Role of conductive channels via CQDs on NiO/g-C3N4 Z-scheme composite as a bi-functional photocatalyst

Abstract

Herein, an innovative graphitic carbon nitride (g-C3N4) based nanocomposite with nickel oxide (NiO) is modified with carbon quantum dots (CQDs) to fabricate CQD/NiO/g-C3N4 ternary composites. The effect of various concentrations of CQDs is investigated for photo electrochemical (PEC) water splitting and photocatalytic degradation of methyl orange (MO). XRD pattern of CQDs/NiO/g-C3N4 composite showed the distinctive peaks of g-C3N4 and NiO. The reduction of band-gap values from 2.62 to 1.8 eV in UV–Visible spectra of nanocomposites confirmed an improvement toward red shift. The existence of required functional groups and successful fabrication of nanosheets of g-C3N4 and its nanocomposites are confirmed by FTIR. PL confirms the decrease in electron-hole recombination in binary and ternary composites. CQDs/NiO/g-C3N4 (4.0 mL) showed enhanced PEC activity and photocatalytic performance in visible light exposure. CQDs/NiO/g-C3N4 (4.0 mL) showed an obvious enhancement in current density of ∼-19 mAcm−2 at potential 0.39 V during hydrogen evolution reaction (HER) and high current density of ∼ 15 mAcm−2 at 1.42 V in oxygen evolution reaction (OER) than all others. The highest degradation rate of MO by CQDs/NiO/g-C3N4 (4.0 mL) was noted due to availability of plenty of active sites and conductive channels provided by CQDs. Incorporated CQDs in samples affect the overall water splitting response and photocatalytic activity by acting as electron conduction bridge for the quick electron transfer from the composite materials to reaction sites on its surface. This combination is active for efficient PEC water splitting and photo degradation purposes.