Low-temperature H2S detection using Fe-doped SnO2/rGO nanocomposite sensor

Abstract

A low-temperature H₂S gas sensor was designed using 3% Fe-doped SnO₂/rGO nanocomposite as the sensing material. Fe-doped SnO₂ quantum dots (QDs) were prepared using a sol-gel combustion method, subsequently leading to the formation of the Fe-SnO₂/rGO nanocomposite through a simple sonication process. To evaluate the performance of the sensor material, the sample underwent comprehensive characterization using XRD, FE-SEM, HRTEM, Raman shift, XPS and BET surface area analysis based on nitrogen (N₂) adsorption-desorption. The XRD pattern HR-TEM confirmed the formation of a well-defined tetragonal crystal phase of SnO₂, indicating high structural integrity. Meanwhile, the BET analysis revealed a specific surface area of 72.7 m² g^-1 with pore size of 7.83 nm. Morphological analysis (HR-TEM) revealed that 3% Fe-doped SnO₂ QDs was uniformly dispersed on the rGO surface, with an average particle size of 5.6 nm. Gas sensing performance of pristine SnO₂ (S1), 3% Fe-doped SnO₂ QDs (S2), and 3% Fe-SnO₂/rGO (S3) nanocomposite based sensors was evaluated at operating temperatures ranging from 25 °C to 175 °C. Incorporation of rGO significantly enhanced the sensitivity of the 3% Fe-doped SnO₂/rGO nanocomposite towards H₂S compared to pristine SnO₂ and 3% Fe-SnO₂ QDs. The 3% Fe-SnO₂/rGO (S3) based sensor demonstrated a significant response of about 42.4 to 10 ppm H₂S at a low operating temperature of 100 °C, with a rapid response time of 21 seconds. It also exhibited excellent selectivity for H₂S against interfering gases such as NH₃, LPG, and CO. The enhanced sensitivity and selectivity are attributed to the synergistic interaction between 3% Fe-SnO₂ and rGO. A possible gas sensing mechanism underlying the improved performance of the nanocomposite is discussed.

Fig. 1. X-ray diffraction pattern of samples (a) S1 (b) S2 and (c) S3 respectively.

Fig. 2. (a–d) Low and high resolution HR-TEM micrographs (e) SEAD pattern and (f) particle size histogram of S3 nanocomposite.

Fig. 3. (a) FE-SEM, (b) EDX spectrum and elemental mapping of the (c) Sn (d) O (e) Fe and (f) C in S3 nanocomposite.

Fig. 4. (a) XPS survey spectrum, (b) Sn 3d, (c) Fe 2p, (d) C 1s XPS and (e) O 1s core level XPS spectrum of S3 nanocomposite.

Fig. 5. (a) Raman spectra of rGO, (b) S1, and (c) S3, (b and d) deconvoluted Raman spectra of S1 and (c and e) S3 nanocomposite in the wavenumber range 200–850 cm⁻¹.

Fig. 6. (a) UV-Vis absorption spectra and (b) Tauc plot of S1, S2 and S3 respectively.

Fig. 7. FTIR spectra for (a) S1, (b) S2 (c) S3 and (d) rGO respectively.

Fig. 8. (a) The gas-sensing performance of the S1, S2 and S3 sensors toward 10 ppm H₂S at various temperatures, (b)–(d) gas sensing curves for H₂S concentrations ranging from 5 ppm to 50 ppm, for S3, S2 and S1 gas sensors at 100 °C, 150 °C and 175 °C.

Fig. 9. Response recovery time for (a) S1, (b) S2 and (c) S3 to 10 ppm H₂S.

Fig. 10. Repeatability of S3 sensor to (a) 10 ppm and (b) 20 ppm H₂S at 100 °C.

Fig. 11. (a) Selectivity of S3 nanocomposite sensor towards NH₃ (50 ppm), CO₂ (300) and LPG (500 ppm) at 100 °C, (b) long term stability of S3 nanocomposite sensor.

Fig. 12. Gas sensing mechanism of S3 nanocomposite sensor in (a) energy band diagram of Fe–SnO₂ and rGO before contact (b) after contact (at equilibrium) (c) air (d) H₂S.

Fig. 13. Nitrogen adsorption–desorption isotherm and inset shows BJH pore size distribution plots of S3 nanocomposite.