Surface Modification Of In₂O₃ Nanomaterials And Their Gas Sensing Performance

Semiconductor metal oxides play a key role in many fields such as physics,chemistry and material science.Semiconductor metal oxides gas sensors have received a lot of attention over the years because of their low cost,easy operation and simple manufacturing process.However,the low sensitivity and high operating temperature of single component semiconductor metal oxides limit applications in gas sensitive fields.Therefore,it is of great important to design and develop gas sensors with high stability and excellent performance to achieve high sensitivity,high selectivity and long-term monitoring of target gas.This paper with the help of precious metals Au and Co₃O₄ on In₂O₃ nanomaterials surface modification,regulating the microstructure,improve the specific surface area of the synthetic samples,provide oxygen and detection of gas molecules rich site,promote the adsorption and diffusion of gas molecule,reduce the working temperature of semiconductor metal oxides gas sensors,improve the selectivity and the response values.The research contents of this paper are as follows:First,The precursor of In（OH）₃ nanospheres was synthesized by solvothermal method,In₂O₃ nanospheres were prepared by calcination,and Au nanoparticles on the surface of In₂O₃ nanospheres by sol-immobilization method were obtained mesoporous In₂O₃ nanospheres modified by Au nanoparticles（Au/In₂O₃-350）.The obtained In₂O₃-350and Au/In₂O₃-350 were analyzed by a series of characterizations.The results show that Au nanoparticles are evenly distributed on the surface of mesoporous In₂O₃-350 nanospheres,and Au/In₂O₃-350 with 1%Au modified has the best ethanol gas sensitivity.The response of1%Au/In₂O₃-350 to ethanol（50 ppm）is up to 55 at the optimal operating temperature of 180°C,which is 8.8 times higher than that of pure In₂O₃-350 nanospheres,and the optimal operating temperature is reduced by 90°C.In addition,1%Au/In₂O₃-350 nanospheres have good selectivity,short response/recovery time,low detection limit,good linearity,repeatability and stability.1%of Au/In₂O₃-350 nanometer microspheres better ethanol gas sensor performance can be attributed to the larger specific surface area and abundant mesoporous channel,Au nanoparticles electronic sensitization effect effectively regulate the resistance of the material,and Au nanoparticles significantly increased the catalysis of the reconciliation from the adsorption capacity of oxygen,and promote the adsorption reaction of oxygen with ethanol gas.Secondly,flower-like In（OH）₃ precursor was synthesized by homogeneous precipitation method,flower-like mesoporous In₂O₃ was prepared by calcination at 300°C,and a series of flower-like mesoporous In₂O₃ modified by Au nanoparticles（Au/In₂O₃）were prepared by sol-immobilization method.The morphology,crystal phase structure and chemical composition of Au/In₂O₃ were characterized by XRD,SEM and XPS,and its gas sensitive properties were investigated.The results show that the flower-like mesopore In₂O₃-300 modified by 1%Au（1%Au/In₂O₃-300）has better gas sensitivity to ethanol gas,and the response value of flower-like mesopore 1%Au/In₂O₃-300 to ethanol gas at 160°C is 115,12 times that of flower-like mesopore In₂O₃-300,and the optimal operating temperature is reduced by 50°C.At the same time,the flower-like mesoporous 1%Au/In₂O₃-300 also has excellent selectivity,low detection limit,good linearity,repeatability and stability.The excellent performance of flower-like mesoporous 1%Au/In₂O₃-300 is attributed to its high specific surface area（130 m²/g）,large number of mesoporous channels and highly dispersed Au nanoparticles,which promotes the adsorption and deionization of oxygen and the adsorption and catalytic oxidation of ethanol gas.Finally,Using Co（NO₃）₂·6H₂O as cobalt source and dimethylimidazole as ligand,ZIF-67 nanoparticles were deposited on the surface of flower-like In（OH）₃ precursor synthesized by homogeneous precipitation method.After calcination at 400°C,Co₃O₄ modified flower-like mesoporous In₂O₃（Co₃O₄/In₂O₃）with different Co contents were prepared.The morphology,crystal phase structure and chemical composition of Co₃O₄/In₂O₃ were characterized by XRD,SEM and XPS,and the gas sensitive properties of Co₃O₄/In₂O₃ were investigated.It is found that the flower-like mesoporous Co₃O₄/In₂O₃-400 has a large specific surface area and a large number of mesoporous structures,among which 5%Co₃O₄/In₂O₃-400 has the largest specific surface area,up to 105m²/g,and has the best gas sensitive performance to formaldehyde gas,at the best working temperature of 160℃,The response value to 50 ppm formaldehyde gas reaches 41,8.5 times higher than that of pure In₂O₃-400.At the same time,the flower mesoporous 5%Co₃O₄/In₂O₃-400also had high selectivity,good linearity,repeatability and stability.The high gas sensing performance of 5%Co₃O₄/In₂O₃-400 is mainly due to the large specific surface area and many active sites of 5%Co₃O₄/In₂O₃-400.Co₃O₄ and In₂O₃ combine to form a p-n heterojunction,which forms more interface defects,promotes the adsorption and activation of oxygen,effectively controls the resistance through electronic sensitization,and significantly increases the variation range of resistance.