Sonolytic, photolytic, and photocatalytic decomposition of atrazine in the presence of polyoxometalates.

Abstract

Aqueous solutions of atrazine [2-chloro-4-(isopropylamino)-6-(ethylamino)-s-triazine] (CIET) decompose upon illumination with a low-pressure Hg-arc lamp (254 nm). However, no decomposition takes place with lambda > 300 nm. On the other hand, addition of polyoxometalates (POM), PW12O40(3-) or SiW12O40(4-), into a solution of atrazine photodecomposes the substrate within a few minutes (cutoff fiter 320 nm). Ultrasound (US) treatment also decomposes aqueous solutions of atrazine within a few minutes. Both methods, sonolysis and photolysis with POM, give common intermediates, namely, 2-hydroxy-4-(isopropylamino)-6-amino-s-triazine (OIET), 2-chloro-4-(isopropylamino)-6-amino-s-triazine (CIAT), 2-chloro-4-amino-6-(ethylamino)-s-triazine (CAET), 2-hydroxy-4,6-diamino-s-triazine (OAAT), and 2-hydroxy-4-hydroxy-6-amino-s-triazine (OOAT) among others. The final products for both methods, US and photolysis with POM, were cyanuric acid (OOOT), NO3-, Cl-, CO2, and H2O. OOOT showed no signs of decomposition by sonication and/or photolysis with POM. It also resisted degradation upon photolysis with plain UV light (254 nm). However, it has been reported to decompose upon photolysis with lambda > 200 nm. Combination of US and photolysis with POM produces only a cumulative effect.