Photocatalytic degradation of 4-chlorophenol under P-modified TiO2/UV system: kinetics, intermediates, phytotoxicity and acute toxicity.

A series of phosphorus-modified titanium dioxide samples with varying P/Ti atomic ratio were conveniently prepared via a conventional solgel route. The effects of phosphorus content and calcination temperature on the crystalline structure, grain growth, surface area, and the photocatalytic activity of P-modified TiO2 were investigated. The XRD results showed that P species slow down the particle growth of anatase and increase the anatase-to-rutile phase transformation temperature to more than 900 degrees C. Kinetic studies on the P-modified TiO2 to degraded 4-chlorophenol had found that the TP5(500) prepared by adopting a P/Ti atomic ratio equal to 0.05 and calcined at 500 degrees C had an apparent rate constant equal to 0.0075 min(-1), which is superior to the performance of a commercial photocatalyst Degussa P25 K(app) = 0.0045 min(-1) and of unmodified TiO2 (TP0(500)) K(app) = 0.0022 min(-1). From HPLC analyses, various hydroxylated intermediates formed during oxidation had been identified, including hydroquinone (HQ), benzoquinone (BQ) and (4CC) 4-chlorocatechol as main products. Phytotoxicity was assessed before and after irradiation against seed germination of tomato (Lycopersicon esculentum) whereas acute toxicity was assessed by using Folsomia candida as the test organism. Intermediates products were all less toxic than 4-chlorophenol and a significant removal of the overall toxicity was accomplished.