In situ approach to fabricate heterojunction p-n CuO-ZnO nanostructures for efficient photocatalytic reactions

This study reports a cost-effective approach for the fabrication of CuO-ZnO nanocomposites with different morphological features via in situ and impregnation approaches of a controlled amount of copper to obtain optimum photocatalytic activity. The impregnation approach results in flower, sheet and coral-shaped CuO particles in junction with ZnO nanowires (NWs). On the other hand, the transformation of ZnO NWs to flower-like (very rough) and pillar-like CuO-ZnO nanostructures with CuO outgrowths has been observed with an in situ approach as a function of molar ratio [(CuNO3 : ZnNO3)]: hexamethylenetetrammine of 2 > 1 > 0.5 > 0.25. CuO-ZnO nanocomposites exhibited a slight red-shift in their band-gap values (3.2 to 2.8 eV) when increasing the copper content during the in situ approach. An increase (∼2 fold) in the photocatalytic efficiency for the degradation of methyl orange has been noticed with in situ grown CuO-ZnO composites on an Si substrate as compared to pristine ZnO NWs. The apparent rate constant (k) was found to be the highest for in situ fabricated CuO-ZnO nanocomposites (1.5 × 10−1 h−1) as compared to 2.6 × 10−2 h−1 for impregnated Cu1:Zn1, and least (1.8 × 10−2 h−1) for pristine ZnO NWs during methyl orange photooxidation. CuO-ZnO nanocomposites with rough exposed surface and CuO outgrowths provide a high active surface area and stable p-n junctioned interfacial contact for application in environmental purification.