A Review on Modification of Zeolite for Photocatalytic Applications

Zeolites are microporous crystalline alumina-silicate materials, widely used as catalysts, ion exchangers and adsorbents due to their chemical structure and surface properties. The unique properties of zeolite such as high adsorption capacity and cation exchange make it interesting to be used as a support material. This review article presents the details of various researches of zeolite used as photocatalyst in photocatalytic application. The modifications of zeolite using several methods are described in details for photocatalytic enhancement. The effect of zeolite nanoparticles in membrane fabrication also provided in this article. Furthermore, the efficiency of zeolite used as adsorbents and photocatalyst in the photocatalytic application also presented.

Mechanical Properties of MgO-Doped Transparent Crystalline Alumina Fabricated by Two-Step Pressureless Sintering

Transparent polycrystalline alumina with high bending strength has been fabricated using two-step pressureless sintering. The microstructure and mechanical property has been investigated by varying the MgO doping concentration and sintering parameters. The results showed that the grain size markedly decreased with the increasing content of MgO addition. Although the density of alumina could be increased by the higher temperature for the first sintering step, the larger grain would depress the bending strength. Hence, the optimum bending strength was achieved with 0.5 wt% MgO with the two-step sintering of 1450°C for 20 min and 1400°C for 20 h. The Vickers hardness of the transparent PCA increased doping content, and the variation tendency was well accelerated with the relative density, indicated that the porosity plays a more important on hardness than the grain size.

Preparation of Al2O3 from the Nepheline Ore of Nanjiang County, Sichuan Province of China

Crystalline alumina samples with Al2O3 content of 95.23 wt.% were prepared directly from the nepheline ore in Nanjiang county, Sichuan province of China. Four steps were involved in the experiment of alumina preparation, including calcination, dissolution, carbonation and re-calcination. Lime was used in the calcination process with the nepheline concentrates powders to generate soluble aluminates and insoluble silicates. NaOH solution was used as the mother solution in the dissolution process. CO2 was introduced into the solution to precipitate the Al (OH)3 precursor, which was then fired to obtain crystalline alumina. Among the crystalline alumina obtained three phases of crystals existed which were detected by XRD and SEM, including δ-Al2O3 as the major phase, while θ-Al2O3 and κ-Al2O3 as the minor phases. Various crystal phases of alumina could be ascribed to the purity and crystal structure of precursor, as well as the re-calcination temperature and time.