Preparation of surface coated nano particles by spray pyrolysis

Abstract

The surface of particle can be tailored to get specific physical, optical, electronic, chemical, and biomedical properties by coating a thin film of material on the surface of the particles while the core particle is given new functions maintaining its fundamental physical properties. In order to prepare the magnetically separable photocatalyst, $TiO_2/SiO_2$ coated $NiFe_2O_4$ was prepared by a continuous multi-step spray pyrolysis process. This new type photocatalyst combined the magnetic property of core part and catalytic property of shell part of particle. Submicron size $NiFe_2O_4$ particle was prepared by ultrasonic spray pyrolysis and titania nano particle was coated continuously. There are no impurities between coated titania layer and core material, $NiFe_2O_4$ under the high reaction temperatures. Prepared photocatalyst showed good photoactivity compared with commercial photocatalyst ($Degussa^＼textregistered P-25$) and titania and silica double layer coated $NiFe_2O_4$ particle had more enhanced photoactivity. To give the hydrophobicity on bare silica surface, fumed silica surface was modified with Octhytriethoxysilane (OTES). From the coating process, surface property of silica powder was easily changed. We investigated an aerosol spray reactor method for modifying the hydrophobicity of silica particle. The aerosol spray reactor method has all the advantages of liquid-phase process, while it produces agglomeration-free particle at lower operating cost than the gas-phase process. Hydrophobicity of the modified particles was compared with the silica particle modified by liquid-phase process and gas-phase process. Hydrophobicity of commercial silica ($Aerosil^＼textregistered R812, Degussa$) was also measured as a reference. In order to non-oxide coating on ceramic powder, lithium-salt was coated on fumed silica surface and its electrical property was measured. Lithium-salt-coated silica was used as new type lithium rechargeable polymer elect...