Theory Research On The Adsorption Of As(?) From Aqueous Solution By Polymer Fe(?)-oxyhydroxides

Arsenic?As?is a metalloid element,which is toxic,carcinogenic and one of the priority control pollutants.Arsenic is widely distributed in nature,which mainly originates from geological origin and human activities.Therefore,the harmful effects of arsenic and its compounds on human body and environmental pollution have aroused widespread concern.This has also led to the prevention and control of arsenic,which becomes an internationally key research direction.In addition,in numerous arsenic removal methods,the adsorption method has the advantages of wide source of materials,simple operation,high removal efficiency,low cost,and environmental friendliness.This makes the adsorption method in the purification and removal of arsenic has been favored by domestic and foreign environmental researchers.In many metal and its metal?hydrogen?oxide adsorbent materials,Fe?III?-oxyhydroxide is widely used for the treatment of heavy metals due to its characteristics such as high specific surface area,strong reactivity,and it has also been proved to be a highly efficient adsorption material.Hence,in this paper,based on the monomer,dimer and trimer Fe?III?-oxyhydroxide complexes as the main research object,combined with experimental infrared spectrum analysis,by adopting the method of density functional theory and Gaussian 09 package for the theoretical calculation study on its adsorption pentavalent arsenic.First,we simulated and designed these material structures and carried out geometric optimization.Then,the optimal stable structures were selected,and the related properties such as structure,bonding properties,orbital interaction and adsorption energy of these substances were calculated and analyzed.Through the study of monomer,dimer and trimer adsorption systems,the main conclusions can be drawn as follows:?1?The structure comparison analysis shows that the length of Fe-OH bond of monomer,dimer and trimer Fe?III?-oxyhydroxide complexes has changed before and after adsorption.The bond lengths of the Fe-O and As-O bonds,which adjacent to the Fe-O-As bond,have been shortened.This also indicates that the adsorption systems formed are stable.?2?The results of bonding and stability analysis show the 3d and 4s orbitals or 3d,4s,and 4p orbitals of the Fe and O atoms are mainly participated in bond formation,while 4s and 4p orbitals of the As and O atoms are mainly participated in bond formation.In addition,the purpose of hybridization between s,p,and d orbits is to form stable chemical bonds,thereby increasing the stability of monomer,dimer,and trimer adsorption structures.The stability analysis shows that the monomer of monodentate?²E?-FeO₂As?OH?₂?Structure 1-3?,dimer of bidentate edge-sharing?²E?-Fe₂O₂As?OH?₂?Structure 2-3?,and trimer of bidentate edge-sharing?²E?-Fe₃O₂As?OH?₂?Structure 3-3and 3-4?adsorption system structure stability are relatively better.?3?The results of infrared spectroscopy show that the absorption intensity of H atoms on the Fe-OH and As-OH bonds is relatively largest in the obtained vibration frequencies.Moreover,after the adsorption of As?V?on the monomer,dimer,and trimer Fe?III?-oxyhydroxide surfaces,a new adsorption system structure was formed.In water environment,Fe?III?-oxyhydroxide may be the main existing structures in the forms of dimer and trimer.?4?The results of thermodynamic analysis show that,in aqueous solution,the monomer,dimer,and trimer Fe?III?-oxyhydroxide structures can exist stably,and they can be interchangeable under certain conditions.What's more,it mainly exists in the form of dimer and trimer Fe?III?-oxyhydroxide.