Enhancing the photocatalytic performance of the g-C3N4/BiOCl heterojunction in gaseous toluene degradation via K+ decoration in g-C3N4

•Performance of K-doped g-C3N4 composite with BiOCl in photocatalysis toluene degradation.•Construction of p-n heterojunction between K-doped g-C3N4 and BiOCl semiconductor.•OH and O2− radicals play a leading role in the degradation process of toluene.•Dominant mechanism of photocatalytic gas-toluene degradation is the directly Z-scheme charge transfer.