A novel structure for enhancing the sensitivity of gas sensors – α-Fe₂O₃ nanoropes containing a large amount of grain boundaries and their excellent ethanol sensing performance

Abstract

Novel one-dimensional (1D) a-Fe 2 O 3 nanostructures containing a large amount of grain boundaries have been synthesized through the combination of electrospinning and precursor-calcination techniques. The as-prepared a-Fe 2 O 3 nanostructures were composed of orderly arranged building blocks (a-Fe 2 O 3 nanoparticles) which are connected to each other. The investigation of the morphology evolution revealed that the template fiber geometry has an influential impact on the grain growth behavior during preparation and thus the nanostructures of the final products. Different a-Fe 2 O 3 nanostructures (nanostrings and nanoropes) were synthesized using different PAN nanofibers as templates. These two samples are similar in microstructures but very different in grain boundary content. FT-IR spectra, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectra, UVvis diffuse reflection spectra and nitrogen adsorption-desorption analysis were used to characterize the structures of the synthesized products. Comparative ethanol sensing measurements between the a-Fe 2 O 3 nanostrings and nanoropes were conducted. The nanoropes which contain more grain boundaries showed a 3 to 4-time enhancement in ethanol response compared to the nanostrings. The results prove that creating a large amount of well-ordered grain boundaries is an effective way to enhance the sensing performance. ; Tel: +86 21 65982620 † Electronic supplementary information (ESI) available: Further details include SEM images of Fe 2 O 3 nanobers calcined at 600 C in air from the A-PAN-Fe precursor with the different immersion times; TG-DSC analysis of the A-PAN 1 -Fe and A-PAN 2 -Fe; XRD diffraction patterns of samples calcined at various temperatures; SEM images of the a-Fe 2 O 3 nanostrings and nanoropes aer calcination at various temperatures; response of a-Fe 2 O 3 nanostrings and nanoropes to different concentrations of C 2 H 5 OH at 240 C and cyclic sensing and recovery performance of a-Fe 2 O 3 nanostrings and nanoropes toward 100 ppm C 2 H 5 OH at 260 C. See

Roles of structure and electron mobilization in enhanced ethanol sensing by Al doped SnO2nanoparticles

“…PL studies have confirmed the absence of additional defect states in aluminium doped samples, thus ruling out contribution from material defects in volume charge mobilization at the sensor operational temperature (see the ESI †). 46 According to the grain boundary model, [47][48][49][50] chemisorption on metal oxide surface leads to change in grain boundary thickness, affecting electron transport. From the room temperature capacitive studies, it has been observed that for all the samples, decrease in capacitance on exposure to ethanol gas is negligible (see the ESI †).…”

Facile synthesis of mesoporous hierarchical Co3O4–TiO2 p–n heterojunctions with greatly enhanced gas sensing performance

“…Therefore, there is a need to develop high-performance gas sensors with high sensitivity, low operating temperature and good stability for real-time monitoring of toluene and xylene. A variety of metal oxide semiconductors have been used as sensing materials to detect VOCs, such as ZnO, [4][5][6] SnO2, [7][8][9] In2O3, [10][11][12] Co3O4, [13][14][15] TiO2, 16,17 WO3, [18][19][20][21] Fe2O3, [22][23][24] Cu2O/CuO, 25,26 and NiO. 27 Among these metal oxide semiconductors, Co3O4 is believed to be a promising candidate for sensing of toluene and xylene because of its excellent catalytic activity for oxidizing them at low temperature which results from its larger adsorption amount of oxygen 28 on the surface than others and multivalent properties facilitating redox reactions.…”

Silver Enhances Hematite Nanoparticles Based Ethanol Sensor Response and Selectivity at Room Temperature

“…Besides, cyclic measurements (inset) for linear regression showed a stable baseline (R 0 ) through the test. Thus, α-Fe 2 O 3 /Ag 3.0 wt% have demonstrated appropriate features for ethanol vapor sensing such as other hematite-based sensors [ 23 , 35 , 36 , 37 , 38 ]. Higher sensibility at 25 °C, short-time gas response, rapid recovery, and excellent repeatability (ΔR/R o ), even at low concentrations (2 mg L −1 ), is the greater contribution of this work.…”

“…Sensors of n-type Fe 2 O 3 nanobelts assembled by Fan et al showed a 2.2 gas response when exposed to 50 mg L −1 of ethanol at 285 °C [ 36 ]. Yan et al prepared α-Fe 2 O 3 nanoropes (specific surface area: 18.95 m 2 g −1 ) sensing 100 mg L −1 of ethanol with 10.2 of relative signal at 240 °C [ 37 ]. The materials described above operate in the range of 250–300 °C to reach optimal response towards ethanol.…”