Optimized NiCo2O4/rGO hybrid nanostructures on carbon fiber as an electrode for asymmetric supercapacitors

The NiCo₂O₄ nanowires and reduced graphene oxide (rGO) hybrid nanostructure has been constructed on carbon fibers (NiCo₂O₄/rGO/CF) via a hydrothermal method. The effects of graphene oxide (GO) concentration on the structure and performance of the NiCo₂O₄/rGO/CF were investigated in detail to obtain the optimized electrode. When the GO concentration was 0.4 mg ml⁻¹, the rGO/NiCo₂O₄/CF composite exhibited a maximum specific capacitance of 931.7 F g⁻¹ at 1 A g⁻¹, while that of NiCo₂O₄/CF was 704.9 F g⁻¹. Furthermore, the NiCo₂O₄/rGO/CF//AC asymmetric supercapacitor with a maximum specific capacitance of 61.2 F g⁻¹ at 1 A g⁻¹ was fabricated, which delivered a maximum energy density (24.6 W h kg⁻¹) and a maximum power density (8477.7 W kg⁻¹). Results suggested that the NiCo₂O₄/rGO/CF composite would be a desirable electrode for flexible supercapacitors.

The NiCo₂O₄ nanowires and rGO hybrid nanostructure was constructed on carbon fibers (NiCo₂O₄/rGO/CF) via a hydrothermal method.     

Hexadecyl trimethyl ammonium bromide assisted growth of NiCo2O4@reduced graphene oxide/ nickel foam nanoneedle arrays with enhanced performance for supercapacitor electrodes

NiCo₂O₄@reduced graphene oxide (rGO)/nickel foam (NF) composites were prepared via a hydrothermal method followed by annealing assisted by hexadecyl trimethyl ammonium bromide (CTAB). NiCo₂O₄@rGO/NF nanoneedle arrays grew directly on Ni foam (NF) without using a binder. The effect of graphene oxide (GO) concentration on the electrochemical properties of the composite was studied. When the GO concentration was 5 mg L⁻¹, the as-prepared NiCo₂O₄@rGO/NF reaches the highest specific capacitance of 1644 F g⁻¹ at a current density of 1 A g⁻¹. Even at 15 A g⁻¹, the specific capacitance is still 1167 F g⁻¹ and the capacitance retention rate is 89% after 10 000 cycles at 10 A g⁻¹. Furthermore, a NiCo₂O₄@rGO/NF//graphene hydrogel (GH) asymmetric supercapacitor cell (ASC) device was assembled and exhibits a high specific capacitance of 84.13 F g⁻¹ at 1 A g⁻¹ and excellent cycle stability (113% capacitance retention) after 10 000 charge/discharge cycles at 10 A g⁻¹. This provides potential for application in the field of supercapacitors due to the outstanding specific capacitance, rate performance and cycle stability of NiCo₂O₄@rGO/NF.

Anisotropic NiCo₂O₄ nanoneedle arrays grew directly on Ni foam in the presence of rGO via the hydrothermal method followed by annealing assisted by hexadecyl trimethyl ammonium bromide (CTAB).     

A multifunctional composite Fe3O4/MOF/l-cysteine for removal,magnetic solid phase extraction and fluorescence sensing of Cd(ii)

Fe₃O₄/MOF (metal organic framework)/l-cysteine was synthesized and applied for the removal of Cd(ii) from wastewater. The adsorption kinetics and isotherms were investigated, and the results indicated that the adsorption obeyed the pseudo-second-order kinetic model and Langmuir isotherm. The maximum adsorption capacity was calculated to be 248.24 mg g⁻¹. Fe₃O₄/MOF/l-cysteine was further applied to determine trace amounts of Cd(ii) in real water samples using ICP-AES (inductively coupled plasma-atomic emission spectroscopy) based on magnetic solid-phase extraction (MSPE). The determination limit was 10.6 ng mL⁻¹. Additionally, Fe₃O₄/MOF/l-cysteine can also be used as a fluorescent sensor for “turn-off” detection of Cd(ii), and the detection limit was 0.94 ng mL⁻¹.

Fe₃O₄/MOF (metal organic framework)/l-cysteine was synthesized and applied for the removal of Cd(ii) from wastewater.     

One-pot synthesis of CoFe2O4/rGO hybrid hydrogels with 3D networks for high capacity electrochemical energy storage devices

CoFe₂O₄/reduced graphene oxide (CoFe₂O₄/rGO) hydrogel was synthesized in situ via a facile one-pot solvothermal approach. The three-dimensional (3D) network structure consists of well-dispersed CoFe₂O₄ nanoparticles on the surfaces of graphene sheets. As a binder-free electrode material for supercapacitors, the electrochemical properties of the CoFe₂O₄/rGO hybrid hydrogel can be easily adjusted by changing the concentration of the graphene oxide (GO) precursor solution. The results indicate that the hybrid material made using 3.5 mg mL⁻¹ GO solution exhibits an outstanding specific capacitance of 356 F g⁻¹ at 0.5 A g⁻¹, 68% higher than the pure CoFe₂O₄ counterpart (111 F g⁻¹ at 0.5 A g⁻¹), owing to the large specific surface area and good electric conductivity. Additionally, an electrochemical energy storage device based on CoFe₂O₄/rGO and rGO was assembled, which exhibits a high energy density of 17.84 W h kg⁻¹ at a power density of 650 W kg⁻¹ and an excellent cycling stability with 87% capacitance retention at 5 A g⁻¹ after 4000 cycles. This work takes one step further towards the development of 3D hybrid hydrogel supercapacitors and highlights their potential application in energy storage devices.

CoFe₂O₄/reduced graphene oxide (CoFe₂O₄/rGO) hydrogel was synthesized in situ via a facile one-pot solvothermal approach.     

N/S co-doped coal-based porous carbon spheres as electrode materials for high performance supercapacitors

N/S co-doped porous carbon spheres (NSPCSs) were prepared by a simple ultrasonic spray pyrolysis (USP) using the mixed solution of coal oxide and l-cysteine, and without a subsequent activation process. The surface properties of carbon materials have been successfully modified by the concurrent incorporation of N and S. So the capacitive performance of NSPCSs was greatly enhanced. It is used as a supercapacitor electrode to achieve a high specific capacitance of 308 F g⁻¹ at a current density of 1 A g⁻¹ and 90.2% capacitance retention even after 10 000 cycles at 5 A g⁻¹. These numerical results show that the supercapacitors based on coal-based carbon materials have great potential in high performance electrochemical energy storage.

N/S co-doped porous carbon spheres were prepared using one step strategy for high performance supercapacitors.     

Preparation of α-Fe2O3/rGO composites toward supercapacitor applications

Reduced graphene oxide (rGO) integrated with iron oxide nanoparticles (α-Fe₂O₃/rGO) composites with different morphologies were successfully obtained through the in situ synthesis and mechanical agitation methods. It was found that the α-Fe₂O₃ was densely and freely dispersed on the rGO layer. By comparing electrochemical properties, the sheet-like α-Fe₂O₃/rGO composites demonstrate excellent electrochemical performance: the highest specific capacitance, and excellent cycling stability and rate capacity. The specific capacitance is 970 F g⁻¹ at a current density of 1 A g⁻¹ and the capacitance retention is 75% after 2000 cycles with the current density reaching 5 A g⁻¹. It is mainly due to the synergistic effect between the α-Fe₂O₃ and rGO, and the high conductivity of the rGO offers a fast channel for the movement of electrons.

Preparation of α-Fe₂O₃/rGO composites for supercapacitor application using in situ synthesis and a mechanical agitation method.     

One-step in situ growth of ZnS nanoparticles on reduced graphene oxides and their improved lithium storage performance using sodium carboxymethyl cellulose binder

ZnS nanoparticles are in situ grown on reduced graphene oxides (rGO) via a simplified one-step hydrothermal method. Sodium carboxymethyl cellulose (CMC) is firstly applied as the binder for ZnS based anodes and shows a more advantageous binding effect than PVDF. To simplify the synthesis procedure, l-cysteine is added as the sulfur source for ZnS and simultaneously as the reducing agent for rGO. The average diameter of ZnS nanoparticles is measured to be 13.4 nm, and they uniformly disperse on the rGO sheets without any obvious aggregation. As anode materials, the CMC bound ZnS–rGO nanocomposites can maintain a high discharge capacity of 705 mA h g⁻¹ at a current density of 500 mA g⁻¹ for 150 cycles. The significantly improved electrochemical performance mainly derives from the combined effects of the small and uniformly dispersed ZnS nanoparticles, the high conductivity and structural flexibility of rGO and the strong binding ability of CMC.

ZnS nanoparticles are in situ grown on reduced graphene oxides (rGO) via a simplified one-step hydrothermal method.     

Ready-to-use binder-free Co(OH)2 plates@porous rGO layers/Ni foam electrode for high-performance supercapacitors

In this work, an outstanding nano-structured composite electrode is fabricated through the co-deposition of Co(OH)₂ nanoplates and porous reduced GO (p-rGO) nanosheets onto Ni foam (NF). Through field emission scanning electron microscopy and transmission electron microscopy observations, it was confirmed that porous reduced graphene oxide sheets are completely wrapped by uniform hexagonal Co(OH)₂ plates. Due to the unique architecture of both components of the prepared composite, a high surface area of 234.7 m² g⁻¹ and mean pore size of 3.65 nm were observed for the Co(OH)₂@p-rGO composite. The constructed Co(OH)₂@p-rGO/NF composite electrode shows higher energy storage capability compared to that of Co(OH)₂/NF and p-rGO/NF electrodes. The Co(OH)₂/NF electrode shows specific capacitances of 902 and 311 F g^–1 at 5 and 30 A g^–1, while the Co(OH)₂@p-rGO/NF electrode delivers 1688 and 1355 F g^–1 under the same current loads, respectively. Furthermore, when the current load was increased from 1 to 30 A g^–1, 74.5% capacitance retention was observed for the Co(OH)₂@p-rGO/NF electrode, indicating its outstanding high-power capability, while the Co(OH)₂/NF electrode retained only 38.5% of its initial capacitance. The fabricated Co(OH)₂@p-rGO/NF//rGO/NF ASC device shows an areal capacitance of 3.29 F cm⁻², cycling retention of 91.2% after 4500 cycles at 5 A g⁻¹ and energy density of 68.7 W h kg⁻¹ at a power density of 895 W kg⁻¹. The results of electrochemical tests prove that Co(OH)₂@p-rGO/NF exhibits good performance as a positive electrode for use in an asymmetric supercapacitor device. The prepared porous composite electrode is thus a promising candidate for use in supercapacitor applications.

Fabrication mechanism of a ready-to-use Co(OH)2@p-rGO/NF electrode: (a) base generation step, (b) electrophoretic deposition of rGO onto NF and (c) chemical formation of Co(OH)2 on rGO.     

Flexible solid-state supercapacitor based on tin oxide/reduced graphene oxide/bacterial nanocellulose

We demonstrate a flexible and light-weight supercapacitor based on bacterial nanocellulose (BNC) incorporated with tin oxide (SnO₂) nanoparticles, graphene oxide (GO) and poly(3,4-ethylenedioxyiophene)-poly(styrenesulfonate) (PEDOT:PSS). The SnO₂ and GO flakes are introduced into the fibrous nanocellulose matrix during bacteria-mediated synthesis. The flexible PEDOT:PSS/SnO₂/rGO/BNC electrodes exhibited excellent electrochemical performance with a capacitance of 445 F g⁻¹ at 2 A g⁻¹ and outstanding cycling stability with 84.1% capacitance retention over 2500 charge/discharge cycles. The flexible solid-state supercapacitors fabricated using PEDOT:PSS/SnO₂/rGO/BNC electrodes and poly(vinyl alcohol) (PVA)-H₂SO₄ coated BNC as a separator exhibited excellent energy storage performance. The fabrication method demonstrated here is highly scalable and opens up new opportunities for the fabrication of flexible cellulose-based energy storage devices.

A novel, simple and scalable method for the incorporation of tin oxide (SnO₂) and graphene oxide (GO) into bacterial nanocellulose during its growth for the fabrication of a flexible, scalable and environmental-friendly energy storage device was reported.     

High electrochemical performance of ink solution based on manganese cobalt sulfide/reduced graphene oxide nano-composites for supercapacitor electrode materials

Large scale supercapacitor electrodes were prepared by 3D-printing directly on a graphite paper substrate from ink solution containing manganese cobalt sulfide/reduced graphene oxide (MCS/rGO) nanocomposites. The MCS/rGO composite solution was synthesized through the dispersion of MCS NPs and rGO in dimethylformamide (DMF) solvent at room temperature. Their morphology and composition were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray diffraction (EDS). The role of rGO on decreasing charge transfer resistance and enhancing ion exchange was discussed. The MCS/rGO electrode exhibits an excellent specific capacitance of 3812.5 F g⁻¹ at 2 A g⁻¹ and it maintains 1780.8 F g⁻¹ at a high current density of 50 A g⁻¹. The cycling stability of the electrodes reveals capacitance retention of over 92% after 22 000 cycles at 50 A g⁻¹.

Large scale supercapacitor electrodes were prepared by 3D-printing directly on a graphite paper substrate from ink solution containing manganese cobalt sulfide/reduced graphene oxide (MCS/rGO) nanocomposites.     

Facile design and synthesis of a nickel disulfide/zeolitic imidazolate framework-67 composite material with a robust cladding structure for high-efficiency supercapacitors

In this paper, a core–shell structure nickel disulfide and ZIF-67 composite electrode material (NiS₂/ZIF-67) was synthesized by a two-step method. Firstly, spherical NiS₂ was synthesized by a hydrothermal method, dispersed in methanol, then reacted and coated by adding cobalt ions and 2-methylimidazole to obtain the NiS₂/ZIF-67 core–shell composite. The NiS₂/ZIF-67 composite shows a high specific capacitance (1297.9 F g⁻¹ at 1 A g⁻¹) and excellent cycling durability (retaining 110.0% after 4000 cycles at 5 A g⁻¹). Furthermore, the corresponding hybrid supercapacitor (NiS₂/ZIF-67//AC HSC) has an energy density of 9.5 W h kg⁻¹ at 411.1 W kg⁻¹ (6 M KOH) and remarkable cycling stability (maintaining 133.3% after 5000 cycles). Its excellent electrochemical performance may be due to the core–shell structure and the synergistic effect between the transition metal sulfide and metal–organic framework. These results indicate that the NiS₂/ZIF-67 composite as an electrode material with a core–shell structure has potential application in high-efficiency supercapacitors.

A core–shell structured ZIF-67 composite electrode material has been synthesized by a two-step method. The sample shows superior specific capacitance and the assembled HSC exhibits prominent power/energy density and durability.     

Template-assisted synthesis of NiCoO2 nanocages/reduced graphene oxide composites as high-performance electrodes for supercapacitors

Here we reported a coordinating etching and precipitating method to synthesize a complex binary metal oxides hollow cubic structure. A novel NiCoO₂/rGO composite with a structure of NiCoO₂ nanocages anchored on layers of reduced graphene oxide (rGO) were synthesized via a simple template-assisted method and the electrochemical performance was investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy tests as a faradaic electrode for supercapacitors at a graphene weight ratio of 1 wt% (1%). When used as electrode materials for electrochemical capacitors, the NiCoO₂/rGO composites achieved a specific capacity of 1375 F g⁻¹ at the current density of 1 A g⁻¹ and maintained 742 F g⁻¹ at 10 A g⁻¹. After 3000 cycles, the supercapacitor based on these nanocage structures shows long-term cycling performance with a high capacity of 778 F g⁻¹ at a current density of 1 A g⁻¹. These outstanding electrochemical performances are primarily attributed to the special morphological structure and the combination of mixed transition metal oxides and rGO, which not only maintains a high electrical conductivity for the overall electrode but also prevents the aggregation and volume expansion of electrochemical materials during the cycling processes.

Here we reported a coordinating etching and precipitating method to synthesize a complex binary metal oxides hollow cubic structure.     

A green l-cysteine modified cellulose nanocrystals biosorbent for adsorption of mercury ions from aqueous solutions

Using a green biosorbent to remove toxic mercury ions from aqueous solutions is a significant undertaking. In the present study, a novel biosorbent, l-cysteine modified cellulose nanocrystals (Lcys-CNCs), was prepared by functionalizing high surface area cellulose nanocrystals with l-cysteine through periodate oxidation and reductive amination reaction. Lcys-CNCs were characterized by FT-IR, ¹³C CP-MAS NMR, elemental analysis, XPS, zeta potential and SEM. As cellulose nanocrystals are the natural nanomaterial, and l-cysteine contains strong mercury chelating groups, Lcys-CNCs show excellent adsorption capacity for mercury ions. The experimental conditions such as pH, contact time, and initial mercury ion concentration are discussed. The pseudo-second order model can describe the removal kinetics of Hg(ii) more accurately than the pseudo-first order model. The adsorption isotherm study of Hg(ii) followed the Langmuir model of monolayer adsorption. The maximum uptake capacity of Lcys-CNCs was determined to be 923 mg g⁻¹. Lcys-CNCs can remove mercury ions with 93% removal efficiency within 5 min from a 71 mg L⁻¹ solution. For Cd(ii), Pb(ii), Cu(ii) and Zn(ii) ions, Lcsy-CNCs can selectively adsorb Hg(ii) ions and the removal efficiency is 87.4% for Hg(ii). This study suggests Lcsy-CNCs are a green and highly efficient biosorbent for adsorption of mercury ions from aqueous solutions.

A green biosorbent, l-cysteine modified cellulose nanocrystals, was successfully synthesized and applied to adsorb mercury ions from aqueous solutions.     

The cross-talk between lateral sheet dimensions of pristine graphene oxide nanoparticles and Ni2+ adsorption

This study investigated the removal of nickel(ii) ions by using two sizes of graphene oxide nanoparticles (GO – 450 nm and GO – 200 nm). The thickness and lateral sheet dimensions of GO are considered to be an important adsorbent and promising method for sufficient removal of metals like nickel, lead, copper, etc. The graphite oxide was prepared by oxidation–reduction reaction (Hummers method), and the final product was labelled as GO – 450 nm. A tip sonicator was used to reduce the size of particles to 200 nm under controlled conditions (time and power of sonication). FTIR spectroscopy shows that both sizes of GO particles contain several types of oxygen groups distributed onto the surface of GO particles. Scanning electron microscopy (SEM) and the statistical analysis confirmed the formation of these two sizes of GO particles. The GO – 200 nm performed better removal of Ni(ii) compared with GO – 450 nm, due to more surfaces being available. The adsorption capacity of GO particles increased drastically from 45 mg g⁻¹ to 75 mg g⁻¹ for GO – 450 nm and GO – 200 nm respectively, these values were carried out after 2 h of incubation. The kinetics of adsorption and several parameters like initial concentration at equilibrium, pH, temperature, and adsorbent dose are controlled and studied by using UV-visible spectroscopy. The results indicated a significant potential of GO – 200 nm as an adsorbent for Ni(ii) ion removal. An additional experiment was performed to estimate the surface area of GO – 450 nm and GO – 200 nm, the results show that the surface areas of GO – 450 nm and GO – 200 nm are 747.8 m² g⁻¹ and 1052.2 m² g⁻¹ respectively.

This study investigated the removal of nickel(ii) ions by using two sizes of graphene oxide nanoparticles (GO – 450 nm and GO – 200 nm).     

Facile preparation of flexible binder-free graphene electrodes for high-performance supercapacitors

A facile two-step strategy to prepare flexible graphene electrodes has been developed for supercapacitors using thermal reduction of graphene oxide (GO) and thermally reduced graphene oxide (TRGO) composite films. The tunable porous structure of the GO/TRGO film provided channels to release the high pressure generated by CO₂ gas. The graphene electrode obtained from reduced-GO/TRGO (1 : 1 in mass ratio) film showed great flexibility and high film density (0.52 g cm⁻³). Using the EMI-BF₄ electrolyte with a working voltage of 3.7 V, the as-fabricated free-standing reduced-GO/TRGO (1 : 1) film achieved a great gravimetric capacitance of 180 F g⁻¹ (delivering a gravimetric energy density of 85.6 W h kg⁻¹), a volumetric capacitance of 94 F cm⁻³ (delivering a volumetric energy density of 44.7 W h L⁻¹), and a 92% retention after 10 000 charge/discharge cycles. In addition, the solid state flexible supercapacitor with the free-standing reduced-GO/TRGO (1 : 1) film as the electrodes and the EMI-BF₄/poly (vinylidene fluoride hexafluopropylene) (PVDF-HFP) gel as the electrolyte also demonstrated a high gravimetric capacitance of 146 F g⁻¹ with excellent mechanical flexibility, bending stability, and electrochemical stability. The strategy developed in this study provides great potentials for the synthesis of flexible graphene electrodes for supercapacitors.

A supercapacitor electrode is developed with a free-standing graphene film by a facile two-step strategy. The graphene electrode achieved a gravimetric capacitance of 180 F g⁻¹ and a volumetric capacitance of 94 F cm⁻³.     

Au–Ag core–shell composite nanoparticles as a selective and sensitive plasmonic chemical probe for l-cysteine detection in Lens culinaris (lentils)

The present work reported is a simple and selective method for the colorimetrical detection of l-cysteine in Lens culinaris (or lentils) using Au–Ag core–shell (Au core Ag shell) composite nanoparticles as a chemical probe. The phenomenon is based on the color change of composite nanoparticles from yellowish brown to light blue, followed by a shift of the localized surface plasmon resonance (LSPR) absorption band in the UV-visible region (i.e., 200–800 nm) with the addition of l-cysteine into the solution of bimetallic nanoparticles. The mechanism for the detection of l-cysteine is based on the electrostatic interaction of the metal ion with the thiol group of the amino acid, which causes the red shift of the LSPR band at 685 nm. The size distribution, morphology, composition and optical properties of the Au–Ag core–shell composite nanoparticles were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), energy dispersive X-ray diffraction (EDX), UV-visible spectrophotometer and Fourier transform infrared spectroscopy (FTIR) techniques. An excellent linearity range for the present method was observed in the range of 20–140 μg mL⁻¹ with a limit of detection at 1.95 μg mL⁻¹ and correlation coefficient (R²) of 0.986. A good% recovery of 4.0% showed the selectivity of the method for l-cysteine determination from sample matrices. The advantageous features of the present method are being simple, rapid, low cost and selectivity towards the determination of l-cysteine in lentils.

The present work reported is a simple and selective method for the colorimetrical detection of l-cysteine in Lens culinaris (or lentils) using Au–Ag core–shell (Au core Ag shell) composite nanoparticles as a chemical probe.     

Diaminopyrene modified reduced graphene oxide as a novel electrode material for excellent performance supercapacitors

In this paper, novel reduced graphene oxide (rGO) composites (DAPrGOs) modified by diaminopyrene (DAP) were successfully synthesized via a facile solvothermal reaction method and used for supercapacitors. Compared with the pristine rGO, the DAPrGO1 electrode showed distinctly better performance (397.63 F g⁻¹vs. 80.29 F g⁻¹ of pristine rGO at 0.5 A g⁻¹) with small charge transfer resistance. When a symmetric device was fabricated using DAPrGO1 as the active material, it also exhibited a high capacitance of 82.70 F g⁻¹ at 0.5 A g⁻¹ with an energy density of 25.84 W h kg⁻¹ at a power density of 375 W kg⁻¹, and even offered a high power density of 7500 W kg⁻¹ (18.71 W h kg⁻¹) at 10 A g⁻¹. Moreover, the device possessed good electrochemical stability up to 20 000 cycles, implying promising applications in energy storage fields.

Schematic illustration of the facile synthesis process of DAPrGOs nanocomposites, Ragone plots and the superior cyclic stability of the assembled DAPrGO1//DAPrGO1 SSS.     

Solution-processed graphene oxide electrode for supercapacitors fabricated using low temperature thermal reduction

We present a low temperature and solution-based fabrication process for reduced graphene oxide (rGO) electrodes for electric double layer capacitors (EDLCs). Through the heat treatment at 180 °C between the spin coatings of graphene oxide (GO) solution, an electrode with loosely stacked GO sheets could be obtained, and the GO base coating was partially reduced. The thickness of the electrodes could be freely controlled as these electrodes were prepared without an additive as a spacer. The GO coating layers were then fully reduced to rGO at a relatively low temperature of 300 °C under ambient atmospheric conditions, not in any chemically reducing environment. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) results showed that the changes in oxygen functional groups of GO occurred through the heat treatments at 180 and 300 °C, which clearly confirmed the reduction from GO to rGO in the proposed fabrication process at the low thermal reduction temperatures. The structural changes before and after the thermal reduction of GO to rGO analyzed using Molecular Dynamic (MD) simulation showed the same trends as those characterized using Raman spectroscopy and XPS. An EDLC composed of the low temperature reduced rGO-based electrodes and poly(vinyl alcohol)/phosphoric acid (PVA/H₃PO₄) electrolyte gel was shown to have high specific capacitance of about 240 F g⁻¹ together with excellent energy and power densities of about 33.3 W h kg⁻¹ and 833.3 W kg⁻¹, respectively. Furthermore, a series of multiple rGO-based EDLCs was shown to have fast charging and slow discharging properties that allowed them to light up a white light emitting diode (LED) for 30 min.

We present a low temperature and solution-based fabrication process for reduced graphene oxide (rGO) electrodes for electric double layer capacitors (EDLCs).     

Chiral fluorescence recognition of glutamine enantiomers by a modified Zr-based MOF based on solvent-assisted ligand incorporation

In this study, three types of chiral fluorescent zirconium-based metal–organic framework materials were synthesized using l-dibenzoyl tartaric acid as the chiral modifier by the solvent-assisted ligand incorporation method, which was the porous coordination network yellow material, denoted as PCN-128Y. PCN-128Y-1 and PCN-128Y-2 featured unique chiral selectivity for the Gln enantiomers amongst seven acids and the highly stable luminescence property, which were caused by the heterochiral interaction and aggregation-induced emission. Furthermore, a rapid fluorescence method for the chiral detection of glutamine (Gln) enantiomers was developed. The homochiral crystals of PCN-128Y-1 displayed enantiodiscrimination in the quenching by d-Gln such that the ratio of enantioselectivity was 2.0 in 30 seconds at pH 7.0, according to the Stern–Volmer quenching plots. The detection limits of d- and l-Gln were 6.6 × 10⁻⁴ mol L⁻¹ and 3.3 × 10⁻⁴ mol L⁻¹, respectively. Finally, both the maximum adsorption capacities of PCN-128Y-1 for the Gln enantiomers (Q_e(l-Gln) = 967 mg g⁻¹; Q_e(d-Gln) = 1607 mg g⁻¹) and the enantiomeric excess value (6.2%) manifested that PCN-128Y-1 had strong adsorption capacity for the Gln enantiomers and higher affinity for d-Gln.

A stable luminescent zirconium-based MOF PCN-128Y-1 was synthesized by the SALI method and applied as a specific chiral selective adsorbent and a chiral fluorescence sensor for the recognition and quantitative analysis of Gln enantiomers.     

Anti-Hepatitis B Virus Activity and Metabolism of 2′,3′-Dideoxy-2′,3′-Didehydro-β-l(?)-5-Fluorocytidine

2′,3′-Dideoxy-2′,3′-didehydro-β-l(−)-5-fluorocytidine [l(−)Fd4C] was found to be at least 10 times more potent than β-l-2′,3′-dideoxy-3′-thiacytidine [l(−)SddC; also called 3TC, or lamivudine]against hepatitis B virus (HBV) in culture. Its cytotoxicity against HepG2 growth in culture was also greater than that of l(−)SddC (3TC). There was no activity of this compound against mitochondrial DNA synthesis in cells at concentrations up to 10 μM. The dynamics of recovery of virus from the medium of cells pretreated with equal drug concentrations were slower with l(−)Fd4C than with l(−)SddC (3TC). l(−)Fd4C could be metabolized to mono-, di-, and triphosphate forms. The degree of l(−)Fd4C phosphorylation to the 5′-triphosphate metabolite was higher than the degree of l(−)SddC (3TC) phosphorylation when equal extracellular concentrations of the two drugs were used. The apparent K_m of l(−)Fd4C phosphorylated metabolites formed intracellularly was higher than that for l(−)SddC (3TC). This may be due in part to a difference in the behavior of l(−)Fd4C and l(−)SddC (3TC) towards cytosolic deoxycytidine kinase. Furthermore, l(−)Fd4C 5′-triphosphate was retained longer within cells than l(−)SddC (3TC) 5′-triphosphate. l(−)Fd4C 5′-triphosphate inhibited HBV DNA polymerase in competition with dCTP with a K_i of 0.069 ± 0.015 μM. Given the antiviral potency and unique pharmacodynamic properties of l(−)Fd4C, this compound should be considered for development as an expanded-spectrum anti-HBV drug.Hepatitis B virus (HBV) infection is one of the most serious health issues in the world today (1, 3). β-l(−)-2′,3′-Dideoxy-3′-thiacytidine [l(−)SddC; also called 3TC, or lamivudine] (Fig. ​(Fig.1)1) is the first β-l(−) nucleoside analog identified by us and others to have potent activity against HBV in culture (4, 8, 12, 17). This drug exerts its action by inhibiting HBV DNA synthesis due to the preferential interaction of the l(−)SddC (3TC) 5′-triphosphate metabolite with HBV DNA polymerase (4). Unlike dideoxycytidine (ddC, or zalcitabine), a β-d(+) nucleoside analog with the natural nucleoside conformation in DNA and RNA, l(−)SddC (3TC) does not have potent activity against mitochondrial DNA (mtDNA) synthesis, which is important for maintaining the function of cells (4). Clinical trials of l(−)SddC (3TC) for the treatment of chronic HBV infection are ongoing and look promising (2, 7, 13, 16, 18, 19). Its potential value for HBV-infected patients undergoing liver transplantation is also being evaluated, since l(−)SddC (3TC) can suppress HBV DNA serum levels in these patients. However, apparent l(−)SddC (3TC)-resistant HBV emerged in some patients upon long-term treatment (13, 16, 18). The HBV-resistant genotype appears to be associated with the mutation of methionine to valine or isoleucine in the YMDD motif of HBV DNA polymerase (13, 16, 18). This mutation was previously demonstrated and could render duck HBV resistant to l(−)SddC (3TC) (11). It is not clear if this mutation alone can lead to resistance and, if so, to what degree HBV resistance to l(−)SddC (3TC) develops. Open in a separate windowFIG. 1Structures of l(−)deoxycytidine analogs.One approach to overcoming clinical drug resistance is to use higher dosages of l(−)SddC (3TC) given the therapeutic index of the compound in vitro. However, the potency of l(−)SddC (3TC) against HBV in the clinic could be a limiting factor given the dosage application. The antiviral potency is determined not only by its antiviral activity but also by the pharmacodynamic nature of its active metabolite, l(−)SddC (3TC) 5′-triphosphate, in vivo. A more potent compound with more favorable pharmacodynamic behavior of intracellularly active metabolites would be worth exploring.In the studies reported herein, we describe the anti-HBV activity, metabolism, and pharmacodynamic properties of 2′,3′-dideoxy-2′,3′-didehydro-β-l(−)-5-fluorocytidine [l(−)Fd4C](Fig. 1) in comparison with those of l(−)SddC (3TC), including its behavior toward deoxycytidine kinase and the interaction of l(−)Fd4C 5′-triphosphate with virion-associated HBV DNA polymerase. Preliminary studies of the anti-HBV and anti-human immunodeficiency virus (HIV) activities of l(−)Fd4C were previously reported by us and others (10, 15).