Electrochemical oxidation and advanced oxidation processes using a 3D hexagonal Co3O4 array anode for 4-nitrophenol decomposition coupled with simultaneous CO2 conversion to liquid fuels via a flower-like CuO cathode

Abstract

A novel electrocatalytic system was developed to realize one-pot conversion of organic pollutants into liquid fuels such as methanol (CH₃OH) and ethanol (C₂H₅OH). The process combines the catalytic oxidation of organic pollutants with electrocatalytic reduction of CO₂. We first coupled the electrocatalytic process with SO₄^•--based advanced oxidation processes (AOPs) for the degradation of 4-nitrophenol (4-NP) using a 3D-hexagonal Co₃O₄ anode. In this step, 4-NP was mineralized to CO₂, and then the CO₂ was converted to CH₃OH and C₂H₅OH by electrocatalytic reduction using a flower-like CuO cathode. The experimental results show the destruction of 4-NP (60 mL, 10 mg/L) can be as high as 99%. In addition, the yields of CH₃OH and C₂H₅OH were 98.29 μmol/L and 40.95 μmol/L, respectively, which represents a conversion of 41.8% of 4-NP into liquid fuels; the electron efficiency was 73.1%. In addition, we found that 3D-hexagonal arrays of Co₃O₄ with different morphologies can be obtained by adding different amounts of urea. We also investigated the formation mechanism of novel 3D-hexagonal Co₃O₄ arrays for the first time. A mechanism was proposed to explain the electrocatalytic steps involved in the conversion of 4-NP to CH₃OH and C₂H₅OH and the synergetic effects between AOPs and electrocatalysis.

Keywords: Advanced oxidation processes; CO(2) reduction; Electrooxidation; Electroreduction; Organic pollutants; Sulfate radical.