In-situ template etching synthesis of BiON/BiOCl0.9I0.1 heterojunction for photocatalytic degradation of tetracycline

•BiOCl0.9I0.1/BiON catalysts are reasonably designed and synthesized via a room temperature in-situ etching method.•BiOCl0.9I0.1/BiON catalysts provide typical sample model to study heterojunction effect for the photodegradation of tetracycline.•Enhanced photodegradation activity due to photogenerated carriers separation and specific surface area optimized by heterojunction design.