Preparation Of Cellulose Nanofibrill Aerogel And Its Adsorption Capacity For CO₂

As a new generation of biomass materials,cellulose aerogel shows excellent characteristics.This bioaerogel not only has unique advantages including biocompatibility,biodegradability,rich raw material and low price,but also possess excellent features of traditional aerogels,such as high porosity,high specific surface area,light weight and low dielectric constant.It meets the requirements of new gas adsorbent materials under the sustainable development social environment.In this paper,cellulose nanofibril?CNF?was obtained by chemical mechanical method which eucalyptus pulp was chosen as a raw material,and then the spherical CNF aerogels with light weight,high porosity and high specific surface area was prepared by ultrasonic freezing,suspension titration,salt solution gelation,tert-butyl alcohol replacement and freeze-drying methods.And then the amino-modified spherical CNF aerogels was successfully fabricated by freeze-drying of spherical CNF hydrogels into which the amine group has been successfully introduced via C-O-Si bonds between CNF and AEAPMDS.The new material retains the three-dimensional network space structure,has high adsorption capacity of carbon dioxide and better reproducible performance.The main conclusions of this paper were as follows:?1?The CNF prepared by the chemical combining mechanical method was in the shape of a long line and had a milky white color.The diameter of the cellulose nanofibril was about 20 nm and the length was in the micron range.Both CNF and spherical CNF aerogels possess cellulose I structure and infrared characteristic absorption peaks of nanocellulose,but the thermal degradation temperature of spherical CNF aerogel were higher than those of CNF.T_max of spherical CNF aerogels was 305?.?2?The density,BET specific surface area,pore size,porosity,pore volume,and micro-morphology of spherical CNF aerogels were related to the mass fraction of CNF.Its density and BET specific surface area decreased with the increase of CNF mass fraction while its pore size first decreased and then increased with the increase of CNF mass fraction.The internal space structure of spherical CNF aerogels was a three-dimensional network structure formed by cellulose nanofibers and cellulose sheets.With the increase of the CNF mass fraction,the number of thin sheets increased and cellulose nanofibers decreased.When the CNF mass fraction of spherical CNF aerogel was 2wt%,the spherical CNF aerogel had the best performance,and its density was 0.0279g/cm³,the porosity could reach 98.25%as the pore diameter was less than20nm.It was a kind of lightweight and high porosity mesoporous materials.?3?The reasonable process for preparation of amino-modified spherical CNF aerogel was when the liquid phase reaction time was10h,the reaction temperature at 90°C and the adding amount of 3-?2-aminoethylamino?propylmethyldimethoxysilane?AEAPMDS?was 12wt%.At the same time the nitrogen mass fraction of the amino-modified spherical CNF aerogel obtained could reach7.233wt%.The amino-modified spherical CNF aerogel retained the crystal structure of cellulose type I,the infrared characteristic absorption peak of cellulose,and the spatial network structure formed by cellulose nanofibers and cellulose sheets.What's more,the FT-IR indicated the CNF aerogel connected with amination agent by C-O-Si bond.The amino-modified spherical CNF aerogel had a porosity of more than 96%,an average pore diameter of less than 20 nm,and a density of less than 0.05 g/cm³.Therefore,the amino-modified spherical CNF aerogel was still a highly porous ultralight material.?4?The nitrogen mass fraction of the amino-modified spherical CNF aerogels had an important influence on its physical and chemical properties.The internal three-dimensional pore structure of the amino-modified spherical CNF aerogels was closely related to the nitrogen mass fraction.With the increase of nitrogen mass fraction,the pore structure formed by the nanocellulose decreased whilethe structure of cellulose sheets increased.Moreoverthe pores on the thin sheets,the porosity and the BET specific surface area of the amino-modified spherical CNF aerogels gradually decreased with the increase of the nitrogen mass fraction as the pore diameter first increased and then decreased.When the nitrogen mass fraction gradually increased,the density of amino-modified spherical CNF aerogels gradually increased,the degree of crystallinity decreased,and the degree of ordering deteriorated.The compressive strength of the amino-modified spherical CNF aerogels gradually increased with the nitrogen mass fraction,when the nitrogen mass fraction was 7.233wt%,the compressive strength was 4 times that of the unmodified CNF aerogels,which reached 0.46MPa.With the increase of the nitrogen mass fraction,the temperature of the maximum weight loss rate(T_max)became larger and larger,range from 305°C to 348°C.?5?The amino-modified spherical CNF aerogels had high CO₂ adsorption performance.The CO₂ adsorption capacity measured by the static method could reach 2.08mmol/g,and the CO₂adsorption capacity measured by the physical adsorption instrument could reach 1.54mmol/g.In addition,the amino-modified spheroidal CNF aerogels had good adsorption thermal stability and the CO₂ adsorption capacity of amino-modified spheroidal CNF aerogels still could reach1.50mmol/g after ten adsorption/desorption cycles.With the increase of nitrogen mass fraction,the CO₂ adsorption capacity of the amino-modified spherical CNF aerogels gradually increased.