Additive manufacturing or 3D‐printing have become promising fabrication techniques in the field of electrochemical energy storage applications such as supercapacitors, and batteries. Of late, a ...commercially available graphene/polylactic acid (PLA) filament has been commonly used for Fused Deposition Modeling (FDM) 3D‐printing in the fabrication of electrodes for supercapacitors and Li‐ion batteries. This graphene/PLA filament contains metal‐based impurities such as titanium oxide and iron oxide. In this study, we show a strong influence of inherent impurities in the graphene/PLA filament for supercapacitor applications. A 3D‐printed electrode is prepared and subsequently thermally activated for electrochemical measurement. A deep insight has been taken to look into the pseudocapacitive contribution from the metal‐based impurities which significantly enhanced the overall capacitance of the 3D‐printed graphene/PLA electrode. A systematic approach has been shown to remove the impurities from the printed electrodes. This has a broad implication on the interpretation of the capacitance of 3D‐printed composites.
Positive impurities: Inherent impurities, TiO2 and Fe3O4 were found in commercial conductive graphene/PLA filaments used in the printing of 3D‐electrodes by a fused deposition modeling technique. These additives contributed towards pseudocapacitive charge storage kinetics of the 3D‐printed electrodes and dramatically enhanced the overall capacitance.
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•Recent research (2017-20) on fluorescence-based chemosensors for Cu2+ ion.•PET, ESIPT and FRET-based fluorescent sensors have been discussed.•Probes working through these three ...recognition mechanisms have been discussed.•Design, structure, selectivity and sensitivity of the sensors have been summarized.•The review will be helpful for future designing of fluorescent sensors of Cu2+ion.
An essential trace element copper plays several physiological roles in living systems. But at excess concentration, it exerts toxicity and becomes associated with numerous disorders. In this article, we have reviewed the recent developments (from 2017 to 2020) in the field of fluorescence-based chemosensors for the detection of Cu2+ ion. The sensing probes which were built to work through transfer of photo-induced electron (PET), excited-state intramolecular proton (ESIPT) and Förster resonance energy (FRET) mechanisms have been included in this review. Emphasis is given on the design, sensitivity and response of the probe molecules for the detection of Cu2+ ion. Using suitable examples, applications of these three recognition mechanisms for the probing of copper ion have been addressed.
Microsupercapacitors (micro-SCs) with mechanical flexibility have the potential to complement or even replace microbatteries in the portable electronics sector, particularly for portable ...biomonitoring devices. The real-time biomonitoring of the human body’s physical status using lightweight, flexible, and wearable micro-SCs is important to consider, but the main limitation is, however, the low energy density of micro-SCs as compared to microbatteries. Here using a temporally and spatially controlled picosecond pulsed laser, we developed high-energy-density micro-SCs integrated with a force sensing device to monitor a human body’s radial artery pulses. The photochemically synthesized spherical laser-induced MXene (Ti3C2T x )-derived oxide nanoparticles uniformly attached to laser-induced graphene (LIG) act as active electrode materials for micro-SCs. The molecular dynamics simulations and detailed spectroscopic analysis reveal the synergistic interfacial interaction mechanism of Ti–O–C covalent bonding between MXene and LIG. The incorporation of MXene nanosheets improves the graphene sheet alignment and ion transport while minimizing self-restacking. Furthermore, the micro-SCs based on a nano-MXene-LIG hybrid demonstrate high mechanical flexibility, durability, ultrahigh energy density (21.16 × 10–3 mWh cm–2), and excellent capacitance (∼100 mF cm–2 @ 10 mV s–1) with long cycle life (91% retention after 10 000 cycles). Such a single-step roll-to-roll highly reproducible manufacturing technique using a picosecond pulsed laser to induce MXene-derived spherical oxide nanoparticles (size of quantum dots) attached uniformly to laser-induced graphene for biomedical device fabrication is expected to find a wide range of applications.
We have fabricated high-energy-density all-solid-state flexible asymmetric supercapacitor by using a facile novel 3D hollow urchin-shaped coaxial manganese dioxide@polyaniline (MnO2@PANI) composite ...as positive electrode and 3D graphene foam (GF) as negative electrode materials with polyvinyl alcohol (PVA)/KOH gel electrolyte. The coaxial MnO2@PANI composite was fabricated by hydrothermal route followed by oxidation without use of an external oxidant. The formation mechanism of the 3D hollow MnO2@PANI composite occurs first by nucleation and growth of the MnO2 crystal species via dissolution–recrystallization and oriented attachment mechanisms followed by the oxidation of aniline monomers on the MnO2 crystalline template. The self-assembled 3D graphene block was synthesized by hydrothermal route using vitamin C as a reducing agent. The microstructures of the composites are analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The morphology is characterized by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), which clearly showed the formation of urchin-shaped coaxial MnO2@PANI composite. The electrochemical studies are explored by cyclic voltammetry, electrochemical impedance spectrometry, and cyclic charge–discharge tests. The symmetric all-solid-state flexible MnO2@PANI//MnO2@PANI and GF//GF supercapacitors exhibit the specific capacitance of 129.2 and 82.1 F g–1 at 0.5 A/g current density, respectively. The solid-state asymmetric supercapacitor shows higher energy density (37 Wh kg–1) with respect to the solid-state symmetric supercapacitors MnO2@PANI//MnO2@PANI and GF//GF, where the obtained energy density are found to be 17.9 and 11.4 Wh kg–1, respectively, at 0.5 A/g current density. Surprisingly, the asymmetric supercapacitor shows a high energy density of 22.3 Wh kg–1 at a high current density of 5 A g–1. The solid-state asymmetric supercapacitor shows a good cyclic stability in which ∼11% capacitance loss was observed after 5000 cycles.
To inhibit the formation of amyloid fibrils by human γd-crystallin (HGD), a series of four flavonoids (quercertin, rutin, morin and hesperetin) was tested. Only morin had demonstrated significant ...inhibition of HGD fibrillation. Results from fluorimetric assay techniques (using thioflavin T and ANS), FTIR, circular dichroism and microscopic imaging (fluorescence microscopy and transmission electron microscopy) confirmed HGD fibrillation inhibition by morin. HGD-morin complex formation at ground state resulted tryptophan fluorescence quenching through static mechanism, which was also confirmed by determining the excited-state life time of HGD tryptophan residues. Förster resonance energy transfer occurs from HGD to morin. Synchronous, three-dimensional fluorescence, FTIR and circular dichroism results suggest that major changes in HGD conformation did not occur on binding with morin. The interactions between HGD and morin involve hydrogen bonding and/or van der Waals forces. Docking predictions also support experimental results.
Communicated by Ramaswamy H. Sarma
A new flexible all-solid-state asymmetric supercapacitor with very high energy density has been fabricated by adopting a 3D heterogeneous composite based on polyaniline (PANI) and graphene and ...enlarging its operating voltage window. This novel supercapacitor is based on the 3D molybdenum oxide/graphene aerogel (MoO3/GF) composite as the negative electrode and the sandwich-type PANI decorated 3D porous manganese dioxide/reduced graphene oxide hybrid film (PANI/(MnO2−RGO)/PANI) as the positive electrode material. Polyvinyl alcohol/potassium hydroxide (PVA/KOH) was used as the gel electrolyte. The self-assembled 3D MoO3/GF was synthesized by hydrothermal route followed by heat treatment in a furnace. For the positive electrode, a facile novel 3D MnO2−RGO porous film was first fabricated by vacuum filtration of MnO2 and GO suspension, followed by hydrothermal chemical reduction. Then, PANI nanofibers were grown on top of the hybrid film. The fabrication steps show a facile formation of the 3D sandwich-type PANI/(MnO2−RGO)/PANI porous hybrid film. The asymmetric supercapacitor (MoO3/GF//PANI/(MnO2−RGO)/PANI) showed a high energy density of 51.91 Wh kg−1 at a power density of 0.838 kW kg−1. The asymmetric cells were flexible, and three cells connected in series could illuminate a green-LED for 62 s.
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•A novel 3D MoO3/graphene aerogel was synthesized using hydrothermal method.•A 3D porous sandwich-type polyaniline/graphene-MnO2/polyaniline hybrid film was developed.•The all-solid-state asymmetric supercapacitor showed excellent electrochemical properties.
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•2-Hydroxy-naphthalene hydrazone based probe (HNP) displayed high colorimetric selectivity towards Cu2+.•The probe demonstrated high selectivity and sensitivity for Al3+ ion ...fluorimetrically.•Naked eye sensor for Cu2+ and Al3+.•Found useful for in vivo detection and imaging of Al3+.•Application of the probe in paper strips and logic gate for detection of metal ions.
2-Hydroxy-naphthalene hydrazone based probe HNP demonstrated high selectivity towards sensing of Cu2+ and Al3+ in colorimetric and fluorimetric methods respectively. HNP can be used as “naked-eye” sensor based on the change of its color from very light yellow to bright yellow (for Cu2+) and colorless (for Al3+). The colorimetric detection mechanism for Cu2+ involved enhancement in internal charge transfer (ICT). In the detection of Al3+ through fluorescence, combined effect of ICT and excited-state intramolecular proton transfer (ESIPT) played major role. Job’s plots based on UV–vis (Cu2+) and fluorescence (Al3+) data along with mass spectral study indicated 1:1 metal to HNP stoichiometry. The binding of the probe HNP with Al3+ and Cu2+ was found chemically reversible on addition of EDTA. Binding mode of the probe with the metal ions was proposed based on spectroscopic data and density functional theory (DFT). Moreover, effect of pH and response time was also determined. The probe was found useful for in vivo detection and imaging of Al3+ in MDA-MB-231 cells. Paper strips of the probe were made and used for naked eye detection of Cu2+ and Al3+. The probe was also used in the construction of logic gate for detection of Al3+.
Iron, an essential trace element exhibits detrimental effects on human health when present at higher or lower concentration than the required. Therefore, there is a pressing demand for sensitive and ...selective detection of Fe
in water, food etc. Unfortunately, in several instances, the traditional approaches suffer from a number of shortcomings like complicated procedures, limited sensitivity, poor selectivity and more expensive and time consuming. The scope of optical tuning and excellent photophysical properties of carbon- based nanomaterials like carbon dots (C-dots) and graphene dots (g-dots) have made them promising optical sensors of metal ions. Moreover, high surface area, superior stability of such materials contributes towards the fruitful development of sensors. The present review offered critical information on the fabrication and fluorimetric applications of these functional nanomaterials for sensitive and selective detection of Fe
. An in-depth discussion on fluorescent C-dots made from naturally occurring materials and chemical techniques were presented. Effect of doping in C-dots was also highlighted in terms of improved fluorescence response and selectivity. In a similar approach g-dots were also discussed. Many of these sensors exhibited great selectivity, superior sensitivity, high quantum yield, robust chemical and photochemical stability and real-time applicability. Further improvement in these factors can be targeted to develop new sensors.
