| Antibiotic water pollution has caused serious harm to human and ecology,so antibiotic water treatment has gradually become a hot issue in many countries.Advanced oxidation technology based on Photo-Fenton is expected to be applied to the treatment of refractory antibiotic wastewater.Graphite-type carbon nitride material(C3N4)is a two-dimensional lamellar polymer,which has been used as a Photo-Fenton.In recent years,it has been found that single-atom modified C3N4 catalyst can catalyze the Photo-Fenton technology efficiently.The efficient and stable catalyst and clear Photo-Fenton catalysis mechanism are of great significance to the practical application of wastewater treatment.Therefore,in this paper,ciprofloxacin was used as a model antibiotic pollutant to study the Photo-Fenton catalyst based on single atom doping C3N4.Three parts of work were carried out from the perspectives of preparation design of catalyst,structure-activity relationship study,catalytic mechanism study and application expansion.Firstly,pure C3N4 and transition metal Co,Ni,Cu,Zn doped C3N4 catalyst(Co-C3N4,Ni-C3N4,Cu-C3N4,Zn-C3N4)were prepared by"supramolecular strategy-calcination" process.Firstly,the materials were characterized by SEM,XRD,TEM and HRTEM,and it was proved that the morphology and structure of C3N4 were not changed by single atom doping.The homogeneous metal single atom was detected in the amorphous structure,indicating the successful preparation of the catalyst.Then,the Photo-Fenton degradation experiments were carried out.The results showed that the Photo-Fenton degradation performance of ciprofloxacin(CIP)was Cu-C3N4>Co-C3N4>Zn-C3N4>Ni-C3N4>C3N4.The results indicate that the doping of Co,Ni,Cu and Zn can improve the Photo-Fenton properties of C3N4.Finally,free radical trapping experiments were carried out,and it was proved that photogenic holes,·OH,·O2-and 1O2 in Co-C3N4/H2O2/visible light system,Ni-C3N4/H2O2/visible light system,and Zn-C3N4/H2O2/visible light system all participated in the reaction,in which photogenic holes and ·O2-played the main role.Different from other systems,the Cu-C3N4/H2O2/visible light system mainly plays the role of photogenic holes and 1O2,which indicates that Cu-C3N4 has excellent catalytic performance and unique catalytic mechanism.The Cu-C3N4 catalyst selected in the last chapter was studied in detail,and Cu single atomic sites could be clearly observed in the spherical electron microscopy.Low temperature EPR test and XANES simulation analysis show that Cu atoms exist in the Cu-N4 structure in the form of Cu-N4 coordination,and the possible atomic model of Cu-C3N4 has been confirmed.By comparing the Photo-Fenton properties of C3N4 and Cu-C3N4 catalysts,it is shown that the addition of Cu single atom improves the degradation efficiency of ciprofloxacin(CIP)in the Photo-Fenton system from 45.1%to nearly 100%within 30 min.The corresponding quasi-first-order kinetic constant k increased from 0.0218 min-1 to 0.0978 min-1.The effects of different catalyst dosage,different hydrogen peroxide dosage,different substrate concentration and different light intensity on the Cu-C3N4 Photo-Fenton system were studied,and the mathematical model was established based on the reaction conditions and corresponding first-order kinetic constant k.Then,the catalysts C3N4 and Cu-C3N4 were characterized by UV-Vis DRS,UPS,PL and TRPL.The structure-activity relationship between Cu single atomic sites and the properties was verified.It was proved that the Cu-N4 site was introduced into C3N4,which effectively expanded the range of light absorption and promoted the ability of charge separation and transfer.The recombination rate of electron and hole generated by light is reduced,and the Photo-Fenton property of Cu-C3N4 is effectively promoted.Finally,the reproducibility and universality of the Cu-C3N4 Photo-Fenton system are studied.The Photo-Fenton mechanism of Cu-C3N4 is further analyzed in detail.The main free radicals produced by Photo-Fenton degradation of Cu-C3N4 were studied in combination with EPR and free radical capture experiments.A new non-free radical mechanism was proposed,and the active site was considered to be the key to study the catalytic mechanism.Therefore,the changes of Cu-N4 active sites were analyzed by XANES and EXAFS,and the existence of the speculative mechanism was verified.The specific steps are as follows:under the action of H2O2 and light,atomically dispersed Cu-N4 will generate O=Cu-N4 and further transform into O=Cu-N4=O,which has strong oxidation capacity and is a key intermediate in the degradation process.CIP is cyclically degraded by the interaction of important intermediates and hydrogen peroxide.Finally,three possible degradation paths were simulated through a series of characterization,among which the important oxidation processes were pyridine ring opening,piperazine ring opening and benzene ring opening.In the continuous degradation process,CIP was oxidized to small molecules such as H2O and CO2. |
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