Piyush Kumar Sonkar

Co(II)-porphyrin-decorated carbon nanotubes as catalysts for oxygen reduction reactions: an approach for fuel cell improvement

The development of high-performance and cost-effective catalysts for the oxygen reduction reaction (ORR) is essential for the advancement of fuel cells. In this work, three different functionalized cobalt porphyrins, meso-tetraphenylporphyrinatocobalt(II) (CoTPP), meso-tetrakis(4′-hydroxyphenyl)porphyrinatocobalt(II) (CoTHPP) and meso-tetrakis(4′-carboxy-phenyl)porphyrinatocobalt(II) (CoTCPP), are prepared. These porphyrins are immobilized non-covalently on multiwalled carbon nanotubes (MWCNTs) and used for the ORR in 0.1 M HClO4, 0.1 M phosphate buffer solution (pH 7.0) and 0.1 M KOH media. The composite materials are characterized by using spectroscopic and electrochemical techniques and their oxygen reduction efficiencies are compared in different media. Kinetic interpretations and hydrodynamic voltammetry (in three media) studies demonstrated that the MWCNT–CoTPP, MWCNT–CoTHPP and MWCNT–CoTCPP composite materials exhibit significant efficiency with decreased overpotential, considerable methanol tolerance and long term operational stability (up to 3000 cycles) for the ORR similar to commercially available platinum carbon (Pt–C) catalysts. These results reveal that the new MWCNT–cobalt porphyrin composite materials can be a potential alternative to the expensive Pt–C catalysts or other commercial cathode materials in fuel cells.

Synthesis and characterization of gold nanoparticles incorporated bentonite clay for electrocatalytic sensing of arsenic(III)

AbstractIn 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. Graphical AbstractBentonite clay supported, gold nanoparticle-based, biocompatible material was synthesized (represented as Au-bt) and it shows remarkable elecrocatalytic activity for As(III) oxidation. Based on the electrocatalytic activity of synthesized Au-bt material, As(III) determination is demonstrated in neutral electrolyte solution.

Methylene blue incorporated mesoporous silica microsphere based sensing scaffold for the selective voltammetric determination of riboflavin

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.

Non-enzymatic electrochemical sensing platform based on metal complex immobilized carbon nanotubes for glucose determination

This work demonstrates the preparation of an electrochemical sensing platform (ESP) based on nickel salophen (abbreviated as NiII–S, where salophen is N,N′-bis(salicylidene)-1,2-phenylenediamine) immobilized multiwall carbon nanotubes (MWCNT) for electrochemical sensing of glucose in an alkaline medium. NiII–S is immobilized onto MWCNT by stirring MWCNT and NiII–S in DMF (MWCNT–NiII–S). The MWCNT–NiII–S is characterized by physicochemical and electrochemical techniques. Then, a glassy carbon (GC) electrode was modifies with the MWCNT–NiII–S composite (GC/MWCNT–NiII–S) and it exhibits efficient electrocatalytic activity towards glucose oxidation when compared to GC modified with NiII–S. Cyclic voltammetry and chronoamperometry techniques are performed to understand the reaction kinetics and to determine the kinetic parameters such as electron transfer coefficient, rate constant of electrode reaction and catalytic rate constant. At the GC/MWCNT–NiII–S ESP a linear calibration range for the glucose determination is observed from 500 nM to 20 mM with a limit of detection of 80 nM (S/N = 3) and sensitivity of 70 μA mM−1. Further, the present ESP is successfully utilized for the detection of glucose in a human blood serum sample with a good recovery (96.4–104.1%).

Electrocatalytic Oxidation and Determination of Cysteine at Oxovanadium(IV) Salen Coated Electrodes

A transition metal complex, oxovanadium(IV) salen (where salen represents N,N′-bis(salicylidene)ethylenediamine) is immobilized on glassy carbon (GC) electrodes and utilized for electrocatalytic oxidation of cysteine. In presence of oxovanadium(IV) salen, increased oxidation current is observed due to the effective oxidation of cysteine by the electrogenerated oxovanadium(V) salen species. The oxidation current linearly varies with the concentration of cysteine from 0.1 to 1.0 mM. The modified electrode has good sensitivity and low limit of detection. These properties make the oxovanadium(IV) salen as an effective electrocatalyst for the determination of cysteine.

Square planar Ni(II) complexes of acetone N4-phenyl-thiosemicarbazone and in situ generated benzoyl thiosemicarbazide ligands: synthesis, spectral and structural characterizations, thermal behaviour and electrochemical studies

Two novel square planar complexes [Ni(Hapt)2] (1) and [Ni(btsc)] (2) have been synthesized from acetone N4-phenyl-thiosemicarbazone (Hapt) and benzoyl-3-thiosemicarbazide (Hbtsc) by the reaction of nickel(II) salt. The ligand and complexes have been characterized by various physicochemical methods. Complexes 1 and 2 crystallize in the monoclinic and orthorhombic systems with space group C2/c and Pbcn, respectively. In complexes 1 and 2 the nickel centre is coordinated through the nitrogen and sulphur atoms forming a square planar geometry. Complexes 1 and 2 are stabilized via various types of intermolecular interactions. The course of the thermal degradations of complexes 1 and 2 has been investigated by TGA which indicated that a metal sulphide/oxide is formed as the final residue. Cyclic voltammetric studies show that complex 1 exhibits a reversible Ni(II)/Ni(III) redox process at 0.525 V (E1/2 value at 20 mV s−1) while complex 2 shows reversible redox behavior with an E1/2 value of 0.43 V. Furthermore, efficient electrocatalytic properties of complexes 1 and 2 toward the oxidation of hydrazine and methanol are demonstrated after immobilizing the complexes into Nafion films. The electrocatalytic properties may find applications in industry, in methanol sensing and in methanol fuel cells.

Use of jaggery and honey as adjunctive cytological fixatives to ethanol for oral smears

Background: Ethanol has satisfactorily been used as cyto-fixative. Owing to its limitations, pathologists have always searched for new fixatives. The present study was conducted to evaluate the efficacy of two natural sweeteners as cyto-fixatives. An attempt has also been made to understand the underlying mechanism by which these fixatives fix the oral mucosal cells. Materials and Methods: Three smears were collected from 25 healthy volunteers. One smear was fixed in ethanol and the other two in 20% aqueous honey solution and 30% aqueous jaggery solution for 15–30 min followed by Papanicolaou staining. Slides were evaluated for nuclear staining, cytoplasmic staining, cell morphology, clarity of staining and uniformity of staining randomly irrespective of the fixatives. Chi-square test and Bonferroni post hoc test were done using SPSS software. P < 0.05 was considered to be statistically significant. In addition, cytological fixatives were analyzed for the pH and amount of reducing sugars. Results: It was found that for all the characteristics studied, no statistically significant difference was seen between the three fixatives. The pH of the both tested fixatives remained acidic even after 1 week. The amount of reducing sugars in 20% aqueous honey solution and 30% aqueous jaggery solution was 19.3 g/100 mL and 2.07 g/100 mL, respectively. Conclusion: Both the test fixatives gave results equivalent to ethanol and thus can be used as alternative fixatives for oral smears. It is proposed that 20% aqueous honey and 30% aqueous jaggery fix the oral smears satisfactorily in a mechanism akin to ethanol by coagulating and denaturing proteins.