Preparation Of Alginate Hydrogel Beads With Interpenetration Polymer Networks And Their Performance Of Adsorbing Phosphate From Water

With the rapid development of industrial and agricultural production,it may cause the eutrophication problem when the phosphorus wastewater is discharged into nature water without treatments for some reasons.However,as the limited phosphorus resources are dwindling,the phosphorus in wastewater may be an important resource for the agricultural production.Therefore,it seems to be imminent to develop an economic and efficient technology to remove and recycle phosphorus in wastewater effectively.Within many technologies for removing phosphorus from wastewater,the adsorption method attracts more and more attention because of its unique advantages,while the selection of adsorbent has a decisive influence on treatment effect.There are many problems for traditional adsorbent materials,such as high cost,low adsorption capacity,being non-biodegradable and poor recycling.In view of these,the study is aimed to develop novel and environmental-friend alginate hydrogel beads with interpenetration polymer network which has the advantages of low cost,high adsorption capacity and easy reuse.It will provide a new thought and theoretical basis for using the adsorption technology to remove and recycle phosphorus.At the same time,it can expand the application of polymer materials in the environmental field.Poly N-isopropyl-acrylamide/zirconium alginate(PNIPAM/SA-Zr)and magnetic poly acrylamide/zirconium alginate(Fe3O4@PAM/SA-Zr)hydrogel beads with interpenetration polymer networks are prepared by the chemical crosslinking method.Their physicochemical properties are characterized by using some technologies such as SEM,FT-IR,and XPS.The performance of adsorbing phosphate is investigated by confecting wastewater containing phosphorus.The adsorption mechanism is studied by adsorption kinetics,adsorption isotherm models and thermodynamic analysis.The properties of desorption,regeneration,reuse and column adsorption are also investigated in order to provide theoretical basis for the practical application of alginate hydrogel bead adsorbents.The main achivements are as follows:(1)Both PNIPAM/SA-Zr and Fe3O4@PAM/SA-Zr hydrogel beads with a sphere structure have a good polymeric form,thermal stability and mechanical strength.The internal structure appears a porous three-dimensional network.Particularly,because of the magnetism,Fe3O4@PAM/SA-Zr hydrogel beads can be easily separated from water under the effect of a magnetic field.(2)The results of static batch adsorption experiments show that the optimum performance of phosphate adsorption by PNIPAM/SA-Zr can be achieved up to 36.63 mg-P/g when the initial solution pH,the adsorbent dosage and the temperature are 2,0.05 g and 35?,respectively.The optimum performance of Fe3O4@PAM/SA-Zr are at the initial solution pH=2,the adsorbent dosage of 0.05 g and 25?,which is up to 42.23 mg-P/g.Increasing the content of Zr4+ can significantly promote the adsorption ability of hydrogel beads.The SO42-has an adverse effect on adsorption effect,and Cl-and NO3-hardly have an effect on adsorption.The hydrogel beads have a good recycle ability.The sphere structure keeps an intact shape,even though after 7 adsorption-desorption tests.(3)Pseudo-second-order dynamic model,intra particle diffusion model and Freundlich isotherm model are fitted well when PNIPAM/SA-Zr and Fe3O4@PAM/SA-Zr hydrogel beads adsorb phosphate from water.The result indicates that the adsorption process is controlled by both surface adsorption and particle diffusion mechanism which belongs to a multilayer and heterogeneous adsorption.And the result of thermodynamic analysis confirms that adsorbing phosphate is a spontaneous and exothermic reaction,and the system's chaotic degree becomes lower after adsorption.(4)The phosphate adsorption processes of PNIPAM/SA-Zr and Fe3O4@PAM/SA-Zr hydrogel beads are influenced by a combination of the physical absorption and chemisorption.The mechanism includes two parts.For one thing,Zr4+ loaded by alginate has a complexation reaction with phosphate ions to generate chemical bonds.For another thing,under the acid condition,the-OH,-NH-and-NH2 on the surface of hydrogel beads may produce protonation and carry positive charge.Then phosphate ions with negative charge can be adsorbed because of the effect of electrostatic force.(5)Dynamic adsorption experiments of PNIPAM/SA-Zr and Fe3O4@PAM/SA-Zr hydrogel beads show that the overlarge inlet velocity or phosphate concentration may result in the decrease of adsorption column capacity and the factors need to be determined according to the actual situations.