Application Of Singlet Oxygen By Photosensitization For Sulfonamides Transformation In Water

In recent years, antibiotics are widely used in pharmaceutical, animal husbandry and aquaculture, which are released to the environment by various pathways and are frequently detected in environment. Antibiotics not only have health and ecological toxicities, but also can induce resistant gene, which might result in serious risks for ecological security and human health. Antibiotics pollution has become one of important environmental issues, which has attracted wide attention from the public and scientific societies.Antibiotics are generally resistant to biodegradation. Low removal efficiencies of antibiotics were reported in traditional wastewater treatment technologies. A lot of research efforts are made on the studies of effective treatment technologies for antibiotics in recent years. Photooxidation technologies have attracted a lot of interests. Currently, most of photooxidation technologies rely on ultraviolet light, which increase the energy consumption and the cost.There are some natural photosensitizers in water environment, such as dissolved organic matter and porphyrin, which can absorb sunlight and subsequently produce low level singlet molecular oxygen (1O2).1O2 was reported to enhance the degradation of some pollutants in water. Rose bengal (RB) is one of man-made photosensitizers, which demonstrates a yield of 1O2 up to 0.76. According to the literatures, RB was applied to photooxidation phenol and 2-chlorophenol by producing 1O2. The second-order reaction rate constants of most antibiotics with 1O2 are greater than phenol and 2-chlorophenol. It is assumed that 1O2 might enhance the transformation of antibiotics in water. Meanwhile, the physical and chemical properties of water and soluble substances might influence the reaction of 1O2 with antibiotics.Sulfonamides (SAs), which are widely used and detected frequently in water, were selected as the target compounds. Under sunlight and simulated sunlight, RB was applied as 1O2 photosensitizer for the transformation of SAs and the influence of pH, soluble substances, and surfactants on the oxidation of SAs were studied.Results showed that the second-order reaction rate constants of five SAs with 1O2 were 0.33×107M-1s-1～9.17×107M-1s-1. Not only under simulated sunlight, but also under sunlight, O2 can significantly promote the transformation constants of SAs compared with the photolysis constant of SAs. The most significant enhancement can be as high as 216 times in sulfadiazine (SD). At different pH, SD has different distribution of dissociation species. SD demonstrated high pH dependence for the reaction rate of SD with 1O2 with the highest rate at pH=7. The effects of different soluble compositions on the reaction of 1O2 and SD were different. Fresh urine and hydrolyzed urine both exerted inhibitions on the oxidation degradation rate of SD. Within the scope of three concentrations,1O2 can all accelerate the decline of SAs. Surfactants can affect 1O2 oxidation of sulfonamides. CTAB, a cationic surfactant, played an importantly promoting role, and a promotion of 530 times of transformation rate was observed in the presence of both CTAB and RB.