Kwok Wei Shah

Synthesis and multiple reuse of eccentric Au@TiO2 nanostructures as catalysts.

In this work, we have synthesized eccentric Au@TiO(2) core-shell nanostructures and demonstrated their multiple reuse in the catalytic reduction of 4-nitrophenol.

Composite Metal–Oxide Nanocatalysts

To incorporate new functionalities, various oxide materials can be composited with metal nanoparticles to form metal–oxide nanostructures, which are very promising for a wide range of applications. In this review, we summarize the recent developments in advanced synthesis of structure‐diversified core–shell, yolk–shell, Janus, and their combined metal–oxide nanostructures. We also summarize their representative catalytic applications including organic reduction and oxidation, CO oxidation, CO2 conversion, water–gas shift reaction, and water splitting. We discuss recyclable metal–oxide nanocatalysts with mesoporous, hollow, or multilayered structures. We highlight perspectives for their challenges ahead and opportunities for their widely used applications in plasmon localization enhanced photocatalysis, artificial enzyme catalysis, and catalytic biomass conversion.

Pyrrolophthalazine dione (PPD)-based donor–acceptor polymers as high performance electrochromic materials

A novel pyrrolophthalazine dione (PPD) acceptor was sophisticatedly designed and synthesized via an inverse electron demand Diels–Alder reaction, followed by aromatization with N-bromosuccinimide. The PPD moiety was incorporated into donor–acceptor type conjugated polymers through Stille coupling polymerization to yield a series of polymers P1–P3 with different linking groups, namely, thiophene, thieno[3,2-b]thiophene, and bithiophene. The polymers reveal excellent solubility in common organic solvents. Due to their low bandgaps of around 1.72–1.78 eV, the polymers show broad absorption that covers most of the visible region. All the polymers reveal electrochromism, switching between dark blue and transmissive sky blue states. In particular, P2 exhibits exceptional electrochromic properties with high optical contrasts of up to 34 and 71% in the visible and NIR regions, high coloration efficiencies of 471 and 651 cm2 C−1 respectively, as well as reasonable switching speeds and good long-term stability.

Optimized production of copper nanostructures with high yields for efficient use as thermal conductivity-enhancing PCM dopant

Copper nanostructures with a high yield are synthesized by a controlled disproportionation of CuCl in oleylamine reaction medium without the involvement of strong reducing agents adopted in conventional approaches. The highest copper yield (50%), a maximum theoretical value, is obtained by optimizing both the initial amount of CuCl added to the reaction medium and the reaction temperature. A potential use of the copper nanostructures in greatly enhancing thermal conductivity of a hydrated CaCl2·6H2O salt phase change material (PCM) is further demonstrated. A high thermal conductivity enhancement of the PCM (>50%) is achieved by doping a small amount (<0.2 wt%) of the copper nanostructures. The great enhancement with the use of a very small amount of the copper nanostructures makes the doping cost-effective for practical thermal energy storage applications.

Rapid Copper Metallization of Textile Materials: a Controlled Two-Step Route to Achieve User-Defined Patterns under Ambient Conditions

Throughout history earth-abundant copper has been incorporated into textiles and it still caters to various needs in modern society. In this paper, we present a two-step copper metallization strategy to realize sequentially nondiffusive copper(II) patterning and rapid copper deposition on various textile materials, including cotton, polyester, nylon, and their mixtures. A new, cost-effective formulation is designed to minimize the copper pattern migration on textiles and to achieve user-defined copper patterns. The metallized copper is found to be very adhesive and stable against washing and oxidation. Furthermore, the copper-metallized textile exhibits excellent electrical conductivity that is ~3 times better than that of stainless steel and also inhibits the growth of bacteria effectively. This new copper metallization approach holds great promise as a commercially viable method to metallize an insulating textile, opening up research avenues for wearable electronics and functional garments.

Perfluoropolyether/poly(ethylene glycol) triblock copolymers with controllable self-assembly behaviour for highly efficient anti-bacterial materials

A series of perfluoropolyether/poly(ethylene glycol) (PFPE/PEG) triblock copolymers PEG/PFPE/PEG (P1–P3) and PFPE/PEG/PFPE (P4–P5) were prepared via thiol–ene click reaction in high yields. Their chemical structures, molecular weights and thermal stability were characterized by 1H nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC) and thermogravimetric analysis (TGA), respectively. The spin coated polymer films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and a contact angle goniometer. The polymer P1–P4 showed a wrinkle-like surface morphology in the film state, but P5 exhibited a segregated morphology due to its poor solubility in the casting solvent. Polymers P1–P4 in thin film states displayed high hydrophilicity with water contact angles in the range of 10.2–12.3° and surface energy of 52.7–55.2 mN m−1 even though hydrophobic PFPE segments were present in the polymer backbone. The anti-bacterial properties of the spin-coated films (P1–P3) were tested against E. coli and S. aureus on a Si surface and remarkable anti-bacterial properties were observed for this series of polymers, particularly for P3 which almost completely prohibits the growth of E. coli and S. aureus, rendering this type of PEG/PFPE/PEG triblock polymer as high performance antimicrobial coating materials.

COLLOIDAL PREPARATION OF MONODISPERSE NANOCRYSTALS

In the field of nanoscience, the ability to prepare high-quality nanocrystals is crucial for fundamental research and technology development. Herein, we review a general route for the colloidal preparation of monodisperse nanocrystals, which is divided into five different stages, namely (i) nucleation, (ii) growth, (iii) Ostwald ripening, (iv) surfactant capping and (v) precipitation. Each of the five stages is discussed in detail to provide a comprehensive understanding of the mechanism behind nanocrystal formation and the subsequent processing steps. We put emphasis on the classical theories and experimental techniques that are most frequently practiced. These are useful for the successful design and fabrication of nanocrystals with properties that are beneficial for use in a plethora of technological applications.

Methods and Structures for Self-assembly of Anisotropic 1D Nanocrystals

In the nanoscience and nanotechnology, the study of nanocrystal self-assembly has been regarded as a key technology in leading future industrial development. The colloidal self-assembly techniques, particularly for one-dimensional (1D) building blocks, have been widely adopted for the systematic fabrication of functional nanocrystals and received an extensive research attention. However, the increase in the building blocks’ anisotropy, e.g. from sphere to rod/wire, has dramatically leveled up the difficulty in organizing them into ordered structures. To realize tailored 1D nanocrystal self-assembled structures, a profound understanding and detailed design of self-assembly mechanism and procedures are much needed. Here, a thorough review over 1D nanocrystal self-assembly methods and alignments are present to achieve large-scale functional structures. Through different techniques, such as evaporation, template, electric field, Langmuir-Blodgett film and chemical bonding, nanocrystals with various shapes can be self-assembled on substrates, at interfaces and in solutions. These assembled structures that have been achieved so far, can exhibit different degrees of alignments, such as stripe pattern as non-close-packed structure, horizontal, vertical alignments as close-packed monolayers, nematic, semectic alignments, AB stacking of vertical alignments, three-dimensional (3D) assembly as close-packed multilayers. In general, these self-assembly techniques can reach much small dimension and create microstructures that possess unique properties different from their individual building blocks.