Peizhi Guo

Thickness‐Gradient Films for High Gauge Factor Stretchable Strain Sensors

High-gauge-factor stretchable strain sensors are developed by utilizing a new strategy of thickness-gradient films with high durability, and high uniaxial/isotropic stretchability based on the self-pinning effect of SWCNTs. The monitoring of detailed damping vibration modes driven by weak sound based on such sensors is demonstrated, making a solid step toward real applications.

Facile Synthesis of ZnFe2O4 Nanoparticles with Tunable Magnetic and Sensing Properties

Nanoparticles (NPs) and colloidal nanocrystal clusters (CNCs) of ZnFe2O4 were synthesized by using a solvothermal method in a controlled manner through simply adjusting the solvents. When a glycerol/water mixture was used as the solvent, ZnFe2O4 NPs were obtained. However, using ethylene glycol solvent yielded well-dispersed ZnFe2O4 CNCs. X-ray diffraction (XRD) and transmission electron microscopy (TEM) data confirmed that the ZnFe2O4 NPs were a single crystalline phase with tunable sizes ranging from 12 to 20 nm, while the ZnFe2O4 CNCs of submicrometer size consisted of single-crystalline nanosheets. Magnetic measurement results showed that the ZnFe2O4 NPs were ferromagnetic with a very small hysteresis loop at room temperature. However, CNCs displayed a superparamagnetic behavior due to preferred orientations of the nanosheets. Electrochemical sensing properties showed that both the size of the NPs and the structure of the CNCs had a great influence on their electrochemical properties in the reduction of H2O2. Based on the experimental results, the formation mechanisms of both the ZnFe2O4 CNCs and NPs as well as their structure-property relationship were discussed.

Rational design of graphitic carbon based nanostructures for advanced electrocatalysis

The development of electrocatalysts plays a pivotal role in electrocatalytic reactions because the catalyst determines not only the overall reaction efficiency but also the cost. Carbon materials with good electrical conductivity and large surface area have been used as efficient electrocatalyst supports for a wide range of electrocatalyses. Recently, it has been realized that carbons themselves are also promising nonmetal electrocatalysts. In this regard, the electrocatalytic activities of carbons can be tailored by surface modification or building in particular dopants/defects. In the accumulation of the profound knowledge of the electrocatalytic nature and the technological advances, there is increasing interest in developing carbon-based catalysts for various applications. In this review, we summarize the recent progress in the rational design and preparation of graphitic carbon-based materials for advanced electrocatalysis including oxygen reduction and evolution reactions, hydrogen evolution reaction, and carbon dioxide reduction, to provide deep insights into the electrocatalysis for advanced energy conversion and storage.

Preparation of Porous Hollow SiO2 Spheres by a Modified Stöber Process Using MF Microspheres as Templates

Using the surface charged and acid dissolvable melamine formaldehyde (MF) microspheres as sacrificial hard templates, silica coated MF core–shell composite microspheres, denoted as MF@SiO2, were synthesized via a surfactant-assisted sol–gel process by using tetraethyl orthosilicate (TEOS) as silica source. Hollow SiO2 spheres with mesoporous shells were then obtained after selective removal of the MF cores and the pore directing surfactant by hydrochloric acid etching or calcinations in air. Interesting shrinkage phenomena were observed in both the hollow products derived from hydrochloric acid etching and calcinations. The influence of the ratio of MF sphere to TEOS and the removal method of the MF core on the size of the hollow spheres, the shell thickness and the shell surface roughness have been studied. The composition, the thermal stability, the morphology, the surface area and pore size distribution, the wall thickness and adsorption properties of the hollow spheres derived from hydrochloric acid etching and calcinations were also investigated and compared based on the FTIR, SEM, TEM, TGA, Nitrogen adsorption–desorption and spectrophotometer techniques or measurements.

Solvothermal synthesis of MnFe2O4 colloidal nanocrystal assemblies and their magnetic and electrocatalytic properties

Submicrometer MnFe2O4 colloidal nanocrystal assemblies (CNAs) have been synthesized controllably by using a solvothermal method through simply adjusting synthetic reagents. The size and microstructure of MnFe2O4 CNAs were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results showed that MnFe2O4 CNAs were well-separated and uniform with the size scales ranging from 230 nm to 950 nm, which were composed of primary crystalline nanoparticles with the sizes ranging from 16 nm to 43 nm. Room-temperature magnetic measurement results showed that MnFe2O4 CNAs were weakly ferromagnetic with small remnant saturation and coercivity values. The magnetization saturation values of CNAs were increased with the increase of the size of primary nanoparticles. Electrochemical measurements showed that the size of primary nanoparticles of MnFe2O4 CNAs had an important effect on the electrochemical reduction of H2O2. However, the electrocatalytic activity of MnFe2O4 CNAs for oxygen reduction reaction closely correlated with both the crystal size and self-assembly of primary nanoparticles. Based on the experimental results, the formation mechanisms of MnFe2O4 CNAs as well as the relationship between their structures and properties have been analyzed and discussed.

One-step solvothermal preparation of Fe3O4/graphene composites at elevated temperature and their application as anode materials for lithium-ion batteries

A one-step high-temperature solvothermal process (can be used up to 400 °C) has been explored for the preparation of Fe3O4/graphene composites. The influence of high temperature (>230 °C) on the structure, morphology and electrochemical properties of the resulting Fe3O4/graphene composites was investigated by XRD, SEM, TEM and N2 adsorption–desorption measurements. Electrochemical performances of the as-prepared Fe3O4/graphene composites at different temperatures were evaluated in coin-type cells as anode materials for lithium-ion batteries. In comparison with the traditional solvothermal method (<240 °C), the high-temperature method does not require an additional calcination process yet it still could result in Fe3O4/graphene composites with pure phase and excellent electrochemical properties. A preferred solvothermal temperature of 280 °C has been deduced based on a series of control experiments. The Fe3O4/graphene composite derived at 280 °C exhibited a high reversible capacity of 907 mA h g−1 at 0.1 C (92.6 mA g−1) even after 65 cycles, showing outstanding cycle stability. It also exhibited a high rate capability of 410 mA h g−1 at 2 C (1852 mA g−1). The role of the graphene substrates in improving the electrochemical properties of the composite is discussed based on the morphology, structure, phase and electrochemical property studies.

Structural Regulation of PdCu2 Nanoparticles and Their Electrocatalytic Performance for Ethanol Oxidation

Two types of PdCu2 nanoparticles were prepared through one-pot synthesis and a two-step reducing process, named as PdCu2-1 and PdCu2-2, respectively. The morphology and structure of as-prepared samples were investigated by transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma-optical emission spectrometry. Results showed that more Pd atoms were buried in the inside of PdCu2-1, whereas more available Pd sites were distributed on the surface of PdCu2-2. The electrochemical measurements indicated that both PdCu2-1 and PdCu2-2 nanoparticles showed a higher electrocatalytic activity than that for pure Pd nanoparticles. In particular, PdCu2-2 predictably exhibited a better stability and durability as well as a lower onset potential and a higher catalytic current density than that of PdCu2-1 toward ethanol oxidation in alkaline media. On the basis of these studies, the formation mechanisms of both the PdCu2 catalysts and the relationship between their structure and properties were discussed in this paper.

An RAPET approach to in situ synthesis of carbon modified Li4Ti5O12 anode nanocrystals with improved conductivity

Carbon modified lithium titanate (Li4Ti5O12) anode nanocrystals for Li-ion batteries were synthesized by directly treating the titanium alkoxide and lithium acetate ethanol solution via the Reaction under Autogenic Pressure at Elevated Temperature (abbreviated to RAPET). The mixture of the liquid precursors decomposed during the RAPET process and then reacted in situ and transformed into carbon-modified Li4Ti5O12 anode nanocrystals. The organic moieties in the titanium alkoxide and the lithium salt provided both the oxygen and carbon for the synthesis. The resulting products were characterized by X-ray diffraction (XRD), elemental analysis, scanning electronic microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), nitrogen adsorption–desorption measurements, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge testing. The influences of the titanium alkoxide precursors, i.e. the length of the alkoxy group, on the properties of the final products and the presence of the in situ resulting carbon on the electrochemical performance have been investigated.

Insights into the electrocatalysis of nitrobenzene using chemically-modified carbon nanotube electrodes

The electrochemical behavior of nitrobenzene and its derivatives at chemically-functionalized multi-wall carbon nanotubes (MWNTs) modified electrodes was studied. Experimental results showed that hydroxyl-containing MWNTs exhibited the highest electrocatalytic activity among the used MWNTs because of its weak capacitive features and oxygen-containing functional groups. The cycle voltammetrys of nitrobenzene derivatives on the MWNTs modified electrodes can be easily tuned by changing the substituted groups of nitrobenzene. Based on the experimental data, the electrochemical reaction mechanisms of nitrobenzene and its derivatives on the MWNTs modified electrodes have been discussed and analyzed.

Preparation of cellulose based microspheres by combining spray coagulating with spray drying

Porous microspheres of regenerated cellulose with size in range of 1-2 μm and composite microspheres of chitosan coated cellulose with size of 1-3 μm were obtained through a two-step spray-assisted approach. The spray coagulating process must combine with a spray drying step to guarantee the formation of stable microspheres of cellulose. This approach exhibits the following two main virtues. First, the preparation was performed using aqueous solution of cellulose as precursor in the absence of organic solvent and surfactant; Second, neither crosslinking agent nor separated crosslinking process was required for formation of stable microspheres. Moreover, the spray drying step also provided us with the chance to encapsulate guests into the resultant cellulose microspheres. The potential application of the cellulose microspheres acting as drug delivery vector has been studied in two PBS (phosphate-buffered saline) solution with pH values at 4.0 and 7.4 to mimic the environments of stomach and intestine, respectively.