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 encapsulation-pyrolysis 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 N 2 atmosphere pyrolysis at 550 °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.