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In this work, we report the synthesis of hexoctahedral (HOH-shaped), elongated tetrahexahedral (ETHH-shaped) and octahedral (OCT-shaped) Au@AuPd nanoparticles (NPs) via co-reduction of a trace amount of Au and Pd precursors by ascorbic acid (AA) with the aid of an elemental silver reservoir on the surface of the corresponding preformed Au NPs enclosed by different facets. Consequently, surface facets of alloy-shells of the resulting Au@AuPd NPs can be tuned, as they can retain the original surface facets of pre-formed, facet-controlled Au cores. It is found that both mass activities and specific activities of the three types of Au@AuPd NPs exhibit “volcano-type” dependence with respect to their Pd content in the surface of ultrathin AuPd alloy-shells. Moreover, HOH-shaped Au@Au0.20Pd2.0 NPs simultaneously display the best activity and excellent stability due to the exposed high-index facets of the AuPd alloy-shell and the appropriate area ratio of active facets and inactive facets on the surfaces of ultrathin alloy-shells. Furthermore, their ECSA value, mass activity and specific activity are 125.8 m2 g−1, 11.9 A mgPd−1 and 9.5 mA cm−2, respectively, which are about 4-fold, 31-fold, and 7-fold better than those (28.4 m2 g−1, 0.38 A mgPd−1, and 1.34 mA cm−2) of commercial Pd/C catalysts, respectively. Thus, this work not only demonstrates that surface facets of core–shell Au@AuPd NPs can be engineered via co-reduction of a trace amount of Au and Pd precursors by AA with the aid of an elemental silver reservoir on the surface of preformed Au NPs, but also will open a new way to improve the electrocatalytic performance of CS Au@AuPd NPs by surface engineering. [ABSTRACT FROM AUTHOR]

Fabrication of nanostructures with multiple functions templated by cellulose nanocrystals (CNCs) has become very attractive, and chiral structures fabricated via evaporation-induced self-assembly (EISA) have become particularly important for building photonic films. However, films obtained so far suffer from low mechanical strength, which significantly hinders their applications. Here, we report a facile way to obtain highly flexible latex films with tunable structural colors via CNC templating. First, composite films (CFs) containing silicone-modified acrylic latexes (SALs) and CNCs were prepared via EISA. At mixing ratios of SALs to CNCs of 0.2–0.4, homogenous films were obtained, where the latexes cohere together to form a network. After alkali treatment followed by rinsing with water or alcohol, CNCs could be removed, leading to the formation of free-standing latex films. The chiral nematic (N*) structure originating from the organization of CNCs via EISA was retained in the latex film, leading to the preservation of the structural color. Due to a reduced helical pitch caused by the deformation of the porous latex network during the removal of CNCs and the subsequent drying process, the reflection of the film could be blue shifted, and the extent was closely related to the type of solvent used during rinsing. Interestingly, the structural color of the latex film could be reversibly tuned by water adsorption and dehydration, which could be ascribed to the expansion/shrinking of the porous latex network. The flexibility of the pores in expansion/shrinking also effectively released the internal stress of the film when it was stretched and/or deformed. This feature, combined with the intrinsic flexibility of the backbones formed by the crosslinking of SALs, imparts the film impressive mechanical strength. The maximum elongation at break reached 34.5%, ∼8 times larger than that of the best film reported so far. [ABSTRACT FROM AUTHOR]

Substituting sustainable/cost-effective catalysts for scarce and costly metal ones is currently among the major targets of sustainable chemistry. Herein, we report the synthesis of N-, S-, and P-tridoped worst-weed-derived carbon nanorings (WWCNRs) that can serve as a metal-free and selective electrocatalyst for the oxygen reduction reaction (ORR). The WWCNRs are synthesized via activation-free polymerization of worst weed, Eclipta prostrata, and then removal of the metallic residues by using HCl. The WWCNRs exhibit good catalytic activity towards the 4 electron-transfer ORR with a low onset potential and high kinetic limiting current density, along with high selectivity (introducing CO, the sample loses only ＜7% of its original activity, in contrast to more than 30% loss of the original activity for 20 wt% Pt/C over 4000 s of the continuous ORR) and long durability (94% of the initial current still persists at the sample electrode compared with a 87% current retention at commercial Pt/C electrodes after 18 000 s). The present work highlights the smart transformation of organic-rich worst weed into value-added functional materials with great potential for applications such as fuel cells, lithium–air batteries, photocatalysis, and heterocatalysis. [ABSTRACT FROM AUTHOR]

Quantitative experiments on the evaporation from sessile droplets of aqueous saline (NaCl) solutions show a strong dependence on salt concentration and droplet shape. The experiments were performed with seven decades of initial NaCl concentrations, with various droplet sizes and with different contact angles. The evaporation rate is significantly lower for high salt concentrations and small contact angles than what is expected from the well-accepted diffusion-controlled evaporation scenario for sessile droplets, even if the change of the vapor pressure due to the salt is taken into account. Particle tracking velocimetry reveals that this modification of the evaporation behavior is caused by marangoni flows that are induced by surface tension gradients originating from the local evaporative peripheral salt enrichment. In addition it is found that already very low salt concentrations lead to a pinning of the three phase contact line. Whereas droplets with concentration ≥10−6 M NaCl are pinned as soon as evaporation starts, droplets with lower salt concentration do evaporate in a constant contact angle mode. Aside from new, fundamental insights the findings are also relevant for a better understanding of the widespread phenomenon of corrosion initiated by sessile droplets. [ABSTRACT FROM AUTHOR]

Single molecule surface enhanced Raman scattering (SM-SERS) is a highly local effect occurring at sharp edges, interparticle junctions and crevices or other geometries with a sharp nanoroughness of plasmonic nanostructures (“hot spots”). The emission of an individual molecule at SM-SERS conditions depends on the local enhancement field of the hot spots, as well as the binding affinity and positioning at a hot spot region. In this regard, the stability of near-field nano-optics at hot spots is critical, particularly in a biological milieu. In this perspective review, we address recent advances in the experimental and theoretical approaches for the successful development of SM-SERS. Significant progress in the understanding of the interaction between the excitation electromagnetic field and the surface plasmon modes at the metallic or metallic/dielectric interface of various curvatures are described. New knowledge on methodological strategies for positioning the analytes for SM-SERS and Raman-assisted SERS or the SERS imaging of live cells has been acquired and displayed. In the framework of the extensive development of SM-SERS as an advancing diagnostic analytical technique, the real-time SERS chemical imaging of intracellular compartments and tracing of individual analytes has been achieved. In this context, we highlight the tremendous potential of SERS chemical imaging as a future prospect in SERS and SM-SERS for the prediction and diagnosis of diseases. [ABSTRACT FROM AUTHOR]

Information regarding a roundtable discussion about chemistry studies is presented. Topics include the use of grazing incidence small-angle X-ray scattering (SAXS) (GISAXS) to detect absence or presence of the nanocrystal lattice structure, the use of long range attraction to find a liquid-gas phase separation in nanoparticle dispersion, and the difference in ligand structure between disordered and ordered states. The panelists include authors Brian Korgel, Régine Perzynski, and Bruce Law.

The article presents a general discussion on the properties of self-assembled nanostructures. Several discussants include Subramanian Sankaranarayanan, Christopher Sorensen, and Yifan Wang. Topics include the mechanical properties of nanoparticle membranes and the optical properties of nanodisks, the strenght of the membranes, and separtion of gold nanoparticle by organic ligands.

Information about the model of nanoparticle self-assembly is presented. Topics discussed include roundtables including Self-Assembly of Magnetite Nanocubes into Helical Superstructures, Diffusion and Filtration Properties of Self-Assembled Gold Nanocrystal Membranes, and Interfacial Localization and Voltage-Tunable Arrays of Charged Nanoparticles.

Information regarding the Faraday Discussions, a roundtable event of the Royal Society of Chemistry (RSC) in 2015 is presented. Topics include the nanoparticle synthesis, the effect of beam irradiation on interaction-pair potential, and radiolysis of water. The panelists mentioned include Christopher Sorensen, Damien Faivre, and Andreas Fery.

The design of new quasi-2D biocompatible films able to release a drug in a controlled manner through the application of physical stimuli is of outstanding interest in biomaterials science. Herein, construction of composite nanofilms with multiple strata of stabilized large unilamellar liposomes is developed. The film has a multilayered architecture formed by the layer-by-layer (LbL) technique utilising two biocompatible polyelectrolytes, hyaluronic acid and poly-l-lysine (HA and PLL), onto which phospholipid liposome "interlayers" are adsorbed and subsequently embedded by further polyelectrolyte adsorption. First of all the morphology of the film surface is characterised and compared to the morphology obtained for a film containing the same polyelectrolytes but stiff polystyrene (PS) latex particles instead of the soft phospholipid vesicles. Both morphologies appear to be similar suggesting that the embedded vesicles keep their spherical shape. As a second step, it has been shown that carboxyfluorescein (CF) encapsulated in the vesicles remains inside without sustained release at room temperature indicating that the liposomes stay intact upon LbL immobilization. A substantial fraction (about 70%) of the vesicles absorbed onto the polyelectrolyte film are desorbed upon further polyelectrolyte adsorption to reach the embedded state. Hence to achieve high loading of the film, multiple vesicle depositions have to be performed. It is shown that the total number of deposited vesicles on the film is proportional to the number m of vesicle deposition steps (up to m = 3). The encapsulated dye can be released in a controlled manner by a temperature increase above the main phase transition temperature of the lipid mixture used to prepare the vesicles. Release kinetics is faster for film-entrapped vesicles than for those in solution due to destabilization of the lipidic bilayer by the polyelectrolyte environment. The developed composite films represent a new surface biocoating able to preserve, in native state, or to release in a controlled way, surface immobilized materials under external stimuli.