Studies On The Preparation And Catalytic Performance Of Ag@AgCl Composites

With the rapid development of technology and the accelerated process of industrialization, environmental problems such as air pollution, soil contamination and the contamination of aquatic system have become primary environmental concern and posed a serious threat to the human living environment. As a cost effective and green chemistry technology, photocatalysis has provided an alternative way in terms of environmental purification and wastewater treatment and has shown a huge advantage. Compared with traditional semiconductor TiO₂ photocatalyst, visible-light plasmonic Ag@AgCl photocatalyst by using solar-light can achieve for degradation of organic pollutants in wastewater, which has captured considerable attention in recent years. Meanwhile, the catalytic activity of Ag@AgCl composite photocatalyst is closely related to the morphology and size of AgCl and Ag nanoparticle on its surface. Therefore, developing a simple and green method to prepare a effective and stable Ag @ AgCl composites will becoming the key point. In this paper, different synthetic routes of Ag@AgCl have been designed and the effect of morphology and size on the photocatalytic activity of Ag@AgCl has been studied. The main contents are as follows:1. A dendritic Ag@AgCl composites with bifunctional catalytic activity has been prepared through a facile one-pot hydrothermal method. The photocatalytic activity and stability of the as-prepared Ag@AgCl were studied using methyl orange（MO） and 4-nitrophenol（4-NP） as the models of pollutant. The results showed that it exhibits high photocatalytic activity and good stability under visible light irradiation. The study of photocatalytic mechanism showed that h⁺, ·OH and ·O₂^– were the reactive species responsible for the degradation of organic contaminants in the photocatalytic process and ·O₂^– was the main reactive species. In addition, dendritic Ag@AgCl prepared for the catalytic reduction of methyl orange, 4-nitrophenol and congo red also exhibited ultra-high catalytic performance in the presence of sodium borohydride. The as-prepared Ag@AgCl composites as bifunctional catalyst possessed the activity of catalytic oxidation as well as catalytic reduction, which make it has a broader range of application.2. Biomolecular-assisted Ag@AgCl flower-shaped microstructures with octa/hexa-symmetric arms have been synthesized. Conducted a series of controlled experiments found that the reaction time, amount of amino acid and relative amount of amino acid and Ag NO₃ in the reaction system were the main factors influenced the morphologies of products. In addition, the growth of flower-like structures was studied and their possible formation mechanism was proposed. The results showed that Ag@AgCl flower-shaped microstructures with octa-symmetric and hexa-symmetric arms may originate from the preferential growth along the eight（111） direction and six（100） direction of cubic crystal seed, respectively. Carried photodegradation experiment indicates photocatalytic activity of synthesized Ag@AgCl microstructures with large size is not very satisfactory.3. Ag@AgCl nanoparticles were prepared with the assistance of L–histidine, which have high photocatalytic activity. Ag@AgCl with different size could be obtained by changing the amount of L-histidine in reaction system. Photodegradation experiment indicates that the amount of L-histidine in reaction system may cause photocatalysts with different catalytic activity. Wherein, the obtained sample has the highest catalytic activity when the amount of L-histidine was 200 mg in reaction system. Furthermore, the substantially unchanged activity indicated the photostability of catalyst after six cycling degradation experiment. In addition, The experiment of photocatalytic mechanism showed that ·O₂^– and h⁺ were the main reactive species in the photocatalytic process.