表面活性剂-纳米粒子协同稳定Pickering乳液的双相反转实验设计

本实验以表面活性剂原位改性纳米粒子协同稳定Pickering乳液为研究对象,通过对乳液的双相反转行为研究,探究表面活性剂分子在纳米粒子表面的吸附模式,加深学生对胶体与界面化学领域相关原理的理解,培养学生综合实验能力和分析推理能力。     

粒子与聚合物协同稳定高内相Pickering乳液

选用二氧化硅纳米粒子(H30)和聚(乳酸-羟基乙酸)共聚物(PLGA)为复合稳定剂, 成功制备出内相体积分数高达90%的高内相Pickering 乳液. 对照实验表明: 单独用H30粒子作稳定剂, 内相体积分数上限为75%; 单独用PLGA 作稳定剂, 发生严重相分离, 不能形成乳液. 无机纳米粒子与聚合物之间的协同作用在制备高内相乳液的过程中起到了关键作用. 因此, 使用无机粒子和聚合物作为混合稳定剂制备高内相乳液是一种新型而有效的方法.     

单分子层保护纳米 Au 粒子表面配位催化剂的制备及其应用

 贵金属纳米粒子由于其小尺寸效应而表现出特殊的催化性能. 综述了纳米 Au 粒子表面配位催化剂的制备方法及其在催化中的应用. 由于 Au 可与硫化物形成配位键, 所以硫化物可在 Au 表面形成有序单分子膜. 单分子膜保护的 Au 纳米粒子具有非常好的溶解性、分散性、稳定性, 以及由不同的表面功能团而导致的不同的催化性能. 该催化体系兼具均相催化剂和多相催化剂的特点, 这对开发新型催化剂具有重要的理论和实际意义.     

Recycling Functional Colloids and Nanoparticles

The stability and separation of colloids and nanoparticles has been addressed in numerous studies. Most of the work reported to date requires high cost, energy intensive approaches such as ultracentrifugation and solvent evaporation to recover the particles. At this point of time, when green science is beginning to make a real impact, it is vital to achieve efficient and effective separation and recovery of colloids to provide environmental and economic benefits. This article explores recent advances in strategies for recycling and reusing functional nanomaterials, which indicate new directions in lean engineering of high‐value nanoparticles, such as Au and Pd.     

Hollow microspheres with covalent‐bonded colloidal and polymeric shell by Pickering emulsion polymerization

Hollow microspheres with SiO₂/polymer binary shell were fabricated from Pickering emulsion stabilized solely by methacryloxypropyltrimethoxysilane‐modified SiO₂ particles, and were characterized by optical microscopy, scanning electron microscopy, Fourier transformation infrared spectrum, thermogravimetric analysis (TGA), and energy dispersive X‐ray spectroscopy. The microspheres were templated by the Pickering droplets and the inner structure was affect by the proportion of crosslinking reagent. TGA result indicated that 60.3% of polymer in the shell was connected with SiO₂ by covalent bond which was formed by copolymerization of styrene and the reactive C?C group on SiO₂ stabilizer. Copyright © 2011 John Wiley & Sons, Ltd.     

One‐Pot Fabrication of Rattle‐Like Capsules with Multicores by Pickering‐Based Polymerization with Nanoparticle Nucleation

Rattle‐like polymer capsules with multicores in one shell are facilely fabricated by oil‐in‐water Pickering emulsion polymerization for the first time. The oil phase contains hydrophobic silica nanoparticles dispersed in polymerizable monomer, styrene, and unpolymerizable solvent, hexadecane. The multicore rattle‐like capsules are facilely produced after the polymerization of monomers in the oil droplets. The key point of this one‐pot method lies in the nucleation of hydrophobic silica and the phase separation between the resulting polystyrene and hexadecane. The influences of the contents of silica, hexadecane, cross‐linker, and stabilizer on the structure and morphology of rattle‐like capsules are systematically investigated. Moreover, functionalization of the rattle‐like capsules can be developed easily by varying hydrophobic nucleation nanoparticles in the oil phase. This work opens up a new route to fabricate multilevel capsules or spheres.

     

A Facile Strategy for Catalyst Separation and Recycling Suitable for ATRP of Hydrophilic Monomers Using a Macroligand

How to simply and efficiently separate and recycle catalyst has still been a constraint for the wide application of atom transfer radical polymerization (ATRP), especially for the polymerization systems with hydrophilic monomers because the polar functional groups may coordinate with transition metal salts, resulting in abundant catalyst residual in the resultant water‐soluble polymers. In order to overcome this problem, a latent‐biphasic system is developed, which can be successfully used for ATRP catalyst separation and recycling in situ for various kinds of hydrophilic monomers for the first time, such as poly(ethylene glycol) monomethyl ether methacrylate (PEGMA), 2‐hydroxyethyl methacrylate (HEMA), 2‐(dimethylamino)ethyl methacrylate (DMAEMA), N,N‐dimethyl acrylamide (DMA), and N‐isopropylacrylamide (NIPAM). Herein, random copolymer of octadecyl acrylate (OA), MA‐Ln (2‐(bis(pyridin‐2‐ylmethyl)amino)ethyl acrylate), and POA‐ran‐P(MA‐Ln) is designed as the macroligand, and heptane/ethanol is selected as the biphasic solvent. Copper(II) bromide (CuBr₂) is employed as the catalyst, PEG‐bound 2‐bromo‐2‐methylpropanoate (PEG₃₅₀‐Br) as the water‐soluble ATRP initiator and 2,2′‐azobis(isobutyronitrile) (AIBN) as the azo‐initiator to establish an ICAR (initiators for continuous activator regeneration) ATRP system. Importantly, well‐defined water‐soluble polymers are obtained even though the recyclable catalyst is used for sixth times.

     

Thermal and pH Dual Responsive Copolymer and Silver Nanoparticle Composite for Catalytic Application

N‐Isopropylacrylamide and vinyl imidazole copolymer, P(NIPAM‐co‐VI), was synthesized by free radical emulsion polymerization. Then, the copolymer and silver nanoparticle composite, P(NIPAM‐co‐VI)‐Ag, was prepared by in situ reduction of AgNO₃ with NaBH₄. Due to the coexistence of thermal‐responsive PNIPAM and pH‐responsive PVI, P(NIPAM‐co‐VI) and P(NIPAM‐co‐VI)‐Ag exhibited both thermal and pH responsibility, their size would change while altering the temperature or pH of the circumvent. Their thermal and pH dual responsive properties were studied by dynamic light scattering (DLS). P(NIPAM‐co‐VI)‐Ag could be stably dispersed in water at a pH range from 3.0 to 9.3, which is favorable to use P(NIPAM‐co‐VI)‐Ag as a catalyst in the reduction reaction of p‐nitrophenol. The reaction rate constant (k_app) increased with the decrease of pH or the increase of VI content in the copolymer.     

Development of Highly Effective Nanoparticle Spinel Catalysts for Aerobic Oxidation of Benzylic Alcoho1s

Spinel catalyst MnFe1.8Cu0.15Ru0.05O4 with partcle size of about 42nm is an effective heterogeneous catalyst for the oxidation of benzylic alcobols.The substitution of Fe for Cu improves its catalytic activity.Based on the characterization of BET,XPS and EXAFS,two factors influencing the structure and texture of the catalyst cauesd by the substitution of Cu for Fe may be assumed:physical factor responsible for the increasing of surface area；chemical factor responsible for the transformation of Ru-O bonds to Ru=O boods.β-Elimination is considered to be an important step in the reaction.     

Development of Highly Effective Nanoparticle Spinel Catalysts for Aerobic Oxidation of Benzylic Alcohols

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Self‐Assembled Colloidal Particle Clusters from In Situ Pickering‐Like Emulsion Polymerization via Single Electron Transfer Mechanism

A simple route is reported to synthesize colloidal particle clusters (CPCs) from self‐assembly of in situ poly(vinylidene fluoride)/poly(styrene‐co‐tert‐butyl acrylate) [PVDF/P(St‐co‐tBA)] Janus particles through one‐pot seeded emulsion single electron transfer radical polymerization. In the in situ Pickering‐like emulsion polymerization, the tBA/St/PVDF feed ratio and polymerization temperature are important for the formation of well‐defined CPCs. When the tBA/St/PVDF feed ratio is 0.75 g/2.5 g/0.5 g and the reaction temperature is 35 °C, relatively uniform raspberry‐like CPCs are obtained. The hydrophobicity of the P(St‐co‐tBA) domains and the affinity of PVDF to the aqueous environment are considered to be the driving force for the self‐assembly of the in situ formed PVDF/P(St‐co‐tBA) Janus particles. The resultant raspberry‐like CPCs with PVDF particles protruding outward may be promising for superhydrophobic smart coatings.

     

Well‐Defined Iron Complexes as Efficient Catalysts for “Green” Atom‐Transfer Radical Polymerization of Styrene,Methyl Methacrylate,and Butyl Acrylate with Low Catalyst Loadings and Catalyst Recycling

Environmentally friendly iron(II) catalysts for atom‐transfer radical polymerization (ATRP) were synthesized by careful selection of the nitrogen substituents of N,N,N‐trialkylated‐1,4,9‐triazacyclononane (R₃TACN) ligands. Two types of structures were confirmed by crystallography: “[(R₃TACN)FeX₂]” complexes with relatively small R groups have ionic and dinuclear structures including a [(R₃TACN)Fe(μ‐X)₃Fe(R₃TACN)]⁺ moiety, whereas those with more bulky R groups are neutral and mononuclear. The twelve [(R₃TACN)FeX₂]_n complexes that were synthesized were subjected to bulk ATRP of styrene, methyl methacrylate (MMA), and butyl acrylate (BA). Among the iron complexes examined, [{(cyclopentyl)₃TACN}FeBr₂] ( 4 b ) was the best catalyst for the well‐controlled ATRP of all three monomers. This species allowed easy catalyst separation and recycling, a lowering of the catalyst concentration needed for the reaction, and the absence of additional reducing reagents. The lowest catalyst loading was accomplished in the ATRP of MMA with 4 b (59 ppm of Fe based on the charged monomer). Catalyst recycling in ATRP with low catalyst loadings was also successful. The ATRP of styrene with 4 b (117 ppm Fe atom) was followed by precipitation from methanol to give polystyrene that contained residual iron below the calculated detection limit (0.28 ppm). Mechanisms that involve equilibria between the multinuclear and mononuclear species were also examined.     

用Dawson型聚氧钨酸乳液催化氧化燃油超深度脱硫

合成了Dawson型聚氧钨酸乳液催化剂Q18P2W18,Q18P2W17,和Q18P2W12.采用红外光谱和固体核磁技术对其进行了表征,并用于温和条件下H2O2氧化4,6-二甲基二苯并噻吩(4,6-DMDBT)、二苯并噻吩(DBT)、苯并噻吩(BT)和2,5-二甲基噻吩(2,5-DMT)等含硫化合物的反应中.结果表明,...     

溶剂诱导翻转Pickering乳液用于原位循环使用酶催化剂

Separation and recycling of catalysts are crucial for realizing the objectives of sustainable and green chemistry but remain a great challenge, especially for enzyme biocatalysts. In this work, we report a new solvent-induced reversible inversion of Pickering emulsions stabilized by Janus mesosilica nanosheets (JMSNs), which is then utilized as a strategy for the in situ separation and recycling of enzymes. The interfacial active solid particle JMSNs is carefully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption experiments, Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA).The JMSNs are demonstrated to show order-oriented mesochannels with a large specific surface area, and the hydrophobic octylgroup is selectively modified on one side of the nanosheets. Furthermore, the inversion is found to be a fast process that is strongly dependent on the interfacial activity of the solid emulsifier JMSNs. Such a phase inversion is also a general process that can be realized in various oil/water phasic systems, including ethyl acetate-water, octane-water, and cyclohexane-water systems. By carefully analyzing the capacity of JMSNs with different surface wettabilities for phase inversion, a triphase contact angle (θ) close to 90° and a critical oil-water ratio of 1 : 2 are identified as the key factors to achieve solvent-induced phase inversion via a catastrophic phase inversion mechanism. Importantly, this reversible phase inversion is suitable for the separation and recycling of enzyme biocatalysts that are sensitive to changes in the reaction medium. Specifically, during the reaction, the organic substrates are dissolved in the oil droplets and the water-soluble catalysts are dispersed in the water phase, while a majority of the product is released into the upper oil phase and the enzyme catalyst is confined inside the water droplets in the bottom layer after phase inversion. The perpendicular mesochannels of JMSNs provide a highly accessible reaction interface, and their excellent interfacial activity allows for more than 10 rounds of consecutive phase inversions by simply adjusting the ratio of oil to water in the system. Using the enzymatic hydrolysis kinetic resolution of racemic acetate as an example, our Pickering emulsion system shows not only a 3-fold enhanced activity but also excellent recyclability. Because no sensitive chemical reagents are used in this phase inversion process, the intrinsic activities of the catalysts can be preserved even after seven cycles. The current study provides an alternative strategy for the separation and recycling of enzymes, in addition to revealing a new innovative application for Janus-type nanoparticles.     

An Operationally Simple Method for Separating the Rare‐Earth Elements Neodymium and Dysprosium

Rare‐earth metals are critical components of electronic materials and permanent magnets. Recycling of consumer materials is a promising new source of rare earths. To incentivize recycling there is a clear need for simple methods for targeted separations of mixtures of rare‐earth metal salts. Metal complexes of a tripodal nitroxide ligand [{(2‐^tBuNO)C₆H₄CH₂}₃N]^3? (TriNOx^3?), feature a size‐sensitive aperture formed of its three η²‐(N,O) ligand arms. Exposure of metal cations in the aperture induces a self‐associative equilibrium comprising [M(TriNOx)thf]/ [M(TriNOx)]₂ (M=rare‐earth metal). Differences in the equilibrium constants (K_eq) for early and late metals enables simple Nd/Dy separations through leaching with a separation ratio S_Nd/Dy=359.     

Anisotropic Nanoparticles with Controllable Morphologies from Non‐Cross‐Linked Seeded Emulsion Polymerization

A simple and elegant approach to fabricate anisotropic P(VC‐co‐AAEM)/PS nanoparticles with controllable morphologies via emulsifier‐free seeded emulsion polymerization is presented. Non‐cross‐linked P(VC‐co‐AAEM) seeds with hydrophilic surface are first synthesized through copolymerization of vinyl chloride (VC) and acetoacetoxyethyl methacrylate (AAEM), which are used to prepare P(VC‐co‐AAEM)/PS NPs with multiple bulges by SEP of styrene. Electron microscopy observation indicates that the content of AAEM in seeds is crucial to control the phase separation and morphology of the composite NPs. Moreover, the thermodynamic immiscibility between PVC and PS is the driving force for the formation of PS bulges onto the P(VC‐co‐AAEM) seeds. The resultant anisotropic NPs with non‐cross‐linked feature may promisingly serve as compatibilizers for further polymer processing.

     

Capture and Recycling of Sortase A through Site‐Specific Labeling with Lithocholic Acid

Enzyme‐mediated protein modification often requires large amounts of biocatalyst, adding significant costs to the process and limiting industrial applications. Herein, we demonstrate a scalable and straightforward strategy for the efficient capture and recycling of enzymes using a small‐molecule affinity tag. A proline variant of an evolved sortase A (SrtA 7M) was N‐terminally labeled with lithocholic acid (LA)—an inexpensive bile acid that exhibits strong binding to β‐cyclodextrin (βCD). Capture and recycling of the LA‐Pro‐SrtA 7M conjugate was achieved using βCD‐modified sepharose resin. The LA‐Pro‐SrtA 7M conjugate retained full enzymatic activity, even after multiple rounds of recycling.