773 research outputs found

    Polymer/ionic liquid pilot scale membrane prototype for the recovery of difluoromethane (R-32) from refrigerant mixtures

    Get PDF
    Difluoromethane (R-32) is a hydrofluorocarbon (HFC) that has been massively used over the last 30 years in refrigeration and air conditioning as a primary component of azeotropic or close boiling refrigerant mixtures. Despite environmental directives commanded to drastically reduce the use of HFCs, R-32 has excellent thermodynamic properties and moderate GWP, thus its recovery from depleted mixtures collected from end-of-life equipment is sought to synthesize alternative low-GWP refrigerant blends. Membrane separation using composite polymer/ionic liquid membranes based on poly-ether-block-amide have shown potential to separate R-32 from other fluorinated hydrocarbons, yet the development of this type of composite membranes still remains at laboratory scale. In this work, a spray coating technique was successfully applied to create defect-free thin selective layers of neat Pebax®1657, Pebax®1657/40 wt% [C2C1im][BF4] and Pebax®1657/40 wt% [C2C1im][SCN] coated on porous PVDF substrates. This methodology was transferred from the lab-scale tests (12.6 cm2) to a custom pilot set-up (300 cm2). The pilot results confirmed the superior performance and stability of [C2C1im][SCN]-based membranes, which allowed the recovery of up to 64.3% and 67.1% R-32 from the refrigerant mixtures R-410A (69.8 mol % R-32 and 30.2 mol % R-125) and R-454B (82.1 mol % R-32 and 17.9 mol % R-1234yf) at 6 bar, increasing the R-32 permeate concentration up to 89.6 and 95.9 mol %, respectively. These results highlight the need to expand the knowledge of this type of gas separation membranes towards thinner and defect-free selective dense layers with the purpose of approaching their real applications.This research is supported by Project KET4F-Gas – SOE2/P1/P0823, Project PID2019-105827RB-I00 funded by MCIN/AEI/10.1039/501100011033 (Spain), and project LIFE4F-Gases (LIFE20CCM/ES/001748) co-funded by the European Union LIFE programme. F.P. acknowledges the post-doctoral fellowship (IJC2020-043134-I, ‘Juan de la Cierva Incorporación’) funded by the Spanish Ministry of Science and Innovation MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR. S. V. G. acknowledges the pre-doctoral fellowship FPI PRE2020-093568, funded by the Spanish Ministry of Science and Innovation MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”

    Semiconducting Polymers for Electronic Biosensors and Biological Interfaces

    Get PDF
    Bioeletronics aims at the direct coupling of biomolecular function units with standard electronic devices. The main limitations of this field are the material needed to interface soft living entities with hard inorganic devices. Conducting polymers enabled the bridging between these two separate worlds, owing to their biocompatibility, soft nature and the ability to be tailored according to the required application. In particular, the intrinsically conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is one of the most promising polymers, having an excellent chemical and thermal stability, reversible doping state and high conductivity. This thesis relies on the use of PEDOT:PSS as semiconducting material for biological interfaces and biosensors. In detail, OECTs were demonstrated to be able to real-time monitor growth and detachment of both strong-barrier and no-barrier cells, according to the patterning of the device active area and the selected geometry. Thus, these devices were employed to assess silver nanoparticles (AgNPs) toxicity effects on cell lines, allowing further insights on citrate-coated AgNPs uptake by the cells and their toxic action, while demonstrating no cytotoxic activity of EG6OH-coated AgNPs. Moreover, PEDOT:PSS OECTs were proved to be capable of detecting oxygen dissolved in KCl or even cell culture medium, in the oxygen partial pressure range of 0-5%. Furthermore, PEDOT:PSS OECTs were biofunctionalized to impart specificity on the device sensing capabilities, through a biochemical functionalization strategy, electrically characterized. The resulting devices showed a proof of concept detection of a fundamental cytokine for cells undergoing osteogenic differentiation. Finally, PEDOT:PSS thickness-controlled films were employed as biocompatible, low-impedance and soft interfaces between the animal nerve and a gold electrode. The introduction of the plasticizer polyethylene glycol (PEG) enhanced the elasticity of the polymer, while keeping good conductivity and low-impedance properties. An in-vivo, chronic recording of the renal sympathetic nerve activity in rats demonstrated the efficiency of the device

    Fabrication and characterization of cellulose acetate-based nanofibers and nanofilms for H2S gas sensing application

    Get PDF
    Electrospun nanofibers and solution-casting nanofilms were produced from an environmentally friendly cellulose acetate (CA) blended with glycerol (as an ionic liquid (IL)), mixed with polypyrrole (PPy, a conducting polymer) and doped with tungsten oxide (WO3) nanoparticles. The sensing membranes fabricated were used to detect H2S gas at room temperature and shown to exhibit high performance. The results revealed that the lowest operating temperature of both nanofiber and nanofilm sensors was 20oC, with a minimum gas detection limit of 1 ppm. Moreover, the sensor exhibits a reasonably fast response, with a minimum average response time of 22.8 and 31.7 s for the proposed nanofiber and nanofilm based sensors, respectively. Furthermore, the results obtained indicated an excellent reproducibility, long-term stability, and low humidity dependence. Such distinctive properties coupled with an easy fabrication technique provide a promising potential to achieve a precise monitoring of harmful H2S gas in both indoor and outdoor atmospheres

    Characterization Of Commercially Available Conductive Filament And Their Application In Sensors And Actuators

    Get PDF
    The primary aim of this study is to contribute to the field of additives that would enable the fabrication of electrical sensors and actuators completely via Material Extrusion based Additive Manufacturing (MEAM). The second aim of the study is to provide the necessary characterization to facilitate the development of applications that predicts electrical part performance. The electrical characterization of two conductive poly-lactic acid (PLA) filaments, namely, c-PLA with carbon black and graphene PLA was performed to study the temperature coefficient of the resistance. Resistivity of carbon black filament was compared to a printed single layer and with that of a cube. The raw and printed c-PLA showed a positive temperature coefficient of resistance (α) ranging from ~0.03-0.01 ℃-1 while its counterpart in the study, graphene PLA, did not exhibit significant (α). Parts from graphene PLA with multilayer MEAM exhibited a negative α to a certain temperature before exhibiting positive α. The resistivity of the printed parts was 300 times higher for c-PLA and 1500 times for graphene PLA. However, no microstructural or chemical compositional changes were observed between the raw filaments and the printed parts. Due to the high α of the c-PLA, it was deemed as the better material for constructing electro thermal sensors and actuators using MEAM. First, c-PLA was used to fabricate and package a completely 3D printed flow meter that operates on the principle of Joule heating and hotwire anemometry. When the designed flowmeter was simulated using a finite element package, a flow sensitivity of -2.33 Ω sccm-1 and a relative change in resistivity of 0.036 sccm-1 was expected. For an operating voltage of 12-15 V, the experimental results showed a flow sensitivity within the range of 0.014-0.032 sccm-1 and the relative change in resistivity ranged from 0.039 – 0.065 sccm-1. Thus, a completely 3D printed flowmeter was demonstrated. Second, using the same principle of Joule heating, an actuator inspired from MEMS chevron grippers was designed, simulated, and fabricated. Simulation showed the feasibility of the structure and further predicted a displacement of a few hundred microns with a potential as low as 3 V with a cooling time as little less than 120 seconds. Experimentally, a displacement of 120.04, 97.05, and 88.96 μm were achieved in 15, 10, and 5 seconds with actuation potentials of 12.7, 13.8, and 17.9 V, respectively. As predicted by the simulation results, it took longer for the gripper to cool (close to 180 seconds) when compared to actuation times. During the above studies, we discovered the printing parameters altered the part resistance. Our final study examined how extrusion temperature and printing speed affects the impedance of the MEAM printed parts. Further, anisotropy in the impedance was observed and the influence of the interface to it was examined. From the experimental results, the anisotropy was quantified with a Z/F ratio and was found to be nearly constant, ~2.15±0.23. Impedance scaling with the number of interfaces was measured and showed conclusively that the interlayer bonding was the sole source for the observed Z/F ratio. Scanning electron microscope images shows the absence of air gaps at the interface, and energy dispersion spectroscopy shows the absence of oxidation at the interface. By investigating the role of print parameters and scaling of impedance with interfaces, a framework to model and predict electrical behavior of electro thermal sensors and actuators made via MEAM can be realized

    The combustion behavior of epoxy‐based multifunctional electrolytes

    Get PDF
    Multifunctional or structural electrolytes are characterized by ionic conductivity high enough to be used in the electrochemical devices and mechanical performance suitable for the structural applications. Preliminary insights are provided into the combustion behavior of structural bi‐continuous electrolytes based on bisphenol A diglycidyl ether (DGEBA), synthesized using the techniques of reaction induced phase separation and emulsion templating. The effect of the composition of the structural electrolytes and external heat flux on the behavior of the formulations were studied using a cone calorimeter with gases formed during testing analyzed using FTIR. The composition of the formulations investigated was changed by varying the type and amount of the ion conductive part of the bi‐continuous electrolyte. Two ionic liquids, 1‐ethyl‐3‐methylimidazolium bis(fluorosulfonyl)imide (EMIM‐TFSI) and 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIM‐BF4), as well as a deep eutectic solvent (DES) based on ethylene glycol and choline chloride, were used. The results obtained confirm that time to ignition, heat release rate (HRR), total mass loss, as well as the composition of the gases released during tests depend on the composition of the formulations. Addition of liquid electrolyte is found to reduce the time to ignition by up to 10% and the burning time by between 28% and 60% with the added benefit of reducing the HRR by at least 34%. Gaseous products such as CO2, CO, H2O, CH4, C2H2, N2O, NO, and HCN were detected for all formulations with the gases SO2, NH3, HCl, C2H4, and NH3 found to be for certain formulations only

    Synthesis and characterisation of ETS-10/acetate-based ionic liquid/chitosan mixed matrix membranes for CO2/N2 permeation

    Get PDF
    Mixed matrix membranes (MMMs) were prepared by incorporating organic surfactant-free hydrothermally synthesised ETS-10 and 1-ethyl-3-methylimidazolium acetate ionic liquid (IL) to chitosan (CS) polymer matrix. The membrane material characteristics and permselectivity performance of the two-component membranes were compared with the three-component membrane and the pure CS membrane. The addition of IL increased CO2 solubility of the polymer, and, thus, the CO2 affinity was maintained for the MMMs, which can be correlated with the crystallinity, measured by FT-IR, and void fraction calculations from differences between theoretical and experimental densities. The mechanical resistance was enhanced by the ETS-10 nanoparticles, and flexibility decreased in the two-component ETS-10/CS MMMs, but the flexibility imparted by the IL remained in three-component ETS-10/IL/CS MMMs. The results of this work provide insight into another way of facing the adhesion challenge in MMMs and obtain CO2 selective MMMs from renewable or green chemistry materials

    Vapour sensing applications and electrical conduction mechanisms of a novel metal-polymer composite

    Get PDF
    A novel metal-polymer composite is presented, comprised of a micron-sized nickel powder dispersed within a silicone polymer matrix. The composite is intrinsically electrically insulating, but displays a dramatic increase in conductivity under compression, tension and torsion. The electrical response to applied compression is characterised. Combined with electron microscopy, the large sensitivity to compression is shown to be due to the uniquely spiky morphology of the filler particles. Low mechanical energy mixing techniques are essential for retaining these sharp tips. In addition, wetting of the nickel particles by the silicone polymer is highly effective, resulting in negligible inter-particle contact between metallic grains even at very high loadings and compressions. Current-voltage characteristics are highly non-linear, displaying peaks, hysteresis, negative differential resistance, trap-filling and radio frequency emission. Evidence points towards an inter-particle conduction mechanism dominated by field emission and Fowler-Nordheim tunnelling, made possible by localised field enhancements at the sharp tips. A novel mechanism of grain charging and the 'pinching-off of conduction pathways is also suggested. Granular forms of the composite display dramatic increases in resistance when exposed to organic solvent vapours, transduced by a polymer swelling mechanism. Responses are dependent upon vapour concentration, and differential responses are obtained with other polymers, indicating excellent potential for applications in artificial olfactory devices (electronic noses). Polymer-solvent interactions follow both Fickian and anomalous diffusion characteristics, and follow basic trends predicted by solubility parameters

    CARBON-SULFUR NANOCOMPOSITES FOR LITHIUM-SULFUR BATTERIES

    Get PDF
    The increasing reliance on energy storage systems is constantly pushing research efforts to find better performing, low cost electrochemical batteries. The lithium-sulfur battery has been deemed one of the most viable candidates due to its high energy density and non-toxic, inexpensive components. In order to reach its full potential, sulfur should be incorporated into a conductive carbon host structure to ensure its electrical conductivity and cycling performance. In addition, rapid capacity fading resulting from the polysulfide shuttle mechanism should be addressed. The goal of this dissertation is to employ transmission electron microscopy (TEM) to study various nanostructured carbon materials that can serve as a cathode component in a lithium-sulfur battery. The dissertation is divided into three topics. The first topic describes the creation of graphene/sulfur composites suitable for in-situ TEM. TEM studies on sulfur are limited due to sulfur’s ability to sublimate at the operating conditions of most conventional TEMs. Therefore, we develop a layered structure in which sulfur is enveloped between two graphene sheets to stabilize the sulfur. We report the fabrication methods and TEM analysis of these structures. The second topic is the study of sulfur which is incorporated into single-walled carbon nanotubes (SWCNTs). The inner cavity of a SWCNT provides a large electrochemical interface, good mechanical stability and the potential to retain polysulfides formed during cycling. We utilize a two-step procedure consisting of thermal oxidation and high-temperature filling to produce sulfur-filled SWCNTs. Our electrochemical testing shows a clear dependence on the cell’s performance with the thermal oxidation temperature. We conclude that 475 °C is the optimal oxidation temperature for sulfur filling and results in the most stable cycling performance. The last topic is in-situ TEM studies of multi-walled carbon nanotube-sulfur composites utilizing various solid electrolytes. We examine the implications of employing a Li2S-P2S5 solid electrolyte and compare with a Li2O solid electrolyte during in-situ TEM studies. When using a Li2S-P2S5 solid electrolyte, we are able to show the formation of a lithium-sulfide phase on the surface of MWCNT-sulfur composites and show evidence of lithium dendrite growth suppression

    Synthesis and evaluation of SOD-ZMOF-chitosan adsorbent for post-combustion carbon dioxide capture

    Get PDF
    A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering September, 2017South Africa emits large amounts of carbon dioxide (CO2) due to its reliance on coal. The emission of CO2 needs to be reduced for clean sustainable energy generation. Research efforts have therefore been devoted to reducing CO2 emissions by developing cost-effective methods for capturing and storing it. Amine-based absorption using monoethanolamine solvent is the most mature technique for CO2 capture despite its huge energy consumption, corrosiveness and difficulty in solvent regeneration. However, CO2 removal by solid adsorbents is a promising alternative because it consumes less energy, and can be operated at moderate temperature and pressure. Metal organic frameworks have received attention as a CO2 adsorbent because they have large surface areas, open metal sites, high porosity and they require less energy for regeneration. This research was aimed at optimizing and scaling-up SOD-ZMOF through structural modification for enhanced CO2 adsorption by impregnating it with chitosan. Scaled-up SOD-ZMOF samples were prepared as described elsewhere and impregnated with Chitosan. Physiochemical properties obtained using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Nitrogen physisorption showed that SOD-ZMOF and SOD-ZMOF-chitosan were successfully synthesized. Qualitatively, the surface area of the SOD-ZMOF synthesized using the scaled up protocol is lower than the one prepared using the non-scaled-up protocol XRD pattern of SOD-ZMOF showed that it was crystalline and was in agreement with literature. The XRD peaks of the SOD-ZMOF decreased after chitosan impregnation showing that chitosan was impregnated on SOD-ZMOF. The FTIR spectrum of SOD-ZMOF showed functional groups present in organic linker used to synthesize SOD-ZMOF, and that of the SOD-ZMOF-chitosan revealed the same functional groups but with disappearance of carboxylic acid functional group. N2 physisorption showed a decrease in BET surface area and pore volume after chitosan impregnation on SOD-ZMOF as well. Performance evaluation of the material was carried out with a demonstration adsorption set-up using a 15%/85% CO2/N2 mixture and as a thermal gravimetric analysis (TGA) using 100% CO2. For both the packed-bed column and the TGA experiments, evaluation was conducted on SOD-ZMOF and SOD-ZMOF with chitosan for comparison. About 50 mg of the adsorbent was used at 25 oC, 1 bar and 25 ml/min for the packed-bed column. For the adsorption with the TGA, 11 mg of adsorbent was used at 25 ℃, 1 bar and 60 ml/min. SOD-ZMOF showed improved adsorption capacity after chitosan impregnation. CO2 adsorption capacity of SOD-ZMOF increased by 16% and 39% using packed-bed column and TGA, respectively, after chitosan impregnation. The increase in adsorption capacity was attributed to the impregnated chitosan that has amine groups that display a high affinity for CO2. A traditional approach was used to investigate the effect of adsorption temperature and inlet gas flowrate on the CO2 adsorption capacity of SOD-ZMOF-chitosan. This was done using both the parked bed column and the TGA. Temperature range of 25-80 ℃ and inlet gas flowrate range of 25-90 ml/min were investigated. Adsorption capacity increased with a decrease in temperature and inlet gas flowrate. For the packed-bed column, maximum of 781 mg CO2/ g adsorbent was obtained at 25℃, 1 bar, 25 ml/min and for the TGA a maximum CO2 adsorption capacity of 23 mg/ g adsorbent at 25 ℃, 1 bar, and 60 ml/min was obtained.MT201

    Integration of Biomolecular Recognition Elements with Solid-State Devices

    Get PDF
    Continued advances in stand-alone chemical sensors requires the introduction of new materials and transducers, and the seamless integration of the two. Electronic sensors represent one of the most efficient and versatile sensing transducers that offer advantages of high sensitivity, compatibility with multiple types of materials, network connectivity, and capability of miniaturization. With respect to materials to be used on this platform, many classes and subclasses of materials, including polymers, oxides, semiconductors, and composites have been investigated for various sensing environments. Despite numerous commercial products, major challenges remain. These include enhancing materials for selectivity/specificity, and low cost integration/ miniaturization of devices. Breakthroughs in either area would signify a transformative innovation. In this thesis, a combined materials and devices approach has been explored to address the above challenges. Biomolecular recognition elements, exemplified by aptamers, are the most recent addition to the library of tunable materials for specific detection of analytes. At the same time, nanoscale electrical devices based on tunnel junctions offer the potential for simple design, large scale integration, field deployment, network connectivity, and importantly, miniaturization to the molecular scale. To first establish a framework for studying sorption properties of solid oligonucleotides, custom designed aptamers sequences were studied to determine equilibrium partition coefficients. Linear-solvation-energy-relationship (LSER) analysis provides quantifications of non-covalent bonding properties and reveals the dominance of hydrogen bonding basicity in oligonucleotides. We find that DNA-analyte interactions have selective sorption properties similar to synthetic polymers. LSER analysis provides a chemical basis for material-analyte interactions. Oligonucleotide sequences were integrated with gold nanoparticle chemiresistors to transfer the selective sorption properties to microfabricated electrical devices. Responses generated by oligonucleotides under dry conditions were similar to standard organic mediums used as capping agents and suggests that DNA-based chemiresistor sensors operate with a similar mechanism based on sorption induced swelling. The equilibrium mass-sorption behavior of bulk DNA films could be translated to the chemiresistor sensitivity profiles. Our work establishes oligonucleotides, including aptamers, as a class of sorptive materials that can be systematically studied, engineered, and integrated with nanoscale electronic sensor devices. Experiments to investigate secondary structure effects were inconclusive and we conclude that further work should investigate DNA aptamers in buffered, aqueous environments to unequivocally establish the ability of chemiresitors to signal molecular recognition. Concurrent with the above studies, device integration and miniaturization was investigated to combine many sensing materials into a single, compact design. Arrays of nanoscale chemiresistors with critical features on the order of 10 – 100 nm were developed, using dielectrophoretic assembly of gold nanoparticles to control placement of the sensing material with nanometer accuracy. The nanoscale chemiresistors achieved the smallest known gold nanoparticle chemiresistors relying on just 2 – 3 layers of nanoparticles within 50 nm gaps, and were found to be more robust and less dependent on film thickness than previously published designs. Due to shorter diffusion paths, the sensors are also faster in response and recovery. A proof-of-concept, integrated single-chip sensor array was created and it showed similar response patterns as non-integrated sensor arrays. Dielectrophoresis is established as a key enabler for nanoscale, integrated devices. Based on the major findings of the thesis work, additional investigations were initiated to investigate the potential for nanoscale chemiresitor sensors to operate in buffered, aqueous (liquid) flow cells. Preliminary experiments show that chemiresistor sensing is transferable to liquid environments where analyte molecules are observed to partition from the bulk liquid to the sensing materials, leading to a detectable change of the device electrical properties. Comparing micron- and nano-scale devices fabricated using aqueous oligonucleotide-functionalized gold nanoparticles, it was found that nanoscale chemiresistors are more resistant to solvent damage than 5 µm chemiresistors. We conclude that future experiments to investigate aptamer sensing in aqueous solutions is a promising direction. Overall, this thesis is a significant contribution to materials development and device design to attain improved sensor selectivity and higher levels of device integration. First, it offers a scheme for design, selection, and validation of materials that confer analyte-specific interactions. Second, it paves the way for large scale sensor integration and parallel operation on a single chip. Lastly, it offers an approach to combine biomolecular recognition elements with electronic devices into robust, nanoscale detection systems. Based on the major findings of the thesis work, additional investigations were initiated to investigate the potential for nanoscale chemiresitor sensors to operate in buffered, aqueous (liquid) flow cells. Preliminary experiments show that chemiresistor sensing is transferable to liquid environments where analyte molecules are observed to partition from the bulk liquid to the sensing materials, leading to a detectable change of the device electrical properties. Comparing micron- and nano-scale devices fabricated using aqueous oligonucleotide-functionalized gold nanoparticles, it was found that nanoscale chemiresistors are more resistant to solvent damage than 5 µm chemiresistors. We conclude that future experiments to investigate aptamer sensing in aqueous solutions is a promising direction. Overall, this thesis is a significant contribution to materials development and device design to attain improved sensor selectivity and higher levels of device integration. First, it offers a scheme for design, selection, and validation of materials that confer analyte-specific interactions. Second, it paves the way for large scale sensor integration and parallel operation on a single chip. Lastly, it offers an approach to combine biomolecular recognition elements with electronic devices into robust, nanoscale detection systems
    corecore