Weikun Li

Encapsulation of Nanoparticles in Block Copolymer Micellar Aggregates by Directed Supramolecular Assembly

Incorporation of inorganic nanoparticles (NPs) into selfassembled block copolymers offers a powerful route for the formation of hybrid materials with desired optical, electronic, and magnetic properties through the choice of NPs and their distribution in polymer assemblies. Nanostructured block copolymer domains act as a scaffold that directs not only the position of the NPs but also their orientation. NPs/polymer hybrid materials have been prepared in solution by incorporating one or multiple hydrophobic NPs into a hydrophobic core of spherical amphiphilic block copolymer micelles. Careful control of micellization conditions will allow other hydrophobic ingredients to co-assemble with the amphiphilic polymers, resulting in micelles that encapsulate therapeutic molecules and NPs for imaging and targeting. Cylindrical or wormlike micelles show particular interest in drug delivery because of their large core volume (per carrier) and elongated structures, which offer additional opportunities to control biodistribution and release profiles of therapeutic agents. The “precipitation method”, which is a practical way to incorporate NPs into micelles, does not easily allow the growth of extended wormlike micelles with NPs encapsulated in the core. Several groups have reported the successful incorporation of NPs into hydrophilic portions of wormlike micelles through electrostatic interaction of corona-forming blocks with NPs. Recently, we reported the encapsulation of iron oxide NPs within wormlike micelle cores through interfacial instabilities of emulsion droplets containing amphiphilic polymers. However, it is hard to achieve high loading and uniform dispersion of NPs in wormlike micelle cores. So far, precise control over NPs position in wormlike micelle cores with homogeneous distribution remains a challenge. Herein we introduce a simple, yet versatile approach for the encapsulation of NPs within wormlike micelle cores through directed supramolecular assembly. The concept for preparation of the hybrid nano-objects is illustrated in Figure 1a. Typically, polystyrene–poly(4-vinylpyridine) (PS20k–P4VP17k, volume fraction of PS fPS= 56%) and pentadecylphenol (PDP) were dissolved in chloroform to form PS–P4VP(PDP)x (x represents the ratio of PDP to 4VP

Understanding the Role of Gold Nanoparticles in Enhancing the Catalytic Activity of Manganese Oxides in Water Oxidation Reactions

The Earth-abundant and inexpensive manganese oxides (MnOx) have emerged as an intriguing type of catalysts for the water oxidation reaction. However, the overall turnover frequencies of MnOx catalysts are still much lower than that of nanostructured IrO2 and RuO2 catalysts. Herein, we demonstrate that doping MnOx polymorphs with gold nanoparticles (AuNPs) can result in a strong enhancement of catalytic activity for the water oxidation reaction. It is observed that, for the first time, the catalytic activity of MnOx/AuNPs catalysts correlates strongly with the initial valence of the Mn centers. By promoting the formation of Mn(3+) species, a small amount of AuNPs (<5%) in α-MnO2/AuNP catalysts significantly improved the catalytic activity up to 8.2 times in the photochemical and 6 times in the electrochemical system, compared with the activity of pure α-MnO2.

Shaping Functional Nano‐objects by 3D Confined Supramolecular Assembly

Nano-objects are generated through 3D confined supramolecular assembly, followed by a sequential disintegration by rupturing the hydrogen bonding. The shape of the nano-objects is tunable, ranging from nano-disc, nano-cup, to nano-toroid. The nano-objects are pH-responsive. Functional materials for example inorganic or metal nanoparticles are easily complexed onto the external surface, to extend both composition and microstructure of the nano-objects.

Multiresponsive Hydrogel Photonic Crystal Microparticles with Inverse-Opal Structure

Hydrogel photonic crystal microparticles (HPCMs) with inverse-opal structure are generated through a combination of microfluidic and templating technique. Temperature and pH responsive HPCMs have firstly been prepared by copolymerizing functional monomers, for example, N-isopropylacrylamide (NIPAm) and methacrylic acid (MAA). HPCMs not only show tunable color variation almost covering the entire wavelength of visible light (above 150 nm of stop-band shift) by simply tailoring temperature or pH value of the solution, but also display rapid response (less than 1 min) due to the small volume and well-ordered porous structure. Importantly, the temperature sensing window of the HPCMs can be enlarged by controlling the transition temperature of the hydrogel matrix, and the HPCMs also exhibit good reversibility and reproducibility for pH response. Moreover, functional species or particles (such as azobenzene derivative or magnetic nanoparticles) can be further introduced into the hydrogel matrix by using post-treatment process. These functionalized HPCMs can respond to the UV/visible light without significantly influencing the temperature and pH response, and thus, multiresponsive capability within one single particle can be realized. The presence of magnetic nanoparticles may facilitate secondary assembly, which has potential applications in advanced optical devices.

Facile Synthesis of Co3O4@CNT with High Catalytic Activity for CO Oxidation under Moisture-Rich Conditions

The catalytic oxidation reaction of CO has recently attracted much attention because of its potential applications in the treatment of air pollutants. The development of inexpensive transition metal oxide catalysts that exhibit high catalytic activities for CO oxidation is in high demand. However, these metal oxide catalysts are susceptible to moisture, as they can be quickly deactivated in the presence of trace amounts of moisture. This article reports a facile synthesis of highly active Co3O4@CNT catalysts for CO oxidation under moisture-rich conditions. Our synthetic routes are based on the in situ growth of ultrafine Co3O4 nanoparticles (NPs) (∼2.5 nm) on pristine multiwalled CNTs in the presence of polymer surfactant. Using a 1% CO and 2% O2 balanced in N2 (normal) feed gas (3-10 ppm moisture), a 100% CO conversion with Co3O4@CNT catalysts was achieved at various temperatures ranging from 25 to 200 °C at a low O2 concentration. The modulation of surface hydrophobicity of CNT substrates, other than direct surface modification on the Co3O4 catalytic centers, is an efficient method to enhance the moisture resistance of metal oxide catalysts for CO oxidation. After introducing fluorinated alkyl chains on CNT surfaces, the superhydrophobic Co3O4@CNT exhibited outstanding activity and durability at 150 °C in the presence of moisture-saturated feed gas. These materials may ultimately present new opportunities to improve the moisture resistance of metal oxide catalysts for CO oxidation.

Ligand‐Assisted Co‐Assembly Approach toward Mesoporous Hybrid Catalysts of Transition‐Metal Oxides and Noble Metals: Photochemical Water Splitting

A bottom-up synthetic approach was developed for the preparation of mesoporous transition-metal-oxide/noble-metal hybrid catalysts through ligand-assisted co-assembly of amphiphilic block-copolymer micelles and polymer-tethered noble-metal nanoparticles (NPs). The synthetic approach offers a general and straightforward method to precisely tune the sizes and loadings of noble-metal NPs in metal oxides. This system thus provides a solid platform to clearly understand the role of noble-metal NPs in photochemical water splitting. The presence of trace amounts of metal NPs (≈0.1 wt %) can enhance the photocatalytic activity for water splitting up to a factor of four. The findings can conceivably be applied to other semiconductors/noble-metal catalysts, which may stand out as a new methodology to build highly efficient solar energy conversion systems.

Encapsulation of pristine fullerene C60 within block copolymer micelles through interfacial instabilities of emulsion droplets

We report a facile and versatile strategy to encapsulate pristine fullerene (C60) within spherical or wormlike block copolymer micelles through interfacial instability of emulsion droplets. C60 and amphiphilic block copolymer polystyrene-b-poly(ethylene oxide) were firstly dispersed in chloroform. The resulting solution was emulsified with aqueous sodium dodecylsulfate solution by simply shaking it. The emulsion droplets were collected in an open container and the solvent was allowed to evaporate. During solvent evaporation, the emulsion droplets became unstable and broke into tiny droplets, i.e., interfacial instabilities occurred, triggering the formation of uniform spherical micelles with encapsulated fullerenes in the micellar cores. More interestingly, fullerene addition induced a morphological transition from cylindrical micelles to string-of-vesicles and then to spherical micelles with increasing fullerene contents of 5 wt%, 10 wt%, and 30 wt%, respectively. We show that the optical properties of the confined C60 molecules can be modified by varying the quantity of fullerenes in the micelles. In addition, poly(3-hexylthiophene) (P3HT) can be co-encapsulated with C60 into the micellar cores when P3HT was dissolved in the initial polymer solution prior to emulsification. Presence of C60 in the micellar cores induced fluorescence quenching of P3HT due to photoinduced energy transfer from electron-donating P3HT to electron-accepting C60 molecules. Hybrid micelles with well-controlled structures and components can be potentially useful in the area of photodynamic therapy and photovoltaics.

Self‐Assembly of Shaped Nanoparticles into Free‐Standing 2D and 3D Superlattices

This article describes a novel supramolecular assembly-mediated strategy for the organization of Au nanoparticles (NPs) with different shapes (e.g., spheres, rods, and cubes) into large-area, free-standing 2D and 3D superlattices. This robust approach involves two major steps: (i) the organization of polymer-tethered NPs within the assemblies of supramolecular comblike block copolymers (CBCPs), and (ii) the disassembly of the assembled CBCP structures to produce free-standing NP superlattices. It is demonstrated that the crystal structures and lattice constants of the superlattices can be readily tailored by varying the molecular weight of tethered polymers, the volume fraction of NPs, and the matrix of CBCPs. This template-free approach may open a new avenue for the assembly of NPs into 2D and 3D structures with a wide range of potential applications.