Synthesis Of TiO₂/magnetic-sepiolite Composite Photocatalyst And The Performance And Mechanism In Photocatalytic Treatment Of Cu（Ⅱ）-EDTA Wastewater

The composite photocatalyst of TiO2/magnetic-sepiolite was prepared using the sol-gel method based on the magnetic-sepiolite as the support material. The characteristics of the catalysts, such as the surface morphology, crystal structure, specific surface area, pore structure and light absorption property,, were analyzed through the various advanced methods. Then, the effects of parameters and conditions for catalyst preparation were optimized. Moreover, the relations between the structure and performances of the catalysts were preliminarily discussed. Meanwhile, the photocatalytic performance of the catalysts toward Cu(II)-EDTA under different operational conditions were systematically studied. These conditions included solution pH, dosage of catalyst, ratio of Cu(II)/EDTA, amount of hydrogen peroxide, different photocatalytic systems. Besides, the magnetic separation and cyclic utilization properties of the composite photocatalyst were also investigated. Finally, the photodegradation mechanism of Cu(II)-EDTA was explored based on the main intermediate products and the characteristics of the reacted catalysts in structure, surface functional groups, elemental composition and valence. The conclusions are as follows:(1)The optimum preparation conditions for TiO2/magnetic-sepiolite were that the magnetic loading of 6% and the calcination temperature of 450℃.(2)When the calcination temperature was lower, the TiO2 in the composite showed poor crystallinity and low catalytic activity. While when the temperature was too high, the phase of TiO2 would transform from the anatase to the rutile and brookite, and the catalysts easily tend to be reunited, thus leading to the decreased specific surface area and the increased particle size, ultimately reducing the performance of catalysts.(3)The composite of Ti O2/magnetic-sepiolite exhibits stronger absorbance both in the UV and visible light region compared with TiO2, which favors the photocatalysis. The specific surface area of the composite photocatalyst is up to 77.219 m2·g-1, which makes it show better adsorption ability to the Cu(II)-EDTA.(4)The maximum photodegradation efficiency of Cu(II)-EDTA(10mg/L)were achieved under the conditions of initial pH value of 4, catalyst quantity of 4g/L and the Cu(II)/EDTA ratio of 1/1, and the values for Cu(II) and Cu(II)-EDTA is 90.1% and 100%, respectively.(5)The maximum photodegradation efficiency of Cu(II) was achieved at the Cu(II)/EDTA ratio of 1/1, which suggests the promotion of the EDTA for Cu(II) reduction. But when the Cu(II)/EDTA ratio was less than 1/1, the competitive adsorption occurred between the dissociated EDTA and Cu(II)-EDTA for the active sites on the surface of catalysts, which restrains the reduction of Cu(II).(6)Under the irradiation of UV light at 360 W, the values for removal efficiency of Cu(II) and TOC is 4.7% and 7% in the absence of catalysts; while when the photocatalyst was added into the reaction system,, the removal efficiency of Cu(II) and TOC was increased to 90.1% and 42.3%, respectively, indicating the excellent catalytic activity of the composite.(7)The degradation pathway of EDTA in the composite photocatalyst system is: EDTAâ†'NTAâ†'iminodiacetic acidâ†'glycineâ†'glycolic acid â†'glyoxylic acidâ†'oxalic acidâ†'acetic acid(or formic acid)â†'CO2 and H2 O. The photocatalytic reduction products of Cu(II) are Cu and CuO(or Cu(OH)2).