Preparation Of Environmental Nanomaterials And Their Applications In Removal Of Pollutants

With the rapid development of industrialization in the world, massive pollutants are released into the environment, leading to various environmental problems, such as soil, water and air pollution. Among these pollutions, the issue of water pollution is particularly concerned. Heavy metals, radionuclides and organic dyes are common pollutants in the wastewater. Once these pollutants are released into the aquatic environment through a variety of anthropogenic activities, they are able to enter the food chains, leading to serious damages to human health and other organisms due to their strong toxicity, environmental persistence and bioaccumulation. Therefore,developing facile and environmentally benign materials to remove various pollutants from wastewater is urgent and crucial. Recently, nanomaterials have attracted worldwide attention for their application in environmental remediation, due to the facile preparation, environmental friendliness and excellent removal performance for various pollutants. In addition, compared with the single nanomaterials, the nanocomposites, consisting of two or more nanomaterials, exhibit superior removal performance for pollutants. In this dissertation, several ecomaterials with nanostructure as well as nanocomposites were prepared and their removal capacities to various pollutants ?eg. Cd???, Congo red, iodide and uranium? were investigated systematically. The important results of this dissertation were summarized as follows:1 . The radioactive iodine, one of the major by-products of uranium and plutonium fission, is common in radioactive wastwater. In addition, in the practical radioactive wastewater,some other radionuclides, like ²38U?¹37Cs?⁹0Sr and ⁹9Tc,generally coexist with radioactive iodine. The different physical and chemical properties of the various contaminant classes make the treatment of radioactive wastewaters more complicated. Thus, the development of facile and green materials to simultaneously remove the multiple radionuclides from wastewaters is urgent.Herein,Ag₂O@Mg?OH?₂ nanocomposite is successfully prepared by a facile one-step method,which combined the Mg?OH?₂ formation with Ag₂O deposition. The as-synthesized nanocomposite exhibits high I^- removal capacity ?368.60 mg/g?, and 200 mg/L of I^- can be completely removed within 10 min. Furthermore, the Ag₂O@Mg?OH?₂ nanocomposite possesses highly selective uptake of I^-, indicating a profound potential for radioactive iodine removal in practical environmental wastewater. In addition, the nanocomposite also shows high efficiency for simultaneous removal of iodine and uranium. Therefore, Ag₂O@Mg?OH?₂ nanocomposite is a suitable candidate for the emergent treatment of multiple radionuclides in radioactive wastewater during and after nuclear leakages.2. In addition to the pollution of concurrent radionuclides, the combined pollution of heavy metals and dyes has also been an increasingly hot topic in environmental field. Herein, Cd??? and CR, the commonest pollutants in the wastewater, were selected as the model pollutants. The hierarchical vaterite spherolites, synthesized by a facile injection-precipitation method at room temperature, were applied for the simultaneous removal of Cd??? and CR. The mutual effect between the copollutants in binary system and the removal mechanism were systematically investigated. Batch experiments reveal that the as-prepared vaterite spherolites show excellent removal performance for Cd?II? and CR, respectively.Furthermore, in the binary Cd?II?-CR system, the removal capacity of vaterite to Cd?II?is significantly enhanced at lower CR concentration ?< 100 mg/L?, but inhibited at higher CR concentration ?> 100 mg/L?. In contrast, the concurrent Cd?II? shows negligible effect on the CR removal. A multistep process involving the preferential adsorption of dye CR, stabilization of CR to vaterite, coordination of the adsorbed CR molecules with Cd?II?, and transformation of vaterite into otavite, may dominate the simultaneous removal of Cd??? and CR in binary system. In a word, this study may provide new insights into the simultaneous removal of heavy metal ions and dyes by carbonates, and our results could be further employed in the practical application for integrative and efficient treatment of complicated wastewater.3. Uranium, a important fuel in the nuclear industry, is one of the commonest radioactive contaminants with potential toxic and carcinogenic. Herein, Mn₃O₄ nanoparticles anchored on the sepiolite nanofibers ?Mn₃O₄@sepiolite? were successfully obtained by a facile microwave-assisted method, and the removal behaviour of Mn₃O₄@sepiolite nanocomposite to U?VI? was studied systematically.Batch experiments reveal that the Mn₃O₄@sepiolite nanocomposite exhibits an excellent removal capacity ?85.5 mg/g? and high removal rate ?<20 min?. According to the XPS analyses, the bonds of U?VI? with the Si-OH and Mn-O may responsible for the U?VI? removal. Due to the simple synthetic procedure and the excellent removal performance for uranium, Mn₃O₄@sepiolite nanocomposite can be potentially applied in radioactive wastewater treatment.