Preparation Of Eco-Friendly Magnetic Rare Earth-Al Dual-Ion Crosslinked SA Polymer Gel Balls And Their Adsorption Properties On Azo Dyes

In order to obtain the efficient green adsorption material,two novel eco-friendly magnetic La-Al dual-ion crosslinked SA polymer gel spheres（Fe3O4@Al-SA-La）and magnetic Y-Al dual-ion crosslinked SA polymer gel spheres（Fe3O4@Al-SA-Y）were prepared by the reaction of La（Ⅲ）-Al（Ⅲ）dual-ion and Y（Ⅲ）-Al（Ⅲ）dual-ion crosslinked Sodium alginate（SA）and Fe₃O₄,respectively,the former is used for the adsorption of Direct Brown 2（DB 2）and Direct Brown 95（DB 95）dyes in water,and the latter is used for the adsorption of Direct Orange S（DOS）and Direct Green 1（DG 1）dyes in water,the effects of preparation and adsorption conditions on the adsorption properties of the two gel spheres were investigated.The adsorption properties of two kinds of gel spheres for dye were evaluated by studying adsorption kinetics,isothermal adsorption and adsorption thermodynamics,and the raw materials and gel balls before and after adsorption were characterized by XRD,SEM,FT-IR,UV-Vis,etc.,the adsorption mechanism of dye on gel spheres was discussed.The specific findings are as follows:（1）The optimal preparation conditions of gel spheres were obtained:0.4 g SA was dissolved in 25 m L distilled water at room temperature,0.08 g Fe3O4 was added to the gel spheres,and no bubbles were found,a syringe was used to evenly cancel 100 m L of dual-ion solution with a certain molar ratio of ion（where the molar ratio of La（Ⅲ）-Al（Ⅲ）ion is3:4 and the molar ratio of Y（Ⅲ）-Al（Ⅲ）ion is 3:2）.After curing for 0.5 h,the gel spheres were taken out,two kinds of gel spheres,Fe₃O₄@Al-SA-La and Fe₃O₄@Al-SA-Y,were prepared after washing and drying.（2）Through a series of characterization analysis,it is determined that both Fe₃O₄@Al-SA-La and Fe₃O₄@Al-SA-Y are macromolecular gel spheres with unique three-dimensional network structure,and their surfaces are characterized by longitudinal and horizontal ravines and rich folds,the diameter of the brown-black particles is about 2.38 mm and 2.03 mm,respectively.The gel spheres has sensitive magnetic response and can be quickly separated from water under an external magnetic field.（3）The optimum adsorption conditions of Fe₃O₄@Al-SA-La gel spheres for the two dyes were as follows:at room temperature,0.05 g gel spheres were used to purify the dye solution of DB 2 at 2500 mg·L^-1 and DB 95 at 2000 mg·L^-1 for 120 min.At p H=2,the adsorption capacity and the removal rate of the two dyes reached the maximum at 1243,985mg·g^-1and 99.5,98.5%,respectively;and decreased slightly with the increase of p H to 8.0,but it still reached 1186,960 mg·g^-1 and 94.9,96%;at p H 10.0,the adsorption amount and removal rate decreased to 950,790 mg·g^-1 and 76.0,79.0%;under the natural p H of the two dyes（DB 2=8.57,DB 95=8.63）,the removal rate of the two dyes can reach over 93.0%.The optimal adsorption conditions of Fe₃O₄@Al-SA-Y gel spheres for the two dyes were as follows:0.03 g of Fe₃O₄@Al-SA-Y gel spheres were used for the purification of DOS and DG 1 dye solutions with the concentration of 3500 mg·L^-1 at room temperature,respectively,the adsorption time was 60 min.At p H=2,the adsorption capacity and the removal rate of the two dyes reached the maximum at 1724 mg·g^-1,98.5%and 1725 mg·g^-1,98.6%,respectively;and decreased slightly with the increase of p H to 8.0,but it still reached 1661 mg·g^-1,94.9%and 1658 mg·g^-1,94.7%;at p H 10.0,the adsorption amount and removal rate decreased to 1473 mg·g^-1,1450 mg·g^-1and 84.1,82.9%;while at their respective natural p H（DOS=9.05,DG 1=8.75）,the gel spheres could remove more than 94.0%of the two dyes.（4）The adsorption process of dye by Fe₃O₄@Al-SA-La and Fe₃O₄@Al-SA-Y is in accordance with the pseudo-second-order rate model and the adsorption rate is affected by the diffusion in the particles.The Langmuir model can accurately describe the adsorption behavior of dye.The thermodynamic parameters of the adsorption of dye on two kinds of gel spheres were as follows:ΔG<0,ΔH<0,ΔS>0,that is the adsorption reaction of dye on gel balls was spontaneous exothermic reaction with increasing confusion.（5）FT-IR,UV vis and XPS spectra of gel spheres before and after dye adsorption were analyzed Fe₃O₄@Al-SA-La and Fe₃O₄@Al-SA-Y Gel spheres are mainly used to achieve efficient adsorption of dyes through electrostatic adsorption,hydrogen bonding and complexation.The two adsorbents Fe₃O₄@Al-SA-La and Fe₃O₄@Al-SA-Y prepared in this study not only have low cost and environmental protection,but also have super high adsorption capacity,and can effectively purify dye wastewater with p H 2.0-10.0,it is easy to be separated after adsorption and will not cause secondary pollution to the environment.It has great potential for development and is expected to play its role in water environmental protection.