Transition‐Metal‐Ions‐Induced Coalescence: Stitching Au Nanoclusters into Tubular Au‐Based Nanocomposites

Rod‐shaped assemblages of Au nanoclusters (AuNCs) can serve as self‐templating solid precursors to produce tubular Au‐based nanocomposites via the coalescence induced by transition metal ions. Specifically, when the AuNC assemblages react with transition metal ions with relatively high standard oxidation potentials such as Cu(II), Ag(I), Pd(II), and Au(III), a series of polycrystalline and ultrathin Au and Au_xM_y (where M = Cu, Ag, and Pd) alloy hollow nanorods (HNRs) can be obtained with further reduction; these metallic products are evaluated for electrooxidation of methanol. Alternatively, the above transition metal ions‐induced transformations can also be carried out after coating the AuNC assemblages with a layer of mesoporous SiO₂ (mSiO₂), giving rise to many mSiO₂‐coated Au‐based HNRs. Onto the formed AuPd_0.18 alloy HNRs, furthermore, a range of transition metal oxides such as TiO₂, Co₃O_4, and Cu₂O nanocrystals can be deposited easily to prepare metal oxide–AuPd_0.18 HNRs nanocomposites, which can be used as photocatalysts. Compared with those conventional galvanic replacement reactions, the controlled coalescence of AuNCs induced by transition metal ions provides a novel and efficient chemical approach with improved element efficiency to tubular Au‐based nanocomposites.     

Wafer‐Scale Double‐Layer Stacked Au/Al2O3@Au Nanosphere Structure with Tunable Nanospacing for Surface‐Enhanced Raman Scattering

Fabricating perfect plasmonic nanostructures has been a major challenge in surface enhanced Raman scattering (SERS) research. Here, a double‐layer stacked Au/Al₂O₃@Au nanosphere structures is designed on the silicon wafer to bring high density, high intensity “hot spots” effect. A simply reproducible high‐throughput approach is shown to fabricate feasibly this plasmonic nanostructures by rapid thermal annealing (RTA) and atomic layer deposition process (ALD). The double‐layer stacked Au nanospheres construct a three‐dimensional plasmonic nanostructure with tunable nanospacing and high‐density nanojunctions between adjacent Au nanospheres by ultrathin Al₂O₃ isolation layer, producing highly strong plasmonic coupling so that the electromagnetic near‐field is greatly enhanced to obtain a highly uniform increase of SERS with an enhancement factor (EF) of over 10⁷. Both heterogeneous nanosphere group (Au/Al₂O₃@Ag) and pyramid‐shaped arrays structure substrate can help to increase the SERS signals further, with a EF of nearly 10⁹. These wafer‐scale, high density homo/hetero‐metal‐nanosphere arrays with tunable nanojunction between adjacent shell‐isolated nanospheres have significant implications for ultrasensitive Raman detection, molecular electronics, and nanophotonics.     

Performance enhancement of paper-based SERS chips by shell-isolated nanoparticle-enhanced Raman spectroscopy

Paper-based flexible surface-enhanced Raman scattering (SERS) chips have been demonstrated to have great potential for future practical applications in point-of-care testing (POCT) due to the potentials of massive fabrication, low cost, efficient sample collection and short signal acquisition time. In this work, common filter paper and Ag@SiO₂core-shell nanoparticles (NP) have been utilized to fabricate SERS chips based on shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS). The SERS performance of the chips for POCT applications was systematically investigated. We used crystal violet as the model molecule to study the influence of the size of the Ag core and the thickness of the SiO₂coating layer on the SERS activity and then the morphology optimized Ag@SiO₂core-shell NPs was employed to detect thiram. By utilizing the smartphone as a miniaturized Raman spectral analyzer, high SERS sensitivity of thiram with a detection limit of 10⁻⁹M was obtained. The study on the stability of the SERS chips shows that a SiO₂shell of 3 nm can effectively protect the as-prepared SERS chips against oxidation in ambient atmosphere without seriously weakening the SERS sensitivity. Our results indicated that the SERS chips by SHINERS had great potential of practical application, such as pesticide residues detection in POCT.     

A Double‐Buffering Strategy to Boost the Lithium Storage of Botryoid MnOx/C Anodes

Transition metal oxides (TMOs) are regarded as promising candidates for anodes of lithium ion batteries, but their applications have been severely hindered by poor material conductivity and lithiated volume expansion. As a potential solution, herein is presented a facile approach, by electrospinning a manganese‐based metal organic framework (Mn‐MOF), to fabricate yolk–shell MnO_x nanostructures within carbon nanofibers in a botryoid morphology. While the yolk–shell structure accomodates the lithiated volume expansion of MnO_x, the fiber confinement ensures the structural integrity during charge/discharge, achieving a so‐called double‐buffering for cyclic volume fluctuation. The formation mechanism of the yolk–shell structure is well elucidated through comprehensive instrumental characterizations and cogitative control experiments, following a combined Oswald ripening and Kirkendall process. Outstanding electrochemical performances are demonstrated with prolonged stability over 1000 cycles, boosted by the double‐buffering design, as well as the “breathing” effect of lithiation/delithiation witnessed by ex situ imaging. Both the fabrication methodology and electrochemical understandings gained here for nanostructured MnO_x can also be extended to other TMOs toward their ultimate implementation in high‐performance lithium ion batteries (LIBs).     

Polypyrrole‐Coated Zinc Ferrite Hollow Spheres with Improved Cycling Stability for Lithium‐Ion Batteries

Here, ZnFe₂O₄ double‐shell hollow microspheres are designed to accommodate the large volume expansion during lithiation. A facile and efficient vapor‐phase polymerization method has been developed to coat the ZnFe₂O₄ hollow spheres with polypyrrole (PPY). The thin PPY coating improves not only the electronic conductivity but also the structural integrity, and thus the cycling stability of the ZnFe₂O₄ hollow spheres. Our work sheds light on how to enhance the electrochemical performance of transition metal oxide‐based anode materials by designing delicate nanostructures.     

Synthesis and characterization of ZnO/SiO2 core/shell nanocomposites and hollow SiO2 nanostructures

In this paper, we prepared the ZnO nanoparticles by a simple hydrothermal method and fabricated the ZnO/SiO₂ core/shell nanostructures through a sol-gel chemistry process successfully. The hollow SiO₂ nanostructures were obtained by selective removal of the ZnO cores. The structure, morphology and composition of the products were determined by the techniques of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The results indicated that the ZnO nanoparticles were sphere-like shape with the average size of 60 nm and belonged to hexagonal wurtzite crystal structure. With the coating of SiO₂, the vibration modes of Si-O-Si and Si-OH were found. Furthermore, the measurement results of optical properties showed that spectra of bare ZnO nanoparticles and ZnO/SiO₂ core/shell nanocomposites exhibited similar emission features, including a blue emission peak and an orange emission band.     

Design of Multifunctional Fluorescent Hybrid Materials Based on SiO2 Materials and Core–Shell Fe3O4@SiO2 Nanoparticles for Metal Ion Sensing

Hybrid fluorescent materials constructed from organic chelating fluorescent probes and inorganic solid supports by covalent interactions are a special type of hybrid sensing platform that has gained much interest in the context of metal ion sensing applications owing to their excellent advantages, recyclability, and solubility/dispersibility in particular, as compared with single organic fluorescent molecules. In recent decades, SiO₂ materials and core–shell Fe₃O₄@SiO₂ nanoparticles have become important inorganic solid materials and have been used as inorganic solid supports to hybridize with organic fluorescent receptors, resulting in multifunctional fluorescent hybrid systems for potential applications in sensing and related research fields. Therefore, recent progress in various fluorescent‐group‐functionalized SiO₂ materials is reviewed, with a focus on mesoporous silica nanoparticles and core–shell Fe₃O₄@SiO₂ nanoparticles, as interesting fluorescent organic–inorganic hybrid materials for sensing applications toward essential and toxic metal ions. Selective examples of other types of silica/silicon materials, such as periodic mesoporous organosilicas, solid SiO₂ nanoparticles, fibrous silica spheres, silica nanowires, silica nanotubes, and silica hollow microspheres, are also mentioned. Finally, relevant perspectives of metal‐ion‐sensing‐oriented silica‐fluorescent probe hybrid materials are provided.     

Hollow Multishelled Heterostructured Anatase/TiO2(B) with Superior Rate Capability and Cycling Performance

TiO₂ is a potential anode material for lithium‐ion batteries due to its high rate capability and high safety. Here, a controllable synthesis for hollow nanostructured TiO₂, with heterostructured shells of TiO₂(B) and anatase phases, is presented for the first time, by using a sequential templating approach. The hollow nanostructures can be easily controlled to produce core–shell and double‐shelled materials with different compositional ratios of anatase to TiO₂(B) by tuning the synthetic conditions. When used as the anode materials for lithium‐ion batteries, a specific discharge capacity of 215.4 mAh g^?1 for the double‐shelled anatase/TiO₂(B) hollow microspheres is achieved at a current rate of 1 C (335 mA g^?1) for the 100th cycle and shows high specific discharge capacities of 141.6 and 125.7 mAh g^?1 at the high rates of 10 and 20 C over 1000 cycles. These results are due to the unique stable hollow multishelled structure, which has a high specific surface area, as well as the interface between the heterostructured anatase/TiO₂(B) phases contributing a substantial number of lithium‐ion storage sites.     

A Gold Nanocage/Cluster Hybrid Structure for Whole‐Body Multispectral Optoacoustic Tomography Imaging,EGFR Inhibitor Delivery,and Photothermal Therapy

Gold nanocages (AuNCs) and gold nanoclusters (AuClusters) are two classes of advantageous nanostructures with special optical properties, and many other attractive properties. Integrating them into one nanosystem may achieve greater and smarter performance. Herein, a hybrid gold nanostructure for fluorescent and optoacoustic tomography imaging, controlled release of drugs, and photothermal therapy (PTT) is demonstrated. For this nanodrug (EA–AB), an epidermal growth factor receptor (EGFR) inhibitor erlotinib (EB) is loaded into AuNCs, which are then capped and functionalized by biocompatible AuCluster@BSA (BSA = bovine serum albumin) conjugates via electrostatic interaction. Upon cell internalization, the lysosomal proteases and low pH cause the release of EB from EA–AB, and also induce fluorescence restoration of the AuCluster for imaging. Irradiation with near‐infrared light further promotes the drug release and affords a PTT effect as well. The AuNC‐based nanodrug is optoacoustically active, and its biodistribution and metabolic process have been successfully monitored by whole‐body and 3D multispectral optoacoustic tomography imaging. Owing to the combined actions of PTT and EGFR pathway blockage, EA–AB exhibits marked tumor inhibition efficacy in vivo.     

Extension of the Stöber Method to Construct Mesoporous SiO2 and TiO2 Shells for Uniform Multifunctional Core–Shell Structures

Core–shell nanoparticles (CSNs) have attracted considerable attention because of their promising applications in a wide range of fields. Recently, substantial efforts have been focused on the development of facile and versatile methods for preparing CSNs with mesoporous SiO₂ or TiO₂ shells because of their fascinating properties, such as high surface area, large pore channels and high pore volume. This Research News reviews the recent progress in facile, versatile and reproducible approaches which are simply extended from the well‐known Stöber method to construct mesoporous SiO₂ and TiO₂ shells for uniform multifunctional core–shell nanostructures. Several strategies, including the surfactant‐templating process, the long‐chain organosilane‐assisted approach, the phase transfer assisted surfactant‐templating process, and the kinetics‐controlled coating approach, are discussed. In addition, new trends in this field for the creation of multifunctional CSNs and novel nanostructures are highlighted.     

Al2O3‐Assisted Confinement Synthesis of Oxide/Carbon Hollow Composite Nanofibers and Application in Metal‐Ion Capacitors

Hollow micro‐/nanostructures are widely explored for energy applications due to their unique structural advantages. The synthesis of hollow structures generally involves a “top‐down” casting process based on hard or soft templates. Herein, a new and generic confinement strategy is developed to fabricate composite hollow fibers. A thin and homogeneous atomic‐layer‐deposition (ALD) Al₂O₃ layer is employed to confine the pyrolysis of precursor fibers, which transform into metal (or metal oxide)–carbon composite hollow fibers after removal of Al₂O₃. Because of the uniform coating by ALD, the resultant composite hollow fibers exhibit a hollow interior from heads to ends even if they are millimeter long. V, Fe, Co, and Ni‐based hollow nanofibers, demonstrating the versatility of this synthesis method, are successfully synthesized. Because of the carbon constituent, these composite fibers are particularly useful for energy applications. Herein, the as‐obtained hollow V₂O₃–C fiber membrane is employed as a freestanding and flexible electrode for lithium‐ion capacitor. The device shows an impressive energy density and a high power density.     

Intrinsic Effect of Nanoparticles on the Mechanical Rupture of Doubled‐Shell Colloidal Capsule via In Situ TEM Mechanical Testing and STEM Interfacial Analysis

The discovery of Pickering emulsion templated assembly enables the design of a hybrid colloidal capsule with engineered properties. However, the underlying mechanisms by which nanoparticles affect the mechanical properties of the shell are poorly understood. Herein, in situ mechanical compression on the transmission electron microscope and aberration‐corrected scanning transmission microscope are unprecedentedly implemented to study the intrinsic effect of nanoparticles on the mechanical properties of the calcium carbonate (CaCO₃)‐decorated silica (SiO₂) colloidal capsule. The stiff and brittle nature of the colloidal capsule is due to the interfacial chemical bonding between the CaCO₃ nanoparticles and SiO₂ inner shell. Such bonding strengthens the mechanical strength of the SiO₂ shell (166 ± 14 nm) from the colloidal capsule compared to the thicker single SiO₂ shell (310 ± 70 nm) from the silica hollow sphere. At elevated temperature, this interfacial bonding accelerates the formation of the single calcium silicate shell, causing shell morphology transformation and yielding significantly enhanced mechanical strength by 30.9% and ductility by 94.7%. The superior thermal durability of the heat‐treated colloidal capsule holds great potential for the fabrication of the functional additives that can be applied in the wide range of applications at elevated temperatures.     

Rapid synthesis of TiO2 hollow nanostructures with crystallized walls by using CuO as template and microwave heating

In this paper, TiO₂ hollow nanostructures with anatase walls have been rapidly fabricated by using CuO as template and microwave heating. These TiO₂ hollow nanostructures have been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Experimental results showed that the TiO₂ shell transformed from amorphous to anatase phase in 3 min, induced by the hot CuO core under microwave irradiation. The diameter of TiO₂ hollow nanostructures is about 50-80 nm, and the length is about 200-300 nm. The thickness of the shell is about 3 nm. This method is promising to be used to synthesize other nanomaterials with a hollow nanostructure.     

Metal Chelation Assisted In Situ Migration and Functionalization of Catalysts on Peapod‐Like Hollow SnO2 toward a Superior Chemical Sensor

Rational design of nanostructures and efficient catalyst functionalization methods are critical to the realization of highly sensitive gas sensors. In order to solve these issues, two types of strategies are reported, i.e., (i) synthesis of peapod‐like hollow SnO₂ nanostructures (hollow 0D‐1D SnO₂) by using fluid dynamics of liquid Sn metal and (ii) metal–protein chelate driven uniform catalyst functionalization. The hollow 0D‐1D SnO₂ nanostructures have advantages in enhanced gas accessibility and higher surface areas. In addition to structural benefits, protein encapsulated catalytic nanoparticles result in the uniform catalyst functionalization on both hollow SnO₂ spheres and SnO₂ nanotubes due to their dynamic migration properties. The migration of catalysts with liquid Sn metal is induced by selective location of catalysts around Sn. On the basis of these structural and uniform functionalization of catalyst benefits, biomarker chemical sensors are developed, which deliver highly selective detection capability toward acetone and toluene, respectively. Pt or Pd loaded multidimensional SnO₂ nanostructures exhibit outstanding acetone (R _air/R _gas = 93.55 @ 350 °C, 5 ppm) and toluene (R _air/R _gas = 9.25 @ 350 °C, 5 ppm) sensing properties, respectively. These results demonstrate that unique nanostructuring and novel catalyst loading method enable sensors to selectively detect biomarkers for exhaled breath sensors.     

Selective Etching Induced Synthesis of Hollow Rh Nanospheres Electrocatalyst for Alcohol Oxidation Reactions

The hollow noble metal nanostructures have attracted wide attention in catalysis/electrocatalysis. Here a two‐step procedure for constructing hollow Rh nanospheres (Rh H‐NSs) with clean surface is described. By selectively removing the surfactant and Au core of Au‐core@Rh‐shell nanostructures (Au@Rh NSs), the surface‐cleaned Rh H‐NSs are obtained, which contain abundant porous channels and large specific surface area. The as‐prepared Rh H‐NSs exhibit enhanced inherent activity for the methanol oxidation reaction (MOR) compared to state‐of‐the‐art Pt nanoparticles in alkaline media. Further electrochemical experiments show that Rh H‐NSs also have high activity for the electrooxidation of formaldehyde and formate (intermediate species in the course of the MOR) in alkaline media. Unfortunately, Rh H‐NSs have low electrocatalytic activity for the ethanol and 1‐propanol oxidation reactions in alkaline media. All electrochemical results indicate that the order of electrocatalytic activity of Rh H‐NSs for alcohol oxidation reaction is methanol (C₁) > ethanol (C₂) > 1‐propanol (C₃). This work highlights the synthesis route of Rh hollow nanostructures, and indicates the promising application of Rh nanostructures in alkaline direct methanol fuel cells.     

Nanostructures for Thermoelectric Applications: Synthesis,Growth Mechanism,and Property Studies

Both heterostructures and hollow nanostructures have been predicted as candidates with excellent thermoelectric performance. In this Research News areticle, recent advances with regard to synthetic strategies, growth mechanisms, and thermoelectric properties of one‐dimensional heterostructures (segmented and core/shell) and tubular nanostructures are reported. The thermoelectric property studies of Te/Bi core/shell heterostructured nanowires and Bi₂Te₃ nanotubes indicate that the Seebeck coefficient and thermal conductivity of these materials can be optimized to improve their thermoelectric performance. In addition, the current issues and future research directions for promising thermoelectric nanostructures will be discussed on the basis of these experimental results.     

Controlled Synthesis of Hollow Cu2‐xTe Nanocrystals Based on the Kirkendall Effect and Their Enhanced CO Gas‐Sensing Properties

This paper develops a facile solution‐based method to synthesize hollow Cu_2‐xTe nanocrystals (NCs) with tunable interior volume based on the Kirkendall effect. Transmission electron microscopy images and time‐dependent absorption spectra reveal the temporal growth process from solid copper nanoparticles to hollow Cu_2‐xTe NCs. Furthermore, the as‐prepared hollow Cu_2‐xTe NCs show enhanced sensitivity for the detection of carbon monoxide (CO), which is often referred to as the “silent killer”. The response and recovery time of the as‐prepared sensor for the detection of 100 ppm CO gas are estimated to be about 21 and 100 s, respectively, which are sufficient to render it a promising candidate for effective CO gas‐sensing applications. Such enhanced performance is achieved owing to the small grain size and large specific area of the hollow nanostructures. Therefore, the obtained hollow NCs based on the Kirkendall effect may have the potential as new functional blocks for high‐performance gas sensors.     

Volume‐Enhanced Raman Scattering Detection of Viruses

Virus detection and analysis are of critical importance in biological fields and medicine. Surface‐enhanced Raman scattering (SERS) has shown great promise in small molecule and even single molecule detection, and can provide fingerprint signals of molecules. Despite the powerful detection capabilities of SERS, the size discrepancy between the SERS “hot spots” (generally, <10 nm) and viruses (usually, sub‐100 nm) yields poor detection reliability of viruses. Inspired by the concept of molecular imprinting, a volume‐enhanced Raman scattering (VERS) substrate composed of hollow nanocones at the bottom of microbowls (HNCMB) is developed. The hollow nanocones of the resulting VERS substrates serve a twofold purpose: 1) extending the region of Raman signal enhancement from the nanocone surface (e.g., surface “hot spots”) to the hollow area within the cone (e.g., volume “hot spots”)—a novel method of Raman signal enhancement, and 2) directing analyte such as viruses of a wide range of sizes to those VERS “hot spots” while simultaneously increasing the surface area contributing to SERS. Using HNCMB VERS substrates, greatly improved Raman signals of single viruses are demonstrated, an achievement with important implications in disease diagnostics and monitoring, biomedical fields, as well as in clinical treatment.     

Formation of CdSe/CdS/ZnS-Au/SiO2 dual-yolk/shell nanostructures through a Trojan-type inside-out etching strategy

In this work we report the development of a rapid and selective etching strategy to synthesize a dual-yolk/shell nanostructure consisting of semiconductor-metal hybrid nanocrystals and hollow SiO₂ for the first time. By utilizing CdSe/CdS/ZnS quantum dot (CSSQD)/SiO₂ core/shell nanoparticles as the template and aurate hydroxyl complexes [Au(OH) ₄ ^? ] as the Trojan-type inside-out etching agent, rapid formation of CSSQD-Au hybrid nanocrystal dual-yolk and SiO₂ hollow shell occur during the reduction of Au(OH) ₄ ^? on CSSQD cores accompanied by localized hydroxyl-liberation from Au(OH) ₄ ^? at the interface between silica and CSSQD. Unlike surface-protected etching strategies, a selective as well as directional etching takes place from the silica internal surface and the thickness of the silica shell can be controlled by varying the etching time. Moreover, the size of attached Au nanoclusters can be tuned by subsequent light exposure. Consequently, the resulting platform offers a number of attractive features: (1) a new, directional, and rapid etching approach toward the formation of hollow silica nanostructures in solution; (2) semiconductor/metal hybrid nanocrystals as yolks within hollow silica nanospheres have been reported for the first time; and (3) the ability, through light exposure, to tune the size of the attached metal nanoclusters on the encapsulated CSSQD within the hollow silica nanospheres. Most importantly, the synthetic method has the capability of introducing additional guest species (e.g. metals) into a primary yolk (e.g. semiconductor) of hollow silica nanoparticles, potentially leading to many promising applications in fuel cells, photocatalysis, bioimaging, and cancer therapy.      

Synthesis of Pt-immobilized on silica and polystyrene-encapsulated silica and their applications as electrocatalysts in the proton exchange membrane fuel cell

Nano sized Pt particles were successfully immobilized onto SiO₂ and polystyrene-encapsulated silica core shell (SiO₂@PS). To make the immobilization of Pt onto both silica and polystyrene-encapsulated silica core shell, SiO₂ was first functionalized with -NH₂ using 3-amino propyl trimethoxysilane (APTMS) while for core shell, the negatively charged surface of polystyrene (PS) was changed with positive charge by cationic surfactant such as cetyltrimethylammonium chloride (CTACl) to make the formation of SiO₂ shell on preformed PS sphere. Transmission electron micrograph (TEM) images shows that Pt nanoparticles immobilized onto SiO₂ and SiO₂@PS were to be 3-4 nm without agglomeraiton. The energy dispersive spectroscope (EDS) shows that Pt contents on both SiO₂ and SiO₂@PS were to be 21.45% and 20.28%, respectively. In case of Pt-SiO₂@PS, it is believed that Pt should have been immobilized onto PS surface and pore within SiO₂ shell as well as SiO₂ surface. The MEA fabricated with Pt-SiO₂@PS shows better cell performance than of Pt-SiO₂.