Study On Antibiotic Degradation By Activation Of Persulfate Through Modified Biochar

In response to the current prominent problem of antibiotic contamination in the environment,especially in water bodies,researchers have been working on the use of various physicochemical and biological means to remove antibiotics from water bodies and to purify them.Among many treatment techniques,the introduction of solid non-homogeneous catalysts into the advanced oxidation processes to activate the persulfate（PS）and produce active substances to attack the contaminants is widely recognized for its outstanding advantages in terms of energy consumption,cost,operation process and removal efficiency.In this study,two biochar-based catalytic materials were synthesized by different preparation processes,which were applied in the advanced oxidation process with tetracycline（TC）and ciprofloxacin（CIP）as the target pollutants.The effects of different factors on the removal efficiency of antibiotics were investigated,and the activation mechanism of catalyst materials on persulfate and the degradation pathway of antibiotics were studied.The specific research results are as follows:（1）The biomass Camellia oleifera shell were first impregnated with a metal mixture solution,followed by low-oxygen torrefaction coupled with pyrolysis,and finally prepared into nickel/iron bimetallic modified biochar（Ni/Fe-BC）.The characterization of Ni/Fe-BC showed its large specific surface area（323.51 m2/g）and abundant reactive groups,and the surface was uniformly loaded with a large number of Fe Ni₃ compound crystal particles,which enabled Ni/Fe-BC to exhibit excellent catalytic performance in the subsequent reaction and successfully activate the persulfate via electron transfer.In the TC degradation experiments,the efficient removal of TC（99.6%）was achieved within 60 min when the Ni/Fe-BC dosage was 0.2 g/L,the concentration of sodium persulfate（Na₂S₂O₈）was 0.5 g/L,p H=5.0,and the reaction temperature was 35°C.Combining electron paramagnetic resonance（EPR）and free radical quenching experiments to speculate the mechanism of activation of Na₂S₂O₈ by Ni/Fe-BC,it was found that the electron cycling transfer process initiated by Ni and Fe and the formation of reactive groups and defective structures on the biochar surface activated the PS to produce SO₄^-·and further produced·OH and ¹O₂,where SO₄^-·and·OH were the main contributors to TC degradation in the radical pathway,and ¹O₂and electron transfer were the main modes of action in the non-radical pathway.From the HPLC-MS and TOC results,it was found that TC was degraded to produce a large number of intermediates and three possible degradation pathways of TC were postulated.The main intermediate product P1 was formed by the cycloaddition reaction of TC in the presence of SO₄^-·and·OH;P2 was based on P1,-OH was oxidized to carbonyl;P3 opened the benzene ring due to the oxidation of ¹O₂.（2）A modified biochar catalyst material（Fe/Mn/B-BC）co-doped with iron/manganese bimetal and heteroatomic boron was prepared for the hard-to-degrade quinolone antibiotic ciprofloxacin.Through various characterizations,it was found that the surface of Fe/Mn/B-BC was uniformly loaded with a large number of Fe₃BO₅ and Mn₃（BO₃）₂ compound crystal particles and contained a large number of reactive organic functional groups and metal compound groups.In particular,the Fe and Mn ions on the surface of Fe/Mn/B-BC exhibited multiple valence states,and the binding energy positions of B corresponded to B-O and B-C functional groups,which enabled Fe/Mn/B-BC to have excellent catalytic properties and successfully activated PS to act efficiently in the subsequent reaction for the degradation of CIP.The Fe/Mn/B-BC+PS+UV system achieved 99.4%removal of CIP within 30 min when 0.1 g/L Fe/Mn/B-BC,0.2 g/L Na₂S₂O₈,p H=5.3 and the reaction temperature was room temperature（about 30°C）were used.After calculating the pseudo-first-order ratio constants and fitting the pseudo-first-order kinetics to each reaction process,it was found that the reaction processes of each batch were highly fitted to the pseudo-first-order kinetic curves,and the largest pseudo-first-order ratio constant(17.05×10^-2 min^-1（R²=0.99）)was obtained by the Fe/Mn/B-BC+PS+UV system under the optimal reaction conditions.In the Fe/Mn/B-BC+PS+UV system,due to the valence change of Fe and Mn,functional groups and defective structures of Fe/Mn/B-BC,and the auxiliary effect of UV light successfully activated the persulfate and released various reactive substances to attack CIP leading to its degradation.The results of quenching experiments demonstrated that SO₄^-·and·OH were the main contributors to the degradation of CIP in the radical pathway,and ¹O₂ and electron transfer were the main modes of action in the non-radical pathway,with ¹O₂ playing a dominant role in the overall degradation process.HPLC-MS confirmed that CIP was degraded to produce a large number of intermediate products.The differences in the molecular structures corresponding to the mass-to-charge ratios inferred five possible degradation pathways,including piperazine ring opening,defluorination,cleavage of quinolone groups and loss of some organic groups.The change of TOC concentration from sudden increase at the beginning of the reaction and then gradually decrease also showed the process of CIP degradation.The results of recycling experiments and ionic leaching proved that Fe/Mn/B-BC has strong structural stability and recyclable potential.（3）Using the above two systems in real water bodies,the experimental results proved that both Ni/Fe-BC+PS and Fe/Mn/B-BC+PS+UV systems showed good catalytic degradation performance in different real water bodies.The Ni/Fe-BC+PS system achieved more than 95.2%removal efficiency for TC in three groups of real water bodies within 60 min,and the Fe/Mn/B-BC+PS+UV system achieved more than98.1%removal efficiency for CIP in three groups of real water bodies within 30 min.In conclusion,the two biochar-based catalyst materials had good catalytic and persulfate activation properties,and both systems also had good pollutant degradation capabilities.This work provides an available strategy for current water treatment.（4）By comparing the performance of Ni/Fe-BC and Fe/Mn/B-BC in their respective experiments,Fe/Mn/B-BC performed better.The two degradation systems have the advantages of simple process operation and good economy,which can be used as a strategy available in current water treatment processes.In particular,the addition of UV-assisted without the aid of a shaker frees some conditions and is more suitable for practical applications.