Research Of Photocatalytic Properties Of Titanium Dioxide Loaded On Modified Zeolite

Heterogeneous photocatalysis using TiO₂as the photocatalyst is an emergingadvanced oxidation process （AOP） for air and water purification, especially in the fieldof dye wastewater, due to its versatility and applicability under ambient conditions.In this paper, TiO₂/HZSM-5nano-composite photocatalysts were prepared bydispersing TiO₂onto the external surface HZSM-5zeolite. HZSM-5was prepared byH+-exchange from NaZSM-5by H3PO4and oxalic acid. TiO₂was dispersed onto theexternal surface of pre-treated NaZSM-5zeolite using a sol-gel process in order toimprove the photocatalytic activity.These materials were characterized by scanning electron microscopy （SEM）, X-raydiffraction （XRD）, Fourier transform infrared spectroscopy （FT-IR）, BET surface areaanalysis, and X-ray photoelectron spectroscopy （XPS） measurements. The degradedsolution of Reactive Brilliand Red X-3B was investigated by ultraviolet–visiblespectroscopy （UV-Vis）. Results showed that modification of support by H3PO4did notchange the surface morphology and structure of ZSM-5zeolite. All the samples calcinedat400℃presented anatase structure. Supporting on HZSM-5improved the dispersionof TiO₂, and restrained the increase of crystalline size. The surface area of HZSM-5andTiO₂/χHZSM-5increases with treatment concentration of phosphoric acid increase,while the surface area of TiO₂/HZSM-5decreases with supported TiO₂increase. Ti-O-Sibonds were not formed between the HZSM-5bulk and the supported TiO₂. The titaniumwas in the oxidation state of Ti4+, and the oxygen was in the form of O^2-in TiO₂.The adsorption ability and photocatalytic degradation activity of TiO₂/HZSM-5nano-composites was better than that of bare TiO₂was due to its large specific surfacearea as HZSM-5adsorbent was used. Meanwhile, photodegradation activity ofTiO₂/HZSM-5changed remarkably when using HZSM-5supports treated with differentconcentrations of H3PO4, giving the optimum H3PO4concentration of0.5mol/l and the optimum TiO₂of50%. After4h of photocatalytic degradation on TiO₂, the absorptionpeaks in UV region almost disappeared. Compared with raw TiO₂, the solution ofReactive Brilliant Red X-3B can be almost degraded within2hours on50%TiO₂/0.5HZSM-5.Results of XRD and XPS showed that modification of support by oxalic acid didnot change the crystal of TiO₂or ZSM-5zeolite and the oxidation state of Ti. Thephotocatalytic degradation activity of HZSM-5, obtained by oxalic acid treating,supported TiO₂nano-composites was better than that of raw TiO₂, giving the optimumoxalic acid concentration of3mol/l and the optimum TiO₂loading amount of60%. Thesolution of Methyl Orange can be almost degraded within2hours on60%TiO₂/3HZSM-5compared to3hours on TiO₂. Since oxalic acid is a weak acid,photodegradation activity of TiO₂/HZSM-5changed little when using HZSM-5supportstreated with different concentrations of oxalic acid.