Construction of isotype heterojunctions in polymeric carbon nitride with thermal modulation and improved photocatalytic hydrogen production activity

Abstract

Subtle structural changes in polymeric carbon nitrides (PCN) influence their photocatalytic activities. Herein, we present a strategy to construct isotype heterojunctions by thermal condensation of dicyandiamide as a single precursor. This avoids the complications that differences in the electronegativity of the coupled materials incur. Heterojunctions were created by depositing a carbon nitride layer processed at 500 °C over the carbon nitride processed at 600 °C utilizing structural defects and uncondensed moieties to form an interconnected structure. This enables the directional stacking of the PCN layers leading to changes in physicochemical properties and electronic band structure. The detailed characterization and testing revealed a type-II heterojunction configuration, whereby photoluminescence quenching measurements confirm longer exciton lifetimes and differences in Mott-Schottky flat band potential energies and low interfacial resistance facilitate mobility of charge carriers. Heterojunction materials exhibit high photocurrent generation and H2 production with visible light, and AQY surpasses 5%. Overall, efficient charge separation owing to the intrinsic electric field of closely related band offsets at the interface of the heterojunction materials enhances the photocatalytic response. The work highlights the importance of fine structural changes in improving the activity of polymeric photocatalytic systems.