Study On The Photocatalytic Degradation Of Azo Dye Methyl Orange By Using Cu²⁺/TiO₂

In China, there is a large drainage volume of azo dye wastewaters, which are complicated in constitution, deep in color and difficult to be degraded. TiO₂ photocatalysis is emerging as a promising technology for wastewater treatment and water purification. This technique possesses advantages over the traditional wastewater treatment including complete mineralization, high degradation efficiency, and good stability, meeting the need of continued development and friendly environment. However, there are still some shortages in application such as high probability of the re-combination of photo-generated electron and hole, low efficiency in the use of sunlight, and so on. As a result, studies on the improvement in the photoactivity of TiO₂ are very hot in present.In this paper, photoactivity of anatase nano-TiO₂ was improved by in-situ modification using Cu²⁺ (or Fe³⁺). Cu²⁺ (or Fe³⁺) was added directly into the photocatalytic system to modify the TiO₂ in the suspension, and promote the photoactivity of TiO₂. Methyl Orange was chosen as the organic compound substrate to be degraded in this paper, and optimum conditions in modificating TiO₂ nanoparticles for the best photoactivity were established: the concentration of Cu²⁺ was 1μM, TiO₂ loading was 1 g/L. Higher photoactivity was observed on the Cu²⁺/TiO₂ compared to neat-TiO₂ at the pH range of 4⁷.5, and the photoactivity was 2 times of that over neat-TiO₂ at pH = 6. The influence of additive inorganic anions such as Cl-,SO42-,NO3- and F- was also studied. Detrimental effect was observed after adding these anions except NO3-, and the inhibiting effect was the greatest in the case of F-. TiO₂ modified by this in-situ method in the paper maintained not only high photoactivity, but also long life time and good mineralization ability. Meanwhile, this method of modificating TiO₂ also had a positive effect on P25. No special treatment is required in the preparation process of TiO₂ catalysts, hence it would have a good application in the future for it is easy to operate and economical both in money and energy, compared to other modification methods. By fluorescence probe, the quantity of hydroxyl free radicals produced in the course of photocatalysis on different TiO₂ systems was measured. And reasons why the photoactivity of TiO₂ was improved by adding Cu²⁺ (or Fe³⁺) were primarily discussed.