Electrocatalytic removal of humic acid using cobalt-modified particle electrodes

Abstract

Humic acid (HA) is a complex polymer compound with no definite chemical formula. It seriously affects water quality and is one of the main precursors of producing disinfection by-products. In the present study, column granular electrodes (Φ×H = 4 × 3 mm) were prepared using cobalt loaded powder active carbon (PAC). The electrodes were applied in a continuous three-dimensional (3D) electrochemical reactor to remove HA. The crystal structure, morphology, surface chemical bonds, and pore structure of as-prepared material were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and N2 adsorption-desorption isotherms. Furthermore, parameters affecting the removal of HA and energy consumption (namely, current, electrolyte type and concentration, and initial pH) were examined. Intermediate products were analyzed using ultraviolet-visible (UV–vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and three-dimensional excitation emission matrix (3DEEM) fluorescence spectroscopy. The results showed that CoO was well loaded in the PAC carriers. The CoO loaded granular electrodes (GAC-Co) had the surface area of 782.6 m2/g, pore volume of 0.6709 cm3/g, and average pore diameter of 3.429 nm. The 95.3% of chemical oxygen demand (COD) removal was obtained under the current of 0.3 A, hydraulic retention time (HRT) of 8 min, influent pH of 7.0, electrolyte of 0.01 mol/L Na2SO4, and initial concentration of 200 mg/L. A large number of H∙ radicals were involved in the electrochemical processes, which were observed using electron spin resonance (ESR) spectroscopy. The analysis of intermediate products indicated that the GAC-Co electrodes showed high electrocatalytic activity for the degradation of HA, in which HA with large molecular weight was decomposed to small molecular weight in the 3D electrochemical system.