Controllable Preparation Of Inorganic Hollow Nanospheres And Their Applications In Environmental Protection

With the continuous and rapid growth of Chinese economy and the urbanization and industrialization, not only has the material well-being of the country been already improved by varying degrees, but environmental deterioration has also occurred. According to the investigation of World Bank, there are about 8-12% of China's GDP was consumed by the "crisis of environment" annually. Consequently, sustainable development of China has been under threat, because of a series of adversely environmental problems, such as the increase of air pollution, in the future. The inorganic hollow nanospheres, due to their high chemical and thermal stability, high specific surface area, high porosity, low density, and good biocompatibility, have been applied in many fields, such as catalysis, magnetics, microwave absorption, lithium ion battery, solar cell, electrocatalysis, hydrogen storage, gas sensoring, and drug delivery. The purpose of our research was to explore the applicative probability of inorganic hollow nanospheres in environmental protection fields based on both theoretical and practical viewpoints.Hollow silica microspheres with various grain sizes and shell thicknesses possess different physicochemical characteristics to satisfy the requirements of different fields. Among the techniques for preparation of hollow microspheres, hard templates methods are palmary for size-controlled preparation. And the key to this technology is that the template sizes must be controllable. The polystyrene and polystyrene-methacrylic acid latex spheres with the average diameters of 1231,580, 465,362, and 224 nm, respectively, were prepared by an emulsifier-free emulsion polymerization method. Whereafter, the hollow silica microspheres with various grain sizes and shell thicknesses were prepared by using hard template method after calcination to remove the templates. The diameter and shell thickness of the hollow silica microspheres were tuned by varying the latex templates diameter and silica loading content. The diameters of the as-prepared hollow silica microspheres ranged from 249 nm to 1348 nm, and the shell thicknesses from 15 nm to 81nm, and mesopore diameters from 3.1 nm to 3.8 nm. In addition, the evolution mechanism of the hollow silica microspheres was studied in detail based on both theoretical and practical viewpoints.The excellent properties of hollow silica micronanospheres carriers, such as eco-friendly, low cost, facile drug-loading and nonselectivity, which are depending on their special hollow structure with mesoporous shell. Due to the surface adsorption and "cage-effect" of hollow silica microspheres, glyphosate contained in hollow silica microsphere with mesoporous shell could be released slowly. The rate of glyphosate releasing from hollow silica microsphere was mainly controlled by the shell thickness, and the release rate decreased with the increase in the shell thicknesses. The release data were well fitted by employing diffusion kinetic model in hollow sphere.Good agreement between modeling and experimental data supported a forecast way for the quantity of drug delivery. This model has significant role in practical application.In order to abate or exterminate heavy metal ion pollution, hollow SiO2 nanospheres of high adsorption capacity and large specific surface area can be used as an adsorbent. Due to the unsaturation of surface oxygen-containg chemical bond, hollow SiO2 nanospheres easily attract heavy metal ions, such as Cu2+, Cr3+, and Pb2+. Because the adsorption capacity was strongly related to covalent index of ion, this adsorption process should belong to chemisorption. The adsorption capacity efficiency was high due to the movement of the adsorbed heavy metal ions in the interior of hollow spheres was low. As the fitting data shown, there was a strong correlation between the adsorption capacity and ion characteristics (covalent index, and charge density), and the adsorption capacity increased with increasing covalent index increasing or decreasing charge density. The adsorption constant was related to electric field intensity of ion (effective nuclear charge), and the adsorption constant increased with the increase in effective nuclear charge of ion. The removal efficiency of the hollow SiO2 nanospheres was better, and the lower initial concentration, the higher removal efficiency.Among the techniques for removal of POPs, the degradation of POPs via photocatalitic action over TiO2 under light irradiation performs the highest efficiency. Unfortunately, due to its large band gap (3.2 and 3.0 eV for anatase and rutile, respectively), TiO2 can only absorb UV light, which only represents a small portion (3～5%) of sunlight. The hollow titania nanosphere photocatalyst activated by visible light without doping and dye sensitizing had been successfully prepared via hydrolysis of TiCl4. The photocatalytic property test showed that all of the hollow titania nanospheres had high visible light photocatalytic activity for the photodegradation of phenol, and the lower the initial concentration of phenol, the higher phenol removal efficiency. The photocatalytic activity of the hollow titania nanospheres increased with the increase in the shell thicknesses, and when the weight ratio of titania to polystyrene-methyl acrylic acid latex template was 1.4:1, the phenol removal efficiency was 67.8% under visible light irradiation at 2h. The effect of condensation of hydroxyl groups and the gases swelling from combustion of the organic core materials during the synthetic process caused that part of the chemical bond energy decreased and the visible light photocatalytic activities increased.Ag+/Ag-modified hollow titania nanosphere photocatalyst had been also successfully synthesized.by surface deposition of Ag2S and calcination of composite materials in air. The photocatalytic property test showed that all of the Ag+/Ag-modified hollow titania nanospheres had visible light photocatalytic activity for the photodegradation of methyl orange, and the lower the initial concentration of methyl orange, the higher methyl orange removal efficiency. When silver contacts with TiO2, the Schottky barrier will be formed and electrons will transfer from TiO2 to silver because of the different work functions between silver and TiO2. Therefore, the existence of silver atoms in surface of hollow titania nanospheres could help more holes transport to the surface and enhance the photocatalytic efficiency. Superficial Ag+ of hollow titania nanospheres is helpful to scavenge photoelectron. However, low quantity of Ag+ could not be enough to prevent recombination of electrons and holes, so the photocatalytic activity of the 10wt% and 15wt% Ag+/Ag-modified hollow titania nanospheres were lower than the hollow titania nanospheres without modifcation. The photocatalytic activity of the Ag+/Ag-modified hollow titania nanospheres increased with the increase in the loadings of Ag2S, and when the weight ratios of Ag2S to TiO2 was 25wt%, the most efficient photocatalystic activity appeared. The methyl orange removal efficiency was 70.6% under visible light irradiation at 2h.All of our research findings will provide some important supports for the application of inorganic hollow nanospheres in environmental protection fields on technology and theory aspects.