Wangqing Zhang

Bio: Wangqing Zhang is an academic researcher from Nankai University. The author has contributed to research in topics: Copolymer & Reversible addition−fragmentation chain-transfer polymerization. The author has an hindex of 37, co-authored 147 publications receiving 4389 citations.

Thermoresponsive Micellization of Poly(ethylene glycol)-b-poly(N-isopropylacrylamide) in Water

Abstract: Thermoresponsive micellization of poly(ethylene glycol)-b-poly(N-isopropylacrylamide) (PEG110-b-PNIPAM44) in water is studied by static light scattering and dynamic light scattering. The critical aggregation temperature of PEG110-b-PNIPAM44 is a little higher than homopolymer PNIPAM, and it depends on the block copolymer concentration, which increases from 33.7 to 38.4°C when the copolymer concentration decreases from 2.0 to 0.20 mg/mL. Above the critical aggregation temperature, thermoresponsive micellization occurs, and the resultant spherical micelles consist of a PNIPAM core and a PEG shell. The block copolymer concentration exerts a strong influence on the size and structure of the resultant micelles. Micellization of PEG110-b-PNIPAM44 at higher copolymer concentration favors formation of narrowly distributed, small, and dense micelles, while large, loose micelles or micellar clusters form at lower block copolymer concentration.

Yolk−Shell Catalyst of Single Au Nanoparticle Encapsulated within Hollow Mesoporous Silica Microspheres

Abstract: Synthesis and catalysis of yolk−shell microspheres containing a single Au nanoparticle core and a mesoporous shell of hollow mesoporous silica microspheres (HMSM) are reported. This synthesis employs polystyrene-co-poly(4-vinylpyridine) microspheres as both template to fabricate the HMSM shell through sol−gel process and scaffold to immobilize the Au nanoparticle. Since the single Au nanoparticle core is supernatant within the inert HMSM shell, the yolk−shell catalyst has minimum support effect and is a promising model to explore the origin of Au catalysis. Catalyzed reduction of 4-nitrophenol with NaBH4 demonstrates size-dependent induction or activation and size-dependent activity of the Au nanoparticle core of the yolk−shell catalyst.

Synthesis of Noble Metal Nanoparticles Embedded in the Shell Layer of Core−Shell Poly(styrene-co-4-vinylpyridine) Micospheres and Their Application in Catalysis

Abstract: The noble metal nanoparticles of Pd, Au, and Ag embedded in the shell layer of core−shell poly(styrene-co-4-vinylpyridine) micospheres were synthesized, and the catalytic activity of the shell-embedded Pd nanoparticles was investigated. To increase the accessible active site and therefore increase the catalytic activity of noble metal nanoparticles, the in situ synthesized noble metal nanoparticles are selectively immobilized in the outer shell layer of the core−shell poly(styrene-co-4-vinylpyridine) microspheres, which are synthesized by one-stage soap-free emulsion polymerization in water and contain a core of polystyrene and a coordinative shell of poly(4-vinylpyridine). It is found the Pd nanoparticles embedded in the shell layer of the core−shell micospheres are an efficient and easily reusable catalyst for Suzuki reactions performed in water.

Micellization of Thermo- and pH-Responsive Triblock Copolymer of Poly(ethylene glycol)-b-poly(4-vinylpyridine)-b-poly(N-isopropylacrylamide)

Abstract: Thermo- and pH-responsive micellization of poly(ethylene glycol)-b-poly(4-vinylpyridine)-b-poly(N-isopropylacrylamide) in water was studied. Micellization of the triblock copolymer, which was synthesized by sequential atom transfer radical polymerization of 4-vinylpyridine and N-isopropylacrylamide, occurred with combined stimulus of temperature and pH changes to form various morphological micelles. The copolymer existed as unimers at pH 2.0 and then associated into spherical core−corona micelles when pH increased from 2.0 to 6.5 at 25 °C. The critical aggregation temperature of the copolymer was about 34.6 °C, which was a little higher than poly(N-isopropylacrylamide). When the copolymer solution was heated above the critical aggregation temperature, the copolymer first self-assembled into compound core−corona micelles or micellar cluster and then converted into core−shell−corona micelles with pH increasing from 2.0 to 6.5. When temperature decreased from 50 to 25 °C, the core−shell−corona micelles furth...

Responsive catalysis of thermoresponsive micelle-supported gold nanoparticles

Abstract: The block copolymer poly(N-isopropylacrylamide)-b-poly(4-vinyl pyridine) (PNIPAM-b-P4VP) self-assembled into core-corona micelles with the P4VP block as core and the thermoresponsive PNIPAM block as corona in water. The diameter of the micelles was about 40 nm and the lower critical solution temperature (LCST) was about 32 °C. Gold nanoparticles of size ranging from 2 to 4 nm were loaded in the micelles to form a responsive catalyst, the activity of which could be modulated due to the thermoresponsive PNIPAM. Below LCST, the PNIPAM chains were hydrophilic and the reactants could easily diffuse through the PNIPAM corona to reach the surface of the gold nanoparticles. Within this temperature range, the catalytic activity of the micelle-supported gold nanoparticles increased with the increase in temperature. Above LCST, the PNIPAM chains collapsed to form a hydrophobic barrier on the gold nanoparticles, which decelerated diffusion of the reactants. Within this temperature range, the activity of the micelle-supported gold nanoparticles decreased with the increase in temperature until to a minimum constant at about 38 °C.

Atomically Precise Clusters of Noble Metals: Emerging Link between Atoms and Nanoparticles

Abstract: Atomically precise pieces of matter of nanometer dimensions composed of noble metals are new categories of materials with many unusual properties. Over 100 molecules of this kind with formulas such as Au25(SR)18, Au38(SR)24, and Au102(SR)44 as well as Ag25(SR)18, Ag29(S2R)12, and Ag44(SR)30 (often with a few counterions to compensate charges) are known now. They can be made reproducibly with robust synthetic protocols, resulting in colored solutions, yielding powders or diffractable crystals. They are distinctly different from nanoparticles in their spectroscopic properties such as optical absorption and emission, showing well-defined features, just like molecules. They show isotopically resolved molecular ion peaks in mass spectra and provide diverse information when examined through multiple instrumental methods. Most important of these properties is luminescence, often in the visible–near-infrared window, useful in biological applications. Luminescence in the visible region, especially by clusters prot...

Synthesis, Properties, and Applications of Hollow Micro-/Nanostructures

Abstract: In this Review, we aim to provide an updated summary of the research related to hollow micro- and nanostructures, covering both their synthesis and their applications. After a brief introduction to the definition and classification of the hollow micro-/nanostructures, we discuss various synthetic strategies that can be grouped into three major categories, including hard templating, soft templating, and self-templating synthesis. For both hard and soft templating strategies, we focus on how different types of templates are generated and then used for creating hollow structures. At the end of each section, the structural and morphological control over the product is discussed. For the self-templating strategy, we survey a number of unconventional synthetic methods, such as surface-protected etching, Ostwald ripening, the Kirkendall effect, and galvanic replacement. We then discuss the unique properties and niche applications of the hollow structures in diverse fields, including micro-/nanocontainers and rea...

Transition metal-catalyzed living radical polymerization : toward perfection in catalysis and precision polymer synthesis

Abstract: 2.1.6. Tacticity and Sequence: Advanced Control 4967 2.2. Transition Metal Catalysts 4967 2.2.1. Overviews of Catalysts 4967 2.2.2. Ruthenium 4967 2.2.3. Copper 4971 2.2.4. Iron 4971 2.2.5. Nickel 4975 2.2.6. Molybdenum 4975 2.2.7. Manganese 4976 2.2.8. Osmium 4976 2.2.9. Cobalt 4976 2.2.10. Other Metals 4976 2.3. Cocatalysts (Additives) 4977 2.3.1. Overview of Cocatalysts 4977 2.3.2. Reducing Agents 4977 2.3.3. Free Radical Initiators 4977 2.3.4. Metal Alkoxides 4977 2.3.5. Amines 4978 2.3.6. Halogen Source 4978 2.4. Initiators 4978 2.4.1. Overview of Initiators: Scope and Design 4978 2.4.2. Alkyl Halides 4978 2.4.3. Arenesulfonyl Halides 4979 2.4.4. N-Chloro Compounds 4979 2.4.5. Halogen-Free Initiators 4979 2.5. Solvents 4980 2.5.1. Overview of Solvents 4980 2.5.2. Catalyst Solubility and Coordination of Solvent 4981 2.5.3. Environmentally Friendly Solvents 4981 2.5.4. Water 4981 2.5.5. Catalytic Solvents: Catalyst Disproportionation 4981