Single‐precursor phase‐controlled synthesis of copper selenide nanocrystals and their conversion to amorphous hollow nanostructures

The crystal phases are essential to the physicochemical properties and functionalities of materials.Copper selenide has emerged as an important and appealing semiconductor,which can exist in a variety of polymorphic phases.However,the richness of polymorphs also makes it a challenge to the direct preparation of copper selenide nanocrystals with tunable phases.Herein,two polymorphs,that is,quasitetragonal Cu2−xSe nanocubes and metastable wurtzite Cu2Se nanodisks,are successfully synthesized by using a single precursor,copper(I)selenocyanate(CuSeCN),as the Cu and Se sources.The key to phase modulation is the optimal choice of the ligand in the synthesis.The as‐prepared nanocrystals possess different morphologies and compositions,giving rise to distinct optical properties and electrical conductivities.Interestingly,the copper selenide nanocrystals can provide a platform for the rational construction of two types of amorphous hollow Au─Cu─Se nanostructures by reaction with Au(I)precursor,in which their final shapes are well kept as that of the original nanocrystal templates.This work provides an easy strategy for the phase‐controlled synthesis of copper selenide nanocrystals and enables the design of new materials for broad applications.

Pd-Ag alloy hollow nanostructures with interatomic charge polarization for enhanced electrocatalytic formic acid oxidation

Formic acid oxidation is an important electrocatalytic reaction in proton- exchange membrane （PEM） fuel cells, in which both active sites and species adsorption/activation play key roles. In this study, we have developed hollow Pd-Ag alloy nanostructures with high active surface areas for application to electrocatalytic formic acid oxidation. When a certain amount of Ag is incorporated into a Pd lattice, which is already a highly active material for formic acid oxidation, the electrocatalytic activity can be significantly boosted. As indicated by theoretical simulations, coupling between Pd and Ag induces polarization charges on Pd catalytic sites, which can enhance the adsorption of HCO0＊ species. As a result, the designed electrocatalysts can achieve reduced Pd usage and enhanced catalytic properties at the same time. This study represents an approach that simultaneously fabricates hollow structures to increase the number of active sites and utilizes interatomic interactions to tune species adsorption/ activation towards improved electrocatalytic performance.

Triblock copolymer-assisted construction of 20 nm-sized ytterbium-doped TiO_2 hollow nanostructures for enhanced solar energy utilization efficiency

Rare-earth doped titania single-crystalline hollow nanoparticles of 20 nm are constructed via a simple sol-gel process. Amphiphilic ABA tri-block copolymers played a key role in assisting the formation of hollow structure, for which a hollow nanostructure growth mechanism is proposed. By introducing rare earth into the synthesis process, the as-prepared nanoparticles exhibit near-infrared light absorption properties. Photo-decomposition efficiency of Orange II azo dye can be successfully evaluated when using Yb3+-doped Ti O2 hollow nanoparticles as photocatalysts; it is more than two times higher than the pure Ti O2 hollow nanoparticles. The hollow nanostructured Yb3+-doped Ti O2 samples are exploited as photoanodes in N719- sensitized solar cells and prove able to improve the photoelectric conversion efficiency by measuring the solar cell parameters of dye-sensitized solar cells(DSSCs) under simulative sunlight.

Design of CuInS2 hollow nanostructures toward CO2 electroreduction

The sharp rise of CO2 in the atmosphere has become a potential threat to global climate, which results from the massive utilization of fossil fuel since the industry revolution. CO2 electroreduction provides us a new possibility of utilizing CO2 as a carbon feedstock for fuel and commercial chemicals generation. In this article, a new method is developed for synthesizing CuInS2 hollow nanostructures through the Kirkendall effect. The CuInS2 hollow nanostructures exhibit excellent catalytic activity for electrochemical reduction of CO2 with particular high selectivity, achieving high faradaic efficiency for HCOOH of 72.8% at -0.7 V. To elucidate the mechanisms, operando electrochemical Raman spectroscopy is employed to examine the CO2 reduction process. This work provides new insights into the design of hollow nanostructures toward electrocatalytic CO2 conversion and offers us an effective and reliable way for real-time investigation of electrochemical CO2 reduction reaction processes.

One-pot Synthesis of Hollow Octahedral Cu_2O Nanostructures at Room Temperature

Homogeneous hollow Cu20 octahedral nanostructures have been fabricated by a facile onepot reduction reaction at roomtemperature. The microscope analysis revealed that the edges of as-prepared hollow structures were around 200 nm with a wall thickness of about 20 nm. To investigate the influence factors and formation mechanism of the hollow octahedral structure, samples subjected to different reaction conditions were studies. The results showed that the morphology and structures of Cu20 particles were greatly affected by the concentration of pH value of the reaction environment and the reaction time. Ostwald ripening process is orooosed to exolain the growth mechanism of the hollow octahedral nanostructures.

An amorphous manganese iron oxide hollow nanocube cathode for aqueous zinc ion batteries

Aqueous zinc ion batteries(ZIBs) are attracting considerable attentions for practical energy storage because of their low cost and high safety.Nevertheless,the traditional manganese oxide cathode materials suffer from the low intrinsic electronic conductivity,sluggish ions diffusion kinetics,and structural collapse,hindering their large-scale application.Herein,we successfully developed a latent amorphous Mn_(1.8)Fe_(1.2)O_(4) hollow nanocube(a-H-MnFeO) cathode material derived from Prussian blue analogue precursor.The amorphous nature endows the cathode with lower diffusion barrier and narrower band gap compared with crystalline counterpart,resulting in the superior Zn^(2+) ions and electrons transport kinetics.Hollow structure can furnish abundant surface sites and suppress the structural collapse during the repeated charge/discharge processes.By virtue of the multiple advantageous features,the a-H-MnFeO cathode exhibits exceptional electrochemical performance,in terms of high capacity,excellent rate capability,and prolonged cycle life.This strategy will pave the way for the structural design of emerging cathode materials.

Template-free synthesis of hollow carbon-based nanostructures from MOFs for rechargeable battery applications

Hollow carbon-based nanostructures(HCNs)have found broad applications in various fields,particularly rechargeable batteries.However,the syntheses of HCNs usually rely on template methods,which are time-consuming,low-yield,and environmentally detrimental.Metal-organic frameworks(MOFs),constructed by organic ligands and inorganic metal nodes,have been identified as effective platforms for preparing HCNs without adding extra templates.This review summarized the recent progress in template-free synthesis of HCNs enabled by MOFs and their applications in rechargeable batteries.Different template-free strategies were introduced first with mechanistic insights into the hollowing mechanism.Then the electrochemical performances of the HCNs were discussed with highlight on the structure-function correlation.It is found that the built-in cavities and nonporous for HCNs is of critical importance to increase the storage sites for high capacity,to enhance charge and mass transport kinetics for high-rate capability,and to ensure the resilient electrode structure for stable cycling.Finally,the challenges and opportunities regarding MOFs-derived HCNs and their applications in rechargeable batteries were discussed.

Carbon-coated Fe2O3 hollow sea urchin nanostructures as high-performance anode materials for lithium-ion battery

Fe2O3 has become a promising anode material in lithium-ion batteries (LIBs) in light of its low cost, high theoretical capacity (1007 mA h g^−1) and abundant reserves on the earth. Nevertheless, the practical application of Fe2O3 as the anode material in LIBs is greatly hindered by several severe issues, such as drastic capacity falloff, short cyclic life and huge volume change during the charge/discharge process. To tackle these limitations, carbon-coated Fe2O3 (Fe2O3@MOFC) composites with a hollow sea urchin nanostructure were prepared by an effective and controllable morphology-inherited strategy. Metal-organic framework (MOF)-coated FeOOH (FeOOH@-MIL-100(Fe)) was applied as the precursor and self-sacrificial template. During annealing, the outer MOF layer protected the structure of inner Fe2O3 from collapsing and converted to a carbon coating layer in situ. When applied as anode materials in LIBs, Fe2O3@MOFC composites showed an initial discharge capacity of 1366.9 mA h g^−1 and a capacity preservation of 1551.3 mA h g^−1 after 200 cycles at a current density of 0.1 A g^−1. When increasing the current density to 1 A g^−1, a reversible and high capacity of 1208.6 mA h g^−1 was obtained. The enhanced electrochemical performance was attributed to the MOF-derived carbon coating layers and the unique hollow sea urchin nanostructures. They mitigated the effects of volume expansion, increased the lithium-ion mobility of electrode, and stabilized the as-formed solid electrolyte interphase films.

Design strategy for low-temperature sulfur etching to achieve high-performance hollow multifunctional electrode material

Zeolite Imidazole Framework(ZIF)has the advantages of large specific surface area,high porosity,and easy functionalization,so it looked like one of the most promising energy storage and conversion materials.In the meantime,transition metal oxides and sulfides have been widely used in environmental and energy conversion applications.Hence,a NaOH-assisted thioacetamide etching strategy is,therefore,designed with the metal-organic framework as precursor to realize the hollow nanostructure of ZIF bimetallic sulfide(Sx-CoCd-350)with abundant sulfur vacancies for enhanced catalysts oxygen evolution reaction(OER)/hydrogen evolution reaction(HER)performance and capacitance performance of capacitor.The overpotential of S_(2)-CoCd-350 in the OER process is 355 m V at 50 m A cm^(-2),which is substantially lower than other reported ZIF-based catalysts.S_(2)-CoCd-350 has an overpotential of 84 m V at 10 m A cm^(-2)when employed as HER catalyst.Furthermore,the S_(2)-CoCd-350 electrode did not alter appreciably during a long-term durability test of more than 10 h.More impressively,S_(2)-Co Cd-350 matches the activated carbon(AC)electrode with excellent capacitance performance 1220μWh cm^(-2)energy density(at 3370μW cm^(-2))and 25,000μW cm^(-2)(at 700μWh cm^(-2))maximum power density.In addition,the assembled supercapacitor has excellent cycling stability.

Flexible hollow TiO_(2)@CMS/carbon-fiber van der Waals heterostructures for simulated-solar light photocatalysis and photoelectrocatalysis

The recycling technology of photocatalyst powdery has hardly been mature in the photocatalytic oxidation so far.In this work,the hollow TiO_(2)microspheres with an appropriate thickness are confined in carbon microspheres(CMSs)to form hollow TiO_(2)@CMSs,which are physically integrated with carbon-fiber textile by van der Waals(vdW)interactions to generate separable and recyclable hollow TiO_(2)@CMSs/carbon-fiber vdW heterostructures.Such separable and recyclable heterostructures show remarkable oxidation of 2,4-dinitrophenol.From our detailed characterization and density functional theory(DFT)calculations,we found that carbon fiber can trap electrons exerted from the excitation of hollow TiO_(2)@CMSs and creates holes in hollow TiO_(2)microspheres,which endow the carbon fiber with photocatalytic activity through coherent charge injection.This study indicates that our general strategy for the fabrication of hollow TiO_(2)@CMSs/carbon-fiber vdW heterostructures can be used as separable and recyclable photocatalyst and photoelectrocatalyst with potential industrial applications in environmentrelated fields.

Solvent-induced synthesis of hollow structured Fe_(3)O_(4)-based anode materials for high-performance Li-ion batteries

High capacity Fe_(3)O_(4)-based anode materials have attracted a great deal of attention as an alternative to commercial graphite in Li-ion batteries(LIBs).However,it is still a challenge to alleviate the fast capacity fading of Fe_(3)O_(4) due to the intercalation of Lit.In this work,we develop a novel and effective strategy to rapidly fabricate the hollow Fe_(3)O_(4) nanostructures via the solvent-induced effect.The influence of the ratio of the tert-butanol(TB)and the water on the microstructure was further discussed.As expected,when the hollow nanostructures based on the 1:1 ratio of TB and water is used as the anode material for LIBs,a high reversible capacity of 1020 mA h g^(-1) after 100 cycles at 1 A g^(-1) and 450 mA h g^(-1) even for 5 A g^(-1) after 1000 cycles can be obtained,paving a new avenue to fabricate the functionally hollow nanostructures for high-performance anode materials or other applications.

MOF-template derived hollow CeO_(2)/Co_(3)O_(4) polyhedrons with efficient cathode catalytic capability in Li-O_(2) batteries

Li-O_(2) batteries(LOBs) have been perceived as the most potential clean energy system for fast-growing electric vehicles by reason of their environmentally friendlier,high energy density and high reversibility.However,there are still some issues limiting the practical application of LOBs,such as the large gap between the actual capacity level and the theoretical capacity,low rate performance as well as short cycle life.Herein,hollow CeO_(2)/Co_(3)O_(4) polyhedrons have been synthesized by MOF template with a simple method.And it is was further served as a cathode catalyst in Li-O_(2) batteries.By means of the synergistic effect of two different transition metal oxides,nano-sized hollow porous CeO_(2)/Co_(3)O_(4) cathode obtained better capacity and cycle performance.As a result,excellent cyclability of exceeding 140 and 90 cycles are achieved at a fixed capacity of 600 and 1000 mAh/g,respectively.The successful application of this catalyst in LOBs offers a novel route in the aspect of the synthesis of other hollow porous composite oxides as catalysts for cathodes in LOBs systems by the MOF template method.

MOF-derived Hierarchical Hollow NiRu-C Nanohybrid for Efficient Hydrogen Evolution Reaction

Designing efficient electrocatalysts for efficient hydrogen evolution is extremely desired but challenging. Herein, we report a facile MOF-assisted strategy to synthesize the hierarchical hollow spherical NiRu-C nanohybrid with closely packed rod-like bulges on the surface. Benefited from the more exposed active sites of NiRu-C nanohybrid and the efficient electron/mass transport in its unique hierarchical hollow spherical nanostructure, the optimized nanohybrid showed excellent performance for alkaline hydrogen evolution with ultralow overpotentials, which are much superior to those of Pt/C and the overwhelming majority of reported electrocatalysts. The interpretation of the reaction mechanism was further discussed with DFT calculations. Our research may provide a guidance for the development of advanced electrocatalysts with controlled morphology and excellent performance for future energy applications.

Insight into the formation of hollow silver nanoparticles using a facile hydrothermal strategy

A facile hydrothermal approach is used to synthesize hollow silver nanoparticles, labeled as hAgNPs, involving an initial formation of metal complexes from Ag＋ ion precursors and dodecylamine in a water]ethanol mixture at room temperature and a subsequent reduction in an autoclave at elevated temperature. A number of characterization techniques are used to characterize the structure and chem- ical composition of the as-formed hAgNPs, and to understand the mechanism behind the formation, The notable simplicity renders this synthetic approach promising for creating hAgNPs on a large scale for a given technological application, and the mechanistic understanding may provide new opportunities to design and fabricate other hollow nanostructures.

Synthesis and Optical Properties of Cubic Gold Nanoframes

This paper describes a facile method of preparing cubic Au nanoframes with open structures via the galvanic replacement reaction between Ag nanocubes and AuCl_(2)^(-).A mechanistic study of the reaction revealed that the formation of Au nanoframes relies on the diffusion of both Au and Ag atoms.The effect of the edge length and ridge thickness of the nanoframes on the localized surface plasmon resonance peak was explored by a combination of discrete dipole approximation calculations and single nanoparticle spectroscopy.With their hollow and open structures,the Au nanoframes represent a novel class of substrates for applications including surface plasmonics and surface-enhanced Raman scattering.

Hydrothermal synthesis of hierarchical SnO_(2)nanomaterials for high-efficiency detection of pesticide residue

Acephate pesticide contamination in agricultural production has caused serious human health problems.Metal oxide semiconductor(MOS)gas sensor can be used as a portable and promising alternative tool for efficiently detection of acephate.In this study,hierarchical assembled SnO_(2)nanosphere,SnO_(2)hollow nanosphere and SnO_2 nanoflower were synthesized respectively as high efficiency sensing materials to build rapid and selective acephate pesticide residues sensors.The morphologies of different SnO_(2)3 D nanostructures were characterized by various material characterization technology.The sensitive performance test results of the 3 D SnO_(2)nanomaterials towards acephate show that hollow nanosphere SnO_(2)based sensor displayed preferable sensitivity,selectivity,and rapid response(9 s)properties toward acephate at the optimal working temperature(300℃).This SnO_(2)hollow nanosphere based gas sensor represents a useful tool for simple and highly effective monitoring of acephate pesticide residues in food and environment.According to the characterization results,particularly Brunauer-Emmett-Teller(BET)and Ultraviolet-Visible Spectroscopy(UV-vis),the obvious and fast response can be attributed to the mesoporous hollow nanosphere structure and appropriate band gap of SnO_2 hollow nanosphere.

Monitoring the rapid nanocrystal transformation via trapped intermediates of silica encapsulation

In transmission electron microscopy(TEM),encapsulation is an important tool to preserve the nanoparticles from aggregation,weathering,and destructive highenergy electron beam.Traditionally,encapsulation can only be used to trap end products.This study pushes the limit of in situ encapsulation so that intermediates of short time scale can be trapped.Nanocrystals of water-soluble salts were generated from a solute-induced phase separation(SIPS)process.By performing a modified Stober encapsulation on different time points of the process,a series of intermediates can be trapped by silica shells.By arranging and comparing the intermediates,it is possible to reconstruct the growing process of those water-soluble salt nanocrystals.Moreover,an example of the transition from nanocrystal to liquid droplet was discovered,unveiling a potentially alternative route of the SIPS process.The reported technique could capture more snapshots for TEM imaging,providing crucial information on the study of nanoscale growth mechanism.