Screen-printed electrodes-based technology: environmental application to real time monitoring of phenolic degradation by phytoremediation with horseradish roots

Abstract

The following is a description of a simple strategy for monitoring phenolic pollutants from highly-contaminated water samples. These phenolic compounds are removed from tap water using horseradish roots (Raphanus sativus) that contain peroxidase as catalyst and H2O2 to generate hydroxyl radicals. The later (•OH) acts on the aromatic structure, causing them to degrade to non-toxic by-products. The tool used to follow up the evolution of the process is based on screen-printed carbon electrodes (SPCEs) as electrochemical sensor for simultaneous detection of hydroquinone (Epa at 0.047 V), m-cresol (Epa at 0.506 V) and 4-nitrophenol (Epa at 0.696 V) by differential pulse voltammetry (DPV). This electroanalytical methodology enables close monitoring of the situation and rapid sensor response time. Furthermore, this direct methodology works for opaque and heterogeneous samples, as tap water with chopped horseradish roots, without any treatment of samples previously to the analysis. For better knowledge of the electrodic-transfer process, the electrochemical behavior of these phenolic compounds by cyclic voltammetry (CV) is also included. This simple methodology shows a low detection limit (below to 5 μM) and an excellent selectivity (peak potential separation between them up to 200 mV or greater) in a linear range of three orders of concentration (from 1–5 μM to 1 mM) for all of the analytes studied. The DPV responses of the phenolic compounds during the phytoremediation process are simultaneously monitored by this direct, cheap, reproducible (RSD < 2.3%) and rapid DPV-SPCE electroanalytical methodology. Portable device as electrochemical sensor with this optimized and validated technology can be applied for decentralized analysis, on-site assays and rapid screening purposes. The use of the horseradish roots achieves the total elimination of phenolic pollutants in concentrations 1000 times higher than the legal limits in less than 1 h.