Lifeng Hao

Preparation of MoO3 QDs through combining intercalation and thermal exfoliation

Lots of top-down approaches by weakening the van der Waals interaction between adjacent layers and breaking up the covalent chemical bonds in each layer have been reported to prepare QDs of layered materials due to the stacked structures. However, much attention has been focused on graphene and layered transition-metal dichalcogenides (TMDs), seldomly on layered transition-metal oxides (TMOs). Herein, a modified top-down method combining intercalation and thermal exfoliation is reported to prepare high-yield QDs of layered MoO3. Alkylamine was first intercalated into MoO3 layers to weaken the van der Waals forces. Then, the covalent bonds in each MoO3 layer were broken down under a sudden increase in gas pressure generated by the decomposition of alkylamines after rapid heating. These fractured particles were further incised to QDs by sonication. The as-prepared MoO3 QD dispersion showed a plasmon resonance after simulated solar light illumination. Surprisingly, their plasmon peak red shifted with an extended illumination time, which was different from the reported MoO3 nanosheets. This reported method is expected to extend to other QDs of layered materials providing that their bulk materials can also be intercalated.

A biomimetic, multifunctional, superhydrophobic graphene film with self-sensing and fast recovery properties for microdroplet transportation

Recently, multifunctional superhydrophobic surfaces with high adhesion behavior have attracted much attention for microdroplet transportation. Here, we report for the first time a multifunctional, rose-petal-like, superhydrophobic graphene film via the self-assembly of graphene oxide (GO) that has self-sensing and fast recovery properties for microdroplet transportation. This superhydrophobic film does not require a hydrophobic coating and has a micro-nanoscale hierarchical structure. Because of its structure, our biomimetic, superhydrophobic film has high adhesive force to water droplets and can be used as a medium for microdroplet transportation. In addition, because the film was constructed using pure graphene, it has excellent conductivity properties and an immediate response system is also built to detect potential damage. Moreover, owing to the gas sensing properties of graphene, our film has self-sensing properties where the resistance of the film increases gradually when water droplets are close to it. Whats more, the film has an ultra-fast Joule heating rate of 18 °C s−1. Based on these properties, the recovery time for the resistance of the film can be reduced by 57.7% for water droplet transportation. Therefore, our multifunctional, superhydrophobic graphene film can be used for smart microdroplet manipulation in the future.

Photothermal healing of a glass fiber reinforced composite interface by gold nanoparticles

The formation of microcracks especially in the interfacial region is a critical problem for fiber reinforced composites. Repairing the microcracks before catastrophic failure of the materials takes place is a promising solution to achieve long lifetime operation. In this context, a novel method is demonstrated for interfacial healing of glass fiber reinforced composites using the photothermal effect of gold nanoparticles (Au NPs). Au NPs were successfully dispersed into the interfacial region of a glass fiber reinforced composite. Once the interfacial damage occurred, a laser could be used to illuminate Au NPs to generate a large amount of heat through the photothermal effect. This would melt the resin and form mechanical interlocking between the fiber and PMMA to create a new interface. It has been confirmed by a micro bond test that the composite containing Au NPs has healing ability with a maximum healing efficiency of 98.5% under optimized conditions. The mechanism of the interfacial healing was also investigated and it is found that the density of Au NPs and irradiation intensity play key roles in the healing process.

Enhanced and tunable photochromism of MoO3–butylamine organic–inorganic hybrid composites

Orthorhombic molybdenum trioxide (α-MoO3) as one kind of potential inorganic photochromic material shows a slow response, poor reversibility and monotonic coloration. Here, we provide an efficient way to improve and tune the photochromism of MoO3. Novel inorganic–organic hybrid composites were successfully prepared by intercalating n-butylamine into the layer space of α-MoO3 and enhanced photochromic properties such as a fast response, superior reversibility, and good stability were achieved. Meanwhile, the solutions of as-prepared hybrids showed solvent-dependent discoloration due to the hole scavenger effect of ethanol. A reversible transformation between an intermediate state and an enhanced, but stable state was realized by switching irradiation. The improved photochromism caused the solutions of hybrids to show diverse discoloration varying from yellow to green to blue color.

Oxidative etching of MoS2/WS2 nanosheets to their QDs by facile UV irradiation

Oxidative etching has been proved to be an efficient top-down method to prepare quantum dots (QDs) of layered transition-metal dichalcogenides which possess unique properties and have potential applications in various areas. Here, one facile and green oxidative etching method induced by UV irradiation is reported to prepare the QDs of MoS2/WS2 in aqueous solution, respectively. A prominent morphology change occurred to the nanosheets of MoS2/WS2 after irradiation and finally they were etched to ultrasmall nanoparticles which were proved to be the QDs. Insight into the etching mechanism was discussed in detail and hydroxyl free radicals (˙OH) were conclusively demonstrated to play the main role in etching nanosheets. From another point of view, this work also proves the crucial long-term photo instability of MoS2/WS2 since there are increasing photo-related applications of them and points out an easy way to degrade their nanosheets.

Preparation of quantum dots from MoO3 nanosheets by UV irradiation and insight into morphology changes

After UV irradiation of orthorhombic molybdenum trioxide (α-MoO3) nanosheets dispersed in two different solvents including water/ethanol mixed solvents and individual N-methyl-2-pyrrolidinone (NMP), we observed remarkable but distinct morphology changes in combination with different photochromic phenomena. MoO3−x quantum dots (QDs) with both different sizes and oxygen vacancy concentrations could be acquired through this facile and efficient method. The consumption of photoexcited holes played an important role in the morphology changes. In water/ethanol, intercalation of H+ originating from the oxidation of water by photoholes contributes to the acquisition of QDs. While in NMP, we provided a new insight and proved that photocorrosion induced by accumulated holes was responsible for the morphology evolution and acquisition of QDs.

Note: Wide band amplifier for quartz tuning fork sensors with digitally controlled stray capacitance compensation

We presented a preamplifier design for quartz tuning fork (QTF) sensors in which the stray capacitance is digitally compensated. In this design, the manually controlled variable capacitor is replaced by a pair of varicap diodes, whose capacitance could be accurately tuned by a bias voltage. A tuning circuit including a single side low power operational amplifier, a digital-to-analog converter, and a microprocessor is also described, and the tuning process can be conveniently carried out on a personal computer. For the design, the noise level was investigated experimentally.

Interfacial healing of carbon fiber composites in the presence of gold nanoparticles as localized “nano-heaters”

In this paper, interfacial healing was achieved in carbon fiber composites via local heating generated by photothermal effect of gold nanoparticles (Au NPs). The interfacial damage can be locally repaired by melting polymethyl methacrylate and re-infiltrating carbon fiber to form a new interface. The Au NPs were coated on carbon fibers by electrophoretic depositions as nano-heaters and the coating density was controlled by varying the electrophoresis time. The healing ability was confirmed in the micro bond test by comparing the interfacial shear strength and surface morphology of the samples before and after healing. Experimental results showed that coating density of Au NPs and irradiation intensity played a key role. Repeated healings can be achieved with only a small reduction in interfacial strength.

Piezoelectric Modal Damping Performance of 0-3 Piezoelectric Composite with Conducting Phase: Numerical Analysis and Experiments

The piezoelectric modal damping performance of 0-3 piezoelectric composite is discussed in this paper. The piezoelectric damping consisting of PZT piezoelectric ceramic, epoxy (EP) and electric carbon black (CB) is analyzed by a numerical prediction method. The finite element analysis (FEA) method is used to predict the effective property of the 0-3 piezoelectric composites. And then the shunted piezoelectric theory is applied to predict the piezoelectric modal damping of 0-3 piezoelectric composites. The results show that the numerical results are accurate to predict the piezoelectric modal damping compared to the experimental results. Doping appropriate amount of CB can improve the damping of 0-3 piezoelectric composite. This work will help to predict the value of piezoelectric modal damping of the 0-3 piezoelectric composite and to optimize the damping design.

Tensile Properties of Epoxy with Microcapsules and Imidazoline Derivatives Curing Agent and Interlaminar Self-Healing Properties of Carbon Fiber Reinforced Epoxy Composites

Microcapsules are inevitable defects in the resin matrix, which would greatly influence on mechanical performance of structural material. Therefore, a balance value of microcapsules content between self-healing properties and mechanical properties should be provided for fabricating adequate self-healing materials. Epoxy resin with epoxy-containing microcapsules and latent hardener 2MZ-AZINE, and carbon fiber reinforced epoxy composites were prepared. The tensile properties of epoxy resin with epoxy-containing microcapsules or 2MZ-AZINE were investigated. As the increase of content of latent hardener 2MZ-AZINE, tensile modulus and tensile stress of epoxy with 2MZ-AZINE decreases. The tensile stress of epoxy samples decreases with the enhancement of content of epoxy-containing microcapsules. Tensile modulus of epoxy with microcapsules decreases with the increase of microcapsule content below 10 wt.%, and tensile modulus increases above 10 wt.%. Considering the self-healing ability of epoxy sample, the content of microcapsules and latent hardener are concluded to 15 w% and 2 w%, respectively, offering a ∼24.7 MPa tensile stress. The maximum interlaminar self-healing efficiency in this research is only 31.98% recovery of interlaminar tensile stress (epoxy resin matrix with 15 w% microcapsule and 2 w% latent hardener 2MZ-AZINE). As a consequence, this research provided the mechanical parameter for fabricating carbon fiber reinforced epoxy composite.