Tailoring Galvanic Replacement Reaction for the Preparation of Pt/Ag Bimetallic Hollow Nanostructures with Controlled Number of Voids

Here we report the synthesis of Pt/Ag bimetallic nanostructures with controlled number of void spaces <i>via</i> a tailored galvanic replacement reaction (GRR). Ag nanocubes (NCs) were employed as the template to react with Pt ions in the presence of HCl. The use of HCl in the GRR caused rapid precipitation of AgCl, which grew on the surface of Ag NCs and acted as a removable secondary template for the deposition of Pt. The number of nucleation sites for AgCl was tailored by controlling the amount of HCl added to the Ag NCs or by introducing PVP to the reaction. This strategy led to the formation of Pt/Ag hollow nanoboxes, dimers, multimers, or popcorn-shaped nanostructures consisting of one, two, or multiple hollow domains. Due to the presence of large void space and porous walls, these nanostructures exhibited high surface area and improved catalytic activity for methanol oxidation reaction

Multishelled Si@Cu Microparticles Supported on 3D Cu Current Collectors for Stable and Binder-free Anodes of Lithium-Ion Batteries

Silicon has proved to be a promising anode material of high-specific capacity for the next-generation lithium ion batteries (LIBs). However, during repeated discharge/charge cycles, Si-based electrodes, especially those in microscale size, pulverize and lose electrical contact with the current collectors due to large volume expansion. Here, we introduce a general method to synthesize Cu@M (M = Si, Al, C, SiO₂, Si₃N₄, Ag, Ti, Ta, SnIn₂O₅, Au, V, Nb, W, Mg, Fe, Ni, Sn, ZnO, TiN, Al₂O₃, HfO₂, and TiO₂) core–shell nanowire arrays on Cu substrates. The resulting Cu@Si nanowire arrays were employed as LIB anodes that can be reused via HCl etching and H₂-reduction. Multishelled Cu@Si@Cu microparticles supported on 3D Cu current collectors were further prepared as stable and binder-free LIB anodes. This 3D Cu@Si@Cu structure allows the interior conductive Cu network to effectively accommodate the volume expansion of the electrode and facilitates the contact between the Cu@Si@Cu particles and the current collectors during the repeated insertion/extraction of lithium ions. As a result, the 3D Cu@Si@Cu microparticles at a high Si-loading of 1.08 mg/cm² showed a capacity retention of 81% after 200 cycles. In addition, charging tests of 3D Cu@Si@Cu-LiFePO₄ full cells by a triboelectric nanogenerator with a pulsed current demonstrated that LIBs with silicon anodes can effectively store energy delivered by mechanical energy harvesters

In Situ “Doping” Inverse Silica Opals with Size-Controllable Gold Nanoparticles for Refractive Index Sensing

We report the fabrication of inverse SiO₂ opals “doped” with gold (i-Au-SiO₂-o) nanoparticles (NPs) via a co-self-assembly method combined with subsequent removal of polystyrene colloidal spheres by calcination. The resulting i-Au-SiO₂-o films demonstrate long-range ordering with uniform distribution of ligand-free Au NPs. The size of Au NPs can be tuned from 6 to 30 nm by varying the calcination temperature. The as-prepared i-Au-SiO₂-o films preserve both localized surface plasmon resonance (LSPR) and Bragg diffraction peaks simultaneously. Both LSPR and Bragg diffraction peaks are sensitive to the refractive index changes of the surrounding mediuman important feature for sensing applications. The method provides a facile and versatile way to fabricate high-quality Au NP “doped” photonic crystals for applications in sensing and others

Thermoresponsive Magnetic Nanoparticles for Seawater Desalination

Thermoresponsive magnetic nanoparticles (MNPs) as a class of smart materials that respond to a change in temperature may by used as a draw solute to extract water from brackish or seawater by forward osmosis (FO). A distinct advantage is the efficient regeneration of the draw solute and the recovery of water via heat-facilitated magnetic separation. However, the osmotic pressure attained by this type of draw solution is too low to counteract that of seawater. In this work, we have designed a FO draw solution based on multifunctional Fe₃O₄ nanoparticles grafted with copolymer poly­(sodium styrene-4-sulfonate)-<i>co</i>-poly­(<i>N</i>-isopropylacrylamide) (PSSS-PNIPAM). The resulting regenerable draw solution shows high osmotic pressure for seawater desalination. This is enabled by three essential functional components integrated within the nanostructure: (i) a Fe₃O₄ core that allows magnetic separation of the nanoparticles from the solvent, (ii) a thermoresponsive polymer, PNIPAM, that enables reversible clustering of the particles for further improved magnetic capturing at a temperature above its low critical solution temperature (LCST), and (iii) a polyelectrolyte, PSSS, that provides an osmotic pressure that is well above that of seawater

Zinc(II)-Tetradentate-Coordinated Probe with Aggregation-Induced Emission Characteristics for Selective Imaging and Photoinactivation of Bacteria

The emergence of drug-resistant bacterial pathogens highlights an urgent need for new therapeutic options. Photodynamic therapy (PDT) has emerged as a potential alternative to antibiotics to kill bacteria, which has been used in clinical settings. PDT employs photosensitizers (PSs), light, and oxygen to kill bacteria by generating highly reactive oxygen species (ROS). PDT can target both external and internal structures of bacteria, which does not really require the PSs to enter bacteria. Therefore, bacteria can hardly develop resistance to PDT. However, most of the PSs reported so far are hydrophobic and tend to form aggregates when they interact with bacteria. The aggregation could cause fluorescence quenching and reduce ROS generation, which generally compromises the effects of both imaging and therapy. In this contribution, we report on a Zn­(II)-tetradentate-coordinated red-emissive probe with aggregation-induced emission characterization. The probe could selectively image bacteria over mammalian cells. Moreover, the probe shows potent phototoxicity to both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Bacillus subtilis)

Fabrication of Well-Ordered Binary Colloidal Crystals with Extended Size Ratios for Broadband Reflectance

Binary colloidal crystals (BCCs) possess great potentials in tuning material properties by controlling the size ratio of small to large colloidal spheres (γ_S/L). In this paper, we present a method for the fabrication of BCCs with much more extended size ratios than those obtained in conventional convective self-assembly method. It is found that γ_S/L can be extended to 0.376 by adding TEOS sol into the colloidal suspension. The resulting polystyrene/silica (PS/SiO₂) BCCs show distinctive reflections, indicating their well-ordered structure. The extended size ratios render more flexibility in engineering the photonic bandgap structures of BCCs and hence provide a better platform for developing a range of applications such as photonics, spintronics, sensing and bioseparation

Controlled Synthesis of Palladium Concave Nanocubes with Sub-10-Nanometer Edges and Corners for Tunable Plasmonic Property

Developing new strategies for tuning the plasmonic properties of palladium nanostructures is of both fundamental and technological interest due to their potential applications in plasmonic hydrogen sensing, in situ surface-enhanced Raman spectroscopy for catalysis, and solar energy harvesting. In this work, a new strategy of tuning the localized surface plasmon resonance (LSPR) property of Pd nanocrystals by selectively sharpening their edges and corners is reported. Through a Cu­(II)-assisted seed-mediated growth approach, sub-10-nm sharp edges and corners were grown on regular Pd nanocubes. The LSPR peaks of the as-formed concave Pd nanocubes could be tuned across the visible spectrum by simply controlling their sizes. Cu­(II) was found to selectively activate the fast growth of Pd atoms along the [110] and [111] directions of the cubic Pd seeds and promote the formation of this new type of Pd concave nanocubes. This strategy of building Pd sharp edges and corners may be applicable for the design of new plasmonic nanostructures by using seeds of different metals, sizes, shapes, and crystal structures

Fabrication of Large Domain Crack-Free Colloidal Crystal Heterostructures with Superposition Bandgaps Using Hydrophobic Polystyrene Spheres

An improved convective self-assembly method was developed to fabricate crack-free colloidal crystal heterostructure over a relatively large area. A composite opaline heterostructure composed of polystyrene (PS) colloids was first fabricated. Subsequent calcination of the opaline heterostructure led to the formation of inverse opaline heterostructure composed of SiO₂ or TiO₂. Both opaline and inverse opaline heterostructures demonstrated long-range ordering in a relatively large domain (>100 × 100 μm²). Optical reflection measurements of the inverse opaline heterostructures showed dual stop bands as a consequence of the superposition of the stop bands from the individual compositional colloidal crystals (CCs). In addition, the relative position of the two stop bands can be adjusted by varying the size of the colloidal spheres in the original CCs template. Both types of colloidal crystal heterostructures can be used for optical filters, high-efficiency back-reflectors or electrodes in solar cells, differential drug release, and protein patterning

Layered V₂O₅/PEDOT Nanowires and Ultrathin Nanobelts Fabricated with a Silk Reelinglike Process

For the first time, a method resembling a cocoon-to-silk fiber reeling process is developed to fabricate layered V₂O₅/PEDOT nanowires (VP NWs) by stirring V₂O₅ powder in an aqueous solution of 3,4-ethylenedioxythiophene (EDOT). A mechanistic study indicates that the growth of VP NWs started from the intercalation/polymerization of EDOT within a few V₂O₅ surface layers, which were then peeled off to produce nanowires. The resulting VP NWs were further exfoliated to form 3.8 nm ultrathin V₂O₅/PEDOT nanobelts (VP NBs) consisting of V₂O₅ atomic bilayers intercalated with PEDOT. These VP NBs can be dispersed well in various solvents including water, ethanol, DMF, and acetonitrile for the preparation of transparent thin films as the hole extraction layer (HEL) to replace PEDOT:PSS in solution-processed inverted planar perovskite solar cells (PSCs). Cell efficiency tests over 7 days revealed that PSCs fabricated with VP NBs as HEL retained the initial power conversion efficiency (PCE), while those with PEDOT:PSS as HEL suffered from an efficiency drop of more than 50%

Silver Nanocube-Enhanced Far-Red/Near-Infrared Fluorescence of Conjugated Polyelectrolyte for Cellular Imaging

We present the study of silver nanocube (Ag NC)-enhanced fluorescence of a cationic conjugated polyelectrolyte (CPE) for far-red/near-infrared fluorescence cell imaging. Layer-by-layer self-assembly of polyelectrolytes on 78 nm Ag NCs is used to control CPE–metal distance and its effect on CPE fluorescence. The highest fluorescence enhancement factor (FEF) is obtained for Ag NCs with two bilayers, corresponding to a CPE–metal spacer thickness of ∼6 nm. At the optimal excitation wavelength, the FEF is 13.8 with respect to the control silica nanoparticles (NPs). The fluorescent NPs are further used for cellular imaging studies. The CPE-loaded Ag NCs with two bilayers exhibit excellent image contrast, superior to the control of CPE–silica NP at a similar uptake efficiency. The viability test indicates low cytotoxicity of the CPE-loaded Ag NCs, rendering them as promising cell imaging agents