Controllable Synthesis Of Metal-Sulfide And Its Nanocomposites With Enhanced Photocatalytic Activity

Nowadays, environment and energy issues become more and more prominent, which human beings have to face with it. Meanwhile, the influence of environmental pollution attracts much attention in our daily life. Especially, the water pollution has become one of the global problems which need to be solved urgently. The traditional methods for water pollution can be broadly divided into three categories:physical adsorption, chemical treatment and biodegradation. These conventional processes have played important roles in the water treatment and environmental protection. However, due to inherent drawbacks in these methods, such as high power cost, long operation period, low efficiency and secondary pollution limit the wide utility in the industrialization production. As an environment-friendly technology for the water pollution, photocatalysis has recently attracted enormous research interest due to its excellent performance in environmental protection. Based on this excellent technology, some active species such as OH and-O2-emerge on the surface of the semiconductor materials which can be activated under the irradiation of sunlight. Metal-sulfide nanocomposite is considered as a series of important photocatalytic material because of its high efficiency in the degradation of organic dyes and heavy metal ions in wastewater treatment process. This article pays attention to the preparation of various metal-sulfide nanocomposites. What is more, the photocatalytic activity for the degradation of the orgnic pollutes using the as-prepared nanocomposites as photocatalyst was further investigated. The contents of this paper were as following:1. Carbon-Coated CdS Petalous Nanostructures with Enhanced Photostability and Photocatalytic ActivityIn this chapter, we have rationally developed a facile route for one-pot solvothermal preparation of CdS petalous nanostructures coated with a thin layer of carbon. The as-prepared nanohybrids have an interesting structure consisting of mostly four petals in a tetrahedral geometry, and the petalous nanoparticles are very uniform in size. Each individual petal unit is cone-shaped and the high surface area is retained after assembly into a multi-petalous geometry. The carbon nanocoating remarkably improves the photostability and the photocatalytic efficiency of the CdS photocatalyst for the degradation of methyl orange (MO) and rhodamine B (RhB). As revealed by optical spectroscopic measurements, the carbon layer not only significantly reduces the amount of surface traps, but also provides perfect chemical protection to inner CdS nanoparticles. As a result of the carbon layer protection, the photocorrosion of CdS is successfully inhibited.2. Formation of Mesoporous BiVO4/Bi2S3Hollow Discoid Hetero-Nanostructures with Enhanced Photo-Activity.In this work, we have developed a facile hydrothermal-assisted anion exchange reaction method for the controllable synthesis of mesoporous BiVO4/Bi2S3hollow discoid hetero-structures with uniform morphology and good structural stability. This approach involves the formation of well-defined3D hierarchical discoid BiVO4nanostructures, and the subsequent chemical transformation in the Na2S aqueous solutions at150℃. We have found that the reaction temperature is a very important role in obtaining hollow nanostructures with mesoporous shells by controlling the anion exchange process accompanied by the nanoscale Kirkendall effect. Moreover, the Bi2S3content in the hollow hetero-nanostructures can be conveniently tuned by varying the Na2S concentration. As expected, the as-obtained mesoporous BiVO4/Bi2S3hollow discoid hetero-structures exhibit superior photocurrent response and photocatalytic reduction of aqueous Cr(Ⅵ) under visible-light illumination. These improvements can be attributed to the higher surface area, and enhanced charge carriers transfer and separation which suppress carriers recombination as a result of the interface interaction between BiVO4and Bi2S3. This work provides a low-cost and facile method for the preparation of mesoporous/hollow hetero-nanostructures and also demonstrates the promising application of such hetero-nanostructures in photocatlytic and optoelectronic fields.3. Controllable one-pot synthesis of various one-dimensional Bi2S3nanostructures and their enhanced visible-light-driven photocatalytic reduction of Cr(VI)In this section, we have developed a facile ethanol-assisted one-pot reaction route to synthesize1D Bi2S3nanostructures(NWs, NRs, and NTs)with high productivity and yield. We found that the size, morphology and structure of the products can be conveniently varied or controlled by simple adjustment of the volume ratio of ethanol and water in the reaction system. Additionally, the experimental result indicates that sulfur source also plays another crucial role in determining the morphologies of Bi2S3products. Due to the higher aspect ratio, the as-prepared ultralong Bi2S3MWs exhibits the best photocatalytic activity among all the1D nanostructures. Furthermove, it exhibit good reusability and stability after washed with dilute HC1. Therefore, the ID Bi2S3NWs may be applied as a promising photocatalyst for treatment of wastewater. It is also believed that the synthesis method reported here can be easily extended to prepare a wide variety of functional1D nanostructres for different applications.