Synthesis And Gas-sensing Properties Study Of Sensors Based On Ferric Oxide

Due to gas sensor based on metal oxide semiconductor possess many advantages, such as low raw materials, has gradually replaced solution. In this article, we choose iron oxide as the study object, using hydrothermal method, by controlling the molar ratio of reagents, reaction temperature and reaction time during the experimental process of synthesizing to obtain ?-Fe₂O₃ nanoparticles which possess an excellent dispersibility and uniformity, then, used the as-prepared ?-Fe₂O₃ nanoparticles as sensing materials fabricating semiconductor based gas sensor, and investigated the sensor's sensing characteristic towards environmental common hazardous gases?H₂S and NH₃? at different operating temperatures by static state method. Finally, using energy-bond theory detailedly demonstrated the sensing mechanism of sensors.The content of the article consists of three parts as follow:1) Using glucose and ethanolamine?MEA? as reductant and complexing agent, respectively, adopt hydrothermal reaction combined thermal treatment method fabricated the solid ?-Fe₂O₃ nanoparticles, then dispersing this ?-Fe₂O₃ powder into absolute ethyl alcohol to obtain ?-Fe₂O₃ gel and fabricate a complete sensing device through spin-coating route. The sensor's sensing performance towards H₂ S gas was investigated at different operating temperature by WS-30 A test system, and determined its optimal operating temperature at 300 oC. In addition, the detection limits, repeatability, long-term stability and response/recovery time of the sensor working at optimal temperature also been investigated. The results indicated that the lowest detectable concentration towards H₂ S gas was 50 ppb, response-recovery time was less than 30 s and 5 s, respectively at 300 oC, which is superior to the sensors based on primary?-Fe₂O₃ sensing performance towards H₂ S gas reported previously.2) Porous ?-Fe₂O₃ nanoparticles were synthesized by simple annealing of ?-FeOOH precursor derived from a facile hydrothermal route. XPS and FT-IR techniques were employed to analysis the chemical element and bond composition of the ?-Fe₂O₃ materials placed in the H₂ S atmosphere and air, respectively, then, dispersing this ?-Fe₂O₃ powder into absolute ethyl alcohol to obtain ?-Fe₂O₃ gel and fabricate a complete sensing device through spin-coating route. The gas-sensing performance showed that the sensor exhibited a high performance in hydrogen sulfide?H₂S? detection at room temperature. The highest sensitivity reached 38.4 for 100 ppm H₂ S gas, and the lowest detectable concentration was as low as 50 ppb. In addition, when sensors were placed in an environment where interfering gases exist together with testing gas, the sensor also exhibits an outstanding anti-interference ability.3) Comprehensive considered the synthesis condition of the above two experiments, through strictly control the molar ratio between urea and ethanolamine, reaction temperature and reaction time during experimental process, successfully synthesized nano-structured ?-Fe₂O₃ with outstanding uniformity and dispersibility. Then, served it as sensing material to fabricate gas sensor and investigated its sensing performance towards common used reducing gases. The results showed that the sensor exhibits excellent sensing performance towards ammonia gas, and the lowest detectable concentration was as low as 1 ppm, the response-recovery time shorter than 10 min. In addition, the sensor based on as prepared ?-Fe₂O₃ didn't showed any response toward other reducing gases include H₂ S, CO, H₂, indicated this sensor possess an excellent selectivity.