ABSTRACT
Holmium-doped TiO2 nanoparticles with high photocatalytic activities were prepared by sol-gel method and characterized by X-ray diffraction, transmission electron microscopy, ultraviolet-visible diffuse reflectance spectroscopy, and surface area measurement by nitrogen adsorption in this study. Experimental results indicated holmium doping could increase the surface area of TiO2 nanoparticles, and inhibit the growth of crystalline size and the anatase-to-rutile phase transformation. The results of photodegrading methyl orange showed holmium doping improved the photocatalytic activity of TiO2, and the reasons could be attributed to the synergetic effects of large surface areas, small crystallite size, lattice distortion and more charge imbalance of holmium-doped TiO2. In our experiment, the optimal doped amount was 0.3mol.% for the maximum photocatalytic degradation ratio when holmium-doped TiO2 was calcined at 500 degrees C, and the optimal calcined temperature was 600 degrees C when the doped amount was 0.5mol.%.
Subject(s)
Holmium/analysis , Holmium/chemistry , Metal Nanoparticles/chemistry , Titanium/chemistry , Catalysis , Diffusion , Metal Nanoparticles/ultrastructure , Microscopy, Electron, Transmission , Photochemistry , Spectrophotometry , X-Ray DiffractionABSTRACT
High-surface-area polyacrylonitrile (PAN) activated carbon fibers having different pore size distribution activated by KOH were investigated. Nitrogen adsorption, XRD, SEM, and TEM were used to characterize the microstructure of PAN-ACFs. The specific surface area of samples was calculated from the standard BET method, and micropore surface area and volume were obtained from the Horvath-Kawazoe equations. The average pore size and characteristic energy were calculated by the Dubinin-Radushkevich equation according to the multistage adsorption mechanism. The whole pore size distribution was calculated by employing the regularization method according to the density functional theory, which is based on a molecular model for the adsorption of nitrogen in porous solids. It was shown that the isotherms were type I, the pore size was around 0.4-0.8 nm, and the mesorpore size was around 2-4 nm. The XRD pattern showed that PAN-ACFs activated by KOH are of amorphous material composed of very small crystallites. The SEM and TEM results showed that the monograph differs with differing activation degree, and the network is uniform or disordered. That all of these methods are in good agreement with one another. Copyright 2001 Academic Press.
