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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.

No MeSH data available.


Related in: MedlinePlus

SEM images of electrospun WO3 NFs: (a) as-spun dense W precursor/PVP composite NFs, (b) as-spun W precursor/PVP composite NFs embedded with 500 nm PS colloids, (c) as-spun W precursor/PVP composite NFs embedded with 200 nm and 500 nm PS colloids, (d) calcined dense WO3 NFs, (e) calcined PS (500)-WO3 NFs, and (f) calcined PS (200&500)-WO3 NFs. TEM images of electrospun WO3 NFs: (g) calcined dense WO3 NFs, (h) calcined PS (500)-WO3 NFs, and (i) calcined PS (200&500)-WO3 NFs.
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f2: SEM images of electrospun WO3 NFs: (a) as-spun dense W precursor/PVP composite NFs, (b) as-spun W precursor/PVP composite NFs embedded with 500 nm PS colloids, (c) as-spun W precursor/PVP composite NFs embedded with 200 nm and 500 nm PS colloids, (d) calcined dense WO3 NFs, (e) calcined PS (500)-WO3 NFs, and (f) calcined PS (200&500)-WO3 NFs. TEM images of electrospun WO3 NFs: (g) calcined dense WO3 NFs, (h) calcined PS (500)-WO3 NFs, and (i) calcined PS (200&500)-WO3 NFs.

Mentions: Microstructural and morphological observation was performed for the porous WO3 NFs synthesized by electrospinning assisted by spherical PS colloid sacrificial templates as well as for pristine WO3 NFs for comparison purposes (Figure 2). Two different sizes of spherical PS colloids having uniform diameters (i.e. average 200 nm and 500 nm) were used during the electrospinning process (Supporting Information, Figure S1). The as-spun W precursor/PVP composite NFs without PS colloid templates showed smooth surfaces (Figure 2a), whereas rough and rugged surface morphology was observed in the case of the PS colloid template assisted W precursor/PVP composite NFs with an average diameter of 1.29 ± 0.48 μm (Figures 2b and c). The spherical PS colloids with uniform size (500 nm in diameter) were well-distributed within the W precursor/PVP composite NFs (Figure 2b). In addition, two different spherical PS colloids were successfully decorated and embedded in the W precursor/PVP composite NFs (Figure 2c). After calcination in air at 500°C, polymeric components, i.e., PS colloids and PVP, were decomposed and burned out, and W precursor was crystallized into WO3 NFs. The pristine WO3 NFs showed densely packed polycrystalline microstructures exhibiting smooth surface morphology (Figure 2d) (hereafter, the pristine WO3 NFs are referred to dense WO3 NFs). However, porous WO3 NFs, obtained by spherical PS colloid templates, having diameters of 633 ± 178 nm, exhibited several pores on the surface and rugged surface morphology (Figures 2e and 2f) (hereafter, the porous WO3 NFs synthesized by PS colloids having 500 nm in diameter are referred to PS (500)-WO3 NFs). The PS (500)-WO3 NFs exhibited a tentacle-like structure with a crater-like pore shape on the surface. A wider distribution range in pore sizes was achieved in the porous WO3 NFs synthesized by the two different PS colloids (Figure 2f) (hereafter, the porous WO3 NFs synthesized by two different PS colloids having diameters of 200 nm and 500 nm are referred to PS (200&500)-WO3 NFs). To investigate the pore size and the distribution in detail, transmission electron microscopy (TEM) analysis was performed (Figures 2g-i and Figure S2 in the Supporting Information). The dense WO3 NF, which was composed of closely packed small WO3 grains exhibiting diameters of approximately 25 nm (Figure 2g), showed the diameter of average 767 ± 325 nm. In contrast, large spherical pores were observed with the PS (500)-WO3 NFs (Figure 2h) and PS (200&500)-WO3 NFs (Figure 2i). In particular, larger numbers of spherical pores were interconnected with each other in the case of PS (200&500)-WO3 NFs. It is noted that the 40–60% reduction in pore sizes were observed after calcination, compared to the original size of the PS colloids. This feature is mainly attributed to the shrinkage of the spherical PS colloids during the thermal decomposition and the migration of W precursor in the early stage of heat treatment. Different pore sizes could be also obtained by varying the PS colloidal sizes, i.e., 100 nm and 200 nm (Supporting Information, Figure S2). It was revealed that WO3 NFs with pore sizes smaller than 50 nm were obtained by using the PS colloids having diameter of 100 nm due to the shrinkage of the PS colloids (Supporting Information, Figures S2a and b). Thus, the utilization of PS colloids with broad size distribution can lead to effective manipulation of the pore sizes. These results revealed that the pore size (from mesopore to macropore size) and the distribution in 1D metal oxide NFs can be easily controlled for a specific application by simply changing the size and the density of sacrificial colloidal templates.


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)

SEM images of electrospun WO3 NFs: (a) as-spun dense W precursor/PVP composite NFs, (b) as-spun W precursor/PVP composite NFs embedded with 500 nm PS colloids, (c) as-spun W precursor/PVP composite NFs embedded with 200 nm and 500 nm PS colloids, (d) calcined dense WO3 NFs, (e) calcined PS (500)-WO3 NFs, and (f) calcined PS (200&500)-WO3 NFs. TEM images of electrospun WO3 NFs: (g) calcined dense WO3 NFs, (h) calcined PS (500)-WO3 NFs, and (i) calcined PS (200&500)-WO3 NFs.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: SEM images of electrospun WO3 NFs: (a) as-spun dense W precursor/PVP composite NFs, (b) as-spun W precursor/PVP composite NFs embedded with 500 nm PS colloids, (c) as-spun W precursor/PVP composite NFs embedded with 200 nm and 500 nm PS colloids, (d) calcined dense WO3 NFs, (e) calcined PS (500)-WO3 NFs, and (f) calcined PS (200&500)-WO3 NFs. TEM images of electrospun WO3 NFs: (g) calcined dense WO3 NFs, (h) calcined PS (500)-WO3 NFs, and (i) calcined PS (200&500)-WO3 NFs.
Mentions: Microstructural and morphological observation was performed for the porous WO3 NFs synthesized by electrospinning assisted by spherical PS colloid sacrificial templates as well as for pristine WO3 NFs for comparison purposes (Figure 2). Two different sizes of spherical PS colloids having uniform diameters (i.e. average 200 nm and 500 nm) were used during the electrospinning process (Supporting Information, Figure S1). The as-spun W precursor/PVP composite NFs without PS colloid templates showed smooth surfaces (Figure 2a), whereas rough and rugged surface morphology was observed in the case of the PS colloid template assisted W precursor/PVP composite NFs with an average diameter of 1.29 ± 0.48 μm (Figures 2b and c). The spherical PS colloids with uniform size (500 nm in diameter) were well-distributed within the W precursor/PVP composite NFs (Figure 2b). In addition, two different spherical PS colloids were successfully decorated and embedded in the W precursor/PVP composite NFs (Figure 2c). After calcination in air at 500°C, polymeric components, i.e., PS colloids and PVP, were decomposed and burned out, and W precursor was crystallized into WO3 NFs. The pristine WO3 NFs showed densely packed polycrystalline microstructures exhibiting smooth surface morphology (Figure 2d) (hereafter, the pristine WO3 NFs are referred to dense WO3 NFs). However, porous WO3 NFs, obtained by spherical PS colloid templates, having diameters of 633 ± 178 nm, exhibited several pores on the surface and rugged surface morphology (Figures 2e and 2f) (hereafter, the porous WO3 NFs synthesized by PS colloids having 500 nm in diameter are referred to PS (500)-WO3 NFs). The PS (500)-WO3 NFs exhibited a tentacle-like structure with a crater-like pore shape on the surface. A wider distribution range in pore sizes was achieved in the porous WO3 NFs synthesized by the two different PS colloids (Figure 2f) (hereafter, the porous WO3 NFs synthesized by two different PS colloids having diameters of 200 nm and 500 nm are referred to PS (200&500)-WO3 NFs). To investigate the pore size and the distribution in detail, transmission electron microscopy (TEM) analysis was performed (Figures 2g-i and Figure S2 in the Supporting Information). The dense WO3 NF, which was composed of closely packed small WO3 grains exhibiting diameters of approximately 25 nm (Figure 2g), showed the diameter of average 767 ± 325 nm. In contrast, large spherical pores were observed with the PS (500)-WO3 NFs (Figure 2h) and PS (200&500)-WO3 NFs (Figure 2i). In particular, larger numbers of spherical pores were interconnected with each other in the case of PS (200&500)-WO3 NFs. It is noted that the 40–60% reduction in pore sizes were observed after calcination, compared to the original size of the PS colloids. This feature is mainly attributed to the shrinkage of the spherical PS colloids during the thermal decomposition and the migration of W precursor in the early stage of heat treatment. Different pore sizes could be also obtained by varying the PS colloidal sizes, i.e., 100 nm and 200 nm (Supporting Information, Figure S2). It was revealed that WO3 NFs with pore sizes smaller than 50 nm were obtained by using the PS colloids having diameter of 100 nm due to the shrinkage of the PS colloids (Supporting Information, Figures S2a and b). Thus, the utilization of PS colloids with broad size distribution can lead to effective manipulation of the pore sizes. These results revealed that the pore size (from mesopore to macropore size) and the distribution in 1D metal oxide NFs can be easily controlled for a specific application by simply changing the size and the density of sacrificial colloidal templates.

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