Zhichuan J. Xu

Synthesis, Functionalization, and Biomedical Applications of Multifunctional Magnetic Nanoparticles

Synthesis of multifunctional magnetic nanoparticles (MFMNPs) is one of the most active research areas in advanced materials. MFMNPs that have magnetic properties and other functionalities have been demonstrated to show great promise as multimodality imaging probes. Their multifunctional surfaces also allow rational conjugations of biological and drug molecules,making it possible to achieve target-specific diagnostics and therapeutics.This review fi rst outlines the synthesis of MNPs of metal oxides and alloy sand then focuses on recent developments in the fabrication of MFMNPs of core/shell, dumbbell, and composite hybrid type. It also summarizes the general strategies applied for NP surface functionalization. The review further highlights some exciting examples of these MFMNPs for multimodality imaging and for target-specific drug/gene delivery applications.

Platinum-gold nanoparticles: a highly active bifunctional electrocatalyst for rechargeable lithium-air batteries.

PtAu nanoparticles (NPs) were shown to strongly enhance the kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable Li-O(2) cells. Li-O(2) cells with PtAu/C were found to exhibit the highest round-trip efficiency reported to date. During ORR via xLi(+) + O(2) + xe(-) --> Li(x)O(2), the discharge voltage with PtAu/C was considerably higher than that of pure carbon and comparable to that of Au/C. During OER via Li(x)O(2) --> xLi(+) + O(2) + xe(-), the charge voltages with PtAu/C fell in the range from 3.4 to 3.8 V(Li), which is slightly lower than obtained with Pt. It is hypothesized that PtAu NPs exhibit bifunctional catalytic activity, having surface Au and Pt atoms primarily responsible for ORR and OER kinetics in Li-O(2) cells, respectively.

Black Phosphorus Quantum Dots

As a unique two-dimensional nanomaterial, layered black phosphorus (BP) nanosheets have shown promising applications in electronics. Although mechanical exfoliation was successfully used to prepare BP nanosheets, it is still a challenge to produce novel BP nanostructures in high yield. A facile top-down approach for preparation of black phosphorus quantum dots (BPQDs) in solution is presented. The obtained BPQDs have a lateral size of 4.9±1.6 nm and thickness of 1.9±0.9 nm (ca. 4±2 layers). As a proof-of-concept application, by using BPQDs mixed with polyvinylpyrrolidone as the active layer, a flexible memory device was successfully fabricated that exhibits a nonvolatile rewritable memory effect with a high ON/OFF current ratio and good stability.

Recent developments in electrode materials for sodium-ion batteries

The rapid consumption of non-renewable resources has resulted in an ever-increasing problem of CO2 emissions that has motivated people for investigating the harvesting of energy from renewable alternatives (e.g. solar and wind). Efficient electrochemical energy storage devices play a crucial role in storing harvested energies in our daily lives. For example, rechargeable batteries can store energy generated by solar cells during the daytime and release it during night-time. In particular, lithium-ion batteries (LIBs) have received considerable attention ever since their early commercialization in 1990s. However, with initiatives by several governments to build large-scale energy grids to store energy for cities, problems such as the high cost and limited availability of lithium starts to become major issues. Sodium, which also belongs to Group 1 of the periodic table, has comparable electrochemical properties to Lithium, and more importantly it is considerably more accessible than lithium. Nonetheless, research into sodium-ion batteries (NIBs) is currently still in its infancy compared to LIBs, although great leaps and bounds have been made recently in terms of research and development into this technology. Here in this review, we summarize the recent advancements made, also covering the prospective materials for both the battery cathode and anode. Additionally, opinions on possible solutions through correlating trends in recent papers will be suggested.

Encapsulating MWNTs into Hollow Porous Carbon Nanotubes: A Tube‐in‐Tube Carbon Nanostructure for High‐Performance Lithium‐Sulfur Batteries

A tube-in-tube carbon nanostructure (TTCN) with multi-walled carbon nanotubes (MWNTs) confined within hollow porous carbon nanotubes is synthesized for Li-S batteries. The structure is designed to enhance the electrical conductivity, hamper the dissolution of lithium polysulfide, and provide large pore volume for sulfur impregnation. As a cathode material for Li-S batteries, the S-TTCN composite with 71 wt% sulfur content delivers high reversible capacity, good cycling performance as well as excellent rate capabilities.

Formation of Uniform Fe3O4 Hollow Spheres Organized by Ultrathin Nanosheets and Their Excellent Lithium Storage Properties

Hierarchical Fe3 O4 hollow spheres constructed by nanosheets are obtained from solvothermally synthesized Fe-glycerate hollow spheres. With the unique structural features, these hierarchical Fe3 O4 hollow spheres exhibit excellent electrochemical lithium-storage performance.

Surface Composition Tuning of Au–Pt Bimetallic Nanoparticles for Enhanced Carbon Monoxide and Methanol Electro-oxidation

The ability to direct bimetallic nanoparticles to express desirable surface composition is a crucial step toward effective heterogeneous catalysis, sensing, and bionanotechnology applications. Here we report surface composition tuning of bimetallic Au-Pt electrocatalysts for carbon monoxide and methanol oxidation reactions. We establish a direct correlation between the surface composition of Au-Pt nanoparticles and their catalytic activities. We find that the intrinsic activities of Au-Pt nanoparticles with the same bulk composition of Au0.5Pt0.5 can be enhanced by orders of magnitude by simply controlling the surface composition. We attribute this enhancement to the weakened CO binding on Pt in discrete Pt or Pt-rich clusters surrounded by surface Au atoms. Our finding demonstrates the importance of surface composition control at the nanoscale in harnessing the true electrocatalytic potential of bimetallic nanoparticles and opens up strategies for the development of highly active bimetallic nanoparticles for electrochemical energy conversion.

Vertically oriented MoS2 and WS2 nanosheets directly grown on carbon cloth as efficient and stable 3-dimensional hydrogen-evolving cathodes

The development of non-noble-metal based hydrogen-evolving catalysts is essential to the practical application of water-splitting devices. Improvement of both the activity and stability of such catalysts remains a key challenge. In this work, a simple solvothermal method is developed to directly grow MoS2 and WS2 on carbon cloth with vertically oriented nanosheet layers. With the unique layer orientation that maximally exposes active edge sites as well as a rapid release of small gas bubbles to maintain a large working area, such prepared 3-dimensional electrodes exhibit high activity towards the HER. In addition, they also exhibit prominent electrochemical durability, thanks to the strong bonding between the nanosheet layers and the substrate along with the self-removal of the as-formed H2 bubbles from the nano-porous electrode surface.

Fuel cell technology: nano-engineered multimetallic catalysts

Fuel cells represent an attractive technology for tomorrows energy vector because hydrogen is an efficient fuel and environmentally clean, but one of the important challenges for fuel cell commercialization is the preparation of active, robust and low-cost catalysts. The synthesis and processing of molecularly-capped multimetallic nanoparticles, as described in this report, serves as an intriguing way to address this challenge. Such nanoparticles are exploited as building blocks for engineering the nanoscale catalytic materials by taking advantage of diverse attributes, including monodispersity, processability, solubility, stability, capability in terms of size, shape, composition and surface properties. This article discusses recent findings of our investigations of the synthesis and processing of nanostructured catalysts with controlled size, composition, and surface properties by highlighting a few examples of bimetallic/trimetallic nanoparticles and supported catalysts for electrocatalytic oxygen reduction.

One-Pot Synthesis of Highly Anisotropic Five-Fold-Twinned PtCu Nanoframes Used as a Bifunctional Electrocatalyst for Oxygen Reduction and Methanol Oxidation.

Five-fold-twinned PtCu nanoframes (NFs) with nanothorns protruding from their edges are synthesized by a facile one-pot method. Compared to commercial Pt/C catalyst, the obtained highly anisotropic five-fold-twinned PtCu NFs show enhanced electrocatalytic performance toward the oxygen reduction reaction and methanol oxidation reaction under alkaline conditions.