Abstract
Hybrid advanced oxidation processes employed to degrade recalcitrant organic pollutants in water have been widely examined in recent years. In the present work, the potential of TiO2-mediated photocatalysis in the presence of the periodate anion (IO4-) toward Safranin O (SO) removal from aqueous solutions was investigated. The findings revealed a high efficiency of the UV/TiO2/IO4- system due to the production of more reactive radicals ((OH)-O-center dot, IO3 center dot and IO4 center dot) and non-radical species (O-3, IO3- and IO4-). Additionally, the presence of IO4- as an effective electron acceptor avoids electron-hole recombination, which induces more oxidative reactions at the hole level, increasing the degradation rate of SO. Kinetically, the involvement of IO4- anions in the UV/TiO2 system enhanced substantially the initial rate of degradation; from 0.295 to 12.07 mg L-1 min(-1). The performance of both systems, i.e., UV/TiO2 and UV/TiO2/IO4-, was examined under different conditions such as initial dye concentration, photocatalyst loading, periodate dosage, initial solution pH, temperature and dissolved gases. The SO degradation was found to be maximized at low concentration of pollutant at the optimum loading of catalyst (0.4 g L-1). The continuous increasing in periodate concentration over the range of 0.01-3 mM improved the system reactivity with no overdose effect. Both systems seemed to be insensitive to minor variations in temperature in the range of 15-45 degrees C, and showed a strong dependence on initial solution pH where the degradation rates increased proportionally with pH values up to pH 10 and decreased afterwards. A slight negative effect on the photocatalytic removal yield was noted under either aeration, nitrogen or argon atmospheres in the presence of periodate (UV/TiO2/IO4-), with minor enhancement under aeration for the classical system (UV/TiO2). The mineralization of the organic substrate was also monitored. The depletion of organic matter with time was measured using total organic carbon (TOC) analysis. Despite the rapid decolorization of the dye solution in the UV/TiO2/IO4- system, a TOC removal efficiency of similar to 62% was obtained with both systems after 180 min of treatment.