•The reduction progress of graphene oxide (GO) by ascorbic acid was studied.•Depending on the reduction time, the properties of the reduced product can be tuned.•High purity grade natural graphite ...from Sri Lanka was used as the raw material.•GO and reduced GO (RGO) was synthesized in a much cheaper and scalable way.
Graphene oxide (GO) and reduced graphene oxide (RGO) are in greater demand in many research fields. As a result, the synthesis of these materials on a large scale in a costeffective manner is more concerned for numerous applications. In the present work, GO was synthesized by oxidizing natural graphite and reduced by ascorbic acid (AA), which is a green reductant. The reduced products obtained at different time periods were in detail characterized by UV–Visible spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopy, Raman spectroscopy, thermogravimetric analysis (TGA), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Results showed that the oxidation of graphite has given highly oxidized GO with a 9.30 Å interlayer space and about 33% of oxygen atomic percentage. Until 50 min of the reduction, both GO and RGO coexist. The reduction rate is fast within the first 30 min. In addition, the suitability of natural graphite over synthetic graphite for the synthesis of GO is shown. The findings of this work pave the way to select GO and RGO for applications of interest in a cheap, green and efficient manner.
Bifunctional catalysts can facilitate two different electrochemical reactions with conflicting characteristics. Here, a highly reversible bifunctional electrocatalyst for rechargeable zinc–air ...batteries (ZABs) is reported featuring a “core–shell structure” in which N‐doped graphene sheets wrap around vanadium molybdenum oxynitride nanoparticles. Single Mo atoms are released from the particle core during synthesis and anchored to electronegative N‐dopant species in the graphitic shell. The resultant Mo single‐atom catalysts excel as active oxygen evolution reaction (OER) sites in pyrrolic‐N and as active oxygen reduction reaction (ORR) sites in pyridinic‐N environments. ZABs with such bifunctional and multicomponent single‐atom catalysts deliver high power density (≈376.4 mW cm−2) and long cycle life of over 630 h, outperforming noble‐metal‐based benchmarks. Flexible ZABs that can tolerate a wide range of temperatures (−20 to 80 °C) under severe mechanical deformation are also demonstrated
Synthesis of multicomponent core–shell structures presents a versatile route to produce bifunctional molybdenum‐based single‐atom‐catalysts. Zinc–air batteries with such multicomponent single‐atom catalysts deliver high power density (≈376.4 mW cm−2) and a long cycle life of over 630 h, significantly outperforming noble‐metal‐based benchmarks.
Reduced graphene oxide (rGO) has huge potential for membrane applications owing to its appropriate interlayer spacing (0.34–0.37 nm) that enables it to block salt ions as small as Na+ with high ...precision. However, fabrication of uniform rGO membranes is a great challenge because of the loss of its polar functional groups during preparation from graphene oxide (GO). Although there have been several studies on GO membranes and a few on rGO for water purification, very few attempts to understand the role of oxygen-containing functional groups in successful rGO membrane formation. The present work deals with the investigation of the key factors and functional groups that govern membrane formation. This work also utilizes the facile approach of synthesizing reduced GO by environmentally viable hydrothermal reduction. Further characterizations show that the hydroxyl and carboxyl groups are principally responsible for the formation of uniform rGO membranes. The rGO (treated at 160°C for 2 h) membrane with a small amount of unreduced GO presented shows the lowest Na+/Cl- ion permeation with the highest membrane flux, which is suggested to be a potential candidate for water desalination.
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•Examination of reduced graphene oxide (rGO) membrane formability by reduction.•Uniform rGO membranes were formed at the partial reduction stage (GO/rGO coexist).•The presence of hydroxyl and carboxyl groups assists membrane formation.•The ion permeation and water transport are manipulated by degree of reduction.
Production of graphene from graphene oxide (GO), having properties similar to pristine graphene, is the most challenging task so far in the graphene sector. Finding an ideal reduction method that can ...remove oxygen-containing functionalities while repairing the lattice defects present in GO is essential. Thermal annealing of GO with an additional carbon source has emerged as a viable solution for this issue where reduction of GO can be conducted with the simultaneous restoration of lattice defects. Herein, we review this topic in-depth, in terms of morphological, structural, and electrical properties of GO films, basically, for the development in the field of graphene-based electronic devices.
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Hydrothermal reduction is a promising approach for graphene oxide (GO) reduction since it is environmentally friendly, simple, and cost effective. We present a detailed study of structural changes ...occurring in graphene oxide during the reduction process. The correlations between the interlayer spacing, chemical states, work functions, surface morphology, level of disorders, the number of layers, and processing time are elucidated. The results reveal that GO flakes remain in the early stage of the reduction process and that they are fully reduced after a 4-h hydrothermal treatment. With an increase in the reduction time, the resulting product, i.e., reduced graphene oxide, has a low oxygen content, small interlayer spacing, and crumbled and wrinkled structures. We are convinced that these properties can be tuned to a desired level for various applications.
Given the rapid deployment of telemedicine at the onset of the COVID - 19 pandemic, updated assessment methods are needed to study and characterize telemedicine programs. We developed a novel semi - ...structured survey instrument to systematically describe the characteristics and implementation processes of telemedicine programs in primary care.
In the context of a larger study aiming to describe telemedicine programs in primary care, a survey was developed in 3 iterative steps: 1) literature review to obtain a list of telemedicine features, facilitators, and barriers; 2) application of three evaluation frameworks; and 3) stakeholder engagement through a 2-stage feedback process. During survey refinement, items were tested against the evaluation frameworks while ensuring it could be completed within 20-25 min. Data reduction techniques were applied to explore opportunity for condensed variables/items.
Sixty initially identified telemedicine features were reduced to 32 items / questions after stakeholder feedback. Per the life cycle framework, respondents are asked to report a month in which their telemedicine program reached a steady state, i.e., "maturation". Subsequent questions on telemedicine features are then stratified by telemedicine services offered at the pandemic onset and the reported point of maturation. Several open - ended questions allow for additional telemedicine experiences to be captured. Data reduction techniques revealed no indication for data reduction.
This 32-item semi-structured survey standardizes the description of primary care telemedicine programs in terms of features as well as maturation process. This tool will facilitate evaluation of and comparisons between telemedicine programs across the United States, particularly those that were deployed at the pandemic onset.
Celotno besedilo
Dostopno za:
CEKLJ, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
7.
Shockwave-based THz emission in air Huang, Hsin-Hui; Nagashima, Takeshi; Hatanaka, Koji
Optics express,
02/2023, Letnik:
31, Številka:
4
Journal Article
Recenzirano
Odprti dostop
THz emission in air under the irradiation of a pair of tightly-focused femtosecond laser pulses (800nm, 35fs) with nanosecond time delay and micro-meter spatial offsets is studied with ...polarization-sensitive THz time-domain spectroscopy and time-resolved imaging. The pre-pulse irradiation induces air-breakdown at its focus, which results in the expansion of shockwave front traveling outward. When the main pulse irradiates such shockwave front far from the pre-pulse focus with nanosecond delay, THz emission intensity was enhanced up to ∼13-times and its linear polarization was aligned along the line between the two focus positions of the pre- and the main pulses which is parallel to the expansion direction of the shockwave front. Asymmetric density profiles of the shockwave fronts prepared by the pre-pulse irradiation define the polarization of THz emission. Mechanisms are discussed from the viewpoint of electron diffusion in such asymmetric density profiles.
In this paper, we report synthesis of novel nanoparticle catalyst of iridium oxide supported on carbon nanotube (IrO2/CNT) and characterization of activity and durability for oxygen evolution ...reaction (OER). The IrO2/CNT catalyst was prepared from iridium complex and COOH-CNT by hydrothermal method. The synthesized IrO2/CNT catalysts was characterized by transmission electron microscopy, x-ray diffraction, Raman microscopy, Fourier transfer-infrared spectroscopy, x-ray photoelectron spectroscopy, thermogravimetric analysis and electrochemical methods. The average particle size of the IrO2 particles on CNT is 1.7 nm and the loading amount of IrO2 is 4 wt%. The XPS measurement reveals that Ir complex was completely converted to iridium oxide through hydrothermal treatment. The IrO2/CNT catalyst showed sufficient performance for OER activity and durability in sulfuric acid solution. Our results indicate that IrO2/CNT is one of the prospective candidate catalysts for water electrolyzer.
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•Iridium oxide nanoparticles supported on CNT are synthesized by hydrothermal method.•The IrO2 nanoparticles of 1.7 nm in diameter were highly dispersed on CNT surface.•IrO2/CNT catalyst shows high activity and durability for oxygen evolution reaction.•The strong interaction between IrO2 and CNT affects catalytic activity and stability.
The present work details the development of IrO
2
nanoparticles (nps) supported on B-doped reduced graphene oxide as an oxygen evolution reaction (OER) electrocatalyst for electrochemical water ...splitting. IrO
2
on boron-doped reduced graphene oxide (B-rGO) is synthesized
via
sequential steps of pyrolysis to prepare B-rGO and a hydrothermal method for modification of B-rGO with IrO
2
nps. With 2 wt% boron doping in graphene, a 0.10 V decrease in the OER onset potential is observed for IrO
2
catalysts on B-rGO (IrO
2
-B-rGO). The Tafel slope for the OER on B-rGO is estimated to be 124.8 mV dec
−1
, which is lower than that on IrO
2
-rGO and suggests strong adsorption of intermediates such as OH on the IrO
2
surface by the B-doping of graphene in acidic solution. In this article, we demonstrate the effect of boron doping on the electronic structure modification of the IrO
2
nps, which is expected to generate more electrocatalytic centers and enhance the catalytic activity.
The present work details the development of IrO
2
nanoparticles (nps) supported on B-doped reduced graphene oxide as an oxygen evolution reaction (OER) electrocatalyst for electrochemical water splitting.
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•β PVDF nano lamellae (PVDF-NL) was achieved with a remarkable thickness of 8 nm.•Reduced graphene oxide (rGO) was used as templates to realize ultrathin PVDF-NL.•Atomic force ...microscopy images revealed the formation of PVDF-NL at the interface of on rGO.•Exceptional piezoresponse of −28.08 pm/V was demonstrated in ultrathin PVDF-NL.
This study proposes a novel approach to fabricate self-assembled ultrathin β-PVDF nano lamellae (PVDF-NL) directly over a sp2 hybridized van der Waals (vdW) carbon lattice support with a remarkable thickness of 8 nm. Needle shaped PVDF-NL were successfully crystallized on thermally reduced graphene oxide sheets (rGO) via a simple melting and recrystallization method. Subsequently, switchable polarization is demonstrated in PVDF using piezoresponse force microscopy (PFM) resulting in a large piezoelectric coefficient (d33) of −28.08 ± 2.26 pm/V. This work delivers an exceptional technique to fabricate and tailor the crystal phases of PVDF using two-dimensional (2D) reduced graphene oxide lattice with a large piezoresponse, opening new avenues in 2D ferroelectric polymers for the usage in nanoelectronic devices.
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