Muwei Ji

Controlling Structural Symmetry of a Hybrid Nanostructure and its Effect on Efficient Photocatalytic Hydrogen Evolution

The existence of lattice strain between two different materials can be used to control the fine structural configuration in a hybrid colloidal nanostructure. Enabled by such, the relative position change of Au and CdX in Au-CdX from a symmetric to an asymmetric configuration is demonstrated, which can further lead to fine tuning of plasmon-exciton coupling and different hydrogen photocatalytic performance. These results provide new insight into plasmon enhanced photocatalytic mechanisms and provide potential catalysts for photoreduction reactions.

Structurally Well-Defined Au@Cu2−xS Core–Shell Nanocrystals for Improved Cancer Treatment Based on Enhanced Photothermal Efficiency

Au@Cu2- x S core-shell nanocrystals (NCs) have been synthesized under large lattice mismatch with high crystallinity, controllable shape, and nonstoichiometric composition. Both experimental observations and simulations are used to verify the flexible dual-mode plasmon coupling. The enhanced photothermal effect is harnessed for diverse HeLa cancer cell ablation applications in the NIR-I window (750-900 nm) and the NIR-II window (1000-1400 nm).

Rigid three-dimensional Ni3S4 nanosheet frames: controlled synthesis and their enhanced electrochemical performance

Rigid three-dimensional (3D) Ni3S4 nanosheet frames assembled from ultrathin nanosheets are synthesized via a facile solvothermal method. Compared to flat Ni3S4 sheets, 3D Ni3S4 nanosheet frames have both a high free volume and high compressive strength. They can deliver a very high specific capacitance of 1213 F g−1 with good rate performance. In addition, these 3D Ni3S4 nanosheet frames are stabilized by plastically deformed ridges. The stabilized nanosheet frames did not unfold or collapse during electrochemical tests, and thus showed enhanced cycling ability.

Plasmon enhanced photoelectrochemical sensing of mercury (II) ions in human serum based on Au@Ag nanorods modified TiO₂ nanosheets film.

Taking advantages of the monodisperse TiO2 nanosheets (NSs) with high active crystal face exposure and the tunable localized surface plasmon resonance (LSPR) properties of Au@Ag nanorods (NRs), this study demonstrated that TiO2 NSs film with trace amount of Au@Ag NRs modification possess a strong enhancement of photocurrent response, which was remarkably inhibited with the addition of mercury (II) ions (Hg(2+)). Based on the selective decrease of photocurrent with the addition of Hg(2+), a simple photoelectrochemical (PEC) sensor has been assembled. The PEC sensor exhibits wide linear range (0.01-10nM), low detection limit (2.5 pM), satisfying selectivity, reproducibility and acceptable stability for Hg(2+) detection. The feasibility of this method for practical application in human serum has been evaluated and the result was satisfactory. This PEC sensing method would provide a potential application for Hg(2+) detection in clinical diagnosis.

Heterovalent‐Doping‐Enabled Efficient Dopant Luminescence and Controllable Electronic Impurity Via a New Strategy of Preparing II−VI Nanocrystals

Substitutional heterovalent doping represents an effective method to control the optical and electronic properties of nanocrystals (NCs). Highly monodisperse II-VI NCs with deep substitutional dopants are presented. The NCs exhibit stable, dominant, and strong dopant fluorescence, and control over n- and p-type electronic impurities is achieved. Large-scale, bottom-up superlattices of the NCs will speed up their application in electronic devices.

Noble metal nanoclusters and their in situ calcination to nanocrystals: Precise control of their size and interface with TiO2 nanosheets and their versatile catalysis applications

In this work, we present a new versatile strategy to prepare noble metal (Au, Ag and Cu) nanoclusters on TiO2 nanosheets in large scales with exposed (001) facets with controlled size, crystalline interface, and loading amount. By precise in situ calcination, the metal (M = Au, Ag, and Cu) nanocrystals with controllable size and better crystalline interface with the TiO2 support have been prepared. The potential application of the as-prepared Au, Ag, and Cu nanoclusters on TiO2 nanosheets as potential heterogeneous catalysts for organic synthesis, such as catalytic reduction of 4-nitrophenol to 4-aminophenol, has been demonstrated. After calcination, Au, Ag, and Cu nanocrystals were found to be proficient cocatalysts for photocatalytic H2 evolution, particularly the Au cocatalyst. Based on precise high-resolution transmission electron microscopy (HRTEM) and inductively coupled plasma optical emission spectrometry (ICP-OES) analyses, the flexible control of their size and loading amount as well as their intimate contact with the TiO2 nanosheet enhanced the photocatalytic H2 evolution activity and the sensitivity of the photocurrent response of the film. Furthermore, this aqueous-directed synthesis of metal nanoclusters on a support will generate further interest in the field of nanocatalysis.

Controllable synthesis of porous TiO2 with a hierarchical nanostructure for efficient photocatalytic hydrogen evolution

TiO2 has been the most suitable candidate for commercial scale-up photocatalysts to date. However, the practical application of TiO2 has been limited, due to its wide band gap (3.0 eV for rutile and 3.2 eV for anatase) and recombination of photoinduced charges. Herein, we report a simple and effective approach to resolve the limitations by manipulating the structure and size of TiO2 to improve the photocatalytic efficiency. By adjusting the volume ratio of hydrochloric acid (HCl) and ethylene glycol (EG), porous TiO2 hierarchical microspheres with controllable size of nanorods were obtained. The nanorods were several hundreds of nanometers long with different average widths, including 5 (TiO2-5), 10 (TiO2-10) and 15 nm (TiO2-15). The band gap of TiO2-5 was as low as 2.75 eV with a super large BET surface area of 216.607 m2 g−1. The rate of photocatalytic hydrogen generation for TiO2-5 was 23.74 mmol g−1 h−1 under UV-visible light irradiation of 200 mW cm−2.

Phosphine-Initiated Cation Exchange for Precisely Tailoring Composition and Properties of Semiconductor Nanostructures: Old Concept, New Applications†

Phosphine-initiated cation exchange is a well-known inorganic chemistry reaction. In this work, different phosphines have been used to modulate the thermodynamic and kinetic parameters of the cation exchange reaction to synthesize complex semiconductor nanostructures. Besides preserving the original shape and size, phosphine-initiated cation exchange reactions show potential to precisely tune the crystallinity and composition of metal/semiconductor core-shell and doped nanocrystals. Furthermore, systematic studies on different phosphines and on the elementary reaction mechanisms have been performed.

Core@shell sub-ten-nanometer noble metal nanoparticles with a controllable thin Pt shell and their catalytic activity towards oxygen reduction

AbstractReducing Pt loading, while improving electrocatalytic activity and the stability of Pt-based nanostructured materials, is currently a key challenge in green energy technology. Herein, we report the controllable synthesis of tri-metallic (Au@Ag@Pt) and bimetallic (Ag@Pt) particles consisting of a controllable thin Pt shell, via interface-mediated galvanic displacement. Through oil-ethanol-H2O interface mediation, the controllable “out to in” displacement of Ag atoms to Pt enables the formation of a thin Pt shell on monodisperse sub-ten-nanometer Au@Ag and Ag nanocrystals. The synthesized nanoparticles with a thin Pt shell exhibited potential catalytic activity towards the oxygen reduction reaction (ORR) due to the high exposure of Pt atoms.

From Cu2S nanocrystals to Cu doped CdS nanocrystals through cation exchange: controlled synthesis, optical properties and their p-type conductivity research

Heterovalent doping represents an effective method to control the optical and electronic properties of semiconductor nanocrystals (NCs), such as the luminescence and electronic impurities (p-, n-type doping). Considering the phase structure diversity, coordination varieties of Cu atoms in Cu2S NCs, and complexity of Cu doping in II-VI NCs, monodisperse Cu2S NCs with pure hexagonal phase were synthesized firstly. Then through cation exchange reaction between Cd ions and well-defined Cu2S NCs, dominant Cu(I) doped CdS NCs were produced successfully. The substitutional Cu(I) dopants with controllable concentrations were confirmed by local atom-specific fine structure from X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) spectroscopy, elemental analysis characterizations from X-ray photoelectron spectroscopy (XPS) and the electron spin resonance (ESR) measurement. The dominant and strong Cu(I) dopant fluorescence was verified by their absorption and photoluminescence (PL) spectra, and PL lifetime. Finally, the band positions and the p-type conductivities of the as-prepared Cu2S and Cu(I) doped CdS NCs were identified by ultraviolet photoelectron spectroscopy (UPS) measurements. The high monodispersity of NCs enables their strong film-scale self-assembly and will hasten their subsequent applications in devices.中文摘要异价掺杂, 能有效调控半导体纳米晶的电学及光学性能, 实现高效掺杂发光及n型、p型导电类型的调控. 因为Cu2S晶型多 变、Cu原子配位繁杂以及Cu掺杂II-VI纳米晶的体系复杂等问题, 本文提出一种全新的方法, 首先可控制备了单分散的高纯度六方相 Cu2S纳米晶, 然后通过可控的离子交换反应, 合成了单分散Cu(I)掺杂的CdS纳米晶. 通过X射线近边吸收谱(XANES)、扩展X射线吸收 精细结构(EXAFS)、X射线光电子能谱(XPS)及电子顺磁共振波谱(EPR)等精确表征手段证实了可控浓度的取代型的异价Cu掺杂. 其紫 外-可见吸收光谱、荧光光谱、荧光寿命光谱等表征证实了以Cu(I)掺杂为主导的掺杂发光, 绝对量子产率可达28.9%. 紫外光电子能谱 (UPS)确认了Cu(I)掺杂的CdS为p型半导体. 高度单分散的CdS掺杂纳米晶可以形成大规模的自组装, 将会加速其在光电器件上的应用.