Fabrication Of Graphitic Carbon Nitride And Bi-based Nanocomposites For Their Photocatalytic Oxidation Of Nitrogen Oxides

With the rapid economic and industrial development of our country since the 21st century,and the rapid growth in the number of cars and factories,China is facing tremendous pressure regarding environmental pollution,especially air pollution,such as acid rain,haze events,photochemical smog,the excess of PM 2.5,ozone layer and global warming,etc.These air pollution incidents affect human daily life and health severely,among which nitrogen oxides NOx(including NO and NO2)is the prime culprit.However,with the continuous improvement of the economic level,the environmental awareness of human is also increasing.The 18th National Congress put forward the strategic decision of"construction of ecological civilization",which attaches great importance to"environmental protection" and "building a beautiful China".In order to purify the air,there are many established conventional techniques and methods for NO purification under ambient contidions,such as adsorption,selective catalytic reduction,selective non-catalytic reduction,etc.However,these methods are suitable for the treatment of high concentration of NO.,and NOx cannot be degraded completly.In order to meet people’s demand for cleaning air,the degradation of low concentration NOx(ppb level)has become the focus of attention.Semiconductor photocatalytic technology is an effective strategy for the degradation of low concentration NOx,which is economical,environmentally friendly,inexpensive and non-toxic.Semiconductor photocatalysts such as graphitic carbon nitride(g-C3N4)and Bi-based materials stand out in the research of degradation of low-concentration NOx due to their suitable band gap,good visible light response and excellent photocatalytic performance.In this paper,g-C3N4 and Bi-based(Bi2WO6,Bi2O2CO3,etc.)photocatalysts are used as substrates,small organic molecules(such as PI molecules)or inorganic semiconductor materials(such as BP,InVO4,MoS2,etc.)with good visible light response are used to modify the photocatalysts,and effective methods are adopted to control the morphology of the photocatalyst to expose more active sites,introducing highly conductive materials(such as BP,GO,etc.)to enhance the carrier migration rate.In addition,the immobilization of the photocatalyst(e.g.,modifying the photocatalytic material onto the carbon fiber membrane,aerogel)is effectively achieved.We applyed the prepared g-C3N4 and Bi-based nanocomposites for the treatment of low-concentration NOx in air in the field of environmental remediation.In order to broaden the application of g-C3N4 and Bi-based nanocomposites in the environment and energy,we also applied it for hydrogen production and treatment of organic pollutants in wastewater.(1)A 3D aerogel of graphitic carbon nitride modified with perylene imide(PI)and grapheme oxide(PICNGA)is prepared and used in the photocatalytic degradation of low concentration NOx in exhaust gas in the field of environmental remediation.The method of copolymerization is used to modify the PI molecules with good planarity and strong visible light response to the surface of g-C3N4,which not only broadened the range and intensity of visible light absorption of g-C3N4,but also effectively inhibited the recombination of photogenerated electrons and holes,and increased the transport rate of photogenerated carriers.3D aerogel materials(PICNGA)were prepared by hydrothermal method.PICNGA exhibits excellent photocatalytic activity,stability and recyclability in the photocatalytic degradation of NO(600 ppb),and the highest efficiency of NO removal ratio up to 66%.(2)In order to expose more catalytically active sites on g-C3N4 photocatalyst,we prepared aerogel materials based on carbon nitride quantum dots and used for photocatalytic degradation of low concentration NOx in air.The bulk g-C3N4 is prepared into carbon nitride quantum dots(CNQDs)with an average diameter of 3 nm by exfoliation method,and then the CNQDs were modified to the surface of graphene(GO)uniformly and then formed a 3D aerogel with heterojunction structure with the inorganic semiconductor InVO4.The synergistic heterojunction exhibit a powerful photocatalytic effect for the removal of NO at the ppb-level under visible-light irradiation,with a maximum efficiency up to 65%.(3)For the purpose of enhance the visible light responsiveness of g-C3N4,we introduced a new type of two-dimensional black phosphorus material which has unique photochemical/electrochemical properties in g-C3N4 system,which has broaden the light response range and intensity of g-C3N4 nanocomposites greatly.In addition,the surface of porous g-C3N4 is modified by the metal organic frameworks(MOFs)HKUST-1 which exhibits excellent adsorption performance of NO because of its extremely high surface areas,porosity and high adsorption capacities(PCN-HK).Finally,the immobilization of photocatalytic nanocomposites is realized,and BP/PCN-HK is modified on the conductive carbon nanotube films(CNF).We have introduced BP materials into the field of waste gas treatment in environmental remediation for the first time,and the BP/PCN-HK membrane exhibits excellent photocatalytic performance,the efficiency of photocatalytic degradation of NO up to 74%,which is much higher than other g-C3N4 related materials.In addition,the BP/PCN heterojunction also exhibits excellent photocatalytic H2 evolution activity with an efficiency reaching 7380 μmol h-1 g-1.(4)A Z-Scheme 2D/2D heterojunction of black phosphorus/monolayer Bi2WO6 nanosheets(BP/MBWO)is prepared by a simple and effective method.A perfect heterojunction structure is formed and the interface effect problem was effectively solved when the smaller Bi2WO6 nanosheets were loaded onto the lager BP nanosheets.The BP/MBWO heterojunction exhibits excellent photocatalytic performance in photocatalytic degradation of low concentration NOx and H2 production experiments,the efficiency of photocatalytic degradation of NO is 67%and photocatalytic H2 evolution activity is 21042μmol g-1.This work not only broadens the application range of black phosphorus,but also improves its application prospects in dealing with environmental pollution and renewable energy issues.(5)To improve the practical application value of photocatalytic materials,we prepared Bi2OCO3 photocatalytic menbranmes by electrospinning and hydrothermal methods,and are used in environmental remediation.Firstly,carbon fiber membranes(CNFs)are prepared by electrospinning and calcination;then the rose-like photocatalyst Bi2O2CO3 is modified on the surface of CNFs by hydrothermal method;then the thin layer of MoS2 is modified on the surface of Bi2O2CO3 to form a heterojunction(BOC-MoS2-CNFs membrane).The BOC-MoS2-CNFs membrane showed excellent performance in the photocatalytic degradation of low concentration NOx in air,and the NO removal ratio up to 68%.In order to further broaden the application range of Bi2O2CO3 in environmental treatment,we modified iodine-doped Bi2O2CO3 on the surface of CNFs(CNFs@IBOC),which can not only reduce the band gap of Bi2O2CO3 and enhance the response range to visible light,but also change the morphology of Bi2O2CO3 into flakes.Finally,the MoS2 sheet is modified on the surface of CNFs@IBOC to form the heterojunction CNFs@IBOC-MoS2.CNFs@IBOC-MoS2 membrane also exhibited excellent performance for photocatalytic treatment of organic pollutants in wastewater,50 mL 1×10-5 M RhB solution could be degraded completely within 5 min by 50 mg CNFs@IBOC-MoS2 membranes.The g-C3N4 and Bi-based as-prepared photocatalytic nanocomposites not only exhibit excellent performance in photocatalytic oxidation of low concentration NOx in waste gas,but also show amazing effects in photocatalytic treatment of organic pollutants in wastewater and H2 evolution.This paper plays a good foundation for the study of environmental remedation and new energy issues by using semiconductor material photocatalysis technology.