Study On Boron Doped Flower-Like Graphite Carbon Nitride And Its Photocatalytic Separation Membrane

Graphitic carbon nitride（g-C₃N₄）is widely used in the field of photocatalysis due to its suitable band gap,low cost and environmental friendliness.However,the practical application of bulk g-C₃N₄ is still limited due to its small specific surface area,low visible light response and low photogenerated charge separation rate.In order to solve the above problems,the morphology control and element doping modification of g-C₃N₄ were carried out at the same time,and B-doped flower-like g-C₃N₄（BMNS）was obtained.By expanding the visible light response and promoting the separation and transfer of photo-induced carriers,the photocatalytic performance was improved.However,photocatalytic powder is still difficult to solve in practical water treatment applications due to problems such as difficult recovery and membrane fouling.In order to solve this problem,this paper combined photocatalytic powder with separation membrane.While solving the problem of recovery and pollution,it also gave the membrane a variety of functions,and provided a new idea for the actual complex wastewater treatment.The main research contents are as follows:（1）BMNS was prepared by supramolecular self-assembly and high temperature calcination using melamine,cyanuric acid and boric anhydride as raw materials.The large specific surface area（160.87 m²/g）and porous structure provided high light absorption capacity.The introduction of B element changed the charge structure,reduced the band gap,delayed the recombination of photogenerated carriers,and promoted the photocatalytic performance.Under visible light irradiation,the degradation efficiency of Rh B was up to 97%in 30 min,and the degradation rate was 0.1247 min^-1,which was 46 times than of BCN.At the same time,the amount of H₂O₂ produced in 75 min was 296μM,which was 3.9 times than that of BCN.（2）The CNTs-PAA/BMNS composite membranes were obtained by vacuum assisted filtration of BMNS and PAA functionalized CNTs.The superhydrophilicity and superoleophobicity of CNTs-PAA/BMNS made it possible to separate most common oil-in-water emulsions.BMNS modification could simultaneously increase the membrane flux(maximum 4082 L m^-2 h^-1 bar^-1)and oil-in-water separation efficiency（～99%）.The unique hierarchical structure of CNTs-PAA/BMNS composite membrane could firmly contain pollutants on the surface of BMNS,fully increased the contact area,and facilitated the degradation of pollutants.At the same time,the smaller band gap（2.48 e V）also indicated the high photocatalytic activity of BMNS.The maximum degradation efficiency of Rh B by CNTs-PAA/BMNS reached 99.2%,and the kinetic rate constant was 0.370 min^-1,which was 24.6 times that of CNTs-PAA/BCN.In addition to photodegradation performance and oil-water separation performance,CNTs-PAA/BMNS had an inactivation effect on Escherichia coli and Staphylococcus aureus,and the maximum sterilization rates were more than 98%.The preparation of the composite membrane overcomes the disadvantage of powder instability.The oil-water separation performance and bactericidal performance provide the possibility for the complex wastewater treatment by the composite membrane.