This study explores the electrochemical reduction of H2O2 on an Au electrode containing potassium thiocyanate (KSCN) in an alkaline medium. The presence of thiocyanate (SCN-) ions in the reaction system modifies the Au electrode surface (SCN--modified Au) via self-assembled compact layer formation, confirmed by voltammetry, amperometry, and X-ray photoelectron spectroscopy (XPS). Acting as a 'gatekeeper', this adsorbed layer (abbreviated as 'adlayer') simultaneously overturns the oxidative degradation of H2O2 with dynamic adsorption-desorption behavior and significantly boosts the reduction reaction. Kinetic diagnosis reveals that the reaction is irreversible and diffusion-controlled, following first-order kinetics with a transfer coefficient (α) of 0.39 ± 0.02. Key analytical merits include a broad linear dynamic range spanning 50 to 2000 µM, a sensitive detection limit of 9.95 µM and operational stability with 97% signal retention. The practical utility of the SCN--modified Au electrode is validated through successful deployment in analyzing real industrial effluents, where it achieved high recovery rates, underscoring its potential for routine environmental and industrial analysis.

Uric acid (UA), a biologically important chemical, exhibits detrimental environmental impacts on farmland as well as groundwater following irrational usage and maintenance. It is well known that determining the con-centration of pollutants is the first step to control environmental pollution. Concerning this fact, a compact thiocyanate (SCN) adlayer based Au electrode was fabricated by a spontaneous immobilization of SCN- ions on a polycrystalline Au surface pertaining to the selective detection of uric acid in a basic medium. The formed adlayer completely shielded the Au surface from routine passivation by uric acid species or its products, pre-venting electrode fouling. To verify the morphology of the electrode surface, cyclic voltammetry (CV), electro-chemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and linear polarization techniques were used. Voltammetric diagnosis revealed that the UA oxidation reaction on the SCN-adlayer based Au electrode basically follows first-order kinetics with a stepped mechanistic approach where one electron transfer is engaged in the rate-determining steps. On top of that, the limit of detection and the sensitivity were estimated to be 0.25 mu M and 0.199 mA cm-2 mM-1, respectively. Interference studies also ascertain the fact that the proposed electrode is reasonably selective in the presence of cohabiting ionic species. Therefore, the developed sensor can be used in the analytical detection of UA in real samples.

Electrochemical oxidation of paracetamol (PCT) has exclusively been investigated using polycrystalline gold electrode modified with iodine adlayer [I(ads)|Au(pc)] in alkaline medium. Irreversible adsorption of PCT makes Au(pc) surface unfeasible for studying PCT oxidation reaction. This limitation of Au(pc) surface could be eliminated simply by iodide (I-) adsorption. It was noticed that the spontaneous I- adsorption blocks PCT adsorption sites on Au(pc) surface, which additionally improves PCT oxidation reaction by increasing electron transfer rate. Iodine adlayer (I-adlayer) formulated electrode facilitated PCT electro-oxidation via an alternative diffusion-controlled pathway with an anodic electron transfer coefficient (beta) of 0.47 and heterogeneous rate constant (ko) of 0.0911 cm s-1 where an electron transfer step determines the reaction rate. The sensing experiments revealed that the [I(ads)|Au(pc)] electrode attained linear dynamic range from 4.5 to 1600 mu M of PCT. The obtained sensitivity and limit of detection (LOD) of the [I(ads)|Au(pc)] electrode surface was determined to be 8.37( +/- 1.6)x 10-4 mA cm-2 mu M- 1 and 0.65 +/- 0.02 mu M, respectively. The formulated [I(ads)|Au(pc)] catalyst was applied to quantify the relative PCT percentage in commercial tablets using batch injection analysis supported by chronoamperometry. Obtained relative percentage closely matched with the corresponding analysis performed with Raman spectroscopy. Therefore, developed I-adlayer coated Au(pc) electrode is analytically robust and validated for routine analysis of PCT concentration in relevant pharmaceutical applications.

Hydrogen peroxide is widely used in various industries for the synthesis of different chemicals and often applied as a fuel in fuel cells instead of oxygen. Thus, quick detection of hydrogen peroxide is important, and consequently the development of a cost-saving methodology is a time-worthy necessity. A Polycrystalline Au [Au(pc)] electrode does not show significant electrocatalytic performance concerning H2O2 oxidation reaction. The catalytic performance is improved tremendously while Au(110) and Au(100) sites of Au(pc) surface are selectively blocked with the thiol group adsorption keeping Au(111) sites unblocked in an alkaline medium. In this article, cysteine molecules were used as the source of the thiol functional group which has coverage on Au(111) with a value of 3.47 x 10(-10) mol cm(-2). While Cysteine molecules are partially adsorbed on Au(110) and Au(100) sites, the unblocked Au(111) sites receive a partially positive charge, which is assumed to catalyze the oxidation of anionic species (HO2-). The current response vs H2O2 concentration relationship showed a wide linear dynamic range (LDR) between 1 and 3000 mu M with LOD of 0.8 mu M having a sensitivity of 58.68 mu A mM(-1) cm(-2). In this article, detailed electrochemical investigations and characterizations of the developed sensor have been attained using cyclic voltammetric (CV), square wave voltammetric (SWV), and amperometric techniques. (C) 2021 Elsevier Ltd. All rights reserved.

In situ chemisorbed hydroxyl ion (OH-) onto clean polycrystalline gold (Au (poly)) electrode showed an extraordinary enhanced electrocatalytic activity towards oxidation of hydrogen peroxide anion (HO2-) in alkaline media. The oxidation of HO2- at the fabricated electrode was found to be a diffusion controlled process. The anodic transfer coefficient of the oxidation reaction was estimated as 0.47. Chloride ion (Cl-) replaced the chemisorbed OH- from the surface of the modified Au (poly) (OH-)Au (poly)) electrode leading to diminishing the observed electrocatalytic activity. The optimized concentration of KOH solution for the highest catalytic activity was found to be ca. 0.1 M. A linear calibration curve for various concentrations of HO2-? in the range of 0.5 to 5 mM was obtained having sensitivity equal to 1.028 A cm-2 M-1.Journal of Bangladesh Academy of Sciences, Vol. 41, No. 1, 29-36, 2017

In the present report, conductometric studies on the kinetic of formation of AgCl by ionic reaction between Ag+ and Cl in aqueous solution have been presented. The order of the mentioned reaction was determined by a new conductometric approach using half-life method. The obtained result showed that the reaction follows a second-order kinetics. The second-order rate constant of the reaction was obtained conductometrically using different initial concentrations of the reactants in the range of 2.5-5.0 mM. The average value of the rate constant was obtained as 20.648 L mol 1 s 1 at

Hydrous gold (Au) oxide, on polycrystalline Au (Au (poly)) electrode was in situ electrogenerated by multi-potential step amperometric (MPSA) technique between 2.2 V and 0.8 V with pulse time 0.001 s at each potential in 0.5 M H2SO4 solution for different times between 5-60 s. Electrodes with active gold over layers (agol) on the Au (poly) electrode (agol vertical bar Au (poly)) were generated by electroreduction of the hydrous Au oxide formed by MPSA technique. The agol. Au (poly) electrodes were characterized by reductive desorption of cysteine self-assembled monolayer (Cyst-SAM) and oxidative stripping of electrodeposited Pb. The in situ fabricated agol vertical bar Au (poly) electrode surface was found to be enriched in Au(100) and Au(110) domains as compared with the untreated Au (poly) electrode. Oxygen reduction reaction at the agol vertical bar Au (poly) electrode was carried out in 0.5 M H2SO4 solution. A significant catalysis of the ORR was achieved. The catalytic properties were explained in terms of crystalline domains and roughness factor of the Au electrode.

Rhodizonic acid (H2RHOD) was reacted with Co(PF6)2.6H2O in the presence of pyridine modified large macrocyclic ligand (H2Lopy) and triethylamine in N,N-dimethylformamide under argon atmosphere. Instead of [Co4(RHOD)2(Lopy)](PF6)2 (1), the main product of this reaction was a crystalline compound [Co4(CROC)2(Lopy)](PF6)2, which was isolated in low yield (< 25%). Based on the elemental analysis, ESI-mass spectroscopy, and infrared spectrum, the isolated compound was confirmed to be [Co4(CROC)2(Lopy)](PF6)2 (2), where CROC2- is croconate anion C5O52-.Journal of Bangladesh Academy of Sciences, Vol. 40, No. 2, 101-108, 2016

Chemisorption of hydroxyl ion (OH-) from aqueous solution of KOH at the polycrystalline gold (Au (poly)) electrode under stirring condition was studied. A pre-wave at ca. 0.19 V was observed due to partial discharging of the chemisorbed OH-. The linear plot of the pre-wave current vs. scan rate passed through the origin suggesting that it was associated with a surface confined process. An extraordinary enhanced electrocatalytic oxidation of hydrogen peroxide (HO - 2 ) at the in situ fabricated OH--modified Au (poly) (OH-ôAu (poly)) electrode was achieved. A mechanism of the observed catalytic activity was proposed on the basis of electrostatic attraction between the chemisorbed OH- and partial positively charged hydrogen (Hd+) of HO - 2 molecules.Journal of Bangladesh Academy of Sciences, Vol. 40, No. 2, 125-135, 2016

The effect of in situ reversible adsorption/desorption of iodide/iodine-adatoms at polycrystalline gold (Au) electrode on the oxygen reduction reaction (ORR) was studied in alkaline media using cyclic voltammetric technique. The ORR was completely inhibited by the compact iodine-adatoms at more positive potential than ca. _ 0.25 V vs. Ag / AgCl / NaCl (sat.). The ORR commences simultaneously with the potential-induced reductive desorption of the iodine-adatoms. The interesting feature observed is the complete inhibition of the heterogeneous catalytic disproportionation reaction of the electrogenerated HO2_ to O2 and OH‑ by the iodine-adatoms chemisorbed at the Au electrode surface. Consequently, compared with the bare Au electrode, a decrease in the first cathodic peak current as well as a large increase (ca. 12 times) of the second consecutive cathodic peak current corresponding to the further reduction of HO2_ to OH_, that is, the two-step four-electron ORR was observed at the iodine-adatoms-modified Au electrode in alkaline media. Effect of the other halides, e.g., bromide, chloride and fluoride was also studied.

Electrocatalytic reduction of NO3− at a polycrystalline Ag electrode in the presence of KCl has been investigated. The measurements made by the stationary and hydrodynamic electrodes revealed that the Ag electrode substantially promoted the activity of the NO3− reduction through a two-electron transfer process. The electrochemical investigations suggested that the reduction process follows first order kinetics. In the bulk electrolysis experiments, the rate constants (k1; 35.1×10−3min−1 and k2; 6.5×10−3min−1) were estimated with respect to NO3− and NO2− reduction, respectively. The voltammetric investigations and the evaluation of rate constants (k1>k2) established that Ag electrode is efficient in the formation of NO2− from the reduction of NO3−.

Polyethyleneterephthalate (PET) based proton exchange membrane for using in fuel cells was successfully prepared by gamma radiation-induced graft copolymerization of styrene monomer onto PET film and the consequent selective sulfonation of the grafting chain in the film state using chlorosulfonic acid (ClSO3H). The effects of grafting conditions (e.g., monomer concentration, irradiation dose) on the degree of grafting and sulfonation condition (e.g., optimum concentration of ClSO3H) on the degree of sulfonation were studied. The degree of grafting, the degree of sulfonation and the physico-chemical properties (such as, water uptake, mechanical strength, thermal durability, hydrolytic stability, oxidative stability) of the gamma radiation-induced grafted membrane were found to be better when compared to those of the UV-radiation grafted membrane. The membrane shows higher ion exchange capacity (0.9 mmol g(-1)) and higher proton conductivity (0.075 S cm(-1)), similar to those of Nafion membrane.

The present article demonstrates the electrochemical oxidation of uric acid (UA) at sulfur-adlayer-coated gold (S-Au) electrode in alkaline media. At S-Au electrode, UA oxidized at a significantly lower overpotential with a higher current density as compared to the bare Au electrode. The oxidation of UA at the S-Au electrode is highly selective in the presence of the other commonly existing bio-molecules in urine. The proposed electrochemical sensor not only exhibited good reproducibility, but also showed a fast amperometric response to UA in the concentration range of 0.0025–5mM with a low detection limit of 0.4μM.

In the present article, oxygen reduction reaction (ORR) at electrochemically fabricated tin-palladium (Sn-Pd) bimetallic electrocatalyst-modified glassy carbon (GC) electrode (Sn-Pd/GC electrode) in acidic media is addressed. Hydrodynamic voltammetric measurements were employed with a view to evaluating various kinetic parameters of the ORR at the Sn-Pd/GC electrode. The obtained results obviously demonstrated that the Sn-Pd bimetallic electrocatalyt substantially promoted the activity of the GC electrode and drove the ORR through an exclusive one-step four-electron pathway forming H2O as the final product.

A novel electrocatalyst, Ta2O5-modified Pt, for the oxidation of formic acid (HCOOH) was prepared by electrodeposition of Ta on Pt electrode from ionic liquid and the subsequent calcination. The modified electrode shows an excellent electrocatalytic activity toward the direct oxidation of formic acid to CO2. The enhancement is attributed to the strong metal–oxide interaction between Pt and Ta2O5 as well as the OH− spillover effect of the Ta2O5-modified Pt electrode, which greatly accelerates the electrooxidation of formic acid. The possible reaction mechanism is proposed.

Bromine (Br)-adatom (Br(ads)) was in situ fabricated onto polycrystalline gold (Au (poly)) electrode in Br−-containing alkaline media. The surface coverage of Br(ads) (ΓBr) varied only in the submonolayer coverage within the investigated potential window under potentiodynamic condition because of the coadsorption of hydroxyl ion (OH−) in alkaline media. The in situ fabricated Br(ads)-submonolayer-coated Au (poly) electrode was successfully used for the electrochemical oxidation of hydrogen peroxide (H2O2). About five times higher oxidation current was achieved at the modified electrode as compared with the bare electrode. The enhancement of the electrode activity towards the electrochemical oxidation of H2O2 was explained based on the enhanced electrostatic attraction between the anionic HO2− molecules and Br(ads)-adlayer-induced positively polarized Au (poly) electrode surface.

In the present report, oxygen reduction reaction (ORR) at polycrystalline gold (Au (poly)) electrode in situ modified by the underpotential deposition (upd) of Sn-adatoms is addressed. The ORR was investigated at the Sn-adatoms-modified Au (poly) electrode by the hydrodynamic voltammetric technique with a view to evaluating the various related kinetic parameters. The results demonstrated that the underpotential deposited Sn-adatoms on the Au (poly) electrode substantially promoted the activity of the electrode towards an exclusive one-step four-electron ORR forming H2O as the final product.

A 1,2-diaminocyclohexane–Pd complex was immobilized onto the surface of silica gel and investigated as a catalyst for Heck coupling reactions. The immobilized catalyst exhibited high catalytic activity in the coupling of activated and nonactivated aryl substrates with various acrylates. Moreover, the catalyst was air-stable that could be recycled and reused without significant loss of catalytic activity.