半互穿海藻酸钠/聚丙烯酰胺凝胶吸附结晶紫动力学/热力学行为和吸/脱附机理

将含有大量—COO-的聚阴离子海藻酸钠(SA)引入聚丙烯酰胺(PAM)凝胶网络中,采用自由基溶液聚合法制备半互穿网络结构的SA/PAM水凝胶.采用扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和傅里叶变换红外光谱(FTIR)分析了SA/PAM水凝胶吸附结晶紫(CV)前后的孔洞形态和化学组成变化,采用多种模型研究了SA/PAM水凝胶对CV分子的吸附动力学和热力学行为,并探讨了脱附效率,提出了吸脱附机理.研究结果表明,SA的引入降低了孔径尺寸,增加了孔洞数量;SA/PAM-10凝胶对CV分子吸附量最大,达到13.5838 mg/g,符合伪一级吸附动力学模型,吸附速率受膜扩散和粒子内扩散过程共同影响;等温吸附过程符合Temkin和D-R模型,属于微孔多层吸附;热力学分析结果表明,吸附过程由熵驱动引起,非化学诱导因素影响所致;采用HCl进行脱附,最大脱附率高达94.18%,加入Na OH可实现SA/PAM水凝胶的可逆吸附;较高的吸附量主要源于SA分子链上的COO-与CV分子的—C N+—存在的静电作用,低pH值时由于—COO-和—NH2质子化导致与CV分子的静电斥力增大,脱附率随之增加.

Adsorption Kinetics/Thermodynamic Behavior and Adsorption/Desorption Mechanism of Crystal Violet by Semi-interpenetrating Sodium Alginate/Polyacrylamide Hydrogel

The sodium alginate ( SA ) , a kind of polyanion electrolyte including many carboxylic acid (—COO-) , was introduced into polyacrylamide hydrogel network to prepare the SA/PAM hydrogels with semi-interpenetrating network structure via free-radical solution polymerization. The pore morphology and chemical composition of SA/PAM hydrogels before and after adsorption of crystal violet( CV) were comparative analyzed by scanning electron microscope ( SEM ) , X-ray photoelectron spectroscopy ( XPS ) and Fourier transform infrared spectroscopy ( FTIR ) . All kinds of models were used to study adsorption kinetics and thermodynamics behavior for the adsorption of crystal violet( CV) on the SA/PAM hydrogel. Meanwhile, the desorption efficiency was discussed, and the mechanism of adsorption and desorption was proposed. The results showed that, with the introduction of SA, the pore size reduced, but pore numbers increased. The SA/PAM-10 hydrogel shows the maximum adsorption amount, about 13. 5838 mg/g. Four kinds of SA/PAM hydrogels agree with pseudo first-order kinetic model, and the adsorption rate depends on both film diffusion and particle diffusion. The isothermal adsorption process is consistent with the Temkin and the D-R model, which belongs to the microporous multi-layer adsorption. Thermodynamic analysis results show that the adsorp-tion process is driven by entropy rather than chemical factor. The desorption was achieved by adding HCl, the maximum desorption rate reached up to 94. 18%, and reversible adsorption of SA/PAM hydrogel could be found by adding NaOH. The high adsorption capacity can be ascribed to the electrostatic interaction between COO- of SA molecular chain and—C N+—of CV molecules. Due to protonation of—COO-and—NH2 un-der low pH value, leading to increased electrostatic repulsion with CV molecules. Accordingly, the desorption rate was naturally increased.