Assessing copolymerisation and exfoliation synergistic effects of graphitic carbon nitride in simulated sunlight photocatalysis

[Display omitted] •Carbon nitride (gCN) was synthesised with different barbituric acid (BA) contents.•gCN photocatalytic response was improved by merging copolymerisation and exfoliation.•More N-vacancies and surface defects increased charge transfer and light absorption.•Positive-shifted VB potential in gCNex-1.6BA material allows a direct RhB oxidation.•BA reduced the bandgap and created mid-gap states for enhanced production of ROS. Graphitic carbon nitride (gCN) photocatalysts were synthesised by copolymerisation of dicyandiamide precursor and different barbituric acid (BA) shares, followed by thermal exfoliation. The morphological, textural, structural, photo- and electrochemical properties of the obtained materials were studied to identify the effect of BA on the material exfoliation. Moreover, its influence on photocatalytic efficiency was investigated by the degradation of a model contaminant (rhodamine B – RhB) under simulated solar irradiation. The results indicated that incorporating carbonyl-based networks of BA into the aromatic moieties of the gCN structure contributed to a higher degree of exfoliation. Furthermore, this endowed the copolymerised materials with a larger surface area since there was a more disordered nanosheet formation and increased porosity. The best-performing catalyst was the 1.6 wt% BA-modified material, owing to the higher density of nitrogen vacancies detected in the exfoliated gCN material. This density of vacancies yielded a larger quantity of active sites at gCN sheet edges, a more rapid electronic transfer and inhibited photo-induced electron/hole pairs recombination. The newly integrated electronic properties, induced by the copolymerisation synthesis with 1.6 wt% of BA, improved the photocatalytic degradation of the RhB by direct oxidation with photogenerated positive holes and more abundant oxy-radicals. The presence of the BA copolymer during gCN synthesis also permitted, after thermal exfoliation, exceptionally lower energy mid-gap positions to occur, which is highly beneficial for an accelerated oxidation mechanism.