Preparation Of Soft Ligand Adsorbents And Study On The Removal Of Heavy Metal Ions

In recent years,industrial productions are booming rapidly in China,which brought pollution problems increasingly serious.Especially,contamination caused by heavy metal badly threatens the safety of drinking water.Therefore,it is a strong practical significance to design the absorbent with high affinity for heavy metal ions.According to the theory of Hard-Soft-Acid-Base,heavy metal ions belong to soft acid generally and can preferentially combine with soft bases to form stable complexes.The dithiocarbamate group?DTC?containing N and S coordination atoms can chelate with most heavy metal ions,but it does not chelate with alkali or alkaline-earth metal ions.Therefore,this group can selectively recover trace heavy metal ions from wastewater.Based on DTC group,three kinds of heavy metal adsorbent with soft ligands were prepared with different materials,and characterized and analyzed the morphology and composition of each adsorbent by FTIR,TGA,BET,SEM,TEM and XPS methods.Taking lead ion as the target pollutant,we explored the influence of pH,adsorption time,initial ion concentration and temperature on the performance of each adsorbent.Concrete operations are as follows:?1?Biological adsorbent?CSDTC?was synthesized from corn stalk with a rich reserve and low price.The reaction with carbon disulfide was performed after the crosslink reaction between corn stalk with polyethylenimine.The branched-chain structure of polyethylenimine enables the generated DTC groups to be distributed densely on the hollow cellulose tube surface,and the saturated adsorption capacity of lead ions is as high as 526.15 mg/g.The material is suitable for aqueous environment with pH>2.5,and can reach the adsorption equilibrium within 20 min.It has the advantages of fast adsorption rate and high removal rate.The adsorption process of CSDTC conforms to the Langmiur adsorption isotherm and pseudo-second-order kinetic model,which is mainly based on surface adsorption and chemisorption.?2?MOFs adsorbent?UiO-66-DTC?was prepared by the direct reaction of carbon disulfide with UiO-66-NH₂.The synthesis method of this material is simple,and it retains the characteristics of high dispersion and porosity.The material is suitable for the aqueous environment with pH>2.5.The saturated adsorption capacity of lead ion is up to 689.47 mg/g,and it can quickly reach the adsorption equilibrium within 30 minutes.The adsorption process is mainly surface adsorption and chemical adsorption.UiO-66-DTC has a strong adsorption capacity for heavy metal ions,and it can still maintain more than 80%adsorption capacity after six adsorption cycles.?3?Graphene adsorbent?GODTC?was prepared by crosslinking polyethyleneimine with flake graphene oxide?GO?,which has a large specific surface area and rich functional groups,and then reacting with carbon disulfide.Polyethyleneimine contains a large number of amino branched chains,which can be cross-linked with a number of lamellar graphene to form three-dimensional porous materials.The large specific surface area provides a platform for rapid and efficient adsorption.The saturated adsorption capacity of lead ions is up to 482.36mg/g,and the main adsorption process is surface adsorption and chemical adsorption.By means of XPS and EDX,the coordination mode between DTC group and lead ion was explored.Lead ion replaced sodium ion in DTC group and formed stable tetrahedral chelation structure with two DTC groups...