Modification of hyperbranched hemicellulose polymer and its application in adsorbing acid dyes

The paper presented a new, non-pollution macromolecule of adsorbing acid dyes, and developed the adsorption mechanism on the basis of effect between the modified groups of hyperbranched hemicellulose polymer and acid dyes. The modified hyperbranched hemicellulose polymer (HHP) with a large number of terminal carboxyl groups and hydroxyl groups was synthesized by hemicellulose maleate and dihydroxymethyl propionic acid. The degree of substitution, kinematic viscosity and thermal stability of HHP was determined. In SEM images, the HHP exhibited the pores and cross-linked structure which were good help for dye adsorption. When the HHP was applied in adsorbing Methyl red dye, Bromocresol green dye and Bromophenol blue dye, it exhibited higher adsorption capacity. The adsorption capacity changed with different adsorbent dosage, pH, temperature and ionic strength, and the optimal adsorption capacity for Methyl red dye, Bromocresol green dye and Bromophenol blue dye could reach 825 mg/g, 675 mg/g and 912 mg/g respectively. The adsorption mechanism, adsorption isotherm and adsorption diffusion mode were demonstrated by Pseudo-order model, Langmuir model, Intraparticle diffusion model and Memberance diffusion model respectively. The adsorption data possessed better correlation with Pseudo-second-order model, Langmuir model and Intraparticle diffusion model. The adsorption isotherms and thermodynamic date indicated the processes of HPP2 adsorbing three acid dyes were endothermic. The N₂-adsorption/desorption isotherms of HPP2 revealed the hyperbranched hemicellulose polymer filled the pore in clusters, and its adsorption process met with monolayer adsorption.