Nowadays, the removal of pollutants and sensing of trivial quantity of heavy metal ions for the prevention of environmental pollution by graphene based materials is attractive research in the field of nanotechnology. Herein, we have designed for the fabrication of a series of g-C3N4/CuO composite by using one-step microwave-assisted synthesis convoyed by the calcinations for the degradation of antibiotic drugs and detection of nano-molar range of toxic heavy metal ions for the development of heterostructured composites. The synthesized g-C3N4/CuO composites were analyzed and characterized by TEM images, powder XRD, FTIR, N2 adsorption-desorption isotherms, UV-vis DRS, and photoluminescence techniques to know the structure, phase, surface area, absorption region, bandgap, and size of the composites. From the observation of TEM and XRD measurements, g-C3N4/CuO composites have hexagonal shape with average diameter of the particles is 25 ± 5 nm. The observed band gap values from UV-vis DRS for g-C3N4nanosheets and CuO NPs are 2.64eV and 1.72 eV. The N2 adsorption-desorption isotherm of the synthesized g-C3N4/CuO composite has prodigious specific surface area (32.47 m2/g), which is the evident for superior heterogeneous catalytic applications. Therefore, the synthesized g-C3N4/CuO composites were tested for the heterogeneous photocatalytic degradation of antibiotics such as tetracycline (TC) and ciprofloxacin (CIP) under UV light illumination, it shows as almost complete degradation was observed within 1 hour due to the matching optical band gap and internal charge transfer of excitons with in the heterojunction surface among g-C3N4 and CuO in the composite. Moreover, the enhanced catalytic performance of g-C3N4/CuO composite over the containing the individual components (g-C3N4 and CuO) due to the high surface area and tiny particles of CuO were randomly deposited on the surface of g-C3N4 nanosheets. The catalytic reduction reaction kinetics for the degradation of antibiotics trails as pseudo-first order kinetic equation and reused the catalyst for 5 consecutive cycles without noteworthy loss of catalytic activity. Moreover, the synthesizedg-C3N4/CuO composites were used as a prominent fluorescence sensing probe for the selective detection of toxic heavy metal ions in nano-molar range of concentration and selective sensing of Pb2+ among various metal ions by the fluorometric analysis was observed.