The Biochar-supported Iron-copper Bimetallic Composite Activating Oxygen System For Simultaneous Adsorption And Degradation Of Tetracycline

Tetracycline（TC）is one of the most common antibiotic residues in nature and is commonly used in human and veterinary treatment.The lack of advanced treatment technology to remove residual TC from domestic and hospital wastewater in wastewater treatment plants poses serious environmental risks.It is important to have an in-depth understanding of the different advanced treatment technologies to effectively remove TC from surface water and sewage treatment plants.The catalytic process of BC-supported metal complexes has become a hot spot based on the efficient and harmless application of advanced oxidation technology and the economic and green application of biochar（BC）.The starting point of this study is based on the good adsorption capacity of BC and the high reactivity of PFRS on BC surface,the activation of oxygen by BC-FeCu was studied.Sludge-based BC was prepared by widely used pyrolysis method.On the basis of pyrolysis method,FeCu and BC-FeCu were synthesized by co-precipitation method.The morphology and crystal structure of the above catalysts were investigated by a series of characterization methods.TC was selected as the target pollutant,the ability of BC,FeCu and BC-FeCu to activate oxygen and simultaneously adsorb and degrade TC was compared.The different ways of removing TC by BC-FeCu,such as adsorption,activation of oxygen to generate reactive oxygen indirect degradation and direct contact degradation of TC,were studied.The possible mechanism of TC degradation by BC-FeCu is proposed,and the degradation pathway of TC by BC-FeCu/O₂system were also studied.Finally,the reusability and application stability of the catalyst were studied.The results of the above studies are summarized as follows:（1）SEM results showed that the surface of BC was rough,loose and porous,and FeCu bimetallic particles were easy to agglomerate,while the surface of BC-FeCu was covered with particles of different sizes and aggregated crystal structures,the distribution was not uniform,indicating that the FeCu particles were successfully loaded on the BC during the calcination process.According to the data,the surface structure of BC-FeCu was more porous than that of FeCu.EDS data showed that C,O,Al,Si,K,Feand Cu were main elements of BC-FeCu,and most of them were oxygen and silicon.（2）The XRD patterns of FeCu and BC-FeCu showed that FeCu was successfully loaded on BC-FeCu,and the XRD pattern of BC-FeCu was almost unchanged before and after the use,which proved the stability of BC-FeCu.The defect degree of carbon materials was determined by the I_D/I_Gratio in Raman spectra,and the I_D/I_Gratio increased from 0.77 to 0.90 after loading bimetallic FeCu on BC,indicating that the defect sites of synthesized BC-FeCu increased,which may play an important role in the catalytic reaction.By comparing the spectra of BC and BC-FeCu,it can be seen that the peak intensity of-OH decreases obviously,followed by C=O and C=C,indicating that FeCu was successfully loaded on BC,and it was inferred that FeCu consumed oxygen-containing functional groups in the loading process.After the removal of TC,the peak of BC-FeCu decreased significantly at 1015 cm^-1,which indirectly proved that the C-O group was one of the main reaction sites.The XPS analysis of the elemental composition and valence states of BC-FeCu before and after the use of BC-FeCu showed that there were Fe,Cu,C,O,Si and other elements,sp²C=C and sp³C-C coexisted in BC-FeCu,indicating that there are graphite and amorphous carbon in BC-FeCu.After the reaction,53.4%Fe（Ⅲ）in BC-FeCu was converted to Fe（Ⅱ）,and about 17.03%Cu/Cu（Ⅰ）was oxidized to Cu（Ⅱ）.（3）The experimental results showed that the TC removal of BC-FeCu（92.50%）was higher than that of FeCu（67.30%）and BC（15.32%）under the same conditions.And the removal efficiency of TC by BC-FeCu constantly increased with the increase of p H from 4.50 to 9.03.Desorption experiments showed that adsorption and degradation accounted for 26.09%and 73.91%of the total TC removal by BC-FeCu,respectively.N₂sparging experiments demonstrated that dissolved oxygen（DO）was involved in the degradation of TC,and the degradation led by O₂and the direct degradation by BC-FeCu accounted for 17.02%and 56.89%of the total TC removal,respectively.ESR tests proved the existence of O₂·-,O₂·-、·OH and ¹O₂were the main active species for the TC degradation by BC-FeCu through radical quenching experiments.The possible mechanism for O₂activation by BC-FeCu was that the single electron transferring from-COOH,-OH in BC-FeCu and Cu/Cu⁺to O₂,thus leading to the production of O₂·^-.Finally,three possible TC degradation pathways were proposed based on the analysis of the eight intermediate products.From the practical point of view,four successive repeated tests were carried out under certain experimental conditions,and BC-FeCu showed excellent stability.