Preparation,Characterization And Performance Of Cellulose-Based Aerogels Doped With Metal Ions

Cellulose-based aerogels possess not only the advantages of cellulose that is renewable,non-toxic,environmentally friendly,biodegradable and easy to be functionalized,but also unique properties of aerogels,such as low density,high porosity,low thermal conductivity and high specific surface area.Therefore,cellulose-based aerogels have great potential for applications such as thermal insulation,filtration,oil-water separation,catalysis and medicine.However,insolubility and functionality of cellulose hinder application of cellulose-based aerogels.To extend the application of cellulose-based aerogels,the primary content and conclusion of this work can be divided into three parts as follows.Firstly,cellulose aerogels with low density(low to 44.99 kg/m3)and high porosity(up to 97.01%)were obtained through freeze-drying with NaOH/urea/H2O and alcohol as solvent and coagulator,respectively.The cellulose aerogels were macroporous consisting of a network of interconnected uniform cellulose fibers.And the diameter of the fibers was about 20 μm.And the formation of cellulose hydrogel was as follows.Because the hydrogen bonding between cellulose molecules was destroyed by sodium hydroxide,cellulose molecules were dispersed.The cellulose molecules were prevented from assembling because they were surrounded by urea.Due to the addition of ethyl alcohol,the concentration of sodium hydroxide was reduced and the encapsulation of urea was damaged.And a stable network of interconnected cellulose fibers was formed at last.Secondly,the method for preparation of metal-ion-doped carboxymethyl cellulose aerogels,the doping mechanism,and the effect of metal-ion doping on structure and properties of the aerogels were investigated.The comparison of Cu2+-doped carboxymethyl cellulose aerogels obtained by the dialysis method and the ion-release method showed that the changes in the molecular structure and the crystal structure were the same,the coordination between Cu2+ and carboxymethyl cellulose was unidentate coordination,the crystallinity of carboxymethyl cellulose decreased significantly,and the intensity of characteristic peaks decreased or even disappeared.Compared with the dialysis method,the advantage of the ion-release method was that bulk carboxymethyl cellulose hydrogels and aerogels with homogeneous structure could be prepared.In the Al3+-doped carboxymethyl cellulose aerogels,Al3+ distributed in the aerogels eventually,and the coordination between Al3+ and carboxymethyl cellulose was bidentate bridging coordination.What’s more,the doping behaviors of Al3+ reduced the stability of the carboxymethyl cellulose aerogels while giving the aerogels good load-bearing capacity,flame retardancy and adsorption capacity.Finally,to explore the hydrothermal treatment process of cellulose aerogels,the influence of reaction time and temperature on formation and characteristics of the final products was also investigated.When the reaction time was long enough and the reaction temperature was high enough,the cellulose aerogels began to be carbonized.At the same time,the crystalline structure also began to be destroyed,the pore structure became more complicated and microspheres appeared.When the reaction time was 6 h,the aerogels began to be carbonized at 220℃.At the same time,the higher the reaction temperature was,the greater the carbonized degree of the aerogels would be.When the reaction temperature was 220℃,the longer the reaction time was,the greater the carbonized degree of the aerogels would be and the more complete the microspheres would be.