Ultrasensitive Metal-oxide Gas Sensors Obtained using Colloidal Templates

Il-Doo Kim,Avner Rothschild,Takeo Hyodo,Harry L. Tuller 한국고분자학회 2006 한국고분자학회 학술대회 연구논문 초록집 Vol.2006 No.10

Transpiration Driven Electrokinetic Power Generator

Yun, Tae Gwang,Bae, Jaehyeong,Rothschild, Avner,Kim, Il-Doo American Chemical Society 2019 ACS NANO Vol.13 No.11

<P>Transpiration is the process by which water is carried in plants from the roots to the leaves where evaporation takes place. Here, we report a transpiration driven electrokinetic power generator (TEPG) that exploits capillary flow of water in an asymmetrically wetted cotton fabric coated with carbon black. Accumulation of protons induced by the electrical double layer formed at the solid (carbon black)/liquid (water) interface gives rise to potential difference between the wet and dry sides. The conductive carbon black coating channels electrical current driven by the pseudostreaming mechanism. A TEPG of 90 mm × 30 mm × 0.12 mm yields a maximum voltage of 0.53 V, maximum current of 3.91 μA, and maximum energy density of 1.14 mWh cm<SUP>-3</SUP>, depending on the loading of the carbon black. Multiple TEPGs generate enough power to light up a light-emitting diode (20 mA × 2.2 V) or charge a 1 F supercapacitor.</P> [FIG OMISSION]</BR>

Selective Detection of Acetone and Hydrogen Sulfide for the Diagnosis of Diabetes and Halitosis Using SnO₂ Nanofibers Functionalized with Reduced Graphene Oxide Nanosheets

Choi, Seon-Jin,Jang, Bong-Hoon,Lee, Seo-Jin,Min, Byoung Koun,Rothschild, Avner,Kim, Il-Doo American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.4

<P>Sensitive detection of acetone and hydrogen sulfide levels in exhaled human breath, serving as breath markers for some diseases such as diabetes and halitosis, may offer useful information for early diagnosis of these diseases. Exhaled breath analyzers using semiconductor metal oxide (SMO) gas sensors have attracted much attention because they offer low cost fabrication, miniaturization, and integration into portable devices for noninvasive medical diagnosis. However, SMO gas sensors often display cross sensitivity to interfering species. Therefore, selective real-time detection of specific disease markers is a major challenge that must be overcome to ensure reliable breath analysis. In this work, we report on highly sensitive and selective acetone and hydrogen sulfide detection achieved by sensitizing electrospun SnO<SUB>2</SUB> nanofibers with reduced graphene oxide (RGO) nanosheets. SnO<SUB>2</SUB> nanofibers mixed with a small amount (0.01 wt %) of RGO nanosheets exhibited sensitive response to hydrogen sulfide (<I>R</I><SUB>air</SUB>/<I>R</I><SUB>gas</SUB> = 34 at 5 ppm) at 200 °C, whereas sensitive acetone detection (<I>R</I><SUB>air</SUB>/<I>R</I><SUB>gas</SUB> = 10 at 5 ppm) was achieved by increasing the RGO loading to 5 wt % and raising the operation temperature to 350 °C. The detection limit of these sensors is predicted to be as low as 1 ppm for hydrogen sulfide and 100 ppb for acetone, respectively. These concentrations are much lower than in the exhaled breath of healthy people. This demonstrates that optimization of the RGO loading and the operation temperature of RGO–SnO<SUB>2</SUB> nanocomposite gas sensors enables highly sensitive and selective detection of breath markers for the diagnosis of diabetes and halitosis.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-4/am405088q/production/images/medium/am-2013-05088q_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am405088q'>ACS Electronic Supporting Info</A></P>

Ultrasensitive and Highly Selective Gas Sensors Based on Electrospun SnO₂ Nanofibers Modified by Pd Loading

Yang, Dae‐,Jin,Kamienchick, Itai,Youn, Doo Young,Rothschild, Avner,Kim, Il‐,Doo WILEY‐VCH Verlag 2010 Advanced functional materials Vol.20 No.24

<P><B>Abstract</B></P><P>This work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO<SUB>2</SUB> fibers. Unloaded and Pd‐loaded SnO<SUB>2</SUB> nanofiber mats are synthesized by electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO<SUB>2</SUB> crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO<SUB>2</SUB> crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO<SUB>2</SUB> grain growth during the calcination step. The Pd‐loaded SnO<SUB>2</SUB> sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H<SUB>2</SUB> and lower sensitivity to NO<SUB>2</SUB> compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO<SUB>2</SUB> crystallites and catalytic effect of PdO in promoting the oxidation of H<SUB>2</SUB> into H<SUB>2</SUB>O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.</P>

Selective Detection of Acetone and Hydrogen Sulfide for the Diagnosis of Diabetes and Halitosis Using SnO2 Nanofibers Functionalized with Reduced Graphene Oxide Nanosheets

Choi, Seon-Jin,Jang, Bong-Hoon,Lee, Seo-Jin,Min, Byoung Koun,Rothschild, Avner,Kim, Il-Doo American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.4

Sensitive detection of acetone and hydrogen sulfide levels in exhaled human breath, serving as breath markers for some diseases such as diabetes and halitosis, may offer useful information for early diagnosis of these diseases. Exhaled breath analyzers using semiconductor metal oxide (SMO) gas sensors have attracted much attention because they offer low cost fabrication, miniaturization, and integration into portable devices for noninvasive medical diagnosis. However, SMO gas sensors often display cross sensitivity to interfering species. Therefore, selective real-time detection of specific disease markers is a major challenge that must be overcome to ensure reliable breath analysis. In this work, we report on highly sensitive and selective acetone and hydrogen sulfide detection achieved by sensitizing electrospun SnO2 nanofibers with reduced graphene oxide (RGO) nanosheets. SnO2 nanofibers mixed with a small amount (0.01 wt %) of RGO nanosheets exhibited sensitive response to hydrogen sulfide (R-air/R-gas = 34 at 5 ppm) at 200 degrees C, whereas sensitive acetone detection (R-air/R-gas = 10 at 5 ppm) was achieved by increasing the RGO loading to 5 wt % and raising the operation temperature to 350 degrees C. The detection limit of these sensors is predicted to be as low as 1 ppm for hydrogen sulfide and 100 ppb for acetone, respectively. These concentrations are much lower than in the exhaled breath of healthy people. This demonstrates that optimization of the RGO loading and the operation temperature of RGO-SnO2 nanocomposite gas sensors enables highly sensitive and selective detection of breath markers for the diagnosis of diabetes and halitosis.

Thin-walled SnO2 nanotubes functionalized with Pt and Au catalysts via the protein templating route and their selective detection of acetone and hydrogen sulfide molecules.

Jang, Ji-Soo,Kim, Sang-Joon,Choi, Seon-Jin,Kim, Nam-Hoon,Hakim, Meggie,Rothschild, Avner,Kim, Il-Doo RSC Pub 2015 Nanoscale Vol.7 No.39

<P>Bio-inspired Pt (???2 nm) and Au (???2.7 nm) catalysts encapsulated by a protein shell, i.e., Pt-apoferritin (Pt@AF) and Au-apoferriten (Au@AF), were synthesized via the hollow protein nanocage (apoferritin) templating route and directly functionalized on the interior and exterior walls of electrospun SnO2 nanotubes (NTs) during controlled single-nozzle electrospinning followed by high temperature calcination with heating rate control. Fast crystallization of the exterior shell and outward diffusion of the interior Sn precursors and crystallites result in the continued growth of a tubular wall, which is related to rapid heating driven Ostwald-ripening behavior. Very importantly, the Pt and Au nanoparticles (NPs) were immobilized onto thin-walled SnO2 NTs with a diameter of ???350 nm and a shell thickness of ???40 nm without any aggregation of catalysts due to high dispersibility, which originated from repulsive electrostatic (Coulombic) forces acting on the surface charged protein shells, leading to an enhanced catalytic effect and outstanding gas sensing properties. Pt-loaded SnO2 NTs exhibited superior acetone response (Rair/Rgas = 92 at 5 ppm) compared to pure SnO2 NFs (Rair/Rgas = 4.8 at 5 ppm) and SnO2 NTs (Rair/Rgas = 11 at 5 ppm) while Au-loaded SnO2 NTs showed a high response when exposed to hydrogen sulfide (Rair/Rgas = 34 at 5 ppm), offering selective gas detection with minimal cross-sensitivity against other interfering gases such as NH3, CO, NO, C6H5CH3, and C5H12. Our results provide a new insight into facile, cost-effective, and highly dispersible catalyst loading on the interior and exterior walls of hollow metal oxide NTs via simple electrospinning as a potential breath analyzer.</P>

Fabrication and gas sensing properties of hollow SnO₂ hemispheres

Chang, Young-Eun,Youn, Doo-Young,Ankonina, Guy,Yang, Dae-Jin,Kim, Ho-Gi,Rothschild, Avner,Kim, Il-Doo Royal Society of Chemistry 2009 Chemical communications Vol.2009 No.27

<P>Close packed arrays of hollow SnO<SUB>2</SUB> hemispheres were prepared using PMMA microspheres as sacrificial templates for subsequent sputter-deposition of SnO<SUB>2</SUB> films, leading to a threefold enhancement in gas sensitivity compared to non-templated (flat) films.</P> <P>Graphic Abstract</P><P>Close packed arrays of hollow SnO<SUB>2</SUB> hemispheres were synthesized through the combination of colloidal sacrificial templates and physical vapor deposition, leading to a threefold enhancement in the NO<SUB>2</SUB> gas sensitivity of the templated films compared to their non-templated counterparts. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b902542a'> </P>

Hollow ZnO Nanofibers Fabricated Using Electrospun Polymer Templates and Their Electronic Transport Properties

Choi, Seung-Hoon,Ankonina, Guy,Youn, Doo-Young,Oh, Seong-Geun,Hong, Jae-Min,Rothschild, Avner,Kim, Il-Doo American Chemical Society 2009 ACS NANO Vol.3 No.9

<P>Thin (0.5 to 1 microm) layers of nonaligned or quasi-aligned hollow ZnO fibers were prepared by sputtering ZnO onto sacrificial templates comprising polyvinyl-acetate (PVAc) fibers deposited by electrospinning on silicon or alumina substrates. Subsequently, the ZnO/PVAc composite fibers were calcined to remove the organic components and crystallize the ZnO overlayer, resulting in hollow fibers comprising nanocrystalline ZnO shells with an average grain size of 23 nm. The inner diameter of the hollow fibers ranged between 100 and 400 nm and their wall thickness varied from 100 to 40 nm from top to bottom. The electronic transport and gas sensing properties were examined using DC conductivity and AC impedance spectroscopy measurements under exposure to residual concentrations (2-10 ppm) of NO(2) in air at elevated temperatures (200-400 degrees C). The inner and outer surface regions of the hollow ZnO fibers were depleted of mobile charge carriers, presumably due to electron localization at O(-) adions, constricting the current to flow through their less resistive cores. The overall impedance comprised interfacial and bulk contributions. Both contributions increased upon exposure to electronegative gases such as NO(2) but the bulk contribution was more sensitive than the interfacial one. The hollow ZnO fibers were much more sensitive compared to reference ZnO thin film specimens, displaying even larger sensitivity enhancement than the 2-fold increase in their surface to volume ratio. The quasi-aligned fibers were more sensitive than their nonaligned counterparts.</P>