Yihuang Chen

Noble metal–metal oxide nanohybrids with tailored nanostructures for efficient solar energy conversion, photocatalysis and environmental remediation

The controlled synthesis of nanohybrids composed of noble metals (Au, Ag, Pt and Pd, as well as AuAg alloy) and metal oxides (ZnO, TiO2, Cu2O and CeO2) have received considerable attention for applications in photocatalysis, solar cells, drug delivery, surface enhanced Raman spectroscopy and many other important areas. The overall architecture of nanocomposites is one of the most important factors dictating the physical properties of nanohybrids. Noble metals can be coupled to metal oxides to yield diversified nanostructures, including noble metal decorated-metal oxide nanoparticles (NPs), nanoarrays, noble metal/metal oxide core/shell, noble metal/metal oxide yolk/shell and Janus noble metal–metal oxide nanostructures. In this review, we focus on the significant advances in tailored nanostructures of noble metal–metal oxide nanohybrids. The improvement in performance in the representative solar energy conversion applications including photocatalytic degradation of organic pollutants, photocatalytic hydrogen generation, photocatalytic CO2 reduction, dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are discussed. Finally, we conclude with a perspective on the future direction and prospects of these controllable nanohybrid materials.

Meniscus-assisted solution printing of large-grained perovskite films for high-efficiency solar cells

Control over morphology and crystallinity of metal halide perovskite films is of key importance to enable high-performance optoelectronics. However, this remains particularly challenging for solution-printed devices due to the complex crystallization kinetics of semiconductor materials within dynamic flow of inks. Here we report a simple yet effective meniscus-assisted solution printing (MASP) strategy to yield large-grained dense perovskite film with good crystallization and preferred orientation. Intriguingly, the outward convective flow triggered by fast solvent evaporation at the edge of the meniscus ink imparts the transport of perovskite solutes, thus facilitating the growth of micrometre-scale perovskite grains. The growth kinetics of perovskite crystals is scrutinized by in situ optical microscopy tracking to understand the crystallization mechanism. The perovskite films produced by MASP exhibit excellent optoelectronic properties with efficiencies approaching 20% in planar perovskite solar cells. This robust MASP strategy may in principle be easily extended to craft other solution-printed perovskite-based optoelectronics.

Hairy Uniform Permanently Ligated Hollow Nanoparticles with Precise Dimension Control and Tunable Optical Properties

The ability to tailor the size and shape of nanoparticles (NPs) enables the investigation into the correlation between these parameters and optical, optoelectronic, electrical, magnetic, and catalytic properties. Despite several effective approaches available to synthesize NPs with a hollow interior, it remains challenging to have a general strategy for creating a wide diversity of high-quality hollow NPs with different dimensions and compositions on demand. Herein, we report on a general and robust strategy to in situ crafting of monodisperse hairy hollow noble metal NPs by capitalizing on rationally designed amphiphilic star-like triblock copolymers as nanoreactors. The intermediate blocks of star-like triblock copolymers can associate with metal precursors via strong interaction (i.e., direct coordination or electrostatic interaction), followed by reduction to yield hollow noble metal NPs. Notably, the outer blocks of star-like triblock copolymers function as ligands that intimately and permanently passivate the surface of hollow noble metal NPs (i.e., forming hairy permanently ligated hollow NPs with superior solubility in nonpolar solvents). More importantly, the diameter of the hollow interior and the thickness of the shell of NPs can be readily controlled. As such, the dimension-dependent optical properties of hollow NPs are scrutinized by combining experimental studies and theoretical modeling. The dye encapsulation/release studies indicated that hollow NPs may be utilized as attractive guest molecule nanocarriers. As the diversity of precursors are amenable to this star-like triblock copolymer nanoreactor strategy, it can conceptually be extended to produce a rich variety of hairy hollow NPs with different dimensions and functionalities for applications in catalysis, water purification, optical devices, lightweight fillers, and energy conversion and storage.

A versatile strategy for uniform hybrid nanoparticles and nanocapsules

A viable strategy for uniform organo-silica hybrid nanoparticles and nanocapsules was developed. The key to our strategy is the implementation of spherical star-like homopolymers and diblock copolymers with well-controlled molecular weights that form unimolecular micelles in solution as nanoreactors. Organo-silica hybrid nanoparticles were crafted by introducing trimethoxysilyl functionalities to the arm of star-like homopolymers. Quite intriguingly, organo-silica hybrid nanocapsules with an interior cavity were created when the trimethoxysilyl moieties were incorporated into the outer block of star-like diblock copolymers. The diameter of hybrid nanoparticles and the shell thickness of hybrid nanocapsules can be readily tailored via the living polymerization of star-like homopolymer and diblock copolymer nanoreactors, respectively. These hybrid nanoparticles and nanocapsules may find promising applications in polymer nanocomposites, water purification, separation, catalysis, and drug delivery. We envision that the nanoreactor strategy is general and robust. By rationally designing nonlinear yet structurally regular polymers possessing metal-containing units, other exotic metal- and metal oxide-containing nanostructures can also be easily accessed for a variety of applications.

From Precision Synthesis of Block Copolymers to Properties and Applications of Nanoparticles

Inorganic nanoparticles have become a research focus in numerous fields because of their unique properties that distinguish them from their bulk counterparts. Controlling the size and shape of nanoparticles is an essential aspect of nanoparticle synthesis. Preparing inorganic nanoparticles by using block copolymer templates is one of the most reliable routes for tuning the size and shape of nanoparticles with a high degree of precision. In this Review, we discuss recent progress in the design of block copolymer templates for crafting spherical inorganic nanoparticles including compact, hollow, and core-shell varieties. The templates are divided into two categories: micelles self-assembled from linear block copolymers and unimolecular star-shaped block copolymers. The precise control over the size and morphology of nanoparticles is highlighted as well as the useful properties and applications of such inorganic nanoparticles.

Light-enabled reversible self-assembly and tunable optical properties of stable hairy nanoparticles

Significance This work reports a versatile and robust strategy for creating monodisperse plasmonic nanoparticles (NPs) intimately and permanently capped with photoresponsive polymers via capitalizing on amphiphilic star-like diblock copolymer nanoreactors. The reversibly assembled nanostructures comprising photoresponsive NPs may exhibit a broad range of new attributes, functions, and applications as a direct consequence of size-dependent physical property from individual NP and the collective property originated from the NP interaction due to their close proximity within nanostructure. The ability to dynamically organize functional nanoparticles (NPs) via the use of environmental triggers (temperature, pH, light, or solvent polarity) opens up important perspectives for rapid and convenient construction of a rich variety of complex assemblies and materials with new structures and functionalities. Here, we report an unconventional strategy for crafting stable hairy NPs with light-enabled reversible and reliable self-assembly and tunable optical properties. Central to our strategy is to judiciously design amphiphilic star-like diblock copolymers comprising inner hydrophilic blocks and outer hydrophobic photoresponsive blocks as nanoreactors to direct the synthesis of monodisperse plasmonic NPs intimately and permanently capped with photoresponsive polymers. The size and shape of hairy NPs can be precisely tailored by modulating the length of inner hydrophilic block of star-like diblock copolymers. The perpetual anchoring of photoresponsive polymers on the NP surface renders the attractive feature of self-assembly and disassembly of NPs on demand using light of different wavelengths, as revealed by tunable surface plasmon resonance absorption of NPs and the reversible transformation of NPs between their dispersed and aggregated states. The dye encapsulation/release studies manifested that such photoresponsive NPs may be exploited as smart guest molecule nanocarriers. By extension, the star-like block copolymer strategy enables the crafting of a family of stable stimuli-responsive NPs (e.g., temperature- or pH-sensitive polymer-capped magnetic, ferroelectric, upconversion, or semiconducting NPs) and their assemblies for fundamental research in self-assembly and crystallization kinetics of NPs as well as potential applications in optics, optoelectronics, magnetic technologies, sensory materials and devices, catalysis, nanotechnology, and biotechnology.

Unconventional Route to Uniform Hollow Semiconducting Nanoparticles with Tailorable Dimensions, Compositions, Surface Chemistry and Near-Infrared Absorption

Despite impressive recent advances in the synthesis of lead chalcogenide solid nanoparticles, there are no examples of lead chalcogenide hollow nanoparticles (HNPs) with controlled diameter and shell thickness as current synthetic approaches for HNPs have inherent limitations associated with their complexity, inability to precisely control the dimensions, and limited possibilities with regard to applicable materials. Herein, we report on an unconventional strategy for crafting uniform lead chalcogenide (PbS and PbTe) HNPs with tailorable size, surface chemistry, and near-IR absorption. Amphiphilic star-like triblock copolymers [polystyrene-block-poly(acrylic acid)-block-polystyrene and polystyrene-block-poly(acrylic acid)-block-poly(3,4-ethylenedioxythiophene)] were rationally synthesized and exploited as nanoreactors for the formation of uniform PbS and PbTe HNPs. Compared to their solid counterparts, the near-IR absorption of the HNPs is blue-shifted owing to the hollow interior. This strategy can be readily extended to other types of intriguing low-band-gap HNPs for diverse applications.