Engineered defect-rich HfOx/metal-doped g-C3N4 Z-scheme heterojunction for enhanced visible-light photocatalytic degradation of antibiotics

Abstract

Hafnium dioxide (HfO₂) is a stable but UV-restricted photocatalyst due to its wide band gap and high charge recombination. This study employs two complementary strategies to overcome these limitations. First, Ovs were introduced into HfO₂ (denoted as HfOx) via a mild, scalable wet-chemical approach, effectively reducing its band gap to ~2.0 eV and enabling visible-light activation. Second, to increase the charge separation efficiency, a Z-scheme heterojunction was constructed by coupling HfOx with Li/Mg-codoped g-C₃N₄ (GCNLM). Co-doping tailored the electronic structure of g-C₃N₄ by suppressing Fermi level pinning, narrowing its band gap, and improving charge mobility. This modification also aligned the valence band of GCNLM closer to the conduction band of HfOx, reducing the interfacial charge transfer resistance. Strong interfacial interactions, evidenced by the formation of C–Hf and N–Hf bonds, facilitated multiple charge transfer pathways. LC‒MS analysis revealed the degradation pathway, and toxicity assessments confirmed the safety of the intermediate products.