Advanced oxidation processes (AOPs) have attracted growing interest for treating recalcitrant organic contaminants. Persulfate (PDS) activation generates sulfate radicals (SO₄^•-) that exhibit high oxidation potentials over a broad pH range. Conventional PDS activation methods by dissolved metal ions, UV, or heat suffers from metal toxicity, poor reusability, and extra energy input. Granular activated carbon (GAC) is a promising catalyst supports because of its large surface area, rich surface functionalities, and operational simplicity. While previous studies have shown that GAC can activate PDS, metal doping often leads to ion leaching and activity loss. Surface graphitization or heteroatom (e.g., N) doping offer a metal-free route to enhance electron transfer efficiency, but investigations on carbon-nitride-modified GAC for PDS activation remain scarce. In this work, nitrogen-modified GAC (N-GAC) was synthesized through impregnation of nitrogen precursor followed by calcination. Synthesized catalyst was evaluated its ability to activate PDS for pollutant removal and elucidated the underlying reaction mechanism. Catalytic persulfate activation experiments were conducted in batch reactor with phenol as a target pollutant. Experimental resulted showed that characterization methods such as SEM, BET, XRD, FT-IR confirmed the successful deposition of nitrogen on GAC. Compared with pristine GAC, N-GAC showed slightly slower adsorption kinetic in the absence of PDS but markedly enhanced phenol degradation when combined with PDS. 4-chlorophenol (4-CP) oxidation experiments was conducted for evaluating effective activation effects of synthesized catalyst. 4-CP released more chloride ion in the presence of N-GAC and PDS than with GAC and PDS, confirming stronger activation efficiency of PDS through N-GAC. Desorption experiments using organic solvent revealed negligible residual phenol on N-GAC, whereas pristine GAC retained adsorbed phenol, indicating faster on-surface oxidation and lower catalyst fouling with N-GAC. These results demonstrate that nitrogen-rich graphitic domains effectively mediate electron transfer from the GAC to PDS, enabling metal-free and reusable PDS activation. The N-GAC catalyst therefore represents feasibility for long-term treatment of phenol-laden and other contaminated waters.

Keywords: granular activated carbon, nitrogen doping, advanced oxidation process, persulfate activation, water treatment