Direct electrochemical detection of bisphenol A at PEDOT-modified glassy carbon electrodes

The electrochemical behavior of bisphenol A (BPA) was studied on poly(3,4-ethylenedioxythiophene) (PEDOT)-modified glassy carbon electrodes by cyclic voltammetry. It was observed that BPA oxidation on PEDOT film produced a BPA polymer (pBPA) showing excellent redox activity with anodic and cathodic peaks at 0.15 and 0.01 V, respectively; the former being evaluated for BPA electrochemical sensing. The amount of deposited pBPA has been estimated by electrochemical and spectroscopic analysis by X-ray photoelectron spectroscopy. The effect of scan rate and pH on the oxidation of pBPA film has been studied. The oxidation current was found to vary linearly with BPA concentration in the range 90–410 μM, and a detection limit of 55 μM was evaluated. Results of BPA amperometric detection have also been collected by using a repetitive potential step program to give a linear response to BPA in the concentration range 40–410 μM with a detection limit of 22 μM and a sensitivity of 1.57 μAμM−1cm−2. The developed sensor showed satisfactory reproducibility and anti-interference properties and was successfully applied to BPA determination in mineral water samples

Site Preferences of Carboxyl Groups on the Periphery of Graphene and their Characteristic IR Spectra

Energetics of carboxyl groups at the periphery of a graphene sheet are studied using density functional theory (B3LYP) with a 6-31G* basis set, augmented with diffuse functions on O. Corner sites are energetically preferred followed by zigzag edges, and armchair edges are least stable. The energy and geometry of each is attributed to a competition between π-conjugation and steric repulsion factors. Vibrational analyses reveal certain features that are characteristic of each site location, which may help in the assignment of experimental spectra of graphene and other polycyclic aromatic hydrocarbons. For example, zigzag sites typically lead to an intense C═O stretching band that occurs below 1700 cm–1, quite uncommon for the carboxyl group