| In recent years, effects of antibiotic on the human health and ecotope have drawnwide attention from the international community. Photocatalysis technology has goodapplication foreground in degradation of antibiotics. Degradation of two sulfaantibiotics using BiOI under visible light was studied in this paper.This experiment has three parts: the first part describes synthesis andcharacterization of the catalyst; the second part describes degradation ofsulfadimethoxine (SDM) by BiOI under simulated sunlight. This part also discussesthe sorption of SDM and photocatalysis degradation reaction kinetics, and theinfluence of H2O2, initial SDM concentration and BiOI dosage on the degradationefficiency. The chemical oxygen demand (COD) and ion concentration of the solutionare measured to estimate the possible degradation mechanism finally; the third part isthe innovation point of experiment, which describes degradation of sulfadiazinesodium (SD-Na) by Bi7O9I3under sunlight. This part also discusses the sorption ofSD-Na and photocatalysis degradation reaction kinetics and the effect of Illuminationintensity in spring, summer, autumn and winter on the degradation efficiency. TheCOD and ion concentration of the solution are also measured to estimate the possibledegradation mechanism finally. The detailed experimental results are as follows:(1) Bi(NO3)3·5H2O is Bi source and KI is I source. When the solvent ispolyvinylpyrrolidone (MW=58000), BiOI is synthesized under the normal condition.When the solvent is ethylene glycol, Bi7O9I3is synthesized. The characterizationtechniques of BiOI and Bi7O9I3include ultraviolet-visible spectrophotometer,scanning electron microscope, transmission electron microscope, X-ray crystaldiffraction and X-ray photoelectron spectroscopy. The results are as follows: About1to2μm balls form BiOI, and the balls pile easily. Bi7O9I3consists of about1μmthick cuboids. The maximum sorption wavelength of BiOI is700nm, and the bandgap is1.77eV. Compared to TiO2P25, BiOI has a red shift. The maximum absorptionwavelength of Bi7O9I3is617nm, and the band gap is2.01eV. The sorptionwavelength of Bi7O9I3is between that of TiO2P25and BiOI.(2) The degradation of SDM by BiOI with H2O2uses350W xenon lamp toprovide simulated sunlight. The experimental results show the following: Sorptiondata fitting model is Langmuir isotherms and correlation coefficients are0.96. Thehighest photodegradation efficiency of SDM was96.9%with a BiOI dosage of g·L-1,initial SDM concentration of10mg·L-1and H2O2initial concentration of50mg·L-1after2hours of visible light irradiation.The degradation kinetics belongs to pseudo-second-order model. The chemical oxygen demand of the solution decreasedsubstantially and the high COD removal achieved88%. During this time, the organicsulphur was recovered in the form of sulfate and the organic nitrogen was retrieved inthe form of nitrate. The N atomic decomposition is not complete and somenitrogenous organic compound may exist in the solution after degradation.(3) The degradation of SD-Na by Bi7O9I3without H2O2uses sunlight as lightsource. The experimental results show the following: Sorption data fitting model isLangmuir isotherms again and correlation coefficients are0.98. The highestdegradation efficiency can achieve82%in spring, and the degradation efficiency insummer, autumn and winter is69%,70%and60%. The illumination intensity inwinter is low and adding H2O2can enhance the degradation efficiency in winter. CODremoval rate is60%without H2O2, and COD removal rate is82%with H2O2. Theorganic sulphur in SD-Na molecules was recovered in the form of sulfate and theorganic nitrogen was retrieved in the form of nitrate. The S atomic decomposition isnot complete and some sulfur organic compounds may exist in the solution afterdegradation.The results show that BiOI series catalyst can be used in the degradation of sulfaantibiotics. The paper provides theoretical basis for practical application ofphotocatalytic degradation, and the paper has potential application value. |
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