Green Strategy To Fabricate Ultrafine Rear Earth Oxides Nanopowders

At present,rare earth oxides nanomaterials especially rare earth ceria have a wide range of applications in military,aerospace industry,high high-precision polishing,electronics and others.The research on high-performance ultrafine rare earth oxides nanopowders with a large surface area and desired size and shape has been a hotspot of the field.Although,there have been some reports on available methods with commercialized potentials for preparation of rare earth oxides nanomaterials,these methods more or less show the drawbacks of complicated operation procedures,high cost,and incapability of precisely controlling the size and shape.More importantly,most of preparation involves the use of acidic or alkaline chemicals and additives,which may cause serious environmental problems and vast waste of resources.To this end,it is urgently needed to develop commercially available green strategy to prepare ultrafine rare earth oxides nanopowders,which may solve the resource waste and environmental problems and reach the goal of precisely controlling their size,shape,and surface area to satisfy the high-performance requirements.In this thesis,we developed a green process with features of free-of-pollution and solvent recycling available for preparation of rare earth oxides nanopowders with large surface area and controlled size and shape.Through modulating the preparative parameters,the structure,particle size,shape,and surface area of the obtained rare earth oxides nanopowders can be well controlled.The rare earth nanopowders may meet the needs of high-performance applications.Furthermore,the green process is environmentally benign,solvent recycling available,wasteless,and capable of scale-up production,which may provide a robust way for production of high-performance rare earth functional nanomaterials.In the first chapter,rare earth resources in China especially in Inner Mongolia Autonomous Region were reviewed and the challenges on preparation and application of ultrafine rare earth oxides nanopowders was commented.Further,the research of this thesis was proposed.In the second chapter,the solvent recycling available green process for synthesis of ultrafine rare earth ceria nanopowders was developed.The process involves the use of a mixture of alcohols and amines as an absorbent that can absorb the greenhouse gas of carbon dioxide to form a precipitate.By adding rare earth salts solution,the reaction can take place between rare earth cerium ion and absorbed CO₂ to form a cerium subcarbonate,which is further subject to the calcination to obtain ultrafine rare earth ceria nanopowders with large surface area and controlled size and shape.The structure,particle size and distribution,shape and surface area of the obtained rare earth ceria nanopowders were studied by means of XRD,SEM,TEM,and BET etc.The feasibility of solvent recycling reutilization for the preparation was investigated.Through optimizing the synthetic parameters,the goal for green preparation with waste discharge free and solvent reutilization was realized.In the third chapter,the precise control of the particle size and distribution,shape,and surface area of rare earth ceria nanopowders was studied based on the above green synthetic strategy by modulating the solvent ratio of alcohols and amines,synthesis through hydrothermal method or solution way,rare earth raw materials,and reaction parameters.The XRD,SEM,TEM,and BET methods were used to characterize the rare earth ceria nanopowders.It is found that the above-mentioned synthetic parameters all have significant impacts on their physiochemical properties.Through optimization,the precise control of particle size and distribution?50-1000 nm?,shapes?spherical,nanorod,and nanotubular?,and surface area(up to 169 m²·g^-1)can be well controlled.In the fourth chapter,the green process for synthesis of rare earth ceria nanopowders was extended to synthesize other rare earth oxides nanopowders of lanthanum oxides and yttrium oxides.Similarly,the optimized system of mixture of alcohols and amines was utilized to absorb greenhouse gas of CO₂ to form a precipitate.Then,rare earth lanthanum or yttrium salt solution was mixed with the above precipitate to generate rare earth lanthanum or yttrium subcarbonate,which was further subject to calcination to achieve ultrafine rare earth lanthanum or yttrium oxide nanopowders.The XRD,SEM,TEM,and BET methods were used to characterize such rare earth lanthanum or yttrium oxide nanopowders.It is found that the green process can be generally used for synthesize of other rare earth oxides nanopowders for various applications.