Encapsulation of nano-sized ZIF-67 derived Co-NC on Au-loaded halloysite as composite catalyst for superior cooperative reduction of nitroaromatic pollutants

The utilization of natural clay minerals for synthesizing nano-sized metal-organic frameworks (MOFs) supported materials offers great advantages for rational design of innovative catalysts, which promotes the low-cost and large-scale environmental remediation applications. This work reported a facile and scalable encapsulationpyrolysis strategy to prepare novel Au-HNTs@Co-NC core-shell catalyst for catalytic reduction of nitroaromatic pollutants. The HNTs were modified with aminosilane on the external surface for effectively anchoring well-dispersed and ultrasmall Au NPs. Uniform nano-sized ZIF-67 crystals controllably embraced the Au-HNTs via in-situ growth induced by electrostatic adsorption. The N2 atmosphere pyrolysis at 550 degrees C resulted in Co NPs embedded into N-doped carbon substrates, and transformed ZIF-67 crystals into Co-NC layers for preferable encapsulation and stabilization of Au NPs. The as-prepared Au-HNTs@Co-NC-550 catalyst manifested splendid catalytic performance for p-nitrophenol reduction, and achieved the reaction rate constant and TOF value estimated as 2.025 min-1 and 49.25 min-1, which significantly exceeded the behaviors of as-prepared control materials. Moreover, the catalyst also displayed excellent catalytic capability toward the reduction of nitroanilines and homologues and isomers of p-nitrophenol, indicative of its decent general applicability. After 8 cycles of reactions, the catalyst still retained brilliant reusability and structural stability with good magnetic property for expedient separation. The advantageous hollow core-shell structure combining HNTs and ZIF-67 derivatives enhanced the reactant diffusion and transfer. The N doping and electronegativity difference between Co and Au aroused higher electron uptake and facilitated electron transport during the reduction process. Meanwhile, the Co-H and Au-H bonds formed the strong synergistic effect for superior cooperative catalytic performance of the catalyst.