Nan Wang,Xing Li,Yanling Yang,Zhiwei Zhou,Yi Shang,Xiaoxuan Zhuang
The photocatalytic degradation of sulfamethoxazole (SMX), sulfadiazine (SDZ) and sulfamethazine (SMT) by Bi 2 O 3 -TiO 2 /PAC under solar light irradiation was studied. The results exhibited that Bi 2 O 3 -TiO 2 /PAC composite prepared by two-stage calcination method contained of rutile and anatase mixed crystal phases, and it had visible light response capability. In addition, Bi 2 O 3 -TiO 2 /PAC had a certain adsorption capacity for SMX, SDZ and SMT, and its saturated adsorption mass was 30.88, 11.28 and 26.24 mg/g, respectively. Compared to photolysis and adsorption process, the photocatalytic degradation efficiencies of the three sulfonamides were significantly improved, and more than 99 % of photocatalytic degradation efficiency was achieved. The EPR measurements showed that both hydroxyl radicals (·OH) and superoxide radicals (·O 2 − ) were produced in the photocatalytic process. However, trapping experiments confirmed that photo-generated hole (h + ) played a lead role in the photocatalytic degradation of SMX. Contrarily, the ·O 2 - was the main oxidative species for SDZ and SMT degradation. Furthermore, the effects of initial pH of solution, sodium bicarbonate, humic acid and natural water (lake and river water) on the photocatalytic degradation were investigated. The photocatalytic degradation pathways of Bi 2 O 3 -TiO 2 /PAC for sulfonamides were discussed. There were differences degradation pathways of the SDZ, SMT and SMX by Bi 2 O 3 -TiO 2 /PAC mainly reflected in: Hydroxylation of benzene ring, extrusion of SO 2 . While, similar pathways existed in the process of sulfanilamide degradation, such as the breaking of S N bond and the cracking of N-containing benzene ring.
Jia-qi Li,Zhi-wei Zhou,Xing Li,Yan-ling Yang,Jing-feng Gao,Rui Yu,Hui-ping Wang,Nan Wang
Photocatalysis-activated sulfate-radical advanced oxidation process (SR-AOP) is an effective approach to remove organic micropollutants from water. Here, we tested a photocatalysis-activated SR-AOP in which peroxydisulfate (PDS) was activated by composites of Bi 2 O 3 -TiO 2 photocatalyst supported onto commercial powdered activated carbon (Bi 2 O 3 -TiO 2 /PAC) under visible light irradiation. This “Vis-Cata-PDS” treatment exhibited outstanding degradation performance (97.96% removal) towards sulfamerazine (SMZ) following optimized reaction conditions of 0.1 g/L Bi 2 O 3 -TiO 2 /PAC and 0.1 g/L PDS at pH of 7. Synergistic effects were observed between the visible-light photocatalytic activation of PDS via direct electron transfer and nonradical PDS activation over pristine PAC within Bi 2 O 3 -TiO 2 /PAC. Both active radicals (SO 4 ·− , h + , ·O 2 − ) and nonradical singlet oxygen ( 1 O 2 ) and the mediated electron transfer of pristine PAC within Bi 2 O 3 -TiO 2 /PAC were contributed to SMZ degradation. Based on intermediates identified by Liquid Chromatograph-Mass Spectrometer (LC-MS) combined with density functional theory (DFT) calculations, three degradation pathways were proposed and that were mostly attributed to SO 2 extrusion/Smiles-type rearrangement and S-N bond cleavage, and toxicity of intermediates were effectively alleviated. An inhibitory effect on SMZ degradation was observed for presence of HCO 3 − , whereas presence of SO 4 2− was less inhibitory and Cl − had no effect. The Bi 2 O 3 -TiO 2 /PAC composite displayed excellent reusability and stability, and it was effective towards a number of tested micropollutants (sulfadiazine, sulfamethoxazole, ciprofloxacin, bisphenol A and methyl orange) and in real water matrixes. This work offers deep insights into the nonradical oxidation mechanism and application of Vis-Cata-PDS over a Bi 2 O 3 -TiO 2 /PAC composite for removal of organic micropollutants.
Xiaoxuan Zhuang,Xing Li,Yanling Yang,Nan Wang,Yi Shang,Zhiwei Zhou,Jiaqi Li,Huiping Wang
The presence of sulfonamides (SAs) in water has received increasing attention due to the risk to ecosystems. The adsorption and photocatalysis performance for sulfamerazine (SMZ) of Bi2O3–TiO2supported on powdered activated carbon (Bi2O3–TiO2/PAC) nanoparticles was evaluated. The amount of doped Bi2O3not only influenced the photocatalytic performance but also impacted the adsorption capacity. The adsorption mass transfer mechanism of Bi2O3–TiO2/PAC was elucidated and is further discussed in combination with the photocatalytic mechanism. It was indicated that Bi2O3–TiO2/PAC(10%–700 °C) performed best, and the SMZ removal by the adsorption–photocatalysis of Bi2O3–TiO2/PAC(10%–700 °C) reached 95.5%. Adsorption onto active sites was a major adsorption step, and external diffusion was assisted. Superoxide radical (●O2−) and hole (h+) were identified as the major reactive oxygen species (ROS) for SMZ removal. Benzene ring fracture, SO2extrusion and nitrogenated SMZ were proposed as the main pathways for photocatalysis. Meanwhile, alkaline conditions enhanced photocatalytic performance, while contrary effects were observed for adsorption. The adsorption–photocatalysis removal performance for SMZ in lake water was better than that for river water. It can be generalized for the potential application of photocatalysis coupling with adsorption to remove refractory antibiotics in water.Keywords:photocatalysis;adsorption;solar irradiation;ternary composite;sulfamerazine
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