Development of Light, Strong, and Water-Resistant PVA Composite Aerogels.

A significant weakness of many organic and inorganic aerogels is their poor mechanical behaviour, representing a great impediment to their application. For example, polymer aerogels generally have higher ductility than silica aerogels, but their elastic modulus is considered too low. Herein, we developed extremely low loading (<1 wt%) 2D graphene oxide (GO) nanosheets modified poly (vinyl alcohol) (PVA) aerogels via a facile and environmentally friendly method. The aerogel shows a 9-fold increase in compressional modulus compared to a pure polymer aerogel. With a low density of 0.04 mg/mm3 and a thermal conductivity of only 0.035 W/m·K, it outperforms many commercial insulators and foams. As compared to a pure PVA polymer aerogel, a 170% increase in storage modulus is obtained by adding only 0.6 wt% GO nanosheets. The nanocomposite aerogel demonstrates strong fire resistance, with a 50% increase in burning time and little smoke discharge. After surface modification with 1H,1H,2H,2H-Perfluorodecyltriethoxysilane, the aerogel demonstrates water resistance, which is suitable for outdoor applications in which it would be exposed to precipitation. Our research demonstrates a new pathway for considerable improvement in the performance and application of polymer aerogels.

Phospholipid-inspired alkoxylation induces crystallization and cellular uptake of luminescent COF nanocarriers.

The porous nature and structural variability of covalent organic frameworks (COFs) make them preferred for drug loading and delivery applications. However, most COF materials suffer from poor luminescent properties and inefficiency for cell uptake. Herein, we experimentally demonstrate the crucial role of long alkoxy chains in the synthesis of crystalline COF nanostructures with high cellular uptake efficiency. After luminescence integration through band engineering, the semiconducting COF exhibits an optical bandgap of 2.05 eV, an emission wavelength of 632 nm, a high quantum yield of 37 %, and excellent fluorescence stability (100 % at 3 h). Such excellent optical properties of the designed COF nanocarriers enable quantitative evaluations of cellular uptake and visual tracking of drug delivery. It was demonstrated that the cellular uptake efficiency was enhanced by orders of magnitude for the COF after the introduction of long n-octyloxy chains, which firstly delivered the anticancer camptothecin (CPT) to cell lysosomes, and then underwent "endo/lysosomal escape" to induce cell apoptosis. In vivo assay evidenced a significant enhancement in the therapeutic effect with a 96 % inhibition of tumor growth after 14 days of treatment. This progress sheds light on designing cutting-edge drug delivery nanosystems based on COF materials with integrated diagnostic and therapeutic functions.

STEM in situ thermal wave observations for investigating thermal diffusivity in nanoscale materials and devices.

Practical techniques to identify heat routes at the nanoscale are required for the thermal control of microelectronic, thermoelectric, and photonic devices. Nanoscale thermometry using various approaches has been extensively investigated, yet a reliable method has not been finalized. We developed an original technique using thermal waves induced by a pulsed convergent electron beam in a scanning transmission electron microscopy (STEM) mode at room temperature. By quantifying the relative phase delay at each irradiated position, we demonstrate the heat transport within various samples with a spatial resolution of ~10 nm and a temperature resolution of 0.01 K. Phonon-surface scatterings were quantitatively confirmed due to the suppression of thermal diffusivity. The phonon-grain boundary scatterings and ballistic phonon transport near the pulsed convergent electron beam were also visualized.

Operando Investigation of Silicon Anodes During Electrochemical Cycling in Li-ion Batteries.

Silicon (Si) is recognized as a promising anode material for next-generation anodes due to its high capacity. However, large volume expansion and active particle pulverization during cycling rapidly deteriorate the battery performance. The relationship between Si anode particle size and particle pulverization, and the structure evolution of Si particles during cycling is not well understood. In this study, a quantitative, time-resolved "operando" small angle X-ray scattering (SAXS) investigation into the morphological change of unwrapped and reduced graphene oxide (rGO) wrapped Si nanoparticles (Si@rGO) is conducted with respect to the operating voltage. The results provide a clear picture of Si particle size change and the role of nonrigid rGO in mitigating Si volume expansion and pulverization. Further, this study demonstrates the advantage of "operando" SAXS in electrochemical environments as compared to other approaches.

Defect engineering enhances plasmonic-hot electrons exploitation for CO2 reduction over polymeric catalysts.

Defect sites present on the surface of catalysts serve a crucial role in different catalytic processes. Herein, we have investigated defect engineering within a hybrid system composed of "soft" polymer catalysts and "hard" metal nanoparticles, employing the disparity in their thermal expansions. Electron paramagnetic resonance, X-ray photoelectron spectroscopy, and mechanistic studies together reveal the formation of new abundant defects and their synergistic integrability with plasmonic enhancement within the hybrid catalyst. These active defects, co-localized with plasmonic Ag nanoparticles, promote the utilization efficiency of hot electrons generated by local plasmons, thereby enhancing the CO2 photoreduction activity while maintaining the high catalytic selectivity.

Peptide Self-Assembly Controlled Photoligation of Polymers.

Highly efficient chemical ligations that operate in water under mild conditions are the foundation of bioorthogonal chemistry. However, the toolbox of suitable reactions is limited. Conventional approaches to expand this toolbox aim at altering the inherent reactivity of functional groups to design new reactions that meet the required benchmarks. Inspired by controlled reaction environments that enzymes provide, we report a fundamentally different approach that makes inefficient reactions highly efficient within defined local environments. Contrasting enzymatically catalyzed reactions, the reactivity controlling self-assembled environment is brought about by the ligation targets themselves─avoiding the use of a catalyst. Targeting [2 + 2] photocycloadditions, which are inefficient at low concentrations and readily quenched by oxygen, short ß-sheet encoded peptide sequences are inserted between a hydrophobic photoreactive styrylpyrene unit and a hydrophilic polymer. In water, electrostatic repulsion of deprotonated amino acid residues governs the formation of small self-assembled structures, which enable a highly efficient photoligation of the polymer, reaching ∼90% ligation within 2 min (0.034 mM). Upon protonation at low pH, the self-assembly changes into 1D fibers, altering photophysical properties and shutting down the photocycloaddition reaction. Using the reversible morphology change, it is possible to switch the photoligation "ON" or "OFF" under constant irradiation simply by varying the pH. Importantly, in dimethylformamide, the photoligation reaction did not occur even at 10-fold higher concentrations (0.34 mM). The self-assembly into a specific architecture, encoded into the polymer ligation target, enables a highly efficient ligation that overcomes the concentration limitations and high oxygen sensitivity of [2 + 2] photocycloadditions.

Molecular Photoswitching of Main-Chain α-Bisimines in Solid-State Polymers.

Photoisomerization of chromophores usually shows significantly less efficiency in solid polymers than in solution as strong intermolecular interactions lock their conformation. Herein, we establish the impact of macromolecular architecture on the isomerization efficiency of main-chain-incorporated chromophores (i.e., α-bisimine) in both solution and the solid state. We demonstrate that branched architectures deliver the highest isomerization efficiency for the main-chain chromophore in the solid state─remarkably as high as 70% compared to solution. The macromolecular design principles established herein for efficient solid-state photoisomerization can serve as a blueprint for enhancing the solid-state isomerization efficiency for other polymer systems, such as those based on azobenzenes.

Optoelectronic and Optomechanical Properties of Few-Atomic-Layer Black Phosphorus Nanoflakes as Revealed by In Situ TEM.

The optoelectronic signatures of free-standing few-atomic-layer black phosphorus nanoflakes are analyzed by in situ transmission electron microscopy (TEM). As compared to other 2D materials, the band gap of black phosphorus (BP) is related directly to multiple thicknesses and can be tuned by nanoflake thickness and strain. The photocurrent measurements with the TEM show a stable response to infrared light illumination and change of nanoflakes band gap with deformation while pressing them between two electrodes assembled in the microscope. The photocurrent spectra of an 8- and a 6-layer BP nanoflake samples are comparatively measured. Density functional theory (DFT) calculations are performed to identify the band structure changes of BP during deformations. The results should help to find the best pathways for BP smart band gap engineering via tuning the number of material atomic layers and programmed deformations to promote future optoelectronic applications.

Boron Dopants in Red-Emitting B and N Co-Doped Carbon Quantum Dots Enable Targeted Imaging of Lysosomes.

Lysosomes are of great significance to cell growth, metabolism, and survival, as they independently maintain acidity and regulate various balances in cells. Therefore, it is essential to develop advanced probes for lysosome visualization and live tracking. Herein, a type of lysosome-targeting probe based on boron (B) and nitrogen (N) co-doped carbon quantum dots (B/N-CQDs) is presented, which exhibits red emission at 618 nm, high quantum yield (28%), and excellent fluorescence stability (97% at 1 h). These B/N-CQDs are prepared by a novel and green solid-state reaction and purified using a simple extraction process without additional chemical modifications. It is found that the boron dopants in the structure play a crucial role in the resultant lysosome-specific targeting property through borate esterification between boronic acid groups in the sample and diol structures in glycoproteins. This can be applied as a powerful tool for cell apoptosis, necrosis, and endosomal escape tracking. This work not only offers a new concept for targeted subcellular probe designs via chemical doping but also demonstrates the feasibility of these tools for analyzing complex cellular physiological activities.

Strategic design of Fe and N co-doped hierarchically porous carbon as superior ORR catalyst: from the perspective of nanoarchitectonics.

In this study, we present microporous carbon (MPC), hollow microporous carbon (HMC) and hierarchically porous carbon (HPC) to demonstrate the importance of strategical designing of nanoarchitectures in achieving advanced catalyst (or electrode) materials, especially in the context of oxygen reduction reaction (ORR). Based on the electrochemical impedance spectroscopy and ORR studies, we identify a marked structural effect depending on the porosity. Specifically, mesopores are found to have the most profound influence by significantly improving electrochemical wettability and accessibility. We also identify that macropore contributes to the rate capability of the porous carbons. The results of the rotating ring disk electrode (RRDE) method also demonstrate the advantages of strategically designed double-shelled nanoarchitecture of HPC to increase the overall electron transfer number (n) closer to four by offering a higher chance of the double two-electron pathways. Next, selective doping of highly active Fe-N x sites on HPC is obtained by increasing the nitrogen content in HPC. As a result, the optimized Fe and N co-doped HPC demonstrate high ORR catalytic activity comparable to the commercial 20 wt% Pt/C in alkaline electrolyte. Our findings, therefore, strongly advocate the importance of a strategic design of advanced catalyst (or electrode) materials, especially in light of both structural and doping effects, from the perspective of nanoarchitectonics.

Expeditious Electrochemical Synthesis of Mesoporous Chalcogenide Flakes: Mesoporous Cu2 Se as a Potential High-Rate Anode for Sodium-Ion Battery.

Nanostructured copper selenide (Cu2 Se) attracts much interest as it shows outstanding performance as thermoelectric, photo-thermal, and optical material. The mesoporous structure is also a promising morphology to obtain better performance for electrochemical and catalytic applications, thanks to its high surface area. A simple one-step electrochemical method is proposed for mesoporous chalcogenides synthesis. The synthesized Cu2 Se material has two types of mesopores (9 and 18 nm in diameter), which are uniformly distributed inside the flakes. These materials are also implemented for sodium (Na) ion battery (NIB) anode as a proof of concept. The electrode employing the mesoporous Cu2 Se exhibits superior and more stable specific capacity as a NIB anode compared to the non-porous samples. The electrode also exhibits excellent rate tolerance at each current density, from 100 to 1000 mA g-1 . It is suggested that the mesoporous structure is advantageous for the insertion of Na ions inside the flakes. Electrochemical analysis indicates that the mesoporous electrode possesses more prominent diffusion-controlled kinetics during the sodiation-desodiation process, which contributes to the improvement of Na-ion storage performance.

Optomechanical Properties of MoSe2 Nanosheets as Revealed by In Situ Transmission Electron Microscopy.

Free-standing few-layered MoSe2 nanosheet stacks optoelectronic signatures are analyzed by using light compatible in situ transmission electron microscopy (TEM) utilizing an optical TEM holder allowing for the simultaneous mechanical deformation, electrical probing and light illumination of a sample. Two types of deformation, namely, (i) bending of nanosheets perpendicular to their basal atomic planes and (ii) edge deformation parallel to the basal atomic planes, lead to two distinctly different optomechanical performances of the nanosheet stacks. The former deformation induces a stable but rather marginal increase in photocurrent, whereas the latter mode is prone to unstable nonsystematic photocurrent value changes and a red-shifted photocurrent spectrum. The experimental results are verified by ab initio calculations using density functional theory (DFT).

Borophene: Two-dimensional Boron Monolayer: Synthesis, Properties, and Potential Applications.

Borophene, a monolayer of boron, has risen as a new exciting two-dimensional (2D) material having extraordinary properties, including anisotropic metallic behavior and flexible (orientation-dependent) mechanical and optical properties. This review summarizes the current progress in the synthesis of borophene on various metal substrates, including Ag(110), Ag(100), Au(111), Ir(111), Al(111), and Cu(111), as well as heterostructuring of borophene. In addition, it discusses the mechanical, thermal, magnetic, electronic, optical, and superconducting properties of borophene and the effects of elemental doping, defects, and applied mechanical strains on these properties. Furthermore, the promising potential applications of borophene for gas sensing, energy storage and conversion, gas capture and storage applications, and possible tuning of the material performance in these applications through doping, formation of defects, and heterostructures are illustrated based on available theoretical studies. Finally, research and application challenges and the outlook of the whole borophene's field are given.

Efficient lithium-ion storage using a heterostructured porous carbon framework and its in situ transmission electron microscopy study.

A heterostructured porous carbon framework (PCF) composed of reduced graphene oxide (rGO) nanosheets and metal organic framework (MOF)-derived microporous carbon is prepared to investigate its potential use in a lithium-ion battery. As an anode material, the PCF exhibits efficient lithium-ion storage performance with a high reversible specific capacity (771 mA h g-1 at 50 mA g-1), an excellent rate capability (448 mA h g-1 at 1000 mA g-1), and a long lifespan (75% retention after 400 cycles). The in situ transmission electron microscopy (TEM) study demonstrates that its unique three-dimensional (3D) heterostructure can largely tolerate the volume expansion. We envisage that this work may offer a deeper understanding of the importance of tailored design of anode materials for future lithium-ion batteries.

Semiconductor nanochannels in metallic carbon nanotubes by thermomechanical chirality alteration.

Carbon nanotubes have a helical structure wherein the chirality determines whether they are metallic or semiconducting. Using in situ transmission electron microscopy, we applied heating and mechanical strain to alter the local chirality and thereby control the electronic properties of individual single-wall carbon nanotubes. A transition trend toward a larger chiral angle region was observed and explained in terms of orientation-dependent dislocation formation energy. A controlled metal-to-semiconductor transition was realized to create nanotube transistors with a semiconducting nanotube channel covalently bonded between a metallic nanotube source and drain. Additionally, quantum transport at room temperature was demonstrated for the fabricated nanotube transistors with a channel length as short as 2.8 nanometers.

Biodegradable and Peroxidase-Mimetic Boron Oxynitride Nanozyme for Breast Cancer Therapy.

Nanomaterials having enzyme-like activities are recognized as potentially important self-therapeutic nanomedicines. Herein, a peroxidase-like artificial enzyme is developed based on novel biodegradable boron oxynitride (BON) nanostructures for highly efficient and multi-mode breast cancer therapies. The BON nanozyme catalytically generates cytotoxic hydroxyl radicals, which induce apoptosis of 4T1 cancer cells and significantly reduce the cell viability by 82% in 48 h. In vivo experiment reveals a high potency of the BON nanozyme for breast tumor growth inhibitions by 97% after 14-day treatment compared with the control, which are 10 times or 1.3 times more effective than the inert or B-releasing boron nitride (BN) nanospheres, respectively. This work highlights the BON nanozyme and its functional integrations within the BN nanomedicine platform for high-potency breast cancer therapies.

Stable single atomic silver wires assembling into a circuitry-connectable nanoarray.

Atomic metal wires have great promise for practical applications in devices due to their unique electronic properties. Unfortunately, such atomic wires are extremely unstable. Here we fabricate stable atomic silver wires (ASWs) with appreciably unoccupied states inside the parallel tunnels of α-MnO2 nanorods. These unoccupied Ag 4d orbitals strengthen the Ag-Ag bonds, greatly enhancing the stability of ASWs while the presence of delocalized 5s electrons makes the ASWs conducting. These stable ASWs form a coherently oriented three-dimensional wire array of over 10 nm in width and up to 1 µm in length allowing us to connect it to nano-electrodes. Current-voltage characteristics of ASWs show a temperature-dependent insulator-to-metal transition, suggesting that the atomic wires could be used as thermal electrical devices.

Highly dispersed secondary building unit-stabilized binary metal center on a hierarchical porous carbon matrix for enhanced oxygen evolution reaction.

Restricting the aggregation and rationally adjusting the electronic structure of binary metal centers in metal-organic framework (MOF) precursors are important for optimizing their performance as electrocatalysts for the oxygen evolution reaction (OER) and achieving low overpotential and high stability in such applications. Herein, we demonstrate the possibility of enhancing the electrochemical activity of MOF-derived binary metal center catalysts by controlling the form of the Fe species. The introduction of Fe-SBU (iron 2,5-dihydroxyterephthalic acid) into ZIF-67 is found to induce a distinct confinement effect and this can be exploited to improve the electroconductivity of binary metal center catalysts, and therefore, to reduce the OER reaction barrier (OOH* → O*). When applied as an OER catalyst in 1 M KOH solution, the Fe-SBU@Co-Matrix catalyst exhibits a low overpotential of 249 mV to reach a current density of 10 mA cm-2 and high stability for over 40 h. This work describes the secondary growth treatment of MOF-derived porous carbons to promote their application as catalysts in energy conversion reactions.

Mesoporous TiO2-based architectures as promising sensing materials towards next-generation biosensing applications.

In the past two decades, mesoporous TiO2 has emerged as a promising material for biosensing applications. In particular, mesoporous TiO2 materials with uniform, well-organized pores and high surface areas typically exhibit superior biosensing performance, which includes high sensitivity, broad linear response, low detection limit, good reproducibility, and high specificity. Therefore, the development of biosensors based on mesoporous TiO2 has significantly intensified in recent years. In this review, the expansion and advancement of mesoporous TiO2-based biosensors for glucose detection, hydrogen peroxide detection, alpha-fetoprotein detection, immobilization of enzymes, proteins, and bacteria, cholesterol detection, pancreatic cancer detection, detection of DNA damage, kanamycin detection, hypoxanthine detection, and dichlorvos detection are summarized. Finally, the future perspective and research outlook on the utilization of mesoporous TiO2-based biosensors for the practical diagnosis of diseases and detection of hazardous substances are also given.

Pristine and Antibiotic-Loaded Nanosheets/Nanoneedles-Based Boron Nitride Films as a Promising Platform to Suppress Bacterial and Fungal Infections.

In recent years, bacteria inactivation during their direct physical contact with surface nanotopography has become one of the promising strategies for fighting infection. Contact-killing ability has been reported for several nanostructured surfaces, e.g., black silicon, carbon nanotubes, zinc oxide nanorods, and copper oxide nanosheets. Herein, we demonstrate that Gram-negative antibiotic-resistant Escherichia coli (E. coli) bacteria are killed as a result of their physical destruction while contacting nanostructured h-BN surfaces. BN films, made of spherical nanoparticles formed by numerous nanosheets and nanoneedles with a thickness <15 nm, have been obtained through a reaction of ammonia with amorphous boron. The contact-killing bactericidal effect of BN nanostructures has been compared with a toxic effect of gentamicin released from them. For a wider protection against bacterial and fungal infection, the films have been saturated with a mixture of gentamicin and amphotericin B. Such BN films demonstrate a high antibiotic/antimycotic agent loading capacity and a fast initial and sustained release of therapeutic agents for 170-260 h depending on the loaded dose. The pristine BN films possess high antibacterial activity against E. coli K-261 strain at their initial concentration of 104 cells/mL, attaining >99% inactivation of colony forming units after 24 h, same as gentamicin-loaded (150 µg/cm2) BN sample. The BN films loaded with a mixture of gentamicin (150 and 300 µg/cm2) and amphotericin B (100 µg/cm2) effectively inhibit the growth of E. coli K-261 and Neurospora crassa strains. During immersion in the normal saline solution, the BN film generates reactive oxygen species (ROS), which can lead to accelerated oxidative stress at the site of physical cell damage. The obtained results are valuable for further development of nanostructured surfaces having contact killing, ROS, and biocide release abilities.