Enhanced photocatalytic organic pollutant degradation and H2 evolution reaction over carbon nitride nanosheets: N defects abundant materials

Post thermal treatment of bulk graphitic carbon nitride (g-C3N4) by ammonia gas acts as a significant structure regulation approach, while pure ammonia-assisted g-C3N4 synthesis from precursors like melamine is rarely investigated. Here we prove the synthesis of N-defects abundant carbon nitride nanosheets (ACN) through a one-pot thermal polymerization of melamine in pure ammonia gas, for photocatalytic organic pollutant removal in water and H2 evolution applications. Compared to bulk g-C3N4 (BCN), ACN-550 (ACN prepared at 550 °C) exhibited thin-layered porous morphology with higher surface area and abundant N defects, resulting in wider distribution of active sites. Moreover, the abundant N defects in the heptazine heterocycle structure could change the electronic structure of g-C3N4, leading to more efficient transport of photogenerated charge carriers and enhanced photoreduction potential, which gives rise to notable improvement activities in photocatalytic reaction. With superoxide ion radical and photoinduced holes as the predominant reactive species, ACN-550 realized efficient photocatalytic bisphenol A (BPA) degradation, which is 1.6- and 4.7-fold high over commercial TiO2 (P25) and BCN, respectively. ACN-550 exhibited excellent reusability and stability in five consecutive photocatalytic BPA degradation tests. In photo-reductive H2 production system by ACN-550, 761.8 ± 4.3 μmol/h/g H2 was produced, which was 11.6-fold as high as that by BCN. [Display omitted] •Thermal polymerization of melamine in pure ammonia gas results in N-defects abundant carbon nitride nanosheets.•Higher pyrolysis temperature (450–550 °C) promotes the formation of N-defect rich porous nanosheet structure.•The relationship between structural parameters and pollutant photodegradation was revealed.•Superoxide ion radical (O2−) and holes (h+) were the predominant reactive species in the photodegradation.•N-defects abundant carbon nitride nanosheets show superior photocatalytic activity for H2 production.