Fabrication of carbon microcapsules containing silicon nanoparticles for anode in lithium ion battery

Carbon microcapsules containing silicon (Si) nanoparticles (NPs) were prepared from silicon-embedded polymer microspheres. The precursors, polymeric microspheres containing silicon nanoparticles were fabricated by a facile emulsion polymerization with surfactants, sodium dodecyl sulfate and dodecyltrimethylammonium bromide. The effects of monomer, surfactant concentration, and ionic character of surfactant on the formation of microspheres were demonstrated. The successful fabrication of polystyrene/polydivinylbenzene microspheres with Si NPs was confirmed by scanning electron microscopy. Subsequent thermal treatment produced carbon microcapsules having Si NPs. Volume shrinkage of polymer spheres during carbonization step resulting in the formation of internal free spaces in carbon microcapsules is the critical process in this experiment, which can accommodate volume changes of Si NPs during Li ion charge/discharge processes. The successful encapsulation of Si NPs with exterior carbon shell was clearly shown by transmission electron microscopy and X-ray diffraction. The change in size distribution and structure of polymer and carbon microspheres was also revealed. The cyclic performances of these Si@C microcapsules were measured with lithium battery half cell tests.     

Fabrication of polyimide nanotubes and carbon nanotubes containing magnetic iron oxide in confinement

Polyimide nanotubes with tunable wall thickness were fabricated by a precursor impregnation method using an AAO template, and carbon nanotubes containing magnetic iron oxide were obtained using ferric chloride-embedded polyimide precursor by a carbonization process.     

Synthesis of hierarchical hollow silica microspheres containing surface nanoparticles employing the quasi-hard template of poly(4-vinylpyridine) microspheres

A facile method of preparing hierarchical hollow silica microspheres containing surface silica nanoparticles (HHSMs) through the sol-gel process of tetraethylorthosilicate employing a quasi-hard template of non-cross-linking poly(4-vinylpyridine) microspheres is proposed. The quasi-hard template contains the inherent catalyst of the basic pyridine group, and a few of the polymer chains can escape from the template matrix into the aqueous phase, which initiates the sol-gel process spontaneously both on the surface of the template used to prepare the hollow silica shell and in the aqueous phase to produce the surface silica nanoparticles. By tuning the weight ratio of the silica precursor to the quasi-hard template, HHSMs with a size of about 180 nm and a shell thickness ranging from 14 to 32 nm and surface silica nanoparticles ranging from 17 to 36 nm are produced initially through the deposition of surface silica nanoparticles onto the silica shell, followed by template removal either by calcination or solvent extraction. The synthesized HHSMs are characterized, and a possible mechanism for the synthesis of HHSMs is proposed.     

YVO4:Eu3+ functionalized porous silica submicrospheres as delivery carriers of doxorubicin

Porous silica microspheres were fabricated by a facile surface-protected etching strategy. Polyvinylpyrrolidone (PVP) was used as a protecting polymer absorbed on the surface of silica microspheres and NaOH was employed as an etching agent. Owing to the protective action of PVP and inhomogeneous etching, mesopores were created in the silica microspheres. Then, based on the Pechini-type sol-gel and impregnating process, YVO(4):Eu(3+) nanocrystals were integrated into the channels to form highly luminescent YVO(4):Eu(3+)@SiO(2) composite microspheres. The biocompatibility tests on L929 fibroblast cells using MTT assay reveal low cytotoxicity of the system. Owing to the large interior space and electrostatic interaction, the porous microspheres show a relatively high loading capacity (438 mg DOX/YVO(4):Eu(3+)@SiO(2) g) and encapsulation efficiency (87.6%) for the anti-cancer drug doxorubicin hydrochloride (DOX). The drug release behavior and cytotoxic effect against human cervical carcinoma cells (HeLa cells) of the DOX-loaded YVO(4):Eu(3+)@SiO(2) carriers were investigated in vitro. It was found that the carriers present a highly pH-dependent drug release behavior due to electrostatic interaction between the silica surface and DOX molecules. The drug release rate became greater at low pH owing to the increased electrostatic repulsion. The DOX-loaded carriers demonstrate a similar or even greater anti-cancer activity with respect to the free DOX against HeLa cells. Furthermore, the PL intensity of the microspheres shows correlation with the cumulative release of DOX. These results suggest that the composite can potentially act as a multifunctional drug carrier system with luminescent tagging and pH-controlled release properties.     

Carbon and SiC macroscopic beads from ion-exchange resin templates

A method for preparing carbon and SiC macroscopic beads using ion-exchange resins as a macrotemplate that determines the macroshape and the pore structure of the product materials is reported. First, silicates are ion-exchanged into the resins to prevent the resin from collapsing during subsequent carbonization and allow them to be used as precursors for SiC formation. SiC is prepared via carbothermal reduction of carbon/silica composite beads obtained upon carbonization of the resin/silicate in an inert atmosphere. Finally, silica is removed by HF etching. Very high-surface area (1670-2026 m2 g-1) micro- or micro-/mesoporous carbon beads and relatively high-surface area (35-63 m2 g-1) macro- and meso-/macroporous SiC beads were prepared by the described method. The pore structure and the macroshape of the particles were controlled by the type of ion-exchange resins employed, gel or macroreticular.     

Triconstituent co-assembly to ordered mesostructured polymer-silica and carbon-silica nanocomposites and large-pore mesoporous carbons with high surface areas

Highly ordered mesoporous polymer-silica and carbon-silica nanocomposites with interpenetrating networks have been successfully synthesized by the evaporation-induced triconstituent co-assembly method, wherein soluble resol polymer is used as an organic precursor, prehydrolyzed TEOS is used as an inorganic precursor, and triblock copolymer F127 is used as a template. It is proposed for the first time that ordered mesoporous nanocomposites have "reinforced concrete"-structured frameworks. By adjusting the initial mass ratios of TEOS to resol, we determined the obtained nanocomposites possess continuous composition with the ratios ranging from zero to infinity for the two constituents that are "homogeneously" dispersed inside the pore walls. The presence of silicates in nanocomposites dramatically inhibits framework shrinkage during the calcination, resulting in highly ordered large-pore mesoporous carbon-silica nanocomposites. Combustion in air or etching in HF solution can remove carbon or silica from the carbon-silica nanocomposites and yield ordered mesoporous pure silica or carbon frameworks. The process generates plenty of small pores in carbon or/and silica pore walls. Ordered mesoporous carbons can then be obtained with large pore sizes of approximately 6.7 nm, pore volumes of approximately 2.0 cm(3)/g, and high surface areas of approximately 2470 m(2)/g. The pore structures and textures can be controlled by varying the sizes and polymerization degrees of two constituent precursors. Accordingly, by simply tuning the aging time of TEOS, ordered mesoporous carbons with evident bimodal pores at 2.6 and 5.8 nm can be synthesized.     

Assessment of nanoparticle loading and dispersion in polymeric materials using optical coherence tomography

The inclusion of small concentrations of nanoparticles can significantly enhance the thermal and electrical properties, and to a lesser degree the mechanical performance, of polymers. Dispersion of nanoparticles during mixing is problematic, with poor mixing resulting in particle agglomeration (i.e. particle clustering), which subsequently limits the potential for property enhancement. Achieving good dispersion is considered key to large-scale production and commercialization of polymer nanocomposites (PNCs), and a measurement technique capable of quantitatively characterizing particle loading and dispersion would significantly enhance product development. This paper presents the results of a study using a static light scattering technique, Fourier domain optical coherence tomography (FD-OCT), for discriminating between different particle loadings and levels of dispersion. The technique has been applied to a range of PNCs including epoxy resins reinforced with nanoclay platelets, silica microspheres or multi-walled carbon nanotubes (MWCNTs), and zinc oxide and lithium aluminate reinforced polypropylene.     

Synthesis of bifunctional polymer nanotubes from silicon nanowire templates via atom transfer radical polymerization

As a way to control the surface properties of nanowires and nanotubes, we present a method for growing polymer from the surface of silicon/silica core/shell nanowires. After modification of nanowire surfaces with polymer initiators, Atom Transfer Radical Polymerization (ATRP) was used to grow methacrylate polymer chains from the surface. The resulting structures were characterized by SEM, TEM, and EELS. After etching the silicon cores, the resulting polymer-coated nanotubes will have hydrophilic silica cores with hydrophobic polymer shells.     

Controlling morphology and particle size of hollow poly(styrene-divinylbenzene) microspheres fabricated by template-based method

Hollow poly(styrene–divinylbenzene) (P(S-DVB)) microspheres were fabricated via template-based method including synthesis of silica particles by sol-gel method, preparation of silica/P(S-DVB) particles by dispersion polymerization and chemical etching of silica cores by NaOH solution. TEM, FTIR and TG analyses confirmed that the hollow P(S-DVB) microspheres were successfully obtained. The morphology of hollow P(S-DVB) microspheres could be controlled by adjusting the amounts of DVB, AIBN and VTES, and the round-ball-like hollow P(S-DVB) microspheres were fabricated when the amount of DVB, AIBN and VTES was 30.0?wt%, 5.0?wt% and 30.0?vol% respectively. Both the size of silica particles and amount of monomers were regarded as the two key factors to control the particle size of the round-ball-like hollow P(S-DVB) microspheres.     

Synthesis of polymer–inorganic patchy microcapsules with tunable patches

We introduce a facile and versatile approach for the formation of ball-like polymer–inorganic patchy microcapsules with a tunable shell by combining sol–gel chemistry of silica precursor and phase separation between the polymer and the precursor. Firstly, chloroform-in-water emulsion droplets containing poly(methyl methacrylate) (PMMA), silica precursor [tetraethyl orthosilicate (TEOS)] and co-surfactant sodium dioctyl sulfosuccinate (Aerosol OT or AOT) were prepared by shaking the mixture by hand. Due to the added AOT, water molecules diffuse into the chloroform droplets, and the tiny water droplets would coalesce gradually, triggering the formation of double emulsion droplets. Upon further solvent evaporation, the concentration of the polymer and the silica precursor in the oil shell of the double emulsions increases, leading to the phase separation between the polymer and the precursors (and partially formed silica through the hydrolysis and condensation of TEOS). Because of the confined geometry of the oil shell in the double emulsions, polymeric disc-like structures, stabilized by AOT, were dispersed in the silica precursors. Meanwhile, the silica precursor hydrolyzed and condensed when brought in contact with the aqueous solution, ultimately leading to the formation of a mineralized shell around the polymer domains and the hybrid patchy microcapsules. Effect of synthesis conditions, such as the amount of TEOS, AOT, and PMMA used, the pH value, and solvent evaporation rate on interfacial behavior of the solvent/water; and the morphology of the patchy microcapsules were investigated. Patchy microcapsules with tunable patch size and shape can be generated through tailoring the experimental parameters. Our study indicates that the hybrid patchy microcapsules can be formed by taking advantage of the sol–gel chemistry and the phase separation process, and the underlying generality of the synthesis procedure allows for a variety of applications, including drug storage, coatings, delivery, catalysis, and smart building blocks in self-assembling systems.     

锂离子电池用多孔硅/石墨/碳复合负极材料的研究

在两步高能球磨和酸蚀条件下制得了多孔硅/石墨复合材料，并对其进行碳包覆制成多孔硅/石墨/碳复合材料。通过TEM，SEM等测试手段研究了多孔硅材料的结构。作为锂离子电池负极材料，电化学测试结果表明多孔硅/石墨/碳复合材料相比纳米硅/石墨/碳复合材料有更好的循环稳定性。同时，改变复合体配比、热解碳前驱物、粘结剂种类和用量也会对材料的电化学性能产生较大的影响。其中使用质量分数为10％的LA132粘结剂的电极200次循环以后充电容量保持在649.9 mAh·g^-1，几乎没有衰减。良好的电化学性能主要归因于主活性体-多孔硅颗粒中的纳米孔隙很好地抑制了嵌锂过程中自身的体积膨胀，而且亚微米石墨颗粒和碳的复合也减轻了电极材料的体积效应并改善了其导电性。     

Fabrication of super-macroporous nanocomposites by deposition of carbon nanotubes onto polymer cryogels

Electrically conducting super-macroporous carbon nanotube/polymer cryogel nanocomposites were fabricated by a novel approach based on deposition of carbon nanotubes (CNTs) onto the inner surface of pre-formed cryogels assisted by cryogenic treatment. Stable aqueous dispersions of multi-walled and single-walled carbon nanotubes were firstly obtained by non-covalent modification of pristine nanotubes with either pyrene containing polydimethylacrylamide or poly(ethylene oxide)₂₆-b-poly(propylene oxide)₄₀-b-poly(ethylene oxide)₂₆ copolymers and, then, exploited for the preparation of nanocomposites. The mechanical and electrical properties of nanocomposite materials were measured and compared to similar materials prepared by established method. The novel approach provided super-macroporous nanocomposites with high electrical conductivity (>10^?2 S/m) at much lower nanotube content (0.12 wt.%).     

Single‐Handed Helical Carbonaceous Nanotubes: Preparation,Optical Activity,and Applications

Carbon‐based nanomaterials have been widely studied in the past decade. Three approaches have been developed for the preparation of single‐handed helical carbonaceous nanotubes. The first approach uses the carbonization of organopolymeric nanotubes, where the organic polymers are polypyrrole, 3‐aminophenol‐formaldehyde resin, and m‐diaminobenzene‐formaldehyde resin. The second approach uses the carbonization of aromatic ring‐bridged polybissilsesquioxane followed by the removal of silica. Micropores exist within the walls of the carbonaceous nanotubes. The third approach uses the carbonization of organic compounds within silica nanotubes. This hard‐templating approach drives the formation of helical carbonaceous nanotubes containing twisted carbonaceous nanoribbons. All of these helical carbonaceous nanotubes exhibit optical activity, which is believed to originate from the chiral π‐π stacking of aromatic rings. They can be used as chirality inducers, and for lithium‐ion storage.     

Green synthesis of polymer nanofibers and their composites as flame‐retardant materials for polymer nanocomposites

Polyaniline nanofibers and their composites with carbon nanotubes were developed as an effective flame‐retardant material using a facile green method. Polyaniline nanofibers were used as a smart flame‐retardant for acrylonitrile–butadiene–styrene polymer. The polyaniline nanofibers were dispersed in polymer matrix forming well‐dispersed polymer nanocomposites. Effect of polyaniline nanofiber mass ratio on the polymer nanocomposite properties was studied. Polyaniline nanofiber composites with carbon nanotubes were also dispersed in polymer matrix. The thermal stability and flammability properties of the polymer nanocomposites were investigated. The rate of burning of polymer nanocomposites achieved 82.5% reduction (7.32 mm/min) compared with virgin polymer (42.5 mm/min). The reduction in peak heat release rate and total heat release of the polymer nanocomposites containing nanofibers achieved 74 and 34%, respectively. Interestingly, the average mass loss rate was significantly reduced by 58% and the emission of carbon monoxide and carbon dioxide gases were suppressed by 20 and 47%, respectively. The effect of polyaniline nanofibers composites on the flammability of polymer nanocomposites was also studied. Polyaniline nanofibers and their composites were characterized using Fourier transform infrared spectroscopy and transmission and scanning electron microscopy. The dispersion of polyaniline nanofibers in polymer nanocomposites was characterized using transmission electron microscopy. The different polymer nanocomposites were characterized using thermogravimetric analysis, UL94 flame chamber, and cone calorimeter tests. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of composites with alternating layers of poly(vinyl chloride) and single-wall carbon nanotubes homogeneously dispersed in carboxymethyl cellulose

For preparation of water-resistant and thermally stable nonlinear optical elements containing single-wall carbon nanotubes, an original method for the formation of layered structures based on alternating layers of poly(vinyl chloride) and a water-soluble polymer (carboxymethyl cellulose) with dispersed singlewall carbon nanotubes is proposed. An analysis of the optical properties of the resulting composites by means of optical-absorption spectroscopy and Raman scattering makes it possible to confirm that the nanocomposites contain individual (not united in bundles) single-wall carbon nanotubes.     

Preparation and properties of polybenzoxazole-silica nanocomposites via sol-gel process

A novel organic/inorganic hybrid material has been prepared through the sol-gel process. A high temperature polymer, polybenzoxazole (PBO), was chosen as the organic phase due to its inherent low dielectric constant and low water absorption. The inorganic phase was generated via sol-gel reaction from a silica precursor, phenyltriethoxysilane (PTEOS). Due to the hydroxyl groups in the PBO precursor backbone and the water release during the cyclization of the precursor, the sol-gel reaction proceeded without the addition of water and any catalyst. After curing at 350 °C, we obtained the PBO/silica nanocomposites. From TEM and SEM photographs, the silica particles dispersed in the PBO matrix were nano-sized. With an addition of 100 wt% of PTEOS, the T_g of PBO was increased 35 °C. The dielectric constant of the hybrid materials increased with the increasing amount of PTEOS.     

Peony pollen derived nitrogen-doped activated carbon for supercapacitor application

Peony pollen is a cheap and readily available biomass material with a relatively high protein content.In this work,it was employed as an N-rich precursor to prepare the nitrogen-doped porous carbon for supercapacitor application.The porous carbon microspheres were prepared through a hydrothermal method and subsequent carbonization process.Notably,ammonium borofruoride and potassium hydroxide were employed respectively as an etchant and an activator to modify the porosity of the materials.The as prepared ANPPCs-700 has a super high BET specific surface area of 824.69 m~2/g.The microstructure,chemical state and electrochemical properties of the product were investigated in detail.The prepared nitrogen-doped carbon microspheres exhibits excellent specific capacity of 209 F/g at a current density of lA/g and remained 92.5% of the initial capacitance after 5000 deep cycles at 5 A/g.     

碳纳米管/活性炭复合微球的制备及其对VB12的吸附应用

采用反相乳液法制备碳纳米管/壳聚糖复合微球(CNTs/CTS), 并对其进一步炭化、活化制得碳纳米管/活性炭复合微球(CNTs/AC). 以此复合微球为吸附材料, 探索了其对中分子代表物质VB12的吸附. 研究结果表明, 碳纳米管含量70%(w)的复合微球经水蒸气适当活化后球形度好、吸附性能优异, 其对VB12的吸附量达23.59 mg·g-1, 分别是活性炭和大孔吸附树脂的5.4和2.7倍. 分析表明这是由于碳纳米管/活性炭复合微球具有发达的中孔结构.     

Multi walled carbon nanotubes induced viscoelastic response of polypropylene copolymer nanocomposites: Effect of filler loading on rheological percolation

Polypropylene random copolymer nanocomposites having 0.2–7.0 vol% multi-walled carbon nanotubes (MWCNTs) were prepared via melt processing. Transmission electron microscopy (TEM) was employed to determine the nano scale dispersion of carbon nanotubes. Linear viscoelastic behavior of these nanocomposites was investigated using parallel plate rheometry. Incorporation of carbon nanotubes in the polymer matrix resulted in higher complex viscosity (η*), storage (G′) and loss modulus (G″) as compared to neat polymer, especially in the low-frequency region, suggesting a change from liquid to solid-like behavior in the nanocomposites. By plotting storage modulus vs. carbon nanotube loading and fitting with a power law function, the rheological percolation threshold in these nanocomposites was observed at a loading of ∼0.27 vol% of MWCNTs. However, electrical percolation threshold was reported at ∼0.19 vol% of MWCNTs loading. The difference in the percolation thresholds is understood in terms of nanotube connectivity with nanotubes and polymer chain required for electrical conductivity and rheological percolation.     

共聚物模板辅助合成高倍率性能多孔Li2FeSiO4@C/CNTs纳米复合正极材料

通过溶胶-凝胶法制备了Li₂FeSiO₄@C/CNTs(LFS@C/CNTs)纳米复合材料,其中三嵌段共聚物P123用作结构导向剂和碳源,碳纳米管作为导电线提高材料的导电性。LFS@C/CNTs不仅具有海绵状纳米孔,能够与电解液充分接触改善锂离子的传输路径,同时由非晶碳和碳纳米管构成的三维桥联导电网络利于电子的快速传递,提高了材料大电流充放电能力和循环稳定性。复合后的LFS@C/CNTs的高倍率性能相比LFS@C明显提高, 当CNTs的掺量为4%,电压窗口为1.5~4.5 V,0.1C电流密度下放电比容量为182 mAh·g^-1。在10C经70次循环后该材料的放电比容量能保持在117 mAh·g^-1,是LFS@C放电比容量(55 mAh·g^-1)的两倍。