Preparation And Sulfamethoxazole Removal Performance Of ZIFs-derived Carbon Supported Cobalt Nanoparticles

Zeolite imidazolate frameworks(ZIFs)-derived carbon materials have drawn tremendous attention as activators of peroxymonosulfate(PMS)in removing antibiotics because of their simple preparation and excellent catalytic activity.However,direct calcination of ZIFs often leads to the irreversible aggregation of metal nanoparticles under high temperature conditions.The ZIFs-derived carbon materials are dominated by micropores,which is not conducive to the exposure of metal sites.In addition,the most of carbon materials derived from ZIFs exhibit insufficient activated sites and poor performance in treating high-concentration(>10 ppm)antibiotic wastewater.Consequently,developing ZIFs-derived carbon materials with highly dispersed and highly exposed metal active sites is of significant scientific importance to efficiently eliminate high concentrations of antibiotics.To solve the problem of metal nanoparticles agglomeration and leaching of metal-carbon materials derived from ZIFs,cobalt-zinc bimetallic ZIFs(CoZn-ZIFs)nanorods and melamine were mixed and calcined to obtain a bilayer carbon substrate loaded cobalt nanoparticles(NPs)composite(Co-NC-C)with highly dispersed and highly exposed Co-active site.To further improve removal performance and reusability of CoZn-ZIFs-derived cobalt carbon composite for sulfamethoxazole(SMX),novel CoZn-ZIFs cubes were prepared by regulating the molar ratio of metal to organic ligand and were directly calcined to obtain three-dimensional cobaltcarbon composites with strong magnetic containing carbon nanotubes(CNTs)and highly dispersed Co nanoparticles(Co-CNTs@NC-3).To address the Co leaching in the above studies,a novel NC-supported highly dispersed Co NPs composite(Co-N@NC-90)was prepared by directly calcinating dopamine-chelated Co modified ZIF-8 derived carbon(NC).Meanwhile,based on the excellent catalytic performance of the above catalysts,the advanced oxidation system of PMS was constructed,which integrated material preparation,property exploration,mechanism exploration,and toxicity evaluation.The specific research contents and conclusions are as follows:(1)A preparation method was developed to achieve high dispersion and exposure of Co active sites in Co-NC-C composites.CoZn-ZIFs nanorods were synthesized using a simple,green,and fast self-assembly method.Co-NC-C composites with high exposure and high dispersion of Co active sites were obtained via pyrolyzing the mixture of CoZn-ZIFs and melamine.The introduction of Zn effectively inhibits the agglomeration of Co atoms during the pyrolysis process via extending the spatial distance between adjacent Co atoms.The in-situ generated ammonia gas from melamine facilitates the exposure of Co sites.The characterization results of transmission electron microscopy(TEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),and Brunauer-Emmett-Teller(BET)specific surface area demonstrated that the mesoporous structure of Co-NC-C with highly dispersed and highly exposed Co sites was successfully prepared.SMX degradation results showed that Co-NC-C(0.1g/L)efficiently activated PMS(0.1g/L)to degrade more than 96.67%of SMX(20 mg/L)within 120 min at the initial pH of 3-9.25.Based on the results of the quenching experiment and electron paramagnetic resonance(EPR)spectrometer analysis,a singlet oxygen(1O2)dominated SMX degradation mechanism was proposed.Four degradation products were detected.Two degradation paths consisting of amino oxidation and hydroxylation of methoxazole rings were proposed.The toxicity of SMX and its products was evaluated by Ecological Structure Activity Relationships(ECOSAR)analysis software.The results of the ECOSAR evaluation showed that none of the intermediates had acute toxicity to fish,daphnia,or green algae,nor chronic toxicity to daphnia or green algae.This study can provide a theoretical and technical reference for synthesizing ZIFs-derived metal-carbon materials with highly dispersed and exposed Co sites.(2)To further enhance the rapid removal ability and reusability of CoZn-ZIFs derived Co carbon materials for higher concentrations of SMX,a novel CoZn-ZIFs cube was firstly prepared via adjusting the molar ratio of metal and ligand.Then,a three-dimensional cobalt carbon composite(Co-CNTs@NC-3)with strong magnetism containing CNTs and highly dispersed Co NPs was obtained by calcining the CoZn-ZIFs cube.XRD,TEM,and BET results indicated that Co-CNTs@NC-3 possessed highly dispersed Co sites and mesoporous structure.Based on the above advantages,Co-CNTs@NC-3(0.1 g/L)rapidly and efficiently activated PMS(0.1 g/L)to degrade more than 92.64%of SMX(30 mg/L)at a pH range of 3-11 for 30 min.The mineralization rate reached 65.72%under neutral conditions.The results of the quenching experiment and EPR indicated that Co-CNTs@NC-3 could activate PMS and dissolved oxygen to produce active species,and a 1O2-dominated non-free radical degradation mechanism of SMX was proposed.Co-CNTs@NC-3 processed excellent anti-interference performance to Cl-,HCO3-and H2PO4-.Adding of humic acid(20 mg/L)slightly inhibited SMX degradation,and resulting in a 28.65%reduction in removal.The XRD results showed that Co-CNTs@NC-3 possessed an excellent stability.The magnetic characterization results displayed that Co-CNTs@NC-3 had a magnetization saturation value of 20.32 emu/g,and the strong magnetic properties make it recyclable.The cyclic results indicated that Co-CNTs@NC3 could remove more than 88.06%of SMX within 60 min after activation at 1000℃ for one hour after three reactions.The results of the ECOSAR analysis confirmed that the toxicity of four products exceeded that of SMX,while the remaining seven products exhibited lower toxicity levels compared to SMX.This study can provide theoretical support and methodological guidance for preparing of ZIFs-derived metal-carbon materials with highly dispersed Co sites and efficient removal of high-concentration antibiotics.(3)To solve the Co leaching problems of the above studies,the novel NC-supported highly dispersed carbon-coated Co NPs composites(Co-N@NC-90)were obtained by calcinating dopamine-chelated Co modified NC.The results of XRD,TEM,XPS,and high-resolution TEM results confirmed that Co NPs were coated with graphite carbon.The results of Raman spectroscopy and XPS demonstrated that adding Co increased the surface defects of NC.Due to the synergistic effect between Co and NC,Co-N@NC-90(0.1 g/L)efficiently activated PMS(0.1 g/L)to degrade more than 96.91%of SMX(20 mg/L)in the initial pH range of 3.65-9.05 and within 90 min.The Co leaching amount(0.86 mg/L)was lower than the national standard(GB 25467-2010,1 mg/L).The results of material characterization and SMX removal demonstrated that Co NPs were the main active site,and the carbonyl functional group also contributed to the degradation of SMX by activating PMS to produce 1O2.The quenching experiment and EPR results confirmed that sulfate radical and 1O2 were the main active species,and 1O2 played a primary role in SMX degradation.In addition,eight products were detected,and three degradation pathways(including amino oxidation,hydroxylation of benzene,and isoxazole)were proposed.The results of total organic carbon analyzer and gas chromatography demonstrated that Co-N@NC-90 could mineralize SMX to produce carbon dioxide by activating PMS.The results of toxicity assessment using activated sludge experiment and ECOSAR analysis indicated that SMX and all the products did not have acute toxicity to green algae,fish,and daphnia.The chronic toxicity to fish of nitro and nitroso-SMX exhibited higher levels compared to SMX,whereas the toxicity of other products demonstrated lower levels than SMX.This work can provide a technical and theoretical foundation for synthesizing of NCsupported metal catalysts and their application in antibiotic degradation.