The BiOBr/Bi2WO6/2K-g-C3N4 tri-heterojunction photocatalyst efficiently catalyzes the degradation of gaseous formaldehyde

The photocatalytic oxidation of formaldehyde (HCHO) to CO 2 and H 2 O is a key method for the green degradation of gaseous HCHO. Graphitic carbon nitride (g-C 3 N 4 ) is widely studied for its stability, non-toxicity, and low cost, but its small specific surface area often leads to electron-hole recombination, limiting its photocatalytic efficiency. This study addresses this by preparing K-doped g-C 3 N 4 via thermal polymerization and synthesising a flower-like spherical BiOBr/Bi 2 WO 6 /2K-g-C 3 N 4 ternary heterojunction catalyst using hydrothermal and hydrolytic precipitation methods. The catalyst demonstrated a 96.00 % photocatalytic degradation efficiency for gaseous HCHO within 5 h, reaching 90.67 % at just 2 h, highlighting its superior charge separation capability. Characterization revealed that the flower-like morphology enhances light absorption by exposing more active sites, while the K-doped g-C 3 N 4 forms a double Z-scheme heterojunction with BiOBr/Bi 2 WO 6 , effectively separating and retaining photogenerated electrons and holes. This structure significantly boosts the catalyst's redox capacity, thereby improving its photocatalytic performance for HCHO degradation.