Ultrasmall Bismuth Nanoparticles Supported Over Nitrogen-Rich Porous Triazine-Piperazine Polymer for Efficient Catalytic Reduction

The development of inexpensive and reusable nanocatalysts to convert the hazardous pollutant 4-nitrophenol (4-NP) into a valuable platform chemical 4-aminophenol (4-AP) is quite demanding due to environmental and public health concerns. Herein, we report a facile strategy for the preparation of supported Bi nanoparticles (NPs) over the surfaces of nitrogen-rich porous covalent triazine-piperazine-3D nanoflowers (BiNPs@3D-NCTP). SEM and TEM image analysis suggested 3D-flower-like morphology of the composite consisting of the self-assembly of interweaving and the slight bending of the nanoflakes. The powder X-ray diffraction (PXRD) analysis also confirmed the loading of Bi NPs. N₂ sorption analysis suggested BET surface areas of 663 and 364 m² g^-1 for the 3D-NCTP and BiNPs@3D-NCTP materials, respectively. The large surface area, bimodal pores and 3D nanoflower architecture enable uniform loading of Bi nanoparticles, while its nitrogen-rich functionality stabilizes and acts as a capping agent restricting further nanoparticle expansion. BiNPs@3D-NCTP showed a 99.85 % conversion for the 4-NP to 4-AP within four minutes. The normalized rate constant of 38.3 min^-1 mg^-1 of BiNPs@3D-NCTP catalyst for the reduction of 4-NP suggested its superior catalytic efficiency. Nitrogen-rich functionality activates the catalytic site to accelerate the reaction, while bimodal pores can promote the diffusion of reactant molecules. After five catalytic cycles, the nanocatalyst showed high chemical stability and negligible activity loss.