Hexavalent chromium[Cr(Ⅵ)]causes serious harm to the environment due to its high toxicity,solubility,and mobility.Ferrihydrites(Fh)are the main adsorbent and trapping agent of Cr(Ⅵ)in soils and aquifers,and they usu...Hexavalent chromium[Cr(Ⅵ)]causes serious harm to the environment due to its high toxicity,solubility,and mobility.Ferrihydrites(Fh)are the main adsorbent and trapping agent of Cr(Ⅵ)in soils and aquifers,and they usually coexist with silicate(Si),forming Si-containing ferrihydrite(Si-Fh)mixtures.However,the mechanism of Cr(Ⅵ)retention by Si-Fh mixtures is poorly understood.In this study,the behaviors and mechanisms of Cr(Ⅵ)adsorption onto Si-Fh with different Si/Fe molar ratios was investigated.Transmission electron microscope,Fourier transform infrared spectroscopy,X-ray diffraction,X-ray photoelectron spectroscopy,and other techniques were used to characterize Si-Fh and Cr(Ⅵ)-loading of Si-Fh.The results show that specific surface area of Si-Fh increases gradually with increasing Si/Fe ratios,but Cr(Ⅵ)adsorption on Si-Fh decreases with increasing Si/Fe ratios.This is because with an increase in Si/Fe molar ratio,the point of zero charge of Si-Fh gradually decreases and electrostatic repulsion between Si-Fh and Cr(Ⅵ)increases.However,the complexation of Cr(Ⅵ)is enhanced due to the increase in adsorbed hydroxyl(A-OH-)on Si-Fh with increasing Si/Fe molar ratio,which partly counteracts the effect of the electrostatic repulsion.Overall,the increase in the electrostatic repulsion has a greater impact on adsorption than the additional complexation with Si-Fh.Density functional theory calculation further supports this observation,showing the increases in electron variation of bonding atoms and reaction energies of inner spherical complexes with the increase in Si/Fe ratio.展开更多
基金supported by the National Natural Science Foundation of China(Nos.42130509 and 42177061)the National Key Research and Development Program of China(No.2020YFC1808300)Jilin Province Science and Technology Development Projects(No.20190303056SF)。
文摘Hexavalent chromium[Cr(Ⅵ)]causes serious harm to the environment due to its high toxicity,solubility,and mobility.Ferrihydrites(Fh)are the main adsorbent and trapping agent of Cr(Ⅵ)in soils and aquifers,and they usually coexist with silicate(Si),forming Si-containing ferrihydrite(Si-Fh)mixtures.However,the mechanism of Cr(Ⅵ)retention by Si-Fh mixtures is poorly understood.In this study,the behaviors and mechanisms of Cr(Ⅵ)adsorption onto Si-Fh with different Si/Fe molar ratios was investigated.Transmission electron microscope,Fourier transform infrared spectroscopy,X-ray diffraction,X-ray photoelectron spectroscopy,and other techniques were used to characterize Si-Fh and Cr(Ⅵ)-loading of Si-Fh.The results show that specific surface area of Si-Fh increases gradually with increasing Si/Fe ratios,but Cr(Ⅵ)adsorption on Si-Fh decreases with increasing Si/Fe ratios.This is because with an increase in Si/Fe molar ratio,the point of zero charge of Si-Fh gradually decreases and electrostatic repulsion between Si-Fh and Cr(Ⅵ)increases.However,the complexation of Cr(Ⅵ)is enhanced due to the increase in adsorbed hydroxyl(A-OH-)on Si-Fh with increasing Si/Fe molar ratio,which partly counteracts the effect of the electrostatic repulsion.Overall,the increase in the electrostatic repulsion has a greater impact on adsorption than the additional complexation with Si-Fh.Density functional theory calculation further supports this observation,showing the increases in electron variation of bonding atoms and reaction energies of inner spherical complexes with the increase in Si/Fe ratio.
