Biomass Carbon-based Catalysts For Antibiotics Degradation Via Peroxymonosulfate Activation

The misuse of antibiotics not only poses a serious threat to the water environment,but also to human life and health.Sulfamethoxazole（SMX）,a kind of frequently detected sulfonamide antibiotic,has become a research hotspot for its efficient removal.Among the reported methods,peroxymonosulfate（PMS）based advanced oxidation processes（PS-AOPs）are widely used in wastewater treatment due to high efficiency,rapid oxidation capacity and low p H dependence.Biomass carbon not only possesses a large specific surface area and well-developed pore structure,which can be used as a catalyst carrier,and the abundance of oxygen-containing functional groups on its surface also makes it an excellent catalyst for activating PMS.Therefore,in this thesis,three biomass carbon-based catalysts were constructed to systematically investigate the performance of activating PMS for the degradation of SMX in water,and to elucidate the degradation mechanism and degradation pathway.The main elements are as follows.（1）The rape straw biochar/cobalt-iron layered double hydroxide（BC/Co₁Fe₁-LDH）composite catalyst was constructed using ZnCl₂ activation to prepare rape straw biochar（BC）,followed by hydrothermal meyhod to produce Co₁Fe₁-LDH on BC in situ,which was used to activate PMS for the degradation of SMX.It was shown that under optimal conditions,BC/Co₁Fe₁-LDH-4 could achieve 94.8%SMX degradation efficiency within 5min and still achieve 80.1%degradation rate after four cycles of experiments.Active species capture and electrochemical experiments confirmed that that both radical and non-radical pathways are jointly involved in the catalytic degradation of SMX and that the latter plays a major role,with the possible reactive sites proving to be the Co²⁺/Co³⁺and Fe²⁺/Fe³⁺redox cycles and the C=O group.The intermediates of SMX degradation were tested with the aid of liquid chromatography-mass spectrometry（LC-MS）and possible SMX degradation pathways were proposed.（2）Nitrogen-doped biochar（NBC）was prepared by a one-step high-temperature charring-activation method using rape straw,urea and ZnCl₂ as raw materials,and its performance in SMX degradation via PMS activation was investigated.It was found that the NBC_2.0 catalyst exhibited the best catalytic activity,with the degradation rate of SMX reaching 99.8%within 5 min and the total organic carbon（TOC）removal rate reaching81.7%within 30 min.In addition,it had good p H adaptability,long-lasting stability,universality and practicality.Further,2-3 mm hydrogel beads(SA/NBC_2.0)were prepared by homogeneously mixing sodium alginate（SA）with nitrogen-doped biochar(NBC_2.0)and filled in a fixed-bed reactor to study the continuous degradation of SMX,which has the potential for practical application with easy recovery.Mechanistic studies showed that the main active species in the system was singly linear oxygen（¹O₂）,and the main active sites of the reaction were graphitic N,pyridinic N and C=O groups,as confirmed by X-ray photoelectron spectroscopy（XPS）and density functional theory（DFT）calculations.The degradation intermediates were tested by LC-MS to reasonably suggest a possible degradation pathway for SMX.（3）NCCA/CoAl-LDH catalysts were prepared by intergrating ZnCl₂-activated nitrogen self-doped chitosan carbon aerogel（NCCA）with cobalt-aluminium layered double hydroxide（CoAl-LDH）,of which NCCA/CoAl-LDH-2 showed the most excellent PMS activation ability with 97.5%degradation of SMX within 5 min,and displayed good degradation in the p H range of 3-9.In addition,the continuous degradation of SMX was investigated by filling the fixed bed reactor with NCCA/CoAl-LDH-2 catalyst.Mechanistic analysis showed that the Co²⁺/Co³⁺redox cycle,C=O groups and graphitic N were the main possible active sites,and that both radical and non-radical pathways were involved in the degradation of SMX,with the latter playing a dominant role.The reaction sites for SMX degradation were inferred by DFT theoretical calculations,and the possible degradation pathways were proposed in combination with the LC-MS measurements.