Preparation Of Microfibrillated Cellulose Macroporous Material And Its Adsorption Performance For Dyes And Oil Contaminations

The nanocellulose-based porous materials have low density and high porosity,incorporates the advantages of cellulose,such as renewable,biodegradable,good biocompatibility and low cost.Become a new generation of materials following minerals and petroleum-based polymers.As a natural polysaccharide-based material,nanocellulose-based porous materials are widely used in the fields of catalyst carriers,thermal insulation,energy storage,electromagnetic interference,biomedicine,and adsorbents.Among them,the use of abundant cellulose to adsorb and separate dyes and oil contaminations in wastewater can effectively solve the problem of wastewater treatment,and is of great significance to the utilization of natural resources and environmental restoration.In this study,microfibrillated cellulose(MFC)as the raw material for structural design to prepare MFC-based functional materials that can effectively adsorb dyes and oil contaminations,provide a possible way for the high-value utilization of nanocellulose.(1)Using MFC as raw material,aldehyde group-modified MFC dispersion(Ox-MFC)was obtained by periodate(NaIO₄)oxidation,then through the aldol condensation reaction between the aldehyde group and the hydroxyl group at-12°C,the freeze-induced chemical crosslinking is used to construct a"three-dimensional network"to realize the gelation process,and the MFC gel is prepared.Subsequently,the secondary crosslinking assembly was achieved by continuing to soak the MFC gel in NaIO₄solution,and the material shrinks during the process.The effects of NaIO₄concentration and soaking time on the shrinkage of MFC gels during this process were analyzed,and the effects of the shrinkage process on the microstructure and mechanical properties were discussed.Finally,the MFC-based macroporous material(MFC-x)with tunable pores and significantly enhanced mechanical strength was successfully prepared after drying by ethanol solvent exchange.In addition,the abundant aldehyde groups on its surface also provide a basis for its later chemical modification.(2)Based on the MFC macroporous material,modified with polyethyleneimine(PEI),amino-functionalized microfibrillated cellulose macroporous material(PEI-MFC)with excellent mechanical performance was prepared,the corresponding structural characterization was carried out,and its adsorption performance for methyl orange(MO)was analyzed.The maximum equilibrium adsorption capacity of PEI-MFC for MO can reach 500 mg·g^-1,showing excellent adsorption capacity,the adsorption isotherms and kinetics obtained according to the experimental data conform to the Langmuir isotherm model and the second-order kinetic model,respectively.And the prepared PEI-MFC has good reusability,it still maintains 95%of the original adsorption capacity after repeated use for 6 times.In addition,the adsorbent has outstanding advantages in the dynamic adsorption process and can efficiently treat dye solutions.Therefore,PEI-MFC is expected to be applied to the treatment of non-ferrous wastewater,as a new type of adsorption material for environmental restoration.(3)Based on MFC macroporous material,modified with hexadecylamine(HDA)to hydrophobization.The Schiff base reaction between amino group and aldehyde group introduces hexadecyl on the surface of the material to obtain hydrophobized microfibrillated cellulose macroporous material(HDA-MFC),and the corresponding structural characterizations were carried out.The HDA-MFC with excellent performance,density less than 29.8 mg/cm~3,porosity more than 98%could be obtained,the contact angle can reach 143°,which could absorb various oils and organic solvents.Furthermore,the sorption capacities reached up to 32 times of its own weight.The HDA-MFC also presented with good oil storage ability and excellent recyclability.The hollow spherical HDA-MFC,oil could quickly and efficiently be transported into the“spherical cavity”,thus,its actual recycling capacity for oil can exceed its adsorption capacity.So our work lays the foundation for developing sustainable sorbents for oil and organic pollutant removal applications.