Synthesis And Studies On Its Photocatalytic Performances Of Novel Polymeric Carbon Nitride Photocatalyst

In recent years,graphitic carbon nitride(PCN)has attracted much attention in the field of photocatalysis.PCN is a kind of stable polymer organic semiconductor with low cost,simple preparation and suitable energy band structure.It has been widely used in the fields of photocatalytic degradation of pollutants,photocatalytic hydrogen production and oxygen production and hydrogen dioxide reduction.However,it still has a great many of disadvantages,for example,high carrier recombination rate,narrow visible light absorption range and insufficient water oxidation capacity,which limit its application in the field of photocatalysis.Therefore,the preparation of highly active PCN by physical and chemical modification approaches is crucial to further expand its application.The main research content of this paper is about the modification of PCN and the preparation of new PCN based photocatalyst,which improves the visible light absorption range,the separation efficiency of photogenerated carriers and the photocatalytic redox performance.The effects of different comonomers on the morphology,crystal structure,photoelectric properties and catalytic performance of PCN were systematically studied by a variety of characterization methods.The prepared PCN based photocatalysts was applied to the production of hydrogen peroxide and organic oxidation reaction.The research contents of this paper mainly include the following contentsA new type of photocatalyst,PCN-TAP with Donor-Acceptor unit was synthesized by copolymerization of Melem with 2,4,6-tris(4-aminophenyl)-1,3,5-triazine(TAP),using Melem as precursor and TAP as the second monomer.The effect of the ratio of Melem to TAP on the catalytic performance of the prepared PCN photocatalyst was systematically studied.The prepared materials were characterized by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),scanning electron microscopy(SEM),transmission electron microscopy(TEM),photoluminescence(PL)and UV-vis-DRS.The experimental results show that the introduction of TAP copolymerization can indeed promote the efficient separation of carriers,and simultaneously improve the photocatalytic oxidation and reduction performance of PCN.The activity of PCN-TAP increased first and then decreased with the increase of copolymer amount.The reason is that TAP can construct donor-acceptor structure by introducing TAP into PCN heptazine ring structure,which can effectively promote the separation of carriers.PCN-TAP3 prepared in this research showed the best photocatalytic activity.Compared with pure PCN,the photocatalytic hydrogen peroxide yield and β-ionone epoxidation yield of PCN-TAP3 were increased by 3 times and 10 times,respectively.In order to further improve the photocatalytic performance of PCN,we used Melem as the precursor and barbituric acid(BTA)as the second monomer for copolymerization.On the basis of preserving the Donor-Acceptor unit,we prepared a series of novel PCN organic semiconductor photocatalysts of PCN-BTA by oxygen doping.The photocatalytic materials prepared were characterized and the effects of different copolymerization amount of BTA on the performance of the catalyst were studied.The results show that when the molar ratio of Melem to BTA is 70:1,PCN-BTA2 catalyst has the best performance.When Donor-Acceptor units are retained,the PCN-BTA2 catalyst can achieve a larger positive transfer of the valence band by oxygen doping,which significantly improves the water oxidation capacity of the holes.Compared with pure PCN,the photocatalytic hydrogen peroxide yield and β-ionone epoxidation yield of PCN-BTA2 were increased by 7 times and 11 times,respectively.Finally,we chemically bonded Perylene-3,4,9,10-tetracarboxylic dianhydride(PTCDA)to PCN-BTA2.PTCDA not only has excellent visible light to near-infrared light absorption range,but also has hydrophobicity.Therefore,we combined it with polymeric carbon nitride to improve the adsorption capacity of the catalyst for organic materials,and improve the selectivity of organic reaction while retaining the high photocatalytic hydrogen peroxide production yield.Then,the prepared catalysts were characterized by SEM,PL,XRD,XPS,UV-vis-DRS and free radical capture.The experimental results show that the photogenerated electrons play a decisive role in the photocatalytic production of hydrogen peroxide,while the photogenerated electrons and holes promote the reaction in the epoxidation of β-ionone synergistically.Compared with PCN and PCN-BTA2,PCN-BTA2-5%has the highest selectivity for β-ionone epoxidation and the selectivity of this reaction has been increased from 46%to 75%of that of pure PCNBy copolymerization,we prepared a variety of new PCN polymer organic semiconductor photocatalytic materials and this method efficiently improved the PCN light catalyst carrier separation,broadening the scope of light absorption,improve the ability of photocatalytic oxidation and reduction,is expected to be applied to other organic semiconductor photocatalyst modification research and application.