In the present study, the copper oxide nanoparticles (gCON) were synthesized from the extract of Prosopis juliflora (Sw.) leaves using copper nitrate, a leachate product of the waste printed circuit boards mediated through the bio-hydrometallurgical process. The synthesized gCON was characterized through the UV–Vis, Raman, FT-IR, zeta potential, XRD, BET model and SEM. Methylene blue (MB) adsorption onto gCON tested in batch trials by varying the pH, initial adsorbate concentration and contact time. The chemical kinetics of MB adsorption followed the pseudo-second-order and chemisorptive Elovich models with a high degree of linearity (r2 > 0.99) and marginal error values. Further, the isotherm data suggested the monolayer coverage of MB as the experimental data aligns well with the Langmuir model (r2 > 0.99) and the maximum dye adsorption capacity (qm) of gCON was computed as 163.93 mg/g. The magnitude of thermodynamic functions identified the chemisorptive removal of MB as spontaneous and endothermic. The mass transfer analysis verified that both intra-particle and liquid film diffusion limits the adsorption process. Desorption results showed that gCON can be regenerated for a maximum of three cycles. The present study demonstrated that gCON can be used as an unconventional adsorbent for the removal of MB from aqueous solutions.