Preparation And Application Of Functionalized Cellulose Nanofibers Aerogels

With the rapid development of industrialization,problems such as resource crisis and environmental pollution are intensifying,and the effective use of renewable resources and environmental governance is very important.In recent years,aerogels prepared with CNFs have become a new type of organic pollutant adsorption material because of their unique structural properties.However,CNFs aerogels are mainly formed by hydrogen bond cross-linking,which have poor mechanical properties and severely limits their applications.Moreover,in the practical application process,CNFs aerogels as the adsorbent only achieve the enrichment of pollutants,and can not achieve complete treatment of pollutants.In view of the above problems,aerogels with good mechanical properties were prepared by introducing chemical cross-linking in CNFs,and in-situ synthesis of TiO2 nanoparticles in CNFs aerogels,thereby CNFs aerogels(TiO2-CNFs aerogels)loaded with TiO2 nanoparticles were prepared.The aerogel can not only achieve the adsorption of organic pollutant molecules,but also enhanced catalysis capability of the TiO2 particles,so the adsorbed molecules can be completely degraded,thus achieving high removal efficiency of organic pollutants.Therefore,the composite material has important significance and application prospects for the treatment of organic pollution in water and the atmosphere.The research content of this thesis mainly includes the following two parts:(1)Preparation of CNFs aerogels with good mechanical properties by introducing chemical cross-linking.The aldehyde-functionalized CNFs(COH-CNFs)and the hydrazide-functionalized CNFs(CNFs-DAD)were prepared by different chemical modifications.The hydrazide bond is formed through the reaction of aldehyde group and hydrazide group,whereby the chemical cross-linking is introduced into the CNFs aerogels.It was found that the chemically cross-linked CNFs aerogels exhibited a multi?stage pore structure,in which the size of the mesopores were distributed around 16 nm and the specific surface area of CNFs aerogels was 123.1 m2·g-1,And the lowest density was7.2 mg·cm-3.The aerogels have good mechanical stability and shape recovery characteristics in an aqueous environment.Because of its unique pore structure,large specific surface area and surface electronegativity,CNFs aerogels have a large adsorption capacity for Rhodamine B(RhB),when the concentration of RhB is 200 mg·L-1,the adsorption amount can reach 180 mg·g-1.(2)In-situ growth of TiO2 was achieved in the chemically cross-linked CNFs aerogels.TiO2-CNFs aerogels composites were prepared by a combination of sol-gel method and hydrothermal method.The hydroxyl group,carboxyl group,aldehyde group on the surface of CNFs and the disulfide bond and hydrazide group carried by the grafted 3,3-dithiodipropionate dihydrazide(DAD)molecule provide more action sites for the adsorption of tetrabutyl titanate on the surface of CNFs aerogels,which realizes the immobilization and uniform distribution of TiO2 on the surface of CNFs aerogels.The effects of repeated times of sol-gel process and hydrothermal reaction conditions on the properties of aerogel materials were explored.It was found that amount of the TiO2 particles loading on the surface of CNFs aerogels increased with the increase of repeating times of sol-gel process and TiO2 with perfect anatase structure can be prepared by hydrothermal reaction at 120 0C for 4 hours.The TiO2-CNFs aerogels also exhibit a multi-stage pore structure with pore size distribution of about 35 nm and specific surface area of 330.6 m2·g-1.The TiO2 nanoparticles exist as a spherical shape,the small particles mainly adhere to a single CNFs,and the large particles adhere on the pore wall of CNFs aerogels.C-O-Ti bond is formed between TiO2 and CNFs,so that TiO2 can be stably present on the surface of CNFs aerogels.TiO2-CNFs aerogels have good photocatalytic performance.Within 120 min,the degradation efficiency of TiO2-CNFs aerogels to 10 mg·L-1 RhB is as high as 99%and within 240 min,the degradation efficiency to 200 mg·L-1 RhB is more than 90%.The composites also have good recyclability.The excellent photocatalytic properties of TiO2-CNFs aerogels are mainly due to the synergistic effect of adsorption and photocatalysis.In addition,the possibility of recombination of photogenerated electrons and holes generated by TiO2 is reduced and the catalytic activity of TiO2 is improved due to the presence of C-O-Ti bonds.To sum up,in this paper CNFs aerogels with good mechanical properties and loading TiO2 in situ was prepared to obtain TiO2-CNFs aerogels composites with both excellent adsorption and photocatalytic properties.This functionalization method provides a new strategy for the preparation of CNFs aerogels functional materials,and the research results of this paper provide theoretical basis and technical support for the application of CNFs aerogels functional materials in the treatment of organic pollutants.