Electrochemical analysis of glyphosate using porous biochar surface corrosive nZVI nanoparticles.

Glyphosate [N-(phosphonomethyl)glycine] is a widely used phosphonate herbicide for different agricultural purposes. Due to its widespread use, suspected toxicity, and ubiquitous bioaccumulation, it is one of the most harmful contaminants found in drinking water. This demands efficient sensing and removal of glyphosate from contaminated water. Here, we report the decoration of novel and highly porous biochar with nanozero-valent iron (nZVI) nanoparticles to develop an efficient electrochemical sensor for the trace detection of glyphosate. The as-synthesized composite was thoroughly characterized by various state-of-the-art instrumental techniques. The electron micrographs of the composite materials revealed the cavity-like structure and the abundant loading of nZVI nanoparticles. FTIR and XPS analyses confirmed the presence of oxygen-rich functionalities and Fe(0) in the composite nanostructure. Electrochemical analysis through CV, LSV, and DPV techniques suggested efficient sensing activity with a limit of detection as low as 0.13 ppm. Furthermore, the chronopotentiometric response suggested excellent and superior stability for long-term applications. To gain more insight into the interaction between glyphosate and the composite material, DFT calculations were carried out. The Frontier Molecular Orbital study (FMO), Molecular Electrostatic Potentials (MEPs), and Density of States (DOS) suggest an increase in the electron density, an increase in the DOS, and a decrease in the HOMO-LUMO band gap by combining nZVI nanoparticles and biochar. The results suggest more facile electron transfer from the composite for trace detection of glyphosate. As a proof of concept, we have demonstrated that real-time analysis of milk, apple juice, and the as-synthesized composite shows promising results for glyphosate detection with an excellent recovery rate.

Biomass-derived carbon quantum dots: a novel and sustainable fluorescent "ON-OFF-ON" sensor for ferric ions.

Fluorescent carbon dot sensing probes have attracted much attention in recent times due to their amazing properties regarding chemical inertness, solubility, non-toxicity, optoelectronic behavior, and charge transport functionality. Herein, we report the green synthesis of lotus stem-derived carbon dots (LS-CQDs) from the naturally available lotus stem by a simple and economical hydrothermal method without the use of an oxidizing agent. HR-TEM and DLS measurements confirm the quasi-spherical shaped LS-CQDs, with a 2.5 nm average diameter. The LS-CQDs possess better aqueous dispersibility and stability due to the presence of hydrophilic hydroxyl, carboxyl, and amine surface functional groups, as manifested by FT-IR analysis. The LS-CQDs demonstrate excellent fluorescence properties that are sensitive to conditions of pH, time, and temperature. Furthermore, the prepared LS-CQDs display an interesting fluorescence "ON-OFF-ON" property. The LS-CQDs depict a selective and sensitive fluorescence quenching response in the presence of ferric ions. Moreover, the prepared LS-CQDs exhibit a quantum yield of about 0.44%. The LS-CQDs show an excellent sensing response with the limit of detection (LOD) equal to 0.212 ppm. The promising sensitivity and selectivity of LS-CQDs were utilized for the detection of ferric ions in the water samples collected from three polluted sources viz. lake water (Dal lake), underground water (tube well), and stream water. For all the collected water samples the results were reasonably good with the achievement of recovery factor above 1. Therefore, we strongly believe that the present study will serve as a good guiding star for the selective and sensitive detection of ferric ions from various polluted water bodies.

Studies on a glutathione coated hollow ZnO modified glassy carbon electrode; a novel Pb(ii) selective electrochemical sensor.

Herein, we report the electrochemical detection of heavy metal ions such as Pb(ii), Cd(ii) and Hg(ii) ions while using glutathione coated hollow ZnO modified glassy carbon electrode (Glu-h-ZnO/GCE). An excellent voltammetric response of the modified electrode towards these metal ions was observed by different voltammetric techniques. Among the different target metal ions, a selective electrochemical response (sensitivity = 4.57 µA µM-1) for the detection of Pb(ii) ions was obtained with differential pulse voltammetric (DPV) measurements. Besides, under optimal experimental conditions and in the linear concentration range of 2-18 µM, a very low detection limit of 0.42 µM was obtained for Pb(ii) ion. The observed electrochemical behaviour of Glu-h-ZnO/GCE towards these metal ions is in conformity with the band gap of the composite in the presence of various test metal ions. The band gap studies of the composite and various "Composite-Metal Ion" systems were obtained by reflectance as well as by computational methods where results are in close agreement, justifying the observed electrochemical behaviour of the systems. The lowest band gap value of the "Composite-Pb" system may be the reason for the excellent electrochemical response of the Glu-h-ZnO modified GCE towards the detection of Pb(ii) ion.

Enhanced and Selective Adsorption of Zn(II), Pb(II), Cd(II), and Hg(II) Ions by a Dumbbell- and Flower-Shaped Potato Starch Phosphate Polymer: A Combined Experimental and DFT Calculation Study.

Microwave-ultrasound-assisted facile synthesis of a dumbbell- and flower-shaped potato starch phosphate (PSP) polymer, hereafter PSP, was carried out by cross-linking the hydroxyl groups of native potato starch (NPS) using phosphoryl chloride as a cross-linking agent. Structural and morphological analysis manifested the successful formation of the dumbbell- and flower-shaped PSP biosorbent with enhanced specific surface area and thermal stability. Viscoelastic behavior of NPS and PSP suggested increased rigidity in PSP, which helped the material to store more deformation energy in an elastic manner. The synthesized PSP biosorbent material was successfully tested for efficient and quick uptake of Zn(II), Pb(II), Cd(II), and Hg(II) ions from aqueous medium under competitive and noncompetitive batch conditions with q m values of 130.54, 106.25, 91.84, and 51.38 mg g-1, respectively. The adsorption selectivity was in consonance with Pearson's hard and soft acids and bases (HSAB) theory in addition to their order of hydrated radius. Adsorption of Zn(II), Pb(II), Cd(II), and Hg(II) followed a second-order kinetics and the adsorption data fitted well with the Langmuir isotherm model. Quantum computations using density functional theory (DFT) further supported the experimental adsorption selectivity, Zn(II) > Pb(II) > Cd(II) > Hg(II), in terms of metal-oxygen binding energy measurements. What was more intriguing about PSP was its reusability over multiple adsorption cycles by treating the metal(II)-complexed PSP with 0.1 M HCl without any appreciable loss of its adsorption capacity.

Microwave-assisted synthesis of glutathione-coated hollow zinc oxide for the removal of heavy metal ions from aqueous systems.

Glutathione has tremendous binding potential with metal ions present in water. However, the solubility of glutathione in water limits its productivity in the removal of these toxic ions from aqueous systems. The removability of heavy ions with glutathione and the associated adsorption capability are enhanced; for this purpose, glutathione is coated over hollow zinc oxide particles. Glutathione-coated hollow zinc oxide (Glu@h-ZnO) was successfully synthesized under microwave (MW) conditions using polystyrene (PS) as the template. The as-synthesized material was characterized by Fourier transform infrared (FTIR) spectroscopy, and the results were supported by X-ray diffraction crystallography (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), dynamic light scattering (DLS), Brunauer-Emmett-Teller (BET) studies and zeta potential (ζ) analysis. The sorption performance of Glu@h-ZnO towards the uptake of Hg2+, Cd2+ and Pb2+ ions from an aqueous medium under non-competitive batch conditions was investigated and the material was found to have the maximum affinity for Hg2+ ions with a maximum adsorption (q m) capacity of 233 mg g-1. The adsorption kinetics for Hg2+ ions and the effects of pH and ζ on the adsorption properties were also studied in detail. Finally, the experimental data were correlated with theoretical data obtained from density functional theory (DFT) studies and good agreement between the two was obtained.