Enhanced charge separation in g-C 3 N 4 -BiOI heterostructures for visible light driven photoelectrochemical water splitting.

Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered graphitic carbon nitride (g-C 3 N 4 ) and few layered graphitic carbon nitride sheets (g-C 3 N 4 -S) are synthesized and investigated as an active photoanode material for sunlight driven water splitting. HR-TEM and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and the carbon nitride (g-C 3 N 4 and g-C 3 N 4 -S) network that consisted of dendritic BiOI nanoplates surrounded by g-C 3 N 4 sheets. The presence of BiOI in g-C 3 N 4 -S/BiOI and g-C 3 N 4 -S/BiOI nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent charge separation in g-C 3 N 4 /BiOI and g-C 3 N 4 -S/BiOI, evident from quenching of the carbon nitride photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical performance is observed for both types of g-C 3 N 4 -BiOI heterojunctions. In comparison to heterojunctions of bulk g-C 3 N 4 with BiOI, the nanocomposite consisting of few layered sheets of g-C 3 N 4 and BiOI exhibits higher photocurrent density due to lower recombination in few layered sheets. A synergistic trap passivation and charge separation is found to occur in the g-C 3 N 4 -S/BiOI nanocomposite heterostructure which results in a higher photocurrent and a lower charge transfer resistance.