Study On The Construction And Adsorption Properties Of Cellulose Based Functional Materials

The massive discharge of industrial and agricultural waste water makes the problem of water pollution even serious all over the world.Its treatment is one of the important issues for the sustainable development of our national economy and society.Porous materials show great potential in environmental remediation due to their advantages of high porosity,low density,and high specific surface area.Traditional petroleum based porous materials such as activated carbon,zeolite,and polyurethane have some disadvantages such as non-degradation,difficult regeneration,and poor adsorption selectivity.Therefore,it is urgent to develop low-carbon alternative materials.Cellulose,as the most abundant natural polymer in nature,has the advantages of renewability,low cost,easy surface modification,good biocompatibility,and biodegradation.Therefore,the development of cellulose based porous adsorption materials is of great significance to keep the balance of ecological environment and promote the sustainable development of national economy.Although researchers have carried out a lot of work on the construction of cellulose based porous adsorption materials,there are still some problems such as complex preparation process,poor adsorption selectivity,and low adsorption capacity,which limit their industrial application.Focused on the above problems,this thesis aims at the characteristics of the target pollutants to construct functional materials by directional modification of cellulose.With the help of the excellent properties of other biopolymers,cellulose based adsorption materials with high adsorption performance and high adsorption selectivity were prepared.The adsorption properties for different types of dyes and mixtures of oil/water were systematically studied.The adsorption mechanism was explained and the adsorption model was constructed.The main research contents and conclusions are as follows:1.One-step acid hydrolysis was used to extract carboxylated nanocellulose from pomelo peel waste by the mixture acid of hydrochloric acid and citric acid and then the carboxylated nanocellulose sponge was prepared by vacuum freeze drying.The results showed that hydrochloric acid could act as catalyst to promote the conversion of hydroxyl group to carboxyl group on cellulose surface during acid hydrolysis.The nanocellulose possessed a typical network entanglement structure and the aspect ratio can be regulated.Theζpotential of nanocellulose suspension was up to-59.2 m V,indicating that the suspension had high dispersion stability.Batch adsorption results showed that the increase of carboxyl group content of nanocellulose could promote the adsorption of methylene blue(MB)on sponge,and the adsorption process could reach equilibrium within 20 min,showing an excellent adsorption rate.The adsorption process of MB by sponge conforms to pseudo-second-order kinetic and Langmuir adsorption isotherm model,with the maximum adsorption capacity of 182.1 mg/g.This indicated that the adsorption process belongs to the monolayer adsorption.Besides,the sponge showed high selectivity for cationic dyes when used for dye mixture.2.Cellulose nanofibrils/chitosan composite sponge(CNF/CS)was prepared by freeze-drying method with cellulose nanofibrils and chitosan as raw materials,and then the physical crosslinking effect of sponge was enhanced by dehydrothermal treatment.The results showed that the composite sponge had good 3D porous structure and shape memory property.The introduction of nanocellulose can effectively improve the crystallinity and thermal stability of composite sponge.Batch adsorption experiments showed that the sponge could efficiently remove reactive blue 221(RB)and congo red(CR)by electrostatic interaction.The adsorption process is in accordance with pseudo-second-order kinetics and Langmuir isothermal model,with the maximum adsorption capacity of 778.5 and 635.8 mg/g,respectively.The porous structure and abundant amino and hydroxyl groups in the composite sponge significantly improved its selective adsorption of anionic dyes.At the same time,the sponge showed the ability of rapid and continuous separation of dyes.The adsorption-desorption experiment showed that the sponge had good regeneration performance and could be reused for 5times.3.Chloroacetic acid and(3-chloro-2-hydroxypropyl)trimethyl ammonium chloride solution were used to modify wood pulp cellulose with anion and cation,respectively.Then the two cellulose derivatives were cooperated into polyvinyl alcohol.Based on the principle of polyvinyl alcohol acetalization,amphoteric cellulose/polyvinyl alcohol sponge was prepared,aiming to achieve the effective adsorption of anionic and cationic dyes.The effect of various factors on the adsorption of CR and MB by the amphoteric sponge was systematically investigated.The adsorption of CR and MB by the sponge conforms to the pseudo-second-order kinetic and Langmuir isotherm model,which indicates that the adsorption of CR and MB is a monomolecular adsorption process dominated by chemical action.The maximum adsorption capacities of the sponge for MB and CR were 77.34 and 178.9 mg/g,respectively.Taking MB as an example,after 5 cycles of adsorption and desorption,the removal can still reach 83.37%,showing good regeneration performance.In addition,the introduction of cationic groups also endowed the sponge with good antibacterial performance.4.With nanocellulose,alkylated chitosan and polyvinyl alcohol as raw materials,self-recoverable and highly hydrophobic nanocellulose/alkylated chitosan/polyvinyl alcohol sponge was prepared by sol-gel method,freeze drying and chemical vapor deposition.The results showed that the 3D porous sponge has ultra-high porosity(96～98%)and ultra-low density(16.61～50.91 mg/cm~3).The hydrophobic sponge modified by silane has good compressibility under 80%strain and could withstand 50loading-unloading cycles,showing excellent fatigue resistance.The results of contact angle test showed that silane deposition can significantly improve the hydrophobicity of sponge,and the contact angle can reach 147°.The hydrophobic sponge could absorb up to 51.08 times of oil/organic solvents.It had high separation efficiency for oil-water mixture and water-in-oil emulsion stabilized by surfactant.In addition,the sponge showed good chemical resistance(strong acid,high salt)and abrasion resistance,making it feasible for the treatment of complex oily wastewater.