季铵型稻草木质素的合成及其对\[PdCl4\]2-的吸附性能

Synthesis of quaternary ammonium rice straw lignin and its adsorption properties on ［PdCl4］2-

摘要:

为经济高效和无污染提取钯，采用硫酸法从稻草中提取木质素，经3-氯-2-羟丙基三甲基氯化铵(CHMAC)化学改性后合成季铵型稻草木质素，并利用其从溶液中吸附[PdCl₄]^2-.利用扫描电镜(SEM)、傅立叶红外光谱(FTIR)和差热-热重分析(TG-DSC)对木质素及其衍生物进行表征，同时考察pH值、[PdCl₄]^2-初始浓度和吸附时间对季铵型稻草木质素吸附性能的影响，并对[PdCl₄]^2-的选择性进行研究.实验结果表明，季铵型稻草木质素为表面多孔且不规则的块状体，在200 ℃内具有良好的热稳定性，1 469 cm^-1处出现季铵离子的弯曲振动特征峰.最佳吸附pH值为2，吸附平衡时间为8 h，在[PdCl₄]^2-初始浓度为4 mmol·L^-1时，季铵型稻草木质素对[PdCl₄]^2-的吸附达到饱和，饱和吸附容量为1.120 mmol·g^-1，吸附过程遵循准二级动力学方程，吸附等温模型与Freundlich方程拟合较好，表明吸附过程为单分子层非均质化学吸附，盐酸浓度低于1 mol·L^-1时，季铵型稻草木质素对[PdCl₄]^2-具有良好的选择性.降低盐酸浓度，提高[PdCl₄]^2-初始浓度和延长吸附时间均有利于提高季铵型稻草木质素对[PdCl₄]^2-的吸附容量和选择性.

Abstract:

In order to extract palladium economically, efficiently and environment friendly, lignin is firstly extracted from rice straw by sulfuric acid method, and then the quaternary ammonium rice straw lignin is synthesized through chemical modification with the 3-chloro-2-hydroxy-propyl-trimethyl ammonium chloride (CHMAC). After that, [PdCl₄]^2- was adsorbed by the quaternary ammonium rice straw lignin. The lignin and its derivants were characterized by the scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis and differential scanning calorimetry (TG-DSC), respectively. Meanwhile, the effects of pH value, the initial concentration of [PdCl₄]^2-, the adsorption time on the adsorption properties of quaternary ammonium rice straw lignin were investigated. Furthermore, its selectivity for [PdCl₄]^2- was also discussed. The results show that the quaternary ammonium rice straw lignin is porous, rough and irregular with excellent thermal stability below 200 ℃ and infrared absorption peak at 1469 cm^-1 is attributed to the bending vibration of quaternary ammonium ion. Moreover, the optimum value of pH for [PdCl₄]^2- adsorption is 2 and the time of adsorption equilibrium is 8 h. The adsorption reaches saturation when the concentration of [PdCl₄]^2- is 4 mmol·L^-1 with 1.120 mmol·g^-1 of the saturated adsorption capacity. At the same time, the adsorption process could be described by pseudo-second order kinetic equation and adsorption isotherm could be simulated by Freundlich equilibrium adsorption equation, which indicates that the adsorption is chemical adsorption of monomolecular and nonhomogeneous. In addition, the quaternary ammonium rice straw lignin presents excellent selectivity for [PdCl₄]^2- when the concentration of hydrochloric acid is less than 1 mol·L^-1. The lower concentration of hydrochloric acid, higher initial concentration of [PdCl₄]^2- and longer adsorption indicate the better of adsorption capacity and selectivity.