非共价改性纳米颗粒稳定Pickering乳液的制备及可逆调控

用具有氧化还原活性分子乙酰基二茂铁吖嗪(Fc⁺A)对磁性纳米颗粒Fe₃O₄@SiO₂进行非共价疏水改性,将改性颗粒作为乳化剂制备Pickering乳液。通过TEM、SEM、FTIR、XRD、接触角测量、光学显微镜等对纳米颗粒及Pickering乳液的结构、形貌和性能进行表征。结果表明：制备的核壳结构纳米颗粒粒径为150 nm左右,分散均匀;Fc⁺A成功修饰到纳米颗粒表面,且随Fc⁺A浓度的增加,改性颗粒的接触角明显增大;Fc⁺A浓度为12.5 mmol/L,乳化剂浓度为0.3%(质量),油水比为4∶6,搅拌速率为10000 r/min,得到的Pickering乳液具有良好的稳定性。而且,所得乳液具双重响应性,通过氧化还原和磁场可实现对乳液稳定性的可逆调控。     

智能响应型Pickering乳液的制备及在物质分离中的应用进展

Pickering乳液是指由微纳米固体粒子代替传统表面活性剂作为乳化剂而稳定的乳液,具有较强的稳定性和超高油/水界面,能够为多相界面反应和物质传输提供高效稳定的场所。Pickering乳液的乳滴结构和性质与固体颗粒的尺寸形貌及表面性质密不可分,通过调控固体颗粒本身或表面的性质可以赋予Pickering乳液特定的响应性功能,拓宽其应用领域。本文对近年来不同响应型（磁性、CO₂、pH、光、温度等响应型）的Pickering乳液的主要研究成果进行了综述,重点介绍了Pickering乳液的稳定性原理、响应型Pickering乳液的制备方法和结构调控策略,以及近年来Pickering乳液在物质分离提取中的应用研究进展,最后对智能响应型Pickering乳液应用研究的发展趋势进行了展望。     

One pot preparation of reduced graphene oxide (RGO) or Au (Ag) nanoparticle-RGO hybrids using chitosan as a reducing and stabilizing agent and their use in methanol electrooxidation

An environment-friendly approach to synthesizing reduced graphene oxide (RGO) was developed by using chitosan (CS) as both a reducing and a stabilizing agent. Factors that affect the reduction of graphene oxide (GO), such as the ratio of CS/GO, pH and temperature, were explored to obtain optimum reaction conditions. The RGO was characterized with UV visible absorption spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction spectroscopy, thermo-gravimetric analysis, and X-ray photoelectron spectroscopy and transmission electron microscopy. Analysis shows that CS macromolecules can efficiently reduce GO at a comparatively low temperature and their adsorption onto the RGO nanosheets allows a stable RGO aqueous dispersion to be formed. Since CS is a natural, nontoxic and biodegradable macromolecule, this approach provides a new green method for GO reduction that would facilitate the large scale production of RGO, which has great value for graphene applications. Moreover, CS can reduce GO and AgNO₃ (or HAuCl₄) in one pot to obtain Ag nanoparticle-RGO hybrids or Au nanoparticle-RGO hybrids that exhibit good electrochemical activity.     

基于纤维素纳米晶稳定的亚微米Pickering乳液制备

与传统表面活性剂稳定的乳液相比,固体纳米颗粒稳定的Pickering乳液具有较强的界面稳定性、多功能性、低毒性等优势,在生物医药领域具有较大的应用潜力。而相较于尺寸较大的微米级Pickering乳液,亚微米Pickering乳液具有更大的比表面积、更有效的递送效率,有望进一步拓展Pickering乳液在生物医药领域的应用。但由于Pickering乳液的制备影响因素众多,且相互制约,刚性的固体颗粒难以在较小的有限油水界面排布,增加了亚微米Pickering乳液的制备难度。本工作以制备稳定的亚微米Pickering乳液为研究目标,采用具有良好生物相容性的天然多糖–纤维素纳米晶(CNCs)为颗粒乳化剂,角鲨烯作为油相,考察了颗粒浓度、油水比例、水相成分、超声时间及频率对Pickering乳液粒径分布及稳定性的影响,最终得到了具有良好的储存稳定性和抗离心稳定性的粒径为638.7?8.40 nm的亚微米Pickering乳液(CNCs-PE)。通过激光共聚焦显微镜证实了CNCs吸附在油水界面,形成了Pickering乳液结构。利用CCK-8法评价了CNCs和CNCs-PE的细胞毒性,结果表明,两者都具有良好的细胞安全性。此外,将其用于吸附模型抗原OVA,吸附率达到约80%,且肌肉注射部位的切片结果也表明其注射安全性良好。此结果为亚微米Pickering乳液进一步研究提供了参考,并有望拓展CNCs稳定的亚微米Pickering乳液在生物医药领域的应用。     

层层自主装法制备GO杂化多壁微胶囊及其稳定性的影响探究

氧化石墨烯(GO)纳米粒子片层结构可用作Pickering乳液分散剂,芯材离子液体的稳定分散是制备微胶囊的关键,以GO作为Pickering乳液分散剂,并设计以GO为单一壁材制备了自润滑微胶囊,考虑到GO具有优异的耐摩擦性能和良好的热稳定性,再通过层层自主装法,使得壁层之间可以通过静电吸附和氢键作用连接,从而合成多层GO壁自润滑微胶囊。重点研究pH值、油水比、GO的质量浓度对GO的Pickering乳液的影响及GO杂化多壁微胶囊制备的最佳稳定条件。实验证明在pH值为2,油水质量比为5%,GO质量浓度为0.1 mg/L的实验条件下制备的微胶囊最佳。     

阴离子多聚糖修饰Pickering乳液的制备及表征

为了提高淀粉纳米晶(SNC)与季铵盐壳聚糖(QCS)共同稳定的Pickering乳液在p H变化时的稳定性,以阴离子多聚糖海藻酸钠和果胶为原料,通过静电作用对乳液进行表面修饰,制得两种Pickering乳液。通过测定乳液粒径、Zeta电位和体外消化情况,对乳液的稳定性和消化特性进行了表征。结果显示:当水相中海藻酸钠和果胶质量分数均为0.1%(以水相为基准)时,修饰后的两种Pickering乳液在p H=2~7内均能保持粒径不变,且该乳液在25℃下放置90 d,粒径无变化,无乳析现象发生。此外,在体外模拟消化条件下,阴离子多聚糖的加入还能抑制Pickering乳液中油脂和淀粉的消化。     

高亲水性纳米二氧化硅颗粒稳定Pickering乳液

用未修饰的高亲水性纳米二氧化硅颗粒(SiO2 NPs)在其等电点附近制备Pickering乳液。结果表明,等电点(pH 2.7)条件下SiO2 NPs借助高能均质与油水界面剧烈混合,并在范德华引力的驱动下以弱吸附的状态在界面处负载,从而稳定得到O/W型Pickering乳液。增加SiO2 NPs的浓度或减小油相体积分数可提高单位油滴界面的颗粒负载率,增大连续相黏度并促进乳液液滴之间形成三维网络结构从而提高乳液稳定性。通过调节连续相的pH以促进SiO2 NPs表面的硅烷醇发生质子化与去质子化的转变,实现乳液多次pH响应循环。     

Facile fabrication of nanocomposite microspheres with polymer cores and magnetic shells by Pickering suspension polymerization

Pickering suspension polymerization was used to prepare magnetic polymer microspheres that have polymer cores enveloped by shells of magnetic nanoparticles. Styrene was emulsified in an aqueous dispersion of Fe₃O₄ nanoparticles using a high shear. The resultant Pickering oil-in-water (o/w) emulsion stabilized solely by magnetic nanoparticles was easily polymerized at 70 °C without stirring. Fe₃O₄ nanoparticles act as effective stabilizers during polymerization and as building blocks for creating the organic–inorganic hybrid nanocomposite after polymerization. The fabricated magnetic nanocomposites were characterized by FTIR, XRD, TGA, DSC, GPC, XPS and SEM. The structures of the polymer core and the nanoparticle shell were analyzed. We investigated the effects on the products of the weight of Fe₃O₄ nanoparticles used to stabilize the original Pickering emulsions. Pickering suspension polymerization provides a new route for the synthesis of a variety of hybrid nanocomposite microspheres with supracolloidal structures.     

Janus graphene oxide nanosheets prepared via Pickering emulsion template

Janus graphene oxide (GO) nanosheets functionalized by amino-containing chemicals were prepared via Pickering emulsion template. A wax-in-water Pickering emulsion was used to mask one side of GO nanosheets in order to achieve asymmetric chemical functionalization. Janus particles were obtained by removing the oil phase. The successful reaction of epoxy groups on the surface of GO with amino-containing chemicals was confirmed by Fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA). The asymmetric surface structure of Janus GO nanosheets was detected by atomic force microscope (AFM) and X-ray diffraction (XRD). The efficient stabilization of an oil-in-water Pickering emulsion by Janus GO was proved. Polymer microspheres fabricated by using Janus GO as Pickering stabilizer had a more hydrophilic surface compared with those stabilized by symmetrically modified GO.     

Evaluation of Pickering emulsions stabilized with nano-cellulose and nano-chitin treated with deep eutectic solvent

Developing bio-friendly and degradable Pickering emulsifiers as surfactants to replace traditional surfactants with bio-toxicity is imperative in the food, coating, cosmetics, and pharmaceutical industries. Nanocellulose and chitin can be used directly as an emulsifier to prepare Pickering o/w emulsions. As the concentration of nanoparticles increases, the stability of the emulsion also increases, and an overly large nanoparticle aspect ratio is not conducive to the stabilization of the emulsion. In comparison, nanocellulose-prepared Pickering emulsion has improved stability. Of these, nanocellulose prepared by DES with a molar ratio of 3:1 to LA:CC has been shown to have the best stability when used to equilibrate the oil/water mass ratio of 2/8. The Zeta potential is −38.4 mV, and the size of the droplets is the most uniform. With a mean droplet diameter of 770 nm. This study had certain research significance and reference value for the development of bio-friendly surfactants.     

Microstructure and properties of carbon fiber sized with pickering emulsion based on graphene oxide sheets and its composite with epoxy resin

The Graphene oxide (GO) sheets were used for preparing the epoxy resin Pickering emulsion. The particle size and the zeta potential of the Pickering emulsion were measured to evaluate its stability. The stable emulsion could be served as the film former of sizing agent for carbon fiber (CF). The effect of the Pickering emulsion stabilized by GO sheets on the properties of CF and the interfacial adhesion property of CF reinforced composite were investigated. Scanning electron microscopy (SEM) images showed that there existed a layer of sizing agent film with GO sheets evenly on the CF surface. Abrasion resistance and stiffness values of CF were tested and the results indicated that the sized CF conformed to the requirement of CF handleability. The interlaminar shear strength (ILSS) test indicated that the interfacial adhesion of the composite could be greatly improved. The fracture surfaces of CF composites were examined by SEM after ILSS tests. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42285.     

Facile solid-state synthesis of Ag/graphene oxide nanocomposites as highly active and stable catalyst for the reduction of 4-nitrophenol

A facile solid-state synthetic route was used to fabricate graphene oxide (GO) decorated with Ag nanoparticles. Ag/GO nanocomposites were prepared by reducing silver acetate with ascorbic acid in the presence of GO at ambient conditions. The characterization results showed that Ag nanoparticles with an average diameter of ~ 50 nm were well dispersed on the surface of GO nanosheets. Moreover, an application of the obtained Ag/GO nanocomposites as a catalyst in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol by NaBH₄ was demonstrated. The Ag/GO nanocomposites exhibited high activity and stability for the catalytic reduction of 4-NP.     

纳米Fe3O4稳定的Pickering型ASA乳液

利用纳米Fe₃O₄作为稳定剂和乳化剂来制备Pickering型ASA（alkenyl succinic anhydride） 施胶乳液,并研究了固体颗粒浓度、油水比、水分散相pH对乳液类型、稳定性、形态及施胶性能的影响。结果表明,纳米Fe₃O₄能够乳化制备均一稳定的Pickering型ASA乳液。乳液在室温下静置稳定,析出油相体积分数随固体颗粒用量的增加而增大,随油水比的增大而减小。油水比为2：1,水分散相浓度为0.1%（质量分数）时制备的ASA乳液稳定性最佳。固体颗粒部分吸附在油/水界面处,部分分散在分散相中,随分散相中固体颗粒浓度的增加,乳液稳定性变差。乳液静置分层之前,ASA发生部分水解。在放置1 h后用于纸页浆内施胶,随ASA乳液用量的增加,纸页表面接触角逐渐增大,且纸页表面粗糙度下降。在ASA的添加量为1.0%（质量分数）时,纸页表面接触角达到93.5°,纸页表面粗糙度为15.924 μm。     

疏水改性核壳结构颗粒对Pickering乳液的稳定作用

为了探究固体颗粒对乳液的稳定作用,采用双亲染料分子罗丹明B对核壳结构的Fe_3O_4@SiO_2纳米颗粒进行疏水改性,并将改性后的纳米颗粒作为稳定剂制备Pickering乳液。通过Zeta电位、FTIR、XRD、SEM、接触角测量、光学显微镜、电导率仪对Fe_3O_4@SiO_2纳米颗粒以及Pickering乳液的结构、形貌和性能进行表征与分析,结果表明:制备的纳米颗粒粒径小,约为150 nm,为单分散球形核壳结构;罗丹明B成功修饰到Fe_3O_4@SiO_2纳米颗粒表面,改性后颗粒接触角由30°增加至120°;随乳化剂颗粒质量浓度的增加,制备的乳液液滴的粒径减小。另外,所得Pickering乳液具有良好的磁场响应性,可通过外加磁场实现对乳液稳定性的可逆调控,且此过程可重复3次以上。     

Excellent electrocatalytic performance of Pt nanoparticles on reduced graphene oxide nanosheets prepared by a direct redox reaction between Na2PtCl4 and graphene oxide

A simple and environment-friendly method was used to prepare Pt/reduced graphene oxide (Pt/RGO) hybrids. This approach used a redox reaction between Na₂PtCl₄ and graphene oxide (GO) nanosheets and a subsequent thermal reduction of the material at 200 °C for 24 h in a vacuum oven. In contrast to other methods that use an additional reductant to prepare Pt nanoparticles, the Pt²⁺ was directly reduced to Pt⁰ in the GO solution. GO was used as the reducing agent, the stabilizing agent and the carrier. The resulting Pt/RGO hybrid was characterized by X-ray diffraction, thermo-gravimetric analysis, X-ray photoelectron spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. Electrochemical measurements showed that the Pt/RGO hybrids exhibit good activity as catalysts for the electro-oxidation of methanol and ethanol in acid media. Interestingly, the Pt/RGO hybrids showed better electrocatalytic activity and stability for the oxidation of methanol than Pt/C and Pt/RGO hybrids made from other Pt precursors. This indicates that the Pt/RGO hybrids should have great potential applications in direct methanol and ethanol fuel cells.     

Pickering emulsions stabilized with PANI-NP. Study of the thermoresponsive behavior under heating and radiofrequency irradiation

Micrometric Pickering emulsions in 1-octanol or cyclohexane were stabilized with water-dispersible electroactive polyaniline nanoparticles (PANI-NP). The emulsions were characterized by optical and electronic microscopy as well as spectroscopic techniques. It was demonstrated that nanoparticles maintain their functional properties (e.g., pH sensitivity and electromagnetic absorption) in the emulsion. Furthermore, as a proof of concept, smart Pickering emulsions employing PANI-NP stabilized with a thermosensitive polymer (PNIPAM) were obtained. The thermal behavior of the obtained structures was evaluated by turbidimetric techniques and an IR camera. The thermoresponsive emulsions have shown an important increment of the local temperature (>12°C) under radiofrequency (RF) irradiation. Phase transition of PNIPAM induced by heating or RF absorption provokes the breaking of the emulsions. In this context, the proposed systems herein could induce endothermal reactions carried out in organic solvents. Besides, Pickering emulsions formed by using electroactive PANI-NP could be applied in several medical or industrial applications.     

Conjugated polymer mediated synthesis of nanoparticle clusters and core/shell nanoparticles

Two water soluble conjugated polymers, poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and ammonium ion stabilized poly(phenylene vinylene) (P2), are found to be able to reduce noble metal ions to zero-valent metals via a direct chemical deposition technique. Au nanoparticle clusters can be obtained through reduction of Au³⁺ ions by PEDOT:PSS and the electronic coupling between them can be controlled by HAuCl₄ concentration. Core/shell Ag/polymer nanostructures are prepared from reduction of Ag⁺ ions by P2, which have a ppb detection limit for 4-MBA using surface-enhanced Raman spectroscopy (SERS). This conjugated polymer mediated synthesis of metal nanoparticles may open a new avenue for fabricating nanomaterials and nanocomposites with tunable optical properties that are dominated by their structure and electronic coupling between nanoparticles.     

High sensitivity surface enhanced Raman spectroscopy of R6G on in situ fabricated Au nanoparticle/graphene plasmonic substrates

Plasmonic gold nanoparticles (AuNP) with controllable dimensions have been fabricated in situ on graphene at moderately elevated temperature for high sensitivity surface enhanced Raman spectroscopy (SERS) of Rhodamine 6G (R6G) dye molecules. Significantly enhanced Raman signature of R6G dyes were observed on AuNP/graphene substrates as compared to the case without graphene with an improvement factor of 400%, which is remarkably greater than previous results obtained in ex situ fabricated SERS substrate. Simulation of localized electromagnetic field around AuNPs with and without the underneath graphene layer reveals an enhanced local electromagnetic field due to the plasmonic effect of AuNPs, while additional Ohmic loss occurs when graphene is present. The enhanced local electromagnetic field by plasmonic AuNPs is unlikely the dominant factor contributing to the observed high SERS sensitivity on R6G/AuNP/graphene substrate. Instead, the p-doped graphene, which is supported by the large positive Dirac point shift away from “zero” observed in AuNP/graphene field effect transistors, promotes SERS signals through enhanced molecule adsorption and non-resonance molecular–substrate chemical interaction.     

The construction of pseudo-Janus silica/surfactant assembly and their application to stabilize Pickering emulsions and enhance oil recovery

Nanoparticles with high surface energy and chemical activity have drawn substantial attention in petroleum industry. Recently, Janus nanoparticles exhibited tremendous potential in enhanced oil recovery (EOR) due to their asymmetric structures and properties. In this study, a series of amphiphilic pseudo-Janus@OTAB (PJ@C18) nanoparticles with different concentrations of stearyltrimethylammoium bromide (OTAB) were successfully fabricated. The structures and properties of PJ@C18 were characterized by Fourier transform infrared spectroscopy and ζ-potential measurements. Based on the emulsification experimental results, the interaction models and the self-assembly behavior between hydrophilic nanoparticles (SiO₂@NH₂) and OTAB molecules at the oil/water interface were proposed, which was further confirmed via the measurements of the contact angle and dynamic interfacial tension. Interestingly, it was found that the change of pH value from 7.5 to 4.0 caused the type reversal of the PJ@C18-1000 stabilized Pickering emulsions. Furthermore, the PJ@C18-1000 stabilized Pickering emulsion system with excellent salt and temperature tolerances (10000 mg∙L^–1, 90 °C) significantly improved the oil recovery in the single-tube (more than 17%) and double-tube (more than 25%) sand pack model flooding tests. The findings of this study could help to better understand the construction mechanism of pseudo-Janus silica/surfactant assembly and the potential application of PJ@C18-1000 stabilized Pickering emulsions for EOR.     

Improved electrochemical performance of graphene oxide supported vanadomanganate (IV) nanohybrid electrode material for supercapacitors

Graphene oxide (GO)-supported polyoxometalates (POMs) have been considered as promising electrode materials for energy storage applications due to their ability to undergo fast and reversible redox reactions. Herein, vanadomanganate-GO composites (K₇Mn^IVV₁₃O₃₈.18H₂O-GO with 2:1 and 4:1 ratio) were investigated for use as potential electrode materials in supercapacitors (SCs). The K₇Mn^IVV₁₃O₃₈.18H₂O (MnV₁₃) was synthesized and anchored on GO through electron transfer interaction and electrostatic interaction to make the composite electrodes for the present study. All synthesized electrode materials were fully characterized by various techniques, e.g., Fourier Transform Infrared (FTIR) Spectroscopy, Powder X-ray Diffraction (XRD), Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy (SEM/EDS) and High Resolution-Transmission Electron Microscopy (HR-TEM). The electrochemical properties of MnV₁₃/GO composites with different MnV₁₃/GO ratios were investigated by two-electrode cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) in different electrolytes. The MnV₁₃/GO composite of ratio 2:1 in 1 M LiCl electrolyte and that of ratio 4:1 in 1 M Na₂SO₄ electrolyte showed significant specific capacitance values of 269.15 F/g and 387.02 F/g, respectively and energy density of 37.38 Wh/kg and 53.75 Wh/kg, respectively for a scan rate of 5 mV/s. Interestingly, the 1:1 (MnV₁₃/GO) composite in 1 M Na₂SO₄ and 1 M LiCl electrolytes showed very low specific capacitance values as the deposition of MnV₁₃ on GO was not sufficient, as indicated by FTIR and SEM. Thus, it is evident that the specific capacitance value of these composite materials depends on the amount of MnV₁₃ deposited on GO and these composite materials exhibit the potential to improve the performance of GO-based SCs.