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This work demonstrates the incorporation of gold nanoparticles (AuNPs) into crosslinker-free poly(N-isopropylacrylamide), PNIPAM, particles in situ and the examination of their structural and catalytic properties. The formation process of the AuNPs across the crosslinker-free PNIPAM particles are compared to that of crosslinked PNIPAM particles. Given the relatively larger free volume across the crosslinker-free polymer network, the AuNPs formed by the in situ reduction of gold ions are detectably larger and more polydisperse, but their overall integration efficiency is slightly inferior. The structural features and stability of these composite particles are also examined in basic and alcoholic solvent environments, where the crosslinker-free PNIPAM particles still offer comparable physicochemical properties to the crosslinked PNIPAM particles. Interestingly, the crosslinker-free composite particles as a colloidal catalyst display a higher reactivity toward the homocoupling of phenylboronic acid and reveal the importance of the polymer network density. As such, the capability to prepare composite particles in a controlled polymer network and reactive metal nanoparticles, as well as understanding the structure-dependent physicochemical properties, can allow for the development of highly practical catalytic systems. [ABSTRACT FROM AUTHOR]

This work demonstrates the rapid coating of gold nanoparticles (AuNPs) onto electrospun composite polyacrylonitrile (PAN) nanofibers containing a large amount of graphene oxide (GO) and reduced graphene oxide (rGO) for photothermally-driven applications. A modification of GO with a cationic surfactant greatly improves its loading efficiency into the PAN nanofibers, and the subsequent hydrazine treatment readily converts the integrated GO into rGO. Rapid loading of AuNPs onto these membranes results in measurably higher photothermal heating characteristics than the pristine PAN, GO-PAN, and rGO-PAN membranes under a solar-simulated light source. The light-induced heating properties are then utilized in the removal of organic dyes in an aqueous solution. While the GO-PAN and rGO-PAN membranes remove the dyes via physical adsorption, the AuNP-loaded membranes show an additional catalytic decomposition process, resulting in detectably faster removal rates. The degradation of the organic dyes is accelerated under a solar simulated light source due to the light-enhanced heating and photocatalytic properties of the integrated AuNPs. The ability to maximize the dual properties of these membranes can greatly reduce toxic organic pollutants, which can lead to the development of practical water purification systems under sunlight irradiation. [ABSTRACT FROM AUTHOR]

This work describes the preparation of gold nanoparticles on flexible paper- and polymer-based substrates, and demonstrates their photothermally-induced heating property and surface-enhanced Raman spectroscopy (SERS) response. Uniform gold nanoparticles were synthesized under light irradiation and were systematically loaded onto these substrates; they were examined in regards to their heating properties under two different light sources. The temperature of the nanoparticle-loaded substrates steadily increased as a function of the gold nanoparticle loading and light intensity. In addition, these substrates were modified with 4-nitrobenzenethiol (4-NBT) and their SERS responses were monitored as a function of the 4-NBT concentration and light intensity. Furthermore, the SERS effects caused by the light-induced heating were examined, allowing for the proper use of the light source and intensity to minimize negative effects during the SERS measurements. Generally, a significant decrease in the SERS signals and an increase in the background noise were observed upon exposure to high intensities of light; these results were possibly due to the desorption, degradation, or disorder of 4-NBT and/or the annealing of gold nanoparticles on the substrate by the local heating and photo-induced damage. The mild photothermal heating by light sources in the presence of physically adsorbed 4-NBT on the substrates resulted in notable SERS enhancements, presumably caused by the conversion of 4-NBT from the precursor state to the chemisorbed state. As such, understanding light-induced heating on SERS measurements provides insight for designing practical and useful SERS detection systems, minimizing the negative effects and maximizing the positive effects. [ABSTRACT FROM AUTHOR]

This report describes the systematic incorporation of gold nanoparticles (AuNPs) onto mesoporous TiO2 (MPT) particles without strong attractive forces to efficiently serve as reactive and recyclable catalysts in the homocoupling of arylboronic acid in green reaction conditions. Unlike using nonporous TiO2 particles and conventional SiO2 particles as supporting materials, the employment of MPT particles significantly improves the loading efficiency of AuNPs. The incorporated AuNPs are less than 10 nm in diameter, regardless of the amount of applied gold ions, and their surfaces, free from any modifiers, act as highly reactive catalytic sites to notably improve the yields in the homocoupling reaction. The overall physical properties of the AuNPs integrated onto the MPT particles are thoroughly examined as functions of the gold content, and their catalytic functions, including the rate of reaction, activation energy, and recyclability, are also evaluated. While the rate of reaction slightly increases with the improved loading efficiency of AuNPs, the apparent activation energies do not clearly show any correlation with the size or distribution of the AuNPs under our reaction conditions. Understanding the formation of these types of composite particles and their catalytic functions could lead to the development of highly practical, quasi-homogeneous catalysts in environmentally friendly reaction conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Systematically forming gold nanoparticles within a polymer particle under light irradiation. • Examining the structural properties and encapsulation degree of gold nanoparticles. • Testing physically encapsulated gold nanoparticles as reactive quasi-homogeneous catalysts. • Observing size-independent activation energies for encapsulated gold nanoparticles. The reduction of gold ions using four different types of mild reducing agents was carried out in the presence of poly(n-isopropylacrylamide), PNIPAM, particles under light irradiation at room temperature. Simply controlling the concentration ratios of the gold ions to reductants allowed for the systematic formation of physically encapsulated gold nanoparticles (AuNPs) within the PNIPAM particles due to the presence of weak interactions between the guest AuNPs and host PNIPAM particles. After the examination of the structural and physical properties of the AuNPs and their loading efficiency, the composite particles were extensively utilized in the aerobic homocoupling of phenylboronic acid in EtOH to examine their catalytic properties associated with the rate of reaction, selectivity, and activation energy (E a). All composite particles showed the highly selective formation of the biphenyl product and comparable E a values, regardless of the size and distribution of the encapsulated AuNPs as catalysts. However, the way the AuNPs were formed within the PNIPAM particles notably influenced the rate of reaction. As such, developing a simple approach to optimize the encapsulation degree of AuNPs and their structural features in the presence of polymer particles can be applied to designing diverse metal-polymer composite particles for rapid and effective catalytic systems. [ABSTRACT FROM AUTHOR]

A simple spray method is utilized to prepare plasmonic paper loaded with gold nanoparticles (AuNPs) to serve as a signal enhancing substrate for surface enhanced Raman scattering (SERS) spectroscopy. The spray coating of plasmonic AuNPs onto hydrophilic porous paper-based materials notably improves their loading efficiency and distribution profile in much shorter time compare to typical dip- or drop-coating methods. This preparation approach involves the rapid drying of the solution to prevent the loss of the nanoparticles on the hydrophilic paper, which results in the improved packing of the plasmonic nanoparticles with local aggregations. Upon treating these spray-coated substrates with Raman reporter molecules, their sensing capability of SERS is a minimum of 2 times higher than that found with a dip-coated platform. Subsequently applying an additional layer of AuNPs onto these two substrates by dip- and spray-coating methods readily leads to greatly enhanced SERS signals over 2–5 times that are mainly caused by the plasmonic couplings and hot spots of sandwich-type structures. Without the modification of the paper substrates, the way the sandwich structure is formed on the paper materials with typical AuNPs significantly influences the packing and structural properties of the plasmonic nanoparticles, thereby highly impacting the SERS enhancement patterns. Image 1 • Plasmonic nanoparticles are rapidly loaded onto porous filter paper to serve as SERS substrates. • Spray coating readily controlled the packing and structural properties of plasmonic nanoparticles. • Applying an additional layer of nanoparticles onto plasmonic paper further improves their SERS response. [ABSTRACT FROM AUTHOR]

Oyster shell waste can be utilized as a colloidal solid support to anchor abundant gold nanoparticles (AuNPs) for use as a highly selective, reactive, and recyclable catalyst in C-C bond forming reactions under base-free green reaction conditions. A deposition precipitation method is utilized to effectively incorporate sub-10 nm AuNPs onto the ground oyster shell powder (OSP). Although the loaded AuNPs mainly possess bare surfaces without any capping agents, the resulting composite particles exhibited great dispersity and stability in various solvents, including EtOH and water. After examining their structural and compositional properties, the composite particles are tested as a catalyst in C-C bond forming reactions. These composite particles reveal an unexpectedly high reactivity and selectivity in the homocoupling of arylboronic acid without using any additives, including necessary inorganic bases. This is presumably because the abundant carbonate groups around the OSP surfaces can effectively play a role as a base, while the bare surfaces of the incorporated AuNPs act as catalytically reactive sites. In addition to these synergistic features of the composite particles, establishing reliable reaction conditions requiring only reactants in a green EtOH solvent results in the easy isolation of the product and catalyst, yielding great recyclability. The utilization of marine wastes along with biocompatible and catalytically active metal nanoparticles will lead to the development of economical multi-purpose catalysts that are extremely practical and recyclable in eco-friendly reaction conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

This work demonstrates the in situ formation of gold nanoparticles (AuNPs) within a series of poly(N-isopropylacrylamide), PNIPAM, particles containing various amounts of crosslinkers from 2.5 wt% to 40 wt%. As the networks of these host PNIPAM particles possess different levels of crosslinking density and free volume, the in situ reduction of gold ions greatly influences the structural features (e.g., size and distribution) of the guest AuNPs while maintaining comparable loading efficiency. After thorough characterization of their physicochemical properties, the resulting composite particles are tested as catalysts in C-C forming homocoupling reactions to understand the relationships between the crosslinking density and catalytic reactivity. Interestingly, decreasing the crosslinking density of PNIPAM particles results in the integration of gradually smaller and more uniform AuNPs whose catalytic activities with turnover frequency (TOF) values of ~38/h are comparatively superior to other AuNP-based systems (e.g., ~20/h). The enhanced catalytic property could also be contributed by the loosely crosslinked polymer particle networks with increased free volume, resulting in efficient mass transfer environments (e.g., faster diffusion of molecules). It is apparent that the crosslinking degree of the PNIPAM particles greatly impacts the overall formation of the guest AuNPs and their catalytic reactivity and recyclability in the homocoupling reaction. As such, examining the influence of host polymer networks on the structural and catalytic properties of the guest nanoparticles provides valuable information for the development of novel composite particles in versatile catalytic applications [Display omitted] • AuNPs are integrated into polymer particles with various crosslinking densities in situ. • Loosely crosslinked polymer particles enabled smaller and faster formation of AuNPs. • Increasing crosslinking density decreases catalytic activities of composite particles. [ABSTRACT FROM AUTHOR]