Preparation And Properties Of Functionalized Cellulose Nanocrystal/MOF-199 Composite System

Metal-organic framework(MOF)materials are a kind of porous crystalline materials with periodic network structure,which are self-assembled from organic ligands connected by transition metal nodes.It has excellent properties such as high specific surface area,abundant pore structure,strong open-site activity,and flexible controllability.Therefore,MOF materials show application prospects in adsorption and separation,sensing electrodes,catalysis,antibacterial,and supercapacitors.However,because MOFs is synthesized in powder form,it is difficult to process and inconvenient to use,which limits the application range.Therefore,finding a suitable carrier to prepare composite materials is an effective way to improve the feasibility of practical application.Cellulose nanocrystals(CNCs)is green and environmentally friendly nanomaterials exfoliated from cellulose,which has the advantages of good biocompatibility,good mechanical properties,and surface group modifiability.Through the carboxylation of hydroxyl groups on the surface of CNCs,the loading of target molecules can be further achieved.CNCs aerogels have been widely used in the loading and preparation of functional materials.In this paper,this dissertation was aimed at the application of a copper-containing MOF(MOF-199)material through an assembly strategy of ionic crosslinking(Cu²⁺with carboxyl)and coordinate bonding(Cu²⁺with trimesic acid organic ligand),composite aerogels of MOF-199 and carboxylated cellulose nanocrystals(CNC-CA)were prepared.The aerogel was a spherical material with a core-shell structure,the outer shell was a dense MOF-199 crystal layer,and the inner core was a three-dimensional network structure formed by CNC-CA and carboxymethyl chitosan(CMCS).The coexistence of CNC-CA and CMCS acted synergistically to form a stable aerogel internal structure,while the p H of the trimesic acid ligand solution determined the coverage of the MOF-199 shell on the CNC-CA/CMCS core.By adjusting the component concentrations and reaction time,the morphology of MOF-199 was found to change with the evolution of the{111}crystal plane.The N₂ adsorption isotherm and pore size distribution confirmed the mesoporous and macroporous structures of the MOF-199@CNC-CA/CMCS aerogel spheres,which also enabled the obtained aerogel spheres to exhibit excellent adsorption capacity for methylene blue(MB).The kinetic adsorption performance data up to 1112.2 mg g^-1 indicated that the adsorption process of MB molecules on aerogels was controlled by the interaction of physisorption and chemisorption.Based on the Freundlich isotherm model,the adsorption equilibrium of MB was identified as multilayer adsorption.Porous carbon materials doped with Cu,Cu O and Cu₂O were obtained after high temperature carbonization of MOF-199@CNC-CA/CMCS aerogel.This product played an efficient catalytic role in the reduction of nitrophenol(4-NP).Among them,CuO species played a major role in catalyzing the reduction of 4-NP.