In situ formation of stable gold nanoparticles in polymer inclusion membranes

The Effect of Surface Confined Gold Nanoparticles in Blocking the Extraction of Nitrate by PVC-Based Polymer Inclusion Membranes Containing Aliquat 336 as the Carrier

Clusters of gold nanoparticles (AuNPs) formed on the surface of PVC-based polymer inclusion membranes (PIMs) with a liquid phase containing Aliquat 336 as the carrier and in some cases 1-dodecanol or 2-nitrophenol octyl ether as plasticizers were found to inhibit the extraction of nitrate by the PIMs. This observation was based on gradually increasing the mass of AuNPs on the membrane surface and testing the ability of the membrane to extract nitrate after each increase. In this way, it was possible to determine the so-called “critical AuNP masses” at which the studied membranes ceased to extract nitrate. On the basis of these results, it can be hypothesized that the surfaces of these PIMs are not homogeneous with respect to the distribution of their membrane liquid phases, which are present only at certain sites. Extraction takes place only at these sites, and at the “critical AuNP mass” of a PIM, all these extraction sites are blocked and the membrane loses its ability to extract.

Simultaneous AuIII Extraction and In Situ Formation of Polymeric Membrane-Supported Au Nanoparticles: A Sustainable Process with Application in Catalysis

A polymeric membrane-supported catalyst with immobilized gold nanoparticles (AuNPs) was prepared through the extraction and in situ reduction of Au^III salts in a one-step strategy. Polymeric inclusion membranes (PIMs) and polymeric nanoporous membranes (PNMs) were tested as different membrane-support systems. Transport experiments indicated that PIMs composed of cellulose triacetate, 2-nitrophenyloctyl ether, and an aliphatic tertiary amine (Adogen 364 or Alamine 336) were the most efficient supports for Au^III extraction. The simultaneous extraction and reduction processes were proven to be the result of a synergic phenomenon in which all the membrane components were involved. Scanning electron microscopy characterization of cross-sectional samples suggested a distribution of AuNPs throughout the membrane. Transmission electron microscopy characterization of the AuNPs indicated average particle sizes of 36.7 and 2.9 nm for the PIMs and PNMs, respectively. AuNPs supported on PIMs allowed for >95.4 % reduction of a 0.05 mmol L^-1 4-nitrophenol aqueous solution with 10 mmol L^-1 NaBH₄ solution within 25 min.

Nanocomposite Based on Functionalized Gold Nanoparticles and Sulfonated Poly(ether ether ketone) Membranes: Synthesis and Characterization

Gold nanoparticles, capped by 3-mercapto propane sulfonate (Au-3MPS), were synthesized inside a swollen sulfonated poly(ether ether ketone) membrane (sPEEK). The formation of the Au-3MPS nanoparticles in the swollen sPEEK membrane was observed by spectroscopic and microscopic techniques. The nanocomposite containing the gold nanoparticles grown in the sPEEK membrane, showed the plasmon resonance λ_max at about 520 nm, which remained stable over a testing period of three months. The size distribution of the nanoparticles was assessed, and the sPEEK membrane roughness, both before and after the synthesis of nanoparticles, was studied by AFM. The XPS measurements confirm Au-3MPS formation in the sPEEK membrane. Moreover, AFM experiments recorded in fluid allowed the production of images of the Au-3MPS@sPEEK composite in water at different pH levels, achieving a better understanding of the membrane behavior in a water environment; the dynamic hydration process of the Au-3MPS@sPEEK membrane was investigated. These preliminary results suggest that the newly developed nanocomposite membranes could be promising materials for fuel cell applications.

The formation of gold nanoparticles in photopolymerized networks

Photopolymer networks containing a phosphonium polyelectrolyte were used as scaffolds for the synthesis of gold nanoparticles (AuNPs). Chloride anions electrostatically bound to the phosphonium salt were exchanged with AuCl4− and then reduced with NaBH4 to form AuNPs. The stiffness of the photopolymer matrix had a pronounced effect on the concentration of AuNPs formed within the material, where softer, more swellable networks provided greater anion-exchange sites and therefore more AuNP formation. Numerous loading/reduction cycles with AuCl4− and NaBH4 increased the concentration of AuNPs upon each cycling step without significantly changing AuNP size, thus providing a means to control AuNP concentration within the material. SEM and TEM analysis revealed particles sizes ranging from 10 to 30 nm with significant microscale heterogeneity likely arising from phase separation of the phosphonium polyelectrolyte from the photopolymer matrix followed by AuNP synthesis within those regions. We also demonstrate how this methodology can be applied to patterned photopolymer networks, providing the means to explore this approach for photolithographic applications.

Electrochemical studies of U(VI)/U(V) in saturated Na2CO3solution at gold nanoparticles embedded CTA-modified electrode

Gold nanoparticles (AuNPs) were prepared in the matrix of cellulose triacetate (CTA) membrane containing a liquid anion exchanger trioctylmethylammonium chloride (Aliquat-336). The AuCl4−ions were transferred in the membrane matrix by anion-exchange process, and then subsequently reduced with NaBH4to form AuNPs in the membrane. The AuNPs-embedded CTA (AuNPs-CTA) membrane was characterized by UV-visible spectroscopy, XRD and AFM. The electrochemical properties of AuNPs-CTA modified electrode were evaluated by studying redox behavior of UO22+/UO2+couple in saturated Na2CO3solution, using voltammetric techniques. In carbonate solution, the predominant species of UO22+is [UO2(CO3)3]4−, and a stable UO2(CO3)35−complex is formed by one-electron reduction of UO2(CO3)34−. Previous reports show that the UO22+/UO2+couple, which is electrochemically reversible in less complexing media, becomes electrochemically irreversible in aqueous CO32−solution. In this study, an electrocatalytic reduction of UO22+to UO2+in saturated Na2CO3solution was observed at AuNPs-CTA-modified electrode with higher current density and faster heterogeneous electron-transfer kinetics than that at bare Au electrode. The standard heterogeneous rate constant,kº, for the reduction process at AuNPs-CTA modified electrode was about 25 times higher than that of bare Au electrode. Therefore, it is concluded that AuNPs-CTA membrane has improved the interfacial electron-transfer properties of electrode, resulting in a better electrochemical response than bare Au electrode.