Explore the vast range of titles available.

We describe herein the significance of a sodium citrate and tannic acid mixture in the synthesis of spherical silver nanoparticles (AgNPs). Monodisperse AgNPs were synthesized via reduction of silver nitrate using a mixture of two chemical agents: sodium citrate and tannic acid. The shape, size and size distribution of silver particles were determined by UV–Vis spectroscopy, dynamic light scattering (DLS) and scanning transmission electron microscopy (STEM). Special attention is given to understanding and experimentally confirming the exact role of the reagents (sodium citrate and tannic acid present in the reaction mixture) in AgNP synthesis. The oxidation and reduction potentials of silver, tannic acid and sodium citrate in their mixtures were determined using cyclic voltammetry. Possible structures of tannic acid and its adducts with citric acid were investigated in aqueous solution by performing computer simulations in conjunction with the semi-empirical PM7 method. The lowest energy structures found from the preliminary conformational search are shown, and the strength of the interaction between the two molecules was calculated. The compounds present on the surface of the AgNPs were identified using FT-IR spectroscopy, and the results are compared with the IR spectrum of tannic acid theoretically calculated using PM6 and PM7 methods. The obtained results clearly indicate that the combined use of sodium citrate and tannic acid produces monodisperse spherical AgNPs, as it allows control of the nucleation, growth and stabilization of the synthesis process. Graphical abstract ᅟ

Electrodialysis (ED) and electrodeionization (EDI) are the new methods that are being used in water desalination processes. Reliable, electrochemically stable and efficient electrodes are the crucial components of the ED/EDI electrodialysers. The article proposes a new material for electrodes in electromembrane desalination systems. Graphene composite electrodes were created by bonding carbon fibres with epoxy resin and then coated with a layer of nanostructured, reduced graphene oxide. The graphene electrode material underwent electrochemical characterization by cyclic voltammetry, electrochemical impedance spectroscopy and potentiostatic polarization techniques. FTIR and Raman spectroscopy were used to determine the material’s chemical structure. The change in the surface morphology and elemental composition of the electrodes after fabrication and exploitation of the composite was studied by SEM and EDS. The electrodes were used successfully in multi-electrode electrodialysis devices, resulting in a desalination rate of over 90%. The electrodes were proven to be functional and durable. It was also confirmed that the oxidation/reduction phenomena on the electrode surfaces were fully reversible after changing their polarization, which was used cyclically to clean the electrodialyser. The parameters obtained indicate that this material can also be successfully used in other electrode processes. Graphical Abstract

The described research aimed to develop the properties of the conductive composite /poly(3,4-ethylenedioxy-thiophene-poly(4-lithium styrenesulfonic acid)/chitosan-AuNPs-glutaraldehyde/ (/PEDOT-PSSLi/chit-AuNPs-GA/) and to develop an electrochemical enzyme sensor based on this composite material and glassy carbon electrodes (GCEs). The composite was created via electrochemical production of an /EDOT-PSSLi/ layer on a glassy carbon electrode (GCE). This layer was covered with a glutaraldehyde cross-linked chitosan and doped with AuNPs. The influence of AuNPs on the increase in the electrical conductivity of the chitosan layers and on facilitating the oxidation of polyphenols in these layers was demonstrated. The enzymatic sensor was obtained via immobilization of the laccase on the surface of the composite, with glutaraldehyde as the linker. The investigation of the surface morphology of the GCE/PEDOT-PSSLi/chit-AuNPs-GA/Laccase sensor was carried out using SEM and AFM microscopy. Using EDS and Raman spectroscopy, AuNPs were detected in the chitosan layer and in the laccase on the surface of the sensor. Polyphenols were determined using differential pulse voltammetry. The biosensor exhibited catalytic activity toward the oxidation of polyphenols. It has been shown that laccase is regenerated through direct electron transfer between the sensor and the enzyme. The results of the DPV tests showed that the developed sensor can be used for the determination of polyphenols. The peak current was linearly proportional to the concentrations of catechol in the range of 2–90 μM, with a limit of detection (LOD) of 1.7 μM; to those of caffeic acid in the range of 2–90 μM, LOD = 1.9 μM; and to those of gallic acid in the range 2–18 μM, LOD = 1.7 μM. Finally, the research conducted in order to determine gallic acid in a natural sample, for which white wine was used, was described.

Biosensors are a very important subject in the contemporary analytics, mainly in biomedical area. This chapter describes biosensors built with the use of conductive polymers. Conductive polymers provide electrical conductivity of the forming layer, they may function as mediators in red-ox processes and they can enable the immobilization of a biological agent on their surface. Nowadays, in the center of attention are composite materials in which, next to conductive polymers, nanostructured materials such as graphene, carbon nanotubes and quantum dots are applied. In the chapter, the basic modes of biosensors of the first, the second and the third generation, are described. The examples of different enzymatic and affinity biosensors are presented.