A Preconcentration Method To Enhance The Response Of Gas Sensors To Formaldehyde

A preconcentration method is used to enhance the response to formaldehyde in this paper. Firstly, the formaldehyde gas was adsorbed with adsorbent, and then formaldehyde gas was desorbed by heating at measurement. The response of gas sensor to formaldehyde increased by using the method without changing the input formaldehyde concentration.Fabrication process of the sensor was described. The optimal operating temperature is 265℃. As operating temperature increasing, the resistance of gas sensor was decreased, then increase and then further decreased. The response to the formaldehyde concentration increased with the increase of formaldehyde.Adsorption theory was studied and a preconcentrator consistes of an sorption-tube, adsorbent, heating wire, thermometer, stainless steel mesh and power supply was built up. Temperature swing adsorption combined gas purge method was selected to for desorption of formaldehyde from adsorbents.The effects of different experimental conditions, including desorption temperature, gas flow, adsorption time, the length and altitude filled with activated carbon, sorbent-tube diameter, characteristics of adsorbent and modification of activated carbon were studied. The optical experimental conditions were summarized as followed: the desorption temperature was 200℃, the adsorption time should be controlled within 15 min, gas flow was 500 sccm, the diameter of adsorption tube was 11 mm, the filled length with activated carbon was 17 cm, the filled height was 2/3 of the adsorption tube diameter. The preconcentration effect of ordinarily activated carbon was best, Kuaihuolin activated carbon followed, MWCNT was worst. The effect of altrasonic modified activated carbon is better than non- modified activated carbon, acid and alkali modified activated carbon is not as good as it. The responses of SnO₂ gas sensor to 10 ppm formaldehyde with and without preconcentration were 10.8 and 10.8, respectively. The responses of Figaro TGS2602 were 4 and 1.6, respectively. Preconcentration method is indeed very useful to enhance the response of semiconductor to formaldehyde gas.