Study On VOCs Gas Sensors Based On Nanocrytalline Semiconductor Oxides

Due to the unique physical properties and great application potentials, ordered three-dimensional inverse opal macroporous structure（3DIO） materials have attracted wide attention all over the world and the studies on 3DIO have been developed to be a hot area. The theoritical porosity of 3DIO is as high as 74%, which promises it to be a kind of material with ideal gas sensing properties. In this work, some semiconductor 3DIO gas sensors were prepared and their gas sensing properties were systemically studied. The results indicate that 3DIO gas sensors possess excellent gas sensing properties; especially they can detect 10 ppb lever volatile organic compounds（VOC） gases. For instance, 3DIO SnO₂ gas sensors not only show excellent selectivity but also could detect methanal（HCHO） as low as 10 ppb. Also, 3DIO In₂O₃ gas sensor can detect acetone as low as 15 ppb and possess good anti-humidity property.On the one hand, volatile organic compounds（VOC） gases widely exist in our daily life environments; on the other hand, clinical data indicate that the VOC concentrations in exhaled gas from specific patients are different from healthy people. Such as the concentration of exhaled acetone from diabetes patients exceeds 1.8 ppm, while for healthy people it is only 0.3–0.9 ppm. At present, the diagnostic approaches of diabetes are usually traumatic. Therefore, to develop a new kind of noninvasive, real-time, and potentially inexpensive diagnostic method is key important. Taking consideration of the high relative humidity（RH） in exhaled breath environment and basing on the detection of common VOC, we systematic studied 3DIO gas sensor properties in high RH environment and researched the gas sensor properties when before and after the removal of humidity interference. In addition, 3DIO gas sensor was applied to clinical breath gas detection and the results showed that preliminary inspection of clinical diabetes is realized. The main results are as follows:（1） We fabricated 3DIO SnO₂ with controlled macroporous size（140 nm, 270 nm and 400 nm）, and investigated their supersensitive performance to HCHO carefully. The results demonstrated that 3DIO SnO₂ could effectively detect acetone at 250°C, and 3DIO SnO₂ gas sensor exhibited more excellent performance than the reference, especially the optimal could detect HCHO as low as 10 ppb. In addition, the results showed that the sensing properties were greatly enhanced by increasing the macropore size of 3DIO SnO₂ samples, and the response of the optimal was 629 when detecting 100 ppm HCHO, which was improved 35 times compared to the reference sample.（2） We prepared 3DIO In₂O₃-Cu O with via-holes firstly, and studied their gas sensing properties. Considering the condition of exhaled breath was a high relative humidity（RH） environment, we also studied 3DIO In₂O₃-Cu O gas sensing properties in high humidity. The results showed that by doping Cu O, the optimal working temperature of the gas sensor was reduced from 400°C to 370°C and the response for the optimal sensor was improved 2 times compared to pure In₂O₃ besides better selectivity. Furthermore, because of the moisture in RH environment, the responses of the sensors in RH were increased systematically than those in air. Moreover, the linear slope in RH was nearly the same with that in air, indicating that the 3DIO sensor could detect low concentration of acetone biomarkers in high RH precisely.（3） 180 nm and 420 nm pore size 3DIO In₂O₃ with additional via-hole architectures were prepared and different amounts of Au NPs were interspersed uniformly on the 3DIO In₂O₃ surface. Then the 3DIO evaluated as a chemiresistive acetone gas sensor towards diabetes biomarkers in exhaled breath. The results demonstrate that 180 nm and 420 nm pore size 3DIO have responses of 5.6 and 6.3 to 5 ppm acetone, respectively. The responses of 3DIO Au/In₂O₃ were significantly higher than that of pure 3DIO In₂O₃ and the response for the optimal gas was 42.4 to 5 ppm acetone. Besides, the optimal working temperature of the gas sensor gradually reduced with the increasing amounts of Au NPs. Importantly, the optimal gas sensor could distinguish clearly acetone biomarkers in human breath.（4） We prepared In₂O₃/Au core-shell hybrids gas sensors and systematically investigated the gas sensing performances of them. The results demonstrated that the optimal In₂O₃/Au NRs sensor could detect acetone at 250°C and ethanol at 400°C effectively, which had response of 2.8 to 1 ppm acetone, 9.8 to 5 ppm ethanol, and low detection limit of 0.1 ppm to acetone, 0.05 ppm to ethanol. Besides, a humidity compensation method was applied to increase the accuracy of the sensor response in high humidity environment. Moreover, clinic tests indicated that the In₂O₃/Au NRs sensor could distinguish acetone biomarkers in exhaled breath at 250°C and could practically detect ethanol in exhaled breath at 400°C.