Study Of Capacitive SO₂ Gas Sensor Based On Zr-MOFs/nanofibers

Sulfur dioxide(SO2)has long been recognized as one of the most hazardous air pollutants due to its adverse impact in both industrial manufacturing and human health,even at trace levels.The development of real-time SO2 monitoring is crucial for detecting trace amounts of SO2 more rapidly and efficiently in an effort to effectively control its emission.Although zirconium-based metal-organic frameworks(MOFs)UiO-66-NH2 shows exciting potential and excellent performance in gas detection,MOFs in powder form severely limit their application for fabricating flexible and air-permeable sensors.Meanwhile,a stable and efficient monitoring of SO2 in complex environment is hard to achieve due to insufficient active sites in UiO-66-NH2 frameworks.This study therefore aimed to overcome the limitations of traditional gas sensors by combining electrospinning technique and MOFs to design a MOFs/nanofiber composite membrane as a capacitive gas-sensitive material.The main challenges faced in designing gas sensors are the lack of flexibility and airpermeability,complicated structure form and limited active sites.To overcome these limitations,we employed test results of the sensor,density functional theory calculation and characterization analysis to optimize related parameters of the sensor.After hierarchy optimization,great stability,high responsivity and good selectivity of the sensor were achieved.The article is divided into three parts:(1)A multilayer gas sensor(PVDF@UiO-66-NH2)is fabricated by spray bonding,and the detection performance for SO2 gas is tested.By combining simulation and characterization analysis,the mechanism of the gas adsorption process and the sensor operation are revealed.(2)The gas sensor with a one-piece structure(UiO-66-NH2/PAN)is prepared by the optimization of the composite method of UiO-66-NH2 and nanofiber membrane through the use of in-situ construction instead of the spray method.(3)Sensor structural composition and air permeability are enhanced through one-piece preparation,effectively improving sensor stability and sensitivity to detect SO2 gas.Therefore,the content of hydroxyl groups in the UiO-66-NH2 framework is increased by post-synthetic modification,and the integrated gas sensor(UiO-66-THB/PAN)is prepared by modification with a polyhydroxy ligand(2,3,4-trihydroxybenzaldehyde).The fabricated UiO-66-THB/PAN gas sensor exhibited excellent performances due to its sufficient active adsorption sites,good air-permeability and high surface-to-volume ratio after modifications.The sensor exhibited a lower detection sensitivity to SO2 at concentrations down to 0.1 ppm,with a response intensity of 1553.16 compared to 46.38 for PVDF@UiO-66-NH2.Additionally,the sensor showed great reproducibility(1 ppm,standard deviation=3.74%,n=8),fast response/recovery time(1 ppm,335 s/185 s)and long-term stability.In terms of cross-sensitivity,under the condition of CO2/SO2=200,the response value of the sensor to 0.5 ppm SO2 still reached 99.95,indicating a strong cross-sensitivity of SO2 gas.