Multiwalled Carbon Nanotube/Fe-Doped ZnO-Based Sensors for Droplet Electrochemical Detection and Degradation Monitoring of Brilliant Green

The present research work aims to contribute toward the sustainable development goal of water cleanliness by monitoring and removing toxic effluents from wastewater. Herein, we present an electrochemical sensing platform made of a glassy carbon electrode modified with Fe-doped ZnO nanoparticles (NPs) and multiwalled carbon nanotubes (MWCNTs) for the detection of brilliant green (BG) using a smart droplet analysis approach. The Fe–ZnO NPs were synthesized via a hydrothermal method and characterized by various analytical techniques such as UV–visible spectroscopy, XRD, SEM, EDX, and FTIR spectroscopy. Fe–ZnO NPs were found to act as a mediator between the transducer and BG for efficient electron transport, while MWCNTs led to the enhanced current response of BG at the electrode surface owing to their conductive and adsorptive characteristics. Under optimized conditions of pH 6, 0.1 V deposition potential, and 40 s deposition time, a 0.40 nM limit of detection was achieved at the designed nanosensor. Photocatalytic degradation of the dye with NPs was also investigated in different pH media using UV–visible spectroscopy. The dye was found to photocatalytically degrade up to 99% in just 30 min, following first-order kinetics with a rate constant of 0.14 min–1. The photocatalytic degradation was also monitored electrochemically at the designed sensing platform, and the findings were found to be in good agreement with the results of UV–visible spectroscopy. The developed electrochemical droplet analysis approach is not only economical but also efficient, ultra-sensitive, and environmentally friendly

Bis-amino Acid Derivatives of 1,1′-Ferrocenedicarboxylic Acid: Structural, Electrochemical, and Metal Ion Binding Studies

We report on the structural and electrochemical investigation of 1,1′-ferrocenedicarboxylic acid derivatives of tryptophan (Fc­[CO-Trp-OMe]₂ - Fc-conjugate <b>1</b>), threonine (Fc­[CO-Thr-OMe]₂ – Fc-conjugate <b>2</b>), aspartic acid (Fc­[CO-Asp-OMe]₂ - Fc-conjugate <b>3</b>) and glutamic acid (Fc­[CO-GluOMe]₂ - Fc-conjugate <b>4</b>) and their hydrolyzed analogues <b>1a</b>–<b>4a</b> respectively (Scheme ). CD and NMR spectroscopy established 1,2′-“Herrick conformation” in solution, having intramolecular interstrand hydrogen bonds for all Fc-conjugates. However, in solid state, Fc­[CO-Trp-OMe]₂ exists in “Herrick conformation” whereas Fc­[CO-Thr-OMe]₂ is present in anti conformation. In solution, the involvement of indole NH of Trp and alcoholic proton of Thr in intermolecular hydrogen bonding has been explored by temperature- and concentration-dependent NMR studies. The half-wave potentials (<i>E</i>_1/2) of ferrocene-conjugates follow the sequence <b>1 < 2 < 4 < 3</b> which is explained by the contribution of amino acid side chain functionalities toward the stability of ferrocenium ion. The CV of the Fc-conjugate <b>1/1a</b> (having Trp moiety) displays two redox processes, one of which is assigned to the Fc group, and the other being related to the indole group. The oxidation peak potential of indole was found to depend strongly on the pH of the medium. The values of diffusion coefficient (<i>D</i>) and electron transfer rate constant (<i>k</i>_sh) for all Fc-conjugates were determined from their corresponding cyclic voltammograms. In addition, metal ion interactions were studied with hydrolyzed Fc-conjugates <b>2a</b>–<b>4a</b> using CV and DPV. Upon binding to metal ions, the electrochemical changes associated with the hydrolyzed Fc-conjugates correlated to the charge density of the binding metal ion

Bis-amino Acid Derivatives of 1,1′-Ferrocenedicarboxylic Acid: Structural, Electrochemical, and Metal Ion Binding Studies

We report on the structural and electrochemical investigation of 1,1′-ferrocenedicarboxylic acid derivatives of tryptophan (Fc­[CO-Trp-OMe]₂ - Fc-conjugate <b>1</b>), threonine (Fc­[CO-Thr-OMe]₂ – Fc-conjugate <b>2</b>), aspartic acid (Fc­[CO-Asp-OMe]₂ - Fc-conjugate <b>3</b>) and glutamic acid (Fc­[CO-GluOMe]₂ - Fc-conjugate <b>4</b>) and their hydrolyzed analogues <b>1a</b>–<b>4a</b> respectively (Scheme ). CD and NMR spectroscopy established 1,2′-“Herrick conformation” in solution, having intramolecular interstrand hydrogen bonds for all Fc-conjugates. However, in solid state, Fc­[CO-Trp-OMe]₂ exists in “Herrick conformation” whereas Fc­[CO-Thr-OMe]₂ is present in anti conformation. In solution, the involvement of indole NH of Trp and alcoholic proton of Thr in intermolecular hydrogen bonding has been explored by temperature- and concentration-dependent NMR studies. The half-wave potentials (<i>E</i>_1/2) of ferrocene-conjugates follow the sequence <b>1 < 2 < 4 < 3</b> which is explained by the contribution of amino acid side chain functionalities toward the stability of ferrocenium ion. The CV of the Fc-conjugate <b>1/1a</b> (having Trp moiety) displays two redox processes, one of which is assigned to the Fc group, and the other being related to the indole group. The oxidation peak potential of indole was found to depend strongly on the pH of the medium. The values of diffusion coefficient (<i>D</i>) and electron transfer rate constant (<i>k</i>_sh) for all Fc-conjugates were determined from their corresponding cyclic voltammograms. In addition, metal ion interactions were studied with hydrolyzed Fc-conjugates <b>2a</b>–<b>4a</b> using CV and DPV. Upon binding to metal ions, the electrochemical changes associated with the hydrolyzed Fc-conjugates correlated to the charge density of the binding metal ion

Humidity-sensing and DNA-binding ability of bis(4-benzylpiperazine-1-carbodithioato<i>-k</i>^<i>2</i><i>S,S′</i>)nickel(II)

<div><p>Bis(4-benzylpiperazine-1-carbodithioato<i>-k</i>^<i>2</i><i>S,Sʹ</i>)nickel(II), <b>1</b>, was prepared by metathesis of sodium salt of 4-benzylpiperazine-1-carbodithioate with nickel(II) chloride in 2 : 1 ratio. Complex <b>1</b> was characterized by analytical techniques including elemental analysis, FT-IR, UV–visible spectroscopy, and X-ray single-crystal analysis. The latter technique confirmed square-planar geometry around Ni with the formation of NiS₄ core with two shorter and two longer Ni–S bonds. The packing diagram revealed a supramolecular chain structure mediated by unconventional H⋯H dihydrogen bonds that resulted in a chair and a ladder-like structure when viewed along the <i>a</i>-axis and <i>c</i>-axis, respectively. The thin-film coating resulted in a microporous film with a band gap of 1.69 eV. Complex <b>1</b>-based sensor was fabricated to check the humidity-sensing properties of the material. Resistance of the device decreased by two orders of magnitude and capacitance was enhanced with the increase of relative humidity. The DNA binding study proved <b>1</b> to be a good DNA binder with binding constant value of 1.4 × 10⁴ M⁻¹.</p></div