In this paper, g-C3N4-WO3 composite materials were prepared by hydrothermal processing. The composites were characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and N2 adsorption-desorption, respectively. The gas sensing properties of the composites were investigated. The results indicated that the addition of appropriate amount of g-C3N4 to WO3 could improve the response and selectivity to acetone. The sensor based on 2 wt% g-C3N4-WO3 composite showed the best gas sensing performances. When operating at optimum temperature of 310°C, the responses to 1000 ppm and 0.5 ppm acetone were 58.2 and 1.6, respectively, and the ratio of the
Graphitic carbon nitride (g-C3N4) nanomaterial exhibits a stable layered structure and п-conjugated s-triazine unit composed of sp2 hybridized carbon atoms and sp2 hybridized nitrogen atom. g-C3N4 nanosheets have attracted the attention of researchers in recent years for its peculiar properties as a semiconductor such as immense specific surface area [
As a gas sensing material, WO3 has been paid much attention in the past decade. Cho et al. [
The photocatalytic activity of g-C3N4-WO3 nanocomposites also has been reported by many researchers [
In this paper, we report the preparation of g-C3N4-WO3 nanocomposites through a hydrothermal method and the investigation of their gas sensing properties. Analysis showed that 2 wt% g-C3N4-WO3 nanocomposite responded highly and selectively to acetone.
g-C3N4 was prepared by heating 2.0 g melamine in an oven at 520°C for 5 hours, while keeping the heating rate at 5°C/min, which was similar to that reported in the literature [
For preparing the nanocomposites, a certain amount of as-prepared g-C3N4 was added to 40 mL deionized water and sonicated for 1 hour to obtain a g-C3N4 suspension. 0.0025 mol Na2WO4·2H2O was dissolved in 20 mL deionized water, and 4 mL concentrated hydrochloric acid was added dropwise in the Na2WO4 solution slowly while stirring resulting in the formation of H2WO4; the g-C3N4 suspension was added slowly to H2WO4 while stirring. The mixture was sealed in a 100 mL Teflon-lined stainless steel autoclave and heated at 200°C for 24 h; the obtained precipitate was filtered and washed with distilled water and ethanol, followed by drying in air at 80°C for 24 hours; finally, the g-C3N4-WO3 composite was obtained. The weight ratios of g-C3N4 powders/WO3 (the weight of WO3 was calculated according to the weight of Na2WO4·2H2O) were 0 wt%, 1 wt%, 2 wt%, 3 wt%, and 4 wt% (the samples were labeled as S-0, S-1, S-2, S-3, and S-4, respectively).
X-ray diffraction (XRD, Bruker D8 Advance, Cu-K
The sensor device preparation process and the gas sensing measurement have been explained in the previous work [
Figure
The XRD patterns of pure g-C3N4, g-C3N4-WO3 (S-1, S-2, S-3, and S-4), and WO3.
Figure
The SEM images of (a) g-C3N4, (b) pure WO3 (S-0), and (c) g-C3N4-WO3 (S-2).
The FTIR spectra of WO3 and g-C3N4-WO3 (S-2) are shown in Figure
The FTIR spectra of WO3 and g-C3N4-WO3 (S-2).
The gas sensing responses of pure WO3, S-1, S-2, S-3, and S-4 to 1000 ppm concentration of acetone at different operating temperatures are shown in Figure
The gas sensing responses of pure WO3, S-1, S-2, S-3, and S-4 to 1000 ppm acetone at different temperatures.
Figure
The responses of an S-2-based sensor to 1000 ppm acetic acid, acetone, formaldehyde, ethanol, acetaldehyde, and ammonia at different operating temperatures.
Figure
The responses of sensors based on S-0 and S-2 to six kinds of gases (1000 ppm) at 310°C.
The response time and recovery time were calculated using the formula defined in a previous literature [
The response transients of the sensor based on the sample S-2 composite to acetone (1000 ppm, 500 ppm, 100 ppm, 10 ppm, 1 ppm, and 0.5 ppm) at 310°C.
The gas sensor stability is a significant parameter for a gas sensor, and the curve of gas sensing response versus time of the S-2 composite-based sensor is shown in Figure
The curve of gas sensing response versus time of the S-2 sensor.
Table
Comparison of acetone gas sensing properties with different acetone gas sensors.
Material | Operating temperature (°C) | Detection limit (ppm) | Response ( |
Selectivity | Stability (days) | Reference |
---|---|---|---|---|---|---|
Au/ZnO | 365 | 20 | 2923 (100 ppm) | 1.8 | 90 | [ |
MgFe2- |
700 | 100 | 1.91 (2000 ppm) | 1.2 | - | [ |
Co3O4 NWS-HCSs | 150 | 1 | 23 (200 ppm) | 4.6 | - | [ |
PrFeO3 | 180 | 10 | 141 (200 ppm) | 2.8 | 75 | [ |
Pt-Fe2O3 | 139 | 0.2 | 25.7 (100 ppm) | 2.9 | 15 | [ |
Rh- doped SnO2 | 200 | 1 | 60.6 (50 ppm) | 8.6 | - | [ |
ZnFe2O4 | 260 | 10 | 52.8 (100 ppm) | 3.2 | 30 | [ |
g-C3N4-WO3 | 310 | 0.5 | 58.2 (1000 ppm) | 3.7 | 30 | This work |
“-” means no data available in the literature.
It can be observed that the content of g-C3N4 in g-C3N4-WO3 composites influences the response and selectivity of g-C3N4-WO3 composite-based sensors to acetone. 2 wt% g-C3N4-WO3 composite (S-2) showed the best gas sensing performances in the series of g-C3N4-WO3 composites, when operating at an optimum temperature of 310°C; the responses to 1000 ppm and 0.5 ppm acetone were 58.2 and 1.6, respectively, with the ratio of the
The underlying data related to this manuscript is available on request.
The authors declare no conflict of interest.
This research was funded by the National Natural Science Foundation of China (Nos. 61671019 and 61971003).
Figure S1: gas sensor used for characterizing gas sensing behavior of samples. Figure S2: XPS spectra of g-C3N4-WO3 (S-2): (a) full spectrum. (b) C1s. (c) N1s. (d) O1s. (e) W. Figure S3: (a) N2 adsorption-desorption isotherm of WO3. (b) Pore size distribution curve of WO3. (c) N2 adsorption-desorption isotherm of g-C3N4-WO3 (S-2). (d) Pore size distribution curve of g-C3N4-WO3 (S-2).