Adsorption synergy electrocatalytic degradation of phenol by active oxygen-containing species generated in Co-coal based cathode and graphite anode

Abstract

Abstract The coal base electrodes and efficient coal base loaded cobalt electrodes (Co-CE) were prepared by pyrolysis method of low rank coal united activation method of KOH in order to develop more pores structures. The morphology of electrodes were characterized by Scanning electron microscopy, meanwhile, the type of elements were detected by energy dispersive spectroscopy (EDS). The electrochemical performance of electrodes were tested by cyclic voltammetry and electrochemical impedance spectroscopy. The lamella structures and pores were observed in microtopography of electrodes and the cobalt were successfully loaded in Co-CE from the EDS analysis. The operating conditions of processing time, current density, electrolyte concentration, pH and initial phenol concentration on this electrochemical system in single factor experiment were separately explored, correspondingly, the value was 180 min, 40 mA·cm−2, 0.01 mol·L−1, 2, 100 mg·L−1, and the phenol removal rate (R) were at the range of 47.64–67.84%. In the optimization experiment of JMP design, the removal rate could reach at 83.47%. The response surface methodology was employed for optimizing operation conditions to improve R. And the prediction model obtained for the response can be represented as: R = 66.5275 + 6.7311X 1 – 5.4197X 4 – 5.2303X 5 + 4.9555X 1 2 – 12.5219X 2 2 – 6.2912X 4 2 + 16.0937X 5 2 + 2.4109X 2 X 4 – 7.910X 3 X 4 – 3.0123X 3 X 5 – 2.183X 4 X 5. The optimized conditions were pH 3, 100 mg·L−1 of phenol concentration, 0.1 mol/L of electrolyte concentration, 35 mA/cm2 of current density, and 180 min of processing time. Meanwhile, the predicted R was 90.86%, the actual R of three parallel experiments were 91.2%, 89.3%, 91.05%, which were well consistent with the predicted value. Additionally, the degradation mechanism was proposed as that the adsorption in pore structures synergy electrocatalytic effect of Co-CE. Micro-electric fields formed in pores and the transition metal catalysis accelerated the transformation of cathode hydrogen peroxide to generate hydroxyl radical (·OH). Furthermore, the ·OH were produced both by cathode and anode which promoted the degradation of phenol. This high catalytic activity and low cost Co-CE is a kind of prospective electrode for electrochemical degradation of phenolic wastewater.