Basic Research On The Preparation Of Bifunctional Modified Corn Stover Cellulose And Its Application In Removing Heavy Metals

In recent years,Water pollution problems has become more and more serious,and the treatment of heavy metal ions in wastewater is particularly important.The use of natural polymer materials from cellulose to prepare green,efficient and environmentally friendly adsorbents has become a attractive research in current wastewater treatment technology.As one of the agricultural wastes with huge annual production in China,corn stovers contain a large amount of cellulose,which is an excellent raw material for the preparation of adsorbents and has the advantages of low price,degradability,and regeneration.In this paper,the cellulose extracted from corn stover was used as the matrix material.The graft-modified cellulose with sufficient epoxy groups was prepared by graft copolymerization.Amintion-Cell was prepared by introducing various amino groups through ring-opening of epoxy groups.Then,according to the special structure of DTC,CS₂were selectively introduced into some amino groups on the surface of Amintion-Cell to obtain DTC-Cell containing both independent amino groups and sulfur-containing groups under appropriate modification conditions.The adsorption effects between Amintion-Cell and DTC-Cell on single or mixed copper and lead ions under different adsorption conditions were also carried out.At the same time,the effect of introducing different functional groups on the adsorption of heavy metal ions on cellulose was deduced by the relevant structural characterization and the comparison of the difference in the adsorption performance of the two adsorbents for copper and lead ions.Based on this,the adsorption mechanisms of the two adsorbents for different heavy metal ions were obtained,which provided the necessary experimental and theoretical basis for the efficient removal of copper and lead ions in water by the adsorbents.The main contents are as follows:（1）The adsorption effect of Amintion-Cell on single and mixed copper and lead ions at two initial concentrations of 100 mg/L and 500 mg/L was investigated under the conditions of pH=4.0,25 ℃,and the mass ratio of material to agent 1:1000.Under the condition of initial concentration of 100 mg/L,the adsorption capacity of Amination-Cell for single copper ion and lead ion were 99.8 mg/g and 70.1 mg/g,while the adsorption capacities in the mixed copper and lead ion system were 86.7mg/g and 40 mg/g,respectively.Under the condition of initial concentration of 500mg/L,the adsorption capacities of Amintion-Cell for single copper ion and lead ion were 180.4 mg/g and 272.2 mg/g,while the adsorption capacity in mixed metal ion system were 159.6 mg/g and 39.5 mg/g,respectively.The experimental results showed that compared with copper ions,Amintion-Cell had a weaker adsorption capacity and poorer selectivity for lead ions,especially in the mixed metal ion system.（2）On the basis of Amintion-Cell,the introduction conditions of carbon disulfide were optimized by a single-factor variable method.CS₂was selectively introduced only on some amino groups to obtain DTC-Cell with coexistence of independent amino groups and sulfur-containing groups.The optimized CS₂introduction conditions were as follows:sodium carbonate was used to create an alkaline environment,the additions of Amintion-Cell,Na₂CO₃and CS₂were 4 g,3 g and 6 m L in turn,the reaction temperature was 40 ℃,and the reaction time was 10 h.The sulfur and nitrogen contents in bifunctional modified cellulose were 14.68 wt%and 7.02 wt%,respectively,which had a good adsorption effect on single copper and lead ions.When dealing with mixed copper and lead ions,the mass ratio of material to agent of 1:1000,the removal rate of copper and lead ions by DTC-Cell can quickly reach more than 99.6%under the conditions of initial concentration of 100 mg/L,pH=4.0,25 ℃.When the initial concentration was 500 mg/L,the adsorption capacities of DTC-Cell for copper and lead ions were 165.9 mg/g and 214.6 mg/g,respectively,which were significantly higher than those of Amintion-Cell for copper and lead in the mixed system under the same conditions.Moreover,the experimental results of adsorption kinetics and thermodynamics showed that the adsorption of copper and lead ions by DTC-Cell conformed to the Langmuir model and the pseudo-second-order kinetic model.The adsorption of copper ions belonged to an endothermic process,and the adsorption of lead ions belonged to an exothermic process.（3）According to the experimental results and related structural characterizations,the main adsorption functional groups and adsorption mechanisms of the two adsorbents for single copper ions and lead ions were clarified.On this basis,it was found that the amino groups and sulfur-containing groups in the DTC structure played an adsorption role,respectively.Both the independent primary/secondary amino groups on the adsorption surface of the adsorbent and the secondary amino groups in the DTC structure showed high adsorption selectivity for copper ions.However,the sulfur-containing groups（C-S/C=S）in the DTC structure only showed extremely strong adsorption selectivity for lead ions.Under the optimized CS₂introduction conditions,4.58 mmol/g C-S/C=S groups were further introduced into the Amintion-Cell surface with 6.99 mmol/g amino groups.The introduced appropriate amount of CS₂preferentially undergone esterification with the primary amino group（-NH₂）on the surface of Amintion-Cell to form a special DTC（-NHCS₂^-）structure containing a secondary amino group（-NH-）.The formation of this special DTC structure not only does not reduced the total amount of primary and secondary amino groups on Amintion-Cell and maintains its good adsorption performance for copper,but also introduced an appropriate amount of sulfur-containing groups to ensure the modified adsorbent.The introduced CS₂would only participate in the esterification with-NH₂groups to form special DTC structures containing-NH-groups（-NHCS₂^-）.The synthesized DTC structures would not reduce total amount of-NH-/-NH₂groups on aminated cellulose to keep its excellent adsorption performance for copper ions,and the introduced appropriate number of C-S/C=S groups could ensure the efficient removal of lead ions.The formation of this special structure not only does not reduce the total amount of primary and secondary amino groups on Amintion-Cell and maintains its good adsorption performance for copper ions,but also introduces an appropriate amount of sulfur-containing groups to ensure the effective removal of lead ions.Finally,the bifunctional modified corn stover cellulose can be used to achieve efficient removal of single or mixed lead and copper ions in water.