Single-step Hydrothermal Method Research Articles

Synergetic effect of ternary MnVMo-oxide electrode by hydrothermal method for high-performance asymmetric supercapacitor

The binder-free deposition facilitates fast electron transfer and smoothens the diffusion path of electrolyte ions into the matrix of electrode material. Herein, the ternary metal oxides, such as manganese vanadium molybdenum oxide (MnVMo-oxide) is directly deposited on nickel foam by a single-step hydrothermal method. X-ray diffraction study confirms formation of MnVMo-oxide phase. The X-ray photoelectron spectroscopy confirms the Mn, V, and Mo are in the +2 (and +3), +5, and +6 oxidation states. Deposition time variation results, change in nanostructures from nanoparticle-assembled sheets to rectangular nanosheets, also the size of micro rods. The porous microrods formed with uneven quasi-rectangular shaped nanosheets of MnVMo-oxide exhibit high areal capacitance of 814.5 mFcm−2 (as compared to other electrodes) measured in 1 M KOH electrolyte at 3 mAcm−2 current density. The enhanced capacitance of the MnVMo-8 electrode is due to the dominance of the diffusion process over the capacitive-controlled contribution and high diffusion coefficient. The fabricated asymmetric supercapacitor device MnVMo-oxide//activated carbon shows good areal capacitance of 40 mFcm−2 with 0.025 mWhcm−2 energy at 1.5 mWcm−2 power density measured at 2 mAcm−2 current density, and cyclic stability of about 71.45 % (Coulombic efficiency of 98 %) quantified up to ∼9000 consecutive cycles.

Hydrothermal deposition of high strength biocompatible magnesium phosphate coating through in situ conversion of AZ91D-3Ca magnesium substrate

Magnesium and its alloys are biodegradable and biocompatible with elastic modulus close to the natural bone which makes them suitable as an orthopedic implant. Poor corrosion resistance and high hydrogen evolution rate are two factors hindering their use as commercial implants. To overcome these challenges, a biocompatible magnesium phosphate coating was deposited using a single step hydrothermal method. Scanning Electron Microscopy (SEM/EDX) and X-Ray Diffraction (XRD) methods were used to analyze the structural and chemical compositions of these coatings. In addition, investigation on their adhesion, degradation, cellular proliferation, and gene expression were studied extensively. SEM analysis confirmed a uniform and defect-free deposition occurs in hydrothermal conditions. XRD validated the presence of Periclase (MgO), magnesium phosphate (Mg3(PO4)2) and Brucite (Mg(OH)2) phases. Degradation studies revealed the hydrogen evolution rate is remarkably decreased and corrosion properties were considerably improved as compared to the bare magnesium alloy. In-Vitro biocompatibility testing with pre-osteoblast (MC3T3-E1) via cell viability assay (Alamar blue reduction test) portrayed almost 100 % host cell proliferation both in coated and positive control samples after 8 days. Comparing coated and untreated magnesium alloy in SEM images, greater cell adhesion was seen to the coated surface. It is concluded that magnesium phosphate coatings can be used commercially as they are compact, highly crystalline, defect-free, bioresorbable, cytocompatibility, well-adhered, and protective in nature. Hence, phosphate-coated magnesium alloy is qualified to be used to protect biodegradable metallic implants.

Ultrasensitive Room-Temperature NO2 Detection Using SnS2/MWCNT Composites and Accelerated Recovery Kinetics by UV Activation

High performance with lower power consumption is one among the essential features of a sensing device. Minute traces of hazardous gases such as NO2 are difficult to detect. Tin disulfide (SnS2) nanosheets have emerged as a promising NO2 sensor. However, their poor room-temperature conductivity gives rise to inferior sensitivity and sluggish recovery rates, thereby hindering their applications. To mitigate this problem, we present a low-cost ultrasensitive NO2 gas sensor with tin disulfide/multiwalled carbon nanotube (SnS2/MWCNT) nanocomposites, prepared using a single-step hydrothermal method, as sensing elements. Relative to pure SnS2, the conductivity of nanocomposites improved significantly. The sensor displayed a decrease in resistance when exposed to NO2, an oxidizing gas, and exhibited p-type conduction, also confirmed in separate Mott-Schottky measurements. At a temperature of 20 °C, the sensor device has a relative response of about ≈5% (3%) for 25 ppb (1 ppb) of NO2 with complete recovery in air (10 min) and excellent recovery rates with UV activation (0.3 min). A theoretical lower limit of detection (LOD) of 7 ppt implies greater sensitivity than all previously reported SnS2-based gas sensors, to the best of our knowledge. The improved sensing characteristics were attributed to the formation of nano p-n heterojunctions, which enhances the charge transport and gives rise to faster response. The composite sensor also demonstrated good NO2 selectivity against a variety of oxidizing and reducing gases, as well as excellent stability and long-term durability. This work will provide a fresh perspective on SnS2-based composite materials for practical gas sensors.

Active-site-enriched dendritic crystal Co/Fe-doped Ni3S2 electrocatalysts for efficient oxygen evolution reaction.

The electrochemical decomposition of water plays a critical role in green and sustainable energy. However, the development of efficient and low-cost non-noble metal catalysts to overcome the high potential of the anodic oxygen evolution reaction (OER) is still challenging. In this work, electrocatalysts with high OER activity were obtained by doping Co/Fe bimetals into Ni3S2 (CF-NS) via a simple single-step hydrothermal method by adjusting the doping ratio of bimetals. A series of characterization studies revealed that the introduction of a Co/Fe co-dopant increased the number of active sites and improved the electroconductibility, while optimizing the electronic structure of Ni3S2. Meanwhile, Fe-induced high valence Ni contributed to the production of an OER active phase NiOOH. The unique dendritic crystal morphology facilitated the disclosure of the active sites and the expansion of mass transfer channels. The optimized sample required a low overpotential of 146 mV to obtain a current density of 10 mA cm-2 in 1.0 M KOH solution. The optimized sample also operated stably for at least 86 h. In sum, the proposed method looks very promising for designing efficient, stable, and low-cost non-precious metal catalysts with high conductivity and multiple active sites, useful for future synthesis of transition metal sulfide catalysts.

Bovine serum albumin-derived poly-l-glutamic acid-functionalized graphene quantum dots embedded UiO-66-NH2 MOFs as a fluorescence ‘On-Off-On’ magic gate for para-aminohippuric acid sensing

Evaluating para-aminohippuric acid (PAH) is emerging as a promising biomarker for the diagnostics of renal disease and other kidney-related illnesses. The present study aims to develop novel bovine serum albumin-derived poly-l-glutamic acid (PLGA) functionalized graphene quantum dots (PLGA-fGQDs) embedded in UiO-66-NH2 metal–organic frameworks (PLGA-fGQDs@UiO-66-NH2 MOFs) for monitoring of PAH. Initially, GQDs were achieved from bovine serum albumin (green precursor) via the single-step hydrothermal method. Here, functionalization with PLGA offers a tremendous increment in optical properties of GQDs. Then, highly luminescent UiO-66-NH2 MOFs were achieved using zirconium tetrachloride (ZrCl4) and 2-Aminoterephthalic acid (2-ATA) as a metal ion source and organic linker. Here, surface modification of GQDs with PLGA offered high quantum yield (QY), and responsiveness. Also, luminous UiO-66-NH2 MOFs afford a wide surface area for decorating of PLGA-fGQDs. The addition of gallium ions (Ga3+) into the probe solution resulted in fluorescence quenching (Turn-Off) whereas the incorporation of PAH resulted in fluorescence recovery (Turn-On). It is because of interaction with carboxylic functionality of PAH to Ga3+ followed by Ga-PAH complex formation. Herein, the wide concentration range and lowest limit of detection (LOD) were found to be 10 ng/mL to 900 ng/mL and 15.88 ng/mL, respectively. The specificity and real-time analysis in artificial urine validated the real-time adoption of a sensor for PAH detection. As well, it demonstrated good intraday/interday precision, stability analysis, and repeatability. In near future, the bundled illuminating PLGA-fGQDs@UiO-66-NH2 MOFs nanoprobe will be an attractive preference for tracking PAH in clinical specimens.

A non-corrosive bifunctional electrocatalyst based on titanate sheet for oxygen reduction and hydrogen evolution reactions

The development of suitable catalysts and catalyst supports is critical in the electrochemical energy generation methods. Herein, a titanate nanosheet-based catalyst support is synthesized and investigated for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). In an in situ single-step hydrothermal method, Pd nanoparticles were anchored onto sodium titanate nanosheet, which imparts excellent stability and methanol tolerance, suggesting its suitability as the cathode catalyst in direct methanol fuel cells. The electrocatalyst also demonstrated high efficiency towards electrochemical and photoelectrochemical hydrogen evolution reactions with an overpotential of −0.29 V and −0.20 V, respectively.

Construction of direct Z-scheme g-C3N4/BiYWO6 heterojunction photocatalyst with enhanced visible light activity towards the degradation of methylene blue.

Construction of the Z-scheme heterojunction photocatalyst achieved highly improved photocatalytic ability by its high redox ability of the photoinduced e--h+ pairs. In the study, Z-scheme g-C3N4/BiYWO6 heterojunction photocatalyst is prepared by the single-step hydrothermal method. Further, its photocatalytic ability was assessed by degrading methylene blue under visible light exposure. Particularly, the optimized 30 wt% of g-C3N4 in the g-C3N4/BiYWO6 composite exposes almost complete degradation after 90min, that is ~ 3.0 times greater than the bare BiYWO6 and g-C3N4 with the rate constant value 0.032min-1. Experimentally, the radical trapping studies indicate O2·- and ·OH radicals are playing a vital role in the photocatalytic degradation process. Also, the Z-scheme g-C3N4/BiYWO6 heterojunction photocatalyst exhibits excellent photoelectrochemical property and it is stable after 5 cycles, which indicates its good reusability nature. These enhancements are due to the newly formed heterostructure that facilitates the migration and separation efficiency of the photoproduced e--h+ pairs. Hence, the synthesized Z-scheme g-C3N4/BiYWO6 heterostructure could be an excellent material for wastewater remediation works.

Synergistic behavior of vanadium pentoxide-carbon sphere electrocatalyst towards iron-based redox flow battery and supercapacitor applications

In this paper, the multifunctional, electron-rich, unique structured vanadium pentoxide-carbon sphere (V2O5-CS) composite was used as a catalyst for energy storage devices such as iron-based redox flow batteries (IRFBs) and supercapacitors. The V2O5-CS composite was synthesized using a single-step hydrothermal method and it was found to have a nano flake-like structure deposited on the surface of spheres. The collective synergistic effect offered by V2O5 and CS in V2O5-CS enables easy flow of electrons and hence improves the reversibility, faradaic redox reaction and stability of the material. The electrocatalytic activity of the composite towards IRBF was tested to analyze the kinetic reversibility and electrode-electrolyte resistance. The charge-discharge and life-cycle studies were carried out to evaluate the stability of the electrode. V2O5-CS modified graphite felt (V2O5-CS GF) electrode was stable up to 50 cycles and the cell resulted in coulombic efficiency (CE) of 89 %. The composite along with V2O5 and CS were coated on Toray carbon electrodes were tested for supercapacitor using CV, EIS, and galvanostatic charge-discharge (GCD) to calculate the specific capacitance (Cs) offered by the material to the variation of voltage and current density applied. The V2O5-CS resulted in a specific capacitance of 612 F/g at 5 A/g and it has been found to have specific capacitance retention of 58 % up to 1500 cycles at a current density of 10 A/g. This is a pioneering work to present V2O5-CS composite as an efficient, peculiar electrocatalyst for energy storage devices.

Molybdenum–Manganese hydroxide microcubes based electrode via hydrothermal method for asymmetric supercapacitor

An electrode with multi electron surfaces facilitates more redox sites during charge storage reaction in the case of transition metal oxides used in supercapacitor application. Molybdenum (Mo) oxide and manganese (Mn) oxide have high theoretical capacitance; this study focused on depositing Mo–Mn together in a single mixed metal oxide. Here, Mo–Mn hydroxide was deposited on Ni-foam by a single-step hydrothermal method. The X-ray photoelectron spectroscopy confirms the presence of Mo and Mn in 4+ and 3+ oxidation states, respectively. The different size of Mo–Mn hydroxide microstructures was observed with varying deposition time. The porous cubes-like microstructure exhibited high areal capacitance of 88.6 mF cm−2 with energy density of 3.08 μWh·cm−2 at 125 μW cm−2 power density within a kinetic potential. This microcubes-like structures and activated carbon were used as positive and negative electrodes, respectively, to fabricate an asymmetric supercapacitor (ASS) device. The ASS device showed capacitance retention of 87% (∼5,000 cycles) and excellent Coulombic efficiency (96%) with energy density of 5.6 μWh·cm−2 at 1.12 mW cm−2 power density at 1.8 V potential.

Tunning self-assembled phases of bovine serum albumin via hydrothermal process to synthesize novel functional hydrogel for skin protection against UVB

Abstract Ultraviolet rays – B (UVB) can be efficiently absorbed by the cellular molecules of skin inducing damage within skin cells and a major cause of melanoma cancer. In recent years, several studies have reported the adverse effects of traditionally used organic and inorganic material-based sunscreens and UVB blockers. In this study, bovine serum albumin (BSA) has been used as a precursor to synthesize temperature- and pressure-dependent phase transition from sol (globular aggregates) – gel (hydrogels) – sol (carbon quantum dots) using a single-step hydrothermal method with an objective to develop an efficient and effective UVB blocker. The synthesized hydrogels exhibit UV – attenuation, self-fluorescence, and high biocompatibility properties that make them a suitable candidate for UV-blocker or sunscreen material. The biological efficacy of the hydrogels was studied through cyto-toxicity studies. Also, UVB blocking efficiency of developed hydrogel in primary mice skin cell culture as well as in vivo in mice model was studied. In vivo study on mice further demonstrated prominent thickening of stratum corneum and epidermis with perivascular edema in the dermis after 5 days of UVB exposure. Hence, this suggesting that hydrogel could be a potential candidate for protecting the skin from UVB exposure and reducing the threat of skin cancer.

Binder free heteroatom‐doped graphene oxide as high energy density electrodes for supercapacitor applications

We explored the potential of heteroatom-doped graphene oxide (GO)-based electrodes for energy storage. Binder-free electrodes were synthesized using the hydrothermal method, where doping of GO and its electrode development was achieved simultaneously in one step. GO was doped with nitrogen (NGO) and boron (BGO) using urea and boric acid as nitrogen (N) and boron (B) sources, respectively. In addition, GO was also co-doped with B and N (BNGO). The atomic percentages of nitrogen and boron in NGO and BGO were found out to be 6.13% and 17.94%, respectively, as revealed by XPS. The BNGO had atomic percentages of boron and nitrogen as 23.76% and 3.64%, respectively. Electrodes were electrochemically characterized in 3 M KOH electrolyte by employing cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge (GCD). CV analysis revealed that NGO and BNGO exhibited superior charge storage capacity with a high specific capacitance of 855 and 811 F g−1, respectively, at 1 m Vs−1. CV data were further analyzed to identify and quantify charge storage mechanism, and it suggested that binder-free-doped electrodes exhibited diffusion-controlled charge storage as dominant behavior. Thus, our results demonstrate an approach to dope GO and develop high-performance, binder-free electrodes for supercapacitor applications in a facile single-step hydrothermal method.

Design of an efficient fluorescent nanoplatform carrier for hydrophobic drugs along with green carbon dot: Possible application in cancer image-guided drug therapy

Nanotechnology has taken novel approaches to advance cancer therapeutic efficacy employing multifunctional nanocarriers with drug delivery and imaging function. In this work, we designed a biocompatible and affordable fluorescence nanocarrier called chitosan (CS)-carbon dot (CD) hybrid nanogel for cell imaging. The green CDs were synthesized using tomato juice through a simple single-step hydrothermal method. Chitosan polymer was used as a carrier for co-delivery CDs and the anti-cancer drug with low solubility, silibinin (Sil), to design the Sil-chitosan carbon dots hybrid nanogels (CCHNs) system. After optimizing the physicochemical properties of nanostructure by DLS, FTIR, FESEM, TEM, and UV-visible techniques, the successful uptake of the fluorescent nanoparticle conjugates into MCF-7 breast cancer cells occurred. Then we embedded CDs in chitosan nanogel. The resultant CCHNs demonstrated optical properties similar to free-CDs, a desirable size distribution (55.22 nm) with a positive surface charge, a suitable loading capacity for Sil (35%), and drug release vulnerable to pH changes. The fluorescent nanocarrier could transfer Sil to MCF-7 cancer cells without remarkable toxicity. The results of the fluorescent microscope indicated that after 4 h, the solid fluorescent signal was received from cells containing CCHNs compared to free CDs and confirmed the ability of hybrid nanogels to high cellular uptake. This study demonstrates a multifunctional nanocarrier containing therapeutic compounds and fluorescent agents that provide cellular imaging to enhance therapeutic efficacy.

Nanoarchitectonics of neomycin-derived fluorescent carbon dots for selective detection of Fe3+ ions.

The first-ever neomycin antibiotic-based carbon dots (Neo-CDs) were synthesized via a low-cost, eco-friendly, and single-step hydrothermal method using neomycin as a single precursor. The as-prepared Neo-CDs exhibited strong and stable blue fluorescence and were well characterized by TEM, UV-vis absorption, fluorescence emission, IR, XRD, Raman and XPS spectroscopy methods. The Neo-CDs showed a well-distributed size within the range of 4.5 to 7.8 nm, comprising various functional groups on the surface of the carbon core. The Neo-CDs exhibited exceptional emission behaviour, and fluorescence quantum yield was calculated to be 55% in double distilled water. Neo-CDs have been used as a fluorescent sensor for selective and sensitive detection of Fe3+ ions in aqueous solution in the fluorescence turn-off mode. From the set of metal ions, only the Fe3+ ion showed quenching of fluorescence due to photoinduced (PET) electron transfer from Neo-CDs to the half-filled 3d orbital of Fe3+ ions. The limit of detection for Fe3+ ions was calculated to be 0.854 μM. Further, the quenching efficiency and Stern-Volmer quenching constant have been calculated which are about 94% and 5.6 × 106 M-1, respectively.

Strain induced study on MoS2 thin films due to ion and gamma irradiation

Single step hydrothermal method was used to synthesize molybdenum disulfide (MoS2) thin films. The hexagonal structure of MoS2 was confirmed by X-ray diffraction techniques (XRD). The nanosheets like morphology of MoS2 films were confirmed using scanning electron microscopy (SEM). The optical band gap of pristine MoS2 was found to be ~1.53 eV. The prepared MoS2 films were irradiated with ion and gamma radiation at different ion fluence and doses respectively. For ion irradiation, the samples were irradiated at ion fluences of 4.7 × 1016 ion/cm2, 7.1 × 1016 ion/cm2, 9.5 × 1016 ion/cm2, 11.9 × 1016 ion/cm2 and 14.3 × 1016 ion/cm2. In case of gamma irradiation, the samples were irradiated for 10 kGy, 100 kGy, 300 kGy, and 500 kGy and 800 kGy doses. The tensile strain induced in the sample was studied with the help of Raman spectroscopy and XRD technique. The defect induced tensile strain in MoS2 films due to ion irradiation is higher as compared to gamma irradiation.

Charge transfer mechanism of AZO-ZnO photoanode based on impedance study for solar cell application

• Studied the effect of growth temperature on the length and defect of ZnO NR. • Charge transfer mechanism of NRs was investigated using electrochemical analysis. • Obtained current density of 0.82 mA/cm 2 and photoconversion efficiency of 0.53 %. • Working mechanism of the NR-based cell was explained using a band diagram. Charge transfer mechanism in ZnO nanorods grown on aluminium doped zinc oxide substrates using a single step hydrothermal method was investigated as a function of ZnO nanorod (NR) growth temperature/nanorod’s length. Band-to-band transition and the defect state transition in the prepared nanorods was confirmed using photoluminescence spectroscopy. The increase in active sites up to an optimum growth temperature/nanorod’s length results in an increase of current density and photoconversion efficiency of the prepared NR. But with the further increase in the latter, the current density decreases due to the recombination of electrons. Nanorod grown at the optimized condition exhibited a current density of 0.82 mA/cm 2 and a photoconversion efficiency η of 0.53 %. Electrochemical impedance spectroscopy and open-circuit photovoltage decay (OCPVD) measurement were employed to determine the charge transfer resistance R ct , double layer capacitance ( C dl ) and the recombination time τ of zinc oxide nanorods of various length. The nanorod prepared at the optimized condition of 140 °C having an average length of 2.4 μm had superior current density and the better charge transfer mechanism. The study confirmed that this was due to the low charge transfer resistance R ct = 1300 Ω value and better recombination time τ = 2.38 s for the sample, which makes ZnO nanorods a promising candidate to be used as a photoanode in quantum dot sensitized solar cells.

Improving the in vitro Degradation, Mechanical and Biological Properties of AZ91-3Ca Mg Alloy via Hydrothermal Calcium Phosphate Coatings

For many years, calcium phosphate coatings to tailor the degradation behavior of magnesium and magnesium-based alloys for orthopaedic applications have received lots of research attention. However, prolong degradation behavior, its effect on biological and mechanical properties as well as osteoblastic response to single-step hydrothermally deposited calcium phosphate coatings remain poorly documented. In this study, Alamar blue assay, cell attachment, live/dead assay, and qRT-PCR were done to study the biological response of the coatings. Furthermore, immersion testing in SBF for 28 days and compression testing of the degraded samples were carried out to examine the degradation behavior and its effect on mechanical properties. The results indicated that coatings have a significant influence on both the substrate performance and structural integrity of coated AZ91-3Ca alloy. Immersion test revealed that coating deposited at pH 7, 100°C (CP7100) improves the hydrogen evolution rate by 65% and the degradation rate by 60%. As the degradation performance of coated samples improves so does the mechanical strength. CP7100 samples successfully retained 90% of their compressive strength after 14 days of immersion while bare AZ91-3Ca alloy lost its mechanical integrity. Furthermore, biological studies show that cells are happily proliferating, differentiating, and adhering to the coating surfaces, which indicates, improved osteointegration and osteogenesis with no sign of alkaline poisoning. qRT-PCR results showed that calcium phosphate coatings enhanced the mRNA levels for RUNX2, Col1A, and ALP that may exhibit a speedy bone recovery. Thus, calcium phosphate coatings produced via a single-step hydrothermal method improve the degradation behavior, mechanical integrity and stimulate the differentiation of osteoblast lining. This leads toward faster bone regeneration, which shows a great potential of these coatings to be used on degradable implants as a bioactive protective layer.

Effect of growth time on structural and surface properties of TiO2 nanostructures deposited by single-step hydrothermal method

In this study, highly pure rutileTiO2 nanorods (NRs) structures were grown on fluorine-doped tin oxide (FTO) coated glass substrates by using a one-step hydrothermal method. The effect of the growth time on the structure and surface properties of the obtained products has been studied. The X-ray diffraction analysis and the Raman spectroscopy indicated that the films were single-crystalline rutile phase. At lower hydrothermal time, TiO2 NRs singly distributed with small diameter are found showing a high contact angle with ethylene glycol. When the hydrothermal reaction increases, nanoflowers (NFs) with a large diameter are formed over the TiO2 NRs leading to superhydrophilic surfaces. These nanostructured thin films can be tailored to the requirements of specific applications involving water and ethylene glycol.

Carbon-Dots-Initiated Photopolymerization: An In Situ Synthetic Approach for MXene/Poly(norepinephrine)/Copper Hybrid and its Application for Mitigating Water Pollution.

The current work presents a facile and green synthesis of carbon quantum dots (C-dots), which could serve as initiators for polymerization. Herein, C-dots have been synthesized from an easily available green herb, dill leaves, by a single-step hydrothermal method. These C-dots were efficiently utilized as initiators for the photopolymerization of the polymer poly(norepinephrine) (PNE) for the first time. The photopolymerization is discussed by a factorial design, and the optimized synthesis conditions were evaluated by a third-order regression model of three reaction parameters: monomer concentration, C-dots concentration, and UV exposure time. The sign convention of the factorial design mode indicated that monomer concentration and time of exposure are the most important factors for polymerization. The photopolymerized poly(norepinephrine) was extensively studied using Fourier transform infrared (FTIR) analysis, X-ray photoelectron spectroscopy (XPS), mass spectra, scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle measurement, and thermogravimetric analysis (TGA). UV-assisted deposition of PNE on six different types of substrates was performed, and their water contact angle and surface morphology were studied to evaluate the coating. This UV-triggered polymerization technique was further applied to fabricate sandwich-like composite catalyst MXene/poly(norepinephrine)/copper nanoparticles. This catalyst displayed good performance in the reduction of 4-NP (4-nitrophenol) at ambient temperature, and the first-order rate constant of the catalysis was 9.39 × 10-3 s-1. The reusability of the catalyst was evaluated in terms of the conversion factor. After 10 catalytic cycles, the conversion to catalyze 4-NP was still greater than 91%. The catalytic performance was also evaluated in the continuous flow condition through a membrane, fabricated from a cellulose filter paper coated with MXene/poly(norepinephrine)/copper nanoparticles. This composite catalyst not only offers a practical mode for the catalytic reaction of MXene-based materials but also lays down the foundation for the development of new catalysts.

Nitrogen-doped carbon spheres-decorated graphite felt as a high-performance electrode for Fe based redox flow batteries

In this paper, the performance of Fe-based redox flow batteries (IRFBs) was dramatically improved by coating N-doped carbon spheres (NDCS) on the graphite felt electrodes. NDCS was synthesized by the single-step hydrothermal method using dextrose and ammonia as a precursor and coated over graphite felt electrodes by electrostatic spraying. The weight of NDCS required for the modification of the electrode to achieve the effective performance of the battery was studied using electrochemical techniques. Cyclic voltammetry (CV) and potentiodynamic polarization study was used to evaluate the kinetic reversibility and linear polarization resistance offered by the electrode towards electrolyte. The characterizing features of the NDCS, untreated graphite felt (UGF) electrode and optimized modified graphite felt (MGF) electrode were analyzed using SEM, EDAX, XRD, and Raman spectroscopy. The charge-discharge studies were performed for the 132 cm2 IRFB using a 2 mg/cm2 MGF electrode as a positive electrode by varying the current densities from 20 to 60 mA/cm2. The cell resulted in an average coulombic efficiency (CE) of 93%, voltaic efficiency (VE) of 72%, and energy efficiency (EE) of 68% for 15 cycles at the current density of 30 mA/cm2. The improvement in the performance of the IRFB is due to the presence of electrochemically active nitrogen-bearing carbon catalysts. In this paper, the pioneering effort has been made to improve the efficiency of the IRFB with an active area of 132 cm2 using glycine as the ligand.

Fabrication of rGO/NiS/AuNCs ternary nanocomposite modified electrode for electrochemical sensing of Cr(VI) at utra-trace level

In the present investigation, ternary nanocomposite of reduced graphene oxide rGO, Nickel sulphde (NiS) and gold nano cube (rGO/NiS/AuNCs) has been synthesized by adopting a facile single step hydrothermal method. The electrochemical interfacial property of the composite materials is obtained from cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The crystal structure, surface morphology and elemental composition of the rGO/NiS/AuNCs ternary nanocomposite are characterized using XRD, SEM and EDX measurements, the characterization of the materials using such techniques have shown the formation of flower shaped NiS and Au in the form of AuNCs, effective formation of composite has been evident from the microscopic and spectroscopic measurements. The square wave voltammetry technique is employed to the determination of Cr(VI) in 0.1 M acetate buffer solution at the optimized pH 5. The influence of various electrochemical parameters affecting the stripping voltammetry are investigated and optimized. Under optimal condition, the limit of detection (LOD) in the present method is found to be 0.09 µgL−1 at the accumulation potential of -0.5V for the duration of 30s. The rGO/NiS/AuNCs ternary nano composite modified electrode showed good stability and high sensitivity towards the detection of Cr(VI) with low response time. The developed method has been applied for the detection of Cr(VI) in environmental samples.