. Photoluminescence emission spectra (PL) results clearly revealed that the recombination of photogenerated electron-hole pairs in CSCN composites was effectively inhibited due to the formation of heterojunctions. Based on the band alignments of g-C3N4 and CdS, the possible photocatalytic mechnism was discussed.