| In the 2021,the dangers of NO2 gas and other air pollutants are highlighted in the"Global Air Quality Guidelines" by the World Health Organization.NO2 can not only directly harm human health,cause acid rain and photochemical smog,but also produce secondary pollutant PM2.5 through chemical transformation.Therefore,it is of great practical significance for NO2 gas detection.Resistive semiconductor NO2 gas sensors are widely used due to their low cost,long service life,ultra-high sensitivity and miniaturization of device size.However,the actual operation of this traditional gas sensor requires higher working temperature and working voltage.The resistive NO2 gas sensor based on the semiconductor photovoltaic effect can realize sensing at room temperature and detection at a lower operating voltage,and has excellent desorption performance at the same time.In this way,it is expected to develop semiconductor optoelectronic sensitive materials and sensors with excellent performance.Recently,g-C3N4 polymer semiconduct materials have great application potential in the field of optoelectronic gas sensing due to their higher band position,special two-dimensional structure,low fabrication cost and stable chemical properties.However,factors such as poor charge separation and few NO2 adsorption sites severely limit the development of gas sensing performance for g-C3N4-based materials.Therefore,it is necessary to develop g-C3N4-based gas sensing materials with excellent charge separation and abundant active sites.Therefore,the structural regulation of g-C3N4 and the design,synthesis and device synthesis of the heterojunction complex were carried out,and the performance and improvement mechanism of NO2 optoelectronic sensing in visible light at room temperature were studied in depth.Firstly,the structure regulation and the NO2 photoelectric sensing performance of nano-g-C3N4 were carried out.The porous ultra-thin g-C3N4 were synthesized by the supramolecular pre-assembly precursor method.Its device can realize the optoelectronic sensing detection of NO2 under the low voltage of 2.5 V and visible light excitation,and the detection limit reaches 1 ppm.The photogenerated charge properties of nano-g-C3N4 with different structures were studied by transient fluorescence and surface photovoltage spectroscopy.The experimental results showed that porous ultra-thin structures are beneficial to photogenerated charge separation and adsorption properties of NO2 for g-C3N4.Secondly,the preparation of SnO2/rGO/g-C3N4 nanocomposite and its effect on NO2 gas sensing performance were investigated.The SnO2/rGO/g-C3N4 nanocomplex and device were prepared by hydrothermal method.Compared with ultra-thin g-C3N4,the detection limit of SnO2/g-C3N4 complex increased 25-fold to 40 ppb at room temperature and the detection limit of SnO2/rGO/g-C3N4 complex was increased by 200 times to 5ppb.The sensors also showed excellent cycling stability and selectivity.Based on time-resolved and atmosphere controlled photophysical tests and NO2 temperature programmed desorption techniques,it was confirmed that SnO2 nanoparticles not only effectively accepted electrons as an electron platform to improve photogenerated charge separation,but also promoted NO2 adsorption as a selective site center.The introduction of rGO improves the interfacial charge transport and separation,and further improves the sensing performance of the complex.Finally,photogenerated charges modulation of ultra-thin g-C3N4 by two-dimensional Ni-MOF composite and its effect on the optoelectronic sensing performance were explored.By means of low temperature control and ultrasonic assistance,the aggregation of Ni-MOF was inhibited during the growth process,and the two-dimensional ultra-thin Ni-MOF with high dispersion was synthesized.The 2D/2D Ni-MOF/g-C3N4 nanocomplex was further prepared by electrostatic assembly method,and the low detection limit of the device was increased by 10 times to 100 ppb.It is confirmed that the introduced two-dimensional ultra-thin Ni-MOF as an electron receiving platform promotes the photogen erated charge separation,and the central metal Ni can also promote the selective adsorption of NO2,which significantly improve the optoelectronic sensing performance of NO2. |
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