Preparation Of Cu～(2+)/TiO₂ Photocatalysts And Their Application In Degradation Of Methyl Orange

In recent years, the photocatalysis technique has been used to decompose many kinds of aqueous pollutants and atomospheric pollutants, which meets the need of continual development and benefit the environment. So it is a promising technique. Titanium dioxide (TiO2) photocatalysts have been the focus of the investigations, for its high photocatalytic activity, no toxicity, low price and chemical stability in comparision with other photocatalysts such as CdS, ZnO, Fe2O3, WO3. Nowadays, research activity based on TiO2 is useful for the destruction of microganisms such as bacteria and viruses, for the recollection of noble or toxic metals, for the decomposition of aqueous pollutants and atomospheric pollutants. However, the band gap of TiO2 is large (Eg=3.2eV), and it is only active in the ultraviolet region which is about 3% of the overall solar intensity. Transition-metal-doping and mixed crystalline effect are two important methods of increasing the photocatalytic activity of TiO2. In this paper, the methods of preparing Cu(Ⅱ)-doped TiO2 nanoparticles were investigated. Cu2+/TiO2 photocatalysts were synthesized with titanium tetrabutoxide as a precursor via refluxing and ultrasound irradiation respectively. The crystalline phase, morphology, crystalline size and specific surface area were tokened by using thermogravimetric analysis and diferential thermalanalysis (TG/DTA), X-ray difraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy (IR) and BET. The results of TG/DTA and XRD show that Cu2+/TiO2 powder dried at 70℃ is a mixed phase of anatase and brookite. From the TEM photograph, we can find that its dispered property is good and the grains are like balls. The diameters of the grains synthesized by the above two techniques are 10～20nm and 5～15nm respectively. The results of BET show that the specific surface areas are 120.8355m2/g and 117.1479 m2/g respectively.The photocatalytic property of Cu2+/TiO2 was investigated under different conditions with methyl orange solution as the stimulated pollutant. The results show that the concentration of methyl orange and TiO2 powder, crystal form of TiO2, synthetic method, H2O2 concentration, pH value, different light will affect the photocatalytic property of Cu2+/TiO2. The experiment results show that the photodegraded rate of methyl orange is much higher under solar light than that under high pressure mercury lamp. Under stronger solar light, the degradation rate is up to 90% in 5 min, which demonstrates that the visible light range uselized for photocatalytic reaction is expanded. And these factors are related. The effect of pH is very complicated, for under certain pH,the electric charge property of TiO2, the appearance of pollutant and the absorption on photocatalysts are affected. At pH=3～5, the photodegraded rate of methyl orange is high inspite of the illuminating lights. At present, TiO2 modified by H2O2 has rarely been discussed. In this paper, the advantages of H2O2 are as follows: ①preventing methyl orange from absorbing on TiO2 and releasing the active sites; ②increasing the photocatalytic activity of Cu2+/TiO2 as a stronger electron-consuming sacrificial agent than O2. In addition, the effects of transition-metal-doping and mixed crystalline effect are discussed in detail. Two worthy problems which are the photocatalytic activity of brookite and the Ti(Ⅳ)-doping TiO2 are put forward.Finally, two different photocatalytic mechanisms were formulated, which based on a lot of references and experiment results. Under UV irradiation, TiO2 first is exicted by UV light. But Cu2+ ions form a short circuit reaction and enhance the recombination of electrons and holes, and decrease the photocatalytic activity. Under solar irridiation, the dye and not the TiO2 is excited by visible light. Cu2+ ions play the role of an electron transfer relay leading to the transference of injected electrons to H2O2 and increasing the photocalystic activity of TiO2.