The same copper phosphate catalysts were synthesized by obtaining the methods involving solid state as well as liquid state reactions in this work. And then the optimised p-n hybrid junction photocatalysts have been synthesized following the same solid/liquid reaction pathways. The synthesized copper phosphate photocatalyst has unique rod, flower, caramel-treat-like morphology. The Mott-Schottky behavior is in accordance with the expected behavior of n-type semiconductor and the carrier concentration was calculated using the M-S analysis for the photocatalyst. And for the p-n hybrid junction of 8RGO-Cu3(PO4)2-PA (PA abbreviated for photoassisted synthesis method), 8RGO-Cu3(PO4)2-EG(EG abbreviated for Ethylene Glycol based synthesis method), 8RGO-Cu3(PO4)2-PEG (PEG abbreviated for Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol based synthesis method)the amount of H2 synthesized was 7500, 6500 and 4500 μmol/h/g, respectively. The excited electrons resulting after the irradiation of visible light on the CB of p-type reduced graphene oxide (RGO) migrate easily to n-type Cu3(PO4)2 via. the p-n junction interfaces and hence great charge carrier separation was achieved. © 2018 The Author(s).