Facile in-situ growth of metal–organic framework layer on carboxylated nanocellulose/chitosan aerogel spheres and their high-efficient adsorption and catalytic performance

Abstract

A core–shell hybrid aerogel sphere material was successfully fabricated by a combined assembly strategy of ionic cross-linking and coordination bonding. The MOF-199 crystal shell was in-situ grown on the surface of Cu2+ ions cross-linked carboxylated cellulose nanocrystals (CNCA) and carboxymethyl chitosan (CMCS) hydrogel sphere templates at room temperature for a short time, and the aerogel spheres (MOF-199@CNCA/CMCS) were obtained after freeze-drying treatment. The pH value of 1,3,5-benzenetricarboxylic acid ligand solution is crucial for the high coverage of MOF-199 shell layer on the CNCA/CMCS cores. And CNCA and CMCS plays a cooperative role in forming the stable aerogel core. The changing morphology of MOF-199 with the evolution of {111} crystallographic plane was found by adjusting the concentration of components and reaction time. The nitrogen sorption isotherm and pore size distribution confirmed the mesopores and macropores structure of MOF-199@CNCA/CMCS aerogel spheres. Consequently, the obtained aerogel spheres exhibited an excellent adsorption capacity towards methylene blue (MB) up to 1112.2 mg·g−1. The adsorption equilibrium of MB was suggested as multilayer adsorption based on the Freundlich isotherm model. The carbonization product Cu/CuO/Cu2O@C of hybrid aerogels was proved as a high-efficient catalyst for the reduction of p-nitrophenol(4-NP). The catalytic rate constant can reach 21.23 × 10-3 s−1. And the CuO species plays a dominant role in catalyzing the reduction of 4-NP.