| Vanadium(V)pollution from industrial production and mining activities has attracted increasing attention due to its toxicity to human health.V mainly exists as vanadate(V(V))in the natural environment,and its migration and transformation in the environment will be influenced by the intense adsorption of iron oxides.The interaction between V(V)and iron oxides has stimulated research about the types of adsorptive complexes.At present,there have been some studies using experimental or theoretical methods to determine the types of V(V)adsorption complexes,but no unified conclusion has been reached,which may be caused by the complexity and diversity of crystal facets exposed on the surface of iron oxides.In addition.the underlying driving force controlling the adsorption of V(V)on the iron oxide surface remains poorly defined,motivating us to perform an in-depth and unified discussion on the adsorption of V(V)at the molecular level.This thesis mainly carries out the following research work:1.The macroscopic adsorption characteristics of V(V)on different hematite(Fe2O3)facets were compared.In this research,three kinds of Fe2O3 nanocrystals exposing {001},{110},and{214} facets respectively were synthesized.Then,kinetics and isotherm characteristics of V(V)on three Fe2O3 facets were compared.According to the results,both of the orders of V(V)adsorption rate and capacity followed {001}>{110}>{214}.The significantly different macroscopic adsorption characteristics indicated that the adsorption mechanism of V(V)on the three facets is probably different,so it is necessary to perform an in-depth study from the microscopic level.2.The types of V(V)adsorption complexes on Fe2O3 facets were investigated.Firstly,the X-ray Absorption Fine Structure(XAFS)study was utilized to explore the complexation types.According to the results,V(V)formed monodentate complexes on the {001} facet and bidentate complexes on the {110} and {214} facets.Subsequently,the protonation information of V(V)adsorption complexes was determined through the in situ attenuated total reflectance Fourier transform infrared(ATR-FTIR)spectra.Specifically,singly protonated complexes were found on the {001} complex,and unprotonated complexes were found on the {110} and {214} facets.In this part,the specific types of V(V)adsorption complexes were determined,providing an experimental basis for understanding the solid-liquid interface behavior of V(V)at the microscopic level.3.The interfacial process of V(V)adsorption was described at the molecular level,and the general rule of metal oxyanion adsorption on the Fe2O3 surface was summarized.In this research,density functional theory(DFT)calculations were utilized to determine the most favorable active Fe sites for V(V)adsorption on Fe2O3 facets from the perspective of thermodynamics.The results showed that the bidentate complex is more thermodynamically stable so that V(V)molecules preferentially bond to the two active Fe sites to form chemical bonds on the {110} and {214} facets.However,the long distance between adjacent active Fe atoms on the {001} facet limits the formation of bidentate complexes.Then,by comparing the structure of other oxyanions and related studies,this study believed that the compatibility in the atomic distance of active Fe-Fe on Fe2O3 facets and O-O in oxyanions shapes the surface complex. |
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