Anodic oxidation of salicylic acid using multi-walled carbon nanotubes modified carbon felt with simultaneous CO2 reduction by electrocoagulated sludge derived MIL-53(Fe/Cu) metal-organic framework cathode decorated with CuFe2O4

Abstract

Salicylic acid (SA) used to treat inflammation and swelling is frequently identified in water habitats. Exposure to SA can affect aquatic species, making it imperative to remediate SA-contaminated water. Besides, plastic waste and electrocoagulated sludge can be hazardous as unscientific management can result in severe environmental damage. Hence, converting them into electrocatalysts can be a feasible choice to combat environmental problems. Herein, a novel anodic oxidation (AO) coupled electrocatalytic reduction (ER) system for CO₂ was developed to degrade SA in the presence of persulfate (PS) to convert SA into formic acid (HCOOH). The SA was mineralized into CO₂ in AO using multi-walled carbon nanotubes (MWCNT) coated carbon felt (CF) anode, and the resulting CO₂ was subsequently reduced to HCOOH at electrocoagulated sludge-based sFe-Cu@MOF cathode. The AO demonstrated 99.1±0.9 % breakdown of SA at 0.033 min⁻¹ in 120 min with the MWCNT-CF + PS system, indicating 1.7-fold (58.0±1.5 %) higher degradation than CF + PS. In addition, the maximum yield of HCOOH was 0.024 mM in the AO-ER system. The stability tests of MWCNT-CF and sFe-Cu@MOF revealed SA degradation and yield of HCOOH were slightly dropped by 9 % and 6 %, respectively; thus, possess exceptional stability. Radical scavenging tests showed SO₄^•− as the primary radical involved in the degradation of SA. Phytotoxicity revealed that MWCNT-CF + PS significantly decreased the toxicity of SA towards Cicer arietinum L. Total operating cost of AO-ER was about 0.468 $/m³, suggesting it could be cost-effectively used to treat wastewater in practical field scenarios.