Synthesis of g-C3N4/NiO p–n heterojunction materials with ball-flower morphology and enhanced photocatalytic performance for the removal of tetracycline and Cr6+

A novel three-dimensional ball-flower-like g-C3N4/NiO (GN) photocatalyst was firstly fabricated by a simple two-step calcination method for enhanced degradation capability. Our investigation focuses on the construction of p–n heterojunction and specific ball-flower-like structure to overcome limitations of single-component semiconductors, such as low surface area, poor light response and fast recombination of the photogenerated electrons and holes. Detailed photocatalytic experiments revealed that the novel ball-flower-like GN (50%) exhibited much higher activity for the removal of TC and Cr6+ than single g-C3N4, NiO and traditional layered GN. The trapping experiments proved that the superoxide radicals ( $$ ^\cdot {\text{O}}₂ ^- $$ ), holes (h+) and electrons (e−)were the main active species in the photodegradation process. Moreover, three different degradation pathways and fourteen intermediate products of TC were also determined by the LC/MS analysis and these intermediates could be further degraded completely into CO2, H2O, $$ {\text{NH}}₄ ⁺ $$ , carboxylic acids and any other inorganic intermediates. These results will benefit the fabrication of other 3D p–n heterojunction photocatalysts and their potential application in treatment of organic pollutants.