Theoretical Study On The Structure And Properties Of Super-Chalcogens Clusters

This dissertation mainly includes two parts:1)A series of sandwich-type sandwich clusters are designed by combining two electron counting rules（Octet rule and Hückel 4n+2 rule）and their properties are systematically studied.2)Theoretical research on the removal of toxic heavy metal cations(Cd²⁺,Hg²⁺and Pb²⁺)in wastewater by superchalcogens clusters based on closed borane structure.2)Theoretical study based on the removal toxic heavy metal cations(Cd²⁺,Hg²⁺and Pb²⁺)from wastewater by the use of superchalcogens.The first part mainly includes the structural design of dianion clusters,the theoretical calculation of the first vertical electron detachment energy（FVDE）and the analysis of various influencing factors.The second part mainly includes the calculation of binding energy of superchalcogens combined with toxic heavy metal cations(Cd²⁺,Hg²⁺and Pb²⁺)in wastewater and the analysis of various properties.The first chapter expounds the background and research significance of superatoms and superchalcogens,including the main characteristics of superchalcogens,the importance of electron counting rules in designing superchalcogens,and the application prospects of superchalcogens in lithium-ion and magnesium-ion batteries and wastewater treatment.The second chapter is an introduction to the computational methods used in this paper.In Chapter 3,the structure and properties of a novel sandwich-structured dianion[M（B₂C₄X₆）₂]^2-（M=Be,Mg and Ca;X=H,F and Cl）,which satisfies two electron counting rules（Octet rule and Hückel 4n+2 rule）are systematically studied.The calculated first vertical electron detachment energy（FVDE）of dianions show that a total of 52 structures satisfy the theoretical criterion of superchalcogens,in addition to[M（B₂C₄H₆）₂]^2-（M=Be,Mg and Ca）clusters.In most cases,the FVDE value of a dianion cluster is positive,and the dianion can overcome the Coulomb repulsion between electrons,thereby binding the second extra electron and preventing its automatic desorption,making the whole cluster stable and become superchalcogens.The result also show that the FVDE values of the dianion clusters can be adjusted by changing the central metal atom,changing the relative positions of the two rings,and replacing the hydrogen atoms of the two rings with highly electronegative substituents,so as to better regulate the properties of the superchalcogens.By comparing the effects of different factors on FVDE,we find that substituents on cluster rings play a dominant role in FVDE values of such sandwich structures,which indicates the importance of substituents in designing the structure of superchalcogens.Therefore,more stable and better superchalcogens can be designed by adjusting the substituents of dianion clusters,which provides effective theoretical guidance for the structural design and experimental synthesis of new superchalcogens.In comparison of calculation methods,we find that B3LYP functional is very close to OVGF method in the calculation of FVDE value.The fourth chapter studies a series of theoretical studies on the binding of B_nH_n^2-（n=6～12）dianions that based on Wade-Mingos rule with heavy metal cations in the aqueous solution.By calculating the binding energy of the composite structure,it is shown that some B_nH_n^2-（n=6～12）clusters have the ability to bind heavy metal cations(Cd²⁺,Hg²⁺and Pb²⁺)in wastewater,among which B₆H₆^2-cluster has the largest binding energies for Cd²⁺,Hg²⁺and Pb²⁺.In addition,by studying hydrated cations,it was found that the adsorption of hydrated[Hg（H₂O）₄]²⁺on B_nH_n^2-（n=6～12）was thermodynamically better than[Cd（H₂O）₄]²⁺and[Pb（H₂O）₄]²⁺.The calculations also show that the adsorption of heavy metals has a significant effect on the electronic properties of B_nH_n^2-（n=6～12）,and the adsorption of heavy metal cations can significantly narrow the wide HOMO-LUMO gap of B_nH_n^2-（n=6～12）clusters.In terms of charge transport,there is a clear charge transfer from B_nH_n^2-（n=6～12）clusters to isolated metal cations.Therefore,it can be concluded that B_nH_n^2-（n=6～12）clusters have strong adsorption capacity for heavy metal cations(Cd²⁺,Hg²⁺and Pb²⁺).Combined with the above work,we can also reasonably design some stable superchalcogens as adsorbents to remove toxic heavy metal cations in wastewater.The theoretical study in this paper will help us to design more stable superchalcogens by using a variety of electron counting rules.At the same time,through the research on the application of superchalcogens,it is found that superchalcogens can treat toxic heavy metal cations in wastewater,which can also provide useful guidance for experiments.