| As the newborn third-generation aerogels,cellulose aerogels not only possess many excellent properties of traditional silica aerogels and polymer-based aerogels(such as high porosity,high specific surface area and low-sonic velocity),but also have some unique characteristics like biocompatibility,biodegradability and hydrophilicity.As a result,cellulose aerogels have broad application prospects in the fields of biological medicine,adsorbents and catalysts.Actually,the excellent structural features and abundant surface oxygen-containing groups of cellulose aerogels make them suitable candidates as green matrices to develop multi-functional nanocomposites.Therefore,it is meaningful to use proper physical-chemical modification and adulteration techniques to extend application domains of cellulose aerogels.The present paper utilized waste and cheap agricultural and forest biomass as feedstock.Two approaches(i.e.,"chemical pretreatment-high-frequency pulsed ultrasonic treatment-solvent replacement—freeze dying" and "dissolution—freezing and thawing—regeneration-freeze drying")were employed to prepare nanofibrillated cellulose(NFC)aerogels and regenerated cellulose aerogels,respectively.For the purpose of extending applications of cellulose aerogels in water environment remediation,antibacterial materials and electromagnetic interference shielding.various facile and cost-effective physicochemical processes were developed to create cellulose aerogels-based nanocomposites.The main research topics of the present paper can be summarized as follows:(1)Ultra-light NFC aerogels were prepared using waste coconut shell as raw material and via a facile preparation process(including chemical pretreatment,high-frequency pulsed ultrasonic treatment,solvent replacement and freeze drying).The bulk density of the aerogels is as loW as 0.84 mg·cm-3.After the hydrophobic Lodification by methyltrichlorosilane via a chemical vapor deposition method,the resultant aerogels have a high water contact angle of 139°,can adsorb 296-669 times of organic liquids,and show favorable oil-water separation effects.(2)Lightweight and high-strength regenerated cellulose aerogels were prepared using bamboo fiber as raw material and via a mild preparation method(including cellulose dissolution in NaOH/polyethylene glycol solution,freezing-thawing,regeneration and freeze drying).The resultant regenerated cellulose aerogels have a strong resistance to compressive deformation.Young's modulus,yield stress and toughness of the aerogels can reach 1.85 MPa,83.57 kPa and 52.34 kJ·m-3,respectively.In addition,after the pyrolysis of regenerated cellulose aerogels,the resultant carbon aerogels not only kept the original cross-linked three-dimensional network structure,but also acquired new functions(such as hydrophobicity,electrical conductivity and flame retardance).(3)A simple chemical co-precipitation method was used to insert superparamagnetic and well-dispersed y-Fe2O3 nanoparticles into the three-dimensional network structure of cellulose aerogels.The diameter of nanoparticles,pore characteristic parameters,magnetic property and mechanical property could be flexibly controlled by adjusting the concentration of initial reactants.The eco-friendly ?-Fe2O3@cellulose aerogels nanocomposites was used to treat water containing Cr(VI).The unique structural characteristics of cellulose aerogels(e.g.,large specific surface area and high porosity)contribute to the improvement of Cr(VI)adsorption and nanoparticles dispersion effects.The nanocomposites have the maximum Cr(VI)adsorption capacity of 10.2 mg·g-1.Moreover.the nanocomposites show a strong magnetic responsiveness,which is beneficial for the subsequent recycle process after the adsorption.(4)Silver nitrate was chosen as an oxidizing agent to induce the oxidation polymerization of pyrrole molecules on the surface of cellulose aerogels.This strategy generated polypyrrole/nano-silver/cellulose aerogels nanocomposites,and both the polypyrrole and nano-silver compositions display good dispersion and interface bonding in the aerogels.Furthermore,the antibacterial activity of the hybrids against Escherichia coli(Gram-negative),Staphylococcus aureus(Gram-positive)and Listeria monocytogenes(intracellular bacteria)was qualitatively and quantitatively studied by parallel streak method and determination of minimal inhibitory concentration,respectively.The results demonstrated a favorable antibacterial activity of the nanocomposites.(5)An easily-operated and feasible method was used to synthesize anatase titania collosol at room temperature.After impregnation and freeze drying processes,anatase titania/cellulose aerogels nanocomposites were prepared.The nanocomposites present a high photocatalvtic activity for indigo carmine dye degradation under ultraviolet light.(6)An ultrasonic method was used to disperse graphene oxide,and the resultant dispersion liquid of graphene oxide was mixed with a cellulose solution.After regeneration and freeze drying,the graphene oxide/cellulose aerogels composites were obtained.The experimental results indicate that the existence of cellulose effectively relieved agglomeration of graphene oxide in the high-concentration NaOH solution and improved the stability of mixed system.Also,the introduction of graphene oxide induced a two-dimensional assemble of cellulose fibers,leading to the formation of uniform sheet structure.The graphene oxide composition in the composites were reduced by L-ascorbic acid for enhancing the electrical conductivity;after the following freeze drying,the resultant reduced graphite oxide/cellulose aerogels were pyrolyzed under nitrogen protection for further improving the electrical conductivity.The end-products(graphene nanosheets/carbon aerogels composites)exhibit an excellent electromagnetic interference shielding performance,and the corresponding SEtotal value reached 58.4 dB.(7)An easy low-cost process(including pyrolysis and vapor phase polymerization)was used to prepare carbon aerogels decorated with a-Fe2O3 and polypyrrole.For the investigation of enhancement effects of ?-Fe2O3 and polypyrrole for electromagnetic interference shielding property,we tested and compared the electromagnetic interference shielding property of the nanocomposites,?-Fe2O3/carbon aerogels,polypyrrole,acid-treated carbon aerogels.After computation,their SEtotal values are 39.4 dB,29.3 dB,13.6 dB and 19.3 dB,respectively,which reveals that the presence of ?-Fe2O3 and polypyrrole compositions contributed to the enhancement of electromagnetic interference shielding effect.Besides,an absorption-dominant shielding mechanism was demonstrated,which is beneficial to alleviate secondary radiation.This feature is considered as a more attractive alternative for the fabrication of electromagnetic radiation protection products. |
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