The Influence of Microstructure on TCR for Inkjet-Printed Resistive Temperature Detectors Fabricated Using AgNO3/Ethylene-Glycol-Based Inks.

This study investigated the influence of microstructure on the performance of Ag inkjet-printed, resistive temperature detectors (RTDs) fabricated using particle-free inks based on a silver nitrate (AgNO3) precursor and ethylene glycol as the ink solvent. Specifically, the temperature coefficient of resistance (TCR) and sensitivity for sensors printed using inks that use monoethylene glycol (mono-EG), diethylene glycol (di-EG), and triethylene glycol (tri-EG) and subjected to a low-pressure argon (Ar) plasma after printing were investigated. Scanning electron microscopy (SEM) confirmed previous findings that microstructure is strongly influenced by the ink solvent, with mono-EG inks producing dense structures, while di- and tri-EG inks produce porous structures, with tri-EG inks yielding the most porous structures. RTD testing revealed that sensors printed using mono-EG ink exhibited the highest TCR (1.7 × 10-3/°C), followed by di-EG ink (8.2 × 10-4/°C) and tri-EG ink (7.2 × 10-4/°C). These findings indicate that porosity exhibits a strong negative influence on TCR. Sensitivity was not strongly influenced by microstructure but rather by the resistance of RTD. The highest sensitivity (0.84 Ω/°C) was observed for an RTD printed using mono-EG ink but not under plasma exposure conditions that yield the highest TCR.

Application of Argon Plasma Technology for the Synthesis of Anti-Infective Copper Nanoparticles.

The synthesis of copper nanoparticles (CuNPs) was accomplished by using a rapid, green, and versatile argon plasma reduction method that involves solvent extraction. With this method, a plasma-solid state interaction forms and CuNPs can be synthesized from copper(II) sulfate using a low-pressure, low-temperature argon plasma. Characterization studies of the CuNPs revealed that when a metal precursor is treated under optimal experimental conditions of 80 W of argon plasma for 300 s, brown CuNPs are synthesized. However, when those same brown CuNPs are placed in Milli-Q water for a period of 10 days, oxidation occurs and green CuNPs are formed. Confirmation of the chemical identity of the CuNPs was performed by using X-ray photoelectron spectroscopy. The results reveal that the brown CuNPs are predominantly Cu0 or what we refer to as CuNPs, while the green CuNPs are a mixture of Cu0 and Cu(OH)2 NPs. Upon further characterization of both brown and green CuNPs with scanning electron microscopy (SEM), the results depict brown CuNPs with a rod-like shape and approximate dimensions of 40 nm × 160 nm, while the green CuNPs were smaller in size, with dimensions of 40-80 nm, and more of a round shape. When testing the antibacterial activity of both brown and green CuNPs, our findings demonstrate the effectiveness of both CuNPs against Escherichia coli and Staphylococcus aureus bacteria at a concentration of 17 µg/mL. The inactivation of S. aureus and E. coli 7-day-old biofilms required CuNP concentrations of 99 µg/mL. SEM images of treated 7-day-old S. aureus and E. coli biofilms depict cell membranes that are completely damaged, suggesting a physical killing mechanism. In addition, when the same concentration of CuNPs used to inactivate biofilms were tested with human fibroblasts, both brown and green CuNPs were found to be biocompatible.

Low-Pressure Microwave Plasma Reduction of Iron and Copper Salt Compounds at Low Temperatures for Oxidation State Alteration and Functional Applications.

The influence of plasma-reduction treatment on iron and copper compounds at different oxidation states was investigated in this study. For this purpose, reduction experiments were carried out with artificially generated patina on metal sheets and with metal salt crystals of iron(II) sulfate (FeSO4), iron(III) chloride (FeCl3), and copper(II) chloride (CuCl2), as well as with the metal salt thin films of these compounds. All the experiments were carried out under cold low-pressure microwave plasma conditions; the main focus was on plasma reduction at a low pressure in order to evaluate an implementable process in a parylene-coating device. Usually, plasma is used within the parylene-coating process as a supporting tool for adhesion improvement and micro-cleaning efforts. This article offers another useful application for implementing plasma treatment as a reactive medium in order to apply different functionalities by an alteration in the oxidation state. The effect of microwave plasmas on metal surfaces and metal composite materials has been widely studied. In contrast, this work deals with metal salt surfaces generated from a solution and the influence of microwave plasma on metal chlorides and sulfates. While the plasma reduction of metal compounds commonly succeeds with hydrogen-containing plasmas at high temperatures, this study shows a new reduction process that reduces iron salts at temperatures between 30 and 50 °C. A novelty of this study is the alteration in the redox state of the base and noble metal materials within a parylene-coating device with the help of an implemented microwave generator. Another novelty of this study is treating metal salt thin layers for reduction purposes in order to provide the opportunity to include subsequent coating experiments to create parylene metal multilayers. Another new aspect of this study is the adapted reduction process of thin metal salt layers consisting of either noble or base metals, with an air plasma pre-treatment prior to the hydrogen-containing plasma-reduction procedure.

Non-Thermal Plasma Reduction of Ag+ Ions into Silver Nanoparticles in Open Atmosphere under Statistically Optimized Conditions for Biological and Photocatalytic Applications.

An environmentally friendly non-thermal DC plasma reduction route was adopted to reduce Ag+ ions at the plasma−liquid interface into silver nanoparticles (AgNPs) under statistically optimized conditions for biological and photocatalytic applications. The efficiency and reactivity of AgNPs were improved by statistically optimizing the reaction parameters with a Box−Behnken Design (BBD). The size of the AgNPs was chosen as a statistical response parameter, while the concentration of the stabilizer, the concentration of the silver salt, and the plasma reaction time were chosen as independent factors. The optimized parameters for the plasma production of AgNPs were estimated using a response surface methodology and a significant model p < 0.05. The AgNPs, prepared under optimized conditions, were characterized and then tested for their antibacterial, antioxidant, and photocatalytic potentials. The optimal conditions for these three activities were 3 mM of stabilizing agent, 5 mM of AgNO3, and 30 min of reaction time. Having particles size of 19 to 37 nm under optimized conditions, the AgNPs revealed a 82.3% degradation of methyl orange dye under UV light irradiation. The antibacterial response of the optimized AgNPs against S. aureus and E. coli strains revealed inhabitation zones of 15 mm and 12 mm, respectively, which demonstrate an antioxidant activity of 81.2%.

A New Methodological Approach on the Characterization of Optimal Charging Rates at the Hydrogen Plasma Smelting Reduction Process Part 2: Results.

To meet the target for anthropogenic greenhouse gas (GHG) reduction, the European steel industry is obliged to reduce its emissions. A possible pathway to reach this requirement is through developments of new technologies for a GHG-free steel production. One of these processes is the hydrogen plasma smelting reduction (HPSR) developed since 1992 at the Chair of Ferrous Metallurgy at the Montanuniversitaet Leoben in Austria. Based on the already available publication of the methodology in this work, potential process parameters were investigated that influence the reduction kinetics during continuous charging to improve the process further. Preliminary tests with different charging rates and plasma gas compositions were carried out to investigate the impacts on the individual steps of the reduction process. In the main experiments, the obtained parameters were used to determine the effect of the pre-reduction degree on the kinetics and the hydrogen conversion. Finally, the preliminary and main trials were statistically evaluated using the program MODDE® 13 Pro to identify the significant influences on reduction time, oxygen removal rate, and hydrogen conversion. High hydrogen utilization degrees could be achieved with high iron ore feeding rates and low hydrogen concentrations in the plasma gas composition. The subsequent low reduction degree and thus a high proportion of oxide melt leads to a high oxygen removal rate in the post-reduction phase and, consequently, short process times. Calculations of the reduction constant showed an average value of 1.13 × 10-5 kg oxygen/m2 s Pa, which is seven times higher than the value given in literature.

Rapid Synthesis of Metal Nanoparticles Using Low-Temperature, Low-Pressure Argon Plasma Chemistry and Self-Assembly.

The synthesis of metal nanoparticles has become a priority for the advancement of nanotechnology. In attempts to create these nanoparticles, several different methods: chemistry, physics, and biology, have all been used. In this study, we report the reduction of cations using argon plasma chemistry to produce nanoparticles of gold (AuNPs), silver (AgNPs), and copper (CuNPs). Although other groups have used plasma-reduction methods to synthesize metal nanoparticles from their cation counterparts, these approaches often require plasma|liquid state interactions, high temperature, specific combinations of gases, and extended treatment times (>10 minutes), for which only specific cations (noble or non-noble) may be reduced. As a result, we have developed a non-thermal, low-pressure argon-plasma|solid state approach for the reduction of both noble and non-noble cations. More specifically, when 50-µL droplets of 2-mM solutions of gold(III) chloride, silver nitrate, or copper(II) sulfate are exposed to vacuum, they undergo an evaporation process. As the pressure in the chamber decreases to 220 mtorr, the droplets become completely evaporated, leaving behind a metal precursor. Nucleation and growth studies reveal that when the metal precursors of gold(III) chloride, silver nitrate, and copper(II) sulfate are treated with 80 watts of argon plasma for 5, 60, and 150 seconds, respectively, nanoparticles could be synthesized with efficiency rates of upwards of 98%. The size of nanoparticles synthesized in this work was studied using Scanning Electron Microscopy, and the scattering properties of the nanoparticles was studied using UV/Vis spectroscopy. Transmission Electron Microscopy with corresponding elemental analysis was also very useful in confirming the identity of the synthesized nanoparticles. The results from this study reveal that we have synthesized metal nanoparticles with distinct chemical and physical properties. Scanning Electron Microscopy depicts AgNPs with a round-shape and diameters from 40 - 80 nm, while AuNPs were hexagonal, with sizes from 40 - 80 nm, and CuNPs were rod-shaped, with dimensions 40 by 160 nm. Our findings demonstrate that the argon plasma approach used in this study is a rapid, green, and versatile reduction method for the synthesis of both noble and non-noble metal nanoparticles.

Concurrent Synthesis and Immobilization of Ag Nanoparticles over TiO2 via Plasma Reduction for Photocatalytic Treatment of Methyl Blue in Water.

Pure TiO2 nanoparticles (TiO2NPs) were produced via the sol-gel method and then coated with silver nanoparticles (AgNPs) to reduce their optical band gap. The concurrent synthesis and immobilization of AgNPs over TiO2NPs was achieved through the interaction of an open-air argon plasma jet with a solution of silver nitrate/stabilizer/TiO2NPs. The one-pot plasma synthesis and coating of AgNPs over TiO2NPs is a more straightforward and environmentally friendly method than others. The plasma-produced Ag/TiO2 nanocomposites were characterized and tested for their photocatalytic potential by degrading different concentrations of methyl blue (MB) in water. The dye concentration, oxidant dose, catalyst dose, and reaction time were also optimized for MB degradation. XRD results revealed the formation of pure AgNPs, pure TiO2NPs, and Ag/TiO2 nanocomposites with an average grain size of 12.36 nm, 18.09 nm, and 15.66 nm, respectively. The immobilization of AgNPs over TiO2NPs was also checked by producing SEM and TEM images. The band gap of AgNPs, TiO2NPs, and Ag/TiO2 nanoparticles was measured about 2.58 eV, 3.36 eV, and 2.86 eV, respectively. The ultraviolet (UV) results of the nanocomposites were supportive of the degradation of synthetic dyes in the visible light spectrum. The AgNPs in the composite not only lowered the band gap but also obstructed the electron-hole recombinations. The Ag/TiO2 composite catalyst showed 90.9% degradation efficiency with a 5 ppm dye concentration after 120 min of light exposure.

Amine-functionalized graphitic carbon nitride decorated with small-sized Au nanoparticles for photocatalytic CO2 reduction.

Amine-functionalized graphitic carbon nitride (g-C3N4) decorated with Au nanoparticles (CN/Au) was prepared by N2 plasma treatment of g-C3N4 powders impregnated with HAuCl4·3H2O. Well-dispersed Au nanoparticles with a small particle size were deposited on g-C3N4 nanosheets. In addition, the amino group was introduced into the CN/Au system. Without the addition of cocatalyst and sacrificial agent, CN/Au exhibited enhanced photocatalytic activity for CO2 reduction under visible-light irradiation. CO and CH4 evolution rates of CN/Au reached 28.3 and 1.3 µmol·h-1·g-1, which were 7.6 and 2.6 times higher than those of pristine g-C3N4 (CN-0), respectively. The enhanced activity can be explained by these factors. (1) The introduced amino group improved the adsorption capacity of CN/Au for CO2; (2) the hot electrons generated by Au nanoparticles activated the surrounding electrons through energy transfer and caused local temperature to rise, increasing the efficiency of the photoreduction reaction of CO2; (3) the Schottky junction between Au and g-C3N4 promoted the migration of electrons from g-C3N4 to Au nanoparticles, suppressing the recombination of the carriers. Time-of-flight secondary ion mass spectrometry confirmed the introduction of amino groups, and solid-state 13C nuclear magnetic resonance spectra provided a support for inferring the position of the amino group.

Fabrication of a Silver-Based Thermistor on Flexible, Temperature-Sensitive Substrates Using a Low-Temperature Inkjet Printing Technique.

Inkjet printing has been identified as a cost-effective method to fabricate sensors on polymeric substrates. However, substrate materials suitable for printing are limited by the annealing temperature required by conventional inks. In this article, we describe the fabrication of an inkjet-printed thermistor on polyethylene and cellophane substrates that are not thermally compatible with the conventional inkjet printing processes. Fabrication on these substrates is made possible by a novel plasma-based postprint treatment step that limits the substrate temperature to <50 °C. The sensors exhibited a temperature sensitivity of 0.25 Ω°C-1 that was independent of substrate material. The utility of the fabrication process was demonstrated by fabricating thermistors for common indoor and outdoor applications.

Storage and reduction of NOx by combining Sr-based perovskite catalyst with nonthermal plasma.

A novel NOx storage and reduction (NSR) system is developed for NOx removal by integrating Sr-based perovskite catalyst with nonthermal plasma (NTP)-assisted process. In this hybrid system, Sr-based perovskite catalyst is applied for NOx adsorption in the lean-burn condition while NTP is used as a desorption-reduction step to convert NOx into N2 under rich-burn condition. Innovative Sr-based perovskites including SrKMnCoO4/BaO/Al2O3 (SKMCBA), SrKMnCeO4/BaO/Al2O3 (SKMCeBA), and SrKCoNiO4/BaO/Al2O3 (SKCNBA) are successfully prepared by impregnation method. Results indicate that SKMCBA possesses the highest NOx trapped (214 µmole NOx/gcatalyst) at 400 °C among 3 Sr-based perovskites investigated. High performance of SKMCBA for NOx adsorption is mainly attributed to the addition of Mn and Co which own good oxidation ability. Further, SKMCBA is combined with NTP-assisted process for NOx reduction. Result indicates that NOx conversion achieved with NTP-assisted process reaches 83% with the applied voltage of 18 kV and frequency of 10 kHz in the absence of reducing agent. Additionally, various reducing agents including hydrogen (H2), carbon monoxide (CO), and propene (C3H6) are introduced, individually, into the NTP reduction process, and the results indicate that performance of NSR with NTP can be effectively enhanced. Especially, 100% NOx conversion is achieved with H2-NTP. This study demonstrates that reduction of NOx via NTP-assisted process is promising.

Utility of Pt in PtNi alloy counter electrodes as a new avenue for cost effective and highly efficient liquid junction photovoltaic devices.

This study presents the synthesis of PtNi alloys with different volume ratios of Pt and Ni precursors in mixture solutions using dry plasma reduction under atmospheric pressure and low temperature. The developed materials are applied as efficient counter electrodes (CEs) in dye-sensitized solar cells (DSCs). The investigation of the Pt utility in PtNi alloys for electrocatalytic activity, and cost effective and highly efficient DSCs are also investigated. Compared with the reference electrodes (Pt and Ni CEs), the developed PtNi alloy CEs exhibit better reversibility as indicated by the peak-to-peak separation and better catalytic activity for the regeneration of iodide ions from triiodide ions. Thus, the DSC with the developed PtNi CEs provides higher efficiency than that of the device fabricated with the reference electrodes.

Regulation of the Deposition Morphology of Inkjet-Printed Crystalline Materials via Polydopamine Functional Coatings for Highly Uniform and Electrically Conductive Patterns.

We report a method to achieve highly uniform inkjet-printed silver nitrate (AgNO3) and a reactive silver precursor patterns on rigid and flexible substrates functionalized with polydopamine (PDA) coatings. The printed AgNO3 patterns on PDA-coated substrates (glass and polyethylene terephthalate (PET)) exhibit a narrow thickness distribution ranging between 0.9 and 1 µm in the line transverse direction and uniform deposition profiles in the line axial direction. The deposited reactive silver precursor patterns on PDA-functionalized substrates also show "dome-shaped" morphology without "edge-thickened" structure due to "coffee-stain" effect. We posit that the highly uniform functional ink deposits formed on PDA-coated substrates are attributable to the strong binding interaction between the abundant catecholamine moieties at the PDA surface and the metallic silver cations (Ag(+) or Ag(NH3)(2+)) in the solutal inks. During printing of the ink rivulet and solvent evaporation, the substrate-liquid ink (S-L) interface is enriched with the silver-based cations and a solidification at the S/L interface is induced. The preferential solidification initiated at the S-L interface is further verified by the in situ visualization of the dynamic solidification process during solvent evaporation, and results suggest an enhanced crystal nucleation and growth localized at the S-L interface on PDA functionalized substrates. This interfacial interaction mediates solute transport in the liquid phase, resulting in the controlled enrichment of solute at the S-L interface and mitigated solute precipitation in both the contact line region and the liquid ink-vapor (L-V) interface due to evaporation. This mediated transport contributes to the final uniform solid deposition for both types of ink systems. This technique provides a complementary strategy for achieving highly uniform inkjet-printed crystalline structures, and can serve as an innovative foundation for high-precision additive delivery of functional materials.

Combining nonthermal plasma with perovskite-like catalyst for NOx storage and reduction.

A new NOx storage and reduction (NSR) system is developed for NOx removal by combining perovskite-like catalyst with nonthermal plasma technology. In this hybrid system, catalyst is mainly used for oxidizing NO to NO2 and storing them, while nonthermal plasma is applied as a desorption-reduction step for converting NOx into N2. An innovative catalyst with a high NOx storage capacity and good reduction performance is developed by successive impregnation. The catalysts prepared with various metal oxides were investigated for NOx storage capacity (NSC) and NOx conversion. Characterization of the catalysts prepared reveals that addition of cobalt (Co) and potassium (K) considerably increases the performance for NSC. Results also show that SrKMn0.8Co0.2O4 supported on BaO/Al2O3 has good NSC (209 µmol/gcatalyst) for the gas stream containing 500 ppm NO and 5 % O2 with N2 as carrier gas. For plasma reduction process, NOx conversion achieved with SrKMn0.8Co0.2O4/BaO/Al2O3 reaches 81 % with the applied voltage of 12 kV and frequency of 6 kHz in the absence of reducing agents. The results indicate that performance of plasma reduction process (81 %) is better than that of thermal reduction (64 %). Additionally, mixed gases including 1 % CO, 1 % H2 and 1 % CH4, and 2 % H2O(g) are simultaneously introduced into the system to investigate the effect on NSR with plasma system and results indicate that performance of NSR with plasma can be enhanced. Overall, the hybrid system is promising to be applied for removing NOx from gas streams. Graphical abstract ᅟ.

Highly-Efficient Plasmon-Enhanced Dye-Sensitized Solar Cells Created by Means of Dry Plasma Reduction.

Plasmon-assisted energy conversion is investigated in a comparative study of dye-sensitized solar cells (DSCs) equipped with photo-anodes, which are fabricated by forming gold (Au) and silver (Ag) nanoparticles (NPs) on an fluorine-doped tin oxide (FTO) glass surface by means of dry plasma reduction (DPR) and coating TiO2 paste onto the modified FTO glass through a screen printing method. As a result, the FTO/Ag-NPs/TiO2 photo-anode showed an enhancement of its photocurrent, whereas the FTO/Au-NPs/TiO2 photo-anode showed less photocurrent than even a standard photo-anode fabricated by simply coating TiO2 paste onto the modified FTO glass through screen printing. This result stems from the small size and high areal number density of Au-NPs on FTO glass, which prevent the incident light from reaching the TiO2 layer.