Gamma irradiation produces graphitic carbon nitride with decreased water affinity

Abstract

Absorption of water on surfaces of graphitic carbon nitride (g–C3N4) can be lessened by organic molecules functionalization or post-annealing treatment. In contrast to this knowledge, we show that γ-irradiation (10–400 kGy) of g–C3N4 results in a defective material with decreased water affinity on surface and at bulk alike without those modifications. Irradiated g–C3N4 samples show diminished water content (2.52 wt% to 1.91–0.96 wt%) and decreased crystallinity but slightly increased surface area, including slit-shape pores formation in platy particles. However, their IR spectra and optical bandgap do not change. Despite the radiation-induced increase of N/C, the diminished water content is consistently observed on surfaces by XPS, and at the depth ∼1 μm deeper by EDX. It is found that γ-irradiation generates a higher proportion of pyridinic N which disfavors water adsorption. This is correlated to a decreasing apparent activation energy of water evaporation in a γ-irradiated material compared to a pristine one (29 vs 47 kJ·mol−1). Also, γ-irradiation generates dangling bonds which facilitate bonding/agglomeration between particles such that the access of water to adsorption sites is prohibited. The demonstrated application of γ-irradiation to reduce water wettability, which is chemical-free and easily controllable, encourages further studies to other hydrophilic materials.