Preparation Of MOFs @ Viscose Spunlaced Nonwoven Materials And Study On The Adsorption Properties For Organic Dyestuff

So far,water pollution caused by industrial wastewater containing organic dyes has been regarded as an urgent environmental pollution problem and poses the serious threat to human health and the environment.Among the various methods for dye wastewater treatment,the adsorption method has raised wide attention due to the simple operation,high adsorption capacity and fast removal rate.Metal organic framework materials（MOFs）consisted of organic ligands and desired metal clusters are a new type of adsorbent materials,and have the advantages of large specific surface area,adjustable pore size,controllable structure,and high affinity for various organic dyes.MOFs can be used as an efficient adsorbent in the field of dye wastewater treatment.However,MOFs with the powder form are difficult to be recycled after use and would cause secondary pollution,thus they can be compounded with the continuous flexible carrier materials as adsorbent materials to solve the above problems.Viscose spunlaced nonwoven material（VSN）with good moisture absorption,and mechanical properties is the sulfonated modified cellulose,and has the raw material of VSN is easily available,and one of the raw materials for the preparation of carbon fibers.Moreover,the macromolecular chain of viscose fibers includes some chemical active groups such as hydroxyl and sulfonic acid groups.Therefore,VSN is suitable for being used as a continuous carrier of MOFs.In this paper,two kinds of MOFs@VSN porous carbon materials were prepared vis in situ solvothermal method by use of VSN as the substrate material.The functional particles of NH₂-MOF-199 and NH₂-MIL-101（Fe）were grown on its surface in one-step situ and calcinated at high temperature respectively.The morphology,structure and organic dye adsorption performance of these two kinds of MOFs@VSN porous carbon materials are analyzed and compared.The specific results of the study are as follows:VSN was first carboxylated in dilute acid solution to expose the reactive groups on its surface.Then,NH₂-MOF-199 was grown in one-step situ on the surface of VSN by solvothermal synthesis by used of copper nitrate hydrate（Cu（NO₃）₂·x H₂O）as the metal ion source,1,3,5-benzenetricarboxylic acid and 2-aminoterephthalic acid as organic ligands,and polyvinylpyrrolidone（PVP）as the surface surfactant to obtain NH₂-MOF-199@VSN composite spunlaced material.After that,NH₂-MOF-199@VSN was calcined at different temperatures to prepare NH₂-MOF-199@VSN composite spunlaced porous carbon material（NH₂-MOF-199@VSNC）.By characterization and analysis,the results showed that when the calcination temperature was no more than 250℃,NH₂-MOF-199with a regular octahedral structure was uniformly immobilized on the surface of VSN and the crystalline structure was perfect.The morphologies and structures of both NH₂-MOF-199 and VSN in the composite spunlaced carbon material were not changed.Compared with the NH₂-MOF-199@VSN without being calcinated,NH₂-MOF-199@VSNC calcinated at different temperatures could adsorbed the acidic Congo red（CR）and acid orange II（AOⅡ）dyes and the basic methylene blue（MB）and rhodamine B（Rh B）dyes to different degrees when the calcination temperature was 200℃.When the adsorption water bath temperature was 30℃and the p H was 7,the adsorption efficiency of NH₂-MOF-199@VSNC for MB was the best.At this time,the adsorption equilibrium was about 120 min,and the adsorption efficiency was 98.42%.After being used five cycles,the adsorption efficiency of NH₂-MOF-199@VSNC for MB could maintained at about65.76%,and had kept good structural stability.After being first used on the MB adsorption,the tensile strength of NH₂-MOF-199@VSNC decreased.Subsequently,NH₂-MIL-101（Fe）were grown in one-step situ on the surface of carboxylated VSN vis solvothermal synthesis by use of iron nitrate ninhydride（Fe（NO₃）₃·9H₂O）as the metal ion source,2-aminoterephthalic acid as the organic ligand and PVP as the surfactant to obtain NH₂-MIL-101（Fe）@VSN composite spunlaced material.Then NH₂-MIL-101（Fe）@VSNC composite spunlaced carbon material was prepared by high-temperature calcination at different temperatures.After testing and analysis,the results showed that NH₂-MIL-101（Fe）with regular spindle polyhedron structure could be uniformly fixed on the surface of VSN,and the crystalline structure was perfect.After high-temperature calcination,the morphologies and structures of the NH₂-MIL-101（Fe）and VSN in the composite spunlaced carbon material were not destroyed.When the calcination temperature was 300℃,NH₂-MIL-101（Fe）@VSNC could adsorb CR,AOⅡ,MB and Rh B.Especially,NH₂-MIL-101（Fe）@VSNC had the highest adsorption efficiency for MB.At the adsorption water bath temperature was 30℃and p H was 9,the adsorption equilibrium time of NH₂-MIL-101（Fe）@VSNC for MB was about 60 min,and the adsorption efficiency could reach 98.34%.After being used five cycles,the adsorption efficiency of NH₂-MIL-101（Fe）@VSNC for MB could reach86.34%,and presented good long-term stability and recyclability.After being first used on the MB adsorption,the tensile strength of NH₂-MIL-101（Fe）@VSNC slightly reduced.Finally,the adsorption thermodynamics and adsorption kinetics of NH₂-MOF-199@VSNC and NH₂-MIL-101（Fe）@VSNC for MB were investigated.The results showed that the MB adsorption process of these two composite spunlaced porous materials was a heat-absorbing,entropy-increasing and spontaneous process.The increasing of the adsorption temperature was favorable for the adsorption process.Compared with the quasi-first-order adsorption kinetic model,the MB adsorption processes of two materials were more suitable to be described by the quasi-second-order adsorption kinetic model,indicating that the MB adsorption processes of two materials were dominated by chemical adsorption.In addition,the adsorption rate constant of both quasi-first-order and quasi-second-order kinetics of NH₂-MIL-101（Fe）@VSNC were higher than those of NH₂-MOF-199@VSNC during the adsorption process,indicating that the MB adsorption rate of NH₂-MIL-101（Fe）@VSNC was faster during the adsorption process.In conclusion,compared with NH₂-MOF-199@VSNC,the MB adsorption equilibrium time of NH₂-MIL-101（Fe）@VSNC is shorter and the recycling performances are higher.Thus,NH₂-MIL-101（Fe）@VSNC has better adsorption performance.