Younan Xia

Hollowing Out Nanofibers for Enhanced Visual Brightness and More Effective Solar Heating

The temperature rise of a solar‐heating textile is controlled by both generation and dissipation of heat. However, current designs mainly focus on increasing light absorption to generate more heat, often darkening the material while leaving thermal management largely overlooked. Herein, hollowing the nanofibers in a nonwoven mat produces a counterintuitive “brighter‐yet‐hotter” advantage over their solid (core–shell) counterparts. The polyacrylonitrile/polypyrrole double‐shelled tubular nanofibers are fabricated by selectively removing the poly(ε‐caprolactone) core from core–shell nanofibers. At outer and inner diameters of about 320 and 160 nm, the hollow nanofibers enhance backscattering in the visible range, making the mat brighter. Under 1 sun irradiation, the mat of hollow nanofibers shows a temperature rise of 28°C, which is 12% greater than that of the paired solid counterpart. Thermal modeling indicates that the higher temperature rise originates from the internal channels, which disrupt heat propagation across the fibers and lower the rate of heat dissipation. Side‐by‐side comparisons under simulated and outdoor sunlight show that the higher‐temperature region consistently appears on the mat of hollow nanofibers. This work highlights the promise of hollow nanofibers as a structural platform for optical and thermal management in solar‐heating textiles.

What is happening at the atomic level during the seed-mediated growth of copper on gold?

Atomic Evolution of Hydrogen Intercalation Wave Dynamics in Palladium Nanocrystals Revealed by Liquid-Phase Transmission Electron Microscopy

Solute-intercalation-induced phase separation creates spatial heterogeneities in host materials, a phenomenon ubiquitous in batteries, hydrogen storage, and other energy devices. Despite many efforts, probing intercalation processes at the atomic scale has been a significant challenge. By utilizing liquid-phase transmission electron microscopy (TEM), we study hydrogen (de)intercalation in palladium nanocrystals as a model system and have achieved unprecedented atomic-resolution imaging of hydrogen intercalation wave dynamics. Our observations reveal that intercalation wave mechanisms, instead of shrinking-core mechanisms, prevail at ambient temperature for palladium nanocubes ranging from ∼60 nm down to ∼10 nm. Systematic image analysis uncovers the atomic evolution of the hydrogen intercalation wave, transitioning from nonplanar and inclined boundaries to those closely aligned with {100} planes. Our kinetic Monte Carlo simulations demonstrate that the observed intercalation wave dynamics correspond to sorption pathways minimizing the lattice mismatch strain at the phase boundary. Unveiling the atomic intercalation pathways holds profound implications for engineering intercalation-mediated devices and advancements in energy sciences.

High-Entropy Alloy Nanocrystals: From Synthesis to Characterization and Catalytic Application

Nanocrystal Geometry Governs Phase Transformation Pathways in Palladium Hydride

Pathways and structural dynamics of phase transformations impact performance of materials in energy and information storage technologies. Palladium hydride (PdHx) nanocrystals are an ideal model system for studying solute-induced phase transformations, where elastic energy from lattice mismatch between α-PdHx and β-PdHx phases is often considered a key to determining the transformation pathways. α/β-PdHx interfacial elastic energy is affected by the confined geometry of a nanocrystal. However, how nanocrystal geometry influences phase transformation pathways is largely unknown. Using in situ liquid phase transmission electron microscopy, we directly visualize hydrogenation in Pd nanocrystals with two geometries, a nanocube and a hexagonal nanoplate. Both follow similar sequences of an initially curved nucleus, interface flattening, and reverse-stage nucleation; however, their evolving α/β-PdHx interfaces exhibit geometry-dependent crystallographic alignments. In nanocubes, {100}-aligned configurations conform to static elastic energy ordering, representing a pathway that maintains a local mechanical equilibrium, whereas nanoplates display both {110}- and {211}-aligned interfaces. Theoretical simulations show that geometry determines the accessibility of alternative phase transformation pathways as the system is driven far from equilibrium during hydrogenation. These findings identify geometry as a fundamental parameter for directing phase transformation pathways, offering design principles for accessing atypical configurations and improving properties of intercalation-based devices.

Rational Synthesis of Virus-Mimicking Nanocarriers for Enhanced Intracellular Delivery through Polyvalent Interactions with Cells

XiaMaterials and Interfaces

Understanding the Surface Oxidation of Ag Nanocrystals Under Different Environmental Conditions

Au@Pd Nanostructures With a Porous Morphology and Their Enhanced Catalytic Activity Toward Formic Acid Oxidation

Silica Nanobottles Filled with Photo-cross-linked GelMA for the Sustained Release of Hydrophilic Biomacromolecules

Nanobottles have garnered attention as a class of advanced carriers for drug delivery, because of their advantages, such as convenient loading, high capacity, and a well-defined wall for surface modification. However, strategies to achieve sustained release of hydrophilic biomolecules remain limited. Here, we report a hybrid delivery platform that integrates silica nanobottles with photo-cross-linked gelatin methacryloyl for the encapsulation and controlled release of proteins, enzymes, and polysaccharides. Upon cross-linking, the payloads show enhanced intracellular stability, with minimal release in A549 cells for up to 24 h. This system also enables control over release kinetics, with the half-life extendible to several weeks depending on the type and/or molecular weight of the payload. Importantly, released biomacromolecules retain structural and functional integrity, and delivery of nerve growth factor promotes robust neurite outgrowth from PC12 cells. This hybrid system provides a versatile and programmable platform for the long-term delivery of diverse hydrophilic therapeutics.

Continuous and Scalable Production of Uniform Au Nanocrystals Capped by Citrate Species in Flow Reactors for Lateral Flow Tests

Spatiotemporally controlled delivery of biological effectors from nanofiber scaffolds accelerates skin wound healing in porcine models

A-394 Scalable and continuous production of monodispersed gold nanospheres capped by citrate species for advanced lateral flow immunoassays

MirkinACS Nano

33 Unresolved Questions in Nanoscience and Nanotechnology

Microfluidic Synthesis of Channel‐Rich Pd‐Cu Alloy Nanodendrites for Efficient Electrocatalytic CO₂ Reduction to Formate

Light-Driven Soft Actuators: Materials, Designs, and Applications

XiaLangmuir

Seeing Is Believing: How Does the Surface of Silver Nanocubes from a Polyol Synthesis Change during Sample Collection, Washing, and Redispersion

High Resolution Image Download MS PowerPoint Slide While the synthesis of Ag nanocubes has been extensively studied, sample preparation (including collection, washing, and redispersion) after the synthesis has received far less attention. Herein, we leverage the unique capability of surface-enhanced Raman scattering to investigate how the solvent used for sample preparation affects the surface chemistry of Ag nanocubes. Our findings reveal that the use of an appropriate solvent for sample preparation plays a vital role in preserving the cubic shape. Crushing the reaction mixture with acetone before centrifugation greatly improves collection efficiency by inducing reversible aggregation among the particles. It also promotes the coadsorption of the carbonyl group from acetone and Cl – ions on the Ag surface to suppress oxidative etching and thereby help preserve the cubic shape. Subsequent washing of the collected nanocubes with water or ethanol enables effective redispersion while facilitating the desorption of Cl – ions and the adsorption of the carbonyl group from poly(vinylpyrrolidone). Collectively, these results underscore the importance of processing conditions after a colloidal synthesis in preserving the desired properties of Ag nanocubes for an array of applications.

Biomimetic Scaffolds with Dual Gradients of Biological Effectors for Tendon‐to‐Bone Repair

Due to the complexspatial gradients in composition and structure at the native tendon-to-bone attachment, it remains a clinical challenge to repair rotator cuff tears. Herein, we describe a biomimetic scaffold with dual gradients in osteogenic and tendon enthesis effectors to regulate the graded differentiation of stem cells for tendon-to-bone repair. Funnel-shaped microchannels prompted stem cells to rapidly infiltrate into the scaffold to experience the dual gradients in biological effectors along the walls of each microchannel. The graded distributions of two different effectors-hydroxyapatite nanorods and hedgehog agonist-worked synergistically to promote the differentiation of stem cells into osteoblasts, chondrocytes, and tenocytes, reproducing the cell phenotypes present in the natural tendon enthesis. The new scaffold offers a versatile platform to address key requirements for successful repair/regeneration of the tendon-to-bone attachment while also presenting an innovative strategy for the repair of connective tissue interfaces in general.

What Makes Au Nanospheres Superior to Octahedral and Cubic Counterparts for the Deposition of a Pt Monolayer Shell?

This study demonstrates that Au nanospheres are advantageous over their octahedral and cubic counterparts as seeds in the synthesis of Au@Pt core-shell nanocrystals with a monolayer shell. In combination with experimental characterization, we show through training a machine-learned interatomic potential that the Au nanospheres exhibit a large fraction of low-coordination atoms which are uniformly distributed over the surface. The corresponding high-index facets, including {211}, {311}, {331}, {210}, and {310}, on a spherical seed promote nucleation while greatly shortening the diffusion distance for adatoms. In addition, the high-index facets are instrumental in retaining the deposited Pt atoms on the outermost surface by retarding their inter-diffusional exchange with the underlying Au atoms. By switching from a monolayer made of pure Pt to those made of Pt-Au alloys, we can optimize both the activity and selectivity of the nanocrystals toward the two-electron oxygen reduction reaction for the electrochemical synthesis of H₂O₂. This method should be extendible to the fabrication of other core-shell nanocatalysts with desired monolayer shells for various catalytic reactions.

Steady-State Synthesis of Colloidal Metal Nanocrystals

Despite remarkable progress, colloidal synthesis of metal nanocrystal is still far away from reaching the goal for robust, reproducible, and scalable production. Even with the adoption of seed-mediated growth, the synthesis can still be complicated by issues such as self-nucleation, galvanic replacement, stochastic symmetry reduction, and unwanted compositional variation. All these issues can be addressed by switching to steady-state synthesis characterized by a slow, constant, and tightly controlled reduction rate. Steady-state synthesis can be achieved by adding one reactant dropwise while using the other reactant in large excess, but this method is not suitable for scale-up production in a continuous flow reactor. There is a pressing need to develop alternative methods capable of establishing the steady-state kinetics characteristic of dropwise addition while introducing both reactants by one-shot injection. In this Perspective, we discuss a number of methods that allow for both one-shot injection and steady-state synthesis.

Understanding the Kinetic Aspects Responsible for the Formation of 3‐Aminophenol‐Formaldehyde Resin Beads with Different Morphologies

This work investigates the kinetics and mechanistic details involved in the synthesis of phenolic resin beads when formaldehyde is added in one‐shot or dropwise to react with an excess amount of 3‐aminophenol. In one‐shot synthesis, the sharp rise in formaldehyde concentration, [F], to a high level leads to a rapid kinetics that triggers simultaneous substitution, condensation, and polymerization reactions for the formation of homogeneous, fully‐cross‐linked beads that cannot be etched by acetone. Conversely, dropwise synthesis, characterized by a significantly lower [F] in the early stage, results in the formation of low‐substitution monomers, which then polymerize into heterogeneous beads consisting of a cross‐linked shell and an etchable core. With dropwise addition, it can precisely control the level of [F] in the reaction mixture to obtain resin beads with tunable diameters. After etching away the lightly‐crosslinked core, the beads can be carbonized to obtain hollow carbon beads sought for applications in catalysis and energy storage.