Fabrication Of Alginate Composite Hydrogel Materials And Their Adsorption Performance For Metal Ions

There are a large number of metal ions in industrial wastewater,which could cause the pollution of ecological environment and threaten human health.Therefore,it is very important to establish an economic and effective method to remove metal ions in wastewater.The common methods include chemical precipitation,ion exchange and adsorption.Adsorption based on biomaterials has been widely researched due to its economic and environment-friendly raw materials,simple design and easy operation.The development of new adsorbents has become a research hotspot for removing metal ions in wastewater.Sodium alginate is one of the frequently-used natural biological materials and could form the hydrogel materials by coordination with calcium ions.Hydrogel adsorbents possess the advantages of non-toxicity and easy recycling.Adsorption performance could be improved by designing sodium alginate composite hydrogel materials.In this thesis,two types of the sodium alginate composite hydrogel materials were prepared and used to remove different metal ions.The specific research contents were as follows:1.The nitrogen-doped carbon dots-sodium alginate composite hydrogel materials(ALG@CDs hydrogel)were synthesized to remove rare earth ions in aqueous solution.The experimental results showed that the adsorption performance of sodium alginate hydrogel could be significantly improved by doping with an appropriate amount of carbon dots.The methodology suggested that the adsorption process was in accord with the Langmuir isothermal adsorption model and pseudo-second-order kinetic model.The maximum theoretical adsorption capacities of ALG@CDs hydrogel for Pr(Ⅲ),Sm(Ⅲ),Gd(Ⅲ),and Dy(Ⅲ)were 172.71 mg/g,185.53 mg/g,201.21 mg/g,and 207.04 mg/g,respectively.The results of competitive adsorption indicated that the affinity for Gd(Ⅲ)on the adsorbent was evidently stronger than that for Al(Ⅲ),Co(Ⅱ),Ni(Ⅱ),Zn(Ⅱ),and Mg(Ⅱ).Meanwhile,the adsorbent could still be recycled after five adsorption-regeneration cycles.Consequently,the ALG@CDs hydrogel has great potential for practical treatment of rare earth wastewater.2.The ZIF-67-sodium alginate composite hydrogel materials(ALG@ZIF-67 hydrogel)were synthesized to remove copper ions in aqueous solution.The experimental results indicated that ZIF-67 grown on the surface of sodium alginate hydrogel could evidently improve the adsorption performance for Cu(Ⅱ).The methodology showed that the adsorption process was in accord with the Langmuir isotherm adsorption model and pseudo-second-order kinetic model.The maximum theoretical adsorption capacity of the adsorbent for Cu(Ⅱ)was 156.99 mg/g.The ALG@ZIF-67 hydrogel has tremendous potential for treatment of heavy metal wastewater.Sodium alginate hydrogel combined with MOFs could also broaden the application of hydrogel materials in other fields.