Preparation Of Chitosan-based Semi-interpenetrating Network Hydrogels And Their Adsorption Properties For Humic Acid From Aqueous Solution

Humic acid（HA）is a complex organic substance composed of naturally occurring macromolecular organic substances.HA is a precursor of carcinogens in water,which has strong persistence and poor degradability.People pay more and more attention to the adverse effects of HA on organisms.Therefore,HA is one of the main substances in water analysis,and effective removal of HA in water is of great significance.Chitosan and its derivatives have attracted attention in the field of water treatment because of their good biocompatibility,safety and environment-friendly.In this dissertation,two novel chitosan-based semi-interpenetrating polymer network hydrogels（PAAm/CS s-IPN and PAAm/HACC s-IPN）were designed and prepared for the purpose of developing efficient and economical new adsorbents,and applied to the removal of HA.The effects of various factors such as pH,ionic strength,contact time,initial HA concentration and temperature on the adsorption were studied,adsorption process and mechanism were discussed through the characterization of the adsorbent materials and the analysis of the results of adsorption experiments to provide a theoretical reference for the design of chitosan-based semi-interpenetrating network hydrogel environment-friendly materials and their application in water treatment.The two main research works are as follows:1.Preparation,characterization of PAAm/CS s-IPN hydrogel and its adsorption properties for HAPAAm/CS s-IPN hydrogel was prepared by in-situ heating polymerization,the effects of monomer molar ratio,crosslinking agent dosage,acid dosage and initiator dosage on the HA adsorption performance were studied.The adsorbent with excellent performance was prepared and characterized by SEM,FT-IR,XRD and TG-DSC,showing that the adsorbent had a pore-like stable structure and enhanced thermal stability,which was beneficial to the adsorption of HA.PAAm/CS s-IPN hydrogel adsorbent showed excellent HA adsorption performance,which could maintain a high adsorption capacity in a wide pH range of 3⁹,a certain ionic strength could promote the HA adsorption.The adsorption process of HA onto the PAAm/CS s-IPN hydrogel is well described by a pseudo-second order adsorption kinetic model,and the interfacial diffusion and intra-particle diffusion act together.The Sips isotherm model fits the equilibrium data better,thermodynamic study showed that adsorption process was spontaneous physical adsorption and electrostatic interaction may be the main adsorption mechanism.2.Preparation,characterization of PAAm/HACC s-IPN hydrogel and its adsorption properties for HAChitosan quaternary ammonium salt was synthesized by quaternization of chitosan.PAAm/HACC s-IPN hydrogels with different content of chitosan quaternary ammonium salt PAAm/HACC s-IPN 1.5 and PAAm/HACC s-IPN 3 were prepared by in-situ heating polymerization.The morphology,structure and stability were characterized by SEM,FT-IR,XRD and TG-DSC.The HA adsorption performances of these two adsorbent were studied.Solution pH has a great influence on HA adsorption by PAAm/HACC s-IPN 1.5 and PAAm/HACC s-IPN 3 adsorbents,and the HA adsorption capacity decreases greatly with the increase of pH value.HA adsorption was enhanced when the ionic strength was low and decreased when the ionic strength was increased.The adsorption processes of HA onto the PAAm/HACC s-IPN 1.5 and PAAm/HACC s-IPN 3 are all well described by a pseudo-second order adsorption kinetic model and Sips isotherm model.Thermodynamics study shows that the HA adsorption onto the PAAm/HACC s-IPN 1.5 and PAAm/HACC s-IPN 3 are all spontaneous physical adsorption.The HA adsorption capacity of PAAm/HACC s-IPN 3adsorbent(238.1 mg·g^-1)was higher than that of PAAm/HACC s-IPN 1.5 adsorbent(1776.3mg·g^-1),which was higher than that of PAAm/CS s-IPN hydrogel adsorbent(166.3 mg·g^-1).They are all higher than the maximum HA adsorption capacity of HA adsorption materials reported.Chitosan-based s-IPN hydrogel materials have good adsorption properties for HA,making them suitable for the adsorption and separation of HA contaminant in water.It provides a theoretical basis for the practical application of chitosan-based s-IPN hydrogels in the field of water treatment.