| Three steps of photocatalytic reaction involves are respectivly:adsorption of pollutants on photocatalytic material, photocatalytic oxidation reactions occurs on photocatalytic material after absorbing specific wavelength of light, degradation products desorbes from the surface of the photocatalytic material. Photocatalytic reaction follows pseudo-first Langmuir-Hinshelwood kinetic equation. An important factor affecting the photocatalytic degradation rate is substrate adsorption on the catalyst surface. Adsorption is the prerequisite for photocatalytic reaction Immobilizing TiO2 nanomaterials on the porous adsorbent material can improve the rate of adsorption and photocatalysis. Zeolites have uniform, molecular sized pores, with a high specific surface area and chemical, thermal, and mechanical stability, high adsorption of organic matter, which make it an excellent adsorbent and environmentally friendly materials. Zeolites can quickly adsorb selectively target pollutants, but can not continue to play a role after reaching the saturation adsorptioa In this paper,13X zeolite molecular was selected as the carrier, utilizing the synergy of 13X and TiO2. Immobilized photocatalysts were prepared by sol-gel method and solid phase diffusion method, respectively. Then different load quality on the photocatalytic activity of was discussed respectively, with secleting methylene blue solution as the target pollutants which concentration was 30 mg/L and Volume was 250 ml. The main contents are as follows:Firstly, nano-TiO2 and different TiO2 content of supported TiO2/13X zeolite composite photocatalyst was prepared by sol-gel method respectively. Then the prepared photocatalyst were characterized by XRD and SEM respectively. And the removal and photocatalytic degradation of 13X zeolite, TiO2, TiO2/13X were respectively studied under UV light with using methylene blue solution as the target pollutants which concentration was 30 mg/L and volume was 250 ml. The results showed that the prepared TiO2 particle size was about 30-40 nm. At lower loading, TiO2 distributed in the three-dimensional pore of zeolite particles. When TiO2 loading was higher, quality of 13X zeolite was smaller in the same amount of TiO2/13X zeolite, which led to adsorption amount of MB decreased and the methylene blue adsorbed molecules can be degraded in time. With decrease ofTiO2 loadings, the adsorptive quality of TiO2/13X increases, leading to the degradation rate of TiO2 on methylene blue gradually to play a major in the whole reactioa When its loading capacity reached 50%, the material achieved the best ratio, In this case, the removal and photocatalytic degradation rates was 74.66% and 62.64% respectively.Followed by different loadings of Degussa P25 of P25/13X immobilized photocatalysts were prepared by solid-phase diffusion method, then the prepared photocatalyst were characterized by XRD and SEM. And the photocatalytic degradation efficiency of the P25 loadings, initial concentration of methylene blue solution, and the solution pH were studied. The results showed that the P25 nanoparticles wrapped around the surface of the zeolite particles, which made the characteristic peaks of 13X zeolite not observed on the XRD patterns. When loading was 50%, the photocatalytic degradation rate reached 71.77%, while the photocatalytic reaction kinetic constant was 0.740. It improved 3.158 times compared with 100 mg pure P25, which photocatalytic reaction kinetic constant was only 0.234, possesed the highest photocatalytic activity. At different concentrations, adsorption had little effect on photocatalytic reaction rate. While the higher the concentration, the smaller UV transmittance in the solution This made less photo generated electron-hole pairs generated by excitation, lesding to a smaller photocatalytic reaction rate. Under acidic conditions, the adsorptive of P25/13X substantially not changed significantly. When pH was 5, the solution can produced more-OH, thus resulting a higher reactivity. At this time photocatalytic reaction kinetic constants improved about 1.207 times compared with what it was of pH= 7. |
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