| Heavy metal ions are one of the most biohazardous and toxic components in wastewater,among which Hg(II)ions seriously threaten ecological security and human health due to their significant bioaccumulation and high toxicity.There are many methods to remove heavy metal ions from water.Adsorption method is widely used in the field of water heavy metal ion removal due to its advantages of simple operation,high efficiency and low cost.Compared with other adsorption materials,hydrogels have the advantages of high efficiency,simple operation,and abundant adsorption sites,but the disadvantages of poor mechanical properties limit their application in the removal of heavy metal ions from water.From the perspective of green chemistry,three bio-based cellulose hydrogels were prepared in this paper,which can not only improve the mechanical properties of the hydrogels,but also increase the adsorption capacity of the hydrogels for Hg(II)ions.The specific research contents are as follows :(1)In order to solve the problem of poor mechanical properties of hydrogels,carboxymethyl cellulose nanofibers(CM-CNFs)were prepared by TEMPO-mediated oxidation method,and cellulose-based hydrogels were prepared by radical polymerization method,the feeding amount and adsorption conditions were optimized,and the effect of CM-CNFs addition on the mechanical properties of the hydrogel was explored.The characterization by scanning electron microscopy shows that the hydrogel has a 3D porous structure,and the compressive modulus of the hydrogel with the addition of 200 u L of CM-CNFs is 39.15 MPa.The adsorption experiments showed that the highest adsorption capacity of cellulose-based hydrogels for Hg(II)ions reached 657.89 mg/g.The adsorption process was in accordance with pseudo-second-order kinetics and Langmuir model.Thermodynamic studies showed that the adsorption process was a spontaneous process and an exothermic process.When Co(II),Hg(II),Ni(II)and Zn(II)ions coexist,the hydrogel has low adsorption selectivity for Hg(II).Cyclic adsorption and desorption experiments show that the adsorption capacity of the hydrogel for Hg(II)in the fifth cycle is only 36.13% of the first adsorption capacity.(2)On the basis of ensuring the mechanical properties of hydrogels,in order to improve the adsorption selectivity and recycling performance of cellulose based hydrogels,cellulose/sodium alginate composite hydrogels with 3D porous structure Semi-IPN were successfully prepared by free radical polymerization,and the inventory and adsorption conditions are optimized.The effect of CM-CNFs concentration on mechanical properties of hydrogel was investigated.When the concentration of CM-CNFs was 0.5wt%,the compression modulus of hydrogel reached 36.61 MPa.The adsorption experiment showed that the maximum adsorption capacity of cellulose/sodium alginate composite hydrogel for Hg(II)ions was 348.43mg/g.Pseudo-second-order kinetics,Langmuir model and thermodynamics showed that the adsorption process was a spontaneous exothermic monolayer adsorption process dominated by chemisorption.With Co(II),Hg(II),Ni(II)and Zn(II)ions coexisting,the hydrogel has strong adsorption selectivity for Hg(II).Cyclic adsorption and desorption experiments showed that the adsorption capacity of the hydrogel for Hg(II)in the fifth cycle was 71% of the initial adsorption capacity.(3)On the basis of ensuring the mechanical properties and recycling performance of hydrogels,in order to improve the adsorption capacity of cellulose-based hydrogels,N,S doped CDs was prepared by hydrothermal method,and CM-CNFs-CDs was prepared by grafting N,S doped CDs to CM-CNFs by amidation method.Finally,cellulose-carbon quantum dots hydrogels with 3D porous structure was prepared by free radical polymerization,and the adsorption conditions were optimized.When the content of CM-CNFs-CDs was 300 u L,the hydrogel had the best mechanical properties and the compression modulus was 86.77 MPa.Adsorption experiments showed that the maximum adsorption capacity of cellulose-carbon quantum dots hydrogels for Hg(II)ion was 943.77 mg/g.The adsorption capacity of cellulose based hydrogels is greatly improved compared with that of cellulose/sodium alginate composite hydrogels,and the adsorption process was in accordance with the pseudo-second-order kinetic model and Langmuir model.Thermodynamic studies show that the adsorption process is exothermic and spontaneous.After 5 cycles,the adsorption capacity of hydrogel is more than 90% of the initial adsorption capacity,indicating that hydrogel has good recycling performance. |
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