Extremely sensitive and selective sub-ppm CO detection by the synergistic effect of Au nanoparticles and core–shell nanowires

Kim, Jae-Hun,Mirzaei, Ali,Kim, Hyoun Woo,Kim, Sang Sub Elsevier Sequoia 2017 Sensors and actuators. B Chemical Vol.249 No.-

<P><B>Abstract</B></P> <P>An extremely sensitive CO sensor based on novel hybrid SnO<SUB>2</SUB>–ZnO core–shell (C–S) nanowires (NWs) functionalized by Au nanoparticles (NPs) was synthesized. First, networked SnO<SUB>2</SUB> NWs were successfully prepared using the vapor–liquid–solid growth method on an electrode layer with special patterns. A ZnO shell was subsequently coated on the SnO<SUB>2</SUB> core using atomic layer deposition, and Au NPs were then attached onto the ZnO shell using γ-ray radiolysis. The resulting sensor exhibited a very high response of 26.6–100ppb CO gas. Furthermore, the responses to other gases such as C<SUB>6</SUB>H<SUB>6</SUB> and C<SUB>6</SUB>H<SUB>7</SUB> were extremely low, indicating the very good selectivity of the sensor to CO gas. Besides acting as heterojunctions, the catalytic effect of the Au NPs on CO gas greatly improved the CO sensing capability of the Au-functionalized SnO<SUB>2</SUB>–ZnO C–S NWs. The high sensitivity and selectivity of this sensor can open a path for prompt toxic monitoring and early detection of fatal diseases related to CO.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel hybrid SnO<SUB>2</SUB>–ZnO core–shell nanowires functionalized by Au nanoparticles. </LI> <LI> The resulting sensor exhibited a very high response of 26.6–100ppb CO gas. </LI> <LI> The very good selectivity of the sensor to CO gas. </LI> <LI> Heterojunctions and the catalytic effect of Au greatly improved the CO sensing capability. </LI> </UL> </P>

규칙적인 신체활동 프로그램이 좌업근로자들의 기초체력, 최대산소 섭취량 및 최대심박수에 미치는 영향

신보삼,최점동,정현정,신창섭 한국스포츠리서치 2004 한국 스포츠 리서치 Vol.15 No.3

This study experimented the difference in the cardiopulmonary functions, such as the maximum oxygen intake and the maximum heart rate, of the office workers or the J, university when they had done regular physical activities such as stretching exercises for 20 minutes, walking for 30 minutes, jogging for 10 minutes and weight training for 10 minutes at the intensity of THR 60~70% more than four times a week for 16 weeks in order to develop the grip strength Sargent jump, trunk flexion, stork standing with closing eyes, back strength and sit-ups, all or which are helpful for the physical development of strength, muscular endurance, flexibility, agility and balance, It measured and compared six basic physical factors and the cardiopulmonary functions such as the VO₂max and the HRmax, of which results was as follows. First, the physical strength items such as the grip strength(left and right sides), sargent jump, trunk flexion, stork standing with closing eyes, back strength and sit-ups all showed the expected results. Second, the cardiopulmonary functions such as the VO₂max and the HRmax also showed the results that had improved after participation in training program.

Co₃O₄-loaded ZnO nanofibers for excellent hydrogen sensing

Lee, Jae-Hyoung,Kim, Jin-Young,Kim, Jae-Hun,Mirzaei, Ali,Kim, Hyoun Woo,Kim, Sang Sub Elsevier 2019 International journal of hydrogen energy Vol.44 No.50

<P><B>Abstract</B></P> <P>The development of outstanding H<SUB>2</SUB>-sensing materials is vital for the realization of ecofriendly devices using H<SUB>2</SUB>-based energy. ZnO nanofibers have excellent H<SUB>2</SUB>-sensing performance. In this study, we synthesized a series of Co<SUB>3</SUB>O<SUB>4</SUB>-loaded ZnO nanofibers with the formula (1-x)ZnO-xCo<SUB>3</SUB>O<SUB>4</SUB> (x = 0.03, 0.05, 0.1, and 0.15, representing the molar ratio of Co<SUB>3</SUB>O<SUB>4</SUB>) via electrospinning to improve the H<SUB>2</SUB>-sensing properties of pristine nanofibers. The sensing results indicated that a sensor with a nominal composition of 0.95ZnO-0.05Co<SUB>3</SUB>O<SUB>4</SUB> had the highest response of ~133 to 10 ppm H<SUB>2</SUB> gas, with good H<SUB>2</SUB> selectivity. The main mechanisms underlying the excellent H<SUB>2</SUB>-sensing capability of the optimized gas sensor involved ZnO surface/grain boundaries and Co<SUB>3</SUB>O<SUB>4</SUB>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The <I>n</I>-<I>p</I> ZnO–Co<SUB>3</SUB>O<SUB>4</SUB> composite nanofibers showed higher H<SUB>2</SUB> sensing response, superior to that of pristine <I>n</I>–ZnO nanofibers. </LI> <LI> The composite nanofibers with composition of 0.95 ZnO-0.05 Co<SUB>3</SUB>O<SUB>4</SUB> showed the highest response to H<SUB>2</SUB> at 300 °C. </LI> <LI> H<SUB>2</SUB> sensing was related to the H<SUB>2</SUB>-induced reduction of resistance in ZnO and formation p-Co<SUB>3</SUB>O<SUB>4</SUB>/n-ZnO heterojunctions. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Change of potential barriers at ZnO/ZnO homointerfaces in the H<SUB>2</SUB> atmospheres, energy levels of ZnO and Co<SUB>3</SUB>O<SUB>4</SUB> after intimate contact, and responses of Co<SUB>3</SUB>O<SUB>4</SUB> loaded ZnO to H<SUB>2</SUB>, CO, NO<SUB>2</SUB> gases.</P> <P>[DISPLAY OMISSION]</P>

SnO₂ (<i>n</i>)-NiO (<i>p</i>) composite nanowebs: Gas sensing properties and sensing mechanisms

Kim, Jae-Hun,Lee, Jae-Hyoung,Mirzaei, Ali,Kim, Hyoun Woo,Kim, Sang Sub Elsevier Sequoia 2018 Sensors and actuators. B Chemical Vol.258 No.-

<P><B>Abstract</B></P> <P>Aiming to optimize SnO<SUB>2</SUB>-NiO nanocomposite sensors for detection of hazardous gases, a series of xSnO<SUB>2</SUB>-(1-x) NiO composite nanowebs with different compositions (x=0.1, 0.3, 0.5, 0.7, and 0.9) were synthesized using an electrospinning process. The formation of long and continuous SnO<SUB>2</SUB>-NiO nanowebs was verified. Depending on the composition, xSnO<SUB>2</SUB>-(1-x) NiO composite nanowebs‎ showed either <I>n</I>-type (SnO<SUB>2</SUB>-rich composition) or <I>p</I>-type (NiO-rich composition) gas-sensing behavior. The best sensing performance was obtained for the nanowebs of 0.5SnO<SUB>2</SUB>-0.5NiO. The presence of plenty of <I>p</I>-<I>n</I> heterojunctions along with the high oxygen adsorption property of NiO were the main reasons for the high response to the NO<SUB>2</SUB> and C<SUB>6</SUB>H<SUB>6</SUB> gases at this optimized composition.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We optimized SnO<SUB>2</SUB>-NiO nanocomposite sensors for detection of hazardous gases. </LI> <LI> Depending on the composition, SnO<SUB>2</SUB>-NiO composite nanowebs showed either <I>n</I>-type or <I>p</I>-type behavior. </LI> <LI> The <I>p</I>-<I>n</I> junctions, NiO with high oxygen adsorption capability, and crystallographic defects generated by possible substitution of Ni<SUP>+2</SUP> in Sn<SUP>+4</SUP> were the main reasons for the efficient sensing. </LI> </UL> </P>

Bifunctional Sensing Mechanism of SnO₂–ZnO Composite Nanofibers for Drastically Enhancing the Sensing Behavior in H₂ Gas

Katoch, Akash,Kim, Jae-Hun,Kwon, Yong Jung,Kim, Hyoun Woo,Kim, Sang Sub American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.21

<P>SnO<SUB>2</SUB>–ZnO composite nanofibers fabricated using an electrospinning method exhibited exceptional hydrogen (H<SUB>2</SUB>) sensing behavior. The existence of tetragonal SnO<SUB>2</SUB> and hexagonal ZnO nanograins was confirmed by an analysis of the crystalline phase of the composite nanofibers. A bifunctional sensing mechanism of the composite nanofibers was proposed in which the combined effects of SnO<SUB>2</SUB>–SnO<SUB>2</SUB> homointerfaces and ZnO–SnO<SUB>2</SUB> heterointerfaces contributed to an improvement in the H<SUB>2</SUB> sensing characteristics. The sensing process with respect to SnO<SUB>2</SUB>–ZnO heterojunctions is associated not only with the high barrier at the junctions, but also the semiconductor-to-metallic transition on the surface of the ZnO nanograins upon the introduction of H<SUB>2</SUB> gas.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-21/acsami.5b01817/production/images/medium/am-2015-01817x_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b01817'>ACS Electronic Supporting Info</A></P>

Selective NO₂ sensor based on Bi₂O₃ branched SnO₂ nanowires

Bang, Jae Hoon,Choi, Myung Sik,Mirzaei, Ali,Kwon, Yong Jung,Kim, Sang Sub,Kim, Tae Whan,Kim, Hyoun Woo Elsevier 2018 Sensors and actuators. B Chemical Vol.274 No.-

<P><B>Abstract</B></P> <P>We present a highly sensitive and selective NO<SUB>2</SUB> sensor based on Bi<SUB>2</SUB>O<SUB>3</SUB> branched SnO<SUB>2</SUB> nanowires (NWs). SnO<SUB>2</SUB> NWs were first synthesized by a vapor-liquid-solid method, were coated with an Au layer, and Bi<SUB>2</SUB>O<SUB>3</SUB> branches were grown on their stems by the same procedure used for pure Bi powders. The fabricated sensor showed a high response (R<SUB>g</SUB>/R<SUB>a</SUB>) of 56.92 to 2 ppm of NO<SUB>2</SUB> gas at an optimal temperature. Furthermore, its response to other interfering gases such as ethanol, acetone, toluene, and benzene, was less than 1.55, which demonstrated excellent selectivity of the sensor towards NO<SUB>2</SUB> gas. For comparison and to better understand the sensing mechanism, a pristine SnO<SUB>2</SUB> NWs sensor was also tested. The superior sensing properties of the branched NW sensor relative to the pristine sensor were mainly attributed to the high surface area of the sensor resulting from Bi<SUB>2</SUB>O<SUB>3</SUB> branching, as well as the formation of homo-and heterojunctions (Bi<SUB>2</SUB>O<SUB>3</SUB>-SnO<SUB>2</SUB>). In addition, several factors including the presence of Au contributed to the excellent selectivity to NO<SUB>2</SUB> gas. Based on the results obtained in this work, we believe that the present sensor with an easy fabrication method, along with its high sensitivity and selectivity towards NO<SUB>2</SUB>, can be used for the detection of NO<SUB>2</SUB> gas in real applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We presented a highly sensitive and selective NO<SUB>2</SUB> sensor based on Bi<SUB>2</SUB>O<SUB>3</SUB> branched SnO<SUB>2</SUB> nanowires. </LI> <LI> The sensor showed a high response (R<SUB>g</SUB>/R<SUB>a</SUB>) of 56.92 to 2 ppm of NO<SUB>2</SUB> gas </LI> <LI> The sensor demonstrated excellent selectivity towards NO<SUB>2</SUB> gas. </LI> <LI> We explored the sensing mechanisms, in regard to the selective sensing to NO<SUB>2</SUB> gas. </LI> </UL> </P>

Room-temperature NO₂ sensor based on electrochemically etched porous silicon

Choi, Myung Sik,Na, Han Gil,Mirzaei, Ali,Bang, Jae Hoon,Oum, Wansik,Han, Seungmin,Choi, Sun-Woo,Kim, Mooshob,Jin, Changhyun,Kim, Sang Sub,Kim, Hyoun Woo Elsevier 2019 Journal of Alloys and Compounds Vol.811 No.-

<P><B>Abstract</B></P> <P>With high-performance room-temperature gas sensors being in great demand from an energy-saving standpoint, in this study, we fabricated porous silicon (PS) sensors by electrochemically etching at different times (30, 60, and 90 min). The porous nature of the etched PSs was studied using scanning electron microscopy, and subsequently gas sensors were fabricated. NO<SUB>2</SUB> sensing studies showed that the highest gas performance can be obtained at room temperature (30 °C). Furthermore, the PS sensor etched for 60 min had the best performance among the sensors, which is related to its higher surface area and high enough initial resistance. In particular for the PS sensor etched for 60 min, the response (R<SUB>a</SUB>/R<SUB>g</SUB>) to 10 ppm NO<SUB>2</SUB> was 9.56, which was much higher than other interfering gases, demonstrating its high selectivity towards NO<SUB>2</SUB> gas. This study reveals the need for optimization of electrochemical etching to realize gas sensors based on PS working at room temperature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We fabricated porous silicon (PS) sensors for room-temperature NO<SUB>2</SUB> sensing, by electrochemically etching at different times. </LI> <LI> The PS sensor etched for 60 min had the best performance among the sensors. </LI> <LI> The response of PS sensor to 10 ppm NO<SUB>2</SUB> was 9.56, demonstrating its high selectivity towards NO<SUB>2</SUB> gas. </LI> </UL> </P>

Ultra-sensitive benzene detection by a novel approach: Core-shell nanowires combined with the Pd-functionalization

Kim, Jae-Hun,Kim, Hyoun Woo,Kim, Sang Sub Elsevier 2017 Sensors and actuators. B Chemical Vol.239 No.-

<P><B>Abstract</B></P> <P>We have realized an excellent selective sensing to benzene (C<SUB>6</SUB>H<SUB>6</SUB>) by means of using SnO<SUB>2</SUB>-ZnO core-shell nanowires functionalized with Pd nanoparticles. We obtained a response of 71 for 100ppb of C<SUB>6</SUB>H<SUB>6</SUB>, which is the highest response reported thus far. The synergistic effects of variation of SnO<SUB>2</SUB>/ZnO potential barriers and chemical sensitization of Pd are responsible for the highest C<SUB>6</SUB>H<SUB>6</SUB>-sensing performance. These results highlight the potential for using Pd functionalized nanowires as a sensing platform in detecting trace concentrations of benzene, which is applicable in the future sensor, including the disease diagnosis and the environmental monitoring.</P>

Graphene-loaded tin oxide nanofibers: optimization and sensing performance

Abideen, Zain Ul,Park, Jae Young,Kim, Hyoun Woo,Kim, Sang Sub IOP Pub 2017 Nanotechnology Vol.28 No.3

<P>We investigated the gas sensing characteristics of graphene nanosheet (NS)-loaded SnO<SUB>2</SUB> nanofibers (NFs) that were synthesized by a low-cost facile electrospinning process. The sensing performance was characterized as a function of the graphene content with various gases such as C<SUB>6</SUB>H<SUB>6</SUB>, C<SUB>7</SUB>H<SUB>8</SUB>, CO, CO<SUB>2</SUB>, and H<SUB>2</SUB>S. The loading of graphene NSs significantly improved the gas sensing performances of SnO<SUB>2</SUB> NFs. The optimal amount of graphene NSs was found to be 0.5 wt%. We proposed a sensing mechanism for the enhanced sensing performance based on the chemical sensitization of graphene NSs and the charge transfer through the heterointerfaces between graphene NSs and SnO<SUB>2</SUB> nanograins. The results show that graphene NS-loaded SnO<SUB>2</SUB> NFs are a promising sensing material system that can detect hazardous gaseous species.</P>

Optimization and gas sensing mechanism of n-SnO₂-p-Co₃O₄ composite nanofibers

Kim, Jae-Hun,Lee, Jae-Hyoung,Mirzaei, Ali,Kim, Hyoun Woo,Kim, Sang Sub Elsevier 2017 Sensors and actuators. B, Chemical Vol.248 No.-

<P><B>Abstract</B></P> <P>Although the employment of n-p heterojunctions is among the most popular strategies to increase the performance of gas sensors, there have been a few systematic studies to determine the optimal composition in n-p heterojunctions. This paper reports the results of a systematic study of (n) xSnO<SUB>2</SUB>-(p) (1-x) Co<SUB>3</SUB>O<SUB>4</SUB> composite nanofibers (NFs) for gas sensing applications. Composite NFs were synthesized by the electrospinning method followed by annealing at 600°C. For gas sensing studies, several gases at optimal working temperature (350°C) were tested. Depending on the nominal composition, the sensors showed either n-or p-type behavior as well as different responses to the target gases. Furthermore, for all gases tested, the 0·5SnO<SUB>2</SUB>-0·5Co<SUB>3</SUB>O<SUB>4</SUB> sensor (nominal composition) showed the best gas sensing characteristics. The underlying gas sensing mechanism was examined in detail. The highest response observed in the 0·5SnO<SUB>2</SUB>-0·5Co<SUB>3</SUB>O<SUB>4</SUB> NFs sensor was primarily attributed to the major role of the p-Co<SUB>3</SUB>O<SUB>4</SUB> nanograins as electron reservoir. In addition, the possible substitution of Co<SUP>+2</SUP>/Co<SUP>+3</SUP> in Sn<SUP>+4</SUP> sites, the catalytic effect of Co<SUB>3</SUB>O<SUB>4</SUB> and generation of defects were likely to be the secondary reasons. This highlights the importance of the optimal composition for achieving the maximum gas-sensing performance in n-p composite NFs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Systematic study on SnO<SUB>2</SUB> (n) −Co<SUB>3</SUB>O<SUB>4</SUB> (p) electrospun composite NFs sensors. </LI> <LI> Transition from p-type to n-type semiconducting behavior by change of composition. </LI> <LI> Among various compositions, 0.5SnO<SUB>2</SUB>-0.5Co<SUB>3</SUB>O<SUB>4</SUB> showed the optimal composition. </LI> <LI> High response to low concentrations of C<SUB>6</SUB>H<SUB>6</SUB>. </LI> <LI> The main reasons for sensing enhancement were heterojunctions and catalytic effect. </LI> </UL> </P>