The Research On Sorbents Constructed By Covalent Organic Frameworks And Iron-based Mateirals For The Trivalent Arsenic Removal From Wastewater

Arsenic is a kind of pollutant with high bioaccumulation and high toxicity,which is essential to lives.When it accumulates in human body through the food chain,it will cause irreversible and serious damage to human body.Generally speaking,arsenic exists in solution as the form of trivalent and pentavalent.As(V)exists as acid anion when pH is higher than 2.4,which is easy to be adsorbed by electrical reaction.When As(III)exists in solution with pH lower than 9.2,the form of which is neutral,it increases the difficulty of arsenic removal.The non-ferrous smelting industry is one of the main sources.Untreated wastewater will be discharged in the form of fouling acid.This part of wastewater owns characteristics of strong acidity,high arsenic concentration and coexistence ions.In the traditional methods of arsenic removal,adsorption is favored by researchers for its advantages of simple operation,less residue and high removal efficiency.However,materials used for depth removal of As(III)need to be explored.It is an effective and feasible method to realize depth removal of arsenic within a high efficient way.In this study,iron-based materials with the advantages of wide source,environmental friendliness and high affinity to arsenic were used as the active sites.And different types of composites constructed with COFs were applied to solve the problems of application.The main research are mentioned as follow:1)Iron-based nano materials have the functions of interface oxidation and high affinity with arsenic,which can be used for the removal of As(III).However,agglomeration often occurs during the using times,which inhibits the function of active sites.In this study,a Covalent Organic Frameworks(TAPB-PDA COFs)with high surface area was used as carrier and Fe⁰ as active site to construct Fe⁰/TAPB-PDA COFs.The dispersion of Fe⁰ was improved by high surface area of COFs and the cooperation between C=N bond and Fe⁰.It was found that the maximum adsorption capacity of As(III)reached 135.78 mg/g,and the arsenic removal efficiency was 90%within 2 hours under low concentration.With the decrease of pH value from 7 to 1,the removal efficiency was reduced to 43%.But the phenomenon of iron exudation existed,and the removal ability in alkaline was obviously weakened.Competitive adsorption existed between arsenic and phosphate,and other coexisting metal ions had no significant effect on arsenic removal.2)In order to solve the problem of iron exudation and separation of nano materials,the core-shell composite named Fe₃O₄@TAPB-PDA COFs was constructed,which took advantage of the strong stability of COFs.And the arsenic removal effect and mechanism under different pH conditions were discussed.In this study,by changing the coating thickness of COFs,the effect of COFs on iron leaching protection and arsenic removal was explored.It was found that the removal rate of arsenic could reach 60%in 2 hours.With the increase of the coating thickness,the removal rate reduced,and the iron leaching alleviated.It was found that the zeta potential increased from 5.9 to 7.0 after COFs coating,that meant the pH range with positive charge of the material is correspondingly widened.In addition,combining the advantages of the two materials mentioned above,Fe₃O₄@TAPB-PDA COFs@Fe⁰ was constructed.In this study,the basic characterizations were carried out and arsenic removal ability was explored.It was found that Fe⁰@TAPB-PDA COFs@Fe3O4 performed better,and 92%removal rate could be achieved within 2 hours.