Three-dimensional bimodal pore-rich G/MXene sponge amalgamated with vanadium diselenide nanosheets as a high-performance electrode for electrochemical water-oxidation/reduction reactions

Exploring new strategies to design non-precious and efficient electrocatalysts can provide a solution for sluggish electrocatalytic kinetics and sustainable hydrogen energy. Transition metal selenides are potential contenders for bifunctional electrocatalysis owing to their unique layered structure, low band gap, and high intrinsic activities. However, insufficient access to active sites, lethargic water dissociation, and structural degradation of active materials during electrochemical reactions limit their activities, especially in alkaline media. In this article, we report a useful strategy to assemble vanadium diselenide (VSe2) into a 3D MXene/rGO-based sponge-like architecture (VSe2@G/MXe) using hydrothermal and freeze-drying approaches. The 3D hierarchical meso/macro-pore rich sponge-like morphology not only prevents aggregation of VSe2 nanosheets but also offers a kinetics-favorable framework and high robustness to the electrocatalyst. Synergistic coupling of VSe2 and a MXene/rGO matrix yields a heterostructure with a large specific surface area, high conductivity, and multi-dimensional anisotropic pore channels for uninterrupted mass transport and gas diffusion. Consequently, VSe2@G/MXe presented superior electrochemical activity for both the HER and OER compared to its counterparts (VSe2 and VSe2@G), in alkaline media. The overpotentials required to reach a cathodic and anodic current density of 10 mA cm-2 were 153 mV (Tafel slope = 84 mV dec-1) and 241 mV (Tafel slope = 87 mV dec-1), respectively. The Rct values at the open circuit voltage were as low as 9.1 Ω and 1.41 Ω for the HER and OER activity, respectively. Importantly, VSe2@G/MXe withstands a steady current output for a long 24 h operating time. Hence, this work presents a rational design for 3D microstructures with optimum characteristics for efficient bifunctional alkaline water-splitting.

Gadolinium doped zinc ferrite nanoarchitecture reinforced with a carbonaceous matrix: a novel hybrid material for next-generation flexible capacitors

Herein, nanostructured Gd-doped ZnFe2O4 (GZFO) has been synthesized via the sol-gel route and its CNT-reinforced nanohybrid was formed via an advanced ultrasonication method. The as-synthesized, hybrid electroactive materials have been supported on aluminum foil (AF) to design a flexible electrode for hybrid capacitor (HC) applications. Nanostructured material synthesis, Gd-doping, and CNT reinforcement approaches have been adopted to develop a rationally designed electrode with a high surface area, boosted electrical conductivity, and enhanced specific capacitance. Electrochemical impedance spectroscopy, galvanostatic charge/discharge, and cyclic voltammetry processes have been used to measure the electrochemical performance of the prepared ferrite material-based working electrodes in a 3M KOH solution. A nanohybrid-based working electrode (GZFO/C@AF) shows superior rate capacitive and electrochemical aptitude (specific capacitance, rate performance, and cyclic activity) than its counterpart working electrodes (ZFO@AF and GZFO@AF). The hybrid working electrode (GZFO/C@AF electrode) shows a high specific capacitance of 887 F g-1 and good retention of 94.5% for 7000 cycles (at 15 Ag-1). The maximum energy density and power density values for the GZFO/C@AF electrode are 40.025 Wh Kg-1 and 279.78 W Kg-1, respectively. Based on the findings of the electrochemical experiments, GZFO/C@AF shows promise as an electrode material for hybrid capacitors that provide energy to wearable electronic devices.

Iron/vanadium co-doped tungsten oxide nanostructures anchored on graphitic carbon nitride sheets (FeV-WO3@g-C3N4) as a cost-effective novel electrode material for advanced supercapacitor applications

In this work, we studied the effect of iron (Fe) and vanadium (V) co-doping (Fe/V), and graphitic carbon nitride (g-C3N4) on the performance of tungsten oxide (WO3) based electrodes for supercapacitor applications. The lone pair of electrons on nitrogen can improve the surface polarity of the g-C3N4 electrode material, which may results in multiple binding sites on the surface of electrode for interaction with electrolyte ions. As electrolyte ions interact with g-C3N4, they quickly become entangled with FeV-WO3 nanostructures, and the contact between the electrolyte and the working electrode is strengthened. Herein, FeV-WO3@g-C3N4 is fabricated by a wet chemical approach along with pure WO3 and FeV-WO3. All of the prepared samples i.e., WO3, FeV-WO3, and FeV-WO3@g-C3N4 were characterized by XRD, FTIR, EDS, FESEM, XPS, Raman, and BET techniques. Electrochemical performance is evaluated by cyclic voltammetry (CV), galvanic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS). It is concluded from electrochemical studies that FeV-WO3@g-C3N4 exhibits the highest electrochemical performance with specific capacitance of 1033.68 F g-1 at scan rate 5 mV s-1 in the potential window range from -0.8 to 0.25 V, that is greater than that for WO3 (422.76 F g-1) and FeV-WO3 (669.76 F g-1). FeV-WO3@g-C3N4 has the highest discharge time (867 s) that shows it has greater storage capacity, and its coulombic efficiency is 96.7%, which is greater than that for WO3 (80.1%) and FeV-WO3 (92.1%), respectively. Furthermore, excellent stability up to 2000 cycles is observed in FeV-WO3@g-C3N4. It is revealed from EIS measurements that equivalent series resistance and charge transfer values calculated for FeV-WO3@g-C3N4 are 1.82 Ω and 0.65 Ω, respectively.

Large-scale sonochemical fabrication of a Co3O4-CoFe2O4@MWCNT bifunctional electrocatalyst for enhanced OER/HER performances

Herein, we have prepared a mixed-phase Co₃O₄-CoFe₂O₄@MWCNT nanocomposite through a cheap, large-scale, and facile ultrasonication route followed by annealing. The structural, morphological, and functional group analyses of the synthesized catalysts were performed by employing various characterization approaches such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The resultant samples were tested for bifunctional electrocatalytic activity through various electrochemical techniques: cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). The prepared Co₃O₄-CoFe₂O₄@MWCNT nanocomposite achieved a very high current density of 100 mA cm^-2 at a lower (290 mV and 342 mV) overpotential (vs. RHE) and a smaller (166 mV dec^-1 and 138 mV dec^-1) Tafel slope in the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, compared to Co₃O₄-CoFe₂O₄. The excellent electrochemical activity of the as-prepared electrocatalyst was attributed to the uniform incorporation of Co₃O₄-CoFe₂O₄ over MWCNTs which provides high redox active sites, a greater surface area, better conductivity, and faster charge mobility. Furthermore, the enhanced electrochemical active surface, low charge-transfer resistance (R_ct), and higher exchange current density (J₀) of the Co₃O₄-CoFe₂O₄@MWCNT ternary composite are attributed to its superior behavior as a bifunctional electrocatalyst. Conclusively, this study demonstrates a novel and large-scale synthesis approach for bifunctional electrocatalysts with a high aspect ratio and abundance of active sites for high-potential energy applications.

An efficient and stable iodine-doped nickel hydroxide electrocatalyst for water oxidation: synthesis, electrochemical performance, and stability

The design of oxygen evolution reaction (OER) catalysts with higher stability and activity by economical and convenient methods is considered particularly important for the energy conversion technology. Herein, a simple hydrothermal method was adopted for the synthesis of iodine-doped nickel hydroxide nanoparticles and their OER performance was explored. The electrocatalysts were structurally characterized by powder X-ray diffraction analysis (P-XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), and BET analysis. The electrochemical performance of the electrocatalysts was assessed by cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. The abundant catalytic active sites, oxygen vacancies, low charge-transfer resistance, and a high pore diameter to pore size ratio of iodine-doped Ni(OH)₂ were responsible for its excellent catalytic activity, whereby OER was initiated even at 1.52 V (vs. RHE) and a 330 mV overpotential was needed to reach a 40 mV cm⁻² current density in 1 M KOH solution. The material also exhibited a low Tafel slope (46 mV dec⁻¹), which suggests faster charge-transfer kinetics as compared to its counterparts tested under the same electrochemical environment. It is worth noting that this facile and effective approach suggests a new way for the fabrication of metal hydroxides rich in oxygen vacancies, thus with the potential to boost the electrochemical performance of energy-related systems.

Oxygen evolution reaction mechanism under alkaline conditions over the iodine-doped Ni(OH)₂ surface.

DyxMnFe2-xO4 nanoparticles decorated over mesoporous silica for environmental remediation applications

An efficient, environment-friendly and economical catalyst to control contaminants of environment is an enduring interest in recent years. In this study, a new composite, Dy_xMnFe_2-xO₄nanoparticles decorated over mesoporous silica was synthesized and utilized for removal of organic pollutant. Highly crystalline nature of Dy_xMnFe_2-xO₄ nanoparticles and amorphous nature of material was confirmed by XRD (X-ray diffraction) technique. Infrared spectra of fabricated material before and after adsorption of dye molecules evidenced the successful adsorption of dye molecules by fabricated adsorbent. From field emission scanning electron microscopic (FESEM) images of Dy³⁺ substituted MnFe₂O₄ composite with mesoporous silica, it was clearly observed that ferrite particles of size 20-30 nm were decorated on the surface of mesoporous silica particles and distributed well over spherical silica balls homogeneously. Its magnificent mesoporous nature was revealed from BET (nitrogen adsorption-desorption measurements) analysis. Surface area, pore volume and average pore size was found 387.95 m²/g, 0.390 cm³/g and 4.02 nm respectively. Tri-modal pore size distribution showed its effective utilization in adsorption. The abundant (SiOH) hydroxyl groups of mesoporous silica, the broad diffraction hump of silica depicted its superior loading capacity of target molecular specie inside its porous network. From band gap analysis, a red shift of 2.43 eV exhibited semiconductor photocatalysis of Dy_xMnFe_2-xO₄ nanoparticles. Degradation efficiency of bare MnFe₂O₄, Dy_xMnFe_2-xO₄ and mesoporous silica-based composite was tested using crystal violet dye. Its explored adsorption-photocatalysis synergy, degradation mechanism, kinetic investigation, easily recovery and remarkable recycling ability suggested that the new fabricated composite is best for environmental remediation.

Exploring the Influence of Critical Parameters for the Effective Synthesis of High-Quality 2D MXene

Recently, a new class of two-dimensional (2D) materials, called MXene, consisting of layers of transition-metal carbides and nitrides/carbonitrides has been introduced. MXene, a multifunctional material with hydrophilic nature and excellent electrical conductivity and chemical stabilities, can be applied in diverse research areas such as energy harvesting and its storage, water purification, thermal dissipation, and gas sensing. To achieve the best quality of MXene, optimization of some important synthetic parameters is highly required such as an optimized etchant concentration to remove an "A" element from the MAX phase and sonication time for the efficient exfoliation of MXene flakes. Besides, there is a need to disclose that particular solvent through which intercalation can easily be achieved. In this work, we optimized the abovementioned critical parameters for the synthesis of good-quality MXene. Our results clearly explain the variations in the quality of MXene under applied etchant concentrations, solvents for better intercalation, and optimization of sonication time for better exfoliation. The obtained results suggest that 30% HF as an etchant, dimethyl sulfoxide (DMSO) as a solvent, and 135 min as the sonication time are effective parameters for the synthesis of good-quality MXene. We expect that this report will be helpful for the young research community to synthesize good-quality MXene with the required properties.

Fabrication of Ce3+ substituted nickel ferrite-reduced graphene oxide heterojunction with high photocatalytic activity under visible light irradiation

In the current investigation, graphene (rGO)-supported cerium substituted nickel ferrite (NiCe_yFe_2-yO₄ y = 0.05) photocatalyst was prepared via two-step wet chemical approach. The resulting NiCe_yFe_2-yO₄/rGO nanocomposite exhibited excellent photocatalytic performance and stability. Moreover, the photocatalytic activity of NiCe_yFe_2-yO₄/rGO nanocomposite was also investigated comparatively with NiCe_yFe_2-yO₄ nanoparticles. As compared to the NiCe_yFe_2-yO₄ nanoparticles, NiCe_yFe_2-yO₄/rGO nanocomposite showed superior photocatalytic efficiency and recycling stability for MB degradation, which is two times that of bare NiCe_yFe_2-yO₄ nanoparticles. After visible light irradiation for 70 min, 94.67 % of MB dye was removed by NiCe_yFe_2-yO₄/rGO nanocomposite whereas only 50 % of MB dye was removed by NiCe_yFe_2-yO₄ nanoparticles. The increase in photocatalytic performance is mainly ascribed to formation of NiCe_yFe_2-yO₄/rGO heterojunction which not only assist in separation of photo-induced charge carriers, but also sustain a strong redox ability. Moreover, the photo-corrosion of NiCe_0.05Fe_1.95O₄ nanoparticles is inhibited through transfer of photo-induced electrons of NiCe_0.05Fe_1.95O₄ nanoparticles to rGO. A possible photo-degradation mechanism based on reactive species trapping experiments has been proposed. The effect of various factors like pH, temperature and catalyst dosage has also been explored. Facile synthesis method, excellent photocatalytic performance for organic pollutants and superior reusability suggest that NiCe_yFe_2-yO₄/rGO photocatalyst possesses high potential for large-scale pollutant treatment.

Seasonal variation’s effect on antidiabetic activity of silver nanoparticles

The present work develops an eco-friendly protocol that was adopted to synthesize silver nanoparticles (AgNPs) from the aqueous extract of Corchorus depressus collected in three different seasons. Visually, the formation of AgNPs was confirmed by the change in the color of extracts to reddish brown and the AgNPs were further characterized by ultraviolet–visible studies of the absorption band at 435–450 nm that is due to surface plasmon resonance of AgNPs. The functional groups that behave as a reducing agent and those that act as a capping agent were determined by the FTIR. The particle size was determined by scanning electron microscopy and the amount of capping agents (organic contents at the surface of AgNPs) was estimated by thermogravimetric analysis. AgNPs showed a remarkable inhibitory activity against α-glucosidase compared to their respective aqueous extracts. Extraction of plant material collected in the month of January and their AgNP formation showed the smallest particle size of 4 ± 2 nm. Moreover, an augmented remarkable inhibitory activity against the carbohydrate-digesting enzyme α-glucosidase with IC50 of 2·48 ± 0·56 μg/ml was also observed compared to other extracts.

Cyclic-RGD penta-peptides cRGDyK derivatized with cyclopentadienyl complexes of technetium and rhenium as radiopharmaceutical probes

The present study reports the syntheses of half-sandwich complexes of the type [M(η⁵ -C₅ H₄ CONH-R)(CO)₃ ] (M═Re,^99m Tc;R═cyclic RGD peptide (cRGDyK) for potential imaging of α_v β₃ integrin expression. The ^99m Tc complex was prepared directly from the reaction of [^99m Tc(OH₂ )₃ (CO)₃ ]⁺ with cRGDyK, doubly conjugated to Thiele's acid [(C₅ H₅ COOH)₂ ] in water. This approach extends the viability of metal-mediated retro Diels-Alder reactions for the preparation of small molecules such as linear tripeptides to a more complex cyclic peptide carrying a [(η⁵ -C₅ H₄ )^99m Tc(CO)₃ ] tag. The Diels-Alder product [(C₅ H₅ CONH-cRGDyK)₂ ] was prepared from Thiele's acid via double peptide coupling. The Re-complex [Re(η⁵ -C₅ H₄ CONH-cRGDyK)(CO)₃ ] was obtained by attaching [Re(η⁵ -C₅ H₄ COOH)(CO)₃ ] directly to the N-terminus of cRGDyK. The identity of the ^99m Tc-complex is confirmed by chromatographic comparison with the corresponding rhenium complex, fully characterized by spectroscopic techniques.