Developing Efficient g-C3N4 structures Based on Hexagonal Rosette-like Assemblies of Cyanuric Acid-Melamine Host-Guest Molecular Adducts as the Precursor for the Environmental Applications

Abstract

First, the hexagonal rosettes of g-C3N4 were simply fabricated via controlled solid-state polymerization of three-dimensional hexagonal rosettes of the cyanuric acid-melamine adduct (CM complex) at 500 °C. These hexagonal rosettes of g-C3N4 showed an amorphous nature with an extremely high surface area of around 408 m2 g-1. Also, the as-obtained catalyst demonstrated remarkable photocatalytic activity in hydrogen production of 1285 µmol g-1 h-1 and hydrogen peroxide production of 150 µmol g-1 h-1. Moreover, these nano-rosettes exhibited a superb photocatalytic activity over the degradation of tetracycline (over 60%) and rhodamine B (100%) under visible light irradiation just for 15 min. They also could maintain their stability during the reaction keeping over 98% of their original degradation even in 5 cycles. Second, Introducing the nitrogen vacancies in the structure and their respective effects on the optoelectronic features of the catalysts were thoroughly investigated by different characterizations. The optimized photocatalyst sample showed a greatly improved H2O2 production rate of 200 µmol g-1 h-1 under visible light irradiation, with acceptable reusability. Finally, a new way for designing and fabrication of the robust graphitic carbon nitride (g-C3N4) structures by incorporating the earth-abundant elements in the cyanuric acid-melamine supramolecular precursor was presented. Potassium phosphate monobasic (KH2PO4) has been introduced as an unprecedented material for the preparation of co-doped g-C3N4 structures through the simultaneous provision of K and P elements. Adding KH2PO4 to the suspension of the CM complex liberated K+, H2PO4- species in the reaction medium. These ions stabilized the CM complex structure by coordinating the K+ in its hexagonal pores through metal ion-ligand interactions along with the formation of hydrogen bonds between H2PO4- species and dangling bonds on the edge sites of CM supramolecular sheets. The resulting reinforced supramolecular structure (KP-CM complex) showed a unique skeleton without distinguishable intrinsic alterations in the CM complex structure. This modified precursor, accordingly, directs the polycondensation process to the formation of K and P co-doped g-C3N4 structures with a distinct coral-like morphology (KP-CN). Employing the KP-CM complex as the precursor not only modified the optoelectronic behavior of the obtained photocatalysts via the synergistic effect of the co-doping process, but it could also be beneficial in terms of economic considerations by boosting the catalyst synthesis yield. The finally obtained g-C3N4 showed a remarkable H2O2 production rate of 216 µmol L-1h-1 and an enhanced catalyst synthesis yield of 11% compared to those of 137 µmol L-1h-1 and 5%, for the pristine sample, respectively. It also exhibited a superb photocatalytic antibacterial performance in E. coli disinfection.