Methylene Blue - New Chemistry Experiments for University Education

The redox reactions of methylene blue on screen printed electrodes (SPEs) can be measured electrochemically by cyclic voltammetry (CV) and spectroscopically by optical and Raman spectroscopy. The combination of cyclic voltammetry and optical or Raman spectroscopy, known as absorpto- or Raman voltammetry, provides not only electrochemical information about redox reactions at electrodes, but also about changes in the visible and Raman properties of the substances used. Raman scattering can be enhanced by a simple electrochemical in-situ modification; this leads to an electrochemically activated surface enhanced Raman effect (EC-SERS). Therefore, chemical reactions, based on the change in vibrational states of the substances under investigation, can be characterized in a very simple way. In this article, we compare different electrodes and show that the electrochemical reactions of methylene blue strongly depend on the electrodes used. In addition, the electropolymerization of methylene blue is discussed. At the end of the article, a script for students for measuring the spectroelectrochemistry of methylene blue is presented in detail. The didactic background is that the combination of electrochemical information, such as potentials and current fluxes, with spectroscopic information, such as absorption and/or vibrational changes, leads to a better understanding of electrochemistry.