Application And Research Of Graphitic Carbon Nitride Photocatalytic Separation Membranes In Water Purification

The complex pollutant composition in actual wastewater presents new challenges to water purification.Combining photocatalytic materials with membrane separation technology can effectively eliminate membrane contamination,increase the service life of separation membranes,and solve the difficulty of powder photocatalyst recovery.Based on the above background,this paper firstly modified the bulk graphitic carbon nitride（g-C₃N₄）by morphology control method to prepare seaweed-like g-C₃N₄,and then constructed high-performance g-C₃N₄-based photocatalytic separation membranes by vacuum self-assembly to achieve effective purification of complex wastewater.The main researches of this paper are as follows:（1）Focusing on the problems of narrow photoresponse range,small specific surface area and easy electron-hole（e^--h⁺）complexation of bulk g-C₃N₄,porous seaweed-like g-C₃N₄photocatalysts were synthesized by morphology control strategy.This special morphology increased the specific surface area,expanded the visible light absorption range,reduced the band gap,promoted the electron-hole separation,and significantly enhanced the photocatalytic activity of g-C₃N₄.Then photocatalytic separation membranes（SCN-X）were constructed by vacuum self-assembly of single-component seaweed-like g-C₃N₄ for multifunctional water purification.The unique porous seaweed-like structure increased the specific surface area and hydrophilicity of the membrane,which facilitated the absorption and utilization of visible light and improved the separation efficiency of e^--h⁺,giving the SCN-2 membrane excellent comprehensive water purification performance.The SCN-2 membrane could efficiently separate five types of oil-in-water emulsions with a maximum flux of 3114.0±113.0 L m^-2 h^-1bar^-1 and a maximum efficiency of 97.4±0.1%.Meanwhile,the SCN-2 membrane had excellent photocatalytic performance with degradation efficiency of up to 100.00%for the organic dyes rhodamine B（Rh B）,methylene blue（MB）and crystalline violet（CV）,and antibacterial efficiency of nearly 100.00%for two bacteria.In addition,the SCN-2 membrane had long-term water purification potential and performed well in continuous oil-water separation and dye degradation experiments.This work offers the possibility of easy construction for multi-functional photocatalytic separation membranes using a single material.（2）To further enhance the separation flux of SCN-X membrane,g-C₃N₄ composite photocatalytic separation membranes（CCNX）were constructed by compounding seaweed-like g-C₃N₄（SCN-X）with g-C₃N₄ nanospheres（CN）.The addition of CN optimized the pore structure and transport channels of the membranes,greatly increasing the oil-water separation flux and cycle separation times of the composite membranes.The separation flux of the CCN2membrane for all five oil-in-water emulsions was greatly increased with a maximum flux of5738.6±229.7 L m^-2 h^-1 bar^-1.Meanwhile,the CCN2 membrane maintained excellent separation capacity after 60 consecutive cycles with a flux exceeding 1327.0 L m^-2 h^-1 bar^-1,and an efficiency of more than 95.5%.In addition,the composite of the two materials did not reduce the excellent photocatalytic performance of the separation membranes.And the CCN2composite membrane still had excellent photocatalytic ability,with degradation efficiency of over 98.13%for Rh B and MB,and antibacterial efficiency of over 93.37%for two bacteria.This work provides a new idea to promote multifunctional g-C₃N₄-based membranes for complex wastewater purification.