Study On Modification And Photocatalytic Properties Of Graphitic Carbon Nitride Materials

Photocatalysis technology stands out from other measures to deal with the increasingly serious environmental and energy crisis and becomes an effective means to solve the energy crisis and repair the environmental pollution.The traditional commercial photocatalyst Ti O₂ is only activated in the ultraviolet region with the wavelength less than 388 nm,which accounts for about 4%of the solar radiation intensity.It is ineffective in the visible light and infrared region,which greatly limits the commercial promotion of photocatalyst.Although it has been more than half a century since the concept of photocatalysis was proposed,the photon energy conversion by photocatalyst at this stage has not reached the level of practical application.Most catalysts today are transition metal-based semiconductors,which are costly and can produce harmful byproducts due to the instability of photocatalysts.Graphitic carbon nitride has attracted much attention since it was reported in 2009 as an excellent visible photocatalyst.Due to its suitable conduction band and valence band location and moderate band gap,it can be used for photocatalytic reactions such as dye degradation,photodissociation of water,CO₂ reduction and nitrogen fixation,etc.The preparation of Graphitic carbon nitride is simple and can be obtained by one-step thermal polymerization of low nitrogen-carbon raw materials.In this paper,graphitic carbon nitride material was selected as the research object.On the one hand,we prepared ultra-thin porous graphitic carbon nitride nanosheets in one step by combining gas stripping with the use of template agent.Broken in this way the graphitic carbon nitride inherentπ-πconjugate electronic structure integrity to reduce light raw electronic-hole recombination efficiency,at the same time introducing defects broaden the light response of graphitic carbon nitride wavelength range,the introduction of porous structure for the mass transport in the photocatalytic reaction channel,accelerate the reaction,the preparation of the sample named CN-PVP showed excellent photoelectric response ability and effective photocatalytic performance.Under the irradiation of 100 m W/cm² white LED light source,the activity of CN-PVP was 297.6μmol/h,9.7 times of that of bulk graphitic carbon nitride.It also showed good activity for degradation of various dyes solution.On the other hand,the prepared graphitic carbon nitride was protonated with strong oxidizing concentrated hydrochloric acid.Through O doping of the prepared nanosheet to regulate the content and distribution of N,and then through the secondary calcinations in different gas atmosphere to regulate the different kinds of defects on the sample surface,the performance of the original sample was improved significantly.The hydrogen production of sample with N vacancy prepared under nitrogen gas and sample prepared under ammonia gas reached 765μmol·g^-1·h^-1 and 721μmol·g^-1·h^-1 respectively.By comparing the hydrogen production and nitrogen fixation data of the samples under the same conditions,the selection bias of the oxygen-doped defective samples to the competitive reaction was obtained,which provided some suggestion for the type of graphitic carbon nitride materials to be used in the photocatalytic reaction in the future.