Ball-milled biochar-modified zero-valent aluminum activates peroxodisulfate for phenol degradation: Enhancement of catalysis by membrane-breaking effect

Zero-valent aluminum (ZVAl) is a potential activator for peroxodisulfate (PDS), yet the dense oxide film on its surface hampers electron transfer for the O-O bond cleavage of PDS. We synthesized zero-valent aluminum-biochar (BM-ZVAl@BC) composites through ball milling, which effectively disrupted the native oxide layer on BM-ZVAl@BC. Within the BM-ZVAl@BC/PDS system, biochar (BC) not only suppressed the rapid oxidation of BM-ZVAl@BC but also enhanced the dispersion and electron transfer rate of ZVAl, thereby improving the overall catalytic efficiency. Consequently, the phenol removal efficacy in the BM-ZVAl@BC/PDS system was notably improved. Optimal catalytic performance of the prepared BM-ZVAl@BC was achieved at a charcoal-to‑aluminum mass ratio of 2:1, resulting in 95.7 % phenol removal after 180 min. Quenching experiments and electron paramagnetic resonance (EPR) analysis revealed that both free radicals (SO