Plasma-Initiated Graft Polymerization of Acrylic Acid onto Fluorine-Doped Tin Oxide as a Platform for Immobilization of Water-Oxidation Catalysts

Plasma-Induced Graft Polymerization for the In Situ Synthesis of Cross-Linked Nanocoatings

Conventional technology for the modification of surfaces loaded with nanomaterials typically requires a three-step process: (1) the construction of a polymer platform, (2) the synthesis of nanoparticles (NPs), and (3) the immobilization or anchoring of NPs. During the immobilization or anchoring process, there is an unavoidable excess of NPs primarily situated at the top of the surface, resulting in the agglomeration of aggregates. These aggregates can form different shapes and sizes, often creating an uneven distribution of NPs, resulting in an unstable coating that gradually releases NPs over time. In this study, argon plasma technology was used to create an innovative nanocoating consisting of polymer chains that are cross-linked to metal NPs, forming a polymer composite. To do this, argon plasma was employed as both an oxidizing and reducing agent during different steps in the nanocoating fabrication process. More specifically, a "grafting-from" approach, coupled with in situ argon plasma-assisted reduction of Cu2+ to Cu0, provided an innovative means for the construction of the nanocoating. With this "grafting-from" approach, the covalent binding of acrylic acid monomers to a surface results in a negatively charged nanocoating when exposed to solutions of a pH greater than 4.5. Due to its negative charge, the nanocoating can bind cations from solution, creating a platform for the in situ argon plasma-assisted reduction of Cu2+ to primarily Cu0 NPs (CuNPs). By controlling grafting conditions, in situ plasma-assisted reduction of NPs, and cross-linking conditions, we can generate nanocoatings with specific (1) polymer graft density and film thickness, (2) NP concentration cross-linked to polymer chains, and (3) NP composition. Under optimal experimental conditions, a nonleaching cross-linkage occurs between the nanocoating and the NPs, with only minimal NP aggregation. We have used this technology to engineer cross-linked nanocoatings possessing extremely low amounts of CuNPs (4.02 μg/cm2), which are distributed within the nanocoating and are capable of preventing infections.

Modified Polysulfone Nanofibers for the Extraction and Preconcentration of Lead from Aqueous Solutions

Since lead is a highly toxic metal, it is necessary to detect its presence in different samples; unfortunately, analysis can be complicated if the samples contain concentrations below the detection limit of conventional analytical techniques. Solid phase extraction is a technique that allows the carrying out of a pre-concentration process and thus makes it easy to quantify analytes. This work studied the efficiency of sorption and preconcentration of lead utilizing polysulfone (PSf) fibers grafted with acrylic acid (AA). The best conditions for Pb(II) extraction were: pH 5, 0.1 mol L^-1 of ionic strength, and 40 mg of sorbent (70% of removal). The sorbed Pb(II) was pre-concentrated by using an HNO₃ solution and quantified using flame atomic absorption spectrometry. The described procedure was used to obtain a correlation curve between initial concentrations and those obtained after the preconcentration process. This curve and the developed methodology were applied to the determination of Pb(II) concentration in a water sample contained in a handmade glazed clay vessel. With the implementation of the developed method, it was possible to pre-concentrate and determine a leached Pb(II) concentration of 258 µg L^-1.

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.

Surface Modification of ETFE Membrane and PTFE Membrane by Atmospheric DBD Plasma

Fluorine resin membranes with excellent chemical resistance have great potential for the application of high-performance chemical protective clothing. However, it is difficult to integrate fluorine resins into other materials such as fabrics due to their lower surface energy and poor bondability, making the fabrication of composite fabrics and the further seal splicing challenging. In this study, atmospheric pressure dielectric barrier discharge (DBD) plasma in helium (He) and helium/acrylic acid (He/AA) mixture atmospheres were used to modify two kinds of fluorine resins, ethylene tetrafluoroethylene (ETFE) and polytetrafluoroethylene (PTFE) membrane. The surface chemical properties, physical morphology, hydrophilicity and adhesion strength of the fluororesin membranes before and after plasma treatments were systematically analyzed. The results showed that the plasma treatment can modify the membrane surface at the nanoscale level without damaging the main body of the membrane. The hydrophilicity of the plasma-treated membrane was improved with the water contact angle decreasing from 95.83° to 49.9° for the ETFE membrane and from 109.9° to 67.8° for the PTFE membrane, respectively. The He plasma creates active sites on the membrane surface as well as etching the membrane surface, increasing the surface roughness. The He/AA plasma treatment introduces two types of polyacrylic acid (PAA)—deposited polyacrylic acid (d-PAA) and grafted polyacrylic acid (g-PAA)—on the membrane surface. Even after ultrasonic washing with acetone, g-PAA still existed stably and, as a result, improved the polarity and adhesion strength of fluororesin membranes. This work provides useful insights into the modification mechanism of DBD plasma on fluorine resins, with implications for developing effective strategies of integrating fluorine resin membrane to chemical protective clothing fabrics.

Strategies for Electrochemically Sustainable H2 Production in Acid

Acidified water electrolysis with fast kinetics is widely regarded as a promising option for producing H2 . The main challenge of this technique is the difficulty in realizing sustainable H2 production (SHP) because of the poor stability of most electrode catalysts, especially on the anode side, under strongly acidic and highly polarized electrochemical environments, which leads to surface corrosion and performance degradation. Research efforts focused on tuning the atomic/nano structures of catalysts have been made to address this stability issue, with only limited effectiveness because of inevitable catalyst degradation. A systems approach considering reaction types and system configurations/operations may provide innovative viewpoints and strategies for SHP, although these aspects have been overlooked thus far. This review provides an overview of acidified water electrolysis for systematic investigations of these aspects to achieve SHP. First, the fundamental principles of SHP are discussed. Then, recent advances on design of stable electrode materials are examined, and several new strategies for SHP are proposed, including fabrication of symmetrical heterogeneous electrolysis system and fluid homogeneous electrolysis system, as well as decoupling/hybrid-governed sustainability. Finally, remaining challenges and corresponding opportunities are outlined to stimulate endeavors toward the development of advanced acidified water electrolysis techniques for SHP.

Plasma-initiated graft polymerization of carbon nanoparticles as nano-based drug delivery systems

Plasma-initiated free radical polymerization was used to engineer carbon nanoparticles (CNPs) with tailored chemical and physical properties. Following surface modification, CNPs were loaded with a highly effective anti-infection agent called metal-free Russian propolis ethanol extract (MFRPEE), thus, creating nano-based drug delivery systems (NBDDSs). The loading of MFRPEE onto grafted CNPs occurred naturally through both electrostatic interactions and hydrogen bonding. When constructed under optimal experimental conditions, the NBDDSs were stable under physiologic conditions, and demonstrated enhanced anti-biofilm activity when compared with free MFRPEE. Mechanistic studies revealed that the enhanced anti-infectious activity of the NBDDSs was attributed to the modified surface chemistry of grafted CNPs. More specifically, the overall positive surface charge on grafted CNPs, which stems from quaternary ammonium polymer brushes covalently bound to the CNPs, provides NBDDSs with the ability to specifically target negatively charged components of biofilms. When studying the release profile of MFRPEE from the modified CNPs, acidic components produced by a biofilm triggered the release of MFRPEE bound to the NBDDS. Once in its free form, the anti-infectious properties of MFRPEE became activated and damaged the extracellular polymeric matrix (EPM) of the biofilm. Once the architecture of the biofilm became compromised, the EPM was no longer capable of protecting the bacteria encapsulated within the biofilm from the anti-infectious agent. Consequently, exposure of bacteria to MFRPEE led to bacterial cell death and biofilm inactivation. The results obtained from this study begin to examine the potential application of NBDDSs for the treatment of healthcare-associated infections (HCAIs).