Miniaturized gas sensors or electronic noses to rapidly detect and differentiate trace amount of chemical agents are extremely attractive. In this paper, we report on the fabrication and characterization of a functional tin oxide nanoparticle gas sensor. Tin oxide nanoparticles are first synthesized using a convenient and low-cost mini-arc plasma source. The nanoparticle size distribution is measured online using a scanning electrical mobility spectrometer (SEMS). The product nanoparticles are analyzed ex-situ by high resolution transmission electron microscopy (HRTEM) for morphology and defects, energy dispersive X-ray (EDX) spectroscopy for elemental composition, electron diffraction for crystal structure, and X-ray photoelectron spectroscopy (XPS) for surface composition. Nonagglomerated rutile tin oxide (<mml:math id="E1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>SnO</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>) nanoparticles as small as a few nm have been produced. Larger particles bear a core-shell structure with a metallic core and an oxide shell. The nanoparticles are then assembled onto an e-beam lithographically patterned interdigitated electrode using electrostatic force to fabricate the gas sensor. The nanoparticle sensor exhibits a fast response and a good sensitivity when exposed to 100 ppm ethanol vapor in air.

Ganhua Lu

Kyle L. Huebner

Leonidas E. Ocola

Marija Gajdardziska-Josifovska

Junhong Chen

Gas Sensors Based on Tin Oxide Nanoparticles Synthesized from a Mini-Arc Plasma Source

A new coprecipitation/hydrolysis synthesis route is used to create a <mml:math id="E2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>TiO</mml:mtext></mml:mrow><mml:mtext>2</mml:mtext></mml:msub><mml:msub><mml:mrow><mml:mtext>-ZnFe</mml:mtext></mml:mrow><mml:mtext>2</mml:mtext></mml:msub><mml:msub><mml:mtext>O</mml:mtext><mml:mtext>4</mml:mtext></mml:msub></mml:mrow></mml:math> nanocomposite that is directed towards extending the photoresponse of <mml:math id="E3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>TiO</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> from UV to visible wavelengths (<mml:math id="E4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>&gt;</mml:mo><mml:mn>400</mml:mn><mml:mtext> </mml:mtext><mml:mtext>nm</mml:mtext></mml:mrow></mml:math>). The effect of <mml:math id="E5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>TiO</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>'s accelerated anatase-rutile phase transformation due to the presence of the coupled <mml:math id="E6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>ZnFe</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mtext>O</mml:mtext><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math> narrow-bandgap semiconductor is evaluated. The transformation's dependence on pH, calcinations temperature, particle size, and <mml:math id="E7" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>ZnFe</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mtext>O</mml:mtext><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math> concentration has been analyzed using XRD, SEM, and UV-visible spectrometry. The requirements for retaining the highly photoactive anatase phase present in a <mml:math id="E8" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>ZnFe</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mtext>O</mml:mtext><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math> nanocomposite are outlined. The visible-light-activated photocatalytic activity of the <mml:math id="E9" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>TiO</mml:mtext></mml:mrow><mml:mtext>2</mml:mtext></mml:msub><mml:msub><mml:mrow><mml:mtext>-ZnFe</mml:mtext></mml:mrow><mml:mtext>2</mml:mtext></mml:msub><mml:msub><mml:mtext>O</mml:mtext><mml:mtext>4</mml:mtext></mml:msub></mml:mrow></mml:math> nanocomposites has been compared to an Aldrich <mml:math id="E10" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>TiO</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> reference catalyst, using a solar-simulated photoreactor for the degradation of phenol.

Sesha S. Srinivasan

Jeremy Wade

Elias K. Stefanakos

Synthesis and Characterization of Photocatalytic <svg style="vertical-align:-3.27605pt" height="15.675" version="1.1" viewBox="0 0 99.612503 15.675" width="99.612503" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"><g transform="matrix(.017,-0,0,-.017,.062,11.537)"><path id="x54" d="M592 498l-30 -3q-13 63 -31 89q-13 19 -33.5 25.5t-75.5 6.5h-70v-493q0 -60 16 -75.5t86 -19.5v-28h-286v28q68 4 83.5 19.5t15.5 75.5v493h-62q-60 0 -83 -7t-33 -24q-12 -17 -32 -90h-29q10 116 12 180h20q10 -16 21 -20.5t34 -4.5h395q19 0 28.5 5t21.5 20h21&#xA;q2 -89 11 -177z" /></g><g transform="matrix(.017,-0,0,-.017,8.868,11.537)"><path id="x69" d="M135 536q-20 0 -35 15.5t-15 35.5q0 22 15 37t36 15t35.5 -15t14.5 -37q0 -21 -15 -36t-36 -15zM252 0h-220v26q48 5 59 17t11 63v206q0 47 -9 58t-54 18v24q78 12 142 39v-345q0 -51 11.5 -63t59.5 -17v-26z" /></g><g transform="matrix(.017,-0,0,-.017,13.424,11.537)"><path id="x4F" d="M381 665q131 0 226.5 -93t95.5 -239q0 -158 -96 -253t-238 -95q-137 0 -231 95t-94 238q0 142 92.5 244.5t244.5 102.5zM359 629q-89 0 -151 -74.5t-62 -208.5q0 -141 69 -233t175 -92q90 0 150.5 74t60.5 211q0 152 -69 237.5t-173 85.5z" /></g><g transform="matrix(.012,-0,0,-.012,26.125,15.613)"><path id="x32" d="M412 140l28 -9q0 -2 -35 -131h-373v23q112 112 161 170q59 70 92 127t33 115q0 63 -31 98t-86 35q-75 0 -137 -93l-22 20l57 81q55 59 135 59q69 0 118.5 -46.5t49.5 -122.5q0 -62 -29.5 -114t-102.5 -130l-141 -149h186q42 0 58.5 10.5t38.5 56.5z" /></g><g transform="matrix(.017,-0,0,-.017,32.45,11.537)"><path id="x2D" d="M300 253l-14 -55h-229l14 55h229z" /></g><g transform="matrix(.017,-0,0,-.017,38.502,11.537)"><path id="x5A" d="M561 176l29 -6q-25 -130 -36 -170h-517l-8 15l420 599h-173q-77 0 -102 -7t-39 -29q-19 -29 -35 -87l-29 1q9 111 12 183h24q9 -16 19 -20.5t34 -4.5h399l7 -14l-413 -594q48 -6 163 -6q94 0 131.5 7.5t58.5 29.5q28 29 55 103z" /></g><g transform="matrix(.017,-0,0,-.017,48.99,11.537)"><path id="x6E" d="M524 0h-209v26q44 5 55 18t11 65v167q0 114 -91 114q-50 0 -109 -51v-235q0 -50 10 -61.5t55 -16.5v-26h-217v26q51 5 62 17t11 61v206q0 47 -9.5 58.5t-50.5 19.5v23q82 15 139 40v-79l67 47q47 30 83 30q60 0 94.5 -40t34.5 -112v-193q0 -50 10 -61.5t54 -16.5v-26z&#xA;" /></g><g transform="matrix(.017,-0,0,-.017,58.288,11.537)"><path id="x46" d="M493 503l-29 -4q-13 56 -28 80q-13 22 -35.5 29.5t-78.5 7.5h-76q-22 0 -27.5 -5t-5.5 -27v-238h103q66 0 82.5 12t25.5 62h29v-193h-29q-9 54 -25.5 67t-82.5 13h-103v-181q0 -64 15 -78.5t84 -19.5v-28h-272v28q61 5 74.5 19.5t13.5 78.5v399q0 64 -13 78t-72 19v28&#xA;h440q1 -40 10 -147z" /></g><g transform="matrix(.017,-0,0,-.017,66.974,11.537)"><path id="x65" d="M380 106l15 -22q-42 -52 -87 -74t-76 -22q-89 0 -142 62t-53 151q0 103 66 175q67 73 146 73h1q61 0 105.5 -46.5t44.5 -105.5q0 -16 -4.5 -22.5t-18.5 -9.5q-54 -10 -262 -17q1 -95 46 -143.5t104 -48.5q61 0 115 50zM225 412q-35 0 -64.5 -32.5t-40.5 -90.5q83 0 170 3&#xA;q14 0 19 4.5t5 15.5q1 41 -23.5 70.5t-65.5 29.5z" /></g><g transform="matrix(.012,-0,0,-.012,74.188,15.613)"><use xlink:href="#x32"/></g><g transform="matrix(.017,-0,0,-.017,80.525,11.537)"><use xlink:href="#x4F"/></g><g transform="matrix(.012,-0,0,-.012,93.225,15.613)"><path id="x34" d="M456 178h-96v-72q0 -51 12.5 -62.5t72.5 -16.5v-27h-256v27q65 5 78 17t13 62v72h-260v28q182 271 300 426h40v-407h96v-47zM280 225v295h-2q-107 -148 -196 -295h198z" /></g></svg> Nanoparticles

A method for the calculation of fractal surfaces of
crystals is presented. The fractal dimension <mml:math id="E1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>D</mml:mi></mml:math> of
fragments of zeolites is calculated. Results compare well with
reference calculations (GEPOL). The active site of Brønsted
acid zeolites is modeled by a set of
Al–OH–Si units. These units form
2–12-membered rings. Topological indices for the different
active-site models are calculated. The comparison between GEPOL
and SURMO2 allows calculating the active-site indices. Most
cavities show no fractal character, while for the 6–8-unit
rings, <mml:math id="E2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>D</mml:mi></mml:math> lies in the range 4.0–4.3. The 6-ring shows the
greatest <mml:math id="E3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>D</mml:mi></mml:math> and is expected to be the most reactive.

Francisco Torrens

Gloria Castellano

Fractal Dimension of Active-Site Models of Zeolite Catalysts

We present a simple and highly reproductive method
for the preparation of thin films consisting of strontium titanate
nanoparticles. The films are produced by spin coating of a sol on
silicon targets and subsequent annealing under ambient conditions.
Analysis by atomic force microscopy shows particles with typical
sizes between 10 nm and 50 nm. X-ray photoelectron
spectroscopy displays a stoichiometry of the films as anticipated
from preliminary experiments with strontium titanate single
crystals. Metastable-induced electron spectroscopy and ultraviolet
photoelectron spectroscopy are used as tools to give evidence to
the similar electronic properties of nanoparticle film and single
crystal. These results support the prospect for an application of
the nanoparticle films as high temperature oxygen sensor with
superior properties.

Florian Voigts

Tanja Damjanovic

Günter Borchardt

Christos Argirusis

Wolfgang Maus-Friedrichs

Synthesis and Characterization of Strontium Titanate Nanoparticles as Potential High Temperature Oxygen Sensor Material

Atomic layer deposition (<mml:math id="E1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>ALD</mml:mtext></mml:mrow></mml:math>) is ideal for applying precise and
conformal coatings over nanoporous materials. We have recently
used <mml:math id="E2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>ALD</mml:mtext></mml:mrow></mml:math> to coat two nanoporous solids: anodic aluminum oxide
(<mml:math id="E3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>AAO</mml:mtext></mml:mrow></mml:math>) and silica aerogels. <mml:math id="E4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>AAO</mml:mtext></mml:mrow></mml:math> possesses hexagonally ordered
pores with diameters <mml:math id="E5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>d</mml:mi><mml:mo>∼</mml:mo><mml:mn>40</mml:mn></mml:math> nm and pore length <mml:math id="E6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>L</mml:mi><mml:mo>∼</mml:mo><mml:mn>70</mml:mn></mml:math>
microns. The <mml:math id="E7" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>AAO</mml:mtext></mml:mrow></mml:math> membranes were coated by <mml:math id="E8" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>ALD</mml:mtext></mml:mrow></mml:math> to fabricate catalytic membranes that demonstrate remarkable selectivity in the
oxidative dehydrogenation of cyclohexane. Additional <mml:math id="E9" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>AAO</mml:mtext></mml:mrow></mml:math>
membranes coated with <mml:math id="E10" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>ALD</mml:mtext></mml:mrow></mml:math> Pd films show promise as hydrogen
sensors. Silica aerogels have the lowest density and highest
surface area of any solid material. Consequently, these materials
serve as an excellent substrate to fabricate novel catalytic
materials and gas sensors by <mml:math id="E11" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>ALD</mml:mtext></mml:mrow></mml:math>.

Jeffrey W. Elam

Guang Xiong

Catherine Y. Han

H. Hau Wang

James P. Birrell

Ulrich Welp

John N. Hryn

Michael J. Pellin

Theodore F. Baumann

John F. Poco

Joe H. Satcher

Atomic Layer Deposition for the Conformal Coating of Nanoporous Materials

A method to prepare monodispersed silica nanospheres as templates
for fabrication of nickel-silica composite hollow spheres is
presented. The structures for both silica nanospheres and
nickel-silica composite hollow spheres were characterized by X-ray
diffraction (XRD), transmission electron microscopy (TEM), and
scanning electron microscopy (SEM). The catalytic activity for
acetone hydrogenation on nickel-silica composite hollow spheres
was evaluated, and high conversion efficiency of 70% with good
selectivity of 82.7% to 2-propanol was observed. The mechanism
of high catalytic activity and good selectivity in acetone
hydrogenation reaction was discussed.

Kaifu Zhong

Pu Jin

Qianwang Chen

Ni Hollow Nanospheres: Preparation and Catalytic Activity

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Chief Editor Stefano Bellucci is Professor of Theoretical Physics at the National Institute for Nuclear Physics in Frascati, Italy. His research interests include&nbsp;nanoscience and nanotechnology, nanocarbon-based composites, and the biomedical applications of nanomaterials.

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