Metal–organic framework-derived carbon-based materials have shown significant potential in advanced oxidation processes. However, mass production of MOFs is still limited mainly due to non-economic, non-green, and complex synthesis methods. This study reports thermal-assisted ball milling as a novel method for the green and efficient synthesis of MOF-235 compared with the solvothermal method. Lamellar metal-free porous carbon was obtained by pyrolysis of MOF-235 and HCl etching to avoid secondary pollution from metal leaching in activating persulfate for thiocyanate degradation. The effect of pyrolysis temperature on the structural characteristics and catalytic performance of MOF-235-derived porous carbon was investigated. The results demonstrated that the porous carbon derived from pyrolysis of MOF-235 at 650 °C with a larger specific surface area (831.48 m² g⁻¹) and a higher sp²-hybridized structure (70.3%) exhibits superior catalytic activity in persulfate activation, as evidenced by 99.9% degradation of thiocyanate within 15 min with 0.4 g L⁻¹ catalyst and [Na₂S₂O₈] : [SCN⁻] = 6.0 at ambient pH (5.5). The thiocyanate degradation experiments and mechanism studies revealed that the dominant pathways were the singlet oxygen-mediated non-radical oxidation and electron transfer processes. Finally, a possible mechanism of persulfate activation on metal-free porous carbon was proposed. This work provides thermal-assisted ball milling as a feasible method for the synthesis of MOF-235 and also discusses the promising application of the derived carbon for persulfate activation in wastewater treatment.