The Preparation Of Iron Oxide Catalysts And The Degradation Of Ciprofloxacin With Persulfate Activated By They

Ciprofloxacin(CIP)is one of the broad-spectrum quinolone antibacterial agents,with its antibacterial property ranking the highest among currently-applied quinolone antibiotics.It is featured by high ecological toxicity and not easy to be removed by conventional water treatment technologies,posing a certain threat to ecosystem.Because of its mild reaction conditions and high reaction rate,the advanced oxidation technology has become a research hotspot.During the application of the traditional advanced oxidation technology,Fenton reagent may generate hydroxyl radicals(·OH)which has the following properties:the huge consumption of oxidant H2O2,low utilization,easy decomposition at room temperature,high transportation cost and poor economic efficiency.In recent years,an advanced oxidation technology based on sulfate radical SO4·-has caught more attention.It generates the new sulfate radical SO4·-with high redox potential through activation of sulface to remove organic pollutants.The sodium persulfate of high stability and low price has been widely used and since it is stable,its reaction rate with organic matters at room temperature is low,requiring activation in practical application.The ongoing researches have been focused on inspecting the degradation effect and influence factors of the technology against specific substances by use of multiple activation methods(heat,light,wave,transition metal and acticarbon etc.),but these methods have shortcomings such as high energy consumption or poor catalytic reproducibility.However,replacing Fe2+ and other transition metal elements with iron oxides,the organic matters cannot only be effectively degraded but also easy to be recycled.In this paper,nano-sized Fe3O4,core-shell Fe@Fe2O3,magnetic-modified diatomite(Fe3O4-DTM)and Fe3O4-Ce nanocomposites were prepared to activate S2O82-and characterized.The method was proposed to employ these catalysts activating sodium persulfate to degrade ciprofloxacin-based pharmaceutical wastewater;it had been explored whether the factors such as the dosage of catalyst,initial concentration of sodium persulfate,initial pH of the solution had influences on degradation efficiency and reaction rate,providing references for the engineering application of advanced oxidation technologies in the treatment of ciprofloxacin-based pharmaceutical wastewater.The main contents were shown as the following:(1)The nano-sized Fe3O4 catalyst was synthesized via a modified reverse co-precipitation method and characterized by use of scanning electron microscope(SEM)and X-ray powder diffraction(XRD).And the degradation efficiency and reaction rate of Fe3O4 in activating sodium persulfate to degrade ciprofloxacin were conducted from catalyst dosage,oxidant concentration and pH value.The results showed that under the conditions of catalyst dosage of 2.0g·L-1,sodium persulfate concentration of 1.0g·L-1 and pH of 7,the degradation rate of ciprofloxacin was 93.73%,removal rate of TOC was 78%,and the first-order reaction constant was 0.06907 min-1 within 40 minutes.It was also demonstrated that the reactive oxygen species in the catalytic system of Fe3O4/sodium persulfate were mainly composed of SO4·-and supplemented by ·OH and HO2· using probe compounds such as ethanol,tertiary butanol and benzoquinone.(2)The core-shell Fe@Fe2O3 nanostructures were synthesized and adopted to activate persulfate to degrade CIP.Furthermore,the influences of pH value,initial concentration of CIP and catalyst dosage on CIP reduction were studied.The results showed that degradation rate of CIP can reach up to 86.99%and the reaction rate 0.08249 min-1 at catalyst loading 2.0g·L-1,sodium persulfate concentration of 1.0g·L-1,pH of 7 and temperature 25℃.Various contaminants and probe compounds(Ethanol,Tert-butanol,benzoquinone)were used to identify the active species involved in the catalytic system.The results revealed that the sulfate radical(SO4·-),hydroxyl radicals(·OH)and superoxide radical(HO2·)may be responsible for the degradation of ciprofloxacin hydrochloride(CIP).Therefore,core-shell Fe@Fe2O3 nanostructures are good activators of persulfate to degrade CIP.(3)In the research,the diatomite purified was chosen as a carrirer of heterogeneous catalytic material.The novel magnetic-modified diatomite(Fe3O4-DTM)had been synthesized Fe3O4 by co-precipitation nanoparticles loaded on the diatom shell surface.The samples were characterized by SEM、EDX、XRD and IR analysizes.The results showed that iron oxide activated persulfate was a surface reaction and CIP degradation fitted pseudo-First-order kinetic model.92.36%CIP removal was achieved,corresponding to the iron content on the diatomite surface of 20mmol Fe/g,initial CIP concentration of 50 mg·L-1,sodium persulfate concentration of 1.0g·L-1 and catalyst dosage of 2.0 g·L-1 after 40min reaction.Various contaminants and probe compounds(Ethanol,Tert-butanol,benzoquinone)were used to identify the active species involved in the catalytic system.The results revealed that the sulfate radical(So4·-),hydroxyl radicals(·OH)and superoxide radical(HO2·)may be responsible for the degradation of ciprofloxacin hydrochloride(CIP).As a result,the synthesized Fe3O4-DTM can be easily separated from solutionwithmagnetic technology,and has simple preparation technology and moderate reaction conditions.(4)The cerium/ferric oxide composites(Fe3O4-Ce)were prepared by chemical co-precipitation method.The composites was characterized by scanning electron microscopy(SEM)and X-ray diffraction(XRD).Results indicated that the presence of Ce successfully accelerates the degradation rate of CIP.The Ce and Fe3O4 ratio 1:20 favored the decompostition.Results also showed that 94.10%decomposition and 75%TOC removal of CIP(50mg/L)could be achieved within 40 min under the optimum conditions and the reaction rate 0.06439 min-1(sodium persulfate concentration of 1.0 g/L,catalysts dosage of 2.0 g/L,and initial solution pH 7).Various contaminants and probe compounds(Ethanol,Tert-butanol,benzoquinone)were used to identify the active species involved in the catalytic system.The results revealed that the sulfate radical(SO4·-),hydroxyl radicals(·OH)and superoxide radical(HO2·)may be responsible for the degradation of ciprofloxacin hydrochloride(CIP).At the same time,the reusability of the catalyst was studied.These phenomena suggest that Fe3O4-Ce/PS oxidation process may be an effective strategy to promote CIP degradation.