Enhancing the efficiency of zero valent iron by electrolysis: Performance and reaction mechanism.

Electrolysis was applied to enhance the efficiency of micron-size zero valent iron (mFe) and thereby promote p-nitrophenol (PNP) removal. The rate of PNP removal by mFe with electrolysis was determined in cylindrical electrolysis reactor that employed annular aluminum plate cathode as a function of experimental factors, including initial pH, mFe dosage and current density. The rate constants of PNP removal by Ele-mFe were 1.72-144.50-fold greater than those by pristine mFe under various tested conditions. The electrolysis-induced improvement could be primarily ascribed to stimulated mFe corrosion, as evidenced by Fe release. The application of electrolysis could extend the working pH range of mFe from 3.0 to 6.0 to 3.0-10.0 for PNP removal. Additionally, intermediates analysis and scavengers experiments unraveled the reduction capacity of mFe was accelerated in the presence of electrolysis instead of oxidation. Moreover, the electrolysis effect could also delay passivation of mFe under acidic condition, as evidenced by SEM-EDS, XRD, and XPS analysis after long-term operation. This is mainly due to increased electromigration meaning that iron corrosion products (iron hydroxides and oxides) are not primarily formed in the vicinity of the mFe or at its surface. In the presence of electrolysis, the effect of electric field significantly promoted the efficiency of electromigration, thereby enhanced mFe corrosion and eventually accelerated the PNP removal rates.