Au functionalized ZnO nanowire gas sensor for detection of benzene and toluence. One novel sensing hybridmaterial of Au nanoparticles (Au NPs)functionalized ZnO nanowires (AuZnO NWs) was successfully synthesized by a twostage solution process. First, ZnO NWs were fabricated via a lowtemperature onepot hydrothermal method with SDSN introduced as structuredirecting agent. Afterward, the asprepared ZnO NWs were used as supports to load Au NPs with small sizes via precipitating HAuCl4 aqueous solution by ammonia. The obtained samples were characterized by means of XRD, SEM, TEM and EDX. Both pristine and AuZnO NWs were practically applied as gas sensors to compare the effect of Au NPs on the sensing performances, and the obtained results demonstrated that after functionalization by catalytic Au NPs, the hybrid sensor exhibited not only faster response and recovery speeds but also higher response to benzene and toluene than the pristine ZnO sensor at 340 oC, especially showed high selectivity and longterm stability to low concentration toluene, which is rarely reported with this method, indicating its original sensor application in detecting benzene and toluene. To interpret the enhanced gas sensing mechanism, the strong spillover effect of the Au NPs and the increased Schottky barriers caused by the electronic interaction between Au NPs and ZnO NW support are believed to contribute to the improved sensor performance.
View Article Online PCCP View Journal Accepted Manuscript This article can be cited before page numbers have been issued, to this please use: L Wang, S Wang, M Xu, X Hu, H Zhang, Y Wang and W Huang, Phys Chem Chem Phys., 2013, DOI: 10.1039/C3CP52392F Volume 12 | Number 43 | 2010 This is an Accepted Manuscript, which has been through the RSC Publishing peer review process and has been accepted for publication ence Physical Chemistry Chemical Physics www.rsc.org/pccp Volume 12 | Number 43 | 21 November 2010 | Pages 14369–14636 PCCP chers 090856 Accepted Manuscripts are published online shortly after acceptance, which is prior to technical editing, formatting and proof reading This free service from RSC Publishing allows authors to make their results available to the community, in citable form, before publication of the edited article This Accepted Manuscript will be replaced by the edited and formatted Advance Article as soon as this is available To cite this manuscript please use its permanent Digital Object Identifier (DOI®), which is identical for all formats of publication ding scientific C has once rst major journal More information about Accepted Manuscripts can be found in the Information for Authors m to advance the n, conversion and the sustainable China ue now! Charity Number 207890 Pages 14369–14636 org/ees ISSN 1463-9076 COMMUNICATION Soler-Illia et al COVER ARTICLE Electrical Conductivity in Hore et al Patterned Silver-Mesoporous Water structure at solid surfaces and its Titania Nanocomposite Thin Films: implications for biomolecule adsorption Towards Robust 3D Nano-Electrodes 1463-9076(2010)12:43;1-V Please note that technical editing may introduce minor changes to the text and/or graphics contained in the manuscript submitted by the author(s) which may alter content, and that the standard Terms & Conditions and the ethical guidelines that apply to the journal are still applicable In no event shall the RSC be held responsible for any errors or omissions in these Accepted Manuscript manuscripts or any consequences arising from the use of any information contained in them www.rsc.org/pccp Registered Charity Number 207890 Page of 34 Physical Chemistry Chemical Physics View Article Online DOI: 10.1039/C3CP52392F Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 benzene and toluene† Liwei Wang,a Shurong Wang*,a Mijuan Xu,ab Xiaojing Hu,a Hongxin Zhang,a Yanshuang Wanga and Weiping Huanga a Tianjin Key Lab of Metal and Molecule-based Material Chemistry, Department of Chemistry, Nankai University, Tianjin, 300071, China b China National Petroleum Corporation Occupational Health Center, No.51 Xinkai Road, Langfang City, 065000, Hebei Province, China *Corresponding author: Tel.: +86–22–23505896; fax: +86–22–23502458 E-mail: shrwang@nankai.edu.cn † Electronic supplementary information (ESI) available Physical Chemistry Chemical Physics Accepted Manuscript Au-functionalized ZnO nanowire gas sensor for detection of Physical Chemistry Chemical Physics Page of 34 View Article Online DOI: 10.1039/C3CP52392F Abstract nanowires (Au/ZnO NWs) was successfully synthesized by a two-stage solution process First, ZnO NWs were fabricated via a low-temperature one-pot hydrothermal method with SDSN introduced as structure-directing agent Afterward, the as-prepared ZnO NWs were used as supports to load Au NPs with small sizes via precipitating HAuCl4 aqueous solution by ammonia The obtained samples were characterized by means of XRD, SEM, TEM and EDX Both pristine and Au/ZnO NWs were practically applied as gas sensors to compare the effect of Au NPs on the sensing performances, and the obtained results demonstrated that after functionalization by catalytic Au NPs, the hybrid sensor exhibited not only faster response and recovery speeds but also higher response to benzene and toluene than the pristine ZnO sensor at 340 oC, especially showed high selectivity and long-term stability to low concentration toluene, which is rarely reported with this method, indicating its original sensor application in detecting benzene and toluene To interpret the enhanced gas sensing mechanism, the strong spillover effect of the Au NPs and the increased Schottky barriers caused by the electronic interaction between Au NPs and ZnO NW support are believed to contribute to the improved sensor performance Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 One novel sensing hybrid-material of Au nanoparticles (Au NPs)-functionalized ZnO Page of 34 Physical Chemistry Chemical Physics View Article Online DOI: 10.1039/C3CP52392F Au/ZnO 50 nm 10 500 ppm Pristine ZnO 200 ppm 100 ppm Au-ZnO 50 ppm 1.8 1.6 ppm 1.4 1.2 1.0 gas in 0.8 ppm 0.6 0.4 Au-ZnO gas out 10 ppm ZnO Response 2.0 Voltage (V) Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 ZnO nanowires 0.2 0.0 500 1000 Time (s) 1500 2000 100 200 300 400 500 Concentration (ppm) Highlight: Au/ZnO NWs were synthesized via a facile two-stage solution process, which were then made as gas sensors and showed favorable sensing properties to nocuous and carcinogenic benzene and toluene Physical Chemistry Chemical Physics Accepted Manuscript TOC/Abstract Art Physical Chemistry Chemical Physics Page of 34 View Article Online DOI: 10.1039/C3CP52392F Introduction air pollutants (HAPs)1 have been produced with serious endangerment Among the toxic volatile organic compounds (VOCs),2-5 aromatic hydrocarbon, such as benzene and toluene, may reasonably be carcinogenic, mutagenic and exhibit other adverse health effects.6 Therefore, the task to detect benzene and toluene as fast and accurate as possible, esp in very low concentration to alarm people the extent of the out-door and in-door inhalation noxious pollutions is of great importance and very imperative Many conventional technologies applied to determine VOCs accompany various shortcomings, e.g for gas chromatography-mass spectrometry (GC-MS), the disadvantages may be that the subsequent analytical procedures are very complex and time-consuming, and the equipment is expensive, complicated, bulky and energy-consuming.7-9 Currently, the gas sensors are widely adopted to meet these requirements, because they facilitate the gas detection, possess high sensitivity to certain target gases and obtain the real-time detection result Furthermore, the equipment handles easily but is low-cost So the appearance of gas sensors is doomed to create novel avenues for VOCs detection.7, 10 As the central part of a gas sensor, the sensing materials always favor various metal oxide semiconductor (MOS) nanomaterials, among which ZnO, an n-type semiconductor, is one of the most promising multifunctional materials and has been extensively used as a promising gas sensor candidate due to its suitability to doping, non-toxicity, high electrochemical stability and low cost.11-14 Moreover, one Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 With the development of science and technology, large numbers of organic hazardous Page of 34 Physical Chemistry Chemical Physics View Article Online DOI: 10.1039/C3CP52392F dimensional (1D) ZnO nanowires (NWs) have received the most attention, due to the transportation properties, which are favorable for gases to diffuse rapidly and effectively through the devices, incurring more surface atoms have chances to participate in the surface reactions.15-18 In recent years, extensive studies have been taken concerning further enhancing the sensor performances Hybrid nanomaterials combine two or more compositions with multiple functions that are not available from the respective component, and thus have gained more attention for various applications in chemical sensor, catalysts, optics, biomedicine and so on.19,20 Moreover, the doping of noble metal nanoparticles (NPs) onto MOS is more popular, since the strong spillover effect of the noble metals (Au, Ag, Pt, Pd, etc.) with unique electronic and catalytic properties and the synergic electronic interaction with the MOS might enhance the surface depletion layers, thus promoting the sensing performance.21-29 Many reports have been focused on the assembly of noble metal onto MOS applied in gas sensors For example, Chai et al reported that the ZnO microwire sensor functionalized by Pd showed reliable natural gas response at room temperature.22 Liao et al found that incorporation of Pt nanocrystals on CeO2 nanowire could significantly increase the sensor response.23 The previous studies also demonstrated that the ZnO nanostructures functionalized by Au NPs presented enhanced gas sensing performances.24,25 Despite the success of the above work, these synthetic processes are high-cost, not facile, toxic or time-consuming Besides, to the best of our knowledge, there are few detailed studies on the gas sensing behaviour of Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 large surface-to-volume ratio, lower tendency to agglomerate and unique electron Physical Chemistry Chemical Physics Page of 34 View Article Online DOI: 10.1039/C3CP52392F Au NPs-functionalized ZnO NWs Especially, it is still scarce about reports on the toluene with good selectivity and high sensitivity Herein, we present a facile two-stage solution process to successfully fabricate the Au NPs-functionalized ZnO NWs The Au NPs with small sizes are anchored onto the surface of ZnO NWs via precipitating HAuCl4 aqueous solution by ammonia This green, nontoxic and cost-effective procedure is general to fabricate other noble metal doped MOS hybrids To demonstrate the practical gas sensing applications, the gas sensing performances of the sensor based on the as-fabricated Au/ZnO NWs have been systematically investigated As expected, the hybrid sensor displays enhanced gas sensing performances including response/recovery speed, sensitivity and selectivity in detecting benzene and toluene in comparison with the pristine ZnO NW sensor Besides, the long-term stability of the sensor has been obtained by testing ppm toluene after months, which indicates its great potential for practical application To explain the enhanced gas sensing properties of the Au NPs-functionalized ZnO NW sensor, the gas sensing mechanism is discussed Experimental 2.1 Materials Chemical reagents (analytical grade) such as Zinc nitrate hexahydrate (Zn(NO3)2·6H2O), sodium carbonate (Na2CO3), sodium dodecyl sulfonate (SDSN), chloroauric acid hydrated (HAuCl4·4H2O) and ammonia were purchased from Tianjin Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 Au/ZnO NW-based sensor for the detection of hazardous and carcinogenic benzene or Page of 34 Physical Chemistry Chemical Physics View Article Online DOI: 10.1039/C3CP52392F Guangfu Fine Chemical Research Institute and used as received without further 2.2 Preparation of Au/ZnO NWs This includes a two-stage solution process First, the fabrication process of ZnO NWs was described elsewhere31 but with some modifications, which is presented in the ESI†, the section of “Preparation of ZnO NWs” Secondly, Au/ZnO NWs were synthesized by adding 0.04 g of the prepared ZnO NWs into 10 mL of deionized water under stirring and then ultrasonic treated for 10 min, then 0.812 mL of 0.01 mol/L HAuCl4 aqueous solution was introduced into the system, followed by adding the diluted ammonia solution till the pH reached After stirring for 0.5 h, the precipitate was centrifuged and washed alternately with deionized water and ethanol till the pH was 7, and then dried at 80 oC overnight 2.3 Characterization The crystalline structure of the product was characterized by powder X-ray diffraction (XRD, Rigaku D/max-2500, Cu Kα, λ=1.5418 Å) The morphology and composition of the samples were characterized by field emission scanning electron microscope (FESEM, JEOL-JSM7500, 30 KV), Transmission electron microscope (TEM, Philips FEI Tecnai 20ST, 200 KV) and energy dispersive X-ray spectroscopy (EDS) 2.4 Gas sensor fabrication and test The detailed fabrication of the gas sensor and processes of gas tests can be seen in our previous works,11-13,24,25,32 which are shown in the ESI†, the section of “Gas sensor fabrication and test” (inserted with Fig S1) The sensor response is defined as the Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 purification Distilled water and absolute ethanol was used throughout the experiment Physical Chemistry Chemical Physics Page of 34 View Article Online DOI: 10.1039/C3CP52392F ratio Ra/Rg, where Ra and Rg are the electrical resistance of the sensor in air and in the interval over which resistance attain a fixed percentage (90%) of final value when sensor is exposed to specific concentration of the gas The recovery time is defined as the time interval over which sensor resistance reduces to 10% of the saturation value when the sensor is exposed to specific gas concentration and then is exposed to clean air Results and discussion 3.1 Characterization The crystal phase of the pristine ZnO NWs and Au/ZnO NWs was characterized by XRD Fig 1a shows the XRD patterns of the pristine ZnO NWs and Au/ZnO NWs, and it is clear that the main reflection peaks in the pattern are in well agreement with the standard data of wurtzite structure of ZnO (JCPDS: 36-1451) with lattice parameters a=3.25 Å and c=5.207Å.25 But in the XRD pattern of Au/ZnO NWs, apart from the characteristic reflection peaks from ZnO, two weak reflection peaks at 2θ=38.2° and 64.6° are currently indistinguishable from the signal noise, which may also be caused by the low content of Au crystals or the small crystal sizes After zooming the two sections (2θ from 35° to 39°, and from 62° to 66°) in a larger scale shown in Fig 1b and c, the two weak peaks can be clearly observed, which can be respectively ascribed to Au (111) and Au (220) planes of face-centered cubic (fcc) Au (JCPDS: 04-0784), respectively This well confirms the presence of Au species Fig Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 tested reductive gas, respectively.13,16,24,29 The response time is defined as the time Page of 34 Physical Chemistry Chemical Physics View Article Online DOI: 10.1039/C3CP52392F shows the low-magnification (a) and high-magnification (b) FESEM images of the composed of wire-like nanostructures The length of ZnO NWs is up to 16 µm and the diameter is about 50–120 nm, and the smooth surface of the ZnO NWs can also be seen from the magnified image in Fig 2b Further structural characterizations of the samples were performed by TEM analysis Fig 3a and b clearly show the details of an individual wire-like ZnO nanostructure with smooth surface Fig 3c displays the HRTEM image from a certain ZnO nanowire, where the crystal lattice fringes are clearly observed and average distance between the adjacent lattice planes is 0.26 nm, corresponding to the (0002) plane lattice distance of hexagonal-structured ZnO, which proves that the prepared ZnO NWs grew along [0001] direction The TEM images with different magnification of the Au/ZnO NWs are shown in Fig 3d and e, and from the images, a high density of Au NPs with small sizes can be seen clearly and uniformly anchored on the surface of ZnO NW, because they present as the small black dots contrast against the support But the irrelevant existence of some individual large Au bulks marked by white arrows in Fig 3d and e is probably due to the aggregation of some small Au NPs that act as initial seeds.19 Supportingly, Fig 3f displays the size distribution histogram for the ca 55 Au NPs in Fig 3e, revealing a particle size range mainly between 2-10 nm with an average particle size of around nm, and such fine size and high disperse of Au NPs might interpret why the diffraction peaks of Au NPs are weak in the XRD pattern (Fig 1a) EDS analysis (shown in the ESI†, Fig S2) was carried out from Fig Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 as-synthesized pristine ZnO products, which indicates that the samples were Physical Chemistry Chemical Physics Page 20 of 34 View Article Online DOI: 10.1039/C3CP52392F Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 21 A Kolmakov, D O Klenov, Y Lilach, S Stemmer and M Moskovits, Nano Lett., 2005, 5, 667–673 22 G Y Chai, O Lupan, E V Rusu, G I Stratan, V V Ursaki, V Sontea, H Khallaf and L Chow, Sens Actuators A, 2012, 176, 64–71 23 L Liao, H X Mai, Q Yuan, H B Lu, J C Li, C Liu, C H Yan, Z X Shen and T Yu, J Phys Chem C, 2008, 112, 9061–9065 24 X H Liu, J Zhang, L W Wang, T L Yang, X Z Guo, S H Wu and S R Wang, J Mater Chem., 2011, 21, 349–356 25 J Zhang, X H Liu, S H Wu, B Q Cao and S H Zheng, Sens Actuators B, 2012, 169, 61–66 26 H J Wu, L D Wang, J Q Zhang, Z Y Shen and J H Zhao, Catal Comm., 2011, 12, 859–865 27 P Rai, Y Kim, H Song, M Song and Y Yu, Sens Actuators B, 2012, 165, 133–142 28 Y H Li, J Gong, G H He and Y L Deng, Mater Chem Phys., 2012, 134, 1172–1178 29 C C Li, L M Li, Z F Du, H C Yu, Y Y Xiang, Y Li, Y Cai and T H Wang, Nanotechnology, 2008, 19, 035501 20 Physical Chemistry Chemical Physics Accepted Manuscript Zhang, J Phys Chem C, 2011, 115, 5352–5357 Page 21 of 34 Physical Chemistry Chemical Physics View Article Online DOI: 10.1039/C3CP52392F 30 X H Liu, J Zhang, X Z Guo, S H Wu and S R Wang, Nanoscale, 2010, 2, 31 H M Hu, X H Huang, C H Deng, X Y Chen and Y T Qian, Mater Chem Phys., 2007, 106, 58–62 32 J Zhang, X H Liu, S H Wu, M J Xu, X Z Guo and S R Wang, J Mater Chem., 2010, 20, 6453–6459 33 A Degen and M Kosec, J Eur Ceram Soc., 2000, 20, 667–673 34 W J Li, E W Shi, W Z Zhong and Z W Yin, J Cryst Growth, 1999, 203, 186–196 35 S Ivanova, C Petit, V Pitchon, Appl Catal A, 2004, 267, 191–201 36 M Meng, Y Q Zha, J Y Luo, T D Hu, Y N Xie, T Liu and J Zhang, Appl Catal A, 2006, 301, 145–151 37 J Wollenstein, H Bottner, M Jaegle, W J Becker and E Wagner, Sens Actuators B, 2000, 70, 196–202 38 K Yu, Z C Wu, Q R Zhao, B X Li and Y Xie, J Phys Chem C, 2008, 112, 2244-2247 39 J Li and H C Zeng, Chem Mater., 2006, 18, 4270–4277 40 V Srivastava and K Jain, Sens Actuators B, 2008, 133, 46–52 41 S J Teichner, Appl Catal., 1990, 62, 1–10 21 Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 1178–1184 Physical Chemistry Chemical Physics Page 22 of 34 View Article Online DOI: 10.1039/C3CP52392F 42 M C Kung, R J Davis and H H Kung, J Phys Chem C, 2007, 111, 43 J Zhang, X H Liu, L W Wang, T L Yang, X Z Guo, S H Wu, S R Wang and S M Zhang, Nanotechnology, 2011, 22, 185501 44 B L Zhu, C S Xie, J Wu, D W Zeng, A H Wang and X Z Zhao, Mater Chem Phys., 2006, 96, 459–465 45 B L Zhu, C S Xie, D W Zeng, W L Song and A H Wang, Mater Chem Phys., 2005, 89, 148–153 46 Y Zeng, T Zhang, L J Wang, M H Kang, H T Fan, R Wang and Y He, Sens Actuators B, 2009, 140, 73–78 47 A Gurlo, Chem Phys Chem., 2006, 7, 2041–2052 48 N Barsan and U Weimar, J Electroceram., 2001, 7, 143–167 49 Y Zhang, Q Xiang, J Q Xu, P C Xu, Q Y Pan and F Li, J Mater Chem., 2009, 19, 4701–4706 22 Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 11767–11775 Page 23 of 34 Physical Chemistry Chemical Physics View Article Online DOI: 10.1039/C3CP52392F Table Response and recovery times of the Au/ZnO NWs sensor to toluene and Test gases Gas concentration (ppm) Response time (s) Recovery time (s) toluene toluene toluene toluene toluene toluene toluene benzene benzene benzene benzene benzene benzene benzene 10 50 100 200 500 10 50 100 200 500 60 52 50 45 36 34 32 80 77 70 68 64 56 49 10 30 35 39 45 52 57 11 22 27 29 43 51 55 23 Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 benzene via 1–500 ppm at 340 oC Physical Chemistry Chemical Physics Page 24 of 34 View Article Online DOI: 10.1039/C3CP52392F Figure Captions magnified patterns of 2θ from 35° to 39° (b) and from 62° to 66° (c) on Au/ZnO NWs Fig FESEM of low-magnification (a) and high-magnification (b) images of the pristine ZnO NWs Fig TEM images (a, b) and HRTEM image (c) of the pristine ZnO NWs, TEM images (d, e) with different magnification of the Au/ZnO NWs, and size distribution histogram (f) for Au NPs in (e) Fig The illustration of the process to fabricate Au/ZnO NWs hybrid Fig Dynamic sensing response–recovery curves of the sensors to different concentrations of toluene (a) and benzene (b) at the working temperature of 340 oC Fig Gas responses of the sensors to different concentrations of toluene (a) and benzene (b) corresponding to Fig Fig Gas responses of Au/ZnO NWs sensor to different concentrations of toluene in the range of 1–100 ppm Fig Gas responses of the sensors to 10 ppm different tested gases at 340 °C Fig The Long Term Stability of Au/ZnO NW sensor to ppm toluene after months at 340 °C Fig 10 Schematic illustration for the sensing mechanism of the Au/ZnO NW sensor 24 Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 Fig XRD patterns of the pristine ZnO NWs and Au/ZnO NWs (a) and the Page 25 of 34 Physical Chemistry Chemical Physics View Article Online (101) DOI: 10.1039/C3CP52392F 50 60 70 80 2θ (degree) c 35 35.5 36 36.5 37 37.5 38 38.5 39 Au(220) Au (111) Intensity (a.u.) b 62 62.5 2θ (degree) 63 63.5 64 64.5 65 65.5 66 2θ (degree) Fig XRD patterns of the pristine ZnO NWs and Au/ZnO NWs (a) and the magnified patterns of 2θ from 35° to 39° (b) and from 62° to 66° (c) on Au/ZnO NWs 25 Physical Chemistry Chemical Physics Accepted Manuscript 40 (202) (103) (200) (102) (112) (201) (004) (110) (100) ZnO Au-ZnO (002) Intensity (a.u.) 30 Intensity (a.u.) Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 a Physical Chemistry Chemical Physics Page 26 of 34 View Article Online DOI: 10.1039/C3CP52392F b μm 100 nm Fig FESEM of low-magnification (a) and high-magnification (b) images of the pristine ZnO NWs 26 Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 a Page 27 of 34 Physical Chemistry Chemical Physics View Article Online b d e c f 100 nm 20 nm 2 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 Particle size (nm) Fig TEM images (a, b) and HRTEM image (c) of the pristine ZnO NWs, TEM images (d, e) with different magnification of the Au/ZnO NWs, and size distribution histogram (f) for Au NPs in (e) 27 Physical Chemistry Chemical Physics Accepted Manuscript a Counts Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 DOI: 10.1039/C3CP52392F Physical Chemistry Chemical Physics Page 28 of 34 View Article Online DOI: 10.1039/C3CP52392F SDSN stirring Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 treatment Zn(OH)2 Zn(NO3)2٠6H2O + Na2CO3 + SDSN ZnO NWs Au stirring ZnONWs HAuCl4 +ammonia pH=9 Fig The illustration of the process to fabricate Au/ZnO NWs hybrid 28 Physical Chemistry Chemical Physics Accepted Manuscript hydrothermal Page 29 of 34 Physical Chemistry Chemical Physics View Article Online DOI: 10.1039/C3CP52392F (b) Pristine ZnO 200 ppm Au-ZnO 100 ppm 50 ppm 1.8 1.6 Voltage (V) Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 1.4 ppm 500 ppm 10 ppm gas out 1.2 1.0 gas in 0.8 ppm 0.6 1.4 2000 gas in ppm 0.6 0.0 1500 10 ppm 0.8 0.2 1000 gas out ppm 0.4 500 500 ppm 200 ppm 1.0 0.2 0.0 100 ppm 50 ppm 1.2 0.4 Pristine ZnO Au-ZnO 1.6 Voltage (V) 2.0 1.8 500 1000 1500 2000 Time (s) Time (s) Fig Dynamic sensing response–recovery curves of the sensors to different concentrations of toluene (a) and benzene (b) at the working temperature of 340 oC 29 Physical Chemistry Chemical Physics Accepted Manuscript (a) Physical Chemistry Chemical Physics Page 30 of 34 View Article Online DOI: 10.1039/C3CP52392F (a) (b) 10 Au-ZnO Au-ZnO ZnO Response Response Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 6 ZnO 3 2 1 100 200 300 400 500 Concentration (ppm) 100 200 300 400 500 Concentration (ppm) Fig Gas responses of the sensors to different concentrations of toluene (a) and benzene (b) corresponding to Fig 30 Physical Chemistry Chemical Physics Accepted Manuscript Page 31 of 34 Physical Chemistry Chemical Physics View Article Online DOI: 10.1039/C3CP52392F Au-ZnO Response Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 1 10 30 50 70 100 Concentration (ppm) Fig Gas responses of Au/ZnO NWs sensor to different concentrations of toluene in the range of 1–100 ppm 31 Physical Chemistry Chemical Physics Accepted Manuscript Physical Chemistry Chemical Physics Page 32 of 34 View Article Online DOI: 10.1039/C3CP52392F Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 benzene acetone chlorobenzene formaldehyde Au-ZnO Pristine ZnO chloroform ether ammonia Response Fig Gas responses of the sensors to 10 ppm different tested gases at 340 °C 32 Physical Chemistry Chemical Physics Accepted Manuscript toluene Page 33 of 34 Physical Chemistry Chemical Physics View Article Online Fig The Long Term Stability of Au/ZnO NW sensor to ppm toluene after months at 340 °C 33 Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 DOI: 10.1039/C3CP52392F Physical Chemistry Chemical Physics Page 34 of 34 View Article Online Fig 10 Schematic illustration for the sensing mechanism of the Au/ZnO NW sensor 34 Physical Chemistry Chemical Physics Accepted Manuscript Published on 19 August 2013 Downloaded by Lomonosov Moscow State University on 26/08/2013 15:19:28 DOI: 10.1039/C3CP52392F ... benzene and toluene† Liwei Wang ,a Shurong Wang* ,a Mijuan Xu,ab Xiaojing Hu ,a Hongxin Zhang ,a Yanshuang Wanga and Weiping Huanga a Tianjin Key Lab of Metal and Molecule-based Material Chemistry, Department... Response and recovery times are very important parameters for gas sensor application A small value of response time means a good sensor and a small recovery time means that the sensor can be used... sensing performance of 10 ppm other gases (acetone, chlorobenzene, formaldehyde, chloroform, ether and ammonia) were also measured, and the results are summarized along with benzene and toluene and