Co-modification Of Carbon Nitride Photocatalytic Material With Manganese And Phosphorus For Degradation Of Organic Pollutants

Continuous improvement of urban water environment quality is an important goal of ecological civilization construction in the 14th Five-year Plan.However,with the development of industrial,the impact of organic pollutants in water on ecological environment and human health has aroused people’s concern,and the treatment technology of organic pollutants has become a research hotspot in environment area.Visible light photocatalytic degradation of pollutants is one of the most economical and environmentally friendly methods,utilizing photocatalyst to convert solar energy into chemical energy and generate active free radicals which can oxidize organic pollutants into non-toxic small molecules.Graphitic carbon nitride(g-C3N4)has become a potential photocatalytic material because of its advantages of simple preparation,cheap raw material and visible light response.However,g-C3N4 prepared by traditional methods has disadvantages such as small specific surface area,narrow light absorption range and high photogenerated electron hole recombination rate,which lead to low photocatalytic efficiency and limits its application in practical water environment.In this paper,the photocatalytic performance of g-C3N4 was improved through co-doping non-metallic phosphorus and metal manganese,and constructing manganese oxide/carbon nitride heterojunction.The relationship between materials preparation process,microstructure and the performance of degrading organic pollutants was explored,providing feasible ideas for the construction of high-efficiency photocatalyst based on g-C3N4.1.Using melamine,phosphoric acid and manganese chloride as raw materials,the supramolecular self-assembly precursor containing manganese and phosphorus was prepared by one-step hydrothermal process,and a hexagonal hollow tubular carbon nitride co-doped with Mn and P(Mn-P-CN),a novel photocatalyst was obtained after calcining.The structure characteristics and photocatalytic performance of Mn-P-CN were studied.The research results showed that doping P and hydrothermal treatment process played a key role in the morphology control of tubular,and introducing Mn reduced band gap and changed the electronic structure of g-C3N4.Co-doping Mn and P produced a synergistic effect which improved the photocatalytic performance of g-C3N4.The best sample 3Mn-P-CN was obtained by adding the optimum content of Mn and P.The removal rates of Rhodamine B(RhB),Tetracycline Hydrochloride(TC-HCl),Bisphenol A(BPA)and Sulfamethoxazole(SMX)by 3Mn-P-CN were 99%,99%,57%and 68%,and the removal rates of Total Organic Carbon(TOC)were 71%,64%,36%and 47%,respectively.The cyclic experiments showed that Mn-P-CN had stable photocatalytic performance.The Density Functional Theory(DFT)was used to calculate Mn-P-CN structure as follows:P replaced some angle C of the tri-s-triazine rings structure;Mn located in the triangular cavity between tri-s-triazine rings,which affected the distribution of Valence Band Maximum(VBM)and Conduction Band Minimum(CBM),and promoted carriers separation and migration.·O2-was proved to be the main active species of degrading pollutants with Mn-P-CN via free radical capture experiment and Electron Spin Resonance test.2.Utilizing phosphorus doped carbon nitride as matrix,a manganese trioxide/phosphorus doping carbon nitride Z-scheme heterojunction(Mn2O3/PCN)was prepared by stirring and calcining manganese acetate and carbon nitride precursor containing P mixture.Using rod-shaped PCN as carrier,Mn2O3 particles grew on the surface of PCN,which not only inhibited the aggregation of Mn2O3,but also prevented the shedding of PCN surface layer.Constructing Mn2O3/PCN heterojunction improved the light absorption capacity,promoted the separation and transfer of photocarriers,and enhanced the photocatalytic performance obviously.The best sample 2Mn2O3/PCN was obtained by using the optimum ratio of precursors.The removal rates of RhB,TC-HCI,BPA and SMX by 2Mn2O3/PCN were 99%,99%,59%and 71%,and the removal rates of TOC were 72%,66%,39%and 49%,respectively.·O2and OH were the main active species of degrading pollutants with 2Mn2O3/PCN.Theoretical calculation results of work function confirmed that the photogenerated electrons of Z-scheme heterojunction Mn2O3/PCN migrated from PCN to Mn2O3.