Study On Surface Modification And Gas Sensing Characteristics Of MXene

The deterioration of air quality caused by various industrial waste gas and its profound impact on human health and surrounding ecosystems have become one of the most concerning issues for most scientists,engineers,and eco-environmentalists.Volatile organic gases(VOCs)in polluted gases can harm the human body through long-term exposure and inhalation.Therefore,there is an urgent need to detect explosive organic gases produced by chemical substances in industrial production,mass fuel combustion,and household products to facilitate good prevention,control,and treatment.Among all kinds of gas sensing materials,Ti₃C₂T_x MXene was favored by researchers due to its good electron charge transfer efficiency,large specific surface area,stable physical and chemical properties,and rich oxygen functional groups on the surface.However,the response value and sensitivity of Ti₃C₂T_x MXene material still cannot meet the increasing demand for pollutant detection.This study adopted methods such as atomic doping modification,p-n heterojunction modification,oxygen plasma irradiation modification,etc.,to chemically modify the surface of Ti₃C₂T_x MXene to improve its gas sensitivity and systematically study.The gas-sensing performance enhancement of the modified material and its gas sensing mechanism was discussed.The main research progress and results obtained are as follows:(1)Using the template method,using melamine-formaldehyde(MF)microspheres as the nitrogen source to release NH₃ during the annealing process,uniformly doping Ti₃C₂T_x MXene with N atoms,and removing the MF microspheres after annealing to form in-situ formation Mesoporous structure,porous N-Ti₃C₂T_x MXene nanomaterials were obtained,and its composition,structure,morphology,and gas-sensing properties were evaluated.The gas sensitivity test results show that at 150?,the N-Ti₃C₂T_x MXene-based gas sensor has an average response of 1.9 to 100 ppm acetone gas analyte,and the response time(tres)and recovery time(trecov)are 210 s and 9,respectively.s.Compared with the pure Ti₃C₂T_x MXene-based gas sensor,the working temperature is reduced by 50?,the response rate and recovery rate are significantly improved,and the response value is also increased by about 18 times.It is because the doping of nitrogen atoms improves the specific surface area and mesopore distribution of the N-Ti₃C₂T_x MXene nanomaterials,increases its surface adsorption capacity,and provides more active sites for the adsorption of target gas analytes and oxygen anions.And a faster reaction kinetic rate.(2)A one-step hydrothermal method was used to oxidize part of the p-type SnO to n-type SnO₂,forming an in-situ p-n heterojunction on the surface of the SnO,and synthesizing a Hamburg type consisting of SnO-SnO₂(p-n junction)and two-dimensional Ti₃C₂T_x MXene SnO-SnO₂/Ti₃C₂T_x MXene nanocomposite material.The crystal composition,element distribution,element content,specific surface area,mesopore distribution,etc.,of the modified composite material,were studied,and its gas sensing performance was evaluated,and its gas sensing mechanism was analyzed.Research shows that at room temperature,the gas sensitivity of SnO-SnO2/Ti₃C₂T_x MXene sensor to acetone gas at a concentration of 100 ppm is 11 times and 4 times higher than that of pure Ti₃C₂T_x MXene and SnO-SnO₂ based gas sensors,respectively.The study concluded that the formation of p-n heterojunction and two-dimensional Ti₃C₂T_x MXene provides many active sites for the edge reaction of oxygen anions and gas analytes and good electron charge transfer efficiency,which is conducive to the adsorption and response rate of gas analytes.(3)The Ti₃C₂T_x MXene two-dimensional nanomaterial was irradiated by the oxygen plasma irradiation method to obtain the modified Ti₃C₂T_x MXene two-dimensional nanomaterial,and the element composition phase structure and element distribution were carried out.Analysis of mesopore distribution and evaluation of its gas sensitivity.The results showed that Ti₃C₂T_x MXene material obtained the largest specific surface area and the best pore size distribution after 0.5 h of irradiation.The TiO₂ defects produced by irradiation would change the carrier mobility of Ti₃C₂T_x MXene.When 90 ppm ethanol gas analyte is passed through at room temperature,the gas response value of Ti₃C₂T_x-0.5P is about 91,and the response time and recovery time are 280 s and 11 s,respectively.Compared with the pure Ti₃C₂T_x MXene-based gas sensor,the gas sensor response value is increased by about 892 times.This is due to the improvement of the specific surface area of the modified material and the control of its structural defects.(4)Through the molten salt method,the polymer C₃N₄(Polymer-C3N4)(PCN)was modified into crystalline C₃N-4(Crystalline-C₃N₄)(CCN)under air atmosphere,and then CCN-Ti₃C₂T_x MXene(CCN-TCT)Nanocomposite materials.The structural composition,element distribution,microscopic morphology,gas sensitivity,and sensing mechanism of the modified composite material are analyzed.The gas sensitivity test results show that the average resistance of the CCN-based gas sensor treated by the molten salt method in ambient air is 1247 times lower than that of PCN,and it has good reproducibility.It has been tested continuously for 60 days against 50 ppm of toluene gas.The sensor response value remains around 350.This is attributed to the improvement of the crystallinity of CCN,the optimized ?-conjugated system,and the intercalation of potassium atoms enhance the Van der Waals interaction.The CCN-TCT nanocomposite material effectively reduces the signal-to-noise ratio of gas analyte detection.The excellent conductivity of the two-dimensional Ti₃C₂T_x MXene provides a good channel for electronic charge transfer in the response process.Multiple synergistic effects improve the composite gas-sensing performance of the material.