This work reports a green and sustainable route for the synthesis of benzimidazoles via C-N bond formation using carbon dioxide (CO2) as a C-1 carbon source. In this work, Cu@U-g-C3N4 catalyst was prepared from urea derived porous graphitic carbonnitride (U-g-C3N4) and CuCl2 and characterized by FT-IR, XRD, XPS, SEM, TPD etc. The Cu@U-g-C3N4 as a heterogeneous recyclable catalyst has been employed first time for the cyclization of o-phenylenediamines (OPD) with CO2 to benzimidazoles using dimethylamine borane (DMAB). The proposed protocol becomes sustainable and efficient due to the use of propylene carbonate/water as a suitable biodegradable, economical and environmentally benign solvent system. The proposed catalytic system showed a wide range of substrate scope for the synthesis of benzimidazoles in good to excellent yields. [GRAPHICS] .