Highly sensitive room-temperature gas sensors based on hydrothermal synthesis of Cr_2O_3 hollow nanospheres

This paper reports that Cr2O3 hollow nanospheres （HNs） were synthesized via a hydrothermal approach and characterized by scanning electron microscopy, x-ray powder diffraction, transmission electron microscopy （TEM）, selective area electron diffraction and high resolution TEM, respectively. In addition, the room-temperature （RT） gas sensing properties of Cr2O3 HNs and conventional powders （CPs） were investigated by means of the surface photovoltage technique. The experimental data demonstrate that the RT gas sensor of the as-fabricated HNs reaches below 5 ppm whereas that of the CPs is about 40 ppm, which results from there being much more adsorbed and desorbed oxygen in HNs than in CPs at RT. The as-prepared Cr2O3 HNs could have potential applications as RT nanosensors.

A NOVEL METHOD TO PREPARE CROSSLINKED POLYETHYLENEIMINE HOLLOW NANOSPHERES

A novel method to prepare crosslinked polyethyleneimine （CPEI） hollow nanospheres was reported. Uniform silica nanospheres were used as templates, 3-aminopropyl trimethoxysilane （APS） was immobilized on the surface of silica nanospheres as couple agent. Aziridine was initiated ring-opening polymerization with the amino groups in APS to form polyethyleneimine （PEI） shell layer. 1,4-Butanediol diacrylate was utilized to crosslink PEI polymeric shell. The silica nanospheres in core were etched by hydrofluoric acid to obtain hollow CPEI nanospheres. The hollow nanospheres were characterized by X-ray photoelectron spectroscopy （XPS）, transmission electron microscopy （TEM）, and thermogravimetric analysis （TGA）.

Preparation of PdCo Bimetallic Hollow Nanospheres and its Electrocatalytic Activity for Oxidation of Formic Acid

The PdCo bimetallic hollow nanospheres with 80 nm average diameter and around 9.0 nm thickness of the shell were prepared with a special reduction method and characterized with transmission electron microscopy （TEM）, X-ray diffraction （XRD） and energy dispersive spectroscopy （EDS）. The electrochemical measurements illustrated that the electrocatalytic activity of the PdCo bimetallic hollow nanospheres for the oxidation of formic acid is much higher than that of the Pd solid nanospheres.

Toward High Capacity and Stable SnO_(2)Hollow Nanosphere Electrode Materials:A Case Study of Ni-substituted Modification

To develop the urgent requirement for high-rate electrodes in next-generation lithium-ion batteries,SnO_(2)-based negative materials have been spotlighted as potential alternatives.However,the intrinsic problems,such as conspicuous volume variation and unremarkable conductivity,make the rate capability behave badly at a high-current density.Here,to solve these issues,this work demonstrate a new and facile strategy for synergistically enhancing their cyclic stability by combining the advantages of Ni doping and the fabrication of hollow nanosphere.Specifically,the incorporation of Ni^(2+)ions into the tetragonal rutile-type SnO_(2)shellsimproves the charge transfer kinetics effectively,leading to an excellent cycling stability.In addition,the growth of surface grains on the hollow nanospheres are restrained after Ni doping,which also reduces theunexpected polarization of negative electrodes.As a result,the as-prepared Ni doped electrode delivers a remarkable reversible capacity of 712 mAh g^(-1)at 0.1 A g^(-1)and exhibits outstanding capacity of 340 mAh g^(-1)at 1.6 A g^(-1),about 2.58 times higher than that of the pure SnO_(2)hollow sample.

Visual test paper based on Au/δ-MnO_(2) hollow nanosphere oxidase-like activity regulation using hexavalent chromium as a smart switch

Paper-based sensing platform is a point of need analytical toolkit for safety testing.However,the sensitivity,specificity,and simplicity are still challenging.Herein,we report a novel strategy(Au/δ-MnO_(2) hollow nanosphere and 3,3′,5,5′-tetramethylbenzidine(TMB)induced test strips for signal-on detection)that can be utilized for hexavalent chromium(Cr^(6+))detection.Interestingly,Cr^(6+)(CrO_(4)^(2−)) as a smart switch can remarkably enhance the oxidase-like activity of Au/δ-MnO_(2) hollow nanosphere.The presence of Cr^(6+) can regulate the surface electronic redistribution of Au/δ-MnO_(2) and adjust the geometric configuration,which leads to the improvement in oxidase-like activity of Au/δ-MnO_(2).As a proof-of-concept application,a visual paper-based sensing platform of Cr^(6+) along with quantitative analysis by the test strips was successfully constructed.This paper-based sensing platform exhibits a linear range with excellent selectivity for other interfering substances and lower limit of detection of 0.09μmol·L^(−1),providing a promising toolkit at-home Cr^(6+) measurement and environmental monitoring.

Copper-induced formation of heterostructured Co_(3)O_(4)/CuO hollow nanospheres towards greatly enhanced lithium storage performance

We report a facile template-free fabrication of heterostructured Co_(3)O_(4)/CuO hollow nanospheres using pre-synthesized Co/Cu-glycerate as conformal precursor.The introduction of copper nitrate in the solvothermal reaction system of glycerol/isopropanol/cobalt nitrate readily induces the conversion from solid Co-glycerate to hollow Co/Cu-glycerate nanospheres,and the effect of the Co/Cu atomic ratio on the structure evolution of the metal glycerates as well as their corresponding oxides were investigated.When examined as anode materials for lithium-ion batteries,the well-defined Co_(3)O_(4)/CuO hollow nanospheres with Co/Cu molar ratio of 2.0 demonstrate excellent lithium storage performance,delivering a high reversible capacity of 930 mAh/g after 300 cycles at a current density of 0.5 A/g and a stable capacity of 650 mAh/g after 500 cycles even at a higher current density of 2.0 A/g,which are much better than their counterparts of bare CuO and Co_(3)O_(4).The enhanced lithium storage performance can be attributed to the synergistic effect of the CuO and Co_(3)O_(4)heterostructure with hollow spherical morphology,which greatly enhances the charge/electrolyte transfer and effectively buffers the volume changes upon lithiation/delithiation cycling.

Self-templating synthesis of Pd_(4)S hollow nanospheres as electrocatalysts for oxygen reduction reaction

Hollow nanostructures with structural advantages have been widely exploited as catalysts in electrochemical reactions.However,there are only limited strategies for constructing hollow Pd-based nanostructures.In this work,Pd4S hollow nanospheres(Pd4S HNSs)are synthesized with a facile wet-chemical method via a self-templating process.Intermediate Pd-L-cysteine solid nanospheres(SNSs)were firstly obtained by the coordination of L-cysteine with Pd^(2+),and then in situ converted to hollow nanospheres in the following reduction process.The formation mechanism of the Pd4S HNSs was studied,and the size of the Pd4S HNSs can be readily adjusted by tuning the size of the SNSs.The hollow morphology would help the exposure of active sites and the prevention of aggregation during the catalytic reactions.As a result,the Pd4S HNSs exhibit improved catalytic performances in the oxygen reduction reactions,with a half-wave potential of 0.913 V vs.reversible hydrogen electrode(RHE)and impressive stability in the accelerated durability test.

Templated synthesis of imine-based covalent organic framework hollow nanospheres for stable potassium-ion batteries

Covalent organic frameworks(COFs), as highly tunable porous crystalline materials, have promising applications in potassium-ion batteries(PIBs) due to their abundant charge carrier transport channels and excellent structural stability. However, the excessive stacking of interlayer electron clouds makes it difficult to expose internal active sites. Strategies to design functional COFs with controllable morphology and copious active sites are promising but still challenging. Herein, by utilizing the condensation between1,3,5-triformylbenzene(TFB) and p-phenylenediamine(PPD) and using amino-modified SiO_(2) nanospheres as templates, we synthesize core-shell NH_(2)-SiO_(2)@TP-COF. Through NaOH etching of NH_(2)-SiO_(2)@TP-COF, we obtain imine-based TP-COF hollow nanospheres, which shows excellent potassium storage performance when applied to the anode for PIBs. Ex-situ analysis and density functional theory calculations reveal that C=N groups and benzenes are active sites for K^(+) storage.

Advanced Pt hollow nanospheres/rubrene nanoleaves coupled with M-shaped DNA walker for ultrasensitive electrochemiluminescence bioassay

Herein,an intense electrochemiluminescence(ECL)was achieved based on Pt hollow nanospheres/rubrene nanoleaves(Pt HNSs/Rub NLs)without the addition of any coreactant,which was employed for ultrasensitive detection of carcinoembryonic antigen(CEA)coupled with an M-shaped DNA walker(M-DNA walker)as signal switch.Specifically,in comparison with platinum nanoparticles(Pt NPs),Pt HNSs revealed excellent catalytic performance and pore confinement-enhanced ECL,which could significantly amplify ECL intensity of Rub NLs/dissolved O_(2)(DO)binary system.Then,the tracks and M-DNA walker were confined on the Pt HNSs simultaneously to promote the reaction efficiency,whose M-structure boosted the interaction sites between walking strands and tracks and reduced the rigidity of their recognition.Once the CEA approached the sensing interface,the M-DNA walker was activated based on highly specific aptamer recognition to recover ECL intensity with the assistance of exonucleaseⅢ(ExoⅢ).As proof of concept,the“on-off-on”switch aptasensor was constructed for CEA detection with a low detection limit of 0.20 fg/m L.The principle of the constructed ECL aptasensor also enables a universal platform for sensitive detection of other tumor markers.

Rationally designed hollow carbon nanospheres decorated with S,P co-doped NiSe_(2) nanoparticles for high-performance potassium-ion and lithium-ion batteries

Hollow nanostructures with external shells and inner voids have been proved to greatly shorten the transport distance of ions/electrons and buffer volume change,especially for the large-sized potassium-ions in secondary batteries.In this work,hollow carbon(HC) nanospheres embedded with S,P co-doped NiSe_(2)nanoparticles are fabricated by "drop and dry" and "dissolving and precipitation" processes to form Ni(OH)2nanocrystals followed by annealing with S and P dopants to form nanoparticles.The resultant S,P-NiSe_(2)/HC composite exhibits excellent cyclic performance with 131.6 mA h g^(-1)at1000 mA g^(-1)after 3000 cycles for K^(+)storage and a capacity of 417.1 mA h g^(-1)at 1000 mA g^(-1)after1000 cycles for Li^(+)storage.K-ion full cells are assembled and deliver superior cycling stability with a ca pacity of 72.5 mA h g^(-1)at 200 mA g^(-1)after 500 cycles.The hollow carbon shell with excellent electrical conductivity effectively promotes the transporta tion and tolerates large volume variation for both K^(+)and Li^(+).Density functional theory calculations confirm that the S and P co-doping NiSe_(2) enables stronger adsorption of K^(+)ions and higher electrical conductivity that contributes to the improved electrochemical performance.

Highly Conductive Proton Selectivity Membrane Enabled by Hollow Carbon Sieving Nanospheres for Energy Storage Devices

Ion conductive membranes(ICMs)with highly conductive proton selectivity are of significant importance and greatly desired for energy storage devices.However,it is extremely challenging to construct fast proton-selective transport channels in ICMs.Herein,a membrane with highly conductive proton selectivity was fabricated by incorporating porous carbon sieving nanospheres with a hollow structure(HCSNs)in a polymer matrix.Due to the precise ion sieving ability of the microporous carbon shells and the fast proton transport through their accessible internal cavities,this advanced membrane presented a proton conductivity(0.084 S·cm^(-1))superior to those of a commercial Nation 212(N212)membrane(0.033S·cm^(-1))and a pure polymer membrane(0.049 S·cm^(-1)).The corresponding proton selectivity of the membrane(6.68×10^(5) S·min·cm^(-3))was found to be enhanced by about 5.9-fold and 4.3-fold,respectively,compared with those of the N212 membrane(1.13×10^(5) S·min·cm^(-3))and the pure membrane(1.56×10^(5) S·min·cm^(-3)).Low-field nuclear magnetic resonance(LF-NMR)clearly revealed the fast protonselective transport channels enabled by the HCSNs in the polymeric membrane.The proposed membrane exhibited an outstanding energy efficiency(EE)of 84%and long-term stability over 1400 cycles with a0.065%capacity decay per cycle at 120 mA·cm^(-2) in a typical vanadium flow battery(VFB)system.

Construction of phosphorus-doping with spontaneously developed selenium vacancies: Inducing superior ion-diffusion kinetics in hollow Cu_(2)Se@C nanospheres for efficient sodium storage

Achieving high-efficiency sodium storage in metal selenides is still severely constrained in consideration of their inferior electronic conductivity and inadequate Na^(+)insertion pathways and active sites.Heteroatom doping accompanied by spontaneously developed lattice defects can effectively tune electronic structure of metal selenides,which give a strong effect to motivate fast charge transfer and Na^(+)accessibility.Herein,we finely designed and successfully constructed a fascinating phosphorus-doped Cu_(2)Se@C hollow nanosphere with abundant vacancy defects(Cu_(2)P_(x)Se_(1-x)@C)through a combination strategy of selenization of Cu_(2)O nanosphere template,self-polymerization of dopamine,and subsequent phosphorization treatment.Such exquisite composite possesses enriched active sites,superior conductivity,and sufficient Na^(+)insertion channel,which enable much faster Na^(+)diffusion rates and more remarkable pseudocapacitive features,Satisfyingly,the Cu_(2)P_(x)Se_(1-x)@C composites manifest the supernormal sodium-storage capabilities,that is,a reversible capacity of 403.7 mA h g^(-1) at 1.0 A g^(-1) over 100 cycles,and an ultrastable cyclic lifespan over 1000 cycles at 20.0 A g^(-1) with a high capacity-retention of about249.7 mA h g^(-1).The phase transformation of the Cu_(2)P_(x)Se_(1-x)@C involving the intercalation of Na^(+)into Cu_(2)Se and the following conversion of NaCuSe to Cu and Na2Se were further demonstrated through a series of ex-situ characterization methods.DFT results demonstrate that the coexistence of phosphorusdoping and vacancy defects within Cu_(2)Se results in the reduction of Na^(+)adsorption energy from-1.47to-1.56 eV improving the conductivity of Cu_(2)Se to further accelerate fast Na^(+)mobility.

Hierarchical sodium-rich Prussian blue hollow nanospheres as high-performance cathode for sodium-ion batteries

Recently, Prussian blue and its analogues （PBAs） have attracted tremendous attention as cathode materials for sodium-ion batteries because of their good cycling performance, low cost, and environmental friendliness. However, they still suffer from kinetic problems associated with the solid-state diffusion of sodium ions during charge and discharge processes, which leads to low specific capacity and poor rate performances. In this work, novel sodium iron hexacyanoferrate nanospheres with a hierarchical hollow architecture have been fabricated as cathode material for sodium-ion batteries by a facile template method. Due to the unique hollow sphere morpholog~ sodium iron hexacyanoferrate nanospheres can provide large numbers of active sites and high diffusion dynamics for sodium ions, thus delivering a high specific capacity （142 mAh/g）, a superior rate capabili, and an excellent cycling stability. Furthermore, the sodium insertion/extraction mechanism has been studied by in situ X-ray diffraction, which provides further insight into the crystal structure change of the sodium iron hexacyanoferrate nanosphere cathode material during charge and discharge processes.

SnO_2 hollow nanospheres assembled by single layer nanocrystals as anode material for high performance Li ion batteries

SnO2 hollow nanospheres were successfully synthesized via a facile one-step solvothermal method.Characterizations show that the as-prepared SnO2 spheres are of hollow structure with a diameter at around 50 nm,and especially,the shell of the spheres is assembled by single layer SnO2 nanocrystals.The surface area of the material reaches up to 202.5 m^2/g.As an anode material for Li ion batteries,the sample exhibited improved electrochemical performance compared with commercial SnO2 particles.After cycled at high current rate of 0.5 C,1 C and 0.5 C for 20 cycles,respectively,the electrode can maintain a capacity of 509 mAh/g.The suitable shell thickness/diameter ratio endows the good structural stability of the material during cycling,which promises the excellent cycling performance of the electrode.The large surface area and the ultra thin shell ensure the high rate performance of the material.

Cobalt hollow nanospheres： controlled synthesis, modification and highly catalytic performance for hydrolysis of ammonia borane

Size tunable cobalt hollow nanospheres with high catalytic activity for the ammonia borane(AB) hydrolysis have been synthesized by using the solvothermal method. The complexation between Co2+and ethylenediamine is observed to be critical for the formation of the cobalt hollow nanospherical structure.The morphology of the cobalt hollow nanospheres can be regulated by adjusting the original ethylenediamine/ethanol volume ratio, reaction time and temperature. Impressively, the magnetic property study reveals that the coercivity of the as-synthesized cobalt hollow nanospheres is much enhanced compared with that of bulk cobalt materials. Meanwhile, Co/Pt bimetal hollow nanospheres(Co Pt HS) and graphene-cobalt hollow composite nanospheres(Co HS-r GO) have also been explored. In comparison with the cobalt hollow nanospheres, both the Co Pt HS and Co HS-r GO show higher catalytic activities and better repeatability for the catalytic hydrogen generation from AB hydrolysis. Moreover, it is noted that these catalysts could be recycled by using the magnetic separation method.

Visible-Light Photocatalytic Conversion of Carbon Dioxide into Methane Using Cu_(2)O/TiO_(2) Hollow Nanospheres

In the past few decades there has been a remarkable rise in the study of visible-light photocatalytic reduction of carbon dioxide (CO_(2)) into value-added chemicals such as methane (CH4) with water as reducing agent in order to prevent global warming and energy crisis. However, so far the conversion efficiency leaves much to be enhanced under sunlight irradiation. In this work, Cu_(2)O hollow nanospheres were synthesized via soft-template method and were combined with TiO_(2) through in-situ hydrolysis of Ti(OBu)4 under sonication. The obtained photocatalysts of Cu_(2)O and Cu_(2)O/TiO_(2) composite were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, UV-visible diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. Compared to Cu_(2)O hollow nanospheres, the Cu_(2)O/TiO_(2) composite exhibited higher efficiency in photocatalytic reduction of CO_(2) into CH4 under visible-light irradiation (λ≥420 nm). This is because of the formation of a p-n heterojunction in the composites, resulting in efficient suppression of recombina- tion of the photogenerated electrons and holes as well as an improved stability of the catalyst and, thereby, the im- proved visible-light photocatalytic activity.

Decorating CoSe2 hollow nanospheres on reduced graphene oxide as adlvanced sulfur host material for performance enhanced lithium-sulfur batteries

Although lithium-sulfur batteries are one of promising rechargeable energy storage devices,their wide applications are impeded by the lithium polysulfides shutle effect,low electronic conductivity of the cathode,and sluggish redox reaction kinetics of lithium polysulfides.In this work,reduced graphene oxide was decorated with CoSe2 hollow nanospheres to form an RGO-CoSe2 composite that was used as a host material to support S in the cathode.The RGO-CoSe2 composite has the following superiorities:(1)enhanced electronic conductity,(2)accommodation of the volumetric change of cathode materials,(3)effective confinement of numerous lithium polysulfides species due to chemisorption,(4)expedition of the redox kinetics of lithium polysulfides.As expected,the RGO-CoSez-based cathode exhibited the reversible specific capacity of 1,044.7 mAh/g at 0.2C and 695.7 mAh/g at 2C,together with ecellent cycling stability of 0.071% average capacity decay per cycle over 400 cycles at 1C.

Self-assembled uniform double-shelled Co_(3)V_(2)O_8 hollow nanospheres as anodes for high-performance Li-ion batteries

Hollow micro-/nanostructures have achieved great success in the field of renewable battery materials by reducing the volume change and promoting the ion transport.Double-shelled Co_(3)V_(2)O__(8)hollow nanospheres(CVODSS)were synthesized using a facile solvothermal method followed by a thermal treatment in the absence of any surfactant.Meanwhile,two other architectures of hollow nanospheres and nanoparticles were obtained by changing the annealing temperature.Benefiting from the desired hollow structure,the CVO-DSS electrode exhibits excellent lithium storage properties as an anode.It exhibits a reversible discharge capacity of 1210 m Ah·g^(-1)at200 m A·g^(-1)after 100 cycles and a satisfactorily high rate capacity of 628 m Ah·g^(-1)after 800 cycles at 5000 m A·g^(-1).These hollow nanostructures can efficiently enhance the contact area of the electrolyte/electrode interface,promote the diffusion of lithium ions and electrons and slow down the capacity loss during long cycles.

AgPdCo hollow nanospheres electrocatalyst with high activity and stability toward the formate electrooxidation

The widespread commercial application of direct formate fuel cell(DFFC)is limited by the lack of efficient electrocatalysts for the formate oxidation reaction(FOR).AgPdCo hollow nanospheres(H-NSs)with jagged surfaces are successfully synthesized via a facile method involving the wet-chemical synthesis of AgPdCo nanospheres(NSs)and galvanic replacement reaction between Pd salt and AgPdCo NSs.Surpassing Ag_(30)Pd_(69)Co_(1) NSs and most of previously reported electrocatalysts,Ag_(9)Pd_(90)Co_(1) H-NSs exhibit extremely high FOR activity with a peak current density of 3.08 A·mg_(Pd)^(−1).Apart from the competitive activity,Ag_(9)Pd_(90)Co_(1) H-NSs show greatly improved chronoamperometric and cycling stability,whereby the current density retains about 0.24 A·mg_(Pd)^(−1) after 3,600 s electrocatalysis and the mass activity maintains 54.06%of the initial value after 500 cycles.The unique hollow nanosphere and synergistic effect are responsible for the enhanced activity and stability.This study will provide new clues for the development of outstanding electrocatalysts.

Fe3O4/ZnS Hollow Nanospheres： A Highly Efficient Magnetic Heterogeneous Catalyst for Synthesis of 5-Substituted 1H-Tetrazoles from Nitriles and Sodium Azide

An efficient route for the synthesis of 5-substituted 1H-tetrazole via [2＋3] cycloaddition of nitriles and sodium azide is reported using Fe3O4/ZnS hollow nanospheres as a magnetic separable heterogeneous catalyst. The catalyst is very efficient, affording excellent yields and can be reused for several circles. In addition, the Fe3O4 inner shell exhibits magnetism, making the catalyst easily separated by a magnet.