Hongwen Huang

Synthesis of CuO nanowalnuts and nanoribbons from aqueous solution and their catalytic and electrochemical properties

One dimensional copper hydroxide nanostrands, two dimensional Cu(2)(OH)(3)NO(3) nanoribbons and three dimensional CuO nanowalnuts were synthesized from the same diluted copper nitrate solution with ethanolamine at room temperature and 10 °C, respectively. The Cu(2)(OH)(3)NO(3) nanoribbons were formed by slowly hydrolyzing ethanolamine at low temperature. The CuO nanowalnuts were formed through dehydration of copper hydroxide nanostrands in aqueous solution at room temperature. Although their average size is about 500 nm, the specific surface area of the CuO nanowalnuts can be as large as 61.24 m(2) g(-1), due to their particular morphology with assembling of 8 nm grains. The Cu(2)(OH)(3)NO(3) nanoribbons were converted to CuO porous nanoribbons, keeping the shape. The catalytic performance of the CuO nanowalnuts for CO oxidation is 160 mL h(-1) g(cat)(-1) which is 23 times higher than those of the CuO porous nanoribbons and 40 nm commercial CuO nanoparticles, respectively. The electrochemical properties of the CuO nanowalnuts were also examined in a lithium-ion battery. After 30 cycles, the capacity of the as-prepared CuO nanowalnuts could sustain 67.1% (407 mA h g(-1)) of the second cycle (607 mA h g(-1)) at a rate of 0.1 C.

Achieving Remarkable Activity and Durability toward Oxygen Reduction Reaction Based on Ultrathin Rh-Doped Pt Nanowires

The research of active and sustainable electrocatalysts toward oxygen reduction reaction (ORR) is of great importance for industrial application of fuel cells. Here, we report a remarkable ORR catalyst with both excellent mass activity and durability based on sub 2 nm thick Rh-doped Pt nanowires, which combine the merits of high utilization efficiency of Pt atoms, anisotropic one-dimensional nanostructure, and doping of Rh atoms. Compared with commercial Pt/C catalyst, the Rh-doped Pt nanowires/C catalyst shows a 7.8 and 5.4-fold enhancement in mass activity and specific activity, respectively. The combination of extended X-ray absorption fine structure analysis and density functional theory calculations reveals that the compressive strain and ligand effect in Rh-doped Pt nanowires optimize the adsorption energy of hydroxyl and in turn enhance the specific activity. Moreover, even after 10000 cycles of accelerated durability test in O2 condition, the Rh-doped Pt nanowires/C catalyst exhibits a drop of 9.2% in mass activity, against a big decrease of 72.3% for commercial Pt/C. The improved durability can be rationalized by the increased vacancy formation energy of Pt atoms for Rh-doped Pt nanowires.

2D Behaviors of Excitons in Cesium Lead Halide Perovskite Nanoplatelets

Fundamental to understanding and predicting the optoelectronic properties of semiconductors is the basic parameters of excitons such as oscillator strength and exciton binding energy. However, such knowledge of CsPbBr3 perovskite, a promising optoelectronic material, is still unexplored. Here we demonstrate that quasi-two-dimensional (quasi-2D) CsPbBr3 nanoplatelets (NPLs) with 2D exciton behaviors serve as an ideal system for the determination of these parameters. It is found that the oscillator strength of CsPbBr3 NPLs is up to 1.18 × 104, higher than that of colloidal II-VI NPLs and epitaxial quantum wells. Furthermore, the exciton binding energy is determined to be of ∼120 meV from either the optical absorption or the photoluminescence analysis, comparable to that reported in colloidal II-VI quantum wells. Our work provides physical understanding of the observed excellent optical properties of CsPbBr3 nanocrystals and would benefit the prediction of high-performance excitonic devices based on such materials.

Thin copper oxide nanowires/carbon nanotubes interpenetrating networks for lithium ion batteries

Thin CuO nanowires with a diameter of 7 ± 3 nm, aspect ratio up to 103–104 and specific surface area of 51.08 m2 g−1 were synthesized by shape-reserved transformation from the corresponding thin copper hydroxide nanowires (CHNs) under an appropriate temperature. A topotactic transition of the crystal structure between Cu(OH)2 and CuO occurred. CdO nanowires were also successfully prepared by this synthetic method. Subsequently, thin CuO nanowires/carbon nanotubes (CNTs) interpenetrating networks were prepared from preformed Cu(OH)2 nanowire/CNT interpenetrating networks and these demonstrated a much higher electrochemical performance than that of pure CuO nanowires for lithium ion batteries. When the CNTs were 33.3 wt% of the CuO nanowires/CNTs interpenetrating networks, they gave the best electrochemical performance, including high capacitance as well as good stability.

High catalytic performance of gold nanoparticle–gelatin mesoporous composite thin films

In this paper, Au nanoparticle (NP)–gelatin mesoporous composite thin films were successfully prepared by the formation of Au NPs in the mesoporous gelatin films through in situ reduction of HAuCl4 at room temperature. The mesoporous gelatin films were prepared by using copper hydroxide nanostrands as both the assembling frames and the pore generators. It was found that both the trace aldehyde groups of the glutaraldehyde cross-linker and the reduction groups of gelatin contributed to the formation of Au NPs. The Au NPs were homogeneously formed and dispersed in the gelatin films. The effects of pH and the reduction time on the formation of the Au NPs were investigated in detail. These Au NP–gelatin mesoporous composite films demonstrated superior catalytic properties for the reduction of o-nitroaniline to 1,2-benzenediamine, and several to tens times higher activity than those reported of the Au NP–polymer (or oxide) composites. Similarly, Pt NP–gelatin mesoporous composite films were also prepared. This process is general and simple for other functional composite films.

Filtration-assembling colloidal crystal templates for ordered macroporous nanoparticle films

Ordered macroporous nanoparticle thin films are achieved on porous substrates by combining ultrathin metal hydroxide nanostrands, colloidal crystal templates and the advantage of filtration technique. The preformed nanostrands layer plays two key roles for both uniform formation of hexagonal close-packed latex colloidal crystals on macroporous substrate and efficiently filling the interstitial voids of the colloidal crystal templates with nanoparticles. The stacking number of the colloids is simply controlled by the filtration volume. The uniformity of the film was guaranteed by the filtration process. After removing the latex templates and copper hydroxide nanostrand layer, free-standing ordered macroporous nanoparticle films were obtained. The robust free-standing gold nanoparticle films could be easily transferred onto various solid substrates and has potential application for electrodes, surface enhanced Raman detectors and catalyst. This method could be extended for the other ordered macroporous functional nanoparticle thin films.

Mesoporous protein thin films for molecule delivery

A simple and easy method was developed for preparation of large-scale free-standing mesoporous protein thin films through a filtration technique by using ultrathin metal hydroxide nanostrands as frames and pore templates. Composite nanofibrous dispersions of nanostrands and proteins were formed by assembling negatively charged protein on the highly positively charged nanostrand surfaces. These dispersions were filtered on a porous substrate. After partially cross-linking the amino groups of the proteins, removing the nanostrands and peeling off from the substrate, free-standing mesoporous protein films were obtained. These films repeatedly demonstrated efficient loading and releasing performance of dye molecules by pH controlling. The delivery capacity was 33.5% relative to the weight of the matrix. This value is several times higher than that of active carbon powders as well as that of metal hydroxide sludge. At pH lower than the isoelectic point of protein, the negatively charged dye molecules were loaded. Subsequently, the preloaded dye molecules were released at pH higher than the isoelectric point of protein. Furthermore, reversible delivery of doxorubicin drug molecules was realized by using these mesoporous protein thin films under physiological conditions. These films hold promising applications for recovering dyes from the dye waste water, and for efficient drug delivery platforms with controllable releasing speed.

Great Disparity in Photoluminesence Quantum Yields of Colloidal CsPbBr3 Nanocrystals with Varied Shape: The Effect of Crystal Lattice Strain

Understanding the big discrepancy in the photoluminesence quantum yields (PLQYs) of nanoscale colloidal materials with varied morphologies is of great significance to its property optimization and functional application. Using different shaped CsPbBr3 nanocrystals with the same fabrication processes as model, quantitative synchrotron radiation X-ray diffraction analysis reveals the increasing trend in lattice strain values of the nanocrystals: nanocube, nanoplate, nanowire. Furthermore, transient spectroscopic measurements reveal the same trend in the defect quantities of these nanocrystals. These experimental results unambiguously point out that large lattice strain existing in CsPbBr3 nanoparticles induces more crystal defects and thus decreases the PLQY, implying that lattice strain is a key factor other than the surface defect to dominate the PLQY of colloidal photoluminesence materials.