Haoliang Cheng

A facile process to prepare one dimension VO2 nanostructures with superior metal–semiconductor transition

VO2 nanobelts with metal–semiconductor properties were prepared through low temperature hydrothermal reaction and post annealing. X-Ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), differential scanning calorimetry (DSC) and UV-vis-NIR spectrophotometry were employed to investigate the evolution of structure, morphology and properties of the VO2 nanobelts. The results illustrate that the pure VO2 (B) nanobelts can be obtained by hydrothermal reaction. The shape of the nanobelts evolves with hydrothermal temperature, time and reactant concentration. With the increasing of hydrothermal temperature from 160 °C to 200 °C, the nanobelts become homogenous and regular. The regular nanobelts are also obtained by the decrease of V2O5 concentration. Samples prepared at 200 °C over 48 h have superior morphology and crystallinity. After annealing, VO2 (B) can be transformed into VO2 (M), which is dependent on the hydrothermal conditions. Samples prepared at 160 °C over 48 h and 180 °C over 48 h can be transformed into VO2 (M) at 450 °C over 2 h, while samples obtained at 200 °C over 48 h should be annealed at 500 °C for 2 h. The nanobelts are transformed into irregular nanostructures, nanorods and nanobelts at the hydrothermal temperatures of 160 °C, 180 °C and 200 °C, respectively. However, samples prepared at 200 °C over 48 h with a V2O5 concentration of 0.0125 M can keep the intact nanobelts after annealing. The DSC analysis proves that the VO2 (M) shows good phase transition behavior around 68 °C and the phase transition temperature can be reduced to 58 °C by 0.5 at% tungsten doping. After mixing the VO2 (M) with acrylic resin, the visible transmission of the VO2 composite coating on glass is up to 52.2% and the solar modulation at 2000 nm is up to 31.5%, which means that it is a good candidate for smart windows.

A simple and low-cost combustion method to prepare monoclinic VO 2 with superior thermochromic properties

In this approach, the VO2 nanoparticles have been successfully fabricated via combusting the low-cost precursor solution consisted of NH4VO3, C2H6O2 and C2H5OH. By the XRD, TEM and XPS analysis, it can be found that the synthetic monoclinic VO2 is single crystal and no impurity is defined. After dispersing the VO2 nanoparticles into the polymer, the solar modulation of VO2-based composite film is up to 12.5% with luminous transmission and haze around 62.2% and 0.5%, respectively. In other words, the composite films show high performance of thermochromic properties. This could open an efficient way to fabricate low-cost and large-scale VO2 (M) nanoparticles and thermochromic films.

A novel method to modify the color of VO2-based thermochromic smart films by solution-processed VO2@SiO2@Au core–shell nanoparticles

In this study, the VO2@SiO2@Au core–shell nanoparticles were synthesized by a solution process to tailor the color of VO2 films on the basis of surface plasmon resonance (SPR). The SiO2 interlayer not only provided more hydroxyl bonding for the silane coupling agent, which was conducive to metal deposition, but also significantly improved the anti-oxidation ability of VO2. We optimized the thickness of silica to maintain the silica layer uniform and thin (14 nm), which would impact on the optical properties. The VO2@SiO2@Au films with various Au particle sizes displayed a series of colors from brick red to purple and blue while maintaining the solar modulation ability (the maximum ΔTsol is up to 7.52%). Moreover, the phase transition temperature decreased by about 6 °C without doping due to electron injection from Au to VO2. This study proposed a novel and facile method to tune the color of VO2-based thermochromic smart films while improving the anti-oxidation ability and decreasing the phase transition temperature. It may constitute a great advance in the development of thermochromic smart films.

Core-Sheath Paraffin-Wax-Loaded Nanofibers by Electrospinning for Heat Storage

Paraffin wax (PW) is widely used for smart thermoregulation materials due to its good thermal performance. However, the leakage and low thermal conductivity of PW hinder its application in the heat storage field. Accordingly, developing effective methods to address these issues is of great importance. In this study, we explored a facile approach to obtain PW-loaded core-sheath structured flexible nanofibers films via coaxial electrospinning technique. The PW as the core layer was successfully encapsulated by the sheath-layer poly(methyl methacrylate). The diameter of the fiber core increased from 395 to 848 nm as the core solution speed rate increased from 0.1 to 0.5 mL/h. In addition, it can be seen that higher core solution speed rate could lead to higher PW encapsulation efficiency according to the transmission electron microscopy results. The core-sheath nanofiber films, moreover, possessed the highest latent heat of 58.25 J/g and solidifying enthalpy of -56.49 J/g. In addition, we found that after 200 thermal cycles, there was little change in latent heat, which demonstrated that it is beneficial for the PW-loaded core-sheath structure to overcome the leakage issue and enhance thermal stability properties for the thermoregulation film.

High performance VO2 thin films fabricated by room-temperature reactive magnetron sputtering and rapid thermal annealing

The VOx thin films are successfully prepared on glass substrate by reactive magnetron sputtering at room-temperature, and subsequently annealed by rapid thermal annealing system in N2 from 0.5Pa to 10000Pa. The effects of annealing pressure on the optical performance and phase transition temperature (Tc) of VOx thin films are systematically investigated. The results show that the VOx thin films exhibit good performance with Tlum of 28.17%, ΔTsol of 12.69%, and Tc of 42. The annealing pressure had an obvious influence on the grain size, which can be attributed to light scattering effects by gas molecule. Compared with oxygen vacancy defects, the grain size plays a decisive role in the regulation of Tc. The restricting the growth of grain can be reduced the Tc, and a little deterioration effect on optical performance can be observed. In addition, the method in this paper not only depressed the Tc, but also simplified the process and improved efficiency, which will provide guidance for the preparation and application of VOx thin films.