In this study, we reported a novel type-I heterojunction between red phosphorus and graphitic carbon nitride under vacuum condition, which is a novel synthesis process. For preparing the red phosphorus composites, the vacuum condition is appropriate to prevent it from self-ignition. The prepared materials were analyzed with different analytic techniques for the confirmation of their heterojunctions and structure formation. The introduction of red phosphorus into graphitic carbon nitride, reduce the structural defects and increase the charge separation ability. After medication, the synthesized composite shows an enhanced photocatalytic activity against acute toxicity category-III non-color (MTSM, Metsulfuron methyl) and color (RhB), organic pollutants. The photocatalytic degradation mechanism (Mott-Schottky and VB-XPS) study reveal that red phosphorus /graphitic carbon nitride possess type-I heterojunction with enhanced catalytic behavior, due to the effective transformation of photo-generated electrons from CB of GCN to CB of RP with the help of heterojunctions and due to unmoved photo holes on VBs. Synthesized composites also maintained their performance after reused them in three cyclic form. [ABSTRACT FROM AUTHOR]