Graphene Oxide@3D Hierarchical SnO2 Nanofiber/Nanosheets Nanocomposites for Highly Sensitive and Low-Temperature Formaldehyde Detection

Abstract

In this work, we reported a formaldehyde (HCHO) gas sensor with highly sensitive and selective gas-sensing performance at low operating temperature based on graphene oxide (GO)@SnO₂ nanofiber/nanosheets (NF/NSs) nanocomposites. Hierarchical SnO₂ NF/NSs coated with GO nanosheets showed enhanced sensing performance for HCHO gas, especially at low operating temperature. A series of characterization methods, including X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) were used to characterize their microstructures, morphologies, compositions, surface areas and so on. The sensing performance of GO@SnO₂ NF/NSs nanocomposites was optimized by adjusting the loading amount of GO ranging from 0.25% to 1.25%. The results showed the optimum loading amount of 1% GO in GO@SnO₂ NF/NSs nanocomposites not only exhibited the highest sensitivity value (R_a/R_g = 280 to 100 ppm HCHO gas) but also lowered the optimum operation temperature from 120 °C to 60 °C. The response value was about 4.5 times higher than that of pure hierarchical SnO₂ NF/NSs (R_a/R_g = 64 to 100 ppm). GO@SnO₂ NF/NSs nanocomposites showed lower detection limit down to 0.25 ppm HCHO and excellent selectivity against interfering gases (ethanol (C₂H₅OH), acetone (CH₃COCH₃), methanol (CH₃OH), ammonia (NH₃), methylbenzene (C₇H₈), benzene (C₆H₆) and water (H₂O)). The enhanced sensing performance for HCHO was mainly ascribed to the high specific surface area, suitable electron transfer channels and the synergistic effect of the SnO₂ NF/NSs and GO nanosheets network.

Keywords: GO@SnO2 NF/NSs; formaldehyde gas sensors; nanocomposites; three-dimensional nanostructure.

Figure 1

XRD patterns of (a) GO, (b) SnO₂ NF/NSs and (c–g) GO@SnO₂ NF/NSs nanocomposites with different GO content.

Figure 2

Raman spectra of pure SnO₂ NF/NSs, 1% GO@SnO₂ NF/NSs and pure GO nanosheets.

Figure 3

SEM images of the as-prepared (a) and (d) SnO₂ NF/NSs, (b) and (e) 1% GO@SnO₂ NF/NSs and (c) and (f) GO; (g) low magnification TEM image; (h) low magnification TEM image, (i) HRTEM image of the 1% GO@SnO₂ NF/NSs nanocomposites.

Figure 4

XPS spectra of SnO₂ NF/NSs and 1% GO@SnO₂ NF/NSs nanocomposites: (a) survey of 1% GO@SnO₂ NF/NSs nanocomposite, (b) C 1s of 1% GO@SnO₂ NF/NSs nanocomposites, (c,d) O 1s of pure SnO₂ NF/NSs and 1% GO@SnO₂ NF/NSs nanocomposites, respectively.

Figure 5

(a) The responses of gas sensors toward 100 ppm formaldehyde at different operation temperatures. (b) Responses of the gas sensors to different test gases at their respective optimal operating temperatures. (c) Response of 1% GO@SnO₂ NF/NSs nanocomposites toward HCHO gas in concentration ranges of 0.25–100 ppm at 60 °C. (d) Linear approximation of the detection limit with 1% GO@SnO₂ NF/NSs nanocomposite.

Figure 6

Schematic illustration of HCHO gas sensing mechanism for (a) pure SnO₂ NF/NSs and GO@SnO₂ NF/NSs nanocomposite; (b) the energy band structures of GO@SnO₂ NF/NSs nanocomposite in different gas atmospheres.

Scheme 1

A schematic demonstration of the preparation process of GO@SnO₂ NF/NSs nanocomposites.

Figure 7

(a) The schematic structure and (b) the working principle of the gas-sensing test system of the gas sensor.