Preparation Of Z-type Heterojunction Photocatalyst Based On GC₃N₄ And Research On Degrading Antibiotics In Water

The overuse of antibiotics is usually directly released into the environment,posing a significant threat to human health and ecosystems.Antibiotic wastewater is highly biotoxic,difficult to biodegradable and toxic to organisms,photocatalytic technology has attracted widespread attention due to its high efficiency and environmental friendliness in the treatment of pollutants.Polymeric graphitic carbon nitride（g-C3N4）has gained intensive concern as a novel photocatalyst,because its band gap of～2.7 e V corresponds to the absorption edge at 460 nm in visible light region and its relatively negative conduction band endows the photogenerated electrons high reduction capability.Nonetheless,it is difficult for pristine g-C3N4 to simultaneously possess broad spectrum absorption,efficient charge separation and high redox ability,limiting the practical applications of g-C3N4 materials.Therefore,it is of great significance to develop new photocatalytic materials based on g-C3N4 with broad spectrum response and fast electron transport rate.In this thesis,tetracycline（TC）and ciprofloxacin（CIP）are used as the target pollutants,and g-C3N4 is used as the reduced semiconductor to build two Z-scheme heterojunction by matching the band gap with the oxidized semiconductor.At the same time,the oxidized semiconductor with local surface plasmonic resonance（LSPR）has broadened the response range to sunlight.First at first,defected WO3 quantum dots（WOQD）are coupled to g-C3N4nanosheets（CN）via WOQD prepared by a one-pot solvothermal method followed by self-assembly through a wet chemical method.The influence of the structure,morphology,composition of WOQD-CN nanomaterials and the amount of WOQD on the photocatalytic activity is investigated.The results indicate that WOQD with the size of～2 nm,defect surface,and quantum size facilitate coupling with CN to obtain a high-quality interface.When the mass ratio of WOQD was 3%of the mass of CN,the degradation of ciprofloxacin and tetracycline hydrochloride is the best under full spectral irradiation for 3h,and the degradation rate reached 98%.Under the optimal condition,the degradation rate of 4 cycles decrease slightly,in addition,the effects of various factors including p H,initial solution concentration,and common cations and anions(i.e.,SO4^2-,HCO3^-,and NO3^-)on the degradation of CIP and TC were evaluated.A possible photocatalytic reaction mechanism is proposed based on the characterization and performance tests.The enhanced photocatalytic activity of nanocomposites in the degradation of antibiotic pollutants may be attributed to the enhanced charge separation due to the Z-scheme heterojunction formed under UV-vis light irradiation and the broadening of the light response to the near-infrared（NIR）region due to the localized surface plasmon resonance effect under NIR light irradiation.In order to further promote the separation efficiency of photo-generated charges and broaden and enhance the photo-response range of photocatalysts,all-solid CN/N-CQDs@W18O49 Z-scheme heterojunction photocatalyst was prepared by using nitrogen-doped carbon quantum dots（N-CQDs）through physical deposition and in-situ growth methods.The introduction of N-CQDs at the interface junction of the two semiconductors of g-C3N4 and W18O49 produces an ohmic contact with the least resistance.Radical trapping control experiments and photocatalytic degradation experiments confirmed that the CN/N-CQDs@W18O49 nanocomposites display high activities in the photo-degradation of CIP and tetracycline TC in antibiotic pollutants in the presence of hydroxyl（·OH）and superoxide radicals（·O2^-）,and the photo-degradation activities of the optimized CN/N-CQDs@W18O49-3 sample are eight times higher than those of CN under Xe light irradiation.The XRD changes before and after the cycles are further investigated.It is confirmed that the CN/N-CQDs@W18O49-3composite photocatalyst had good photocatalytic performance and stable performance.The cooperative synergy effect of dual-channel charge-carrier transfer path in such CN/N-CQDs@W18O49 composites,including Z-scheme charge transfer and surface plasmon resonance effect,which interactively leads to the boosted photocatalytic performance.In addition,CN has a large specific surface area,which can provide enough active sites.The match of the band gap results in the Z-scheme reaction mechanism and brought both the strong redox ability and promotion of the transfer rate of the photogenerated charges;the addition of N-CQDs and the LSPR effect of nonmetal plasmonic W18O49 can broaden the light response of the prepared CN/N-CQDs@W18O49 to NIR region,leading to enhanced utilization of solar energy.In conclusion,the results highlight the high efficiency charge transfer of Z-scheme heterostructure photocatalyst based on g-C3N4 and its great potential in expanding the range of light response effectively,which provides a solid theoretical basis for the economic and environmental applications of antibiotic wastewater degradation.