Fabrication of carbon microcapsules containing silicon nanoparticles-carbon nanotubes nanocomposite by sol-gel method for anode in lithium ion battery

Carbon microcapsules containing silicon nanoparticles (Si NPs)-carbon nanotubes (CNTs) nanocomposite (Si-CNT@C) have been fabricated by a surfactant mediated sol-gel method followed by a carbonization process. Silicon nanoparticles-carbon nanotubes (Si-CNT) nanohybrids were produced by a wet-type beadsmill method. To obtain Si-CNT nanocomposites with spherical morphologies, a silica precursor (tetraethylorthosilicate, TEOS) and polymer (PMMA) mixture was employed as a structure-directing medium. Thus the Si-CNT/Silica-Polymer microspheres were prepared by an acid catalyzed sol-gel method. Then a carbon precursor such as polypyrrole (PPy) was incorporated onto the surfaces of pre-existing Si-CNT/silica-polymer to generate Si-CNT/Silica-Polymer@PPy microspheres. Subsequent thermal treatment of the precursor followed by wet etching of silica produced Si-CNT@C microcapsules. The intermediate silica/polymer must disappear during the carbonization and etching process resulting in the formation of an internal free space. The carbon precursor polymer should transform to carbon shell to encapsulate remaining Si-CNT nanocomposites. Therefore, hollow carbon microcapsules containing Si-CNT nanocomposites could be obtained (Si-CNT@C). The successful fabrication was confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). These final materials were employed for anode performance improvement in lithium ion battery. The cyclic performances of these Si-CNT@C microcapsules were measured with a lithium battery half cell tests.     

硅纳米粒子聚苯胺包覆改性及其嵌/脱锂电化学性能

利用直流电弧等离子体蒸发法合成硅纳米粒子（Si NPs）,粒径为20~30 nm。采用对氨基苯甲酸（ABA）处理Si NPs,并在ABA-Si NPs表面进行苯胺（ANi）原位化学氧化聚合,形成核/壳型聚苯胺包覆硅纳米复合粒子（PANi-Si NPs）。FTIR、DSC、XRD、TEM等分析结果表明,ABA与Si NPs之间形成了化学键,粒子表面引入了ANi基团,复合粒子中PANi质量含量约为62%。电化学性能测试表明,PANi包覆层的存在大幅度提高了Si NPs的循环稳定性能,在100 mA·g^-1的电流密度下循环100次后,电池容量保持率为92.5%,远高于未改性的Si NPs的性能。聚苯胺包覆改性Si NPs,改善其导电性能的同时,可以极大地缓冲充/放电过程中的体积变化,提高电极的循环稳定性能。     

硅纳米粒子聚苯胺包覆改性及其嵌/脱锂电化学性能

利用直流电弧等离子体蒸发法合成硅纳米粒子(SiNPs),粒径为20~30 nm。采用对氨基苯甲酸(ABA)处理SiNPs,并在ABA-SiNPs表面进行苯胺(ANi)原位化学氧化聚合,形成核/壳型聚苯胺包覆硅纳米复合粒子(PANi-SiNPs)。FTIR、DSC、XRD、TEM等分析结果表明,ABA与SiNPs之间形成了化学键,粒子表面引入了ANi基团,复合粒子中PANi质量含量约为62%。电化学性能测试表明,PANi包覆层的存在大幅度提高了SiNPs的循环稳定性能,在100 mA·g~(-1)的电流密度下循环100次后,电池容量保持率为92.5%,远高于未改性的SiNPs的性能。聚苯胺包覆改性SiNPs,改善其导电性能的同时,可以极大地缓冲充/放电过程中的体积变化,提高电极的循环稳定性能。     

Fabrication of novel multihollow superparamagnetic magnetite/polystyrene nanocomposite microspheres via water-in-oil-in-water double emulsions

We herein present a novel and simple synthetic strategy for fabricating multihollow superparamagnetic magnetite/polystyrene nanocomposite microspheres via water-in-oil-in-water double emulsions. Amphipathic magnetite nanoparticles surface-modified with oleic acid act as an oil-soluble emulsifier and sodium dodecyl sulfate acts as a water-soluble surfactant in the system. The final products were thoroughly characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and field-emission scanning electron microscopy, which showed the formation of multihollow magnetite/polystyrene nanocomposite microspheres. Preliminary results of magnetic properties of multihollow magnetite/polystyrene microspheres were reported. The effect of the content of amphipathic magnetite nanoparticles on the morphology of nanocomposite microspheres was studied. Furthermore, the mechanism of formation of multihollow magnetic nanocomposite microspheres was also discussed.     

Synthesis of microcapsules with polystyrene/ZnO hybrid shell by Pickering emulsion polymerization

Polystyrene/zinc oxide (ZnO) hybrid microcapsules having polystyrene as inner shell and ZnO nanoparticles as outer shell were synthesized by Pickering emulsion polymerization method. ZnO nanoparticles were used to form the colloidosomes that worked as the polymerization vessels, where both styrene monomer and crosslink agent were polymerized together. Fourier transform infrared spectra and thermogravimetric thermograms showed the existence of ZnO and polystyrene in the shell of hybrid microcapsules. The hollow structure and the different morphology under various conditions were also observed by field emission scanning electron microscopy. In addition, the shell thickness of hybrid microcapsules increased as the monomer concentration increased. The photoluminescence property of PS/ZnO hybrid microcapsules could be maintained without any noticeable variation by comparing with the pure ZnO particles. It could be reasonably deduced that hybrid hollow microspheres with multifarious polymer as inner shell and ZnO nanoparticles as outer shell would be produced for many applications.     

One-step synthesis of hollow structured Si/C composites based on expandable microspheres as anodes for lithium ion batteries

Si/C composites of carbon hollow structures loaded with Si nanoparticles (NPs) (Si/C-HSs) were prepared by one-step pyrolysis of a mixture of Si NPs and expandable microspheres (EMs). For the Si/C-HSs, hollow carbon shells with rough surfaces were formed by directly carbonizing the polymer shells of EMs, and the Si NPs fell into the void space or were loaded on the rough surfaces of the carbon shells. The EM-based carbon shells accommodated the volume expansion of the Si NPs and improved the electrical conductivity of the composites. As a result, the Si/C-HSs exhibited a high capacity (initial reversible capacity: 854.4 mAh g^− 1 at 300 mA g^− 1), stable cycling performance (capacity retention: 80% after 50 cycles), and excellent rate capability.     

Organosulfur-functionalized Au, Pd, and Au-Pd nanoparticles on 1D silicon nanowire substrates: preparation and XAFS studies

A hybrid preparative method was developed to prepare organosulfur-functionalized Au nanoparticles (NPs) on silicon nanowires (SiNWs) by reacting HAuCl(4) with SiNW in the presence of thiol. A number of organosulfur molecules-dodecanethiol, hexanethiol, 1,6-hexanedithiol, and tiopronin-were used to functionalize the Au surface. Size-selected NPs ranging from 1.6 to 7.5 nm were obtained by varying the S/Au ratio and the concentration of HAuCl(4). This method was further extended to the preparation Pd and Pd-Au bimetallic NPs on SiNWs. The morphology of the metal nanostructures was examined by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The local structure and bonding of the SiNW-supported metal nanostructures were studied using X-ray absorption fine structures (XAFS) [including both X-ray near-edge structures (XANES) and extended X-ray absorption fine structures (EXAFS)] at the Au L(3)-, Pd K-, S K-, and Si K-edges. It was also found that the annealing of the thiol-capped Au NPs up to 500 degrees C transforms the surface of the thiol-capped NPs to gold sulfide, as identified using Au L(3)- and S K-edge XANES. We also illustrate that this preparative approach can be used to form size-controllable Au NPs on carbon nanotubes.     

Fabrication of dendritic gold nanoparticles by use of an ionic polymer template

A facile method for the fabrication of dendritic gold nanoparticles (NPs) by use of an ionic polymer template has been developed. In situ generation of an imidazolium-based (cationic) polymer, poly[1-methyl-3-(4-vinylbenzyl)imidazolium], with AuCl4- counteranions is achieved by addition of HAuCl4 into a solution containing poly[1-methyl-3-(4-vinylbenzyl)imidazolium chloride]. Subsequent reduction with NaBH4 in water or in a mixture of ethanol and water affords various NPs depending on the conditions, including large dendritic gold NPs that have been analyzed by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and selected area electron diffraction (SAED). The structures of the dendritic gold NPs were found to depend on the ethanol concentration. Scanning electron microscopy (SEM) images of the ionic polymer reveal that the solvent used to deposit the polymer strongly influences its structure and may be correlated to the structure of the resulting NPs.     

Preparation of microspheres by an emulsification-complexation method

Microspheres were prepared by complexation of a cationic polymer, polyquaternium-24, and an anionic surfactant, sodium lauryl sulfate (SLS). The cationic polymer solution was emulsified in dimethylsiloxane to give water in silicone emulsion (W/Si), and it was used as a template for the formation of microspheres. The emulsion was dispersed into the SLS solution. In this process, two kinds of droplets, silicone dropletes and microspheres composed of the cationic polymer and SLS, were formed, evidenced by X-ray energy dispersive spectra. The mean diameter of the microspheres was reduced from 105.7 to 64.8 mum as the stirring rate for W/Si preparation increased from 300 to 1000 rpm. It is believed that water droplets in W/Si emulsion, when exposed to SLS solution, could be solidified by the complexation of the cationic polymer and the anionic surfactant.     

Pt纳米颗粒在氮掺杂空心碳微球上的高分散负载及其氧还原性能

通过热解自聚合多巴胺法制备了氮掺杂空心碳微球(N-HCMS), 并采用微波辅助乙二醇还原方法把Pt纳米粒子负载于N-HCMS上制得了Pt/N-HCMS催化剂. 催化剂的表面形貌、晶体结构及其比表面积和孔径分布等分别采用扫描电子显微镜、透射电子显微镜、X射线衍射仪及比表面分析仪等进行表征. 采用循环伏安法和线性扫描伏安法研究了Pt/N-HCMS 催化剂在酸性条件下的电催化氧还原性能. Pt/N-HCMS 催化剂由于Pt纳米粒子的均匀分散、N-HCMS载体的快速电子传递及其独特的微孔和中空结构而具有很高的电催化氧还原活性, 其质量比活性是E-TEK Pt/C 催化剂的近两倍. Pt/N-HCMS 催化剂还具有优良的稳定性. 本工作对于开发高性能的燃料电池阴极催化剂具有重要意义.     

Formation of wormlike aggregates of fluorocarbon-hydrocarbon hybrid surfactant by Langmuir-Blodgett transfer and alignment of gold nanoparticles

A novel anionic fluorocarbon-hydrocarbon hybrid surfactant (SS-Hyb-Na+) with a disulfide group has been synthesized from 11-bromo-1-undecanal and perfluorohexylethyl iodide via three steps. The Langmuir-Blodgett (LB) transfer of the 1:100 (mol/mol) mixed monolayer of SS-Hyb-Na+ and stearyl alcohol (C18OH) formed on an aqueous solution containing a cationic polymer, poly(diallyldimethylammonium chloride) (PDDA+Cl-) onto a hydrophobic silicon wafer yields the formation of wormlike aggregates consisting of SS-Hyb-/PDDA+ polyion complexes. It is found that the aggregates align along the withdrawal direction of the wafer substrate. When the wafer on which the wormlike aggregates exist is immersed into the dispersion of gold nanoparticles (Au NPs) prepared by the citrate reduction method, Au NPs align along the wormlike structures. Even though the surface of the wafer is placed either vertical or parallel to the monolayer compression direction during the LB transfer, the one-dimensional (1D) array of Au NPs is observed along the withdrawal direction of the wafer. This indicates that the wormlike aggregates of SS-Hyb-/PDDA+ complexes are aligned during the LB transfer, and the aligned aggregates behave as a scaffold in the 1D array of Au NPs.     

Magnetic poly(N‐isopropylacrylamide) microspheres by dispersion and inverse emulsion polymerization

The aim of this study was to develop novel thermally responsive polymer microspheres with magnetic properties. Dispersion and inverse emulsion copolymerization of N‐isopropylacrylamide (NIPAAm) and N,N′‐methylenebisacrylamide (MBAAm) was investigated in the presence of γ‐Fe₂O₃ nanoparticles. The resulting microspheres were characterized in terms of morphology, size, polydispersity, iron content, and temperature‐dependent swelling using optical microscopy, transmission electron microscopy, scanning electron microscopy, QELS, and AAS. The effects of several variables, such as the concentration of γ‐Fe₂O₃, MBAAm crosslinking agent, Span 80 surfactant, 2,2′‐azobis(2‐methyloctanenitrile) (AMON) initiator, and polymerization temperature on the properties of the microspheres were studied. Swelling and thermoresponsive behavior of the microspheres containing γ‐Fe₂O₃ nanoparticles were also investigated. The microspheres contained about 8 wt % of iron. The presence of magnetic nanoparticles and their concentration changes did not have any significant effect on the temperature sensitivity of the composites. The particles gradually shrink into an increasingly collapsed state when the temperature is raised to 40 °C since the increase in temperature weakens the hydration and PNIPAAm chains gradually become more hydrophobic, which leads to the collapse of the particles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5884–5898, 2007     

新型耐甲醇氧还原电催化剂——氮掺杂中空碳微球@铂纳米粒子复合材料

通过模板法制备了一种新型耐甲醇氧还原电催化剂——氮掺杂中空碳微球@铂纳米粒子复合材料(HNCMS@PtNPs)。首先,将铂纳米粒子负载于氨基化二氧化硅微球上,获得PtNPs/SiO₂复合材料。然后通过多巴胺自聚合反应在PtNPs/SiO₂复合材料上包裹聚多巴胺(PDA)膜,将其在氮气气氛中直接进行碳化处理并通过氢氟酸溶液刻蚀去除SiO₂,获得了内嵌有PtNPs的氮掺杂中空碳微球,标记为HNCMS@PtNPs复合材料。采用扫描电子显微镜、透射电子显微镜、X射线衍射仪、拉曼光谱仪、比表面积分析仪和X射线光电子能谱仪对HNCMS@PtNPs复合材料的形貌和结构进行了表征。采用循环伏安法和线性扫描伏安法研究了HNCMS@PtNPs复合材料的电催化氧还原性能。结果表明：HNCMS@PtNPs催化剂的Pt载量高达11.9%(w,质量分数),对氧还原反应具有高电催化活性、高稳定性和优良的抗甲醇性能,是一种具有应用潜力的直接甲醇燃料电池(DMFCs)阴极电催化剂。     

One pot synthesis of Ag nanoparticle modified ZnO microspheres in ethylene glycol medium and their enhanced photocatalytic performance

Ag nanoparticles (NPs) modified ZnO microspheres (Ag/ZnO microspheres) were prepared by a facile one pot strategy in ethylene glycol (EG) medium. The EG played two important roles in the synthesis: it could act as a reaction media for the formation of ZnO and reduce Ag⁺ to Ag⁰. A series of the characterizations indicated the successful combination of Ag NPs with ZnO microspheres. It was shown that Ag modification could greatly enhance the photocatalytic efficiency of ZnO microspheres by taking the photodegradation of Rhodamine B as a model reaction. With appropriate ratio of Ag and ZnO, Ag/ZnO microspheres showed the better photocatalytic performance than commercial Degussa P-25 TiO₂. Photoluminescence and surface photovoltage spectra demonstrated that Ag modification could effectively inhibit the recombination of the photoinduced electron and holes of ZnO. This is responsible for the higher photocatalytic activity of Ag/ZnO composites.     

Preparation and characterization of multi‐walled carbon nanotubes decorated with silver nanoparticles through ultraviolet irradiation reduction

A facile, green and efficient approach was applied to synthesize multi‐walled carbon nanotubes (MWNTs) decorated with silver nanoparticles (MWNT‐Ag) for further potential application. Oxidized MWNTs were decorated with silver nanoparticles (Ag NPs) via a method combining ultraviolet irradiation‐induced reduction and conventional silver mirror reaction without any reducing agent. The obtained product was characterized using various methods. X‐ray diffraction proved that the Ag NPs were synthesized successfully. Moreover, Ag NPs with a diameter of 80 nm, attached onto MWNTs, could be clearly observed in field emission scanning electron microscopy images, which also confirmed Ag NPs. Energy‐dispersive spectroscopy and transmission electron microscopy also indicated the presence of Ag NPs. Furthermore, thermogravimetric analysis was used to measure the content of Ag NPs in MWNT‐Ag, the result indicating that the weight content of Ag NPs was up to 31.88%. UV–visible absorption spectroscopy was adopted to evaluate the dispersion property of MWNT‐Ag. The result illustrated that MWNT‐Ag had a good dispersibility and stability in water. Characterization was also carried out through Fourier transform infrared spectroscopy, Raman spectroscopy and dynamic light scattering analysis.     

High capacity binding of antibodies by poly(hydroxyethyl methacrylate) nanoparticles

Poly(hydroxyethyl methacrylate) (PHEMA) nanoparticles with an average size of 150 nm in diameter and with a poly-dispersity index of 1.171 were produced by a surfactant free emulsion polymerization. Specific surface area of the PHEMA nanoparticles was found to be 1779 m(2)/g. Reactive imidazole containing 3-(2-imidazoline-1-yl)propyl(triethoxysilane) (IMEO) was used as a pseudo-specific ligand. IMEO was attached covalently onto the nanoparticles. PHEMA-IMEO nanoparticles were used for the affinity binding of immunoglobulin-G (IgG) from human plasma. To evaluate the degree of IMEO loading, the PHEMA nanoparticles were subjected to Si analysis by using flame atomizer atomic absorption spectrometer and it was estimated as 64.5 mg/g of polymer. The nanoparticles were characterized by transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). IgG binding onto the PHEMA nanoparticles was found to be 5.2 mg/g. Much higher binding values (up to 843 mg/g) were obtained for the PHEMA-IMEO nanoparticles. IgG could be repeatedly bound and eluted on PHEMA-IMEO nanoparticles without noticeable loss in the IgG binding capacity.     

Synthesis of poly(2‐hydroxyethyl methacrylate)‐based molecularly imprinted polymer nanoparticles containing timolol maleate: morphological,thermal, and drug release along with cell biocompatibility studies

This work was aimed to synthesize and characterize poly(2‐hydroxyethyl methacrylate) [poly (HEMA)]‐based molecularly imprinted polymer nanoparticles (MIP NPs) containing timolol maleate (TM) via precipitation polymerization. The molecular structures of the MIP and non‐imprinted polymer (NIP) NPs were compared by means of Fourier transform infrared spectroscopy. The morphological observations by using scanning electron microscopy and transmission electron microscopy confirmed the formation of MIP NPs as small as 128 nm in average diameter with appropriate synthesis conditions. Thermal behaviors of the samples were also studied by the use of thermogravimetric analysis and differential scanning calorimetry. By considering a series of key factors such as monomer : template ratio, cross‐linker type, pH, and temperature, the sample with promising characteristics was found to be that of HEMA : TM ratio of 10:1, 40 mmol of ethylene glycol dimethacrylate as cross‐linker, and polymerization temperature of 60°C in acetonitrile as porogenic solvent. Furthermore, the ultraviolet‐visible (UV‐vis) spectrophotometry results proved a controlled release of TM from the MIP NP samples compared with NIP ones at extended periods. Moreover, the cytotoxicity of the MIP and NIP NPs samples was evaluated on mesenchymal stem cells, and the obtained observations showed that they had no adverse side effect on the living cells; especially the surface of the MIP NPs sample depicted highly cell's biocompatibility. Finally, the outcomes from designed different experiments conducted us that the HEMA‐based MIP NPs have great potential as an ocular nanocarrier for TM delivery. Copyright © 2016 John Wiley & Sons, Ltd.     

Superior Lithium‐Ion Storage Properties of Si‐Based Composite Powders with Unique Si@Carbon@Void@Graphene Configuration

Composite powders of the configuration Si@carbon@void@graphene were prepared by a one‐step spray pyrolysis process, by adding polyvinylpyrrolidone (PVP) to a precursor solution containing graphene oxide (GO) sheets and silicon nanoparticles (NPs). Morphological analysis indicates that the individual Si NPs are coated with amorphous carbon and encapsulated in a micrometer‐sized graphene ball structure that offers a large amount of buffer space. The addition of PVP improves the stability of the colloidal spray solution containing the GO sheets and the Si NPs. Consequently, the prepared Si@C@void@graphene composite powders have a relatively more uniform morphology than the Si@void@graphene composite powders prepared from the spray solution without PVP. The first charge and discharge capacities of the Si@C@void@graphene electrode measured at 0.1 A g^?1 are as high as 3102 and 2215 mA h g^?1, respectively. With an increase in the current rate from 0.5 to 11 A g^?1, 46 % of the original capacity (i.e., 2134 mA h g^?1) is maintained. After 500 cycles at a high rate of 7 A g^?1, the Si@C@void@graphene electrode shows 84 % capacity retention and 99.8 % of the average Coulombic efficiency. The superior cycling and rate capabilities of the prepared Si@C@void@graphene electrode could be attributed to the uniform carbon coating of the Si NPs and the graphene ball structure, which facilitates efficient diffusion of Li ions and prevents the penetration of electrolyte into graphene ball during cycling.     

Cellulose/silver nanoparticles composite microspheres: eco-friendly synthesis and catalytic application

Cellulose/silver nanoparticles (Ag NPs) composites were prepared and their catalytic performance was evaluated. Porous cellulose microspheres, fabricated from NaOH/thiourea aqueous solution by a sol–gel transition processing, were served as supports for Ag NPs synthesis by an eco-friendly hydrothermal method. The regenerated cellulose microspheres were designed as reducing reagent for hydrothermal reduction and also micro-reactors for controlling growth of Ag NPs. The structure and properties of obtained composite microspheres were characterized by Optical microscopy, UV–visible spectroscopy, WXRD, SEM, TEM and TG. The results indicated that Ag NPs were integrated successfully and dispersed uniformly in the cellulose matrix. Their size (8.3–18.6?nm), size distribution (3.4–7.7?nm), and content (1.1–4.9?wt%) were tunable by tailoring of the initial concentration of AgNO₃. Moreover, the shape, integrity and thermal stability were firmly preserved for the obtained composite microspheres. The catalytic performance of the as-prepared cellulose/Ag composite microspheres was examined through a model reaction of 4-nitrophenol reduction in the presence of NaBH₄. The composites microspheres exhibited good catalytic activity, which is much high than that of hydrogel/Ag NPs composites and comparable with polymer core–shell particles loading Ag NPs.     

Preparation of polymer hollow microspheres covered by polymer solid particles via two polymerization steps

A novel surface modification method for titania nanoparticles is provided via the surface‐initiated photocatalytic polymerization with the aid of acrylic acid (AA) or sodium styrene sulfonate (NaSS). The properties of modified titania nanoparticles are investigated with aqueous electrophoresis measurements, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Then the modified titania is used as Pickering stabilizer for further polymerization and the morphology of the resulted polymer microspheres is characterized by TEM and field‐emission scanning electron microscopy. It is proven that the addition of AA or NaSS for the surface‐initiated polymerization can obviously affect the structure and morphology of the final polymer composite microspheres. The formation mechanism of several kinds of polymer particles is also proposed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011