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Nanomaterials
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Nanomaterials, Volume 3, Issue 3 (September 2013) – 13 articles , Pages 317-571

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535 KiB  
Communication
Hydrothermal Synthesis of Nanoclusters of ZnS Comprised on Nanowires
by Zafar Hussain Ibupoto, Kimleang Khun, Xianjie Liu and Magnus Willander
Nanomaterials 2013, 3(3), 564-571; https://doi.org/10.3390/nano3030564 - 9 Sep 2013
Cited by 30 | Viewed by 9845
Abstract
Cetyltrimethyl ammonium bromide cationic (CTAB) surfactant was used as template for the synthesis of nanoclusters of ZnS composed of nanowires, by hydrothermal method. The structural and morphological studies were performed by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission [...] Read more.
Cetyltrimethyl ammonium bromide cationic (CTAB) surfactant was used as template for the synthesis of nanoclusters of ZnS composed of nanowires, by hydrothermal method. The structural and morphological studies were performed by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) techniques. The synthesized ZnS nanoclusters are composed of nanowires and high yield on the substrate was observed. The ZnS nanocrystalline consists of hexagonal phase and polycrystalline in nature. The chemical composition of ZnS nanoclusters composed of nanowires was studied by X-ray photo electron microscopy (XPS). This investigation has shown that the ZnS nanoclusters are composed of Zn and S atoms. Full article
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Figure 1
<p>X-ray diffraction (XRD) of ZnS nanoclusters comprised on nanowires.</p> Full article ">Figure 2
<p>Scanning electron microscopy (SEM) images of ZnS nanomaterial: (<b>a</b>) low magnification, (<b>b</b>) high magnification, (<b>c</b>) effect of higher concentration of cetyltrimethyl ammonium bromide cationic (CTAB).</p> Full article ">Figure 3
<p>The transmission electron microscopy (TEM) study of ZnS nanoclusters: (<b>a</b>) TEM, (<b>b</b>) high resolution transmission electron microscopy (HRTEM), (<b>c</b>) selected area electron diffraction (SAED).</p> Full article ">Figure 4
<p>The XPS analysis of ZnS nanostructures (<b>a</b>) Core shell scan XPS spectrum of sample, (<b>b</b>) Zn2p XPS spectrum, (<b>c</b>) S2p XPS spectrum.</p> Full article ">
1054 KiB  
Article
Influence of Nanoclay Dispersion Methods on the Mechanical Behavior of E-Glass/Epoxy Nanocomposites
by Victor A. Agubra, Peter S. Owuor and Mahesh V. Hosur
Nanomaterials 2013, 3(3), 550-563; https://doi.org/10.3390/nano3030550 - 28 Aug 2013
Cited by 83 | Viewed by 9674
Abstract
Common dispersion methods such as ultrasonic sonication, planetary centrifugal mixing and magnetic dispersion have been used extensively to achieve moderate exfoliation of nanoparticles in polymer matrix. In this study, the effect of adding three roll milling to these three dispersion methods for nanoclay [...] Read more.
Common dispersion methods such as ultrasonic sonication, planetary centrifugal mixing and magnetic dispersion have been used extensively to achieve moderate exfoliation of nanoparticles in polymer matrix. In this study, the effect of adding three roll milling to these three dispersion methods for nanoclay dispersion into epoxy matrix was investigated. A combination of each of these mixing methods with three roll milling showed varying results relative to the unmodified polymer laminate. A significant exfoliation of the nanoparticles in the polymer structure was obtained by dispersing the nanoclay combining three roll milling to magnetic and planetary centrifugal mixing methods. This exfoliation promoted a stronger interfacial bond between the matrix and the fiber, which increased the final properties of the E-glass/epoxy nanocomposite. However, a combination of ultrasound sonication and three roll milling on the other hand, resulted in poor clay exfoliation; the sonication process degraded the polymer network, which adversely affected the nanocomposite final properties relative to the unmodified E-glass/epoxy polymer. Full article
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Figure 1
<p>Transmission electron microscopy (TEM) micrographs of dispersied nanoclay particles for (<b>a</b>) 2 wt.% magnetic + 3 roll milling; (<b>b</b>) 3 wt.% magnetic + 3 roll milling; (<b>c</b>) 3 wt.% sonication + 3 roll milling.</p> Full article ">Figure 2
<p>X-ray diffraction for pristine nanoclay, neat epoxy and nanocomposite polymer of 2 wt.% for sonication and magnetic mixing methods.</p> Full article ">Figure 3
<p>X-ray diffraction for pristine nanoclay, neat epoxy and nanocomposite polymer of 3 wt.% for sonication and magnetic mixing methods.</p> Full article ">Figure 4
<p>SEM micrographs of factured surface for the nanocomposite laminates (<b>a</b>) Neat E-glass/epoxy; (<b>b</b>) 2 wt.% magnetic + 3 roll milling; (<b>c</b>) 3 wt.% Sonication + 3 roll milling.</p> Full article ">Figure 5
<p>Three roll Milling process [<a href="#B5-nanomaterials-03-00550" class="html-bibr">5</a>].</p> Full article ">
5655 KiB  
Review
Current Trends in Sensors Based on Conducting Polymer Nanomaterials
by Hyeonseok Yoon
Nanomaterials 2013, 3(3), 524-549; https://doi.org/10.3390/nano3030524 - 27 Aug 2013
Cited by 272 | Viewed by 15782
Abstract
Conducting polymers represent an important class of functional organic materials for next-generation electronic and optical devices. Advances in nanotechnology allow for the fabrication of various conducting polymer nanomaterials through synthesis methods such as solid-phase template synthesis, molecular template synthesis, and template-free synthesis. Nanostructured [...] Read more.
Conducting polymers represent an important class of functional organic materials for next-generation electronic and optical devices. Advances in nanotechnology allow for the fabrication of various conducting polymer nanomaterials through synthesis methods such as solid-phase template synthesis, molecular template synthesis, and template-free synthesis. Nanostructured conducting polymers featuring high surface area, small dimensions, and unique physical properties have been widely used to build various sensor devices. Many remarkable examples have been reported over the past decade. The enhanced sensitivity of conducting polymer nanomaterials toward various chemical/biological species and external stimuli has made them ideal candidates for incorporation into the design of sensors. However, the selectivity and stability still leave room for improvement. Full article
(This article belongs to the Special Issue Nanomaterials in Sensors)
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Graphical abstract
Full article ">Figure 1
<p>Multidimensional poly(3,4-ethylenedioxythiophene) (PEDOT) nanostructures with unique surface substructures. (<b>a</b>–<b>h</b>) The poly(methyl methacrylate) (PMMA) nanofibers function as a template and substrate for the growth of PEDOT under different synthetic conditions (temperature and pressure). The morphologies of the resulting nanomaterials were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) (right top inset images): PMMA nanofibers (<b>a</b>) before and (<b>b</b>) after ferric ion adsorption; PMMA/PEDOT nanofibers with smooth layer surface (<b>c</b>) before and (<b>d</b>) after core etching; PMMA/PEDOT nanofibers with nanorod surface (<b>e</b>) before and (<b>f</b>) after core etching; PMMA/ PEDOT nanofibers with nanonodule surface (<b>g</b>) before and (<b>h</b>) after core etching. With permission from [<a href="#B33-nanomaterials-03-00524" class="html-bibr">33</a>]; Copyright 2012, American Chemical Society.</p> Full article ">Figure 2
<p>(<b>a</b>) Schematic illustration of the preparation of PPy nanoparticles in a cationic surfactant (DTAB)/co-surfactant (decanol) emulsion system; (<b>b</b>) TEM image of monodisperse PPy nanoparticles prepared through micelle templating (inset: photograph showing a Petri dish containing 12 g of PPy nanoparticles obtained in a single polymerization reaction). With permission from [<a href="#B13-nanomaterials-03-00524" class="html-bibr">13</a>]; Copyright 2005, Wiley-VCH Verlag GmbH &amp; Co. KGaA.</p> Full article ">Figure 3
<p>Schematic illustration of the formation of PPy nanoparticles in an aqueous dispersion of water-soluble polymer (PVA)/metal cation (ferric ion) complexes, and SEM images of the resulting nanoparticles. (<b>a</b>) Hydroxyl groups of PVA chains coordinate with ferric ions by an ion-dipole interaction in an aqueous medium; (<b>b</b>) The ferric ions act as the oxidizing agent for chemical oxidation of pyrrole monomers. After polymerization, the resulting PPy nanoparticles are stabilized by PVA chains; (<b>c</b>) Tilted and cross-section SEM images of the PPy nanoparticles stacked on a substrate (scale bar: 100 nm). With permission from [<a href="#B34-nanomaterials-03-00524" class="html-bibr">34</a>]; Copyright 2010, Wiley-VCH Verlag GmbH &amp; Co. KGaA.</p> Full article ">Figure 4
<p>Partial ternary phase diagram for the hexane/AOT/aqueous FeCl<sub>3</sub> solution system determined at 15 °C. The molar concentration of the aqueous FeCl<sub>3</sub> solution was 16.2 M. The marked area corresponds to the AOT reverse cylindrical micelle phase region. With permission from [<a href="#B22-nanomaterials-03-00524" class="html-bibr">22</a>]; Copyright 2005, American Chemical Society.</p> Full article ">Figure 5
<p>Schematic illustration of the formation mechanism of Ag-PPy nanoparticles: the reaction process could be divided into three stages (I, II, and III). Right bottom: the scheme describing the chemical reaction between pyrrole and silver cation. With permission from [<a href="#B47-nanomaterials-03-00524" class="html-bibr">47</a>]; Copyright 2012, American Chemical Society.</p> Full article ">Figure 6
<p>(<b>a</b>) Photograph of a developed gas sensor electrode. SEM images of PPy nanowires deposited on the electrode substrate: (<b>b</b>) 65° tilted view (scale bar = 1 μm) and (<b>c</b>) top view showing PPy nanowires bridging the insulating gap between the gold electrodes (scale bar = 10 μm). With permission from [<a href="#B52-nanomaterials-03-00524" class="html-bibr">52</a>]; Copyright 2012, American Chemical Society.</p> Full article ">Figure 7
<p>(<b>a</b>) A hybrid nanosensor consisting of a conducting polymer nanojunction (polymer bridged between WE1 and WE2) and a working electrode (WE3) on a Si chip. The chip is covered with a thin layer of ionic liquid (BMIM-PF<sub>6</sub>) serving as an electrolyte and preconcentration medium. Upon heating TNT particulates (to 60 °C), TNT vapor is generated which is collected by the ionic liquid layer. The analyte is reduced and detected electrochemically on WE3, and the reduction products are detected by the polymer nanojunctions. Inset: Optical micrograph of the sensor chip used and an SEM image of the PEDOT nanojunction; (<b>b</b>) Current (<span class="html-italic">I</span><sub>d</sub>) via the PEDOT nanojunction plotted as a function of WE1 potential before and after exposure to TNT; (<b>c</b>) Cyclic voltammograms of a blank BMIM-PF<sub>6</sub> solution (black) and 4 ppm TNT in BMIM-PF<sub>6</sub> (red). The large reduction current in the latter case is due to the reduction of TNT. Note that an Ag wire quasi-reference electrode and a Pt counter electrode are used. With permission from [<a href="#B55-nanomaterials-03-00524" class="html-bibr">55</a>]; Copyright 2010, American Chemical Society.</p> Full article ">Figure 8
<p>Sensing performance of chemical nerve agent sensor based on hydroxylated PEDOT nanotubes (HPNTs). (<b>a</b>) Histogram showing the response of HPNTs toward similar organophosphorus compounds at 1 ppb (TCP, MDCP, DMMP, TMP); (<b>b</b>) 3D graphics showing the formation of hydrogen bonds between nerve agent stimulant molecules and HEDOT; (<b>c</b>) Principal components analysis plot using response intensity inputs from four different conducting polymer nanomaterials (two different HPNTs, pristine PEDOT nanotubes, and PPy nanotubes) to the 16 analytes (including DMMP): each analyte concentration was fixed at around 4 ppm. With permission from [<a href="#B59-nanomaterials-03-00524" class="html-bibr">59</a>]; Copyright 2012, American Chemical Society.</p> Full article ">Figure 9
<p>Schematic structures of the two types of waveguide sensors: (<b>a</b>) conventional waveguide sensor; (<b>b</b>) multilayer integrated waveguide sensor. With permission from [<a href="#B60-nanomaterials-03-00524" class="html-bibr">60</a>]; Copyright 2008, American Chemical Society.</p> Full article ">Figure 10
<p>Schematic illustration of (<b>a</b>) reaction steps for the fabrication of a sensor platform based on carboxylated PPy nanotubes; and (<b>b</b>) a liquid ion-gated FET sensor; (<b>c</b>) SEM image of carboxylated PPy nanotubes that are deposited on the interdigitated microelectrode substrate. With permission from [<a href="#B62-nanomaterials-03-00524" class="html-bibr">62</a>]; Copyright 2008, Wiley-VCH Verlag GmbH &amp; Co. KGaA.</p> Full article ">Figure 11
<p>(<b>a</b>) Schematics of maskless electrodeposition of gold along with (<b>b</b>) optical images of before and after selective gold electrodeposition on gold microelectrodes separated by a 3 μm gap connected with a single PPy nanowire; (<b>c</b>) A calibration curve in terms of normalized conductance change of a single PPy nanowire biosensor in spiked human blood plasma suggesting the utility of this sensor for real sample measurements. With permission from [<a href="#B73-nanomaterials-03-00524" class="html-bibr">73</a>]; Copyright 2009, American Chemical Society.</p> Full article ">Figure 12
<p>(<b>a</b>) The change in resistance of the strain sensor under different external strains; (<b>b</b>) The current response of the strain sensor with cyclical bending and unbending actions of the finger. With permission from [<a href="#B84-nanomaterials-03-00524" class="html-bibr">84</a>]; Copyright 2011, Royal Chemical Society.</p> Full article ">
999 KiB  
Review
Conducting Polyaniline Nanowire and Its Applications in Chemiresistive Sensing
by Edward Song and Jin-Woo Choi
Nanomaterials 2013, 3(3), 498-523; https://doi.org/10.3390/nano3030498 - 7 Aug 2013
Cited by 361 | Viewed by 22613
Abstract
One dimensional polyaniline nanowire is an electrically conducting polymer that can be used as an active layer for sensors whose conductivity change can be used to detect chemical or biological species. In this review, the basic properties of polyaniline nanowires including chemical structures, [...] Read more.
One dimensional polyaniline nanowire is an electrically conducting polymer that can be used as an active layer for sensors whose conductivity change can be used to detect chemical or biological species. In this review, the basic properties of polyaniline nanowires including chemical structures, redox chemistry, and method of synthesis are discussed. A comprehensive literature survey on chemiresistive/conductometric sensors based on polyaniline nanowires is presented and recent developments in polyaniline nanowire-based sensors are summarized. Finally, the current limitations and the future prospect of polyaniline nanowires are discussed. Full article
(This article belongs to the Special Issue Nanomaterials in Sensors)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>A general chemical structure of polyaniline and its repeating units. (<b>a</b>) A general chemical structure of polyaniline, (<b>b</b>) Reduced repeating unit, and (<b>c</b>) oxidized repeating unit.</p> Full article ">Figure 2
<p>Electrochemical redox states and the corresponding doped form of polyaniline.</p> Full article ">Figure 3
<p>A typical cyclic voltammetry (CV) curve of polyaniline in HCl (pH 1) showing two sets of redox couples. The direction of potential scan is shown with the arrows.</p> Full article ">Figure 4
<p>Conductance current <span class="html-italic">vs.</span> potential of polyaniline in various pH solutions: pH range 1–4 (<b>a</b>) and pH range 4–6 (<b>b</b>). I<sub>0</sub> indicates maximum current observed.</p> Full article ">Figure 5
<p>The electronic conduction path of the polyaniline nanowires: (<b>a</b>) internanotubular contacts between polyaniline nanowires, and (<b>b</b>) conductive granular region encapsulated in the insulating region of the nanowire. The drawings were adopted from [<a href="#B60-nanomaterials-03-00498" class="html-bibr">60</a>].</p> Full article ">Figure 6
<p>Interfacial polymerization process with 0.32 M of aniline in chloroform (bottom layer) interfacing 0.08 M of ammonium peroxydisulfate (top layer): (<b>a</b>) 1 min, (<b>b</b>) 5 min, and (<b>c</b>) 10 min of the reaction time after the reaction started.</p> Full article ">Figure 7
<p>SEM images of the electrochemically synthesized polyaniline nanowires. Scale bars are 2 μm (<b>a</b>) and 10 μm (<b>b</b>).</p> Full article ">
1335 KiB  
Article
Magnetism of Amorphous and Nano-Crystallized Dc-Sputter-Deposited MgO Thin Films
by Sreekanth K. Mahadeva, Jincheng Fan, Anis Biswas, K. S. Sreelatha, Lyubov Belova and K. V. Rao
Nanomaterials 2013, 3(3), 486-497; https://doi.org/10.3390/nano3030486 - 7 Aug 2013
Cited by 31 | Viewed by 8215
Abstract
We report a systematic study of room-temperature ferromagnetism (RTFM) in pristine MgO thin films in their amorphous and nano-crystalline states. The as deposited dc-sputtered films of pristine MgO on Si substrates using a metallic Mg target in an O2 containing working gas [...] Read more.
We report a systematic study of room-temperature ferromagnetism (RTFM) in pristine MgO thin films in their amorphous and nano-crystalline states. The as deposited dc-sputtered films of pristine MgO on Si substrates using a metallic Mg target in an O2 containing working gas atmosphere of (N2 + O2) are found to be X-ray amorphous. All these films obtained with oxygen partial pressure (PO2) ~10% to 80% while maintaining the same total pressure of the working gas are found to be ferromagnetic at room temperature. The room temperature saturation magnetization (MS) value of 2.68 emu/cm3 obtained for the MgO film deposited in PO2 of 10% increases to 9.62 emu/cm3 for film deposited at PO2 of 40%. However, the MS values decrease steadily for further increase of oxygen partial pressure during deposition. On thermal annealing at temperatures in the range 600 to 800 °C, the films become nanocrystalline and as the crystallite size grows with longer annealing times and higher temperature, MS decreases. Our study clearly points out that it is possible to tailor the magnetic properties of thin films of MgO. The room temperature ferromagnetism in MgO films is attributed to the presence of Mg cation vacancies. Full article
(This article belongs to the Special Issue Magnetic Nanomaterials)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>X-ray diffraction (XRD) patterns of MgO films deposited in different oxygen partial pressures: (<b>a</b>) 10%, (<b>b</b>) 20%, (<b>c</b>) 40%, and (<b>d</b>) 80%.</p> Full article ">Figure 2
<p>The XRD patterns of the (<b>a</b>) as-grown film deposited at P<sub>O2</sub> of 10%, annealed for 1 h at (<b>b</b>) 600 °C, (<b>c</b>) 700 °C, (<b>d</b>) 800 °C respectively.</p> Full article ">Figure 3
<p>The XRD patterns of the (<b>a</b>) as-grown film deposited at P<sub>O2</sub> of 10% annealed at 700 °C for (<b>e</b>) 1 h, (<b>f</b>) 2 h respectively.</p> Full article ">Figure 4
<p>The variation of grain size with 1h anneals at various temperatures (inset: the variation of grain size with annealing time).</p> Full article ">Figure 5
<p>A typical cross-section of MgO films, obtained using Focused Ion Beam (FIB), in their (<b>a</b>) as-grown, and (<b>b</b>) annealed at 800 °C in air for 1 h states.</p> Full article ">Figure 6
<p>The film thickness as a function of oxygen partial pressure (P<sub>O2</sub>).</p> Full article ">Figure 7
<p>Scanning Electron Microscopy (SEM) images of (<b>a</b>) as-grown, and annealed films at (<b>b</b>) 700 °C, and (<b>c</b>) 800 °C for 1 h respectively.</p> Full article ">Figure 8
<p>The energy dispersive spectroscopic (EDS) spectrum for MgO film deposited with O<sub>2</sub> content of 10% in the working gas.</p> Full article ">Figure 9
<p>The (<b>a</b>) EDS spectrum and (<b>b</b>) M-H loop for the 1.22 µm thick Mg film.</p> Full article ">Figure 10
<p>Room-temperature M-H loops for the as-grown (<b>a</b>), and annealed MgO films in air for 1 h at (<b>b</b>) 600 °C, (<b>c</b>) 700 °C, and (<b>d</b>) 800 °C, respectively. The (M-H) loops are shown after correcting for the diamagnetic contribution from Si-substrate. The Inset shows the M<sub>S</sub> values at room-temperature (RT) observed as a function of annealing temperature.</p> Full article ">Figure 11
<p>The room temperature M-H of the as-grown (<b>a</b>), and annealed MgO Films at 700 °C for 1 h (<b>b</b>) and 2 h (<b>c</b>) respectively. The (M-H) loops are shown after correcting for the diamagnetic contribution from Si-substrate. Inset shows the M<sub>S</sub> values as a function of annealing time.</p> Full article ">Figure 12
<p>The room temperature (M-H) loops for as-deposited MgO films with different O<sub>2</sub> contents in the working gas: (<b>a</b>) 10%, (<b>b</b>) 20%, (<b>c</b>) 40%, (<b>d</b>) 80%. The loops are shown after correcting for the diamagnetic contribution from Si-substrate. Inset: dependence of room temperature M<sub>S</sub> values for films deposited under different P<sub>O2</sub> in the working gas.</p> Full article ">Figure 13
<p>The M<sub>S</sub> value as a function of film thickness for as-deposited MgO films in an ambience of different O<sub>2</sub> contents.</p> Full article ">
381 KiB  
Article
Nanostructure-Directed Chemical Sensing: The IHSAB Principle and the Effect of Nitrogen and Sulfur Functionalization on Metal Oxide Decorated Interface Response
by William I. Laminack and James L. Gole
Nanomaterials 2013, 3(3), 469-485; https://doi.org/10.3390/nano3030469 - 7 Aug 2013
Cited by 12 | Viewed by 6777
Abstract
The response matrix, as metal oxide nanostructure decorated n-type semiconductor interfaces are modified in situ through direct amination and through treatment with organic sulfides and thiols, is demonstrated. Nanostructured TiO2, SnOx, NiO and CuxO (x [...] Read more.
The response matrix, as metal oxide nanostructure decorated n-type semiconductor interfaces are modified in situ through direct amination and through treatment with organic sulfides and thiols, is demonstrated. Nanostructured TiO2, SnOx, NiO and CuxO (x = 1,2), in order of decreasing Lewis acidity, are deposited to a porous silicon interface to direct a dominant electron transduction process for reversible chemical sensing in the absence of significant chemical bond formation. The metal oxide sensing sites can be modified to decrease their Lewis acidity in a process appearing to substitute nitrogen or sulfur, providing a weak interaction to form the oxynitrides and oxysulfides. Treatment with triethylamine and diethyl sulfide decreases the Lewis acidity of the metal oxide sites. Treatment with acidic ethane thiol modifies the sensor response in an opposite sense, suggesting that there are thiol (SH) groups present on the surface that provide a Brønsted acidity to the surface. The in situ modification of the metal oxides deposited to the interface changes the reversible interaction with the analytes, NH3 and NO. The observed change for either the more basic oxynitrides or oxysulfides or the apparent Brønsted acid sites produced from the interaction of the thiols do not represent a simple increase in surface basicity or acidity, but appear to involve a change in molecular electronic structure, which is well explained using the recently developed inverse hard and soft acids and bases (IHSAB) model. Full article
(This article belongs to the Special Issue Nanomaterials in Sensors)
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Figure 1
<p>Comparison of responses to 1, 2, 3, 4, 5 and 10 ppm NH<sub>3</sub> for (<b>a</b>), (<b>c</b>) and (<b>e</b>), sensors, consisting of an untreated <span class="html-italic">n</span>-type porous silicon (PS) interface with those treated with (<b>b</b>) TiO<sub>2</sub>, (<b>d</b>) SnO<span class="html-italic"><sub>x</sub></span> and (<b>f</b>) NiO fractional nanostructured island depositions. The PS interface in (a) is that treated with TiO<sub>2</sub> in (b) and similarly for SnO<span class="html-italic"><sub>x</sub></span> and NiO.</p> Full article ">Figure 2
<p>Estimated hard and soft acidities and basicities based on resistance change relative to a <span class="html-italic">p</span>- and <span class="html-italic">n</span>-type porous silicon interface. The acidic metal oxides that decorate the semiconductor interface can be modified through <span class="html-italic">in situ</span> nitridation and sulfurization, decreasing their Lewis acidity. The analytes remain as positioned. A horizontal line is used to separate the metal oxides used to modify the interface (above) and the analytes below in the figure.</p> Full article ">Figure 3
<p>Response corresponding to decreasing resistance as NH<sub>3</sub> contributes electrons to an untreated porous silicon (PS)-, TiO<sub>2</sub>- and TiO<sub>2 </sub><sub>−</sub> <sub><span class="html-italic">x</span></sub>N<span class="html-italic"><sub>x</sub></span>-treated PS interfaces. The TiO<sub>2</sub> <sub>−</sub> <sub><span class="html-italic">x</span></sub>N<span class="html-italic"><sub>x</sub></span>-treated interface is basic relative to the PS- and TiO<sub>2</sub>- treated PS acidic sites.</p> Full article ">Figure 4
<p>Response corresponding to decreasing resistance as NH<sub>3</sub> contributes electrons to a Cu<span class="html-italic"><sub>x</sub></span>O-treated porous silicon (<b>blue line</b>) and nitridated Cu<span class="html-italic"><sub>x</sub></span>O nanostructure-treated PS (<b>green line</b>). The nitridated Cu<span class="html-italic"><sub>x</sub></span>O-treated interface is basic relative to the PS- and Cu<span class="html-italic"><sub>x</sub></span>O-treated PS acidic sites.</p> Full article ">Figure 5
<p>Response of a Cu<span class="html-italic"><sub>x</sub></span>O-treated PS interface to NO (<b>blue line</b>) and after nitridation with triethylamine (<b>green line</b>). The boxes (<b>red line</b>) denote the analyte concentration from 1 to 10 ppm.</p> Full article ">Figure 6
<p>Response of diethyl sulfide, Et<sub>2</sub>S, -treated TiO<sub>2</sub>-deposited porous silicon (PS) interface to NH<sub>3</sub>. Exposure to TiO<sub>2</sub>-treated PS interface (<b>blue line</b>). Response of diethyl sulfide-treated TiO<sub>2</sub> nanostructure-deposited PS interface to NH<sub>3</sub> (<b>green line</b>). The Et<sub>2</sub>S-treated TiO<sub>2</sub> deposited interface is made more basic relative to the PS and TiO<sub>2</sub>-treated PS acidic sites.</p> Full article ">Figure 7
<p>Response of diethyl sulfide, Et<sub>2</sub>S, -treated tin oxide-deposited porous silicon (PS) interface to NH<sub>3</sub>. Exposure to SnO<span class="html-italic"><sub>x</sub></span>-treated PS interface (<b>blue line</b>). Initial exposure to Et<sub>2</sub>S with water present (<b>green line</b>). Response of diethyl sulfide-treated tin oxide nanostructure-deposited PS interface to NH<sub>3</sub> after gentle heating to 80 °C to remove water (<b>red line</b>). The Et<sub>2</sub>S treated SnO<span class="html-italic"><sub>x</sub></span>-deposited interface is a weaker Lewis acid relative to the PS and SnO<span class="html-italic"><sub>x</sub></span>-treated PS acidic sites, where it is more acidic in the presence of water (See, also, the thiol results).</p> Full article ">Figure 8
<p>Response of diethyl sulfide-treated nickel oxide nanostructure-deposited porous silicon (PS) interface to NH<sub>3</sub>. Initial response of nickel oxide-treated PS (<b>blue line</b>), after treatment for 10 s with diethyl sulfide (<b>red line</b>), and after treatment for 15 s with diethyl sulfide (<b>green line</b>). The Et<sub>2</sub>S-treated NiO-deposited interface treated for 15 s is a weaker Lewis acid made more basic relative to the PS- and NiO-treated (<a href="#nanomaterials-03-00469-f001" class="html-fig">Figure 1</a>) PS interface.</p> Full article ">Figure 9
<p>Response of ethanethiol-treated tin oxide nanostructure-deposited porous silicon (PS) interface to NH<sub>3</sub> after exposure for 30 s (<b>green line</b>) <span class="html-italic">vs.</span> only tin oxide (<b>blue line</b>). The response of the thiol-treated SnO<span class="html-italic"><sub>x</sub></span>-deposited interface is consistent with the introduction of S-H groups on the interface and an increased Brønsted acidity relative to the PS- and SnO<span class="html-italic"><sub>x</sub></span>-treated PS acidic sites (<a href="#nanomaterials-03-00469-f002" class="html-fig">Figure 2</a>) after a 30 s exposure.</p> Full article ">Figure 10
<p>Response of ethanethiol-treated nickel oxide nanostructure-deposited porous silicon (PS) interface to NH<sub>3</sub> exposure for 30 s (<b>green line</b>), and exposure only to nickel oxide (<b>blue line</b>). The thiol-treated NiO-deposited interface is more acidic than the NiO-treated PS acidic sites (<a href="#nanomaterials-03-00469-f001" class="html-fig">Figure 1</a>) after a 30 s exposure.</p> Full article ">
387 KiB  
Review
Inkjet Printing of Carbon Nanotubes
by Ryan P. Tortorich and Jin-Woo Choi
Nanomaterials 2013, 3(3), 453-468; https://doi.org/10.3390/nano3030453 - 29 Jul 2013
Cited by 160 | Viewed by 14567
Abstract
In an attempt to give a brief introduction to carbon nanotube inkjet printing, this review paper discusses the issues that come along with preparing and printing carbon nanotube ink. Carbon nanotube inkjet printing is relatively new, but it has great potential for broad [...] Read more.
In an attempt to give a brief introduction to carbon nanotube inkjet printing, this review paper discusses the issues that come along with preparing and printing carbon nanotube ink. Carbon nanotube inkjet printing is relatively new, but it has great potential for broad applications in flexible and printable electronics, transparent electrodes, electronic sensors, and so on due to its low cost and the extraordinary properties of carbon nanotubes. In addition to the formulation of carbon nanotube ink and its printing technologies, recent progress and achievements of carbon nanotube inkjet printing are reviewed in detail with brief discussion on the future outlook of the technology. Full article
(This article belongs to the Special Issue CNT based Nanomaterials)
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<p>Random carbon nanotube network showing both isolated carbon nanotube and formation of electron pathway via overlapping carbon nanotubes.</p> Full article ">Figure 2
<p>Estimated sheet resistance versus number of prints for two recent reports on carbon nanotube inkjet printing [<a href="#B38-nanomaterials-03-00453" class="html-bibr">38</a>,<a href="#B39-nanomaterials-03-00453" class="html-bibr">39</a>] and our own recent test results on carbon nanotube inkjet printing. Sheet resistance values are normalized.</p> Full article ">Figure 3
<p>Surfactant-assisted dispersion of carbon nanotubes: (<b>a</b>) cross-section of carbon nanotube; and (<b>b</b>) side view of carbon nanotube.</p> Full article ">Figure 4
<p>Effect of surfactant on surface tension: (<b>a</b>) 3 µL droplet of water without surfactant; and (<b>b</b>) 3 µL droplet of water with surfactant. Surfactant clearly decreases the surface tension of the droplet.</p> Full article ">
2572 KiB  
Article
Synthesis of Microspherical LiFePO4-Carbon Composites for Lithium-Ion Batteries
by Linghui Yu, Dandan Cai, Haihui Wang and Maria-Magdalena Titirici
Nanomaterials 2013, 3(3), 443-452; https://doi.org/10.3390/nano3030443 - 22 Jul 2013
Cited by 17 | Viewed by 8562
Abstract
This paper reports an “all in one” procedure to produce mesoporous, micro-spherical LiFePO4 composed of agglomerated crystalline nanoparticles. Each nanoparticle is individually coated with a thin glucose-derived carbon layer. The main advantage of the as-synthesized materials is their good performance at high [...] Read more.
This paper reports an “all in one” procedure to produce mesoporous, micro-spherical LiFePO4 composed of agglomerated crystalline nanoparticles. Each nanoparticle is individually coated with a thin glucose-derived carbon layer. The main advantage of the as-synthesized materials is their good performance at high charge-discharge rates. The nanoparticles and the mesoporosity guarantee a short bulk diffusion distance for both lithium ions and electrons, as well as additional active sites for the charge transfer reactions. At the same time, the thin interconnected carbon coating provides a conductive framework capable of delivering electrons to the nanostructured LiFePO4. Full article
(This article belongs to the Special Issue Nanomaterials in Energy Conversion and Storage)
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<p>SEM images of LiFePO<sub>4</sub>/C spheres before (<b>a</b> and <b>b</b>) and after (<b>c</b> and <b>d</b>) calcination. (<b>a</b>) LFP180-2; (<b>b</b>) LFP250-1; (<b>c</b>) LFP 180-2-700; and (<b>d</b>) LFP250-1-700.</p> Full article ">Figure 2
<p>XRD patterns of the materials before (<b>a</b> and <b>b</b>) and after (<b>c</b> and <b>d</b>) calcination. (<b>a</b>) LFP-180; (<b>b</b>) LFP-180-700; (<b>c</b>) LFP-250; and (<b>d</b>) LFP-250-700.</p> Full article ">Figure 3
<p>TEM images of ultramicrotome cross-sections of LiFePO<sub>4</sub>/C spheres. (<b>a</b>) and (<b>b</b>) LFP180-2-700; (<b>c</b>) and (<b>d</b>) LFP250-1-700; (<b>b</b>) and (<b>d</b>) are magnified images from inner parts. The insert in (<b>d</b>) is a high resolution tunnelling electron microscopy (HRTEM) image of LFP250-1-700.</p> Full article ">Figure 4
<p>N<sub>2</sub> adsorption data at 77.4 K. (<b>a</b>) N<sub>2</sub> adsorption isotherm and (<b>b</b>) pore size distribution of LFP250-1-700.</p> Full article ">Figure 5
<p>(<b>a</b>) SEM and (<b>b</b>–<b>d</b>) TEM images of the carbon coating from LFP250-1-700 after removing LiFePO<sub>4</sub> by HCl (37%); (<b>c</b>) magnified TEM image; (<b>d</b>) TEM image of a broken part of the pure carbon.</p> Full article ">Figure 6
<p>Electrochemical properties of LFP250-1-700. (<b>a</b>) Galvanostatic charge/discharge curves at different rates; and (<b>b</b>) corresponding cycling performance. 1 C = 170 mA g<sup>−1</sup>.</p> Full article ">
1788 KiB  
Review
Theory of Carbon Nanotube (CNT)-Based Electron Field Emitters
by Grigory S. Bocharov and Alexander V. Eletskii
Nanomaterials 2013, 3(3), 393-442; https://doi.org/10.3390/nano3030393 - 17 Jul 2013
Cited by 82 | Viewed by 10277
Abstract
Theoretical problems arising in connection with development and operation of electron field emitters on the basis of carbon nanotubes are reviewed. The physical aspects of electron field emission that underlie the unique emission properties of carbon nanotubes (CNTs) are considered. Physical effects and [...] Read more.
Theoretical problems arising in connection with development and operation of electron field emitters on the basis of carbon nanotubes are reviewed. The physical aspects of electron field emission that underlie the unique emission properties of carbon nanotubes (CNTs) are considered. Physical effects and phenomena affecting the emission characteristics of CNT cathodes are analyzed. Effects given particular attention include: the electric field amplification near a CNT tip with taking into account the shape of the tip, the deviation from the vertical orientation of nanotubes and electrical field-induced alignment of those; electric field screening by neighboring nanotubes; statistical spread of the parameters of the individual CNTs comprising the cathode; the thermal effects resulting in degradation of nanotubes during emission. Simultaneous consideration of the above-listed effects permitted the development of the optimization procedure for CNT array in terms of the maximum reachable emission current density. In accordance with this procedure, the optimum inter-tube distance in the array depends on the region of the external voltage applied. The phenomenon of self-misalignment of nanotubes in an array has been predicted and analyzed in terms of the recent experiments performed. A mechanism of degradation of CNT-based electron field emitters has been analyzed consisting of the bombardment of the emitters by ions formed as a result of electron impact ionization of the residual gas molecules. Full article
(This article belongs to the Special Issue CNT based Nanomaterials)
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<p>Typical current-voltage characteristics of an individual emitter on the basis of a multiwalled nanotube 8 nm in diameter and 1.1 mm in length, measured before (triangles) and after (rhombi) thermal treatment [<a href="#B45-nanomaterials-03-00393" class="html-bibr">45</a>].</p> Full article ">Figure 2
<p>The typical spatial distribution of the electrical field potential in the vicinity of a sharp tip [<a href="#B46-nanomaterials-03-00393" class="html-bibr">46</a>].</p> Full article ">Figure 3
<p>Field enhancement factor of a nanotube <span class="html-italic">vs</span>. its aspect ratio. The dependences approximated by (<b>1</b>) <span class="html-italic">β</span> = 0.31 + 0.71<span class="html-italic">h</span>/<span class="html-italic">r</span> [<a href="#B47-nanomaterials-03-00393" class="html-bibr">47</a>], and (<b>2</b>) <span class="html-italic">β</span> = 5.93 + 0.73<span class="html-italic">h</span>/<span class="html-italic">r</span> − 0.001(<span class="html-italic">h</span>/<span class="html-italic">r</span>)<sup>2</sup> [<a href="#B48-nanomaterials-03-00393" class="html-bibr">48</a>].</p> Full article ">Figure 4
<p>(<b>a</b>)–(<b>e</b>) Various shapes of the carbon nanotube (CNT) tip for which the field enhancement factor versus the aspect ratio was calculated. Curves <b>1</b><span class="html-italic">–</span><b>5</b> in panel (<b>f</b>) correspond to panels (<b>a</b>)–(<b>d</b>). The inter-electrode spacing and the applied voltage are 200 μm and 1000 V, respectively [<a href="#B49-nanomaterials-03-00393" class="html-bibr">49</a>].</p> Full article ">Figure 5
<p>Field enhancement factor <span class="html-italic">β</span> <span class="html-italic">vs</span>. the distance between the nanotube top and anode surface for nanotubes of 400 nm in diameter with different heights. (□, Δ, ○ for <span class="html-italic">h</span> = 1, 2 and 3 μm, respectively). Calculations for nanotubes 3, 2, and 1 μm high, respectively, by approximant (8) (points <b>1</b>–<b>3</b>) and interpolation Equation (7) (points <b>4</b>–<b>6</b>). (<b>a</b>) Cartesian and (<b>b</b>) semilog coordinates.</p> Full article ">Figure 6
<p>Field enhancement factor <span class="html-italic">vs</span>. the angle of tilting the nanotube to the cathode surface calculated for nanotubes of 1 μm in height and of 1.4 (<b>1</b>), 3.0 (<b>2</b>), 6.0 (<b>3</b>), and 10.0 (<b>4</b>) nm in diameter. Solid lines depict the parabolic approximation of the results calculated by Equation (9) [<a href="#B30-nanomaterials-03-00393" class="html-bibr">30</a>].</p> Full article ">Figure 7
<p>Results of the solution of the heat conduction Equation (10) in combination with the Fowler-Nordheim Equation (1) [<a href="#B57-nanomaterials-03-00393" class="html-bibr">57</a>]: (<b>a</b>) <span class="html-italic">I</span>–<span class="html-italic">V</span> characteristics of a carbon nanotube 5 nm in radius and 1.6 mm in length calculated for various model temperature dependences of transport coefficients: <b>1</b>: experiment [<a href="#B63-nanomaterials-03-00393" class="html-bibr">63</a>]; <b>2</b>: <span class="html-italic">α</span> = 4; <b>3</b>: <span class="html-italic">α</span> = −1; <b>4</b>: <span class="html-italic">α</span> = 0; <b>5</b>: <span class="html-italic">α</span> = 0; <span class="html-italic">λ</span> = const; <b>6</b>: <span class="html-italic">α</span> = 1. The inset presents an enlarged part of the current-voltage characteristics. (<b>b</b>) Dependences of the emission current <span class="html-italic">I</span><sub>max</sub> on the ratio <span class="html-italic">R/λ</span> calculated for various model temperature dependences of transport coefficients: <b>1</b>: <span class="html-italic">α</span> = 0, <span class="html-italic">λ</span> = const; <b>2</b>: <span class="html-italic">α</span> = 4; <b>3</b>: <span class="html-italic">α</span> = −1; <b>4</b>: <span class="html-italic">α</span> = 0; and <b>5</b>: <span class="html-italic">α</span> = 1.</p> Full article ">Figure 8
<p>Configuration of the nanotube inclined relative to the substrate and aligned under the action of the electric field; <span class="html-italic">θ</span> is the initial angle of inclination of the nanotube and <span class="html-italic">φ</span> is the resultant angle of inclination.</p> Full article ">Figure 9
<p>Dependences of angle of inclination <span class="html-italic">α</span> = <span class="html-italic">θ</span> – <span class="html-italic">φ</span> on the local value of the electric field strength, computed for the CNTs with parameters given in the table. The values of <span class="html-italic">L</span>, nm, are as follows: (<b>a</b>) 100–300, (<b>b</b>) 500–800, and (<b>c</b>) 10<sup>3</sup>–5 × 10<sup>3</sup>.</p> Full article ">Figure 10
<p>The model configuration of the emitter under consideration.</p> Full article ">Figure 11
<p>Energy dependences of the ionization cross section of a nitrogen molecule by an electron impact σ [<a href="#B76-nanomaterials-03-00393" class="html-bibr">76</a>] and ion sputtering coefficient <span class="html-italic">Y</span> [<a href="#B78-nanomaterials-03-00393" class="html-bibr">78</a>] for the bombardment of the graphite surface by molecular nitrogen ions. <span class="html-italic">E</span><sub>th</sub> is the threshold sputtering energy.</p> Full article ">Figure 12
<p>Distribution of the ion current <span class="html-italic">J</span> over the target surface <span class="html-italic">ρ</span> calculated at various magnitudes of the applied voltage <span class="html-italic">U</span>. (<b>a</b>) The main calculation parameters: nanotube’s radius <span class="html-italic">R</span> = 5 nm, nanotube’s height <span class="html-italic">H</span> = 1 μm, residual gas pressure <span class="html-italic">P</span> = 10<sup>−4</sup> torr, temperature <span class="html-italic">T</span> = 1000 K, inter-electrode distance <span class="html-italic">L</span> = 100 μm. The electrical field strength near the nanotube’s tip <span class="html-italic">Е</span> = 10 V/nm, 5 V/nm and 1 V/nm correspondingly. The curves for <span class="html-italic">V</span> = 5000 V and 1000 V are given in an enlarged scale. (<b>b</b>) The main calculation parameters: <span class="html-italic">R</span> = 5 nm, <span class="html-italic">H</span> = 10 μm, residual gas pressure <span class="html-italic">P</span> = 10<sup>−4</sup> torr, temperature <span class="html-italic">T</span> = 1000 K, inter-electrode distance <span class="html-italic">L</span> = 100 μm. <span class="html-italic">Е</span> = 10 V/nm, 5 V/nm and 1 V/nm correspondingly. The curves for <span class="html-italic">V</span> = 5000 V and 1000 V are given in an enlarged scale.</p> Full article ">Figure 13
<p>The results of calculations: (<b>a</b>) Comparison of the dependences calculated with (A) and without (B) taking into account the initial thermal motion of residual gas molecules. <span class="html-italic">R</span> = 5 nm, <span class="html-italic">H</span> = 10 µm, <span class="html-italic">L</span> = 100 µm. (<b>b</b>) The dependences <span class="html-italic">t</span>(<span class="html-italic">U</span>) calculated taking into account the initial thermal motion of residual gas molecules for various parameters of the system: (A) <span class="html-italic">L</span> = 100 µm, <span class="html-italic">H</span> = 10 µm, <span class="html-italic">R</span> = 5 nm; (B): <span class="html-italic">L</span> = 200 µm, <span class="html-italic">H</span> = 10 µm, <span class="html-italic">R</span> = 5 nm; (C): <span class="html-italic">L</span> = 100 µm, <span class="html-italic">H</span> = 20 µm, <span class="html-italic">R</span> = 5 nm. All the calculations were performed for <span class="html-italic">P</span> = 10<sup>−4</sup> torr, <span class="html-italic">T</span> = 1000 K. (<b>c</b>) Ratio of the degradation rate calculated with and without taking into account the initial thermal motion of residual gas molecules. Calculation parameters: (A) nanotube radius <span class="html-italic">R</span> = 5 nm; height <span class="html-italic">H</span> = 10 μm; residual gas pressure <span class="html-italic">P</span> = 10<sup>−4</sup> torr; temperature <span class="html-italic">T</span> = 1000 K; interelectrode distance <span class="html-italic">L</span> = 100 µm. In the rest calculations one parameter has been changed as shown on the relevant curves.</p> Full article ">Figure 14
<p>Spatial distribution of the electric potential in a vicinity of three CNTs calculated for various inter-tube distances (arbitrary units) [<a href="#B28-nanomaterials-03-00393" class="html-bibr">28</a>]. The closer nanotubes the lower electrical field enhancement factor.</p> Full article ">Figure 15
<p>Results of the solution of the 3D Laplace equation for an array of similar vertically aligned nanotubes 1 nm in diameter and 1 μm in height having a flat cap [<a href="#B29-nanomaterials-03-00393" class="html-bibr">29</a>]: (<b>a</b>) dependence of the electric field amplification factor of a nanotube involved in the array on the average intertube distance <span class="html-italic">S</span> and the surface density <span class="html-italic">γ</span> of nanotubes; (<b>b</b>) dependence of the emission current density of the CNT array on <span class="html-italic">S</span>, calculated taking into account the screening effect.</p> Full article ">Figure 16
<p>Illustration of the influence of the statistical spread of CNT parameters on the operating characteristics of a field emission cathode: (<b>a</b>) comparison of the Fowler-Nordheim characteristic (dashed-dotted line) with the calculated results obtained on the basis of generalized Equation (62) (solid line), and with the measured data [<a href="#B86-nanomaterials-03-00393" class="html-bibr">86</a>] (dots); (<b>b</b>)–(<b>d</b>) the images of the distribution of the luminescence intensity over the phosphor surface, obtained at various values of the electric field strength and the emission current [<a href="#B86-nanomaterials-03-00393" class="html-bibr">86</a>].</p> Full article ">Figure 17
<p>Current-voltage characteristics of a CNT-based cathode calculated taking into account the nanotube's inclination according to Equation (66) [<a href="#B30-nanomaterials-03-00393" class="html-bibr">30</a>]. The case disregarding the inclination effect corresponds to <span class="html-italic"><span class="html-overline">θ</span></span> = 0.</p> Full article ">Figure 18
<p>Current-voltage characteristics of the arrays containing 1000 CNTs of length <span class="html-italic">L</span>, nm: 100–300 (<b>1</b>), 500–800 (<b>2</b>), 1000–5000 (<b>3</b>), with diameter <span class="html-italic">D</span> = 10–50 nm and the Young modulus in the range <span class="html-italic">Y</span> = 10–50 GPa. The initial angle of inclination of the CNT was selected from the range <span class="html-italic">θ</span> = 50°–80°; <span class="html-italic">A</span> is the result of computations based on Equations (1), (9) and (44); <span class="html-italic">B</span> is the result of computation under the assumption that all nanotubes are aligned vertically; and <span class="html-italic">C</span> is the result of computation disregarding the effect of field orientation.</p> Full article ">Figure 19
<p>Model configuration of the CNT array under consideration. Here (<span class="html-italic">r</span>, <span class="html-italic">θ</span>, <span class="html-italic">z</span>) are the cylindrical coordinates; <span class="html-italic">S</span><sub>1</sub> and <span class="html-italic">S</span><sub>2</sub> are the distances from the CNT rows to the array center.</p> Full article ">Figure 20
<p>Dependences of the CNT orientation angle on the position on the substrate: (<b>a</b>) on the distance to the center, computed for the arrays with different distances <span class="html-italic">S</span> between the rows under the assumption that the contact potential difference between the CNT and the substrate material is Δ<span class="html-italic">φ</span> = 1 eV; the CNT diameter <span class="html-italic">D</span> = 10 nm, length <span class="html-italic">L</span> = 1 μm, Young modulus <span class="html-italic">Y</span> = 30 GPa; (<b>b</b>) the same dependences computed for the CNT arrays with Young modulus <span class="html-italic">Y</span> = 30 GPa, diameter <span class="html-italic">D</span> = 10 nm, and various lengths, spacing <span class="html-italic">S</span> between the rows being 200 nm; (<b>c</b>) the same dependences, computed for the CNT arrays with different Young moduli; and (<b>d</b>) the dependences of the CNT orientation angle on the distance to the array edge, which were measured for the nanotubes synthesized under different pressures of the buffer gas [<a href="#B93-nanomaterials-03-00393" class="html-bibr">93</a>].</p> Full article ">Figure 21
<p>Current–voltage characteristics of the CNT cylindrical array (see <a href="#nanomaterials-03-00393-f019" class="html-fig">Figure 19</a>), computed disregarding (A) and taking into account (B) the self electric field of the nanotubes for the distances <span class="html-italic">S</span> = 1000 and 100 nm between the rows. The height of the nanotubes <span class="html-italic">L</span> = 1 μm, diameter <span class="html-italic">D</span> = 5 nm, electron work function <span class="html-italic">φ</span> = 4.6 eV, and Young modulus <span class="html-italic">Y</span> = 50 GPa. Contact potential difference Δ<span class="html-italic">φ</span> = 1 V. The array radius in both cases is equal to 10 μm, which corresponds to the number of rows 10 and 100, respectively, in the array.</p> Full article ">Figure 22
<p>Dependences of the emission current density of a CNT array on (<b>a</b>) the nanotube height, and (<b>b</b>) the inter-tube distance calculated for various average electric field strengths. <span class="html-italic">E</span><sub>o</sub> = 50 (■), 20 (●), and 10 (▲) V/μm; (○) maximum value [<a href="#B94-nanomaterials-03-00393" class="html-bibr">94</a>].</p> Full article ">Figure 23
<p>Dependences of the emission current density on the inter-tube distance calculated at various average electric field strengths with taking into account the screening effect and thermal instability: (□) points with a maximum in the <span class="html-italic">J</span>(<span class="html-italic">S</span>) dependences, (▼) points where thermal instability appears, and (Δ) optimized <span class="html-italic">J</span>(<span class="html-italic">S</span>) curve for a certain CNT array. The nanotube diameter is <span class="html-italic">d</span> = 10 nm and the nanotube height is <span class="html-italic">h</span> = 10 μm. <span class="html-italic">E</span><sub>o</sub> = (<b>1</b>) 11.4, (<b>2</b>) 20, (<b>3</b>) 30, (<b>4</b>) 40, (<b>5</b>) 50, (<b>6</b>) 60, (<b>7</b>) 70, (<b>8</b>) 80, (<b>9</b>) 90, and (<b>10</b>) 100 V/μm.</p> Full article ">Figure 24
<p>Dependences of (<b>a</b>) optimum internanotube distance <span class="html-italic">S</span><sub>o</sub> and (<b>b</b>) maximum emission current density <span class="html-italic">J</span><sub>max</sub> on average electric field <span class="html-italic">E</span><sub>o</sub> calculated for CNTs of diameter = 10 nm and various heights. Solid lines: Approximation by Equations (69) and (70) at <span class="html-italic">h</span> = 10 (■), 20 (●), and 40 (▲) μm.</p> Full article ">Figure 25
<p>Optimization curves calculated for an array of CNTs of height <span class="html-italic">h</span> and various diameters <span class="html-italic">d</span> calculated under different assumptions regarding the absolute values and temperature dependences of the transfer coefficients: <span class="html-italic">d</span> = 1 (<b>1</b>), 2 (<b>2</b>), 5 (<b>3</b>), 14 (<b>4</b>), and 50 (<b>5</b>) nm. Approximation for (●) <span class="html-italic">α</span> = 1, <span class="html-italic">l<sub>p</sub></span>= 100 nm; ( <span class="html-fig-inline" id="nanomaterials-03-00393-i071"> <img alt="Nanomaterials 03 00393 i071" src="/nanomaterials/nanomaterials-03-00393/article_deploy/html/images/nanomaterials-03-00393-i071.png"/></span>) <span class="html-italic">α</span> = 1, <span class="html-italic">l<sub>p</sub></span> = 480 nm; (■) <span class="html-italic">α</span> = 1.5, <span class="html-italic">l<sub>f</sub></span> = 480 nm.</p> Full article ">
3917 KiB  
Article
Alkyl and Aromatic Amines as Digestive Ripening/Size Focusing Agents for Gold Nanoparticles
by Yijun Sun, Deepa Jose, Christopher Sorensen and Kenneth J. Klabunde
Nanomaterials 2013, 3(3), 370-392; https://doi.org/10.3390/nano3030370 - 5 Jul 2013
Cited by 10 | Viewed by 7640
Abstract
Both long chain alkyl thiols and alkyl amines behave as size focusing agents for gold nanoparticles, a process that is under thermodynamic control. However, amines do not oxidize surface gold atoms while thiols do oxidize surface gold to gold(I) with evolution of hydrogen [...] Read more.
Both long chain alkyl thiols and alkyl amines behave as size focusing agents for gold nanoparticles, a process that is under thermodynamic control. However, amines do not oxidize surface gold atoms while thiols do oxidize surface gold to gold(I) with evolution of hydrogen gas. Therefore, alkyl amines participate in digestive ripening by a different mechanism. The efficiency of alkyl amines for this process is described and compared, and ultimate gold particle size differences are discussed. Reported herein is a detailed investigation of alkyl chain lengths for alkyl amines, aromatic amines (aniline), and unusually reactive amines (2-phenylethyl amine). Also, two methods of preparation of the crude gold nanoparticles were employed: gold ion reduction/inverse micelle vs. metal vaporization (Solvated Metal Atom Dispersion—SMAD). Full article
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Figure 1

Figure 1
<p>Schematic representation of the synthesis of gold colloid by inverse micelle method and digestive ripening process.</p> Full article ">Figure 2
<p>Schematic representation of the synthesis of gold colloid by Solvated Metal Atom Dispersion (SMAD) method and digestive ripening process.</p> Full article ">Figure 3
<p>TEM images of Au-DDAB colloid in toluene by the inverse micelle method, before digestive ripening.</p> Full article ">Figure 4
<p>TEM images of (<b>A</b>) as prepared Au-butylamine colloid in toluene by inverse micelle method; (<b>B</b>) Au-butylamine colloid after digestive ripening 2 h in toluene.</p> Full article ">Figure 5
<p>UV-Visible spectrum of Au-butylamine colloid by inverse micelle method before and after digestive ripening 2 h.</p> Full article ">Figure 6
<p>TEM images of (<b>A</b>) as prepared Au-octylamine colloid in toluene by inverse micelle method; and (<b>B</b>) Au-octylamine colloid after digestive ripening 2 h in toluene.</p> Full article ">Figure 7
<p>UV-Visible spectrum of Au-octylamine colloid by inverse micelle method before and after digestive ripening 2 h in toluene.</p> Full article ">Figure 8
<p>TEM images of (<b>A</b>) as prepared Au-dodecylamine colloid by inverse method in toluene; (<b>B</b>) Au-dodecylamine colloid after digestive ripening 2 h in toluene.</p> Full article ">Figure 9
<p>UV-Visible spectrum of Au-dodecylamine colloid by inverse micelle method before and after digestive ripening 2 h in toluene.</p> Full article ">Figure 10
<p>TEM images of (<b>A</b>) as prepared Au-hexadecylamine colloid by inverse micelle method in toluene; (<b>B</b>) Au-hexadecylamine colloid after digestive ripening 2 h in toluene.</p> Full article ">Figure 11
<p>UV-Visible spectrum of Au-hexadecylamine colloid by inverse micelle method before and after digestive ripening 2 h in toluene.</p> Full article ">Figure 12
<p>TEM images of (<b>A</b>) as prepared Au-octadecylamine colloid in toluene; (<b>B</b>) Au-octadecylamine colloid after digestive ripening 2 h in toluene.</p> Full article ">Figure 13
<p>UV-Visible spectrum of Au-octadecylamine colloid before and after digestive ripening 2 h in toluene.</p> Full article ">Figure 14
<p>TEM images of (<b>A</b>) Au-C<sub>4</sub>N; (<b>B</b>) Au-C<sub>8</sub>N; (<b>C</b>) Au-C<sub>12</sub>N; (<b>D</b>) Au-C<sub>16</sub>N; and (<b>E</b>) Au-C<sub>18</sub>N colloids after digestive ripening in toluene.</p> Full article ">Figure 15
<p>Comparison of surface plasmon resonance of these gold-amine colloids after digestive ripening in toluene.</p> Full article ">Figure 16
<p>UV-visible spectrum of Au-aniline in butanone before and after digestive ripening, and the digestive ripening process kept going for 2 h.</p> Full article ">Figure 17
<p>Photographs of (<b>A</b>) Au-aniline colloids in butanone seven days after digestive ripening; and (<b>B</b>) Au-aniline colloids in toluene seven days after digestive ripening.</p> Full article ">Figure 18
<p>UV-Vis spectrum of Au-aniline colloids before and after digestive ripening 2 h in toluene.</p> Full article ">Figure 19
<p>TEM images of (<b>A</b>) Au-pure aniline colloids after 7 days; (<b>B</b>) Au-pure aniline colloids after digestive ripening. The particle size distributions of the Au-aniline colloid are given in the inset of (<b>A</b>) and (<b>B</b>), the mean diameter of the particle size is 7.1 ± 5.3 nm, 4.6 ± 0.9 nm respectively.</p> Full article ">Figure 20
<p>Photographs of (<b>A</b>) Au-pure aniline colloids after digestive ripening 2 h; and (<b>B</b>) the Au-pure aniline colloids that was ripened for 7 days.</p> Full article ">Figure 21
<p>TEM images of (<b>A</b>) As prepared Au-phenethylamine colloids in butanone; (<b>B</b>) Au-phenethylamine colloids after 2 h digestive ripening in butanone; and (<b>C</b>) Au-phenethylamine after 3 h digestive ripening.</p> Full article ">Figure 22
<p>UV-visible spectrum of Au-phenethylamine colloids before and after digestive ripening.</p> Full article ">
1418 KiB  
Article
CO and NO2 Selective Monitoring by ZnO-Based Sensors
by Mokhtar Hjiri, Lassaad El Mir, Salvatore Gianluca Leonardi, Nicola Donato and Giovanni Neri
Nanomaterials 2013, 3(3), 357-369; https://doi.org/10.3390/nano3030357 - 5 Jul 2013
Cited by 98 | Viewed by 9534
Abstract
ZnO nanomaterials with different shapes were synthesized, characterized and tested in the selective monitoring of low concentration of CO and NO2 in air. ZnO nanoparticles (NPs) and nanofibers (NFs) were synthesized by a modified sol-gel method in supercritical conditions and electrospinning technique, [...] Read more.
ZnO nanomaterials with different shapes were synthesized, characterized and tested in the selective monitoring of low concentration of CO and NO2 in air. ZnO nanoparticles (NPs) and nanofibers (NFs) were synthesized by a modified sol-gel method in supercritical conditions and electrospinning technique, respectively. CO and NO2 sensing tests have demonstrated that the annealing temperature and shape of zinc oxide nanomaterials are the key factors in modulating the electrical and sensing properties. Specifically, ZnO NPs annealed at high temperature (700 °C) have been found sensitive to CO, while they displayed negligible response to NO2. The opposite behavior has been registered for the one-dimensional ZnO NFs annealed at medium temperature (400 °C). Due to their adaptable sensitivity/selectivity characteristics, the developed sensors show promising applications in dual air quality control systems for closed ambient such as automotive cabin, parking garage and tunnels. Full article
(This article belongs to the Special Issue Nanomaterials in Sensors)
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<p>(<b>a</b>) TEM images of ZnO NPs; (<b>b</b>) X-ray diffraction pattern of these nanoparticles.</p> Full article ">Figure 2
<p>SEM images of ZnO/PVA as-spun nanofibers.</p> Full article ">Figure 3
<p>SEM images showing the morphology of samples annealed at 400 °C and deposited on the sensor substrate. (<b>a</b>) ZnO NPs; (<b>b</b>) ZnO NFs; (<b>c</b>) Higher magnification of ZnO NFs.</p> Full article ">Figure 4
<p>Picture of the home-made probe.</p> Full article ">Figure 5
<p>Transient responses to various CO concentrations in air at the operating temperature of 350 °C of the ZnO nanoparticles (NPs) sensor annealed at different temperatures.</p> Full article ">Figure 6
<p>Response of ZnO nanoparticles annealed at 400 °C (red) and 700 °C (black) as a function of CO and NO<sub>2</sub> concentrations at 350 °C.</p> Full article ">Figure 7
<p>Response of ZnO NFs sensor to 50 ppm of CO as a function of the temperature.</p> Full article ">Figure 8
<p>Transient responses of the nanofibers (NFs) based sensor tested to different NO<sub>2</sub> concentrations in air at the operating temperature of 350 °C. In the inset is shown the calibration curve.</p> Full article ">Figure 9
<p>Schematic representation of the distribution of semiconducting particles on the substrate and related sensitivity pattern.</p> Full article ">
849 KiB  
Review
Photoelectrochemical Properties of Graphene and Its Derivatives
by Alberto Adán-Más and Di Wei
Nanomaterials 2013, 3(3), 325-356; https://doi.org/10.3390/nano3030325 - 3 Jul 2013
Cited by 103 | Viewed by 12708
Abstract
Graphene and its derivatives combine a numerous range of supreme properties that can be useful in many applications. The purpose of this review is to analyse the photoelectrochemical properties of pristine graphene, graphene oxide (GO) and reduced graphene oxide (rGO) and their impact [...] Read more.
Graphene and its derivatives combine a numerous range of supreme properties that can be useful in many applications. The purpose of this review is to analyse the photoelectrochemical properties of pristine graphene, graphene oxide (GO) and reduced graphene oxide (rGO) and their impact on semiconductor catalysts/quantum dots. The mechanism that this group of materials follows to improve their performance will be cleared by explaining how those properties can be exploited in several applications such as photo-catalysts (degradation of pollutants) and photovoltaics (solar cells). Full article
(This article belongs to the Special Issue Graphene Quantum Dots)
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<p>Graphene oxide structure representation. Reprinted with copyright permission from reference [<a href="#B15-nanomaterials-03-00325" class="html-bibr">15</a>]. Copyright © 2012, American Chemical Society.</p> Full article ">Figure 2
<p>Photodegradation of malachite green (MB) under (<b>a</b>) UV light; and (<b>b</b>) Visible light (λ &gt; 400 nm) over (1) P25; (2) P25-CNTs; and (3) P25-GR photocatalysis respectively. Reprinted with copyright permission from reference [<a href="#B95-nanomaterials-03-00325" class="html-bibr">95</a>]. Copyright © 2010, American Chemical Society.</p> Full article ">Figure 3
<p>Proposed mechanism for the photodegradation of methylene blue (MB) by graphene-wrapped anatase nanoparticles under visible-light irradiation [<a href="#B10-nanomaterials-03-00325" class="html-bibr">10</a>,<a href="#B83-nanomaterials-03-00325" class="html-bibr">83</a>]. Reprinted with copyright permission from reference [<a href="#B83-nanomaterials-03-00325" class="html-bibr">83</a>]. Copyright © 2012 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim, Germany.</p> Full article ">Figure 4
<p>The introduced 2D rGO bridges perform as an electron acceptor and transfer the electrons quickly. Hence, the recombination and back reaction are suppressed. Reprinted with copyright permission from [<a href="#B107-nanomaterials-03-00325" class="html-bibr">107</a>]. Copyright © 2010, American Chemical Society.</p> Full article ">Figure 5
<p>Schematic diagrams of the energy levels in the reduced graphene oxide-CdSe based quantum dot sensitized solar cell [<a href="#B60-nanomaterials-03-00325" class="html-bibr">60</a>]. Reprinted with copyright permission from [<a href="#B108-nanomaterials-03-00325" class="html-bibr">108</a>]. Copyright © 2011, American Institute of Physics.</p> Full article ">Figure 6
<p>Degradation of Rh. B as a function of catalysis and irradiation time. Reprinted with copyright permission from reference [<a href="#B112-nanomaterials-03-00325" class="html-bibr">112</a>]. Copyright © 2013, Elsevier.</p> Full article ">Figure 7
<p>Schematic representation of photo-generated electron transfer processes in a layered reduced graphene oxide/quantum dot (QD) structure with TiO<span class="html-italic"><sub>x</sub></span> interlayer (<b>a</b>) and the Energy Band Diagram (<b>b</b>) showing the main electronic processes at the interface in QDs: (1) Electron injection; (2) electron transfer; (3) Trapping of the electron at surface states; the two charge recombination pathways of trapped electron recombination with; (4) the hole at the valence band of QDs and; (5) the oxidized redox couple; (6) hole extraction. The recombination between the electron at Fermi level of rGO and the hole at the valence band of QDs and the oxidized redox couple was inhibited by TiO<span class="html-italic"><sub>x</sub></span> layer. Reprinted with copyright permission from reference [<a href="#B111-nanomaterials-03-00325" class="html-bibr">111</a>]. Copyright © 2011, American Chemical Society.</p> Full article ">Figure 8
<p>Two proposed mechanisms for the photodegradation of MB by rGO/ZnO composite under visible light and energy diagram of excited MB, graphene and the conduction band of ZnO. (<b>a</b>) The excitation of the semiconductor produced by light irradiation generates an electron-hole pair. The reaction with the organic pollutant takes place in the movement of those charges towards the particle surface. (<b>b</b>) The dye, which act as a light sensitizer, is excited and transfers electrons. It becomes a cationic radical that self-degrades. Reprinted with copyright permission from reference [<a href="#B131-nanomaterials-03-00325" class="html-bibr">131</a>]. Copyright © 2013, Elsevier.</p> Full article ">Figure 9
<p>Scheme the hybrid G/PbS phototransistor. Reprinted with copyright permission from reference [<a href="#B139-nanomaterials-03-00325" class="html-bibr">139</a>]. Copyright © 2012, Nature Publishing Group.</p> Full article ">
424 KiB  
Article
A Strategy for Hydroxide Exclusion in Nanocrystalline Solid-State Metathesis Products
by Jiaqi Cheng and Kristin M. Poduska
Nanomaterials 2013, 3(3), 317-324; https://doi.org/10.3390/nano3030317 - 24 Jun 2013
Cited by 20 | Viewed by 8109
Abstract
We demonstrate a simple strategy to either prevent or enhance hydroxide incorporation in nanocrystalline solid-state metathesis reaction products prepared in ambient environments. As an example, we show that ZnCO3 (smithsonite) or Zn5(CO3)2(OH)6 (hydrozincite) forms extremely [...] Read more.
We demonstrate a simple strategy to either prevent or enhance hydroxide incorporation in nanocrystalline solid-state metathesis reaction products prepared in ambient environments. As an example, we show that ZnCO3 (smithsonite) or Zn5(CO3)2(OH)6 (hydrozincite) forms extremely rapidly, in less than two minutes, to form crystalline domains of 11 ± 2 nm and 6 ± 2 nm, respectively. The phase selectivity between these nanocrystalline products is dominated by the alkalinity of the hydrated precursor salts, which may in turn affect the availability of carbon dioxide during the reaction. Thus, unlike traditional aqueous precipitation reactions, our solid-state method offers a way to produce hydroxide-free, nanocrystalline products without active pH control. Full article
(This article belongs to the Special Issue New Developments in Nanomaterial Analysis)
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<p>Representative photographs of the paste-like reaction products from (<b>a</b>) Zn(NO<sub>3</sub>)<sub>2</sub>·6H<sub>2</sub>O and NaHCO<sub>3</sub> precursors, which yields ZnCO<sub>3</sub>; and (<b>b</b>) ZnCl<sub>2</sub> + Na<sub>2</sub>CO<sub>3</sub>, which yields Zn<sub>5</sub>(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>6</sub>.</p> Full article ">Figure 2
<p>Representative indexed X-ray diffraction (XRD) data. In (<b>a</b>), all major peaks corresponding to ZnCO<sub>3</sub> (JCPDS 8-0449) are present when starting with Zn(NO<sub>3</sub>)<sub>2</sub> and NaHCO<sub>3</sub> precursors. In (<b>b</b>), the product matches Zn<sub>5</sub>(OH)<sub>6</sub>(CO<sub>3</sub>)<sub>2</sub> (JCPDS 19-1458).</p> Full article ">Figure 3
<p>Representative (<b>a</b>) Fourier transform infrared spectroscopy (FTIR) spectra and (<b>b</b>) Raman spectra for ZnCO<sub>3</sub> (ZC, blue) and Zn<sub>5</sub>(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>6</sub> (HZ, red). Spectra are offset along the vertical axis for clarity.</p> Full article ">Figure 4
<p>(<b>a</b>) ZnCO<sub>3</sub> (ZC, blue) and Zn<sub>5</sub>(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>6</sub> (HZ, red) show one-step decomposition toward the formation of ZnO. The mass loss curves are shown as solid lines, and their derivatives are shown as dashed lines; (b) The decomposition products match ZnO (JCPDS 36-1451). The representative data shown here are for the product from ZC decomposition.</p> Full article ">
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