Gang Chang

The Effects of Ta Substitution and K/Na Ratio Variation on the Microstructure and Properties of (K,Na)NbO3-Based Lead Free Piezoelectric Ceramics

Abstract[(Na0.5+yK0.5−y)0.94Li0.06][(Nb0.94Sb0.06)1−xTax]O3 + 0.08 mol% MnO2 lead-free piezoelectric ceramics were fabricated successfully by a conventional solid-state reaction method. The effects of Ta5+ substitution and K/Na ratio variation on the microstructure and properties of the ceramics have been systematically investigated. With the increasing of Ta5+ substitution content, the orthorhombic–tetragonal transition temperature To–t presents obvious “V” type variation while the Curie temperature Tc decreases monotonically. The ceramics properties were further enhanced by adjusting the Na/K ratio of the A-site. Under systematical optimization of the A-site and B-site elements, good overall electrical properties of d33 = 276 pC/N, kp = 44.5%, ε33T/ε0 = 1,175, tanδ = 0.027, Tc = 309 °C, Pr = 21.0 μC/cm2, and Ec = 1.14 kV/mm were obtained for ceramics with Ta5+ content x of 0.05 and Na/K ratio of 57/43 (y = 0.07).

Facile and rapid synthesis of ultrafine PtPd bimetallic nanoparticles and their high performance toward methanol electrooxidation

Uniform and sub-10 nm size bimetallic PtPd nanoparticles (NPs) have been synthesized via a simple and facile method without using any surfactants at an ambient temperature. As a green and clean reductive agent, ascorbic acid (AA) was employed for the coreduction of K2PtCl4 and K2PdCl4 in aqueous solution. The morphology, composition, and structure of PtPd NPs had been characterized by transmission electron microscopy (TEM), field emission high resolution transmission electron microscopy (FE-HRTEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscope (XPS). Comparing with both the monometallic Pt and Pd, the as-prepared alloy nanoparticles show superior electrocatalytic activity and better tolerance against poisoning by intermediates generated during methanol electrooxidation, which makes them a promising electrocatalysts for direct methanol fuel cells (DMFCs). Meanwhile, the green and simple approach could be easily extended to the manufacture of bimetallic or trimetallic alloy nanomaterials.

Pulse Laser Deposition Fabricating Gold Nanoclusters on a Glassy Carbon Surface for Nonenzymatic Glucose Sensing.

A One-step technique for depositing gold nanoclusters (GNCs) onto the surface of a glassy carbon (GC) plate was developed by using pulse laser deposition (PLD) with appropriate process parameters. The method is simple and clean without using any templates, surfactants, or stabilizers. The experimental factors (pulse laser number and the pressure of inert gas (Ar)) that affect the morphology and structure of GNCs, and thus affect the electrocatalytic oxidation performance towards glucose were systematically investigated by means of transmission electron microscopy (TEM) and electrochemical methods (cyclic voltammograms (CV) and chronoamperometry methods). The GC electrode modified by GNCs exhibited a rapid response time (about 2 s), a broad linear range (0.1 to 20 mM), and good stability. The sensitivity was estimated to be 31.18 μA cm(-2) mM(-1) (vs. geometric area), which is higher than that of the Au bulk electrode. It has a good resistance to the common interfering species, such as ascorbic acid (AA), uric acid (UA) and 4-acetaminophen (AP). Therefore, this work has demonstrated a simple and effective sensing platform for the nonenzymatic detection of glucose, and can be used as a new material for a novel non-enzymatic glucose sensor.

A Novel Electrochemical Biosensor Based on a Double-Signal Technique for d(CAG)n Trinucleotide Repeats

Electrochemical sensors now play an important role in analysis and detection of nucleic acids. In this work, we present a novel double-signal technique for electrochemically measuring the sequence and length of the d(CAG)n repeat. The double-signal technique used an electrochemical molecular beacon (a hairpin DNA labeled with ferrocene), which was directly modified on the surface of a gold electrode, while a reporter probe (a DNA sequence labeled with horseradish peroxidase) was hybridized to the target DNA. First a simple single-signal sensor was characterized in which d(CAG)n repeats were detected using a short reporter DNA strand labeled with horseradish peroxidase. To obtain a reliable signal that was dependent on repeat number, a double-signal biosensor was created in which the single strand capture DNA in single-signal sensor was replaced by an electrochemical molecular beacon labeled with ferrocene. When the hairpin DNA hybridized to the target-reporter DNA complex, it opened, resulting in a decreased ferrocene current. Both electrochemical biosensors exhibited high selectivity and sensitivity with low detection limits of 0.21 and 0.15 pM, respectively, for the detection of d(CAG)n repeats. The double-signal sensor was more accurate for the determination of repeat length, which was measured from the ratio of signals for HRP and ferrocene (H/F). A linear relationship was found between H/F and the number of repeats (n), H/F = 0.1398n + 9.89788, with a correlation coefficient of 0.974. Only 10 nM of target DNA was required for measurements based on the value of H/F in the double-signal technique. These results indicated that this new double-signal electrochemical sensor provided a reliable method for the analysis of CAG trinucleotide repeats.

Localized surface plasmon resonance sensing properties of photocatalytically prepared Ag/TiO2 films

Photocatalytic deposition of Ag nanoparticles from a mixed aqueous solution of AgNO 3 and polyvinylpyrrolidone (PVP) onto TiO 2 film supported on indium-tin oxide-coated glass slide (Ag/TiO 2 film) was carried out by using UV light irradiation. The size and shape of the Ag nanoparticles were controlled by the addition of PVP during the photodeposition. In the optical absorption spectra of the Ag/TiO 2 film, the localized surface plasmon resonance (LSPR) absorption of the Ag nanoparticles was observed. When the film was immersed in various kinds of alcohols with the refractive index at 20°C ( ), ranging between 1.3292 and 1.4103, the peak LSPR absorption was shifted to longer wavelengths and the peak absorbance increased with increasing . The spectral change of the Ag/TiO 2 film with larger spherical Ag nanoparticles was more prominent than that with smaller ones.

A novel electrochemical method based on screen-printed electrodes and magnetic beads for detection of trinucleotide repeat sequence d(CAG)n

Electrochemical sensors have been highly developed and play an important role in the early diagnosis of different diseases. In this work, a simple and rapid electrochemical method was developed for the quantitative detection of a trinucleotide repeat (TNR) sequence d(CAG)n based on magnetic beads and screen-printed carbon electrodes. Their combination greatly simplified the operation process. The intensity of the electrochemical signal was linearly correlated against the concentration of the TNR sequence d(CAG)n in the range from 100 pM to 1 μM, with a limit of detection as low as 24 pM. Furthermore, the number of repeats of the TNR sequence d(CAG)n could be detected and also showed a good linear relationship. The proposed method provides a promising rapid and simple method for the detection of a CAG TNR sequence for point-of-care testing in clinical applications.

Energy storage characteristics of (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics with high Sn content

(Pb,La)(Zr,Sn,Ti)O3 (PLZST) antiferroelectric (AFE) materials have been widely investigated for advanced pulsed power capacitors because of their fast charge-discharge rates and superior energy-storage capacity. For practical applications, pulsed power capacitors require not only large energy density but also high energy efficiency, which are very difficult to achieve simultaneously. To address this problem, we herein investigate the energy-storage properties of PLZST AFE ceramics with a high Sn content by considering that the introduction of Sn can make the polarization versus electric-field (P-E) hysteresis loops slimmer. The results show that an optimum Sn content leads to the realization of both large recoverable energy density (Wre) and high energy efficiency (η) in a single material. With a Sn content of 46%, the PLZST AFE ceramic exhibits the best room-temperature energy storage properties with a Wre value as large as 3.2 J/cm3 and an η value as high as 86.5%. In addition, both its Wre and η vary very slightly in the wide temperature range of 20–120 °C. The high Wre and η values and their good thermal stability make the Pb0.97La0.02(Zr0.50Sn0.46Ti0.04)O3 AFE ceramic a promising material for making pulsed power capacitors usable in various conditions.(Pb,La)(Zr,Sn,Ti)O3 (PLZST) antiferroelectric (AFE) materials have been widely investigated for advanced pulsed power capacitors because of their fast charge-discharge rates and superior energy-storage capacity. For practical applications, pulsed power capacitors require not only large energy density but also high energy efficiency, which are very difficult to achieve simultaneously. To address this problem, we herein investigate the energy-storage properties of PLZST AFE ceramics with a high Sn content by considering that the introduction of Sn can make the polarization versus electric-field (P-E) hysteresis loops slimmer. The results show that an optimum Sn content leads to the realization of both large recoverable energy density (Wre) and high energy efficiency (η) in a single material. With a Sn content of 46%, the PLZST AFE ceramic exhibits the best room-temperature energy storage properties with a Wre value as large as 3.2 J/cm3 and an η value as high as 86.5%. In addition, both its Wre and η vary v...