| Sulfonamide antibiotics are antibacterial agents composed of characteristic functional groups of p-aminobenzenesulfonamide,which are widely used in the treatment of human and animal diseases or as animal feeding additives.However,it cannot be completely metabolized by animals,resulting in excretion into water bodies.The prevalence and continued spread of antibiotic resistance in water is a serious threat to human health.Therefore,the effective removal of residual sulfonamides in the environment has become a research hotspot.In recent years,photocatalytic technology is considered as a promising advanced oxidation technology,which has the advantages of clean,high efficiency,low cost,and low secondary pollution.TiO2 is one of the most common used photocatalytic materials.It has excellent photocatalytic activity,good photochemical stability,low cost and low pollution.However,its forbidden band width is wide,and only the ultraviolet light can be used.As a typical bismuth-based semiconductor material,bismuth oxybromide exhibits good photocatalytic activity.Further research showed that reducing the Br/O ratio of synthesized bismuth-rich bismuth oxybromide can lower the position of the semiconductor valence band and improve the utilization of visible light.In this study,based on Bi4O5Br2 photocatalysts,a series of modification methods were investigated to inhibit the recombination of photogenerated electron-hole pairs and enhance their photocatalytic activity.Sulfathiazole,sulfamethazine and sulfachloropyridazine were selected as target pollutants.The photocatalytic activity of the composite photocatalyst was evaluated by photodegradation of antibiotics.Moreover,XRD,XPS,UV-DRS,TEM,and other material characterization techniques were used to explore the morphology,crystal form,and light absorption capacity of the photocatalysts.In addition,the intermediate products were analyzed by LC-MS,and the degradation pathway of the target pollutants was speculated.Combined with the intermediates detection results,the mechanism of the photocatalyst in the photodegradation process was explored.A free radical quenching experiment was carried out to analyze the main reactive species in the photodegradation reaction.The stability and environmental applicability of the photocatalysts were investigated by cycling experiments and Box-Behnken experiments.The main research contents are as follows:(1)g-C3Ns is prepared by introducing additional nitrogen into the triazine unit of g-C3N4.Compared with g-C3N4,g-C3Ns has more reactive sites and a wider visible light response range.A novel g-C3N5/Bi4O5Br2 heterojunction was synthesized via in-situ growth of Bi-rich Bi4O5Br2 on g-C3N5 nanosheets,and the sulfathiazole(STZ)was chosen as target pollutant to evaluate its photocatalytic activity under solar irradiation.At the optimal g-C3N5 ratio(2 wt%),the composite achieved 99.9%of STZ degradation within 60 min,which is 3.6 and 16.0 times of pristine Bi4O5Br2 and g-C3N5,respectively.The nitrogen enriched g-C3N5 exhibits shifted down conduction band,which is favorable to harvest visible light more efficiently.Compared with gC3N4,CB of g-C3N5 significantly shifts down to shorten the band gap due to the interlayer stacking morphology and the introduction of extra nitrogen into triazine units.The bismuth rich Bi4O5Br2 could prolong charge carrier lifetime,and the matched energy band structure of the type-II surface heterojunctions offers remarkable charge transfer and separation.The photoluminescence,electrochemical impedance spectroscopy and transient photocurrent spectra analysis demonstrate that the promoted charge separation and transfer efficiency were achieved by introducing the N-rich g-C3N5 in the Bi4O5Br2.Moreover,the promoted charge carrier separation played a more important role on improving the STZ degradation than the increased light capturing.The contribution order of reactive species was as follows:O2·->h+>·OH.Acorrding to experiments and density functional theory(DFT)calculation,the STZ degradation mechanism and pathways were speculated.Moreover,the toxicity evolution of STZ was evaluated,and sufficient mineralization is suggested to ensure safe discharge.The BoxBehnken experimental design methodology,applied to discuss the influence of water parameters on the photocatalysis performance,reveals that g-C3N5/Bi4O5Br2 exhibits high reactivity for contaminants degradation under different water matrix condition.This study shows that g-C3Ns/Bi4O5Br2 has great potential in the removal of organic pollutants using photocatalytic techniques.(2)Bi4O5Br2/C-g-C3N4(carbon self-doped g-C3N4)was synthesized by ionic liquid microemulsion method.Simulated sunlight photodegradation experiments were carried out with sulfamethazine as the target pollutant.The experimental results show that the optimal composite ratio is 1 wt%C-g-C3N4.The introduction of C-g-C3N4 is beneficial to improve the utilization of visible light and further enhance the photocatalytic activity of Bi4O5Br2.Degradation experiments and material characterization show that the Bi4O5Br2/C-g-C3N4 interface has lower charge transfer resistance and better separation of photogenerated electronhole pairs.The free quenching experiment show that O2·-is the most dominant active species,followed by h+,and the system contained little·OH.After five cycles of experiments,the degradation rate of sulfamethazine was 83%,which remained at a relatively high level,indicating that the Bi4O5Br2/C-g-C3N4 composite photocatalyst had good stability.BoxBehnken experiments showed that the photocatalytic activity is mainly affected by pH value.The photocatalytic activity was also significantly enhanced when the pH value increased from acidic to basic.(3)Bi4O5Br2/AgI composites were prepared by co-precipitation method,and sulfachloropyridazine was selected as the target pollutant to conduct simulated sunlight degradation experiments.The results showed that the composite showed the best photocatalytic effect at the AgI mass ratio of 40 wt%,and the photocatalytic rate was 2.14 times that of Bi4O5Br2.Compared with Bi4O5Br2,the pore volume and specific surface area of Bi4O5Br2/AgI are increased,which indicates that the porous structure with high specific surface area can provide an effective transport pathway for reactants and products,and provide sufficient active sites for the adsorption and degradation of pollutants.The heterojunction structure formed between Bi4O5Br2 and AgI can accelerate electron-hole separation,broaden the spectral response surface effectively.In the photocatalytic process of Bi4O5Br2/AgI system,the contribution order of active radicals was as follows:O2·->h+>·OH. |
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