In this work, Pt-SnO2 heteroaggregate nanocatalysts were synthesized by in situ transformation of Pt@Sn core–shell nanoparticles and their catalytic performance for hydrogenation of various substituted nitroaromatics was investigated. The Pt@Sn nanoparticles were prepared by a one-step method, and the alumina-supported Pt@Sn nanoparticles were further transformed in situ into Pt-SnO2 heteroaggregate nanostructures by calcination. The structures of Pt@Sn and Pt-SnO2 nanomaterials were characterized, and FT-IR with CO probes, HRTEM, XRD, and XPS characterizations revealed that the as-synthesized Pt@Sn nanoparticles were core@shell-like structures with Sn-rich shells and Pt-rich cores and the obtained Pt-SnO2 heteroaggregate nanostructures consisted of close-contact pure Pt and SnO2 phases. The Pt-SnO2/Al2O3 nanostructures demonstrated a better catalytic performance for hydrogenation of various substituted nitroaromatics relative to individual Pt/Al2O3 nanocatalysts. Theoretical calculations suggested that Pt-SnO2 nanocatalysts can slightly facilitate the adsorption of H2 and o-chloronitrobenzene and strongly weaken the binding of Pt/o-chloroaniline, resulting in more available reactants and easier release of products from the catalyst surfaces. The theoretical calculations indicated that the enhanced catalytic performance may originate from a cooperative interaction between Pt and SnO2.Keywords: core@shell; hydrogenation; nanocatalysts; nitroaromatics; Pt-SnO2;

ABSTRACTBiomimetic polyelectrolyte of Dopa modified poly(acrylic acid) (PAADopa) was synthesized taking advantage of Dopa, the major unit of marine adhesive proteins. Zinc crosslinked PAADopa (PAADopa-Zn) were formed at acidic pH for more compact structure and assembled with the positively charged polyethylenimine (PEI) to build robust polyelectrolyte multilayers at high salt concentration. Effects of pH, crosslinking degree, and salt concentration on polymer structure, film building process, and morphology were investigated, respectively. An “odd-even” effect was observed by quartz crystal microbalance with dissipation and AFM in the presence of zinc ion, which becomes more obvious with an optimum crosslinking degree (Zn/Dopa = 2.0) under high salt concentration (0.6 M NaCl). It indicates the different swollen properties of PEI chain and PAADopa-Zn complexes during the layer-by-layer building process under optimum crosslinking degree of PAADopa-Zn at high salt concentration. Such odd-even phenomenon of the biocompatible system is of critical importance for understanding the mechanism of layer formation and film structures. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 245–255

A series of polymer–carbon nanotube composite materials (CNT-P-SO3H) were prepared by covalent grafting of multiwalled carbon nanotubes (CNTs) with sulfonic acid-functionalized polymers (P-SO3H) including poly(3-vinyl-1-sulfonic acid imidazolium chloride)-grafted multiwalled CNTs (CNT-PVSAIC), poly(4-vinyl-1-sulfonic acid pyridinium chloride)-grafted multiwalled CNTs (CNT-PVSAPC), and poly(4-styrenesulfonic acid)-grafted multiwalled CNTs (CNT-PSSA). Such a functionalization method provides a facile route to obtain various polyelectrolyte brushes on the surfaces of CNTs in order to improve the dispersibility and modulate the acidity of CNTs to selectively introduce functional groups and densely create active sites over CNTs for potential catalytic applications. Both CNT-PVSAIC and CNT-PVSAPC consist of cationic polyelectrolyte chains functionalized by sulfonic acid groups, whereas CNT-PSSA is composed of anionic polymer brushes grafted by sulfonic acid groups. The physicochemical properties of CNT-P-SO3H were analyzed by BET, TGA, XRD, FT-IR, XPS, Raman, and HRTEM techniques. The resulting CNT-P-SO3H materials exhibit excellent catalytic activity as CNT-based solid acids in liquid phase transesterification of triglycerides with methanol and esterification of oleic acid with methanol, which are typical model reactions for biodiesel production. The outstanding catalytic performance of the CNT-P-SO3H catalysts is attributed to the combination of the mesoporous structure together with a well-extended P-SO3H coating over the outer surface of the CNTs, providing the formation of a dense but uniform surface distribution of active sites.Keywords: Biodiesel; Carbon nanotubes; Esterification; Solid acid; Transesterification

A strategy to construct different stimuli-responsive polymers from postpolymerization modifications of a single polymer scaffold via thiol–disulfide exchange has been developed. Here, we report on a random copolymer that enables the design and syntheses of a series of dual or multi-stimuli-responsive nanoassemblies using a simple postpolymerization modification step. The reactive functional group involves a side chain monopyridyl disulfide unit, which rapidly and quantitatively reacts with various thiols under mild conditions. Independent and concurrent incorporation of physical, chemical, or biologically responsive properties have been demonstrated. We envision that this strategy may open up opportunities to simplify the synthesis of multifunctional polymers with broad implications in a variety of biological applications.

•In situ reduction of graphene loaded FeAg bimetallic nanocomposite.•Antibacterial activity of these nanocomposite was investigated.•Mechanism study for the antibacterial activity through oxidative stress has been studied.We report the simple one pot synthesis of iron-silver (FeAg) bimetallic nanoparticles with different compositions on graphene support. The nanoparticles are well dispersed on the graphene sheet as revealed by the TEM, XRD, and Raman spectra. The antibacterial activity of graphene-FeAg nanocomposite (NC) towards Bacillus subtilis, Escherichia coli, and Staphylococcus aureus was investigated by colony counting method. Graphene-FeAg NC demonstrates excellent antibacterial activity as compared to FeAg bimetallic without graphene. To understand the antibacterial mechanism of the NC, oxidative stress caused by reactive oxygen species (ROS) and the glutathione (GSH) oxidation were investigated in the system. It has been observed that ROS production and GSH oxidation are concentration dependent while the increase in silver content up to 50% generally enhances the ROS production while ROS decreases on further increase in silver content. Graphene loaded FeAg NC demonstrates higher GSH oxidation capacity than bare FeAg bimetallic nanocomposite. The mechanism study suggests that the antibacterial activity is probably due to membrane and oxidative stress produced by the nanocomposites. The possible antibacterial pathway mainly includes the non-ROS oxidative stress (GSH oxidation) while ROS play minor role.One pot in situ synthesis of graphene supported FeAg bimetallic nanoparticles which show outstanding performance in the antibacterial activity of different bacteria (Such as B. subtilis, E. coli and S. aureus).

Biomimetic multilayers based on layer-by-layer (LbL) assembly were prepared as functional films with compact structure by incorporating the mussel-inspired catechol cross-linking. Dopamine-modified poly(acrylic acid) (PAADopa) was synthesized as a polyanion to offer electrostatic interaction with the prelayer polyethylenimine (PEI) and consecutively cross-linked by zinc to generate compact multilayers with tunable physicochemical properties. In situ layer-by-layer growth and cross-linking were monitored by a quartz crystal microbalance with dissipation (QCM-D) to reveal the kinetics of the process and the influence of Dopa chemistry. Addition of Dopa enhanced the mass adsorption and led to the formation of a more compact structure. An increase of ionic strength induced an increase in mass adsorption in the Dopa-cross-linked multilayers. This is a universal approach for coating of various surfaces such as Au, SiO2, Ti, and Al2O3. Roughness observed by AFM in both wet and dry conditions was compared to confirm the compact morphology of Dopa-cross-linked multilayers. Because of the pH sensitivity of Dopa moiety, metal-chelated Dopa groups can be turned into softer structure at higher pH as revealed by reduction of Young’s modulus determined by MFP-3D AFM. A deeper insight into the growth and mechanical properties of Dopa-cross-linked polyelectrolyte multilayers was addressed in the present study. This allows a better control of these systems for bioapplications.

Flash nanoprecipitation (FNP) is an easily scalable and fast processing method for the preparation of nanoparticles (NPs) with simple vortex equipment. By using the FNP method, fluorescent NPs are prepared in less than 1 s in a multi-inlet vortex mixer, in which hydrophobic aggregation-induced emission (AIE)-active dye of EDP is incorporated within the biocompatible block copolymer poly(ethylene glycol)-b-poly(ε-caprolactone) for EDP NP assembly. The formulation parameters of stream velocity, dyes, and loading and concentration in FNP are optimized. The sizes of the NPs ranged from 20 to 60 nm with a ratio change of mixed solvents. As a control, an aggregation-caused quenching (ACQ) molecule of BDP was also synthesized for BDP NPs. To gain insight into the effect of the polymer on the aggregation state of hydrophobic dyes, the preparation of EDP and BDP NPs without block copolymer was also investigated. Apparently, the sizes of the NPs display large distributions without an amphiphilic block copolymer as the engineering template, suggesting that the block of polymers plays a key role in tuning the aggregation state of encapsulated dyes in FNP processes. Moreover, the peak shifts of dye with different microenvironments also confirmed the successful encapsulation of fluorescent dye in the NP cores. Finally, by externally applied forces in the FNP method, the engineered assembly of AIE-active fluorescent NPs possessing a narrow size distribution with desirable fluorescence properties was obtained. These features provide the possibility of rapidly constructing controllable AIE-active fluorescent NPs as biomedical tracers.

To mimic the underwater adhesion of marine mussels, a bioadhesive has been prepared with a poly(acrylic acid) backbone functionalized with 30% catechol appendants. The polyelectrolyte chains can be reversibly crosslinked through metal chelation and irreversibly gelled by oxidative crosslinking. Surprisingly, the reported “poor” metal chelator Zn2+ not only imparts this injectable adhesive with superior adhesion after the formation of coacervation compared to the one chelated by a stronger metal crosslinker (e.g. Fe3+), but also generates good mechanical performance of the self-healing hydrogel after the oxidation of catechol groups with a pH trigger. Such a pH-responsive material with strong adhesion and good self-healing property at different conditions could be an ideal candidate in biomedical adhesion and tissue engineering.

•SPB coating was fabricated with silver nanoparticles stably immobilized.•The surfaces modified with SPB display significant antibacterial performance.•New strategy for efficient immobilization of silver nanoparticles as antibacterial materials.A more efficient and convenient strategy was demonstrated to immobilize silver nanoparticles (NPs) with a crystalline structure into the spherical polyelectrolyte brushes (SPB) as an antibacterial material. The SPB used for surface coating (Ag immobilized PVK–PAA SPB) consists of a poly(N-vinylcarbazole) (PVK) core and poly(acrylic acid) (PAA) chain layers which are anchored onto the surface of PVK core at one end. Well-dispersed silver nanoparticles (diameter ∼ 3.5 nm) then formed and were electrostatically confined in the brush layer. Ag content is controlled by a repeated loading process. Thin film coatings were then constructed by layer-by-layer depositions of positive charged poly(diallyldimethylammonium chloride) (PDDA) and SPB. The multilayer composites display excellent stability as well as antibacterial performance but not for simple PVK–PAA coated surface. The results show that almost complete bacteria growth including both dispersed bacterial cells and biofilms was inhibited over a period of 24 h. This approach opens a novel strategy for stable and efficient immobilization of Ag NPs in fabrication of antibacterial materials.

Novel fluorescence-labeled spherical polyelectrolyte brushes consisting of a fluorescent polystyrene (PS) nanocomposite core and a poly(acylic acid) (PAA) brush shell were successfully prepared. Quantum dots (QDs) were well confined in the PS core through hybrid emulsion polymerization. PAA chains were then grafted onto the surface of the fluorescent PS core to form a brush structure through photoemulsion polymerization. The obtained fluorescent spherical polyelectrolyte brushes are highly pH sensitive in addition to their excellent dispersibility in water. Fluorescent nanoclusters were introduced into spherical polyelectrolyte brushes to acquire high sensitive detection in the applications of spherical polyelectrolyte brushes as catalyst tracer, as biosensor, and in protein coding.

•Protein selectivity can be achieved by polyelectrolyte solely through electrostatics.•Selective binding is influenced by protein charge anisotropy, protein binding affinity, polyelectrolyte characters, and polyelectrolyte assembling.•Correlation between protein binding affinity and phase separation is evaluated.This review discusses the possible relationship between protein charge anisotropy, protein binding affinity, polymer structure, and selective phase separation. We hope that a fundamental understanding of primarily electrostatically driven protein–polyelectrolyte (PE) interactions can enable the prediction of selective protein binding, and hence selective coacervation through non-specific electrostatics. Such research will partially challenge the assumption that specific binding has to be realized through specific binding sites with a variety of short-range interactions and some geometric match. More specifically, the recent studies on selective binding of proteins by polyelectrolytes were examined from different assemblies in addition to the electrostatic features of proteins and PEs. At the end, the optimization of phase separation based on binding affinity for selective coacervation and some considerations relevant to using PEs for protein purification were also overviewed.