Photocatalytic Nitrogen Removal From Water Using CdS/TiO₂

Nitrogen is one of the most popular pollutants in the water, to remove it by photocatalysis, CdS/TiO₂ composite photocatalysts were prepared by using a sol-gel method together with other techniques and heating treatment in this paper, and characterized by different analysis methods. Also studied was the nitrogen removal rates under different conditions, and the main content and conclusions are as follows.1. Preparing the CdS/TiO₂ nano-power catalysts, and analyze it through XRD, TEM, UV-Vis. The catalysts activities were determined in removing inorganic nitrogenous pollutant in water. The effects of the ratio of catalyst, CdS to TiO₂ ratio, light used, addition of nitrite or nitrate to the solution on nitrogen removal were investigated. The test results showed that the optimum ratio of n(CdS) to n(TiO₂) is 0.17:l,with 50mg/L ammonium in water, the removal of NH₄⁺-N reaches 41.5% after 2 hours of irradiation. When purged with nitrogen gas, both ammonium nitrogen and nitrate/nitrite can be simultaneously removed. It is concluded that the ratio of n(CdS):n(TiO₂) is important for the synergetic photocatalytic activity.When purged with air, fixed NH₄⁺-N at 25mg/L and adding nitrite/nitrate to the ammonia solution, the removal of NO₂^--N and NO₃^--N under UV was best while the ratio of NH₄⁺-N to NO₂^--N and NH₄⁺-N to NO₃^--N get to 1:1 and 1:2 respectively, in that condition, the removal efficiency reached 22.2% and 40.1% respectively, with N₂ or other gas as main product.2. Using sol-gel and dip-coating method, prepared CdS compounded TiO₂ film on glass substrate, and characterized via UV-Vis spectra. The effects of concentration of CdS, coating times, heating treatment temperature and original nitrogen concentration on photocatalysis activity were investigated. The test results showed that the photocatalytic activity was best while the concentration of CdS was 20%, heating treatment temperature of films was 500℃ with 2 coating cycles. The films showed high activity in the whole wavelength range, and the nitrogen removing efficiency/ ability remained high while the nitrogen concentration changed in a certain range. When purged with nitrogen gas, with 50mg/L nitrogen in water (NH₄⁺-N:NO₂^--N=1:1), the removal of NH₄⁺-N and NO₂^--N reach 34.0% and 27.4% after 2 hours of irradiation, with N₂ and/or other gas as the main product.Also studied was photo corrosion of the CdS in catalyst, which varied as the ratio of CdS to TiO₂ changed and influenced by the different inorganic nitrogen forms.