Preparation Of Lignin-Based Composite Aerogel And Its Adsorption Performance

At present,the treatment of printing and dyeing wastewater and oily wastewater is still a pressing problem worldwide.The physical adsorption method is simple and pollution-free,and it is expected to be used in the treatment of printing and dyeing wastewater and oily wastewater on a large scale.The commonly used adsorption materials like activated carbon are expensive and difficult to regenerate.Therefore,it is important to prepare an adsorbent material with excellent performance.In this paper,sodium lignosulfonate,carboxymethyl xylan,acrylamide,N,N’-methylene bisacrylamide were used as raw materials,ammonium persulfate and tetramethylethylene diamine were used as initiators,and a new lignin-based composite aerogel was prepared by simple solution blending and freeze-drying,and its preparation process was studied,and the aerogel was structurally characterized and tested.Further,the effects of six factors,including p H of methylene blue solution,adsorption time,methylene blue concentration,adsorbent mass,adsorption temperature,and type of organic pollutant,on the adsorption performance of lignin-based composite aerogel were investigated using methylene blue as a simulated pollutant.In addition,in order to make the lignin-based composite aerogel better for the treatment of oily wastewater,a lignin-based composite aerogel with good hydrophobicity was prepared by a simple impregnation method using n-dodecanethiol as a hydrophobic modifier in this paper,and the structure and oil absorption properties of the hydrophobically modified lignin-based composite aerogel were investigated.The main findings of this thesis are as follows:1.Lignin-based composite aerogels were synthesized using sodium lignosulfonate,carboxymethyl xylan,acrylamide,N,N’-methylenebisacrylamide,ammonium persulfate and tetramethylethylenediamine as raw materials.The synthetic materials were characterized by FTIR,SEM and BET,and the synthesis conditions of lignin-based composite aerogels were optimized with the adsorption capacity of methylene blue as the evaluation standard.In addition,the adsorption amount of methylene blue by the aerogel was used as the index for the synthesis of aerogels.The experimental results showed that the optimum conditions for synthesizing lignin-based composite aerogels were as follows:the amount of acrylamide was 10.0wt%,the amount of carboxymethyl xylan was 8.0wt%,the amount of sodium lignosulfonate was 4.0wt%,the amount of N,N’-methylenebisacrylamide was 5.0wt%,and the amount of initiation system（ammonium persulfate and tetramethylethylenediamine）was 1.5wt%.2.Using methylene blue solution to simulate dye wastewater,the effects of six factors,such as p H value of methylene blue solution,adsorbent addition,adsorption time,adsorption temperature,adsorbent concentration and types of organic pollutant,on the adsorption properties of lignin-based composite aerogels were investigated.The experimental results showed that the optimal adsorption conditions of lignin-based composite aerogel for methylene blue were p H=11,adsorption time of720 min,methylene blue concentration of 200 mg·g^-1,aerogel mass of 0.0100 g and adsorption temperature of 313.15 K.The adsorption amount of lignin-based composite aerogel for methylene blue was up to 39.80 mg·g^-1.The adsorption amounts of lignin-based composite aerogel for cationic methylene blue and rhodamine B dyes were higher than those of anionic dyes methyl orange.The kinetic fitting results showed that the adsorption of methylene blue by the lignin-based composite aerogel was more consistent with the pseudo-secondary kinetic model.The fitting results of isothermal adsorption model showed that the adsorption of methylene blue by lignin-based composite aerogel was more consistent with the Langmuir isothermal adsorption model.The adsorption thermodynamic model was fitted and theΔH^θof the adsorption process was 31.01 k J·mol^-1,indicating that the adsorption process is a heat absorption reaction.ΔS^θwas 160.01 J·mol^-1·K^-1,indicating that the adsorption process is an entropy increase process.And theΔG^θof the reaction is less than 0 in the temperature interval of 293.15 K-313.15 K,indicating that the adsorption process can be proceed spontaneously from 293.15 K to313.15 K.3.The hydrophobic modified lignin-based composite aerogel materials were prepared by impregnation method using n-dodecanethiol.The FTIR and SEM characterization showed that the lignin-based composite aerogel was successfully introduced with polydopamine hydrophobic film on the surface.The effects of n-dodecanethiol dosage,sonication time and solution p H on the contact angle size of the hydrophobically modified lignin-based composite aerogels were investigated.The results showed that the contact angle of the prepared hydrophobic modified lignin-based composite aerogel could reach 118.1°when the amount of n-dodecanethiol was 0.5 m L,the sonication time was 50 min,and the p H of the solution was 9.5.The hydrophobically modified lignin-based composite aerogel was tested for oil-water separation performance and cycling experiments,and the results showed that the prepared aerogel had good adsorption effect on stained oil droplets after hydrophobic modification.