Nanosheet thickness control of nitrogen-doped polyimide/ammonium phosphotungstate composite for photocatalytic mineralization of imidacloprid

A series of polyimide/ammonium phosphotungstate composite photocatalysts were prepared by varying the the amine monomers, including melamine (MAPIPW), melem (MEPIPW), and carbon nitride (CNPIPW). As the heterocycle in these molecules gets larger, the nano-layer thickness reduces progressively. This results in an increased specific surface area for those photocatalysts possessing thin layers. For instance, the specific surface areas recorded for MAPIPW, MEPIPW and CNPIPW are 8.1863, 51.3379, and 142.6756 m2/g respectively. Thanks to their high surface areas, these composites exhibited improved substrate adsorption and demonstrated significant enhancement in imidacloprid degradation rates increasing to 70.06%, 76.39%, and 71.39% for MAPIPW, MEPIPW, and CNPIPW respectively. MEPIPW exhibited the highest degradation efficiency due to its superior physical adsorption, besides exhibiting excellent photovoltaic properties. An intricate POM-π interaction exists between polyimide and the Keggin structure of ammonium phosphotungstate, extending ligand conjugation to this framework so as to disperse electrons across the hybrid material's backbone. Nonetheless, this interaction may be weakened with reduced nano-sheet thickness, impacting composite photon absorption ability. Further enhancing photocatalysis was possible via nitrogen doping using urea, resulting in degradation rates of 93.69%, 95.13%, and 91.39%, for MAPIPW-20%U, MEPIPW-20%U and CNPIPW-20%U respectively.