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Highly efficient electronic sensitization of non-oxidized graphene flakes on controlled pore-loaded WO3 nanofibers for selective detection of H2S molecules.

Choi SJ, Choi C, Kim SJ, Cho HJ, Hakim M, Jeon S, Kim ID - Sci Rep (2015)

Bottom Line: A tentacle-like structure with randomly distributed pores on the surface of electrospun WO3 NFs were achieved, which exhibited improved surface area as well as porosity.Porous WO3 NFs with enhanced surface area exhibited high gas response (Rair/Rgas = 43.1 at 5 ppm) towards small and light H2S molecules.In contrast, porous WO3 NFs with maximized pore diameter showed a high response (Rair/Rgas = 2.8 at 5 ppm) towards large and heavy acetone molecules.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea.

ABSTRACT
Tailoring of semiconducting metal oxide nanostructures, which possess controlled pore size and concentration, is of great value to accurately detect various volatile organic compounds in exhaled breath, which act as potential biomarkers for many health conditions. In this work, we have developed a very simple and robust route for controlling both the size and distribution of spherical pores in electrospun WO3 nanofibers (NFs) via a sacrificial templating route using polystyrene colloids with different diameters (200 nm and 500 nm). A tentacle-like structure with randomly distributed pores on the surface of electrospun WO3 NFs were achieved, which exhibited improved surface area as well as porosity. Porous WO3 NFs with enhanced surface area exhibited high gas response (Rair/Rgas = 43.1 at 5 ppm) towards small and light H2S molecules. In contrast, porous WO3 NFs with maximized pore diameter showed a high response (Rair/Rgas = 2.8 at 5 ppm) towards large and heavy acetone molecules. Further enhanced sensing performance (Rair/Rgas = 65.6 at 5 ppm H2S) was achieved by functionalizing porous WO3 NFs with 0.1 wt% non-oxidized graphene (NOGR) flakes by forming a Schottky barrier (ΔΦ = 0.11) at the junction between the WO3 NFs (Φ = 4.56 eV) and NOGR flakes (Φ = 4.67 eV), which showed high potential for the diagnosis of halitosis.

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(a) Ultraviolet photoelectron spectroscopy (UPS) spectrum of PS (500)-WO3 NFs with a magnified image in the inset, and (b) schematic illustration of the bend structure of the NOGR and the PS (500)-WO3 NFs and electron transport characteristic when the electrical junction is formed.
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f7: (a) Ultraviolet photoelectron spectroscopy (UPS) spectrum of PS (500)-WO3 NFs with a magnified image in the inset, and (b) schematic illustration of the bend structure of the NOGR and the PS (500)-WO3 NFs and electron transport characteristic when the electrical junction is formed.

Mentions: To explain the significant improvement in sensing performance of the NOGR-loaded WO3 NFs, we measured the energy band alignment between WO3 NFs and NOGR flakes using ultraviolet photoelectron spectroscopy (UPS) analysis (Figure 7). The UPS spectrum of PS (500)-WO3 NFs exhibited a cut-off energy (Ecut-off) of 16.64 eV (Figure 7a) and a HOMO energy (EHOMO) of 1.46 eV (in the inset of Figure 7a), indicating that the work function and the electron affinity of the PS (500)-WO3 NFs are 4.56 eV and 3.22 eV, respectively. The work function of the NOGR flakes was measured using UPS as well, which showed 4.67 eV (Supporting Information, Figure S10); thus, electron transfer from the low work function of PS (500)-WO3 NFs to the high work function of NOGR flakes can be accomplished by forming a Schottky barrier of 0.11 eV between the junction of NOGR flakes and PS (500)-WO3 NFs (Figure 7b). Therefore, the improved sensing properties were achieved by the modulating electrons in the WO3 NFs sensitized by NOGR flakes. The functionalization of NOGR derives the lower electron concentration at the surface of the WO3 NFs in air, which results in the large conductivity changes upon the exposure of reducing gases such as H2S and acetone45. Nevertheless, the base resistance of the PS (500)-WO3 NFs functionalized by NOGR flakes (4.00 MΩ) was lower than that (10–16 MΩ) of single phase WO3 NFs (Figure 6a). In addition, I–V characteristics showed lower the resistance of PS (500)-WO3 NFs functionalized by NOGR flakes as compared to PS (500)-WO3 NFs (Supporting Information, Figure S11). This is attributed to the high electrical conductivity through the NOGR flakes, facilitating charge carrier transport2531. In addition to the electronic sensitization of NOGR flakes, facile surface reaction process of H2S with chemisorbed oxygen species4647, i.e., H2S (gas) + 3O− (chemisorbed) → SO2 + H2O + 3e−, generates highly H2S selective detection.


Highly efficient electronic sensitization of non-oxidized graphene flakes on controlled pore-loaded WO3 nanofibers for selective detection of H2S molecules.

Choi SJ, Choi C, Kim SJ, Cho HJ, Hakim M, Jeon S, Kim ID - Sci Rep (2015)

(a) Ultraviolet photoelectron spectroscopy (UPS) spectrum of PS (500)-WO3 NFs with a magnified image in the inset, and (b) schematic illustration of the bend structure of the NOGR and the PS (500)-WO3 NFs and electron transport characteristic when the electrical junction is formed.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4308697&req=5

f7: (a) Ultraviolet photoelectron spectroscopy (UPS) spectrum of PS (500)-WO3 NFs with a magnified image in the inset, and (b) schematic illustration of the bend structure of the NOGR and the PS (500)-WO3 NFs and electron transport characteristic when the electrical junction is formed.
Mentions: To explain the significant improvement in sensing performance of the NOGR-loaded WO3 NFs, we measured the energy band alignment between WO3 NFs and NOGR flakes using ultraviolet photoelectron spectroscopy (UPS) analysis (Figure 7). The UPS spectrum of PS (500)-WO3 NFs exhibited a cut-off energy (Ecut-off) of 16.64 eV (Figure 7a) and a HOMO energy (EHOMO) of 1.46 eV (in the inset of Figure 7a), indicating that the work function and the electron affinity of the PS (500)-WO3 NFs are 4.56 eV and 3.22 eV, respectively. The work function of the NOGR flakes was measured using UPS as well, which showed 4.67 eV (Supporting Information, Figure S10); thus, electron transfer from the low work function of PS (500)-WO3 NFs to the high work function of NOGR flakes can be accomplished by forming a Schottky barrier of 0.11 eV between the junction of NOGR flakes and PS (500)-WO3 NFs (Figure 7b). Therefore, the improved sensing properties were achieved by the modulating electrons in the WO3 NFs sensitized by NOGR flakes. The functionalization of NOGR derives the lower electron concentration at the surface of the WO3 NFs in air, which results in the large conductivity changes upon the exposure of reducing gases such as H2S and acetone45. Nevertheless, the base resistance of the PS (500)-WO3 NFs functionalized by NOGR flakes (4.00 MΩ) was lower than that (10–16 MΩ) of single phase WO3 NFs (Figure 6a). In addition, I–V characteristics showed lower the resistance of PS (500)-WO3 NFs functionalized by NOGR flakes as compared to PS (500)-WO3 NFs (Supporting Information, Figure S11). This is attributed to the high electrical conductivity through the NOGR flakes, facilitating charge carrier transport2531. In addition to the electronic sensitization of NOGR flakes, facile surface reaction process of H2S with chemisorbed oxygen species4647, i.e., H2S (gas) + 3O− (chemisorbed) → SO2 + H2O + 3e−, generates highly H2S selective detection.

Bottom Line: A tentacle-like structure with randomly distributed pores on the surface of electrospun WO3 NFs were achieved, which exhibited improved surface area as well as porosity.Porous WO3 NFs with enhanced surface area exhibited high gas response (Rair/Rgas = 43.1 at 5 ppm) towards small and light H2S molecules.In contrast, porous WO3 NFs with maximized pore diameter showed a high response (Rair/Rgas = 2.8 at 5 ppm) towards large and heavy acetone molecules.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea.

ABSTRACT
Tailoring of semiconducting metal oxide nanostructures, which possess controlled pore size and concentration, is of great value to accurately detect various volatile organic compounds in exhaled breath, which act as potential biomarkers for many health conditions. In this work, we have developed a very simple and robust route for controlling both the size and distribution of spherical pores in electrospun WO3 nanofibers (NFs) via a sacrificial templating route using polystyrene colloids with different diameters (200 nm and 500 nm). A tentacle-like structure with randomly distributed pores on the surface of electrospun WO3 NFs were achieved, which exhibited improved surface area as well as porosity. Porous WO3 NFs with enhanced surface area exhibited high gas response (Rair/Rgas = 43.1 at 5 ppm) towards small and light H2S molecules. In contrast, porous WO3 NFs with maximized pore diameter showed a high response (Rair/Rgas = 2.8 at 5 ppm) towards large and heavy acetone molecules. Further enhanced sensing performance (Rair/Rgas = 65.6 at 5 ppm H2S) was achieved by functionalizing porous WO3 NFs with 0.1 wt% non-oxidized graphene (NOGR) flakes by forming a Schottky barrier (ΔΦ = 0.11) at the junction between the WO3 NFs (Φ = 4.56 eV) and NOGR flakes (Φ = 4.67 eV), which showed high potential for the diagnosis of halitosis.

No MeSH data available.


Related in: MedlinePlus