Study On Performance And Mechanism Of Photoelectrocatalytic Oxidation Of Methane Over ZnO Nanomaterials And Its Composite Catalysts

Methane is the main component of mine gas.Gas accidents can lead to suffocation,fire,explosion and other disasters,causing a large number of casualties and property losses.At present,Chinese coal mine gas prevention and control mainly through physical methods such as ventilation and drainage,but such methods cannot meet the safety requirements for prevention and control of coal mine gas disasters.At the same time,methane is also a kind of greenhouse gas,and its emissions have caused global warming and climate change to some extent.Therefore,the conversion and utilization of methane has been a research hotspot for scholars at home and abroad for many years.In this paper,based on semiconductor energy level theory and carrier transport theory,nano-ZnO and its composite catalysts were designed and prepared.The performance and mechanism of photocatalytic oxidation of methane were studied.The green economy conversion of methane under normal temperature and pressure was explored.Based on the theory of semiconductor energy level and the theory of thermodynamics,the theoretical calculations of quantum chemistry are carried out to match the energy levels of each semiconductor catalyst with methane oxidation,and the ZnO is chosen as the basic catalyst for photocatalytic oxidation of methane.Based on the theory of carrier transport,the photo-generated carrier transportation model in the process of nano-ZnO photocatalytic oxidation of methane is established,and the carrier transport mechanism was revealed.Based on the behavior control interface engineering of nano-ZnO photo-generated carriers,optimization methods such as modification of ZnO with plasma metal nanoparticles,insertion of highly conductive layers and construction of p-n junctions was developed.A photoelectric catalytic oxidation experimental system for methane was built.One-dimensional ZnO nanowire arrays,ZnO/Au,ZnO/graphene(GR)and ZnO/Polyaniline(PANI)composite catalyst were prepared.The structural properties and light absorption properties of nano-ZnO and its composite catalysts were studied.The results show that the one-dimensional rod-like nanostructure with vertical alignment of nano-ZnO exposes more chemically active sites,which is beneficial to the adsorption and reaction of methane molecules.The combination of Au nanoparticles,GR films and flocculent PANI can further increase the surface area of the catalyst and enhance the absorption of visible light,thereby improving the utilization of simulated sunlight and facilitating the methane oxidation reaction.The surface microscopic reaction process,photoresponse performance,photocarrier transport impedance,carrier concentration,electrochemical active area and other photoelectrochemical properties of nano-ZnO and its composite catalysts were tested.The current density of catalytic oxidation of methane over nano-ZnO catalysts is 0.21 mA cm-2;the phototransistor transmission impedance is 39225 ? in the dark,17307 ? under illumination;the carrier concentration is 2.18×1017 cm-3;the electrochemical active area is 0.0405 mF cm-2;Compared with pure ZnO,the photocurrent density of composite catalysts with decoration of nano-Au particles,GR film and flocculent PANI has increased,the photo-carrier transport resistance decreased,the carrier concentration increased,and the electrochemical active area increased.It shows that the photoelectrochemical performance of the composite catalyst is comprehensively improved.The photoelectrocatalytic oxidation of methane reaction products and reaction efficiency of nano-ZnO and its composite catalysts were carried out.The results show that the main product of the nano-ZnO and ZnO/Au photoelectrocatalytic oxidation of methane reaction is methanol,and the corresponding Faraday efficiencies are 10.48%and 35.19%,respectively.The main products of the ZnO/GR and ZnO/PANI photoelectrocatalytic oxidation of methane reaction are methanol and formic acid and the Faraday efficiencies corresponding to the conversion to methanol were 11.74%and 15.02%,respectively,and the Faraday efficiencies corresponding to conversion to formic acid were 39.44%and 43.83%,respectively.The carrier transport model of photoelectrocatalytic oxidation of methane of each catalyst was established,and the generation of photogenerated holes and the mechanism of methane oxidation were revealed.The reaction path of methane to methanol and formic acid was clarified.The nano-ZnO and ZnO/Au,ZnO/GR,ZnO/PANI composite catalysts were designed and prepared in this paper.The performance of photoelectrocatalytic oxidation of methane by the above catalysts was studied and compared.The mechanism of photo-generated holes for oxidizing methane was revealed.New methods are put forward for the treatment and comprehensive utilization of mine gas and the development of clean energy.