Preparation Of Gas Sensors Using Nonwoven Fabric Loaded With UiO-66-based Composite Conductive Material

With the rapid development of industrialization,the detection of toxic and volatile organic compounds(VOC)gases has great potential in production safety and environmental governance.Gas sensors are usually used to monitor their content in the air.Finding low-cost and efficient gas sensor materials is very important for monitoring the concentration of harmful gases in the air.UiO-66 metal-organic skeleton materials have the advantages of large specific surface area and multiple adsorption sites,which makes them have potential application value in the field of sensing.However,UiO-66 crystal materials in sensing applications are mainly achieved through powder or MOFs thin films,usually lack sensitivity and machinability,and UiO-66 crystal materials themselves are extremely resistance,can not show electrical conductivity.In this study,the functionalized design of UiO-66 was carried out and combined with conductive materials,and then loaded into nonwovens with excellent air permeability and flexibility,which could not only improve its electrical conductivity,but also improve the gas absorption of UiO-66 crystal materials,so as to improve the selectivity and response value of UiO-66 composite conductive materials to a single gas.Specific research contents are as follows:(1)UiO-66-NH2/MoS2 composites were synthesized by hydrothermal method using sodium molybdate(Na2MoO4),thiourea(CH4N2O4S)and homemade UiO-66-NH2 as raw materials.UiO-66-NH2 and UiO-66-NH2/MoS2 were loaded on the nonwoven fabric by impregnation method.The nonwovens based flexible gas sensors(UiO-66-NH2@nonwovens and UiO-66-NH2/MoS2@nonwovens)are obtained.X-ray diffraction(XRD),X-ray photo electron spectroscopy(XPS)and field emission scanning electron microscopy(SEM)were used to demonstrate the feasibility of the synthesis route of UiO-66-NH2/MoS2@nonwovens.The four-probe resistivity test results showed that the untreated nonwovens and UiO-66-NH2@nonwovens had no electrical conductivity,while the UiO-66-NH2/MoS2@nonwovens had a resistivity of 7.67 kΩ/cm and an electrical conductivity of 2.81×10-3 s/cm.The water contact angle of UiO-66-NH2/MoS2@nonwovens was 167.8°,showing excellent hydrophobicity.The gas sensitive test results showed that the UiO-66-NH2/MoS2@nonwovens had excellent selectivity to ammonia,methanol and ethanol.At 50 ppm ammonia concentration,the response value of UiO-66-NH2/MoS2@nonwovens reached 130%,and at 1 ppm ammonia concentration,there was still 43%response value.In the range of 1～50 ppm concentration,the response value showed a good linear relationship(R2=0.91).Before and after gas-sensitive test,XRD and SEM images showed that UiO-66-NH2/MoS2 on the fiber did not change,which was a physical adsorption process with excellent cycling performance.The response value of UiO-66-NH2/MoS2@nonwovens was still about 80%after 10 times of gas sensitivity test at 10 ppm ammonia concentration.After washing in water for 10 times,the electrical conductivity of UiO-66-NH2/MoS2@nonwovens was basically unchanged.Within 24 h of washing,the gas-sensitive property of the material did not significantly decrease,indicating that the UiO-66-NH2/MoS2@nonwovens had excellent reusability.(2)A novel petal-like structure composite material(UiO-66-NH2/MoS2/Ag)was synthesized by in situ synthesis of Ag and UiO-66-NH2/MoS2/MoS2.The material was loaded onto a nonwoven fabric by impregnation to produce a flexible nonwoven-based conductive sensing material(UiO-66-NH2/MoS2/Ag@Nonwovens)for the selective detection of ammonia gas.This method prevents Ag aggregation and provides a large number of exposed adsorption sites for ammonia gas.XRD,SEM and XPS results confirm successful synthesis and uniform loading of UiO-66-NH2/MoS2/Ag on the nonwoven surface with a unique petal-type structure that fully exposes the active sites,and the pore channels remain unblocked.The introduction of Ag did not affect the mechanical properties of the nonwoven.UiO-66-NH2/MoS2/Ag@N onwovens’ water contact angle was 131.7°,indicating some washing resistance.The gas sensing test results showed that UiO-66-NH2/MoS2/Ag@Nonwovens exhibited excellent selectivity for ammonia,with a 96%response at 10 ppm ammonia concentration and a response time of 85 s.Compared with UiO-66-NH2/MoS2@Nonwoven,the response time improved by 45 s,and at a low concentration of 1 ppm ammonia,it still had a response of 47%.The material showed a good linear(R2=0.96)ammonia response at 1～50 ppm concentration.XRD and SEM analyses revealed that the adsorption of gases by UiO-66-NH2/MoS2/Ag@Nonwovens,both before and after gas sensitization testing,was primarily a result of physical adsorption.Results from cyclic gas sensitivity testing and water washing performance testing indicated that the response values of UiO-66-NH2/MoS2/Ag@Nonwovens remained around 95%after 10 cycles.Although the conductivity of UiO-66-NH2/MoS2/Ag@Nonwovens slightly decreased after 10 washes in water,the material demonstrated remarkable stability as it was washed in water for 24 hours at 1～50 ppm ammonia,with only a 15%and 12%decrease in response values.These findings highlight the exceptional cycling stability of UiO-66-NH2/MoS2/Ag@Nonwovens.