The Core-shell Structure Photocatalyst With Visible Light Photocatalytic Degradation Of Organic Compounds

Nowadays, environmental pollution caused by organic compounds has far-reaching negative consequences in the lives of human being. Hazardous pollutants emitted from various sources post severe ecological problem as most existing methods are usually not ideal enough. In this regard, heterogeneous photocatalysis has been believed to be the most appealing means for the decontamination and mineralization of these recalcitrant toxicants because of its low energy consumption, high efficiency, satisfactory environmental compatibility and the utilization of the permanent solar energy. TiO₂ has appeared to be the most common catalyst owing to its advantages such as high activity, excellent chemical stability, low toxicity and low cost. However, due to its wide band gap, its response to solar light is rather poor. As for various sensitization methods so far, concerns still exist for the stability of the sensitizer and the efficiency of the electron transfer between the sensitizer and TiO₂. As a semiconductor with a relative narrow band gap, CdS have shown great prospect in visible light induced photocatalysis. With a proper band gap (2.4 eV) and the appropriate absolute redox potential, CdS acquires good response to the solar spectrum and exhibits significant photophysicochemical properties for the photocatalytic removal of organic pollutants. However, CdS is prone to react with the photogenerated holes and then undergo photocorrosion under light irradiation, resulting in poor chemical stability during photocatalytic processes. Furthermore, cadmium species generated by photocorrosion will escape to the liquid phase, leading to a secondary pollution of heavy metal. The photocorrosion together with the consequent leakage of cadmium species has become the biggest obstacle for the practical application of CdS catalyst in water treatment.Herein, an unusually stable and regeneratable CdS photocatalyst for the removal of organic pollutants is fabricated via in situ generating CdS nanoparticles in modified hexagonal mesoporous silica (HMS) sphere followed by coating a polyelectrolyte layer outside. The catalyst not only shows high efficiency in photocatalytic removal of organic pollutants, but also exhibits unusual working longevity and resistance to cadmium leakage under light irradiation. Importantly, the catalyst can be completely regenerated through simple H₂S treatment and no decay of its performance was observed even after 6 regenerations (corresponding to 600 hours of irradiation). CdS and TiO₂ catalysts with hollow microcapsule structure are also fabricated by Layer-by-Layer (LbL) method.With a series of characterization including X-ray diffraction, UV-visible, Raman and atomic absorption spectroscopy, these distinguished features are proved to be attributed to the anti-leakage and the photocorrosion-suppressing effects of the polyelectrolyte layer.