New metal-free catalytic systems with carbon dots (CDs) have been presented for the degradation of thymol blue at room temperature. It was found that degradation efficiency was influenced by the pH value, the concentration of H2O2 and the addition of KI. The degradation mechanisms of catalytic systems were studied by means of electron spin resonance and a free radical quenching technique. The results show that HO˙ and ˙O2− originating from the decomposition of H2O2 in the presence of CDs contribute to the degradation of the dyes. The most important merits of the catalytic system are high degradation efficiency of thymol blue in a near-neutral solution and avoiding secondary pollution from metal ions, which make them environmentally-friendly systems for the treatment of pollutants.
By hydrothermal reaction, the hydrangea-like ZnS/ZnIn 2 S 4 microspheres were prepared in the presence of thioacetamide. X-ray photoelectron spectroscopy and high resolution transmission electron microscopy confirmed that the ultra-long nanowires are composed of ZnS and ZnIn 2 S 4 . Scanning electron microscopy showed the morphology of ultra-thin nanosheets with an average thickness of 8.5 nm cross from inside to outside, forming ZnS/ZnIn 2 S 4 microspheres with a porous diameter of about 2.8 μm. Nitrogen adsorption desorption isotherm determined that the BET specific surface area of the microspheres was 109.19 m 2 /g which showed that they have a large specific surface area. The obtained ZnS/ZnIn 2 S 4 microspheres showed broad absorbance ranging from UV (200 nm) to visible (520 nm) with low indirect band gaps of 2.08 eV. It leads to outstanding visible-light-driven photocatalysis for the degradation of xylenol orange (XO) and thymol blue (TB) in water, and the two dyes were almost completely degraded after 60 and 135 min, respectively. This provides new potential to explore nanomaterials for efficient photo-driven degradation of organic dyes under visible light irradiation.
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