Study On The Photodegradation Of Salicylic Acid In Water

Salicylic acid (SA) as a utility extremely extensive disinfection antiseptic, was detected in a variety ofenvironmental water. Salicylic acid on the respiratory tract irritant causes cough and chest discomfort afterinhaling; Prolonged exposure can cause eye damage due to the ocular irritation; Prolonged or repeated skincontact can cause dermatitis, or even burns; Intake of it can cause gastrointestinal tract irritation, tinnitusand renal damage; And it can cause water and air pollution. So its environmental behavior has alreadyaroused people's more and more attention. Photodegradation is important in many ways. The present studyconcerns the environmental behavior of SA under simulated sunlight.After establishing the analysis method of salicylic acid in water, we studied the degradation conditionsin the dark or under500W Xenon light. The research results showed that: no photodegradation occurred inthe dark while in the light of500W xenon lamp to light degradation, salicylic acid degradation occurred,which indicated that photodegradation is an important degradation pathway. A kinetic model was used forsalicylic acid degradation in water, and the variations of the photodegradation of SA in the presence ofdifferent initial concentrations.Through the ventilation with oxygen and nitrogen to study the impact about different oxygen levels ofsalicylic acid photodegradation, research shows that in the light conditions, ventilation with oxygenpromotes degradation; Ventilation with nitrogen inhibits degradation. This is because three forms ofphotodegradation of salicylic acid are recognized: direct photodegradation, indirect photodegradation andself-sensitized photodegradation. With access to oxygen, this response includes direct photodegradation,indirect photodegradation and self-sensitized photodegradation. When N2is present, directphotodegradation of salicylic acid can occur under anaerobic conditions.We also studied the different influences on photodegradation of salicylic acid with differentconcentrations of nitrate, nitrite, ammonium ions, and different pE values when these three forms of Nelements coexisted. The result showed that nitrate and nitrite promoted the degradation of salicylic acid,reactions of salicylic acid with hydroxyl radicals and other active substances can occur, leading toself-sensitized reactions that promote degradation. But because nitrite could quench some of the hydroxyl radicals, degradation slowed. Ammonium ions have no effect on the photodegradation of salicylic acid.When the pE value increase gradually, NH₄⁺to NO₂^-and NO3-transformation occurs.SA photodegradationrate shows first increase, then decrease, finally, increase again. Result shows that when NO₂^and NH₄coexist, there is no effect on the photodegradation of SA; when NO₃^-and NO₂^-coexist, there is antagonismbetween NO₂^-and NO₃^-ions, which can be generated by photosensitization of hydroxyl radicals, producinginactive substances that inhibit the photodegradation of salicylic acid.