Unique Multi-Hetero-Interface Engineering of Fe-Doped Co-LDH@MoS2-Ni3S2 Nanoflower-Based Electrocatalyst for Overall Water-Splitting: An Experimental and Theoretical Investigation.

Herein, a self-supported, robust, and noble-metal-free 3D hierarchical interface-rich Fe-doped Co-LDH@MoS2-Ni3S2/NF heterostructure electrocatalyst has been prepared through a controllable two-step hydrothermal process. The resultant electrode shows low overpotential of ~95 mV for hydrogen evolution reaction (HER), ~220 mV for the oxygen evolution reaction (OER), and the two-electrode system requires only a cell voltage of ~1.54 V at 10 mA cm-2 current density, respectively. Extensive ab initio calculations were carried out to find out the overpotential for HER, orbital interaction through the determination of electron density of states and quantification of charge transfer by Bader charge analysis. The computed overpotential matched closely with the experimental data. The superior HER performance of the tri-layer is enhanced due to the charge transfer (1.7444 e) to Fe-doped Co-LDH from Ni3S2-MoS2 hybrid. This research strategy paves an effective pathway for affordable green H2 production and future efficient non-precious bifunctional electrocatalyst design for overall water electrolysis.

Integration of a Bismuth-Based Tris-Mononuclear Complex with 2D Functional Materials for Highly Efficient and Durable Aqueous Electrocatalytic Hydrogen Evolution.

The eminence of transitioning from traditional fossil fuel-based energy resources to renewable and sustainable energy sources is most evidently crucial. The potential of hydrogen as an alternative energy source has specifically focuses the electrocatalytic water splitting (EWS) as a promising technique for generating hydrogen. Development of efficient electrocatalysts to facilitate the EWS process while rationalizing the limitations of noble metal catalysts like platinum has become one of the daunting tasks. Consequently, porous functional materials such as metal complexes (MCs) and graphene oxide (GO) can act as potential catalysts for EWS. Therefore, a composite of GO and a mononuclear bismuth metal complex is synthesized through in situ facile synthesis, which is further utilized as an efficient electrocatalyst for the hydrogen evolution reaction (HER). Several potential electrocatalytic MC@GO composite (BMGO-3,5,7) materials were prepared with compositional variation of GO (3, 5, and 7 wt %). The experimental results demonstrate that the BMGO5 composite exhibits excellent HER activity with a low overpotential value of 105 mV at 10 mA cm-2 and a low Tafel slope of 44 mV dec-1 in 1 M KOH solution. Furthermore, a comprehensive investigation on the potentiality of the BMC-GO composite for hydrogen evolution from river water splitting was performed in order to address the issue of freshwater depletion. Inclusion of a mononuclear MC for facile synthesis of functional GO-based efficient electrocatalyst material is very scanty in the literature. This unique approach could assist future research endeavors toward designing efficient electrocatalysts for sustainable renewable energy generation. This is one of the first of its kind, where mononuclear MCs were utilized to develop GO-based functional composite materials for efficient electrocatalysis toward sustainable renewable energy generation.

Metal-organic framework-derived advanced oxygen electrocatalysts as air-cathodes for Zn-air batteries: recent trends and future perspectives.

Electrochemical energy storage devices with stable performance, high power output, and energy density are urgently needed to meet the global energy demand. Among the different electrochemical energy storage devices, batteries have become the most promising energy technologies and ranked as a highly investigated research subject. Recently, metal-air batteries especially Zn-air batteries (ZABs) have attracted enormous scientific interest in the electrochemical community due to their ease of operation, sustainability, environmental friendliness, and high efficiency. The oxygen electrocatalytic reactions [oxygen reduction reaction (ORR) and oxygen evolution reaction (OER)] are the two fundamental reactions for the development of ZABs. Noble metal-based electrocatalysts are widely considered as the benchmark for oxygen electrocatalysis, but their practical application in rechargeable ZAB is hindered due to several shortcomings. Thus, to replace noble metal-based catalysts, a wide range of transition-metal-based materials and heteroatom-doped metal-free carbon materials has been extensively investigated as oxygen electrocatalysts for ZABs. Recently, metal-organic frameworks (MOFs) with unique structural flexibility and uniformly dispersed active sites have become attractive precursors for the synthesis of a large variety of advanced functional materials. Herein, we summarize the recent progress of MOF-derived oxygen electrocatalysts (MOF-derived carbon nanomaterials, MOF-derived alloys/nanoparticles, and MOF-derived single-atom electrocatalysts) for ZABs. Specifically, we highlight MOF-derived single-atom electrocatalysts owing to the wide exploration of these emerging materials in electrocatalysis. The influence of the active sites, structural/compositional design, and porosity of MOF-derived advanced materials on the oxygen electrocatalytic performances is also discussed. Finally, the existing challenges and prospects of MOF-derived electrocatalysts in ZABs are briefly highlighted.

Selective recognition of ammonia and aliphatic amines by C-N fused phenazine derivative: A hydrogel based smartphone assisted 'opto-electronic nose' for food spoilage evaluation with potent anti-counterfeiting activity and a potential prostate cancer biomarker sensor.

In real day scenario, it is an urge to provide a single solution of multiple problems. In this regard, herein rapid, selective and highly efficient chromo-fluorogenic detection of ammonia/aliphatic amines over aromatic amines has been investigated by means of a novel "opto-electronic nose", CN-2, synthesized in a single-step via multiple inter/intramolecular C-N fusion reactions. The in-situ generated mono-protonated CN-2 can selectively detect primary to secondary to even tertiary aliphatic amines over aromatic amines within ∼40 S with extremely low detection threshold values of 27.2 ppb, 0.7 ppm, 5.4 ppm, 1.7 ppm from UV-Vis and 42.5 ppb, 1.61 ppm, 5.5 ppm, 6.14 ppm from fluorescence spectral data for NH3, hydrazine (primary amine), diethanolamine (secondary amine) and triethylamine (tertiary amine) respectively with the hypsochromic shift in the UV-Vis spectra along with fluorescence attenuation via target-specific deprotonation. The colorimetric signal can also be examined by Smartphone APP, which is well correlated with spectrophotometric outcomes. Interestingly, due to presence of a unique protonated antenna centre CN-2 with anti-oxidant activity can also detect aliphatic biogenic amines, like putrescine, spermidine, which are frequently released from spoiled food. Therefore, it may be exploited as smart food-spoilage indicator in real-time. Again, the aliphatic biogenic amines recognition capability from human urine made it as a potential prostate cancer biomarker sensor for clinical use, which alleviates the need of biopsies. CN-2 could also be employed towards one-to-two decoder logic-circuitry formulation to monitor the ammonia levels. Moreover, CN-2-functionalized hydrogel-membrane based portable, handy prototype could be utilized for easy on-site recognition of amine vapour. Reversible sensing behaviour in presence of HCl enables CN-2 to exhibit anti-counterfeiting activity. To the best of our knowledge, this is the first all-in-one phenazine-based Smartphone-assisted chromo-fluorogenic-chemosensor, which would be of enormous interest in food-packaging industry, information technology as well as in early-stage-cancer diagnosis.

Molecular Crowded ″Water-in-Salt″ Polymer Gel Electrolyte for an Ultra-stable Zn-Ion Battery.

Recently, the use of a gel polymer electrolyte for the development of robust, flexible, quasi-solid, ultra-stable, high-performance zinc-ion batteries (ZiBs) as an alternative to lithium-ion batteries has attracted widespread attention. However, the performance of ZiBs is limited due to the lack of suitable gel electrolytes. Herein, a ″water-in-salt″ (WiS)-based hydrophilic molecular crowded polymer gel electrolyte and binder free V2O5@MnO2 cathode are introduced to augment the durability, flexibility, safety, and electrochemical performance of ZiBs. The ″free water trapping″ capability of the WiS-based cross-linked molecular crowded polymer electrolyte provides an extended electrochemical stability window (ESW) of the device. The quasi-solid-state ZiB delivers ∼422 mAh g-1 discharge capacity and shows excellent cycling stability as high as ∼79.83% retention of the initial capacity after 5000 cycles. The durable, flexible, and ultra-stable ZiB with the polymer gel electrolyte performs well under various severe conditions where both the battery safety and energy density are of high priority. This work demonstrates a new approach and application for the development of durable, flexible, ultra-stable, quasi-solid-state ZiBs.

Activation Strategy of MoS2 as HER Electrocatalyst through Doping-Induced Lattice Strain, Band Gap Engineering, and Active Crystal Plane Design.

Doping engineering emerges as a contemporary technique to investigate the catalytic performance of MoS2. Cation and anion co-doping appears as an advanced route toward electrocatalytic hydrogen evolution reaction (HER). V and N as dopants in MoS2 (VNMS) build up a strain inside the crystal structure and narrow down the optical band gaps manifesting the shifting of the absorbance band toward lower energy and improved catalytic performance. FE-SEM, HR-TEM, and XRD analysis confirmed that V and N doping decreases agglomeration possibility, particle size, developed strain, and crystal defects during crystal growth. Frequency shift and peak broadening in Raman spectra confirmed the doping induced strain generation in MoS2 leading to the modification of acidic and alkaline HER (51 and 110 mV @ 10 mAcm-2, respectively) performance. The improved donor density in VNMS was confirmed by the Mott-Schottky analysis. Enhanced electrical conductivity and optimized electronic structures facilities H* adsorption/desorption in the catalytically active (001) plane of cation and anion co-doped MoS2.

Discerning Detection of Mutagenic Biopollutant TNP from Water and Soil Samples with Transition Metal-Containing Luminescence Metal-Organic Frameworks.

Two luminescent MOFs, Mn@MOF and Cd@MOF, have been reported herein, which are capable of selectively detecting 2,4,6-trinitrophenol (TNP), one of the potent organic water pollutants in the class of mutagenic explosive nitroaromatic compounds (epNACs). It is perceived that the d10-based Cd(II)-constituting MOF shows a better response in the realm of TNP-like nitroaromatic sensing in comparison to the d5-based Mn@MOF which may possess lower electron density over the conjugated building blocks. The sensing competences of these chemosensors have been explored by means of various spectroscopic experimentations, and it is observed that for both d5 and d10-containing MOFs, the initial fluorescence intensity is significantly quenched in response to an aqueous solution of TNP. However, Cd@MOF is more selective and sensitive toward TNP over several other epNACs than Mn@MOF. The high chemical stability of the MOF samples, as well as its amusing sensing efficiency of Cd@MOF, further instigated to investigate the sensing ability in various environmental specimens like soil and water culled from several zones of West Bengal, India.

Selective Identification and Encapsulation of Biohazardous m-Xylene among a Pool of Its Other Constitutional C8 Alkyl Isomers by Luminescent d10 MOFs: A Combined Theoretical and Experimental Study.

Separation of C8 alkyl-aromatics (o-xylene, m-xylene, and p-xylene) remains one of the most challenging tasks to date due to their similar physical and chemical properties. Cd2+- and Zn2+-based luminescent metal-organic frameworks (MOFs) have been synthesized for the selective identification of m-xylene in a pool of other isomers by fluorometric methods. Inhibition of the photoinduced electron transfer process is the prime reason for fluorescence enhancement, owing to the comparable molecular orbital energies for m-xylene in comparison with o- and p-xylene. Density functional theory calculations signify that the extraordinary selectivity is mainly due to the high dipole moment of m-xylene that might enhance the ring current, leading to a strong π-π interaction with the MOF's co-ligand. As a practical application, fluorometric sensing could be used for the estimation of m-xylene in different solvent media. Moreover, X-ray structural analysis reveals that the Zn2+-MOF can encapsulate m-xylene selectively within its framework among other constitutional isomers, which also emphasizes its capability for practical implementation.

Efficient tribological properties of azomethine-functionalized chitosan as a bio-lubricant additive in paraffin oil: experimental and theoretical analysis.

A simple condensation of chitosan (from shrimp shells) and 4-hydroxybenzaldehyde was performed to yield bio-lubricant additive comprised of azomethine functional groups to be used with paraffin lube oil in industries. The synthesized Schiff base derivative of chitosan (SBC) additive was characterized using a CHN analyzer and FT-IR spectroscopy, and the thermal stability was explored using thermogravimetry. The rheological properties of SBC additives in paraffin oil were studied and are discussed herein. The tribological properties of SBC were tested in paraffin as the base oil employing a four-ball tester with different experimental conditions (viz. the concentration of the additive, applied load, speed and time duration), following ASTM D4172A standards. The optimum concentration of the additive in the base oil was found to be 150 ppm, exhibiting minimum coefficient of friction, but with higher concentrations of additive in base oils, the coefficient of friction increased. UV-Vis spectroscopy studies were also performed to confirm the formation of SBC and dispersion stability. The determined tribological parameters, such as the coefficient of friction, mean wear scar diameters and mean wear scar volumes, were found to significantly reduce the coefficient of friction of paraffin oil upon the addition of SBC. The state of steel balls upon exposure to various experimental conditions was analyzed and explained based on outcomes from FESEM, EDX, ferrography and AFM spectroscopy. The insights into interactions of the synthesized SBC with the metal surface were explored using ab initio density functional theory, Fukui indices, molecular dynamics simulation and radial distribution function.

Effect of Ion Diffusion in Cobalt Molybdenum Bimetallic Sulfide toward Electrocatalytic Water Splitting.

The electrocatalyst comprising two different metal atoms is found suitable for overall water splitting in alkaline medium. Hydrothermal synthesis is an extensively used technique for the synthesis of various metal sulfides. Time-dependent diffusion of the constituting ions during hydrothermal synthesis can affect the crystal and electronic structure of the product, which in turn would modulate its electrocatalytic activity. Herein, cobalt molybdenum bimetallic sulfide was prepared via hydrothermal method after varying the duration of reaction. The change in crystal structure, amount of Co-S-Mo moiety, and electronic structure of the synthesized materials were thoroughly investigated using different analytical techniques. These changes modulated the charge transfer at the electrode-electrolyte interface, as evidenced by electrochemical impedance spectroscopy. The Tafel plots for the prepared materials were investigated considering a less explored approach and it was found that different materials facilitated different electrocatalytic pathways. The product obtained after 12 h reaction showed superior catalytic activity in comparison to the products obtained from 4, 8, and 16 h reaction, and it surpassed the overall water splitting activity of the RuO2-Pt/C couple. This study demonstrated the ion diffusion within the bimetallic sulfide during hydrothermal synthesis and change in its electrocatalytic activity due to ion diffusion.

Electrochemical Detection of H2O2 Using Copper Oxide-Reduced Graphene Oxide Heterostructure.

Three dimensional heterostructure of CuO nanoparticle decorated reduced graphene oxide (rGO) was prepared by a facile and cost-effective technique. The structure and electrochemical properties of the CuO-rGO heterostructure composites were evaluated by various techniques. Transmission electron microscopy image analysis confirmed the presence of CuO nanoparticles onto the surface of the rGO sheets. It was also noticed that the electrochemical properties were dependent on the morphology of the heterostructure. The CuO-rGO heterostructure showed better hydrogen peroxide sensing performance as compared to the pure CuO nanoparticle. The sensitivity and limit of detection (LoD) were found to be 57.6 µA mM-1 cm-2 and 4.3 nM. The CuO-rGO heterostructure also showed good selectivity in the presence of various interfering electrolytes like ascorbic acid, dopamine, uric acid and glucose.

Band Gap Engineering of Boron Nitride by Graphene and Its Application as Positive Electrode Material in Asymmetric Supercapacitor Device.

Nanostructured hexagonal boron nitride (h-BN)/reduced graphene oxide (RGO) composite is prepared by insertion of h-BN into the graphene oxide through hydrothermal reaction. Formation of the super lattice is confirmed by the existence of two separate UV-visible absorption edges corresponding to two different band gaps. The composite materials show enhanced electrical conductivity as compared to the bulk h-BN. A high specific capacitance of ∼824 F g(-1) is achieved at a current density of 4 A g(-1) for the composite in three-electrode electrochemical measurement. The potential window of the composite electrode lies in the range from -0.1 to 0.5 V in 6 M aqueous KOH electrolyte. The operating voltage is increased to 1.4 V in asymmetric supercapacitor (ASC) device where the thermally reduced graphene oxide is used as the negative electrode and the h-BN/RGO composite as the positive electrode. The ASC exhibits a specific capacitance of 145.7 F g(-1) at a current density of 6 A g(-1) and high energy density of 39.6 W h kg(-1) corresponding to a large power density of ∼4200 W kg(-1). Therefore, a facile hydrothermal route is demonstrated for the first time to utilize h-BN-based composite materials as energy storage electrode materials for supercapacitor applications.

Development of high energy density supercapacitor through hydrothermal synthesis of RGO/nano-structured cobalt sulphide composites.

Co9S8/reduced graphene oxide (RGO) composites were prepared on nickel foam substrate through hydrothermal reaction and used directly as supercapacitor electrode. The field emission scanning electron microscopy analysis of the composites showed the formation of Co9S8 nano-rods on the RGO surfaces. The average crystal size of the Co9S8 nano rods grown on the RGO sheets were ∼25-36 nm as calculated from x-ray diffraction analysis. The reduction of graphene oxide (GO) was confirmed by Raman and x-ray photoelectron spectroscopy analysis. The electrical conductivity of the Co9S8/RGO composite was recorded as 1690 S m(-1) at room temperature, which is much higher than that of pure GO further confirming the hydrothermal reduction of GO. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy were investigated to check the electrochemical performances of the Co9S8/RGO composites. The Co9S8/RGO composites supported on nickel foam showed very high specific capacitance (Sc)(1349 F g(-1) at a current density of 2.2 A g(-1)), energy density (68.6 W h kg(-1)) and power density (1319 W kg(-1)) in 6 M KOH electrolyte. The retention in Sc of the composite electrode was found to be ∼96% after 1000 charge-discharge cycles.

Covalent surface modification of chemically derived graphene and its application as supercapacitor electrode material.

A simple and effective method using 6-amino-4-hydroxy-2-naphthalenesulfonic acid (ANS) for the synthesis of water dispersible graphene has been described. Ultraviolet-visible (UV-vis) spectroscopy reveals that ANS-modified reduced graphene oxide (ANS-rGO) obeys Beers law at moderate concentrations. Fourier transform infrared and X-ray photoelectron spectroscopies provide quantitative information regarding the removal of oxygen functional groups from graphene oxide (GO) and the appearance of new functionalities in ANS-rGO. The electrochemical performances of ANS-rGO have been determined by cyclic voltammetry, charge-discharge and electrochemical impedance spectroscopy analysis. Charge-discharge experiments show that ANS-rGO is an outstanding supercapacitor electrode material due to its high specific capacitance (375 F g(-1) at a current density of 1.3 A g(-1)) and very good electrochemical cyclic stability (∼97.5% retention in specific capacitance after 1000 charge-discharge cycles). ANS-rGO exhibits promising characteristics with a very high power density (1328 W kg(-1)) and energy density (213 W h kg(-1)).