A series of isostructural metal-organic frameworks for an enhanced electro-catalytic oxygen evolution reaction.

Three new isostructural MOFs (ZnTIA, CoTIA and CdTIA) were synthesized by the solvothermal synthesis of the organic linker 5-triazole isophthalic acid (5-TIA) with the transition metals Zn(II), Co(II) and Cd(II) in the presence of the structure directing agent tetramethyl ammonium chloride (TMA). These three MOFs were characterized thoroughly by ScXRD, PXRD, FT-IR, TGA, BET and SEM. They have excellent thermal and water stabilities. Among all these MOFs mentioned, pristine CoTIA exhibited excellent electrocatalytic activity toward the oxygen evolution reaction (OER). It exhibits a Tafel slope of 68.9 mV dec-1 with an overpotential of 337 mV at 10 mA cm-2 current density. The OER activity of the CoTIA MOF is relatively equivalent to that of the state-of-the-art catalyst (RuO2). Furthermore, the mechanical stability of crystalline ZnTIA, CoTIA and CdTIA MOFs was tested under ball mill pressure. The result showed that all the MOFs exhibit low tolerance to mechanical force because their structure was highly distorted or collapsed under such pressure, which is reflected by their poor electrocatalytic OER activity.

Metal-free carbon-based anode for electrochemical degradation of tetracycline and metronidazole in wastewater.

Degradation of antibiotics through electrocatalytic oxidation has recently been comprehended as a promising strategy in wastewater treatment. Herein, nitrogen and sulphur doped graphene oxide (N,S-rGO) nanosheets were synthesized and employed as metal-free anodic material for electrochemical degradation of antibiotics, viz. metronidazole (MNZ) and tetracycline (TC). The synthesized anodic material was characterized using various spectral techniques and further the electrochemical behaviour of N,S-rGO was thoroughly examined. Thereafter, the N,S-rGO material was then employed as the anode material towards the electrocatalytic degradation of antibiotics. Parameters such as initial concentration of the antibiotics and current densities were varied and their effect towards the degradation of MNZ and TC were probed. Notably, the N,S-rGO based anode has shown impressive removal efficiency of 99% and 98.5%, after 120 min of reaction time for MNZ and TC, respectively, under optimized conditions. The obtained results including the kinetic parameters, removal efficiency and electrical efficiency ensure that the prepared anodic material has huge prospective towards real-time application for removal of antibiotics from water.

Robust Zeolitic Tetrazole Framework for Electrocatalytic Dopamine Detection with High Selectivity.

A novel zeolitic tetrazolate framework (ZTF-8) has been synthesized by solvent-free heat-assisted (70 °C) mechanochemical grinding of zinc acetate and 5-methyl tetrazole in the presence of NaOH powder. The structure of ZTF-8 adopts the zeolitic sodalite (SOD) topology with uncoordinated N-heteroatom sites and resembles the structure of the well-known zeolitic imidazole framework ZIF-8. ZTF-8 is exceptionally stable in 0.1 M aqueous acid and base solutions for 60 days at 25 °C. The unique structure with uncoordinated N-heteroatom active sites and exceptional stability of ZTF-8 facilitated the electrocatalytic oxidation of dopamine to dopamine quinone at neutral pH. Without any postsynthetic modification, ZTF-8 is directly used for the facile electrochemical detection of dopamine over a wide range of concentrations (5-550 µM) with a high sensitivity (2410.8 µA mM-1 cm-2). It also demonstrated promising selectivity over other interferents of similar oxidation potential, such as ascorbic acid and uric acid. The DFT study revealed that the ZTF-8 framework has a higher binding energy (-145.07 kJ/mol) and stronger interaction with dopamine than its isostructural ZIF-8 structure (-130.42 kJ/mol).

Phase Purity Regulated by Mechano-Chemical Synthesis of Metal-Organic Frameworks for the Electrocatalytic Oxygen Evolution Reaction.

Three new metal organic frameworks (ZnTIA-1mc, CuTIA-1mc, and CoTIA-1mc) were synthesized by the mechanochemical grinding (mc) method in the unadulterated form. They compared with their solvothermally synthesized (st) counterparts, where the mixtures of isomeric forms have been isolated. Kinetics study with the function of grinding time during the mechanosynthesis process revealed the formation of new metastable phases. Less crystallinity and short of mechanical defects in the structure of synthesized mc metal organic frameworks showed enhanced electrocatalytic activity toward oxygen evolution reaction (OER). Among all, CoTIA-1mc showed high OER activity with 289 mV overpotential, 10 mA cm-2 current density, and 55.4 mV dec-1 Tafel slope in 1 M KOH which is close to the commercially used RuO2.

Snowflake-like Metastable Wurtzite CuGaS2/MoS2 Composite with Superior Electrochemical HER Activity.

In the present work, we report the synthesis of wurtzite CuGaS2 and its composite with MoS2 and explored their efficacy toward two important applications, viz. electrocatalytic hydrogen evolution reaction (HER) and adsorption of Rhodamine B dye. The CuGaS2 was synthesized via a low-temperature ethylenediamine-mediated solvothermal method. The obtained products were characterized by various techniques such as X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy to ascertain the phase formation, surface morphology, and elemental oxidation states. The electrocatalytic activity of the wurtzite CuGaS2 and CuGaS2/MoS2 composites toward HER was investigated, wherein the CuGaS2/MoS2 composite exhibited superior activity when compared to the pristine sample with a small Tafel slope of 56.2 mV dec-1 and an overpotential value of -464 mV at the current density of 10 mA cm-2. On the other hand, the synthesized CuGaS2 also showed an impressive adsorption behavior toward Rhodamine B dye with 99% adsorption in 60 min, which is relatively better than that observed with the composite material.

Functional group-specific multilateral derivatization cum extraction method for simultaneous quantification of genotoxic impurities in carvedilol phosphate drug using GC-MS and their toxicity assessments.

A simple and facile functional group-specific multilateral derivatization cum extraction method coupled with GC-MS based analytical methodology has been developed for the rapid identification and determination of five potential genotoxic impurities (GTIs), including epichlorohydrin, hydrazine, phenylhydrazine, 3-chloro-1,2-propanediol and 1-(2-chloroethoxy)- 2-methoxybenzene in the carvedilol phosphate (CRV-P) drug active pharmaceutical ingredient (API). A generic synthetic route has been explored to apply the current investigation to the majority of the market available synthetic routes for the carvedilol process. Five significant GTIs were identified, and their toxicity was examined using in-silico model. The pharmacokinetic and pharmacodynamic properties of the impurities were compared with the drug molecule to evince the associated risk of impurities during therapeutic action. Furthermore, a quantitative comparison has been made for each impurity with the drug molecule for their ADMET properties, and the potential nature of the impurities has been thoroughly assessed. The developed method encompasses simple derivatization cum extraction-oriented GC-MS method for the reported GTIs, which was also validated as per current ICH guidelines. The obtained LOD and LOQ for the method were between 0.06 ~ 0.61 µg/g and 0.17 ~ 1.8 µg/g, respectively, and the r2 values (0.994 ~ 0.997) show that the method is very sensitive and linear over a wide range (LOQ to 120 % of the target concentration). The percentage recoveries and relative standard deviation obtained were between 85.3 and 109.5 and 0.1-4.7, respectively, showing fit for purpose. Moreover, method precision, intermediate precision, and robustness of the method have also been successfully demonstrated. Thus, this method could be directly engaged as the quality forecasting tool for the marketed drug samples aimed at the estimation of the reported GTIs at trace level.

Novel delipidated chicken feather waste-derived carbon-based molybdenum oxide nanocomposite as efficient electrocatalyst for rapid detection of hydroquinone and catechol in environmental waters.

Chicken poultry industry produces a vast amount of feather waste and is often disposed into landfills, creating environmental pollution. Therefore, we explored the valorization of chicken feather waste into lipids and keratinous sludge biomass. This study demonstrates the successful utilization of keratinous sludge biomass as a unique precursor for the facile preparation of novel keratinous sludge biomass-derived carbon-based molybdenum oxide (KSC@MoO3) nanocomposite material using two-step (hydrothermal and co-pyrolysis) processes. The surface morphology and electrochemical properties of as-prepared nanocomposite material were analyzed using HR-SEM, XRD, XPS, and cyclic voltammetric techniques. KSC@MoO3 nanocomposite exhibited prominent electrocatalytic behavior to simultaneously determine hydroquinone (HQ) and catechol (CC) in environmental waters. The as-prepared electrochemical sensor showed excellent performance towards the detection of HQ and CC with broad concentration ranges between 0.5-176.5 µM (HQ and CC), and the detection limits achieved were 0.063 µM (HQ) and 0.059 µM (CC). Furthermore, the developed modified electrode has exhibited excellent stability and reproducibility and was also applied to analyze HQ and CC in environmental water samples. Results revealed that chicken feather waste valorization could result in sustainable biomass conversion into a high-value nanomaterial to develop a cost-effective electrochemical environmental monitoring sensor and lipids for biofuel.

Switching the solubility of electroactive ionic liquids for designing high energy supercapacitor and low potential biosensor.

Ionic liquids are regarded as one of the most prodigious materials for sustainable technological developments with superior performance and versatility. Hence, in this study, we have reported the design and synthesis of electroactive disubstituted ferrocenyl ionic liquids (Fc-ILs) with two different counter anions and demonstrated the significance of their anion tuneable physicochemical characteristics towards multifunctional electrochemical applications. The Fc-IL synthesized with chloride counter anion (Fc-Cl-IL) displays water-solubility and can be used as a redox additive in the fabrication of supercapacitor. Supercapacitor device with Fc-Cl-IL based redox electrolyte exhibits outstanding energy and power densities of 91 Wh kg-1 and 20.3 kW kg-1, respectively. Meanwhile, ferrocenyl IL synthesized with perchlorate anion (Fc-ClO4-IL) exhibits water-insolubility and can serve as a redox mediator towards construction of a glucose biosensor. The biosensor comprising Fc-ClO4-IL is able to detect glucose at an exceptionally lower potential of 0.2 V, with remarkable sensitivity and selectivity. This study implies that the introduction of electroactive ILs could afford supercapacitor devices with high energy and power densities and biosensors with less detection potential.

Direct electrochemistry of covalently immobilized hemoglobin on a naphthylimidazolium butyric acid ionic liquid/MWCNT matrix.

Monitoring the concentration levels of hydrogen peroxide (H2O2) is significant in both clinical and industrial applications. Herein, we develop a facile biosensor for the detection of H2O2 based on direct electron transfer of hemoglobin (Hb), which was covalently immobilized on a hydrophobic naphthylimidazolium butyric acid ionic liquid (NIBA-IL) over a multiwalled carbon nanotube (MWCNT) modified glassy carbon electrode (GCE) to obtain an Hb/NIBA-IL/MWCNT/GCE. Highly water-soluble Hb protein was firmly immobilized on NIBA-IL via stable amide bonding between the free NH2 groups of Hb and COOH groups of NIBA-IL via EDC/NHS coupling. Thus fabricated biosensor showed a well resolved redox peak with a cathodic peak potential (Epc) at -0.35 V and anodic peak potential (Epa) at -0.29 V with a formal potential (E°') of -0.32 V, which corresponds to the deeply buried FeIII/FeII redox centre of Hb, thereby direct electrochemistry of Hb was established. Further, the modified electrode demonstrated very good electrocatalytic activity towards H2O2 reduction and showed a wide linear range of detection from 0.01 to 6.3 mM with a limit of detection and sensitivity of 3.2 µM and 111 µA mM-1 cm-2, respectively. Moreover, the developed biosensor displayed high operational stability under dynamic conditions as well as during continuous potential cycles and showed reliable reproducibility. The superior performance of the fabricated biosensor is attributed to the effective covalent immobilization of Hb on the newly developed highly conducting and biocompatible NIBA-IL/MWCNT/GCE platform.

Water insoluble, self-binding viologen functionalized ionic liquid for simultaneous electrochemical detection of nitrophenol isomers.

Herein, a water insoluble viologen functionalized ionic liquid (Vio-IL) was designed for the simultaneous electrochemical detection of 2-nitrophenol and 4-nitrophenol. Carboxyl functionalized benzimidazolium based ILs were hierarchically synthesized and the water insoluble carboxylic IL was covalently attached with aminopropylmethyl viologen through DCC coupling to obtain water insoluble Vio-IL gel. Vio-IL was immobilized by simple dropcasting over a multiwalled carbon nanotube deposited screen printed carbon electrode to obtain Vio-IL/MWCNT/SPE. The Vio-IL/MWCNT/SPE exhibited two sets of well-resolved redox peaks corresponding to V2+ to V+• and V+• to V0 redox couple. Furthermore, Vio-IL/MWCNT/SPE has shown excellent electrocatalytic activity towards the reduction of 2- and 4-nitrophenol individually, and also for the simultaneous determination of 2- and 4-nitrophenol. The linear range, sensitivity and detection limit for simultaneous detection of 2-nitrophenol at Vio-IL/MWCNT/SPE were found to be 4-494 µM, 0.884 µA µM-1 cm-2, 1.5 µM and that for 4-nitrophenol were 2-259 µM, 2.615 µA µM-1 cm-2, 0.70 µM. The Vio-IL/MWCNT/SPE established excellent sensitivity and selectivity towards the simultaneous determination of 2- and 4-nitrophenol together with impressive stability and reproducibility. The exemplary analytical parameters achieved are due to the rational immobilization of the mediator covalently in the highly conducting IL/MWCNT backbone which maintained the mediator characteristics effectively.

Gold Nanoparticle-Redox Ionic Liquid based Nanoconjugated Matrix as a Novel Multifunctional Biosensing Interface.

Creation of interfaces with a prudent design for the immobilization of biomolecules is substantial in the construction of biosensors for real-time monitoring. Herein, an adept biosensing interface was developed using a nanoconjugated matrix and has been employed toward the electrochemical determination of hydrogen peroxide (H2O2). The anionic gold nanoparticle (AuNP) was electrostatically tethered to cationic redox ionic liquid (IL), to which the horseradish peroxidase (HRP) enzyme was covalently immobilized to form a nanobioconjugate. The anthracene-substituted, aldehyde-functionalized redox IL (CHO-AIL) was judiciously designed with the (i) imidazolium cation for electrostatic interaction with AuNPs, (ii) anthracene moiety to mediate the electron transfer, and (iii) free aldehydic group for covalent bonding with a free amine group of the enzyme. Thus, the water-soluble HRP is effectively bonded to the CHO-AIL on a glassy carbon electrode (GCE) via imine bond formation, which resulted in the formation of the HRP-CHO-AIL/GCE. Electrochemical investigations on the HRP-CHO-AIL/GCE reveal highly stable and distinct redox peaks for the anthracene/anthracenium couple at a formal potential (E°') of -0.47 V. Electrostatic tethering of anionic AuNPs to the HRP-CHO-AIL promotes the electron transfer process in the HRP-CHO-AIL/AuNPs/GCE, as observed by the reduction in the formal potential to -0.42 V along with the enhancement in peak currents. The HRP-CHO-AIL/AuNPs/GCE has been explored toward the electrocatalytic detection of H2O2, and the modified electrode demonstrated a linear response toward H2O2 in the concentration range of 0.02-2.77 mM with a detection limit of 3.7 µM. The developed biosensor ascertained predominant selectivity and sensitivity in addition to remarkable stability and reproducibility, corroborating the suitableness of the platform for the effectual biosensing of H2O2. The eminent performance realized with our biosensor setup is ascribed to the multifunctional efficacy of this newly designed nanobioconjugate.

Rationally designed naphthyl substituted amine functionalized ionic liquid platform for covalent immobilization and direct electrochemistry of hemoglobin.

Herein, we have designed and demonstrated a facile and effective platform for the covalent anchoring of a tetrameric hemoprotein, hemoglobin (Hb). The platform comprises of naphthyl substituted amine functionalized gel type hydrophobic ionic liquid (NpNH2-IL) through which the heme protein was covalently attached over a glassy carbon electrode (Hb-NpNH2-IL/GCE). UV-vis and FT-IR spectral results confirmed that the Hb on NpNH2-IL retains its native structure, even after being covalently immobilized on NpNH2-IL platform. The direct electron transfer of redox protein could be realized at Hb-NpNH2-IL/GCE modified electrode and a well resolved redox peak with a formal potential of -0.30 V and peak separation of 65 mV was observed. This is due to the covalent attachment of highly conducting NpNH2-IL to the Hb, which facilitates rapid shuttling of electrons between the redox site of protein and the electrode. Further, the fabricated biosensor favoured the electrochemical reduction of bromate in neutral pH with linearity ranging from 12 to 228 µM and 0.228 to 4.42 mM with a detection limit and sensitivities of 3 µM, 430.7 µA mM-1 cm-2 and 148.4 µA mM-1 cm-2 respectively. Notably, the fabricated biosensor showed good operational stability under static and dynamic conditions with high selectivity and reproducibility.

Aldehyde functionalized ionic liquid on electrochemically reduced graphene oxide as a versatile platform for covalent immobilization of biomolecules and biosensing.

An aldehyde functionalized ionic liquid, (3-(3-formyl-4-hydroxybenzyl)-3-methylimidazolium hexafluorophosphate) (CHO-IL) has been employed herein as a multiple host platform for the covalent immobilization of mediator as well as enzyme. The CHO-IL was immobilized on electrochemically reduced graphene oxide (ERGO) through the π-π stacking of hydroxybenzyl and imidazolium groups with ERGO and subjected to further covalent attachment of Azure A (Azu-A) mediator or glucose oxidase (GOx) enzyme. Electroactive, water soluble organic dye Azu-A was effectively immobilized to the host IL through simple Schiff base reaction. Azu-A was rendered leak-free in the electrode setup and also responded well for the amperometric determination of H2O2 over a linear range of 0.03-1mM with a detection limit and sensitivity of 11.5µM and 133.2µAmM-1cm-2, respectively. Further, attempts were made to explore the CHO-IL platform for the covalent immobilization of GOx enzyme which served well in retaining the enzyme nativity, reactivity and stability. Under optimized conditions, mediatorless GOx biosensor developed based on direct electrochemistry has exhibited an impressive analytical signal towards glucose detection in the linear range of 0.05-2.4mM with a detection limit and sensitivity of 17µM and 17.7µAmM-1cm-2, respectively. The reliability of the proposed Azu-A based chemical sensor and GOx based biosensor towards the determination of H2O2 and glucose in the real samples have been demonstrated. The remarkable analytical parameters and long term stability of both the sensors could be envisioned as a result of facile immobilization platform and immobilization strategy.

A bioinspired ionic liquid tagged cobalt-salophen complex for nonenzymatic detection of glucose.

The development of efficient and cost effective nonenzymatic biosensors with remarkable sensitivity, selectivity and stability for the detection of biomolecules, especially glucose is one of the major challenges in materials- and electrochemistry. Herein, we report the design and preparation of nonenzymatic biosensor based on an ionic liquid tagged cobalt-salophen metal complex (Co-salophen-IL) immobilized on electrochemically reduced graphene oxide (ERGO) for the detection of glucose via an electrochemical oxidation. The bioinspired Co-salophen-IL complex has been synthesized and immobilized on ERGO, which was previously deposited on a screen printed carbon electrode (SPE) to form the Co-salophen-IL/ERGO/SPE nonenzymatic biosensor. The electrochemical behaviour of this modified electrode was studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Notably, the Co-salophen-IL/ERGO/SPE biosensor exhibited excellent electrocatalytic activity towards glucose oxidation in 0.1M NaOH, based on which an amperometric sensor has been developed. The modified electrode has shown prominent performance towards glucose detection over a wide linear range from 0.2µM to 1.8mM with a detection limit and sensitivity of 0.79µM and 62µAmM-1 respectively. The detection was carried out at 0.40V and such a less working potential excludes the interference from the coexisting oxidizable analytes. The role of Co-salophen, IL and ERGO in the electrocatalytic activity has been systematically investigated. Furthermore, the biosensor demonstrated high stability with good reproducibility.