Self-Assembled Conjugated Coordination Polymer Nanorings: Role of Morphology and Redox Sites for the Alkaline Electrocatalytic Oxygen Evolution Reaction.

Electrocatalytic water splitting provides a sustainable method for storing intermittent energies, such as solar energy and wind, in the form of hydrogen fuel. However, the oxygen evolution reaction (OER), constituting the other half-cell reaction, is often considered the bottleneck in overall water splitting due to its slow kinetics. Therefore, it is crucial to develop efficient, cost-effective, and robust OER catalysts to enhance the water-splitting process. Transition-metal-based coordination polymers (CPs) serve as promising electrocatalysts due to their diverse chemical architectures paired with redox-active metal centers. Despite their potential, the rational use of CPs has faced obstacles including a lack of insights into their catalytic mechanisms, low conductivity, and morphology issues. Consequently, achieving success in this field requires the rational design of ligands and topological networks with the desired electronic structure. This study delves into the design and synthesis of three novel conjugated coordination polymers (CCPs) by leveraging the full conjugation of terpyridine-attached flexible tetraphenylethylene units as electron-rich linkers with various redox-active metal centers [Co(II), Ni(II), and Zn(II)]. The self-assembly process is tuned for each CCP, resulting in two distinct morphologies: nanosheets and nanorings. The electrocatalytic OER performance efficiency is then correlated with factors such as the nanostructure morphology and redox-active metal centers in alkaline electrolytes. Notably, among the three morphologies studied, nanorings for each CCP exhibit a superior OER activity. Co(II)-integrated CCPs demonstrate a higher activity between the redox-active metal centers. Specifically, the Co(II) nanoring morphology displays exceptional catalytic activity for OER, with a lower overpotential of 347 mV at a current density of 10 mA cm-2 and small Tafel slopes of 115 mV dec-1. The long-term durability is demonstrated for at least 24 h at 1.57 V vs RHE during water splitting. This is presumably the first proof that links the importance of nanostructure morphologies to redox-active metal centers in improving the OER activity, and it may have implications for other transdisciplinary energy-related applications.

Multivariate modeling and process optimization of Hg(II) remediation using solvothermal synthesized 2D MX/Fe3O4 by response surface methodology: characteristics and mechanism study.

Two-dimensional MXene with layered structure has recently emerged as a nanomaterial with fascinating characteristics and applicability. Herein, we prepared the newly modified magnetic MXene (MX/Fe3O4) nanocomposite using solvothermal approach and investigated its adsorption behavior to study the removal efficiency of Hg(II) ions from aqueous solution. The effect of adsorption parameters such as adsorbent dose, time, concentration, and pH were optimized using response surface methodology (RSM). The experimental data fitted well with quadratic model to predict the optimum conditions for maximum Hg(II) ion removal efficiency which were found to be at adsorbent dose 0.871 g/L, time 103.6 min, concentration 40.17 mg/L, and 6.5 pH respectively. To determine the adequacy of the developed model, a statistical analysis of variance (ANOVA) was used, which demonstrated high agreement between the experimental data and the suggested model. According to isotherm result, the experimental data were following the best agreement with the Redlich-Peterson isotherm model. The results of the experiments revealed that the maximum Langmuir adsorption capacity of 699.3 mg/g was obtained at optimum conditions, which was closed to the experimental adsorption capacity of 703.57 mg/g. The adsorption phenomena was well represented by the pseudo-second-order model (R2 = 0.9983). On the whole, it was clear that MX/Fe3O4 has lot of potential as a Hg(II) ion impurity removal agent in aqueous solutions.

Green-synthesized, pH-stable and biocompatible carbon nanosensor for Fe3+: An experimental and computational study.

Brightly fluorescent Carbon Dots (CDs) were synthesized by green hydrothermal method using commonly available biomass (Aloe vera) as carbon precursor. Their physiochemical and optical characterization was done by standard microscopic and spectroscopic techniques. Photophysical features of their aqueous dispersion were investigated in detail. The influence of wide pH range (2-12), high ionic load (2M) and temperature on their photoluminescence behavior was investigated. Their in-vitro cytotoxicity examination was conducted on Human Cervical Cancer Cells (HeLa) using MTT assay. Testing of their ion-recognition property for common metal ions was done in aqueous medium. These CDs exhibited preferential interaction with Fe3+ over other tested metal ions, without any functionalization. Interaction between CDs and Fe3+ was analyzed in the light of Density Functional Theory (DFT). The work demonstrates that these CDs are acting as nanoprobe for Fe3+ and sensing it at ultra-trace level (5 nM).

Synthesis of highly fluorescent and water soluble graphene quantum dots for detection of heavy metal ions in aqueous media.

Fluorescent graphene quantum dots (GQDs) are nanomaterials which possess unique properties that show great potential in different applications. In this work, GQDs were synthesized using graphene oxide (GO) as precursor via thermal treatment at high temperature. The obtained GQDs were highly fluorescent and were suitable for the determination of heavy metal ions. X-ray diffraction, FTIR spectroscopy, and UV visible spectroscopy confirm the formation of GQDs. TEM images show that formed GQDs have size ranging from 2 to 10 nm. Emission profile of aqueous GQDs was taken by exciting GQDs at different wavelength. The intensity of GQDs remains the same for 4-5 months. Furthermore, as prepared, GQDs were used for selective recognition of Fe3+, Pb+2, and Cr3+ from the bunch of different metal ions in aqueous media. Lower limit of detection obtained for Fe3+, Cr3+ and Pb2+ using GQDs were 50, 100 and 100 nM, respectively, which indicates that the GQDs can be utilized as a promising material for sensing of the heavy metal ions. Graphical abstract.