Design novel morphologies of L-cysteine surface capped 2D covellite (CuS) nanoplates and study the effect of CuS morphologies on dye degradation rate under visible light

Pure self-assembled L-cysteine stabilized covellite nanoplates (CuS@L-Cys NPs) with the best control of size, phase purity structure, morphology, and electrochemical properties were synthesized by using a template free, the facile hydrothermal route. The effect of temperature (100-180 oC), reaction time (8-24 h), pH of reaction medium (7-14), the concentration of base (0.1-2.4 mL NH3) and concentration of thiourea (1-4 mmol) on the morphologies of CuS@L-Cys nanoplates was studied. The photocatalytic performance of the CuS@L-Cys NPs under visible light was studied by using methyl orange (MO) as a model dye. CuS@L-Cys NPs were reused successfully for photodegradation of dye due to the recycling ability of CuS@L-Cys NPs. The hydroxyl radicals (•OH) generated by CuS@L-Cys NPs were detected by using terephthalic acid (TA) as a probe molecule through the photoluminescence (PL) technique. The successful capping of L-Cys on the surface of CuS NPs was confirmed by FTIR spectroscopy. The BET surface areas of the CuS@L-Cys hexagonal NPs and CuS@L-Cys oblong NPs were measured to be 11.87 and 5.66 m2g-1, respectively. The optical band gaps of CuS@L-Cys hexagonal NPs (2.0 eV) and CuS@L-Cys oblong NPs (2.04 eV) determined according to the direct bandgap calculations. These results support the presence of CuS@L-Cys hexagonal NPs catalysts as efficiently accelerate the photodegradation of MO. Furthermore, the L-cysteine (L-Cys) protective layer could efficiently alleviate the photocorrosion of CuS, giving rise to excellent stability. The high photocatalytic activity of CuS@L-Cys hexagonal NPs can be ascribed to the reduction of photoinduced electron-hole pair recombination and high specific surface area as other representative samples confirmed by BET.