Preparation Of ?-Fe₂O₃/g-C₃N₄ Heterostructural Nanocomposites And The Gas Sensing Properties

With the increasing in air pollution and the increasing awareness of occupational safety issues,there is a growing need for an instrument that can monitor air quality to protect human health.Gas sensor is a kind of equipment under certain conditions can be sensed gas composition and concentration changes,and this signal into an output of electrical or optical signals,it plays an important role in air quality monitoring and detection of explosives and toxic and harmful gases.Metal oxide gas sensors are currently the most widely used in all kinds of the gas sensor,the semiconductor materials which have been used to make metal oxide gas sensors are ZnO?In₂O₃?SnO₂??-Fe₂O₃?MoO₃ and WO₃,the iron oxide??-Fe₂O₃?is a hexagonal crystal structure of the n-type metal semiconductor materials,the band gap is typically 2.2 eV,because of its rich storage,non-toxic,high corrosion resistance,excellent heat resistance and chemical stability has been widespread concern.Many of the morphologies of ?-Fe₂O₃ have been successfully synthesized and tested for gas-sensing properties.However,the current problem is that the response sensitivity is not high enough,the selectivity is not good enough,and the response time is long.In this paper,the new structure of ?-Fe₂O₃ porous nanotubes was synthesized by controlling the experimental conditions.The results showed that the response-recovery time was shortened,but the other problems did not improve obviously.We found that the ?-Fe₂O₃ composite material with other suitable materials can effectively improve the performance of gas-sensitive sensor.In other functional materials,graphite phase carbonitride?g-C₃N₄?is a two-dimensional layered material with a band gap of 2.7 eV,which is the most stable in the environment of various CN isoforms,similar to other non-local conjugated ?-structured materials such as C₆₀,graphene and carbon nanotubes,g-C₃N₄ has a rapid charge separation and a fairly slow charge recombination performance during the electron transfer process,the difference is that g-C₃N₄ is a soft polymer that can be easily attached to the surface of other compounds to promote the formation of heterogeneous structures,and different from the organic conjugated ? material such as polyaniline,g-C₃N₄ layered structure facilitates charge transfer.In addition g-C₃N₄ high nitrogen content,can provide more than other CN material active reaction sites and in principle on the adsorption of oxygen has a stronger reduction.Therefore,g-C₃N₄ has attracted a great deal of scientific research because of its excellent abrasion resistance,chemical stability and thermal stability.Master's research work has the following contents:?1?synthesis of ?-Fe₂O₃ porous nanotube structure and the relevant gas-sensing performance testFe?NO3?3·9H2O was used as the source of iron,and a new type of ?-Fe₂O₃ porous nanotube was synthesized by controlling the experimental conditions after hydrothermal and annealing.After the basic XRD and SEM characterization of ?-Fe₂O₃ materials,the performance test was carried out.The results show that the response of the gas sensor with ?-Fe₂O₃ material to the ethanol gas to be measured is very short,and the recovery time can reach 7.7s and 2.6s at the optimum working temperature,indicating that this porous tubular structure provides more channels and reaction sites for gas diffusion and adsorption chemical reactions.However,the problem is that the sensitivity is not high enough and the selectivity is not good enough,in order to solve these problems we will ?-Fe₂O₃ materials to complex.?3?Preparation of ?-Fe₂O₃/g-C₃N₄ Composite Nanomaterials and its Gas Sensing PropertiesThe ?-Fe₂O₃ was combined with the calcined g-C₃N₄ nanosheet by high temperature annealing.The chemical composition and morphology of the complex were also analyzed by basic characterization.The relevant gas-sensing performance test conditions are the same as those of pure ?-Fe₂O₃,the results show that the response sensitivity of ?-Fe₂O₃/g-C₃N₄ composite material is 2.8 times of that of pure ?-Fe₂O₃ material under the optimum temperature condition,it has good selectivity to ethanol gas and the response time is more short.The results show that the composites combine with the advantages of two materials,forming n-n heterostructures which are favorable for gas transmission,adsorption and reaction,and make a theoretical analysis on their gas-sensing performance.