Yaqing Liu

An organic terpyridyl-iron polymer based memristor for synaptic plasticity and learning behavior simulation

Memristors have been extensively studied for nonvolatile memory storage, neuromorphic computing, and logic applications. Particularly, synapse emulation is viewed as a key step to realizing neuromorphic computing, because the biological synapse is the basic unit for learning and memory. In this study, a memristor with the simple structure of Ta/viologen diperchlorate [EV(ClO4)2]/terpyridyl-iron polymer (TPy-Fe)/ITO is fabricated to simulate the functions of the synapse. Essential synaptic plasticity and learning behaviours are emulated by using this memristor, such as spike-timing-dependent plasticity and spike-rate-dependent plasticity. It is demonstrated that the redox between a terpyridyl-iron polymer and viologen species leads to our memristor behavior. Furthermore, the learning behavior depending on different amplitudes of voltage pulses is investigated as well. These demonstrations help pave the way for building bioinspired neuromorphic systems based on memristors.

Ag Nanoparticles‐Modified 3D Graphene Foam for Binder‐Free Electrodes of Electrochemical Sensors

Ag nanoparticles-modified 3D graphene foam was synthesized through a one-step in-situ approach and then directly applied as the electrode of an electrochemical sensor. The composite foam electrode exhibited electrocatalytic activity towards Hg(II) oxidation with high limit of detection and sensitivity of 0.11 µM and 8.0 µA/µM, respectively. Moreover, the composite foam electrode for the sensor exhibited high cycling stability, long-term durability and reproducibility. These results were attributed to the unique porous structure of the composite foam electrode, which enabled the surface of Ag nanoparticles modified reduced graphene oxide (Ag NPs modified rGO) foam to become highly accessible to the metal ion and provided more void volume for the reaction with metal ion. This work not only proved that the composite foam has great potential application in heavy metal ions sensors, but also provided a facile method of gram scale synthesis 3D electrode materials based on rGO foam and other electrical active materials for various applications.

Facile method to synthesize silver nanoparticles on the surface of hollow glass microspheres and their microwave shielding properties

In this paper, a facile method for the fabrication of hollow glass microspheres–Ag composite particles with core–shell structures is investigated. Ag-coated hollow glass microspheres with raspberry morphology have been prepared by an in situ composite technique in the presence of polyvinylpyrrolidone (PVP). The as-prepared composite particles are characterized by XRD, SEM, EDS, TEM, IR, and XPS. The results show that 3-aminopropyltriethoxysilane (APTS) coupling can remarkably improve the adhesion between the palladium colloid particles and the surface of hollow glass microspheres, increasing the amount of active sites on such surfaces. With the increase in pH value, the equilibrium of the [Ag(NH3)2]+ solution is destroyed, which is beneficial to the output of Ag nanoparticles. The shell thickness of silver-coated hollow glass microspheres increases from 30 nm to 52 nm with an increase in the concentration of the [Ag(NH3)2]+ solution. The shielding property of the composite particles increases gradually and shows an obvious increase in the range of 30% to 35% with an increase in the volume fraction of the composite particles. When the volume fraction of the filler reaches 35%, electromagnetic shielding effectiveness is between 70 dB and 80 dB with the frequency of electromagnetic wave ranging from 2 GHz to 12 GHz. These results indicate that the Ag-coated glass microspheres core–shell particles could have extensive applications in the electromagnetic compatibility field.

Influence of graphene oxide and multiwalled carbon nanotubes on the dynamic mechanical properties and heat buildup of natural rubber/carbon black composites

In this study, graphene oxide (GO) and multiwalled carbon nanotubes (MWNTs) were incorporated into natural rubber (NR) to study the influence of each of these materials when substituted for carbon black (CB) on the structure and properties of NR/CB composites. The influence of stirring time on the composites used to prepare the masterbatch was also studied. Morphological observations revealed that the dispersion of the filler was improved by partially substituting GO and MWNTs for CB. Improvements in the static mechanical properties and dynamic properties were achieved when the concentration of GO or MWNTs was 1 phr. The highest modulus and hardness was found in the composites with a short stirring time used for the preparation of the masterbatch. When compared to CB-filled vulcanizates, composites with GO had a greater tensile strength and equivalent heat buildup, which is mainly attributed to the larger cross-link density. In this article, compared with the MWNTs, GO is more beneficial to the preparation of rubber composite with high mechanical properties and low heat buildup. This is mainly due to the common functional groups carboxyl, hydroxyl, and epoxide in the GO can improve the dispersion of GO within a matrix.

Highly selective, rapid-functioning and sensitive fluorescent test paper based on graphene quantum dots for on-line detection of metal ions

In this study, test papers based on N-doped graphene quantum dots and graphene quantum dots were designed and prepared. They exhibited a highly selective fluorescence quenching response to Hg(II) and Fe(III) in water for 3.0 s to 2.0 min, respectively. Furthermore, low detection limit (0.1 μM) of the test papers was obtained, which was lower than the toxic level of Hg(II) and Fe(III). Moreover, the concentration of metal ions in water was directly determined according to the quenching time of the fluorescent test paper observed by the naked eye. Therefore, a convenient paper sensor for the rapid, sensitive and selective detection of metal ions in water was developed, which was expected to be applied in the accurate detection and large-scale monitoring of heavy metal pollution in the environment.

Formation and mechanism of a super-hydrophobic surface with wear and salt spray resistance

A super-hydrophobic surface with excellent wear and salt spray resistance was prepared based on bisphenol A-aniline benzoxazine (BA-a), mesoporous material (SBA-15) and imidazole. The mechanism for these resistances was explored. Density gradient structures, organic–inorganic interpenetrating networks and self-similar structures formed in BA-a/SBA-15/imidazole. The tin sheeting surface coated with BA-a/SBA-15/imidazole hardly changed after 10 days of salt spraying, but its contact angle decreased to lower than 90°. After soaking and heat treatment, the contact angle recovered to 168° ± 2°.

Morphological transformations of silver nanoparticles in seedless photochemical synthesis

Photochemical synthesis is an easily controlled and reliable method for the fabrication of silver (Ag) nanoparticles with various morphologies. In this work, we have systematically investigated the seedless photochemical synthesis of anisotropic Ag nanoparticles with and without PVP as surface capping agent. The time evolution of anisotropic Ag nanoparticles during the synthesis process are studied using UV–visible spectra, optical images and transmission electron microscopy. The results show that the light irradiation precisely controls the start and termination of the reaction, and the presence or absence of PVP greatly affects the morphology evolution of anisotropic Ag nanoparticles. With PVP as the surface capping agent, Ag nanoparticles grow into decahedra or prism by the deposition of Ag atoms on {111} or {110} facets through epitaxial growth. However, a different morphology evolution could happen when Ag nanoparticle is synthesized without PVP as surface capping agent. In this case, Ag nanoparticles can fuse into the decahedrons through an edge-selective particle fusion mechanism, which involves attachment, rotation and realignment of Ag nanoparticles. This process was evidenced with HRTEM images at the different stages of the transformation from Ag colloid to decahedra nanoparticles. Oriented attachment and Ostwald ripening also play important role in the transformation process.

Layer-by-layer decoration of MOFs on electrospun nanofibers

The design and fabrication of novel organic–inorganic nanocomposite membranes using metal–organic frameworks as building blocks have attracted numerous scientists. Here, HKUST-1 particles were decorated on crosslinked polymer nanofibers through a layer-by-layer method. The immersion sequence, the crosslinking and the number of the deposition cycles have a significant impact on the formation of the HKUST-1 decorated nanofibrous membranes. Moreover, it has been shown that such a membrane could be applied as a catalyst for visual detection of hydrogen peroxide.

Interfacial modification of basalt fiber filling composites with graphene oxide and polydopamine for enhanced mechanical and tribological properties

Due to the chemical inertness of the basalt fiber (BF) surface, the weaker interfacial bonding between BF and polymer matrices will seriously affect the further application of basalt fiber enhanced composites. In this study, a continuous and compact graphene oxide (GO) layer was grafted onto the surface of basalt fiber (BF) using biomimetic polydopamine (PDA) as a bridge to improve the mechanical and tribological properties of polyamide 6. The impact and flexural strength of the PA6 composites filled by the GO grafting BF (GO–PDA–BF/PA6) indicated that the introduction of GO has made a larger improvement in interface bonding performance between BF and PA6 matrix. The friction and wear tests showed the wear rate of the GO–PDA–BF/PA6 composite decreased by 51% compared with BF/PA6 composites and it also showed the best wear resistance and load-carrying capacity under various applied loads and sliding speeds, explained by the improved interface bonding between GO–PDA–BF and PA6 matrix and the anti-wear protective transfer film formed by GO in the worn surface. This study provided a considerable flexibility strategy of tailoring the interfacial compatibility between reinforcement and matrix for effectively improving the comprehensive performance of composites.