Effect of iron oxides and carboxylic acids on photochemical degradation of bisphenol A

gamma-FeOOH was initially prepared by hydrothermal process and then sintered at 280 C, 310 C, and 420 C, and four kinds of iron oxides were obtained and named as lepidocrocite, IO-280, IO-310, and IO-420. They were characterized by XRD, SEM, and BET techniques to disclose the crystal composition, morphology, and surface area. The XRD results show that IO-280 and IO-310 should consist of maghemite and hematite, while IO-420 should be pure hematite. With the increase of temperature, the specific surface area significantly decreased. To test the photocatalytic activity of iron oxides, bisphenol A (BPA) was selected as a model chemical. The results show that BPA photocatalytic degradation should depend strongly on pH value, light source, and the crystal structure of iron oxides and that IO-310 had the highest activity in the absence of oxalic acid under UV or visible light illumination. The dependence of BPA photodegradation on carboxylic acids in lepidocrocite-carboxylate systems was investigated. BPA degradation was promoted greatly by the addition of oxalic and citric acid, and slightly by tartaric, malonic, and malic acid. The first-order kinetic constant (k) of BPA degradation follows the order oxalic >>> citric >> tartaric > malonic > malic > without acid approximate to succinic acid. In iron oxide-oxalic acid systems, the reaction rate and efficiency of BPA degradation under UV light was much more than under visible light illumination, and the k value follows the order: lepidocrocite > IO-280 > IO-310 > IO-420 under both UV and visible illumination. It is concluded that BPA photodegrdation should be dependent on the kind of carboxylic acid, iron oxides, and light sources in iron oxide-carboxylate system. The photochemical investigation of iron oxide-carboxylate complex systems is essential to the full understanding of the interactive mechanism of iron oxides and organic pollutants on the surface of soil in subtropical and tropical regions.