Study On Preparation Of TiO₂/Fe₃O₄ With Maize Straw Templated And Catalytic Oxidation Of Tetracycline

In recent years,the pollution of aquatic systems by tetracycline antibiotics has become increasingly serious,and is now one of the most concerned environmental issues for environmental scientist.Fenton technology can degrade most organic pollutants under normal temperature and pressure,and has the technical advantages of low energy consumption and environmental friendliness.However,some technical shortcomings limit its wide application,for instance,controlling the coversion rate of Fe³⁺to Fe²⁺in Fenton catalytic system is very important.The combination of photocatalysis and Fenton oxidation technology can effectively solve the conversion of Fe³⁺/Fe²⁺.In addition,the structural morphology of the catalyst has a significant effect on its catalytic performance.At present,the biological template method is the most direct and effective research method for material morphology and structure control in the field of inorganic material preparation.In this research,new types of catalytic materials were prepared using maize straw as template,and the composition,structure,morphology,electrochemical properties of the materials were analyzed by series of characterization methods,and tetracycline as the target pollutant was used to investigate the catalytic activity and stability of each material.The research results will provide theoretical basis and technical support for the development of economical and efficient refractory organic wastewater treatment technology.A novel TiO₂ was prepared by biotemplate method using natural biomass material-maize straw as template?MST-TiO₂?.The catalytic activity of the prepared MST-TiO₂ photocatalytic material for the degradation of tetracycline in a homogeneous UV-Fenton system was first investigated.It was found that the template controlled the structure and morphology of MST-TiO₂,which formed the hierarchical porous structure of the straw and restricted the growth of the sample.At the same time,a small amount of carbon was doped into the MST-TiO₂ lattice.Results revealed that at pH 4.5,initial concentration of H₂O₂ 10 mmol/L,molar ratio of Fe²⁺/H₂O₂ 1:10,dosage of catalyst 1.0mg/L,initial concentration of tetracycline 50 mg/L,the degradation rate of tetracycline by UV-Fenton after 40 min is 99%.The main active radical group in the UV/Fenton/MST-TiO₂ system is·OH.The Fe³⁺formed in the system can accept photogenerated electrons as an electron acceptor,which will not only inhibit photo-generated holes and electron recombination,but also accelerates the conversion of Fe³⁺to Fe²⁺in the system.To solve the problems of narrow pH range and difficult recovery of homogeneous Fenton system,MST-TiO₂/Fe₃O₄ heterogeneous UV-Fenton catalyst was further synthesized by hydrothermal method on the basis of MST-TiO₂.Studies have shown that an interfacial interaction between TiO₂ and Fe₃O₄ forms a heterojunction;compared with pure Fe₃O₄,Fe₃O₄ in MST-TiO₂/Fe₃O₄ composite catalyst has smaller particle size and higher dispersion,which can enhance catalytic reaction.Active sites,wherein the heterostructure of MST-TiO₂/Fe₃O₄?1:2?are more uniform.The initial pH has a certain effect on the degradation of tetracycline in UV/MST-TiO₂/Fe₃O₄/H₂O₂ system,mainly due to its determination of Fe³⁺/Fe²⁺cycle,the prsence of H₂O₂ and·OH,and the surface charge and photoexcitation of TiO₂.The optimal reaction conditions of MST-TiO₂/Fe₃O₄ catalyzed UV-Fenton treatment of tetracycline were obtained by response surface methodology as:initial pH 6.74,H₂O₂ dosage 11.52 mmol/L,catalyst dosage 0.38 g/L,reaction time 56.63 min and the predicted tetracycline degradation rate was 98.13%.In addition,it was discovered that the MST-TiO₂/Fe₃O₄ composite catalyst has stable performance,after 5 cycles,the degradation rate of tetracycline is still above90%,and the amount of dissolved iron in the system is 0.3mg/L?weigh ratio 0.42%?.Further experiments were carried out to improve the UV-Fenton catalytic activity of MST-TiO₂/Fe₃O₄ composites.A new TiO₂/Fe₃O₄ maize straw carbon skeleton material?MSTC-TiO₂/Fe₃O₄?was synthesized using maize straw as template.The results showed that Fe₃O₄ and TiO₂ are successfully supported on the maize straw carbon.The carbon skeleton has no effect on the chemical structure of Fe₃O₄ and TiO₂,and it provides more active sites reducing the agglomeration of nano-Fe₃O₄ particles.Under neutral condition,the results revealed that the catalytic effect is best at molar ratio of Fe₃O₄ to TiO₂ 5:1,as the removal rate of tetracycline in 40 min is close to 100%,and the mineralization rate is 71.2%.When the tetracycline influent concentration is 50mg/L,at hydraulic retention time 120 min,initial pH 4.5,H₂O₂ dosage 10 mmol/L,and ultraviolet light intensity 1.76².53 mW/cm²,the tetracycline effluent concentration is5 mg/L,indicating a removal rate of more than 90%in the dynamic test of UV-Fenton reaction catalyzed by MSTC-TiO₂/Fe₃O₄.The HPLC-MS/MS and GC-MS were used to analyze the degradation of tetracycline in the UV-Fenton system catalyzed by MSTC-TiO₂/Fe₃O₄.These intermediate products are obtained by hydroxylation reaction and demethylation of tetracycline by an oxidizing group such as a hydroxyl radical,and the possible degradation pathways were proposed.