Dialysis‐Exfoliation of Poly(Heptazine Imide) Ultrathin Nanosheets With Boosted Photocatalytic Activity

Poly(heptazine imide) ultrathin nanosheets (PHIuns) are efficient photocatalysts, yet current synthetic methods remain inefficient, costly, and not scalable for industrial applications. Herein, we present a facile dialysis process to synthesize PHIuns via exfoliation from sodium poly(heptazine imide) (PHI-Na), driven by the loss of Na⁺ ions. The exfoliation process yields PHIuns with a thickness of ∼0.5 nm, revealing a distinct quantum size effect, and thus PHIuns exhibit considerably enhanced photogenerated charge separation and photocatalytic performance compared to PHI-Na and acid-treated PHI-Na (PHI-H, devoid of Na⁺ ions). Notably, photocatalytic overall water splitting activity of Pt@CrO_x and CoOH co-modified PHIuns is approximately 14 and 252 times higher than that of corresponding PHI-H and PHI-Na, respectively. This work introduces a cost-effective, efficient, and scalable approach for the synthesis of PHIuns.