Greenhouse Gas Sensors Fabricated with New Materials for Climatic Usage: A Review

With the increasing utilization of fossil fuels in today’s technological world, the atmosphere’s concentration of greenhouse gases is increasing and needs to be controlled. In order to achieve this goal, it is imperative to have sensors that can provide data on the greenhouse gases in the environment. The recent literature contains a few publications that detail the use of new methods and materials for sensing these gases. The first part of this review is focused on the possible effects of greenhouse gases in the atmosphere, and the second part surveys the developments of sensors for greenhouse gases with coverage on carbon nano-materials and composites directed towards sensing gases like CO2, CH4, and NOx. With carbon dioxide measurements, due consideration is given to the dissolved carbon dioxide gas in water (moisture). The density functional calculations project that Pd-doped single-walled carbon nanotubes are ideal for the development of NOx sensors. The current trend is to make sensors using 3D printing or inkjet printing in order to allow for the achievement of ppb levels of sensitivity that have not been realized before. This review is to elaborate on the need for the development of greenhouse gas sensors for climatic usage by using selected examples

2D Materials

Two-dimensional (2D) materials have attracted a great deal of attention in recent years due to their potential applications in gas/chemical sensors, healthcare monitoring, biomedicine, electronic skin, wearable sensing technology and advanced electronic devices. Graphene is one of today's most popular 2D nanomaterials alongside boron nitrides, molybdenum disulfide, black phosphorus and metal oxide nanosheets, all of which open up new opportunities for future devices. This book provides insights into models and theoretical backgrounds, important properties, characterizations and applications of 2D materials, including graphene, silicon nitride, aluminum nitride, ZnO thin film, phosphorene and molybdenum disulfide

Чутливий елемент оптичного сенсора діоксиду сірки

У статті у якості газочутливого матеріала первинного перетворювача оптоелектронного сенсора діоксиду сірки запропоновано використати холестеричний рідкий кристал допований нанотрубками нітриду алюмінію. Проведено оптимізацію складу нанокомпозиту на основі холестеричного рідкого кристалу і нанотрубок нітриду алюмінію для отримання максимальної чутливості його до молекул діоксиду сірки.В статье в качестве газочувствительного материала первичного преобразователя оптоэлектронного сенсора диоксида серы предложено использовать холестерический жидкий кристалл допированных нанотрубками нитрида алюминия. Проведена оптимизация состава нанокомпозита на основе холестерического жидкого кристалла и нанотрубок нитрида алюминия для получения максимальной чувствительности его к молекулам диоксида серыIn paper we propose to use the cholesteric liquid crystal doped by aluminum nitride nanotubes as the material for primary transducer of sulfur dioxide gas optoelectronic sensor. We carried out the optimization of nanocomposites components concentration based on cholesteric liquid crystal doped by aluminum nitride nanotubes for the maximum sensitivity to sulfur dioxide molecules

Interaction of CNCl molecule and single-walled AlN nanotubes using DFT and TD-DFT calculations

AbstractDensity functional theory (DFT) calculations are used to study the influence of cyanogen chloride (CNCl) adsorption over the geometrical and electronic properties of single-walled (5, 0), (8, 0), and (10, 0) AlN nanotubes as an adsorbent for adsorbate. It has been found that, the CNCl can be adsorbed on (5, 0), (8, 0), and (10, 0) AlN nanotubes with the energy values of −0.645, −0.493, −0.470eV, respectively. In addition, the effect of nanotube diameter over the charge transfer between the molecule and nanotube has been studied. Based on the DOS plots, interaction of CNCl over AlN nanotubes has slightly changed the electronic properties of the nanotubes, being insensitive to the adsorption of the CNCl molecule

Development of Thermoplastic Polyurethane-Hexagonal Boron Nitride Composite Foams with Enhanced Effective Thermal Conductivity

Thermoplastic polyurethane (TPU)-hexagonal boron nitride (hBN) composites fabricated by batch foaming were studied in this study. The results of this research demonstrated that by CO2 foaming it was possible to produce TPU foams at relatively low temperatures (60C). The results indicated that the cell size and cell density range are significantly wider at lower saturation pressures to varying foaming temperatures. While TPU foams usually yield extremely high cell population density and small cell size, by applying the appropriate foaming conditions, we prepared foams with a wide range of cell sizes, from 21 to 170 m, and cell population density from 105 to 108 pore/cm3. These conditions have been used to investigate the foaming-assisted filler alignment in TPU composite and nanocomposite foams for tailoring the thermal conductivity. Foamed samples at lower saturation temperatures (i.e. 20 and 40C) yielded higher thermal conductivity than solid counterparts

Group III-nitrides: synthesis and sensor applications

Submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in the Faculty of science Department of Chemistry University of the Witwatersrand. November 2016.An overview of the evolution of synthesis and applications of indium nitride and gallium nitride in modern science and technology is provided. The working principles and parameters of chemical vapour deposition (CVD) synthesis technique are explored in this study. In this study indium oxide, indium phosphate, indium nitride and gallium nitride materials are prepared by CVD. The versatility of CVD on the fabrication of one-dimensional (1D) structures is portrayed. Both change in dimensionality and change in size are achieved by a CVD technique. 1D indium oxide (In2O3) nanowires, nanonails and nanotrees are synthesised from vapour deposition of three-dimensional In2O3 microparticles. While 1D structures of the novel indium phosphate known as triindium bisphosphate In3(PO4)2 were obtained from reactions of In2O3 with ammonium phosphate. The effect of temperature, activated carbon and the type of indium precursor on dimensionality of the synthesized materials is studied. The inter-dependency between temperature and precursors is observed. The presence of activated carbon at high temperatures encouraged growth of secondary structures via production of excess indium droplets that act as catalysts. The combination of activated carbon and high temperature was found responsible for the novel necklace, nanonail, nanotree and nanocomb structures of In2O3. Indium nitride (InN) has for the first time been made by a combined thermal/UV photoassisted process. In2O3 was reacted with ammonia using two different procedures in which either the ammonia was photolysed or both In2O3 and ammonia were photolysed. A wide range of InN structures were made that was determined by the reaction conditions (time, temperature). Thus, the reaction of In2O3 with photolysed NH3 gave InN rod like structures that were made of cones (6 h/ 750 oC) or discs (6 h/ 800 oC) and that contained some In2O3 residue. Photolysis of In2O3 and NH3 by contrast gave InN nanobelts, InN tubes and pure InN tubes filled with In metal (> 60 %). The transformation of the 3D In2O3 particles to the tubular 1D InN was monitored as a function of time (1-6 h) and temperature (700-800 oC); the product formed was very sensitive to temperature. The band gap of the InN tubes was found to be 2.19 eV and of the In filled InN tubes to be 1.89 eV. Gallium nitride (GaN) and indium gallium nitride (InGaN) nanostructures were synthesized from thermal ammonification of gallium oxide (Ga2O3) as well ammonification of a mixture of In2O3 and Ga2O3 respectively. The effect of temperature on preparation of high purity GaN was studied. The GaN materials synthesized at 800 °C showed a mixture of the gallium oxide and the gallium nitride phases from the XRD analysis. However at temperatures ≥ 900 °C high quality GaN nanorods were obtained. The band-to-band ultraviolet optical emission value of 3.21 eV was observed from the GaN nanorods. However, the preparation of InGaN was complicated by the thermally stable In2O3. At lower temperatures inhomogeneous materials consisting of GaN nanorods and In2O3 were obtained. While at high temperatures (≥ 1050 °C) InGaN was obtained. However because indium has a high vapour pressure and a low melting point only a minute amount of it was incorporated in the crystal lattice. Hexagonally shaped nanoplates of In0.01Ga0.99N were successfully obtained. A shift in optical emission to longer wavelengths was observed for the InGaN alloy. A blue optical emission with the energy value of 2.86 eV was observed for the InGaN nanoplates. The two n-type group III-nitrides (InN, GaN) prepared in this study were used for the detection of CO, NH3, CH4 and NO2 gases in the temperature range between 250 and 350 °C. The InN sensor and GaN sensor responses were compared to the response of the wellestablished n-type SnO2 sensor under the same conditions. All the three sensors responded to all the four gases. However, InN and GaN were much more selective in comparison to SnO2. InN sensitivity to CO at 250 °C surpassed its sensitivity to any other gas at the studied temperature range. Its response towards CO at 250 °C was about five times more than that of SnO2 towards CO at the same temperature. While, GaN was the best CH4 sensor at 300 °C in comparison to InN and SnO2 sensors at all temperatures. Meanwhile SnO2 responded remarkably to both NH3 and CO across the studied temperature range with its performance improving with increasing temperature. The ability for InN to respond to both NH3 and NO2 at 250 °C opens up the possibility for an application of InN as an ammonia sensor in diesel engines. InN and SnO2 sensors were found susceptible to humidity interference in a real environmental situation. On the contrary, GaN sensor presented itself as an ideal candidate for indoor and outdoor environments as well as in bio-sensors because it showed robustness and inertness towards humidity. InN and GaN by showing activity at high temperatures only, presented themselves as good candidates for in-situ high temperate gas sensing applications. Response and recovery times for all sensors showed improvement with increasing temperature.MT201

Sensing of Letrozole Drug by Pure and Doped Boron Nitride Nanoclusters: Density Functional Theory Calculation

Background: Letrozole is a non-steroidal drug utilized as a treatment of hormone-sensitive breast cancer. It has been shown that letrozole has harmful side effects. Therefore, it seems necessary to design a letrozole drug sensor. In this work, we scrutinized the sensing properties of the B30N30, AlB29N30, and GaB29N30 nanoclusters toward the letrozole drug in various adsorption sites. Methods: Investigations were done using the density functional theory (DFT) calculation with the B3PW91/6-311G(d, p) level of theory. The time-dependent density functional theory (TD-DFT) calculations were used to investigate Ultraviolet-visible (UV-vis) spectrums with the same level of theory. Results: The adsorption energy of B30N30, AlB29N30, and GaB29N30 in the most stable complexes were calculated at -16.81, -34.62, and -27.41 kcal mol-1, respectively. The results obtained from the study of electronic properties showed a high sensitivity for the detection of letrozole in B30N30 compared to AlB29N30 and GaB29N30. The calculated recovery time for the B30N30 is 0.13 × 10-5 s, which indicates a very short recovery time. The UV-vis spectrums showed that the letrozole/B30N30 exhibits shift toward the higher wavelengths (red shift). Conclusion: Therefore, these results showed that the B30N30 is a good candidate for identifying letrozole. Further, B30N30 would be more effective than AlB29N30 and GaB29N30 due to the simple synthesis

Micro-Fabricated Hydrogen Sensors Operating at Elevated Temperatures

In this dissertation, three types of microfabricated solid-state sensors had been designed and developed on silicon wafers, aiming to detect hydrogen gas at elevated temperatures. Based on the material properties and sensing mechanisms, they were operated at 140°C, 500°C, and 300°C. The MOS-capacitor device working at 140°C utilized nickel instead of the widely-used expensive palladium, and the performance remained excellent. For very-high temperature sensing (500°C), the conductivity of the thermally oxidized TiO2 thin film based on the anodic aluminum oxide (AAO) substrate changed 25 times in response to 5 ppm H2 and the response transient times were just a few seconds. For medium-high temperatures (~300°C), very high sensitivity (over 100 times’ increment of current for H2 concentration at 10 ppm) was obtained through the reversible reduction of the Schottky barrier height between the Pt electrodes and the SnO2 nano-clusters. Fabrication approaches of these devices included standard silicon wafer processing, thin film deposition, and photolithography. Materials characterization methods, such as scanning electron microscopy (SEM), atomic force microscopy (AFM), surface profilometry, ellipsometry, and X-ray diffractometry (XRD), were involved in order to investigate the fabricated nano-sized structures. Selectivities of the sensors to gases other than H2 (CO and CH4) were also studied. The first chapter reviews and evaluates the detection methodologies and sensing materials in the current research area of H2 sensors and the devices presented this Ph.D. research were designed with regard to the evaluations

Label-free detection of human prostate-specific antigen (hPSA) using film bulk acoustic resonators (FBARs)

Label-free detection of cancer biomarkers using low cost biosensors has promising applications in clinical diagnostics. In this work, ZnO-based thin film bulk acoustic wave resonators (FBARs) with resonant frequency of ∼1.5 GHz and mass sensitivity of 0.015 mg/m2 (1.5 ng/cm2) have been fabricated for their deployment as biosensors. Mouse monoclonal antibody, anti-human prostate-specific antigen (Anti-hPSA) has been used to bind human prostate-specific antigen (hPSA), a model cancer used in this study. Ellipsometry was used to characterize and optimise the antibody adsorption and antigen binding on gold surface. It was found that the best amount of antibody at the gold surface for effective antigen binding is around 1 mg/m2, above or below which resulted in the reduced antigen binding due to either the limited binding sites (below 1 mg/m2) or increased steric effect (above 1 mg/m2). The FBAR data were in good agreement with the data obtained from ellipsometry. Antigen binding experiments using FBAR sensors demonstrated that FBARs have the capability to precisely detect antigen binding, thereby making FBARs an attractive low cost alternative to existing cancer diagnostic sensors.This work was supported by the Engineering and Physical Sciences Research Council [grants EP/F062966/1, EP/F063865/1 and EP/F06294X/1], the Royal Society [grant RG120061] and the National Natural Science Foundation of China (NSFC) [grant 61150110485].This is the accepted manuscript version. The final published version of the article is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0925400513011052