| Sulfonamide antibiotics were extensively used in poultry feeding and healthcare industry and they were hard to be completely metabolized by animals and humans.Therefore,various kinds of sulfonamide antibiotics have been detected in surface waters and wastewaters,among which sulfadiazine(SDZ)was a representative one with doughty durability.It can cause serious human health problems and environmental risks via inducing antibiotic-resistant bacteria/gene formation and changing in microbial community composition.Therefore,it is urgent to explore efficient and green treatment methods for SDZ.In recent years,basedpersulfate advanced oxidation technology was becoming a research hotspot in the field of organic wastewater degradation.The heterogeneous activation of peroxydisulfate(PDS)has attracted an inordinate amount of attention because of its high efficiency,easy operation and energy saving.In addition,carbonaceous materials,especially biochar have become the green and applicable alternatives to transition metal-based catalysts for PDS activation due to their bulk availability,environmental friendliness,low price and ease of functionalization.However,biochar obtained from the pyrolysis of biomass usually exhibited inferior PDS activation performance possibly due to its low surface area and pore volume and scarce catalytic active sites.The pore-making(activation)is a very effective route to ameliorate the performance of biochar in pollutant adsorption and catalytic reactions.However,common activating agents(KOH,Zn Cl2 and H3PO4)are caustic and toxic with storage and environment challenges restricting their industrial applications.Therefore,some harmless bicarbonates,organic salts and thiosulfates of alkali metal with benign chemical properties have been used as activating agents.In this study,a suite of porous biochar catalysts was prepared with the addition of a hard template,a porogenic agent or their combination.A series of characterization of these biochar catalysts have been carried out.And these biochar catalysts were utilized as catalysts for PDS activation to explored the performance and mechanism of SDZ degradation.This study provides a new strategy for constructing porous carbonaceous catalyst using a low-cost hard template and a green porogenic agent for the driving PDS to degrade pollutants.The main research results are as follows:(1)Using the high temperature pyrolysis synthesis method,biomass corn straw as raw material,a series of carbonaceous catalysts(K-C,S-C,SK-C,KK-C,Na K-C and Na2K-C)were fabricated using a sole template(KCl),a sole activating agent(Na2S2O3)or a combination of template and activating agent(KCl/Na2S2O3,KCl/KHCO3,KCl/Na HCO3,and KCl/Na2C2O4).The results of scanning electron microscopy(SEM)and transmission electron microscopy(TEM)showed that the S-C catalyst exhibited an irregular carbon bulk with rough surface and visible pore structure.The K-C catalyst showed a sponge-like structure consisting of many smooth and thick carbon sheets without obvious pores.The SK-C exhibited an interconnected porous structure forming by the stacking of smooth and thin carbon sheets.BET results revealed that SK-C had the largest specific surface area(1796.1 m2g-1)and porosity(0.8399 cm3g-1).(2)The biochar synthesized by KCl and Na2S2O3(SK-C)exhibited the optimum degradation performance.The SDZ of 20 mg/L can be completely degraded within 60 min at room temperature 25 oC by adding 2 m M PDS and 0.1 g/L SK-C.When the dose of PDS and SK-C was increased,the degradation efficiency of SDZ by SK-C activated PDS can be improved.The co-existing anions(NO3-,H2PO4-and Cl-)and solution p H in water had little influence on the degradation efficiency of SDZ in SK-C/PDS system,while the significant influence of anion HCO3-on the degradation effect of SDZ can be attributed to the selfquenching reaction.Overall,the reaction system had a wide range of application.(3)The results of chemical quenching experiment and electron paramagnetic resonance(EPR)showed that hydroxyl radical(·OH),sulfate radical(SO4·–),superoxide radical(O2·–)and singlet oxygen(1O2)had no effect on the degradation of SDZ by SK-C activated PDS.(4)Through the combination of X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and BET results,it was found that the specific surface area(SSA)and its C-sp3 content of the catalyst had a key effect on the ability of the catalyst to activate PDS to degrade SDZ,and a quantitative relationship could be established between SSA,C-sp3 content and the degradation performance.The recycling experiments showed that the C-sp3 content of catalyst had a crucial effect on its activation,and SK-C had good stability and reusability.(5)The results of electrochemical oxidation experiment(GOP)provided direct evidence for the occurrence of electron transfer mediated by SK-C/PDS degradation process of SDZ;Linear sweep voltammetry(LSV),in situ attenuated total reflection infrared Fourier transform(ATR-FTIR)and in situ Raman spectroscopy confirmed the formation of SK-C/PDS*metastable complex with strong oxidation capacity.The experimental results of three types representative organic pollutants indicated that the SK-C/PDS system mainly exerted its catalytic degradation activity by single electron transfer pathway Ionic strength experiments showed that there was a strong inner-sphere interaction between the catalyst and PDS.(6)Thirteen transformation products of SDZ by SK-C/PDS system can be detected by UHPLC-MS technology.The SDZ degradation was discovered by four main pathways including S-N bond cleavage,Smile rearrangement,N-C bond cleavage,and pyrimidine ring open and thirteen transformation products were identified with much less toxicity than the SDZ. |
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