Preparation Of Lignin-Based Adsorption Materials,Adsorption Properties Of Dyes And Their Mechanisms

Lignin is a biomass resource with reserves second only to cellulose in nature.It is widely found in the cell walls of woody and herbaceous plants.It helps plant cell walls obtain good strength and transport water and salt in the vascular system.At present,industrial lignin mainly comes from the chemical pulping process of pulp and paper industry.Due to the complexity of its structure,lignin has not been fully utilized for a long time.However,due to its advantages of low cost,renewable and environmentally friendly,the development and utilization of lignin has been paid attention by many researchers.In recent years,lignin has shown wide application value and prospect in chemical industry,medicine,energy,food and agriculture and forestry.Based on the structure,high carbon content and functional groups of lignin,this study prepared lignin-based carbon materials,lignin/montmorillonite composite aerogel materials and lignin/cellulose composite hydrogel materials,and studied the adsorption performance and adsorption mechanism of three adsorption materials for dye ions in aqueous solution.Specific research contents and results are as follows:（1）Using sodium lignosulfonate as raw material and glutaraldehyde as crosslinking agent,lignin based adsorbent carbon material（LC）was prepared by activated carbonization method,and the adsorption of cationic dye malachite green as adsorbent was discussed.The effects of glutaraldehyde dosage,LC dosage,pH value of solution,initial concentration of dye solution,adsorption time and temperature on adsorption properties were investigated.When the mass ratio of lignin to glutaraldehyde was 2:1,the optimal adsorption conditions for malachite green were as follows:pH 8,the amount of LC carbon material was 25 mg,the initial dye concentration was 300mg/L,the temperature was 55℃,the adsorption time was 2 h,and the optimal adsorption capacity was 750.03 mg/g.The adsorption of malachite green by LC carbon material conforms to the quasi second-order kinetic model and Langmuir isotherm model.The single-molecule layer adsorption is dominated by chemisorption.The internal diffusion model shows that the adsorption process is influenced by internal diffusion,boundary layer diffusion and equilibrium process.Thermodynamic studies show that the adsorption of malachite green by LC carbon material is a process of entropy increase and spontaneous adsorption.（2）Using alkali lignin and montmorillonite as raw materials,Mg²⁺was doped into lignin/montmorillonite composite aerogel material（L-M-T）,and its adsorption performance was studied.The optimum adsorption conditions of L-M-T composite as adsorbent for Congo red dye were as follows:mass ratio of L-T to Mg²⁺was 2:1,pH value was 8,initial dye concentration was 300 mg/L,adsorption time was 300 min,and temperature was 55℃.The maximum adsorption capacity was 282.09 mg/g.The adsorption of Congo red by L-M-T conforms to the quasi-second-order kinetic model dominated by chemical adsorption.The Freundlich isothermal adsorption model can better fit the adsorption data,indicating that the adsorption process is heterogeneous multimolecular layer adsorption.The internal diffusion model shows that the boundary layer diffusion is the main factor affecting the adsorption rate.Thermodynamic analysis shows that the adsorption process is spontaneous entropy increase at higher temperature.（3）Using sodium lignosulfonate and cellulose as raw materials,using 0.1%acetic acid solution as solvent,lignin/cellulose hydrogel material was prepared,and the adsorption properties of two dyes of Congo red and malachite green as adsorbent were studied,and the effects of solution pH value,adsorption time and temperature on the adsorption properties were investigated.The results showed that the optimal adsorption conditions of lignin/cellulose hydrogel for the dye Congo red were as follows:adsorption time of 4 h,pH value of 6,and adsorption temperature of 45℃.The adsorption process was consistent with Langmuir isothermal model and quasi second-order kinetic model,which belonged to single-molecular layer adsorption,and the maximum adsorption capacity was 294.01 mg/g.The optimal adsorption conditions for malachite green are as follows:adsorption time of 4 h,pH value of 4 and adsorption temperature of 60℃.The adsorption process conforms to Freundlich isothermal model and pseudo-second-order kinetic model,belonging to the chemisorpis-dominated multimolecular layer adsorption with the maximum adsorption capacity of 129.82 mg/g.