Cyclic catalytic Fe-N doped composite particle electrodes derived from gasification fine slag for non-selective mineralization of organic wastewater

Abstract

As a typical coal-based solid waste, coal gasification fine slag (GFS) will have an annual discharge of more than 50 million tons in 2025 in China alone. However, the difficulty of its resource utilization lies in the precise separation of carbon and ash due to their complex distribution pattern. There is an urgent need to develop GFS-based materials for comprehensive utilization of carbon and ash. In this study, a combined process of acid leaching and pyrolysis was designed, in which active metal iron was leached from ash and immobilized on the surface of residual carbon in the form of Fe-N-C. The unique structure of Fe-N doped carbon/ash synergistically improved the efficiency of electrocatalytic degradation of organic wastewater by 72.78 ± 1.37%. The hierarchical porous structure of residual carbon considerably enhanced the accessibility of ash catalytic sites. Abundant ash defects and Fe-N active sites promoted the conversion of free radical precursors to reactive oxygen species (ROS). The removal rate of various organic wastewater within 35 min reached more than 100 ± 1.83% %, with excellent electrocatalytic performance and pH adaptability. Fe-NCPE had a high specific surface area (318.36 m2·g−1), orderly graphite phase (002 crystal surface size 1.3 nm), and abundant catalytic sites. We also proposed the catalytic mechanism by combining molecular simulation with experiments. The high adsorption capacity above 24.07 ± 0.12 mg·g−1 ensured the continuous and rapid supply of pollutants and H2O2 near the catalytic site·H2O2 was converted into ROS mainly composed of hydroxyl groups through the valence state change of aluminum or Fenton-like reaction of nitrogen-linked iron. The ROS then attacked organic molecules to degrade pollutants. The above two processes corresponded to two cyclic catalytic reactions. Therefore, this study provides an innovative and promising approach for comprehensive utilization of carbon and ash in GFS.