• Coal tar pitch-based nanosheets (CPN-9) exhibit high specific surface area (466.34 m2/g) and hierarchical porosity, enhancing ion transport and accessibility.
• Nitrogen doping (pyrrolic and pyridinic N) synergistically improves electron transfer and reduces charge transfer resistance, boosting capacitive performance.
• In flow-electrode capacitive deionization (FCDI), CPN-9 achieves a desalination rate of 0.039 mg/(cm2 min) with high charge efficiency (48.47%) and low energy consumption (0.012 kWh/mol).
• The study provides a sustainable route for high-salinity wastewater treatment using coal-derived carbon materials, addressing environmental challenges in mining regions.