The influence of particle size of TiO2 on the photocatalytic degradation of methylene blue (MB) in a suspended aqueous solution has been studied. The results suggested that the adsorption rate and adsorbability of MB on suspended TiO2 particles increased as the particle sizes of TiO2 decreased. Photocatalytic activity of TiO2 also increased as the particle size of TiO2 became smaller, especially when the particle size is less than 30 nm. The half-life (t 0.5) of the photocatalytic degradation of MB also decreased as the particle sizes of TiO2 decreased. The first-order reaction rate constant for photodegradation of MB increased as the particle size of TiO2 decreased. The initial degradation rate of MB in a suspended model was higher than that of a fixed-bed model. This will overcome the difficulty of preparation of ultrafine TiO2 catalyst particles. Once the problem of separation of fine TiO2 particles is solved, a TiO2 suspended photoreactor could be provided on an industrial basis.

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In this paper, the effects of synthesis conditions, including the seeding approach, gel composition, and hydrothermal treatment process, on the quality of porous R-alumina-supported Y-type FAU membranes were studied. Defect-free, pure NaY-type zeolite membranes have been synthesized and investigated for separation of equimolar CO 2 /N 2 mixtures under dry and moist conditions at atmospheric pressure. At room temperature, the CO 2 selectivity was about 31.2 for the CO 2 / N 2 dry gas mixture with a CO 2 permeance of 2.1 × 10 -8 mol/m 2 ‚Pa‚s. The addition of water vapor to the feed stream decreased the permeance for both CO 2 and N 2 in a temperature range of 23-200 °C. The existence of water vapor significantly enhanced the CO 2 selectivity at 110-200 °C but drastically lowered the CO 2 selectivity below 80 °C. At 200 °C, with increasing water partial pressure, the CO 2 selectivity increased and then decreased after reaching a maximum of 4.6 at a water partial pressure of 12.3 kPa.