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Single phasic magnetite samples co-substituted with cobalt and nickel, with the formula CoxNi(0.4−x)FeII0.6FeIII2O4 (x = 0, 0.1, 0.2, 0.3, and 0.4) were synthesized in the nanoregime via a co-precipitation technique. Being an inverse spinel, magnetite will preferentially expose the octahedral sites and make metal cations available on the surface, which will play a conducive role in both hydrogen evolution (HER) and oxygen evolution (OER) reactions. We demonstrate that the partial substitution of Fe2+ (either by Ni2+ or Co2+ ions) on the octahedral sites of the inverse spinel structure of CoxNi(0.4−x)FeII0.6FeIII2O4 significantly enhance the bifunctional electrocatalytic activity of the magnetite samples in an alkaline medium. The spinel ferrite with the formula Co0.2Ni0.2FeII0.6FeIII2O4 exhibits outstanding bifunctional electrocatalytic activity in 1 M KOH with the lowest onset overpotential (ƞOER = 190 and ƞHER = 200 mV), small overpotential at η10 (OER = 270 mV and HER = 275 mV), excellent kinetics (Tafel slopes, bOER = 44 mV dec−1 and bHER = 99 mV dec−1), and high durability (>10 h). Furthermore, Co0.2Ni0.2FeII0.6FeIII2O4 can serve as both cathode and anode for the overall water-splitting reaction, and delivered a current density of 10 mA cm−2 at a very low cell voltage of 1.72 V with excellent stability (>10 h at 10 mA cm−2). Thus, this work provides a lucid approach to engineer a highly efficient non-noble transition metal-based electrocatalyst for renewable energy applications via simple micro-structural and surface engineering.

A novel vertical non-van der Waals (non-vdW) heterostructure of graphene and hexagonal boron nitride (G/hBN) is realized and its application in direct four-electron oxygen reduction reaction (ORR) in alkaline medium is established. The G/hBN differs from previously demonstrated vdW heterostructures, where it has a chemical bridging between graphene and hBN allowing a direct charge transfer - resulting in high ORR activity. The ORR efficacy of G/hBN is compared with that of graphene-hBN vdW structure and individual layers of graphene and hBN along with that of benchmark platinum/carbon (Pt/C). The ORR activity of G/hBN is found to be on par with Pt/C in terms of current density but with much higher electrochemical stability and methanol tolerance. The onset potential of the G/hBN is found to be improved from 780 mV at a glassy carbon electrode to 930 mV and 940 mV in gold and platinum electrodes, respectively, indicating its substrate-dependent catalytic activity. This opens possibilities of new benchmark catalysts of metals capped with G/hBN atomic layers, where the underneath metal is protected while keeping the activity similar to that of pristine metal. Density functional theory-based calculations are found to be supporting the observed augmented ORR performance of G/hBN.

Due to exceptional electronic, optoelectronic and catalytic properties, MoS2 has attracted extensive research interest in various applications. In the present scenario, the exploitation of noble-metal-free catalysts for hydrogen evolution is of great interest. Herein, we report the structural, optical, magnetic and electrocatalytic properties of pure and nickel-substituted MoS2 nanostructures synthesized by the hydrothermal method. X-ray diffraction (XRD) analysis reveals that all samples exhibit the hexagonal structure of MoS2 and the formation of NiS2 at higher concentrations of nickel. Vibrating sample magnetometer (VSM) measurements of the Mo1−xNixS2 nanostructures show a hysteresis loop at room temperature with a higher saturation magnetization for 1% Ni-substituted MoS2 nanostructures, confirming the ferromagnetic behaviour of the sample. The indirect-to-direct band gap transition of few-layered nanostructures was confirmed by the optical absorption spectrum showing bands in the 600–700 nm and 350–450 nm regions. This study also highlights the excitation wavelength-dependent down- and up-conversion photoluminescence of the as-synthesized samples, providing new horizons for the design of MoS2-based optical and spintronic devices. The electrocatalytic effect of 3% Ni-substituted MoS2 nanostructures has been found to be higher than that of other deposit concentrations as it corresponds to the efficient hydrogen evolution reaction (HER).

An enzyme-free sensitive hydrogen peroxide (H2O2) amperometric sensor is developed to detect H2O2 released from living cells using palladium nanoparticles supported on sulfonic acid functionalized mesoporous silica microspheres (Pd@SO3H-MSM). It is synthesized by an easy and facile method and is subsequently used for fabrication of an electrochemical sensing scaffold via drop-casting modification of a glassy carbon electrode (represented as GC/Pd@SO3H-MSM). Comprehensive characterizations including transmission electron microscopy, scanning electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, UV–vis spectrophotometry and electrochemical impedance spectroscopy to confirm the existence and nature of Pd nanoparticles in Pd@SO3H-MSM. GC/Pd@SO3H-MSM electrode demonstrates electrocatalytic activity for H2O2 reduction in phosphate buffer, leading to a sensitive H2O2 amperometric sensor with wide linear range (47.0 nM-1.0 mM), low detection limit (14.0 nM) and high sensitivity (0.36 μA mM−1 cm-2). It exhibits high selectivity, good reproducibility and long-term stability. More importantly, Pd@SO3H-MSM exhibits no toxicity to living cells and based on its remarkable analytical advantages, it is further unswervingly used to execute real-time detection of H2O2 released from living tumor cells and healthy normal cells. Thus Pd@SO3H-MSM acts as promising material for amperometric determination of H2O2 as well as used to accomplish real-time quantitative detection of H2O2 in biological environment.

Herein, a simple microwave assisted combustion approach is utilized for the synthesis of nano-sized Cr substituted Ni ferrites (NiCrxFe2-xO4). The as obtained materials were further sintered at 450°C in air and then utilized for physicochemical and electrochemical characterizations. X-ray diffraction (XRD) patterns showing sharp peaks confirmed the formation of single phase cubic spinel structure. TEM image reveals the formation of nanocrystalline particles having size in range of 10-20 nm. Further, the electrocatalytic oxygen evolution reaction (OER) of as-synthesized materials was studied by linear sweep voltammetry in alkaline solution. The OER results showed that co-substitution of Cr in NiFe2O4 matrix improved the electrocatalytic activity of the oxides towards OER. The NiCr0.5Fe1.5O4 shows the best OER performance in 1.0 M KOH solution. It achieved a low overpotential of about 320 mV at 10 mA/cm2 current density, which is comparable to other reported electrocatalysts. Tafel parameters and order of reaction were also in close agreements with literature values. DOI: http://dx.doi.org/10.17807/orbital.v12i3.1507

A sacrificial template, Fe-MIL-88 is used to synthesize Ni–Fe layered double hydroxide (Ni–Fe LDH). The metal-organic framework (Fe-MIL-88) is synthesized from the precursors, ferric nitrate and terephthalic acid. Electrocatalytic oxidation of kojic acid (KA) is realized by Ni–Fe LDH film which is coated on a glassy carbon electrode (GC). Under the optimized conditions, amperometry measurements at the Ni–Fe LDH coated GC as a function of KA concentration demonstrates a sensitive determination of KA. The calibration curve shows two linear ranges, 1–1500 µM and 1500–4500 µM for the KA determination. Detection limit for the KA determination is estimated as 0.73 µM. The practical applicability of this method is confirmed by measuring the KA concentration present in various real samples. A new sensor for the determination kojic acid is developed based on Ni–Fe layered double hydroxide which is synthesized through the Fe-MIL-88 templated route. Further, the synthesized material is used for the determination of kojic acid present in different brands of commercial tomato sauces.

An electrochemical sensor for hydrogen peroxide (H2O2) present in face bleach cream is fabricated using a composite based on bentonite (Bt) clay and copper oxide (CuO) nanoparticles (CuO-Bt). The CuO nanoparticles’ immobilization into Bt was carried out by a two-step process in which Cu2+ is ion-exchanged into Bt layers (Cu2+-Bt) in the first step followed by the chemical reaction of NaOH with Cu2+-Bt in the second step to get the target material, CuO nanoparticles immobilized Bt (CuO-Bt). The successful immobilization of CuO nanoparticles into Bt is investigated by a variety of techniques like scanning electron microscopy, transmission electron microscopy, FT-IR spectroscopy, UV-Vis spectroscopy, and electrochemical methods. The CuO-Bt composite is coated on a glassy carbon electrode and used as a selective electrochemical sensing platform for the determination of H2O2 based on the significant electrocatalytic property of CuO-Bt towards the H2O2 oxidation. This amperometric electrochemical sensor shows two linear detection ranges (5–50 μM and 50–10000 μM) with a limit of detection of 4.9 μM. The sensitivity is calculated to be 0.06 µA µM−1 cm−2. This electrochemical sensor exhibits high selectivity, stability, and practical applicability for the H2O2 determination in real samples.

Metal-graphene composites are sought after for various applications. A hybrid light-weight foam of nickel (Ni) and reduced graphene oxide (rGO), called Ni-rGO, is reported here for small molecule oxidations and thereby their sensing. Methanol oxidation and non-enzymatic glucose sensing are attempted with the Ni-rGO foam via electrocatalytically, and an enhanced methanol oxidation current density of 4.81 mA/cm2 is achieved, which is ~1.7 times higher than that of bare Ni foam. In glucose oxidation, the Ni-rGO electrode shows a better sensitivity over bare Ni foam electrode where it could detect glucose linearly over a concentration range of 10 μM to 4.5 mM with a very low detection limit of 3.6 μM. This work demonstrates the synergistic effects of metal and graphene in oxidative processes, and also shows the feasibility of scalable metal-graphene composite inks development for small molecule printable sensors and fuel cell catalysts.

Low Z element based room temperature ferromagnetic materials are highly sought after for many applications. In this work, we report the development of fluorine functionalized graphene-hBN out-of-plane heterostructures (hBNCF), which possess large room temperature ferromagnetic ordering (magnetization ∼ 0.05 emu/g and coercivity ∼ 420 Oe) and exhibit T2 relaxation enhancement (0.55 s−1 found for D2O was increased to ∼7 s−1 at 1 mg/ml) in water without causing the T1. The ferromagnetic nature of the hBNCF powder devoid of any metallic magnetic impurities was further shown by magnetic force microscopy. Layered structures of hBNCF that have an optical bandgap of ∼3.89 eV were produced using a two step method: Shear exfoliated hBN layers were modified by surface graphitisation to result into layered graphene heterostructures (hBNC), which were then functionalized with fluorine. Apparent ferromagnetic properties arise from these large scale, vertical, non-van der Waals connected, crystalline layer structures. Density functional calculations show the role of out-of-plane covalently connected BN domains and their interaction with fluorine, that causes the formation of new states in the graphitic lattice. These states exhibit a spin splitting, which contributes to the observed large magnetic ordering.

A new redox-free electrochemical approach for driving the deposition of two-dimensional (2D) layered MoS2 nanosheets is described. First, poly(acylic acid) (PAA) functionalized layered MoS2 nanosheets (PAA-MoS2) is prepared to form a stable aqueous PAA-MoS2 dispersion, which is subsequently used for the electrochemical deposition. In contrast to previous electrodeposition methods of MoS2, which involve the redox of molecular precursors of Mo and S, herein we introduce an electrochemical approach for the deposition of 2D layered MoS2 nanosheets directly from their nanometric building blocks, namely from their aqueous dispersion. This “nano to nano” approach is based on altering the ionic strength at the vicinity of the electrode surface by applying a potential. Specifically, the electrogeneration of Cu2+ ions, cause the PAA-MoS2 nanosheets in the dispersion to aggregate and deposit on the copper electrode. Scanning electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy analysis show clearly that the deposited layered MoS2 maintains its original structure. Furthermore, the electrodeposited PAA-MoS2 nanosheets on copper show excellent catalytic activity for the hydrogen evolution reaction with low overpotential. Hence, we believe that these findings could lead to a generic approach for the formation of thin films or patterns of 2D nanomaterials.

In this report, an electrochemical sensing scaffold (ESS) for hydrazine (HZ) and nitrobenzene (NB) have been developed based on gold nanoparticles decorated mesoporous silica microspheres (Au-MSM) modified glassy carbon (GC) electrode (represented as GC/Au-MSM). The presence and formation of gold nanoparticles in Au-MSM composite material is verified by X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy and by electrochemical methods. The textural and thermal properties are studied by nitrogen adsorption-desorption and thermogravimetric analysis, respectively. The electrocatalytic sensing behavior of GC/Au-MSM towards HZ and NB are investigated in detail employing various electrochemical techniques. Amperometry measurements as a function of HZ concentration exhibit two linear calibration ranges of 5.0 μM to 0.5 mM and 0.5–18.0 mM. Similarly, the differential pulse voltammetry measurements as a function of NB concentration show a linear calibration range of 0.1 μM to 2.5 mM. The limit of detection is evaluated to be 0.11 μM and 15.0 nM for HZ and NB, respectively. The kinetic parameters for HZ oxidation and NB reduction are discussed using chronoamperometry. The proposed GC/Au-MSM ESS shows good selectivity over potent interferences and applied to determine HZ and NB in various water samples.

Anionic redox mediator-incorporated polymer scaffold on glassy carbon (GC) electrode has been used for the electrocatalytic determination of nitrite. The polymer based on branched polyethylenimine (BPEI) crosslinked with ethylene glycol diglycidyl ether (EGDE) (BPEI-EGDE) has been employed as the potent scaffold. BPEI-EGDE film on GC electrode has been used to immobilize anionic redox mediator [Fe(CN)6]3− by ion-exchange and utilized as the scaffold for the electrochemical determination of nitrite. The voltammetric analysis confirms the confinement of the redox mediator inside the polymer film. This polymeric scaffold, GC/BPEI-EGDE/[Fe(CN)6]3− exhibits a reversible redox response for [Fe(CN)6]3−/4− and retains its redox activity and stability even in strong acidic conditions. The redox mediator confined into the polymer scaffold catalyzes the reduction of nitrite. Significant enhancement in the cathodic current associated with the concomitant decrease in the anodic current was observed in the presence of nitrite. The electrocatalytic response of the scaffold was exploited for the amperometric sensing of nitrite at the potential of 450 mV. The polymer scaffold is highly sensitive (28.5 µA mM−1 cm−2) and it could detect nitrite at micromolar levels (detection limit is 4.8 µM). The scaffold has been successfully used for the real sample analysis and high selectivity, stability, and reproducibility have been achieved.

Due to exceptional electronic, optoelectronic and catalytic properties, MoS

An electrochemical sensing platform which comprises gold nanoparticles (Au NPs) incorporated zinc based metal-organic framework (MOF-5) is developed for the sensitive determination of nitrite and nitrobenzene. MOF-5 and Au NPs incorporated MOF-5 (Au-MOF-5) are synthesized and characterized by UV-vis absorption, powder X-ray diffraction, FT-IR, scanning electron microscopy with energy dispersive X-ray analysis and elemental mapping, transmission electron microscopy and atomic force microscopy. Oxidation of nitrite is effectively electrocatalyzed at Au-MOF-5 with significant increase in oxidation current (41 and 38% in comparison with bare glassy carbon (GC) and MOF-5 coated GC (GC/MOF-5) electrodes, respectively) and with considerable decrease in the oxidation potential (0. 17 and 0.25 V in comparison with bare GC and GC/MOF-5 electrodes, respectively). The electrocatalytic reduction of nitrobenzene at GC/Au-MOF-5 is confirmed by an appreciable increase in the reduction current (79 and 36% in comparison with bare GC and GC/MOF-5 electrodes, respectively) and a small shift in the reduction potential (20 mV in comparison with GC/MOF-5). The detection limit is calculated as 1.0 μM with a sensitivity of 0.23 μAμM −1 cm −2 for nitrite and 15.3 μM with a sensitivity of 0.43 μAμM −1 cm −2 for nitrobenzene determinations. The Au-MOF-5 based electrochemical sensing platform shows high stability and selectivity even in the presence of several interferences (including phenols, inorganic ions and biologically important molecules) with a broad calibration range. Certain kinetic parameters of nitrite oxidation and nitrobenzene reduction have also been studied by hydrodynamic voltammetry.

In the present manuscript, a simple and easy route to synthesize bentonite (bt) clay-supported gold nanoparticles (Au NPs) is reported (represented as Au-bt). Application of this new environmentally benign material in electrocatalytic determination of arsenite (As(III)) was studied. The successful synthesis and incorporation of Au NPs into the bt clay is supported by spectroscopic, microscopic and electrochemical methods. The synthesized Au-bt material was used to modify glassy carbon electrode (GC) by the evaporation of Au-bt aqueous suspension dropped on the surface of the GC (GC/Au-bt). Cyclic voltammetry and chronoamperometry studies of As(III) solutions were performed with this GC/Au-bt electrode which act as efficient platform for the electro-oxidation of As(III) to As(V) at a very low overpotential. Kinetic parameters were evaluated for the oxidation of As(III) at the GC/Au-bt platforms. A wide linear calibration range for the determination of As(III) from 1 to 1700 μM was obtained with high reproducibility and stability. A limit of detection, 0.1 μM was achieved with high sensitivity. Additionally, it showed a good selectivity for the determination of As(III) in the presence of copper(II) and other interfering ions suggesting a promising new route for trace level determination of As(III) in neutral conditions.

This study reports the simple, selective and sensitive voltammetric detection of riboflavin (RF) using methylene blue (MB) incorporated sulfonic acid functionalized mesoporous silica microspheres (MSM), represented as MB-SO3H-MSM. MB-SO3H-MSM is synthesized and characterized by spectroscopic and microscopic methods. This material is coated on a glassy carbon (GC) electrode (symbolized as GC/MB-SO3H-MSM) to utilize it in electroanalytical applications. The electrochemical behavior of MB-SO3H-MSM is established using the GC/MB-SO3H-MSM electrode by cyclic voltammetry (CV) and electrochemical impedance spectroscopy techniques. The electrochemical behavior of RF at the GC/MB-SO3H-MSM electrode is also studied by CV. Compared to bare GC and SO3H-MSM coated GC, the GC/MB-SO3H-MSM electrode shows favorable electron transfer kinetics as well as an enhanced and stable electrochemical response of RF. Furthermore CV and differential pulse voltammetry (DPV) are used for the quantitative determination of RF at the GC/MB-SO3H-MSM electrode. The DPV response shows two linear calibration ranges of 10.0 nM to 15.0 μM and 15.0 to 50.0 μM. The detection limit based on the first linear calibration range is calculated as 5.0 nM with a sensitivity of 393.0 μA mM−1 cm−2. The fabricated sensing scaffold shows an excellent selectivity for RF over other soluble vitamins and interfering ions. The stability, reproducibility and determination of RF in pharmaceutical products are also demonstrated effectively.

The electrocatalytic activity of silver nanoparticle-incorporated bentonite clay (Ag-Bt) for hydrogen peroxide (H2O2) reduction is investigated in 0.1 M pH 7.0 phosphate buffer solution. Ag-Bt material-coated glassy carbon (GC) electrode displays high electrocatalytic activity for H2O2 reduction with increased current response in comparison with GC/Bt electrode. The catalytic current increases linearly with incremental addition of H2O2 from 10 µM to 5.0 mM (based on the amperometric experiments at an applied potential −0.3 V). The apparent diffusion coefficient for H2O2 and catalytic rate constant for H2O2 reduction at the GC/Ag-Bt platform are calculated to be 2.3 × 10−5 cm2 s−1 and 2.20 × 104 M−1 s−1, respectively. The practical application using the Ag-Bt material is shown for the determination of H2O2 in real sample. The GC/Ag-Bt platform exhibits low detection limit (9.1 µM), high selectivity, reproducibility and stability.

The present work introduces partially reduced graphene oxide (pRGO)-silica (SiO2) particles hybrid system (pRGOSHs) for sensitive and cost effective free cholesterol detection. Fabricated out of thin layers of pRGOSHs, these proposed ChOx/pRGOSHs/ITO based biosensors have a detection range of 2.6–15.5 mM with an appreciable detection limit of 1.3 mM and sensitivity of 11.1 μA/mM/cm2. Low Michaelis–Menten constant (Km) (4.9 × 10− 4 mM) and high diffusivity constant (D) (3.2 × 10− 10 cm2/s) values clearly indicate enhanced immobilization of enzyme over the substrate. Additionally, electrochemical impedance studies indicate that the synergistic combination of SiO2 and pRGO also results in much lower impedance values (40% and 18% decrease in comparison to SiO2 and pRGO respectively) for an overall enhanced sensing performance. These results are further corroborated by the density functional theory based theoretical simulations indicating enhanced electron density (theoretically) in case of the proposed hybrid system. Finally, the present work also highlights the importance of Si–OH bonds formation in the proposed pRGOSHs composite system for attaining such enhanced biosensing ability.

Acceleration of protons by transient strong electric fields formed with intense ultrashort laser pulses is important for advancements in radiography and biomedical applications. Controlling the absorption mechanisms by material modification or adding structural features to the solid substrate is important to enhance ion energies for a given laser intensity. We present here an experimental demonstration of enhanced proton acceleration when a BK-7 glass target is coated with 150 nm diameter silica hollow spheres. The hollow particle coated target yielded a maximum proton energy of ≥ 800 keV at a peak intensity of 1018 W cm−2 while the maximum energy is only up to 200 keV with a plain glass target under otherwise identical conditions. Two-dimensional particle in cell simulations demonstrate the role of local fields in the hollow spherical cavities that lead to the enhanced proton energies comparable to the experiments.

Here we demonstrate a new strategy for electrochemical determination of uric acid (UA) using a cationic polymer as an electrochemical sensing platform (ESP). The cationic polymer is based on branched polyethylenimine (BPEI) cross-linked with ethylene glycol diglycidyl ether (EGDE). Ion exchange property of this cross linked cationic polymer (BPEI-EGDE) with negatively charged electroactive species is studied by cyclic voltammetry. Furthermore, this cationic cross-linked BPEI-EGDE polymer is coated on a glassy carbon electrode (GC) to construct the ESP for the quantitative analysis of biologically important molecule, UA at pH 7.0. It shows efficient oxidation of UA with respect to bare GC due to favorable electrostatic interaction of anionic UA with the positively charged BPEI-EGDE film. Finally it is demonstrated that the BPEI- EGDE films can be used as efficient ESP for non-enzymatic UA determination in the concentration range of 5 to 1500 µM with a sensitivity of 153 µA μM-1cm-2.

A novel electrochemical sensing platform (ESP) for nitrobenzene (NB) has been developed using palladium nanoparticles decorated polymer-silica nanocomposite (represented as Pd-GG-g-PAM-silica). The polymeric part of the nanocomposite is based on a biodegradable copolymer, guar gum grafted polyacrylamide (GG-g-PAM). The nanocomposite is characterized by spectroscopic, microscopic and electrochemical methods. Pd-GG-g-PAM-silica efficiently catalyzes the electro-reduction of NB. The mechanism and kinetic parameters of the electrocatalytic reduction of NB at Pd-GG-g-PAM-silica modified glassy carbon electrodes (GCE) are evaluated in 0.1 M phosphate buffer solution (pH 7.0) using linear sweep voltammetry, differential pulse voltammetry and chronoamperometry. The observed electrochemical responses at Pd-GG-g-PAM-silica modified GCE exhibit excellent analytical performance for NB detection with high stability, reproducibility, and acceptable selectivity. This novel ESP exhibit a detection limit of 0.06 μM with two linear calibration ranges from 1.0 to 1900 μM and from 1900 to 3900 μM for NB. The diffusion coefficient and catalytic rate constant for NB reduction at the Pd-GG-g-PAM-silica modified GCE is calculated to be 3.88 × 10 −6 cm 2 s −1 and 1.82 × 10 4 M −1 s −1 respectively. In addition, the material is successfully used for the determination of NB in real water samples and the recoveries of the spiked NB are quite satisfactory.

Development of an efficient amperometric sensor for nitrites using Fe(phen) 3 2+ (where phen = 1,10-phenanthroline) incorporated a bentonite film as electrochemical sensing platform (ESP) is reported. The ESP showed high electrocatalytic activity for nitrite oxidation by decreasing the nitrite oxidation potential and increasing the peak current. It shows linear increase in current with increase in the concentration of nitrite from 1.0 μM to 100.0 mM and 1.0 μM to 25.0 mM by cyclic voltammetry and amperometry, respectively. Kinetic parameters such as catalytic rate constant, diffusion coefficient, etc . are evaluated using chronoamperometry and chronocoulometry. Magnitude of interference caused by other species has been examined in simulated mixtures containing high concentration of interfering species and the influence of interferences was found to be negligible. The constructed sensor is successfully applied for the determination of nitrite in potable water samples.

A new palladium nanoparticles immobilized organic-inorganic hybrid nanocomposite material is prepared to combine the mechanical strength offered by the inorganic matrix with flexible binding sites provided by the organic polymer. The organic polymer is based on a natural polysaccharide, gaur gum grafted with poly(acrylamide) and the inorganic matrix is based on silica. The nanocomposite is characterized by physico-chemical methods, surface characterization techniques and electrochemical methods. This material is coated on a glassy carbon electrode and utilized for electrocatalytic oxidation of hydrazine (HZ). Electrocatalytically HZ is oxidized at lowest overpotential (-0.15 V vs. SCE) than ever reported. Based on the linear increase in catalytic current, a sensitive HZ amperometric sensor is constructed. The sensor displays two linear calibration ranges from 50.0 μM to 0.6 mM and from 0.6 mM to 180 mM for HZ with high stability and reproducibility. Limit of detection is found to be 4.1 μM with high sensitivity and selectivity. These properties make the nanocomposite film a promising electrochemical sensing platform for the determination of HZ. Chronoamperometry and cyclic voltammetry studies are used to evaluate kinetic parameters.

In this paper, we report a facile route to synthesize silver nanoparticles (Ag NPs) incorporated into a copolymer of methyl methacrylate (MMA) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) (abbreviated as P(MMA-co-AMPS)) and its application to construct an electrochemical nitrite (NO2−) sensor. The copolymer nano-composite material (Ag–P(MMA-co-AMPS) is characterized by means of transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, UV-vis spectroscopy, X-ray powder diffraction methods, thermogravimetric analysis and electrochemical impedance spectroscopy. Further, Ag–P(MMA-co-AMPS) is used to prepare an electrochemical sensing platform (ESP) on a glassy carbon electrode (GC) surface. NO2− is electrocatalytically oxidized at the ESP (GC/Ag–P(MMA-co-AMPS), which leads to a sensitive determination of NO2−. The oxidation current of NO2− is linear to its concentration in the range of 1.0–100 000.0 μM and the detection limit is found to be 0.2 μM with a sensitivity 104.6 μA mM−1 cm−2. The observed analytical parameters such as wide linear range, low detection limit, high sensitivity and short response time are comparable or superior to other previously reported NO2− sensors. Kinetic parameters are evaluated using cyclic voltammetry and chronoamperometry. Finally it is demonstrated that the proposed sensor can be used for the selective determination of NO2− present in water samples and the results are quite promising.

The construction and characterization of an electrochemical sensing platform based on a cationic polymer modified electrode are described in this work. The cationic polymer is prepared as a thin film on a glassy carbon electrode (GC) surface by in situ cross-linking of branched polyethylenimine (BPEI) with ethylene glycol diglycidyl ether (EGDE). Positively charged amino groups of this polymer (BPEI-EGDE) act as effective anion exchange groups. The ion exchange properties of BPEI-EGDE are investigated by determining the permeability of electroactive anions through the polymer film using cyclic voltammetry. Furthermore, the modified electrodes are used for the electrochemical detection of ascorbic acid (AA), which is feasible with the films alone or when hexacyanoferrate ([Fe(CN)6]4−), is electrostatically confined (by ion exchange) in the cationic BPEI-EGDE film. When compared with bare GC electrodes, a large decrease in AA oxidation overpotential is observed at the [Fe(CN)6]4−-modified electrode surface. Kinetic parameters of electrocatalytic oxidation of AA by electrogenerated [Fe(CN)6]3− are evaluated by cyclic voltammetry and chronoamperometry. Finally, this method is employed for the determination of AA in a pharmaceutical tablet.

This work is aimed to demonstrate the use of ion exchange voltammetry in the electroanalysis of biologically important molecules based on polymer modified electrodes. To produce improved polymer coatings on electrodes, a random copolymer of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and N-hydroxymethyl acrylamide (NHMA) (represented as P(AMPS-co-NHMA)) was prepared. Sulfonic acid groups allow this copolymer, P(AMPS-co-NHMA) to be used as an effective ion exchanger. The electrochemical behaviors of [Ru(NH 3 ) 6 ] 3+ and [Fe(CN) 6 ] 4− are studied at platinum and glassy carbon electrodes modified with the P(AMPS-co-NHMA). The electroactive cations are efficiently preconcentrated by the polymeric coating whereas the anions are not preconcentrated on the electrode surface. Thus the P(AMPS-co-NHMA) has permselective behavior based on either favorable or unfavorable electrostatic interactions with the analytes. The influence of hydrophobicity of the analytes on the electrochemical properties at P(AMPS-co-NHMA) modified electrodes is studied by methylene blue and thionine. The high preconcentration efficiency of P(AMPS-co-NHMA) at low analyte concentration highlights its possible application in the analysis of catecholamines.

Graft copolymers of polyacrylamide (PAM) and dextran (Dx) are synthesized by grafting PAM chains onto a Dx backbone (Dx-g-PAM) with ceric ion induced solution polymerization technique. Partial hydrolysis of Dx-g-PAM is carried out with sodium hydroxide solution to obtain HDx-g-PAM. To synthesize silver nanoparticles dispersed copolymer nano-composite (Ag-HDx-g-PAM), reduction of silver ions with HDx-g-PAM is carried out using microwave heating. The environmentally benign and biodegradable copolymer, HDx-g-PAM acts as both stabilizer and reducing agent. The copolymer nano-composite, Ag-HDx-g-PAM is characterized by FT-IR, transmission electron microscopy, scanning electron microscopy and optical spectroscopy. Further, the catalytic activity of Ag-HDx-g-PAM nano-composite towards the reduction of environmental pollutants like phenosafranine dye and aromatic nitro compounds are studied.

A random copolymer of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and N-hydroxymethyl acrylamide (NHMA) was prepared by solution polymerization using ceric ammonium nitrate as an initiator. A grade of poly(AMPS)-co-poly(NHMA) (PAMPS-co-PNHMA) random copolymer was synthesized with AMPS and NHMA. The homopolymerization of AMPS and NHMA was also carried out by the same way as that of random copolymer. PAMPS-co-PNHMA and homopolymers of AMPS and NHMA were characterized by FTIR, rheology, FT-NMR, scanning electron microscope, thermal analysis, and X-ray diffaractometry. Cyclic voltammetry is used to explain the ion exchange properties of PAMPS-co-PNHMA and its possible application in the trace analysis. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Graft copolymers based on dextran (Dx) and 2-acrylamido-2-methyl-1-propane sulphonic acid (AMPS) were synthesized by free radical initiated solution polymerization technique using ceric ammonium nitrate as initiator. These graft copolymers were used to prepare Cu(II) and Ni(II) chelates by reactions with Cu(II) and Ni(II) metal ions respectively. Graft copolymer and metal chelates were characterized by elemental analysis, intrinsic viscosity, FT-IR, scanning electron microscopy (SEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA) and powder X-ray diffraction (XRD). Elemental analysis, intrinsic viscosity and FT-IR studies revealed the incorporation of metal ions to form metal chelates. SEM studies showed the change in morphology due to metal incorporation. From AFM studies it was observed that there was increase in Root mean square (RMS) roughness values in case of metal complexes. Metal chelates were observed to be thermally more stable than graft copolymer from TGA. UV–vis spectroscopy study revealed increase in absorbance values and cyclic voltammetric (CV) studies showed more than tenfold increase in redox current due to formation of Cu(II) and Ni(II) metal chelates. The binding constants of each complex determined by using UV–visible spectroscopy revealed that Cu(II) has more binding ability than Ni(II).