Liangmiao Zhang

Transparent wood containing CsxWO3 nanoparticles for heat-shielding window applications

CsxWO3 nanoparticles were dispersed in prepolymerized methyl methacrylate (PMMA) and filled in nanopores of delignified wood to prepare transparent wood. The wood-based composite showed excellent near-infrared (NIR, ranging from 780 to 2500 nm) shielding ability and high visible light transparency. The CsxWO3/transparent wood also showed excellent mechanical properties with a fracture strength up to 59.8 MPa and modulus up to 2.72 GPa. CsxWO3/transparent wood is expected to serve as a potential material for smart-window applications.

Phase and morphology evolution during the solvothermal synthesis of VO2 polymorphs

The phase and morphological features of materials are often tunable by adjusting the reaction parameters of solvothermal synthesis but this versatility also poses a challenge for preparing materials with a desired phase and morphology if the behaviors of phase and morphological evolution during the solvothermal synthesis are not known. In this work, the formation and growth of VO2 nanomaterials in the solvothermal systems via the reduction of V2O5 by ethylene glycol (EG) were investigated by in situ powder X-ray diffraction (PXRD). The results show that both fast and slow heating produce the same VO2(B) final product but the phase evolution during the synthesis is very sensitive to the heating rate. Fast heating (10 °C min−1) involves an unknown intermediate while V3O7·H2O is the intermediate phase at slow heating (2 °C min−1). The formation mechanism was employed to design the synthesis of VO2(B) nanorods and the phase transformation paths were verified by large-scale batch synthesis. Furthermore, ex situ PXRD and SEM were employed to follow the structure and morphology evolution during growth. This research indicates that in situ PXRD, as a powerful tool to monitor the whole reaction process and to collect information such as phase evolution and the fate of the transient intermediates, can be used to direct the controlled synthesis of materials.

Controllable synthesis of VO2(D) and their conversion to VO2(M) nanostructures with thermochromic phase transition properties

VO2(M) nanostructures of various shapes were synthesized by a hydrothermal-calcination method. First, VO2(D) nanoparticles were synthesized by the surfactant-free hydrothermal reduction of ammonium metavanadate by oxalic acid at 160–220 °C. Then, the produced VO2(D) was further calcined at 250–600 °C to obtain the VO2(M) nanoparticles. To understand the hydrothermal reduction processes, both in situ powder X-ray diffraction (PXRD) and ex situ characterization were carried out. The results indicate a sequential process starting from the reduction of ammonium metavanadate and nucleation of the vanadium precursor, followed by the formation of intermediate VO2(B) nanosheets or nanorods, and finally phase transformation from VO2(B) to VO2(D) with a variety of morphologies. A crystal growth mechanism based on self-assembly and Ostwald ripening was proposed to explain the formation process of these unique nanostructures. The as-prepared VO2(M) nanoaggregates exhibited a lower thermochromic phase transition temperature (41.0 °C) and a narrower thermal hysteresis width (6.6 °C) than those nanopowders prepared by other methods.

Synthesis and formation mechanism of VO2(A) nanoplates with intrinsic peroxidase-like activity

Monocrystalline VO2(A) nanoplates have been synthesized via a one-pot hydrothermal process. In situ powder X-ray diffraction was used to monitor the hydrothermal synthesis and it was found that VO2(A) nucleates and grows directly from solution after the complete hydrolysis of a 2.0 M VO(acac)2 precursor solution, rather than involving a previously reported intermediate phase VO2(B). A hydrating–exfoliating–splitting mechanism was established to explain the formation of the nanoplate architecture. The synthesized VO2(A) nanoplates showed outstanding peroxidase-like activity and hence are a promising candidate for artificial peroxidase.

Low temperature fabrication of thermochromic VO2 thin films by low-pressure chemical vapor deposition

VO2(M) is of special interest as the material with the most potential for future application in smart windows and switching devices. However, a number of drawbacks need to be overcome, including the high processing temperature of current synthesis techniques and low thermochromic properties. This work reports the fabrication of high-performance thermochromic VO2 thin films at low temperatures below 400 °C based on a low-pressure chemical vapor deposition (LPCVD) with a vanadium(III) acetylacetonate precursor. Proper tuning of the process parameters is found to be critical in fabricating thickness-controllable highly-crystalline VO2 films. For an ∼62 nm thick VO2 film, visible transmittances of 52.3% (annealed at 400 °C) and 52.7% (annealed at 350 °C) were obtained. The corresponding solar energy modification abilities (ΔTsol) were 9.7% and 7.1%, and the transition temperatures were 45.1 °C and 50.9 °C. The underlying microscopic mechanism was studied by first-principles calculations and the results indicated that improved performances, including a low transition temperature, could be achieved by properly controlling the annealing temperature, ascribed to the combined effect of strain and oxygen vacancies. Moreover, the initial use of a pre-grown seed layer induced fast grain growth, which is favorable for further decreasing the deposition and annealing temperature to 325 °C.

Solvothermal synthesis of Co3O4/Al2O3 hollow core–shell microspheres for the catalytic oxidation of CO

A facile template-free solvothermal strategy has been developed for the synthesis of uniform and hollow core–shell Co3O4/Al2O3 microspheres composed of numerous tiny nanorods. The morphology, structure, and composition of the spheres have been investigated using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, H2-temperature programmed reduction (H2-TPR) and X-ray diffraction analysis (XRD). The specific surface area and pore-size distribution of the obtained products as determined by gas sorption measurements show that the core–shell microspheres exhibit a high surface area and porosity. The formation of the hollow structure involves a trisodium citrate (TSC)-assisted Ostwald ripening process. The structure and factors that govern the shape evolution of the core–shell Co3O4/Al2O3 microspheres have been carefully studied, such as the Co wt% content, the TSC/Al ratio and the temperature. The catalytic activity of the as-prepared core–shell Co3O4/Al2O3 microspheres has been evaluated for CO catalytic oxidation. Their high performance may be attributed to their large specific surface area, high porosity and mesoporous structure.

VO2(D) hollow core–shell microspheres: synthesis, methylene blue dye adsorption and their transformation into C/VOx nanoparticles

In this work, we report the fabrication of novel VO2(D) hollow core–shell microspheres (VO2(D)-HCSMs) via a facile hydrothermal method. Microscopic examination revealed that the VO2(D)-HCSMs consisted of numerous nanocrystals and had an average size of 1–10 μm and a shell thickness of 300 nm. An inside-out Ostwald ripening process was responsible for the formation of the VO2(D)-HCSMs. Meanwhile, citric acid played dual roles, acting as a reductant for reducing vanadium pentoxide and as a morphology directing agent for producing core–shell microspheres. The resulting VO2(D)-HCSMs exhibited excellent adsorption performance with a maximum adsorption capacity of 97.5 mg g−1 for methylene blue (MB). The C/VOx particles were generated by the calcination of the VO2(D)-HCSMs with adsorbed MB dye at 250 °C in air for 4 h, and the microspheres showed enhanced adsorption capacity and good reusability (over 99% MB removal after four cycles) because of the existence of amorphous carbon nanowires, making them a potential adsorbent for removing organic dyes from wastewater.

A large array MTJ biosensor chip: Design, manufacturing and evaluation

Since the basic concept of using magnetic sensor to detect biomolecules labelled with magnetic particles (MP) was first disclosed by Baselt, significant development has been made on the material and structure of magnetic transducers . The tri-layer spin-valve GMR device can yield 4 times as much signal as the magnetoresistive device mentioned by Baselt . Magnetic tunnel junction (MTJ) device can produce 100 times as much signal as the magnetoresistive devices . In this work, an active biochip consisting of 12 million magnetic-tunnel-junction (MTJ) transducers was developed for high throughput and high sensitivity detection of biomolecules . This chip can detect 12 million different types of molecules simultaneously .