Gas separation through carbon nanotubes

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Layering phenomena of carbon dioxide and methane transported through carbon nanotubes are being examined through molecular dynamics. The layering formation is investigated for carbon nanotubes ranging from (6,6) to (20,20) subjected to pressures spanning between 5-20 bar at 300 K. Well defined layers are developed both in the internal and external surface of the nanotubes for all the examined cases. It is also shown that the number of layers along with their absolute strength varies as a function of the nanotube's diameter, carbon dioxide and methane's density and gas-structure interactions. Finally, the diffusion inside the interior of the nanotubes has been examined showing a Fickian diffusion mode

Nanoscale Au-ZnO heterostructure developed by atomic layer deposition towards amperometric H2O2 detection

Nanoscale Au-ZnO heterostructures were fabricated on 4-in. SiO2/Si wafers by the atomic layer deposition (ALD) technique. Developed Au-ZnO heterostructures after post-deposition annealing at 250 degrees C were tested for amperometric hydrogen peroxide (H2O2) detection. The surface morphology and nanostructure of Au-ZnO heterostructures were examined by field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), etc. Additionally, the electrochemical behavior of Au-ZnO heterostructures towards H2O2 sensing under various conditions is assessed by chronoamperometry and electrochemical impedance spectroscopy (EIS). The results showed that ALD-fabricated Au-ZnO heterostructures exhibited one of the highest sensitivities of 0.53 mu A mu M(-1)cm(-2), the widest linear H2O2 detection range of 1.0 mu M-120mM, a low limit of detection (LOD) of 0.78 mu M, excellent selectivity under the normal operation conditions, and great long-term stability. Utilization of the ALD deposition method opens up a unique opportunity for the improvement of the various capabilities of the devices based on Au-ZnO heterostructures for amperometric detection of different chemicals

III-nitride-based optochemical transducers for gas detection

Customers of modern airplanes not only demand that manufacturers address more efficient propulsion systems but also pollution created by the overall aircraft system. One way of decreasing pollution is the replacement of kerosene burning auxiliary power units (APU) with hydrogen fuel cells. The usage of fuel cells requires a gas sensor system for safe application in an aircraft, and this can be achieved using a novel gas sensitive InGaN/GaN nanowire arrays (NWA) with an optical read out. These NWAs are investigated in this thesis and exhibit an efficient photolumines-cence (PL) which extends to temperatures of 200°C and beyond and show a chemical sensitivity towards gases and liquids. The gas sensing test revealed that InGaN/GaN NWA can have a quenching or an enhancing PL when exposed to different gas atmos-pheres which depends on both the type of adsorbate and the operation conditions of the transducer. All groups of tested analytes have in common that they can be described using a Langmuir adsorption isotherm. However, the adsorption energy and the response direction is gas species dependent. Oxidizing gases such as O2, NO2 and O3 quench the PL intensity whereas hydrocarbons, under the certain conditions, can increase the PL. Evaluation of the Langmuir adsorption energy showed an approximately linear increase with temperature in the range from room temperature to 150°C. This phenomenon was attributed to a competitive adsorption process onto a limited number of adsorption sites on the InGaN/GaN surfaces. Hydrocarbons showed an insignificant gas response when these are diluted in nitrogen. However, a PL enhancing effect can be observed when these gases are diluted in synthetic air and this effect is increased at elevated temperatures. This behavior is attributed to an indirect gas sensing process which includes a surface oxidation reaction of the analytes and a removal of PL quenching pre-adsorbed oxygen and formation of combustion products such as CO2 and H2O. CO2 hardly shows any effect on the PL intensity but H2O shows an interesting effect on the PL intensity as it can be of PL quenching and PL enhancing nature depending on the operation conditions. In the low temperature and excitation energy regime water molecules are able to increase the surface recombination process but at elevated temperatures and due to electrochemically dissociated water molecules these recombination channels are passivated and the PL is enhanced.Auf den Anforderungslisten für moderne Flugzeuge stehen nicht nur effiziente An- triebssysteme, sondern ein möglichst ökologisches Gesamtflugzeugsystem. Eine Möglichkeit, die Umweltverschmutzung zu verringern, ist der Ersatz von kerosinbetriebenen Hilfsaggregaten (APU) durch Wasserstoff-Brennstoffzellen. Der Einsatz von Brennstoffzellen erfordert ein Gassensorsystem für den sicheren Betrieb in einem Flugzeug, was mit einem neuartigen gasempfindlichen InGaN/GaN-Nanodraht-Array (NWA) mit optischer Auslesung erreicht werden kann. Solche NWA, dessen Photolumineszenz (PL) auch bei Temperaturen über 200°C stabil ist und eine Sensitivität gegenüber Gasen und Flüssigkeiten aufweist, wurden im Rahmen dieser Arbeit untersucht. Gassensor-Tests ergaben, dass die PL des InGaN/GaN NWA sowohl verstärkt als auch reduziert werden kann wenn es unterschiedlichen Gasatmosphären ausgesetzt wird, was sowohl von der Art des Adsorbats als auch von den Betriebsbedingungen des Transducers abhängt. Bei allen untersuchten Gasen konnten Langmuir-Adsorptionsisothermen deren Adsorption beschreiben. Die Adsorptionsenergie und die Richtung des Gasresponses sind jedoch von der Art des Gases abhängig. Oxidierende Gase wie O2, NO2 und O3 reduzieren die PL-Intensität, während Kohlenwasserstoffe unter bestimmten Bedingungen die PL erhöhen können. Die Auswertung der Langmuir-Adsorptionsenergie ergab einen annähernd linearen Anstieg im Bereich von Raumtemperatur bis 150°C. Dieses Phänomen wurde auf einen konkurrierenden Adsorptionsprozess auf der InGaN/GaN-Oberfläche zurückgeführt. Kohlenwasserstoffe zeigten eine unwesentliche Gasreaktion wenn diese in Stickstoffhintergrund gemessen wurden. Ein PL-verstärkender Effekt kann jedoch beobachtet werden, wenn diese Gase in synthetischer Luft gemischt werden und dieser Effekt wurde bei erhöhten Temperaturen noch weiter verstärkt. Dieses Verhalten wird einem indirekten Gasdetektionsprozess zugeschrieben, der eine Oberflächenoxidationsreaktion der Analyten mit einer Verdrängung von adsorbiertem Sauerstoff und der Bildung von Verbrennungsprodukten wie CO2 und H2O beinhaltet. CO2 hat kaum einen Einfluss auf die PL, aber H2O zeigt einen interessanten Einfluss auf die PL-Intensität, da es je nach Betriebsbedingungen der NWA von PL-reduzierender als auch PL-verstärkender Natur sein kann. Im Niedrigtemperatur- und Anregungsenergiebereich sind Wassermoleküle in der Lage, den Oberflächenrekombinationsprozess zu verstärken, aber bei erhöhten Temperaturen und durch elektrochemisch-dissoziierte Wassermoleküle werden diese Rekombinationskanäle passiviert und die PL erhöht

Tunable Assembly of Gold Nanorods in Polymer Solutions to Generate Controlled Nanostructured Materials

Gold nanorods grafted with short chain polymers are assembled into controlled open structures using polymer-induced depletion interactions and structurally characterized using small angle x-ray scattering. When the nanorod diameter is smaller than the radius of gyration of the depletant polymer, the depletion interaction depends solely on the correlation length of the polymer solution and not directly on the polymer molecular weight. As the polymer concentration increases, the stronger depletion interactions increasingly compress the grafted chains and push the gold nanorods closer together. By contrast, other structural characteristics such as the number of nearest neighbors and fractal dimension exhibit a non-monotonic dependence on polymer concentration. These parameters are maximal at intermediate concentrations, which are attributed to a crossover from reaction-limited to diffusion-limited aggregation. The control over structural properties of anisotropic nanoscale building blocks demonstrated here will be beneficial to designing and producing materials \emph{in situ} with specific direction-dependent nanoscale properties and provides a crucial route for advances in additive manufacturing

Microfluidics: Fluid physics at the nanoliter scale

Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Péclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world

Recent advances in the field of bionanotechnology: An insight into optoelectric bacteriorhodopsin, quantum dots, and noble metal nanoclusters

Molecular sensors and molecular electronics are a major component of a recent research area known as bionanotechnology, which merges biology with nanotechnology. This new class of biosensors and bioelectronics has been a subject of intense research over the past decade and has found application in a wide variety of fields. The unique characteristics of these biomolecular transduction systems has been utilized in applications ranging from solar cells and single-electron transistors (SETs) to fluorescent sensors capable of sensitive and selective detection of a wide variety of targets, both organic and inorganic. This review will discuss three major systems in the area of molecular sensors and electronics and their application in unique technological innovations. Firstly, the synthesis of optoelectric bacteriorhodopsin (bR) and its application in the field of molecular sensors and electronics will be discussed. Next, this article will discuss recent advances in the synthesis and application of semiconductor quantum dots (QDs). Finally, this article will conclude with a review of the new and exciting field of noble metal nanoclusters and their application in the creation of a new class of fluorescent sensors