Mohammad A. Hasnat

Development of highly-sensitive hydrazine sensor based on facile CoS2–CNT nanocomposites

Cobalt pyrite-decorated carbon nanotube nanocomposites (CoS2–CNT NCs) were prepared by a simple wet-chemistry method in an alkaline medium. The characterization of the resulting CoS2–CNT NCs was performed in detail by field-emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, FT-IR spectroscopy, and X-ray diffraction patterns (XRD). A glassy carbon electrode (GCE) was fabricated from the CoS2–CNT NCs and developed into a chemical sensor for hydrazine (HZ) using a simple and reliable I–V method. The poisonous chemical HZ was selected as the target analyte in a selectivity study, which demonstrated the fast response of the GCE sensor fabricated from CoS2–CNT NCs using the I–V method. It also displayed an excellent sensitivity, a very low detection limit, long-term stability, and reproducibility. In a diagnostic study, a linear calibration plot (r2 = 0.9992) was obtained for a 0.1 nM to 1.0 mM aqueous solution of HZ, with a sensitivity of 4.430 μA nM−1 m−2 and low detection limit (LOD) of 0.1 nM. The potential of CoS2–CNT NCs in terms of chemical sensing is also discussed in this report. This approach is emerging as an effective technique for developing efficient chemical sensors for the detection of environmental pollutants in a large scale.

Fabrication of a selective 4-amino phenol sensor based on H-ZSM-5 zeolites deposited silver electrodes

H-ZSM-5 zeolite is an inorganic material with large surface area and well-defined internal structure with porous uniform cages, cavities or channels. In this study, H-ZSM-5 was synthesised by calcination of the NH4-form at 500 °C for 3 h in air flow. This protonated H-ZSM-5 has been characterized in detail, which includes its optical, structural, morphological, and elemental properties by various conventional methods. For probable chemical sensor development, H-ZSM-5 was deposited on a silver electrode (AgE, surface area, 0.0216 cm2) to fabricate a sensor with a fast response towards selective 4-amino phenol (4-AMP) in the liquid phase. The sensor exhibited good sensitivity and long-term stability and enhanced electrochemical responses. The calibration plot was linear (r2 = 0.9979) over the 0.1 nM to 1.0 mM 4-AMP concentration ranges. The sensitivity was ∼2.085 μA cm−2 nM−1 and the detection limit was 0.02 nM (at a signal-to-noise ratio (SNR) of 3). By employing CV and EIS techniques, it was unveiled that the sensor is not well-operative in the absence of air. This shows a promising future for sensitive sensor development using mesoporous H-ZSM-5 by I–V methods for applications in the detection of hazardous and carcinogenic phenolic compounds in environmental and health care fields.

Aggregated Pt–Pd nanoparticles on Nafion membrane for impulsive decomposition of hydrogen peroxide

Pt–Pd aggregated nanoparticles were immobilized on a Nafion-117 membrane to decompose hydrogen peroxide. The Pt or Pd particles alone decompose hydrogen peroxide at an insignificant rate. But a bimetallic Pt–Pd catalyst, having a Pt to Pd composition between 0.33 and 0.75, causes steady decomposition at an appreciable rate at room temperature. The Pd and Pt sites have been proposed to initiate and to complete, respectively, the impulsive hydrogen peroxide decomposition reaction.

Influence of electrode assembly on catalytic activation and deactivation of a Pt film immobilized H + conducting solid electrolyte in electrocatalytic reduction reactions

Symmetric (Cu–Pt|Nafion|Pt–Cu) and asymmetric (Pt|Nafion|Pt–Cu) assemblies were fabricated to study the nitrate reduction processes at the cathode. The electrocatalytic nitrate reduction reactions were performed in these assemblies in order to investigate the prerequisite for the enhanced catalytic activity, electrochemical cell durability as well as preferable product selectivity resulting from the reduction of nitrate at the cathode. It has been observed for the symmetric assembly that Cu particles were oxidized on the anode surface under an applied potential and the resulting copper ions migrated to the cathode surface through the Nafion membrane, which deposited as copper oxide on the cathode surface. The formation of this copper oxide covering layer on the Pt–Cu cathode surface is attributed as the reason for the deactivation of the cathode that governed the reduced nitrate reduction along with increasing nitrite selectivity. These problems were addressed and resolved with the asymmetric design of the electrocatalytic reactor, where enhanced hydrogen evolution activates the surface by eroding the CuO over layer as well as speeding up the slow rate determining hydrogenation reactions.

Surface Modification of the ZnO Nanoparticles with γ-Aminopropyltriethoxysilane and Study of Their Photocatalytic Activity, Optical Properties and Antibacterial Activities

Abstract Surface modification of Zinc oxide nanoparticles (ZnO) with γ-aminopropyltriethoxy silane (APTES) was investigated. Successful surface modification of the nanoparticles was confirmed experimentally by X-ray Photoelectron Spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The effect of the surface modifier concentration on the grafting density and surface area was studied by CHN elemental analysis and Brunauer–Emmett–Teller (BET) analysis. The photocatalytic activity and UV shielding ability of the surface-modified particles prepared in water-ethanol solvent in the presence of the surface modifiers were compared to those of non-modified particles. As a case study, It was observed by methylene blue (MB) dye degradation experiment that the photocatalytic activity in the presence of modified nanoparticles was lower than that observed with non-modified ZnO nanoparticles. Dispersion stability tests visually showed that APTES grafted nanoparticles had acquired better stability than non-modified ZnO nanoparticles in aqueous solution.

Electrochemical and spectroscopic insights of interactions between alizarin red S and arsenite ions

Interferences of arsenite ions on electrocatalytic oxidation of alizarin red S (ARS) was studied using Pt and ITO electrodes. A Pt electrode can oxidize both arsenite ions and ARS molecules simultaneously. The oxidation wave of ARS exceeds that of arsenite until the [AsO2−]/[ARS] ratio surpasses 0.07. Meanwhile, an ITO electrode can oxidize only ARS molecules. It was seen that the diffusion coefficient of ARS molecules decreased from 4.3 × 10−6 cm2 s−1 to 1.68 × 10−7 cm2 s−1 in the presence of arsenite ions. The electrokinetic investigation shows that ARS oxidation was a two-electron transfer consecutive process. The EIS studies showed that charge transfer resistance was increased in the presence of arsenite ions during ARS oxidation.

Nitrate detection activity of Cu particles deposited on pencil graphite by fast scan cyclic voltammetry

Electrocatalytic nitrate reduction and sensing activities of Cu deposits from 0.01 M CuSO4 · 5H2O solution by fast scan (1000 mV/s) cyclic voltammetry on pencil graphite (PG) was investigated. The content of Cu particles on PG surface was controlled by fixing the deposition cycles between 0 and −300 mV. The performance of the different Cu/PG electrodes has been explained in terms of reduction current, kinetic order, exchange current density, specific electrical capacitance and nitrate sensing abilities. All these activities were modestly dependent on the content of Cu particles on the PG surface. The minimum catalytic sites on PG surface were generated even by the single Cu deposition cycle. Depending on the Cu content, the electrodes exhibited lowest nitrate detection limits in the range between 1.0 × 10−4 to 1.1 × 10−3 M. The nitrate detection performance of the Cu/PG electrode was justified with the ion chromatographic method.

Inverse effects of supporting electrolytes on the electrocatalytic nitrate reduction activities in a Pt|Nafion|Pt–Cu-type reactor assembly

In this article, the effects of Cl− and SO42− ions on the electrocatalytic nitrate reduction activities in a sandwich-type reactor assembly are illustrated. It was noticed that a Pt|Nafion|Pt–Cu assembly offers its best efficiency in the absence of any supporting electrolytes. The Pt–Cu thin layers adsorb chloride and sulphate ions firmly, and this adsorption blocks the H+ reducing sites at the cathode end of the catalytic assembly, leading to a decrease in catalytic efficiency. In the presence of chloride and sulphate ions, the reduction reactions of NO3− and NO2−, respectively, are relatively favoured.

Optimisation of the batch reactor for the removal of cobalt ions from chloride media

A series of experiments were carried out to determine the best medium for the recovery of cobalt by means of an electrogenerative system. Use of the electrogenerative system with a chloride medium had shown promising performance with the highest free energy of -389.8 kJ mol(-1) compared to that with sulphate and nitrate media. Subsequently, the influence of catholyte concentrations on cobalt recovery using the electrogenerative process was carried out by varying the initial cobalt concentration and sodium chloride concentration. The results showed that almost 100% recovery was attained within 1-4 h of the recovery process. Influence of pH was investigated where the electrogenerative system performed best between pH 5.0 and 7.0. Maximum cell performance of 83% with 99% cobalt removal was obtained at 90 min when 100 mg L(-1) of Co(2+) in 0.5 M NaCl was taken as catholyte solution. The values of ΔH(o) and ΔS(o) of the process were evaluated as 33.41 kJ mol(-1) and 0.13 kJ mol(-1), respectively.

Electrochemical oxidation of As(III) on Pd immobilized Pt surface: kinetics and sensing performance

Pd nanoparticles were electrochemically immobilized on a Pt surface in the presence of sodium dodecyl sulfate (SDS) molecules to study the electrokinetics of arsenite oxidation reactions and the corresponding sensing activities. The X-ray photoelectron spectroscopy (XPS) analysis showed that on the Pt surface, Pd atoms exist as adatoms and the contents of Pd(0) and Pd(II) were 75.72 and 24.28 at%, respectively, and the particle sizes were in the range of 61–145 nm. The experimental results revealed that the catalytic efficiency as well as the charge transfer resistance (at the redox potential of the Fe(II)/Fe(III) couple) increased in the order of Pt < Pt–Pd < Pt–Pdsds. A Pt–Pdsds electrode exhibited an open circuit potential (OCP) of 0.65 V in acidic conditions; however, when 50.0 mM NaAsO2 was present, the OCP value shifted to 0.42 V. It has been projected that the As(III) oxidation proceeds using a sequential pathway: As(III) → As(IV) → As(V). After optimization of the square wave voltammetric data, the limits of detection of As(III) were obtained as 1.3 μg L−1 and 0.2 μg L−1 when the surface modification of the Pt surface was executed with Pd particles in the absence and presence of the SDS surfactant, respectively. Finally, real samples were analyzed with excellent recovery performance.