Composite Spheres Research Articles

ZnO/Carbon Spheres with Excellent Regenerability for Post-Combustion CO2 Capture.

This paper examines the synthesis of the ZnO/carbon spheres composites using resorcinol—formaldehyde resin as a carbon source and zinc nitrate as a zinc oxide source in a solvothermal reactor heated with microwaves. The influence of activation with potassium oxalate and modification with zinc nitrate on the physicochemical properties of the obtained materials and CO2 adsorption capacity was investigated. It was found that in the case of nonactivated material as well as activated materials, the presence of zinc oxide in the carbon matrix had no effect or slightly increased the values of CO2 adsorption capacity. Only for the material where the weight ratio of carbon:zinc was 2:1, the decrease of CO2 adsorption capacity was reported. Additionally, CO2 adsorption experiments on nonactivated carbon spheres and those activated with potassium oxalate with different amounts of zinc nitrate were carried out at 40 °C using thermobalance. The highest CO2 adsorption capacity at temperature 40 °C (2.08 mmol/g adsorbent) was achieved for the material after activation with potassium oxalate with the highest zinc nitrate content as ZnO precursor. Moreover, repeated adsorption/desorption cycle experiments revealed that the as-prepared carbon spheres were very good CO2 adsorbents, exhibiting excellent cyclic stability with a performance decay of less than 10% over up to 25 adsorption-desorption cycles.

Characterization of sphere-plane contact loss nonlinearity inside a cylindrical container using nonlinear ultrasound resonance spectroscopy.

Cylindrical containers, such as liquid tanks and pressure vessels, are ubiquitous in storage applications. Traditional lines of non-destructive evaluation (NDE) are mostly focused on the integrity of containers, but studies on solid contents within using external sensors are lacking. In previous work, metrics were developed to estimate the structural integrity of mock-up fuel assemblies inside a lab-scale nuclear dry storage cask. Linear acoustic resonance techniques were shown to be sensitive down to single assembly level. In this work, this problem is further examined by studying contact nonlinearity in a simplified system using Nonlinear Ultrasound Resonance Spectroscopy (NRUS). This system consists of a single layer of identical spheres with varying composition and size evenly distributed at the bottom of a cylindrical aluminum container. The resonance frequency shifts due to varying amplitudes were mostly affected by the total mass of spheres inside, while diameter and composition of spheres played minor roles. A phenomenological model was developed based on the resulting shifts and was studied numerically using finite element simulations. The agreement between simulations and experiments suggests that the contact nonlinearity is predominated by a contact loss mechanism. This NRUS technique may complement linear acoustic techniques for solid cargo NDE inside sealed vessels.

Dendritic Silica Nanospheres Loaded with Red‐Emissive Enhanced Carbon Dots for Zika Virus Immunoassay

AbstractEnhanced red emissive carbon dots (CDs) and their enrichment in spheres are ideal for sensing applications. Here, we propose a novel strategy for enhancing the red emission of CDs and enriching it in dendritic SiO2 nanospheres. The surface carboxylated and red emissive CDs obtained by alkali/acid treatment of blue emissive CDs are dissolved in N‐β‐(aminoethyl)‐γ‐aminopropyltrimethoxysilane for silanization. Electron injection and long chain passivation greatly enhance the red emission of CDs. Through the reaction of silane with the hydroxyl groups of dendritic SiO2 spheres, the silanized CDs can be enriched in dendritic SiO2 spheres. Encapsulation of composite spheres with (3‐Aminopropyl)‐trimethoxysilane protects CDs and facilitates bioconjugation. These fluorescence SiO2 spheres exhibit high quantum yields in red emission (48.5 % for aqueous solution and 35.7 % for solid state) and maintain good monodispersity. It is further used as a signal of lateral flow test strips to target Zika virus, and demonstrates an ultra‐sensitive, specific and effective immunoassay. And considerable results have been achieved in the analysis of actual samples.

Quantitative Coassembly for Precise Synthesis of Mesoporous Nanospheres with Pore Structure-Dependent Catalytic Performance.

Precise synthesis of porous materials is essential for their applications. Self-assembly is a widely used strategy for synthesizing porous materials, but quantitative control of the assembly process still remains a great challenge. Here, a quantitative coassembly approach is developed for synthesizing resin/silica composite and its derived porous spheres. The assembly behaviors of the carbon and silica precursors are regulated without surfactants and the growth kinetics of the composite spheres are quantitatively controlled. This assembly approach enables the precise control of the size and pore structures of the derived carbon spheres. These carbon spheres provide a good platform to explore the structure-performance relationships of porous materials, and demonstrate their pore structure-dependent performance in catalytic water decontamination. This work provides a simple and robust approach for precise synthesis of porous spheres and brings insights into function-oriented design of porous materials.

Investigation on the acoustic properties of structural gradient 316L stainless steel hollow spheres composites

Abstract In this study, a kind of structural gradient metal hollow spheres composites (SG-MHSCs) were fabricated using two kinds of 316L stainless steel hollow spheres with different diameters and A356 aluminum through the casting method. Then the density of the SG-MHSCs was measured by the direct measurement; the microstructure of the SG-MHSCs was characterized by the Scanning Electron Microscope. Meanwhile, the acoustic performance of MHSCs was tested by the impedance tube, and the sound absorption and insulation mechanism SG-MHSCs were discussed and analyzed.

Flower-Like Interlayer-Expanded MoS2- x Nanosheets Confined in Hollow Carbon Spheres with High-Efficiency Electrocatalysis Sites for Advanced Sodium-Sulfur Battery.

The room-temperature sodium-sulfur (RT-Na/S) battery is one of the most promising technologies for low-cost energy storage. However, application of RT-Na/S batteries is currently impeded by severe shuttle effects and volume expansion that limits both energy density and cycling stability. Herein, first, the first-principal calculation is used to find that the introduction of sulfur vacancies in MoS2 can effectively enhance polysulfide adsorption and catalytic ability as well as both the ion and electron conductivities. Then, unique MoS2- x /C composite spheres are further designed and synthesized with flower-like few-layer and interlayer-enlarged MoS2- x nanosheets space-confined in hollow carbon nanospheres by a "ship-in-a-bottle" strategy. With this novel design, the mass loading of S in the MoS2- x /C composite can be reached to as high as 75wt%. Owing to the synergetic effect of interlayer-expanded and few-layer MoS2- x nanosheets and hollow carbon spheres matrix with high electronic/Na+ conductivity, the RT-Na/S batteries deliver highly stable cycle durability (capacity retention of 85.2% after 100 cycles at 0.1 A g-1 ) and remarkable rate capability (415.7 mAh g-1 at 2 A g-1 ) along with high energy density. This design strategy of defect- and interlayer-engineering may find wide applications in synthesizing electrode materials for high-performance RT-Na/S batteries.

Static and dynamic characteristics of a compound sphere using Initial Stress Reference Independence

We study the influence of residual stress on the static and dynamic characteristics of a spherical structure. We consider a shrink-fitted compound sphere, where residual stress is developed due to the interference between outer and inner spherical layers. We calculate this residual stress and model the residually stressed material with suitable hyperelastic strain energy satisfying Initial Stress Reference Independence (ISRI). Under the action of inhomogeneous residual stress, the compound sphere behaves as an anisotropic, functionally graded composite sphere, which is reflected by the model. We apply this model to obtain stress distributions and inflation characteristics of the compound sphere. Our results demonstrate the hypothesis that residual stress moderates the stress concentration and reduces the stress gradient in biological/engineering structures. We obtain critical stretch and pressure for spherically symmetric deformations. An increase in interference/residual stress increases the critical stretch/pressure and improves the structural stability. We then apply an analytical approach to calculate the natural frequency of the compound sphere for small amplitude radial vibration. We observe that an increase in residual stress increases the natural frequency and widens the range of stable free vibration. We numerically investigate the free and forced vibration of the compound sphere. Forced vibration amplitude reduces as interference/residual stress increases, which is reflected in the frequency–amplitude plots. The frequency response shows a small hardening non-linearity. We investigate the subharmonic and superharmonic responses for small and large amplitude vibration.

Effect of shape and size of carbon materials on the thermophysical properties of magnesium nitrate hexahydrate for solar thermal energy storage applications

In this paper, the effect of various carbon materials having different shapes and sizes on the thermophysical properties of magnesium nitrate hexahydrate (MNH), salt hydrate is studied. The carbon materials such as carbon sphere, multi-walled carbon nanotubes (MWCNTs), mesoporous carbon, graphene nanoplatelets(GNPs), and nano graphite (NG) were used as filler independently in the matrix of MNH to prepare MNH-carbon composite by melt mixing technique. The scanning electron microscopy (SEM) and Energy-dispersive X-ray Spectroscopy (EDX) analysis were done to analyze the uniform dispersion of carbon materials in MNH matrix. Fourier transformed infrared (FTIR) analysis was done to investigate the interaction between carbon materials and MNH in MNH-carbon composites. The cyclic stability of developed composites was verified by thermogravimetric analysis. The thermal conductivity of MNH enhanced significantly by 100%, 82.5%, 75%, 72.5%, and 65% upon adding carbon sphere, MWCNTs, mesoporous carbon, GNPs, and NG respectively, at a mass fraction of 0.5 wt.%. Differential scanning calorimetry results reveal that the addition of carbon materials improves the phase change properties of composites without compromising on the latent heat capacity of the material and also reduces the supercooling effect. To investigate the practical viability of prepared MNH-carbon composites, the heat transfer characteristics were evaluated by a conventional heating system. The maximum reduction in charging time was observed in the case of MNH-carbon sphere composite. Finally, the best MNH-carbon composite having highest thermal conductivity and stability, least supercooling, was used as active material in an indigenously built instant solar water heating system for solar thermal energy storage applications.

Sol-gel Synthesis of Boron Doped TiO2/hollow Glass Bubbles Composite Powders for Photocatalytic Degradation of Azophloxine

Background: B-TiO2 was supported on the surface of iM16K glass bubbles to achieve a suitable density for the B-TiO2/iM16K composite hollow spheres. Aeration or stirring in the wastewater can lead to thorough mixing of photocatalyst and wastewater. Solid-water separation is quite easy because the materials can float on the water surface while stopping aeration or stirring. Methods: The iM16K glass bubbles were used to prepare boron-doped B-TiO2/iM16K composite hollow spheres through a sol-gel route. The materials were characterized by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, UV-Visible diffuse reflectance spectrometry, and N2 adsorption-desorption techniques. Photocatalytic degradation of azophloxine on the composites was determined. Results: The bandgap energy of the B-TiO2/iM16K composite was slightly less than 3.0 eV when the calcination temperature was below 500oC. The sample calcined at 350oC had a BET surface area of 88.6 m2 /g, while the value of the sample calcined at 800oC was 1.2 m2 /g. The maximum photocatalytic degradation efficiency was obtained for the sample calcined at 450oC, and nearly all of the original azophloxine molecules were decomposed after 120 min of irradiation. Photocatalytic degradation efficiency after 30 min of irradiation was enhanced from 18.8% to 47.9% when B-TiO2 dosage increased from 100 to 800 mg/L. Conclusion: Crystallization of anatase TiO2 was temperature dependent, and the properties of B-TiO2/iM16K composite hollow spheres were affected by phase composition of the boron-doped TiO2 layer. The change in calcination temperature can have significant effect on photocatalytic degradation of azophloxine. The production of hydroxyl radical depended on photocatalytic activity of the B-TiO2/iM16K composite hollow spheres.

Carbon nanotubes interpenetrating MOFs-derived Co-Ni-S composite spheres with interconnected architecture for high performance hybrid supercapacitor

Recently, carbon nanotubes (CNT)-based interconnected architectures exhibit promising prospects in supercapacitors due to their flexibility and high electrical conductivity. Herein, a three-dimensional (3D) interconnected network structure combined with conductive carbon nanotubes interpenetrating MOFs-derived Co-Ni-S composite spheres (Co-Ni-S/CNTs) was synthesized. Such 3D interconnected architecture significantly leads to a favorable electronic structure, fast charge-transfer capacity, and more pseudocapacitive. The Co-Ni-S/CNTs-based hybrid electrode exhibits an extraordinary specific capacitance of 540.6C g−1 at 1 A g−1 and competitive rate performance (capacity retention rate of 69.9% when the current density increases to 10 times). Subsequently, a hybrid supercapacitor is assembled using Co-Ni-S/CNTs as the positive electrode and commercial activated carbon as negative electrode. The device delivers a high energy density of 63.5 W h kg−1 at 800 W kg−1 and keeps 83.0% initial capacitance retention after 10,000 cycles. The encouraging performances demonstrate the significant contribution of the 3D interconnected architecture for the future energy storage.

Creeping flow around a spherical particle covered by semipermeable shell in presence of magnetic field

This paper deals the MHD slow viscous motion of electrically conducting fluid over a rigid sphere surrounded by a concentric permeable sphere. Darcy’s equation is adopted to describe the motion in semipermeable region and Stokes equation is applied to describe the flow of viscous fluid region. For both flow fields, stream functions are calculated. The resistance force on composite sphere is obtained and variation of drag force with respect to different parameters has been plotted graphically. Some limiting cases are deduced and compared with the solution derived in other research papers. We observed that drag force increases with increasing magnetic field.

Label-free photoelectrochemical immunosensor for aflatoxin B1 detection based on the Z-scheme heterojunction of g-C3N4/Au/WO3

Aflatoxin B1 (AFB1) is the most toxic mycotoxin, is widely found in foods and animal feeds, and can pose a serious threat to our lives. A label-free photoelectrochemical (PEC) immunosensor was fabricated for the sensitive detection of AFB1. A Z-scheme heterojunction of gold nanoparticles (Au NPs) loaded on graphitic carbon nitride sheet and tungsten trioxide sphere composite (g-C3N4/Au/WO3) acted as the highly sensitive platform. The g-C3N4/Au/WO3 is capable, not only of immobilizing antibodies via Au NPs, but also enhancing the separation of electron-hole pairs due to its good energy band matching efficiency. The mechanism of photo-generated electron/hole transfer on g-C3N4/Au/WO3 was explored using scavengers to eliminate active components. On this basis, an electron transfer pathway for the immunosensor was deduced. The PEC immunosensor displayed a linear concentration range from 1.0 pg mL−1 to 100 ng mL−1 and a low detection limit of 0.33 pg mL−1 (S/N = 3) for AFB1. Good reproducibility, stability, and specificity provide a solid foundation for the practical application of this immunosensor.

Compact Magneto-Fluorescent Colloids by Hierarchical Assembly of Dual-Components in Radial Channels for Sensitive Point-of-Care Immunoassay.

Exploring signal amplification strategies to enhance the sensitivity of lateral flow immunoassay (LFIA) is of great significance for point-of-care (POC) testing of low-concentrated targets in the field of in vitro diagnostics. Here, a highly-sensitive LFIA platform using compact and hierarchical magneto-fluorescent assemblies as both target-enrichment substrates and optical sensing labels is demonstrated. The large-pored dendritic templates are utilized for high-density incorporation of both superparamagnetic iron oxide nanoparticles (IOs) and quantum dots (QDs) within the vertical channels. The hierarchical structure is built via affinity-driven assembly of IOs and QDs from organic phase with silica surface and mercapto-organosilica intermediate layer, respectively. The sequential assembly with central-radial channels enables 3D loading of dual components and separately controlling of discrete functionalities. After the alkyl-organosilica encapsulation and silica sealing, the composite spheres exhibit high stabilities and compatibility with LFIA for procalcitonin (PCT) detection. With the assistance of liquid-phase antigen-capturing, magnetic enrichment, and fluorescence-signal amplification, a limit of detection of 0.031 ng mL-1 for PCT is achieved with a linear range from 0.012 to 10 ng mL-1 . The current LFIA is robust and validated for PCT detection in real serum, which holds great diagnostic significance for precise guidance of antibiotic therapy with POC manner.

Sphere-shaped SiGe micro/nanostructures with tunable Ge composition and size formed by laser irradiation* *Project supported by the National Natural Science Foundation of China (Grant Nos. 62004218, 61991441, and 61804176), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB01000000), and the Youth Innovation Promotion Association of Chinese Academy of Sciences (Grant No. 2021005).

SiGe spheres with different diameters are successfully fabricated on a virtual SiGe template using a laser irradiation method. The results from scanning electron microscopy and micro-Raman spectroscopy reveal that the diameter and Ge composition of the SiGe spheres can be well controlled by adjusting the laser energy density. In addition, the transmission electron microscopy results show that Ge composition inside the SiGe spheres is almost uniform in a well-defined, nearly spherical outline. As a convenient method to prepare sphere-shaped SiGe micro/nanostructures with tunable Ge composition and size, this technique is expected to be useful for SiGe-based material growth and micro/optoelectronic device fabrication.

Numerical Simulation of Thermal Diffusivity Measurements With the Laser-Flash Method to Evaluate the Effective Property of Composite Materials

Abstract The laser-flash method (LFM) is a technique commonly used to measure thermal diffusivity of homogeneous and isotropic materials, but can also be applied to macroscopically inhomogeneous materials, such as composites. When composites present thermal anisotropy, as fiber-reinforced, LFM can be used to measure the effective thermal diffusivity (αeff) in the direction of heat flux. In this work, the thermal behavior of composites during thermal diffusivity measurements with the LFM was simulated with a finite element model (FEM) using a commercial software. Three composite structures were considered: sandwich layered (layers arranged in series or parallel), fiber-reinforced composites, and particle composite (spheres). Numerical data were processed through a nonlinear least-square fitting (NL-LSF) to obtain the effective thermal diffusivity of the composite. This value has the meaning of “dynamic effective thermal diffusivity.” Afterward, the effective thermal conductivity (λeff) is calculated from the dynamic effective thermal diffusivity, equivalent heat capacity, and density of the composite. The results of this methodology are compared with the analytically calculated values of the same quantity. This last assumes the meaning of “static effective thermal conductivity.” The comparison of the dynamic and static property values is so related to the inhomogeneity of the samples, and a deviation of the temperature versus time trend from the analytical solution for the perfectly homogeneous sample gives information about the lack of uniformity of the sample.

Synergistic effect of Co3Fe7 alloy and N-doped hollow carbon spheres with high activity and stability for high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have attracted extensive attention as a promising next-generation electrochemical energy storage technology, owing to their high energy density and low material cost. However, issues such as severe polarization and poor cycle stability caused by shuttle effect and slow sulfur redox kinetics limit their practical applications. Here, Co 3 Fe 7 alloy embedded into nitrogen-doped hollow carbon sphere composite (CoFe/NHCS) was synthesized as an electrocatalyst for Li-S batteries. The Co 3 Fe 7 alloy demonstrates a strong chemisorption and superior electrocatalytic conversion towards polysulfides, while the nitrogen-doped carbon hollow spheres promote Li + /electron transfer and physically suppress polysulfides shuttling. Their synergistic effect therefore could both accelerate the polysulfides redox conversion and inhibit the polysulfides loss. As a consequence, the Li-S batteries assembled with CoFe/NHCS-modified separators exhibit a superior rate capacity (1029 mAh/g at 2 C) and excellent cycling stability (644 mAh/g at 1 C after 500 cycles). Furthermore, even at a high sulfur loading of 6.7 mg/cm 2 , a high areal capacity of 5.58 mAh/g is achieved, which is retained at 4.45 mAh/cm 2 after 100 cycles. In addition, the CoFe/NHCS possesses an excellent stability in both physical structures and chemical properties over extended cycles, demonstrating its great potential for high-performance and long-cycle-life Li-S batteries. The Co 3 Fe 7 alloy embedded into nitrogen-doped hollow carbon sphere composite exhibits an excellent cycling performance with a high sulfur loading for lithium-sulfur batteries. • Co 3 Fe 7 alloy embedded into nitrogen-doped hollow carbon sphere (CoFe/NHCS) was synthesized for Li-S batteries. • CoFe/NHCS demonstrates an improved adsorptive and electrolytic effect towards polysulfides. • CoFe/NHCS enables Li-S batteries with an excellent rate performance and superior cycling stability. • With a high sulfur loading of 6.7 mg/cm 2 , a high areal capacity of 4.45 mAh/cm 2 is retained after 100 cycles. • CoFe/NHCS possesses an excellent stability in both physical structures and chemical properties over extended cycles.

One-step synthesis of fluorescence-enhanced carbon dots for Fe (III) on−off−on sensing, bioimaging and light-emitting devices

Carbon quantum dots (CDs), as one of the most potential fluorescent sensing materials, have attracted lots of attention in recent years. However, the low quantum yields, complicated separation and purification procedures have limited its application and large-scale production. In this paper, a facile and universal method was successfully developed to synthesize CDs-silica (SiO2) spheres composites (CS composites), which not only demonstrates 10-fold fluorescence enhancement compared with single CDs but also enables the purification with a simple centrifugation step. Meanwhile, fabricated composites also presented superior photoluminescence (PL) stability and high PL intensity, even in some tough environments such as acid/alkali aqueous solution, high/low temperature, and high ion concentration aqueous solution. This simple, fast, low-cost, and efficient synthesis method would potentially expand the application of CDs for clinical analysis, optical sensing (ferric ion (Fe3+) and pyrophosphate), bioimaging and light-emitting diodes (LEDs).

Construction of a composite-sphere model for molecules of tetrahedral symmetry

We propose a ‘composite sphere’ model for molecules of tetrahedral symmetry. In particular, we choose as an example the hydrocarbon neopentane. We disassemble the molecule into five moieties: four methyl groups (species A) and one carbon atom (species B). By imparting pair potentials of spherical symmetry to the A–A (hard sphere type), B–B (hard sphere type), and A–B (square-well type) pairs, we are able to reconstitute the pentamer structure via Monte Carlo simulation. This is demonstrated for four density states: ρσ 3 = 0.03, 0.10, 0.15, and 0.20. We apply two criteria in assessing the per cent formation of pentamers: namely the proximity rule and the energy rule. The proximity rule gives 57% formation of pentamers, while the energy rule is able to give 99% pentamers. The structures are also calculated via the spherical Ornstein-Zernike integral equations with the Percus-Yevick (PY) closure. It is found that the PY closure is inadequate for predicting quantitatively the MC radial distribution functions. The root cause of the lack of agreement is attributed to the improper application of the isotropic version of the Ornstein-Zernike integral equations to a fluid that has become anisotropic.

Enhanced photocatalytic H2 production performance of CdS hollow spheres using C and Pt as bi-cocatalysts

Photocatalytic H2 production from water splitting is an effective method to solve energy crisis and environmental pollution simultaneously. Herein, carbon@CdS composite hollow spheres (C@CdS-HS) are fabricated via a facile hydrothermal method using porous carbon hollow spheres (C-HS) as the template. The C@CdS-HS shows an excellent photocatalytic H2-generation rate of 20.9 mmol h−1 g−1 (apparent quantum efficiency of 15.3% at 420 nm), with 1.0 wt% Pt as a cocatalyst under simulated sunlight irradiation; this rate is 69.7, 13.9, and 3.9 times higher than that obtained with pure CdS hollow spheres (CdS-HS), C@CdS-HS, and CdS-HS/Pt, respectively. The enhanced photocatalytic H2-evolution activity of C@CdS-HS/Pt is due to the synergistic effect of C and Pt as the bi-cocatalyst. The C-HS serves not only as an active site provider but also as an electron transporter and reservoir. Moreover, C-HS has a strong photothermal effect that is induced by near infrared light, which kinetically accelerates the H2-production reaction. Additionally, the underlying charge transfer pathway and process from CdS to C−HS is revealed. This work highlights the potential application of C-HS-based nanocomposites in solar-to-chemical energy conversion.

Facile synthesis of multi-shelled MnO2–Co3O4 hollow spheres with superior catalytic activity for CO oxidation

Nano-oxide hollow structures have a wide range of applications in catalysis, but the preparation of multi-shelled composite oxide hollow structures still presents a major challenge. Herein, well-dispersed multi-shelled MnO2–Co3O4 hollow spheres have been successfully prepared via a facile “Kirkendall effect” method employing carbon spheres as sacrifice templates. The shell of the hollow spheres was constructed by interconnected Co3O4 nanosheets and catkin-like MnO2 nanorods. The interdiffusion of Carbon chain and MnO4− during synthesis could be the possible formation mechanism for the special morphology. Benefiting from the hierarchical porous structure, high surface area and strong synergistic effect between Co3O4 and MnO2 was obtained, the as-prepared Co–Mn composite hollow spheres showed reliably high activity and recycle stability for CO oxidation, achieving the complete CO conversion at 137 °C without significant decrease in activity after five cycles and 10h constant-temperature reaction. We believe that this work will provide a new method for the preparation of multi-shell composite hollow spheres.