Synthesis and Characterization of Highly Crystalline Bi-Functional Mn-Doped Zn2SiO4 Nanostructures by Low-Cost Sol-Gel Process.

Herein, we demonstrate a process for the synthesis of a highly crystalline bi-functional manganese (Mn)-doped zinc silicate (Zn2SiO4) nanostructures using a low-cost sol-gel route followed by solid state reaction method. Structural and morphological characterizations of Mn-doped Zn2SiO4 with variable doping concentration of 0.03, 0.05, 0.1, 0.2, 0.5, 1.0, and 2.0 wt% were investigated by using X-ray diffraction and high-resolution transmission electron microscopy (HR-TEM) techniques. HR-TEM-assisted elemental mapping of the as-grown sample was conducted to confirm the presence of Mn in Zn2SiO4. Photoluminescence (PL) spectra indicated that the Mn-doped Zn2SiO4 nanostructures exhibited strong green emission at 521 nm under 259 nm excitation wavelengths. It was observed that PL intensity increased with the increase of Mn-doping concentration in Zn2SiO4 nanostructures, with no change in emission peak position. Furthermore, magnetism in doped Zn2SiO4 nanostructures was probed by static DC magnetization measurement. The observed photoluminescence and magnetic properties in Mn-doped Zn2SiO4 nanostructures are discussed in terms of structural defect/lattice strain caused by Mn doping and the Jahn-Teller effect. These bi-functional properties of as-synthesized Zn2SiO4 nanostructures provide a new platform for their potential applications towards magneto-optical and spintronic and devices areas.

An ultra high performance, lead-free Bi2WO6:P(VDF-TrFE)-based triboelectric nanogenerator for self-powered sensors and smart electronic applications.

Obtaining sustainable, high output power supply from triboelectric nanogenerators still remains a major issue that restricts their widespread use in self-powered electronic applications. In this work, an ultra-high performance, non-toxic, flexible triboelectric nanogenerator based on bismuth tungstate (Bi2WO6):polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) is fabricated. A hydrothermal technique is used to synthesize highly crystalline Bi2WO6 nanoparticles that are then incorporated inside the P(VDF-TrFE) matrix nanofiber mat using electrospinning over an aluminum-coated PET substrate to yield a nanogenerator with a device configuration of Cu-coated PET/(Bi2WO6:P(PVDF-TrFE)) nanofiber mat/Al-coated PET. The highly crystalline nature of the biconcave shaped Bi2WO6 nanoparticles and ß - P(VDF-TrFE) is confirmed by X-ray powder diffraction (XRD) and Raman spectroscopic techniques. The dielectric constant of the Bi2WO6:P(PVDF-TrFE) nanofiber mat was studied and a high dielectric constant of 44 was observed. The as-fabricated nanogenerator delivers a very high output voltage (open circuit) of 205 V and current density (short circuit) of 11.91 mA m-2 at ∼0.15 kgf without any electric poling, which is higher than all the prior reports in this field. The fabricated nanogenerator possesses very high output stability and ultra-sensitivity with a swift response time of 60 ms. This outstanding performance of the nanogenerator can be ascribed to the synergistic combination of the ß-phase P(VDF-TrFE) polymer and non-centrosymmetric nature of Bi2WO6 nanoparticles. Furthermore, a Bi2WO6-based pH sensor is driven by the energy obtained from the as-fabricated nanogenerator and the real time demonstration of the nanogenerator powering a calculator is also demonstrated. The strategy outlined here presents a cost-effective, high performance alternative for driving various portable bio-compatible self-powered electronic devices.

Humidity Sustainable Hydrophobic Poly(vinylidene fluoride)-Carbon Nanotubes Foam Based Piezoelectric Nanogenerator.

Light weight lead free, polymer, and carbon nanotubes based flexible piezoelectric nanogenerators have prompted widespread concern for harvesting mechanical energy and powering next generation electronics devices. Herein, lightweight polyvinylidene fluoride (PVDF)-carbon nanotube (CNT) foam was prepared to fabricate humid resistant hydrophobic flexible piezoelectric nanogenerator to converts mechanical energy into electricity for the first time. Hydrophobic piezoelectric PVDF-CNT foam with density of 0.15 g/cm3 was prepared by solution route. PVDF-CNT foam exhibited crystalline and a well-defined chain likes structure with 65% fraction of ß-phase. Self-poled PVDF-CNT foam shows piezoelectric charge coefficient (d33) of 9.4 pC/N. High d33 of PVDF-CNT foam is caused by dipole alignment induced by local electric field of CNT in the microcellular structure of PVDF. The developed foam exhibits ultrahigh dielectric constant (ε') ∼ 3048 at 150 Hz. Flexible piezoelectric PVDF-CNT foam based nanogenerator was fabricated, which generates high output voltage ∼12 V and current density of 30 nA/cm2 at small compressive pressure of 0.02 kgf. Piezoelectric output performance was measured under different humid condition and an output voltage up to 8 V was achieved even under 60% RH condition. PVDF-CNT foam exhibited hydrophobic behavior and high surface water contact angle of 139°. Such high output voltage even under small pressure, without applying electrical poling and under humid condition was originated though CNT induced self-alignment of electric dipoles in PVDF polymer. These excellent performances of developed foam based device confirmed its potential application in organic based ultrasensitive self-powered nanosensors and nanosystems.

A high performance flexible two dimensional vertically aligned ZnO nanodisc based piezoelectric nanogenerator via surface passivation.

Herein, we present the growth of pristine vertically aligned flexible two dimensional (2D) pure ZnO nanodiscs via a simple seed assisted solution route and their use in the fabrication of a piezoelectric nanogenerator. The preferred growth direction and morphology of wurtzite ZnO nanodiscs were investigated using X-ray diffraction and field emission scanning electron microscopy (FESEM) studies. A flexible piezoelectric nanogenerator was fabricated using the vertically aligned ZnO nanodiscs as the active piezoelectric material and a carbon nanotube-polydimethylsiloxane (CNT : PDMS) film as the top electrode. This unique 2D-type ZnO nanodisc-based nanogenerator generated a direct current (DC) type output voltage and current density of about 2.5 V and 30 nA cm-2 under compressive vertical strain, respectively. Significant enhancement of the piezoelectric output voltage from the flexible nanogenerator based on the vertically aligned two dimensional (2D) zinc oxide (ZnO) nanodiscs was achieved via thermal annealing. An output voltage and current density of 17 V and 150 nA cm-2 were detected from the thermally annealed 2D ZnO nanodisc based nanogenerator which is approximately 8 times higher (voltage) than that from the pristine nanogenerator. It is proposed that the output performance of the vertically aligned ZnO nanodisc based nanogenerators increases due to surface passivation and reduction of oxygen vacancies.