Preliminary Study On Urea Photolysis

Photochemistry is widely accepted as a new and potential means to solve the organic pollutions. In this paper, the fundamental photo-chemical properties of urea, irradiated by the 300 W high-pressure mercury lamp, are studied. Reaction time, initial concentration, pH and aeration are taken as factors to study urea photo-properties. The influence of some potential photo-activators to urea, such as NO₃^-,NO₂^-,Fe³⁺,Fe₂O₃,TiO₂, are also discussed. These tell some necessary information about urea photo-mineralization.The results are as follows:1. In 4 hours, urea, with concentration of 0.1-2.0 mmol/L, is hardly photo-degraded at room temperature; if the samples keep more than 4h, urea will hydrolyze and produce some ammonia.2. Both pH and dissolved air contribute much to the photolysis of urea. Urea photo-degraded easily at both acid and alkaline medium, and produce some ammonia,nitrate and nitrite. With the increased acidity or alkaline, the urea photolysis rate increased evidently. Dissolved air can accelerate urea photolysis and total nitrogen loss distinctly.3. Both NO₃^- and NO₂^- accelerate urea photolysis.Urea keeps stable in the Urea-nitrate mixture except irradiating under the High Pressure Mercury Lamp (HPMC). As the nitrate ratio enhances, urea degradation rate increases, and the main dissolved products are nitrite and ammonia.Compared to nitrate, a similar photochemical reaction occurs in urea-nitrite mixture; and more urea is degraded, both nitrate and ammonia are the products of the photoreaction. The loss of TN shows a positive relation with nitrite concentration. A dissimilar case is that the loss of TN also happens in the dark reaction.4. Fe³⁺ is an activator to urea photolysis, and when Fe³⁺ concentration is less than 8 mmol/L, urea degradation rate increase with Fe³⁺ concentration, than the degradation rate keeps stable. Fe(3+) is also helpful to urea hydrolyzation; In the photoreaction, Fe(3+) is deoxidized to Fe(2+), and a light extent of TN loss is observed.5. TiO₂ can hasten urea photolysis, and produce some ammonia,nitrite and nitrate. Both the degradation rate and TN loss increase quickly with TiO₂ concentration.6. The impact of Fe₂O₃ on urea photolysis is very similar to TiO₂. Compared to TiO₂, the degradation rate of urea is a little smaller, but the TN loss is similar to TiO₂.