| A large amount of waste cotton fabrics can be produced each year,of which about 90%cannot be used effectively.In order to realize the goal of"carbon emission peak and carbon neutrality",China should develop recycling economy,and promote the high-value development of waste textiles and efficient utilization.The preparation of waste cotton fabric into cellulose-based aerogel not only conforms to the green development,but also can broaden its application fields and increase added value.However,cellulose indicates some problems,such as poor adsorption capacity,high crystallinity,and processing difficulties,which limit the functional application of cellulose-based materials.To solve the above problems,the preparation mehtod of nanocellulose from cotton fabrics was first optimized here and carboxylated cellulose aerogels（CCAs）were further obtained.Then,the chitosan/carboxylated cellulose composite aerogel（CS/CCA）with controllable isoelectric point was prepared by acid adjusting method,and the efficient removal of negative and cationic pollutants in one bath and the selective adsorption of proteins were realized.On this basis,the preparation and adsorption processes were optimized.By means of Fourier Transform infrared Spectroscopy（FTIR）,X-ray Diffraction（XRD）,scanning electron microscopy（SEM）,Gaussian calculation and data fitting,the structure and adsorption properties of polysaccharide-based aerogels were systematically characterized,which provided theoretical support for the application of polysaccharide-based aerogels in the treatment of printing and dyeing wastewater and the separation and purification of proteins.In the first part,CCAs with different solid contents were prepared and their physicochemical properties and adsorption properties for cationic dyes were studied.The particle size test showed that the cotton fabric was transformed to carboxylated cellulose nanofibril（CCNF）with a size about 20 nm after being oxidized by sodium periodate/sodium chlorite and crushed at a high speed.CCAs with micro/nano structure and directional channel structure were prepared by freeze-drying.The results of conductivity and p H titration showed that CCAs contained 3.20 mmol/g carboxyl groups,which made CCAs simultaneously exhibit excellent static adsorption capacity（751 mg/g）and dynamic adsorption capacity（more than 700 mg/g）for methylene blue（MB）.The Gaussian calculation proves that the effect of p H on the MB adsorption is higher than that of neutral salts.When CCAs adsorb MB,the most stable adsorption site of MB is N2,and the electrostatic attraction between CCA and MB plays an important role in the adsorption.It is proved that the adsorption of MB by 2.0-CCA accords with the Langmuir adsorption model and the pseudo second-order kinetic model.Thermodynamic parameters show that the adsorption process is a spontaneous process of endothermic and entropic increasing.CCAs indicate certain recyclability,excellent ion tolerance,and p H tolerance.At the same time,CCAs also show good recyclability and realize the recycling of both wastewater and adsorbent.Although CCAs in the first partindicate excellent adsorption performance for cationic dyes,they are unable to adsorb anionic substances.And its structure is fragile after repeated use.Therefore,how to obtain adsorbent materials with high adsorption capacity and adsorption efficiency,strong morphological stability,and active to both negative and cationic pollutants has become the focus of further research.Based on this,the second part studies the preparation technology and adsorption performance of the CS/CCAs.The p H/conductivity titration curve showed that CS and CCNF can aggregate due to electrostatic attraction under weakly acidic conditions.Therefore,the influence of solution p H on the particle size of CS/CCNF system and the morphology of CS/CCAs was investigated.Finally,acid adjusting method（p H=1.5～2）was used to prepare CS/CCAs with controllable structure.The porous skeleton structure formed through the electrostatic attraction between CS and CCNF gives CS/CCAs excellent structural stability and resilience in water.After 100 times of dry compression,CS/CCAs can recover to the initial state.Wet compression shows a higher rebound rate than dry compression.The chemical composition of different CS/CCAs and the structural stability of-NH3OOC-under acidic conditions were analyzed by FTIR.Through Gaussian calculation,the electrostatic potential surface of the composite at different p H values was analyzed.It is proved that CS/CCAs has adsorption capacity for both negative and cationic pollutants under weakly acidic conditions.At p H=6,CS/CCAs showed excellent same-bath removal ability for cationic blue X-BL（adsorption capacity of 530 mg/g）and active red 3BS（adsorption capacity of 1178 mg/g）.Zeta potential test results show that the isoelectric point of CS/CCAs can be controlled by adjusting the composite ratio,so as to further achieve the selective adsorption of high-value proteins.CS/CCAs with different composite ratios can selectively adsorb bovine serum albumin（BSA）and lysozyme（LZM）by gravity drive at p H=6,showing excellent static adsorption capacity（1619 mg/g,1428mg/g）and dynamic adsorption capacity（1046 mg/g,1107 mg/g）,respectively,realizing the separation and recovery of BSA and LZM proteins.In addition,CS/CCAs also have stable recyclability,easy operation,and environmental friendliness,showing good performance for practical applications. |
