Synthesis of boron-doped nafion membranes and investigation of phenol removal efficiency in an H-type electrochemical cell

ABSTRACT SYNTHESIS OF BORON-DOPED NAFION MEMBRANES AND INVESTIGATION OF PHENOL REMOVAL EFFICIENCY IN AN H-TYPE ELECTROCHEMICAL CELL The primary objective of this doctoral thesis is to enable the electrochemical oxidation of phenol in aqueous solutions by utilizing Nafion membranes modified with various boron-based materials in a split, H-type cell equipped with Pt-Ir and BDD (Boron-Doped Diamond) anodes and Fe cathodes. In this study, Nafion membranes without additives and those incorporating 1% and 2% of ulexite (NU-1, NU-2), colemanite (NK-1, NK-2), and Etidot-67 (NE-1, NE-2) were prepared for application in the H-type cell. The characterization of these prepared membranes was carried out using FTIR, RAMAN, XRD, SEM, and EDX analyses. During the experimental investigations, the influence of Pt-Ir and BDD anode electrodes, applied current density, presence of NaCl electrolyte in the anolyte region, the existence of FeSO4 and Al2(SO4)3 coagulants in the catholyte region, as well as the type of membrane employed in the H-type cell on the removal of phenol in both the anolyte and catholyte regions was thoroughly examined. The optimal conditions were identified as utilizing the NE-1 membrane with Pt-Ir anode, 500 mg/L initial phenol concentration in the 0.5 M H2SO4 + 5 g/L NaCl anolyte solution, and 500 mg/L initial phenol concentration in the 0.5 M H2SO4 + 5 g/L FeSO4 catholyte solution, with an applied current density of 50 mA/cm2. Under these optimum conditions, phenol was entirely removed in the anolyte region within 30 minutes using Pt-Ir anode, whereas the utilization of BDD anode reduced this time to 8 minutes. Regarding the reaction kinetics results for phenol removal under the optimal experimental conditions, a first-order reaction with a rate constant of 0.0702 min-1 was observed in the anolyte region when Pt-Ir electrode was employed, whereas in the catholyte region, the rate constant was determined to be 0.076 min-1. On the other hand, when BDD electrode was used, the first-order rate constant for the anolyte region was found to be 0.3988 min-1, and in the catholyte region, it was 0.0139 min-1. When NaCl electrolyte was employed in the anolyte region, intermediate products such as 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol were detected. Conversely, the use of 0.5 M H2SO4 resulted in the formation of intermediates such as hydroquinone, benzoquinone, and catechol. This experimental study successfully facilitated the preparation of boron-modified Nafion membranes and achieved the electrochemical oxidation of phenol in both the anolyte and catholyte regions of the H-type cell. Keywords: Phenol, Oxidation, Nafion, Membrane, H-type cell Advisor: Prof. Dr. Bahadır Kürşad KÖRBAHTİ, Mersin Üniversity, Chemical Engineering Department, Mersin.