Properties Of FeOOH/g-C₃N₄ Composites For Photocatalysis And Coupling Membranes

In recent years,photocatalytic technology has been widely used in the field of environmental remediation due to its advantages of green environmental protection,sustainability,and efficient mineralization of almost all organic pollutants.However,due to the difficulty of recycling powder photocatalysts and the high cost of application,it is difficult to promote photocatalytic technology in industrial applications.As a new process in the 21st century,membrane separation technology is broadly used in the field of sewage treatment due to its low energy consumption,operation,and good treatment effect.However,membrane fouling,short membrane life and concentrated solution treatment have always limited its industrial application.Recently,studies have shown that coupling photocatalysis with membrane separation technology is a feasible way to solve these problems.Therefore,in this study,FeOOH NPs/CNNS catalysts with N defects or O doping were prepared,and and the degradation performance of a series of photocatalysts for OTC was investigated.And developed a photocatalytic membrane based on FeOOH NPs/CNNS photocatalyst.The main research contents are as follows:（1）FeOOH NPs/Nvac-CNNS photocatalysts were prepared by thermal polymerization and in situ synthesis.Under visible light irradiation,(OTC degradation efficiency of FeOOH NPs/Nvac-CNNS（92.83%）was significantly higher than that of CNNS（39.45%）and Nvac-CNNS（46.22%）.At the same time,the response surface method（RSM）predicted that under the optimal conditions（current of 18.586 A,initial p H of 6.371,and dosage of 0.6 g/L）,OTC degradation efficiency could reach 94.331%.FeOOH NPs/Nvac-CNNS exhibited the excellent reutilization and practical application potential in OTC pollution purification of high（10 mg/L）and low（0.5 mg/L）concentration.By constructing a heterojunction between FeOOH and Nvac-CNNS,CNNS has the advantages of fast carrier separation,wide visible light response range,fast decomposition of H₂O₂,and excellent molecular oxygen activation.Meanwhile,combining LC-MS and T.E.S.T（Toxicity Estimation Software Tool）results,FeOOH NPs/Nvac-CNNS can realize green treatment of OTC.（2）FeOOH NPs/O-CNNS photocatalysts were successfully prepared through in situ synthesis.The synergistic effect between FeOOH coupling and O doping promoted the photocatalytic degradation efficiency of OTC from 55.47%to 78.95%within 90 min,and TOC mineralization efficiency was 45%.Meanwhile,the optimal conditions of the FeOOH NPs/O-CNNS/vis system predicted by response surface methodology（RSM）are as follows:the dosage is 0.594 g/L,the current is 17.665 A,the initial p H is 5.82,and OTC degradation efficiency can reach 81.337%.FeOOH coupling can effectively reduce the recombination of carriers and promote visible light absorption;oxygen doping can build a strong coupling interface by forming Fe-O bonds,and at the same time optimize the electronic structure and promote the dissociation of excitons.FeOOH NPs/O-CNNS exhibited good degradation performance for OTC under natural light and different water matrices.On the basis of LC-MS analysis,the possible degradation pathways of OTC were proposed,and combined with QSAR toxicity prediction,it was confirmed that FeOOH NPs/O-CNNS photocatalysis can realize the harmless treatment of OTC.（3）FeOOH NPs/CNNS/PDA/PVDF photocatalytic membranes were prepared through a three-step method（i.e.,membrane modification,negative pressure coating and chemical cross-linking）.The composite membrane has a high flux(5820 L m^-2h^-1bar^-1)and a good rejection of Rh B（83.96%）.For salt-containing Rh B,the composite membrane can achieve high Rh B rejection while passing most of the salt,so as to achieve the purpose of separation and recovery of dye and salt.The static degradation experiments confirmed that the FeOOH NPs/CNNS/PDA/PVDF composite membrane had good photocatalytic performance,and Rh B degradation efficiency tended to be～100%after adding PMS.For dye-contaminated composite membrane,the membrane flux can be recovered by more than 90%after 30 min of light treatment,and the membrane flux can be recovered more effectively by coupling H₂O₂or PMS,indicating that the composite membrane has good self-cleaning performance.