Electrolytes with excellent chemical stability and high proton conductivity are key materials for protonic ceramic fuel cells and electrolyzers. Doping aliovalent cations to increase the number of oxygen vacancies is a common method to increase conductivity. However, determining proper sites for efficient doping is a matter of general concern because in many cases, there are several cation sites in complex oxides. In this work, we used EXAFS analysis to probe the changes in the local structure of proton-conducting pyrochlore oxides, La2(Nb0.4Y0.6)2O7−δ (LNY60) and La2(Nb0.35Y0.65)2O7−δ (LNY65), upon hydration and found that the coordination number of the oxygen sites in the vicinity of La and Y increased after hydration, indicating that these oxygen sites were active for the hydration reaction to introduce protons. Thereafter, the trivalent La sites were doped with divalent Ca, Sr and Ba cations to introduce more oxygen vacancies into the adjacent oxygen sites to facilitate the hydration reaction. As expected, the proton conductivity increased with increasing content of Ca, Sr and Ba. The conductivities of 2.54 at% Ca-doped LNY60 and 0.98 at% Sr-doped LNY65 were both 1.16 × 10−3 S cm−1 at 700 °C, nearly four times higher than those of the pristine oxides. These results indicate that assisted by EXAFS analysis, proper dopant sites can be determined precisely to further elevate proton conductivity in oxides.
Kaiyue Song,Chengjun Zhang,Jun Shan,Wenting Wang,Huiji Liu,Mengchang He
Simulating the adsorption behavior of Sb(V) on goethite is of great significance for predicting the mobility of Sb(V) in soil. However, there is still a lack of charge distribution and multisite surface complexation (CD-MUSIC) models that conform to the actual adsorption mechanism. Therefore, our research combined the previous EXAFS results with the SCMs and established two CD-MUSIC models (Model I, which introduced bidentate binuclear and bidentate mononuclear complexes, and Model II, which introduced bidentate mononuclear and monodentate mononuclear complexes). It is also one of the rare cases that bidentate edge- and corner-sharing adsorption complexes have been distinguished by introducing different amounts of H + . The results showed that Model I was more suitable for predicting the adsorption behavior of Sb(V) on the goethite surface than Model II. However, at low pH and high Sb(V) loading, the presence of the monodentate complex ≡FeOHSb(OH) 5 0.5- was possible due to the fast and slow two-step mechanism. Using the optimized CD-MUSIC model parameters, the contribution of surface species to the equilibrium adsorption under different conditions was determined. In the adsorption edge and adsorption isotherm simulation process, the edge-sharing bidentate mononuclear complex ≡(FeO) 2 H 2 Sb(OH) 4 was always the most important product, which was consistent with the results of extended X-ray absorption fine structure (EXAFS) analysis. The applicability of the model parameters was verified by predicting the competitive adsorption between PO 4 3− and Sb(V). The CD-MUSIC model established in the present study could be a useful tool for evaluating the equilibrium distribution behavior and environmental risk of Sb(V) in different types of soils.
Nanoscale zero-valent iron (nZVI) and modified nZVI have shown great removal capacities towards various heavy metals. However, the aging process of nZVI during the reaction is crucial for the long-term affinity and stability of heavy metals in the environment. In this study, the aging and iron oxide evolution of amorphous nZVI (A-nZVI) and nZVI during the reaction with Sb(III) were investigated and compared. The results indicated that after reacting with Sb(III), iron oxides in A-nZVI were mainly composed of γ-Fe2O3 (33.9%) and γ-FeOOH (29.8%), whereas α-Fe2O3 (24.9%) and α-FeOOH (31.8%) were dominant in the aged nZVI. The removal capacities for Sb(III) of γ-Fe2O3 (69.8 mg g−1) and γ-FeOOH (42.3 mg g−1) were both much higher than those of α-Fe2O3 (4.3 mg g−1) and α-FeOOH (8.4 mg g−1). Sb(III) was partially oxidized during the reaction, and DFT calculation showed that the adsorption energies of both Sb(III) and Sb(V) on γ-Fe2O3 and γ-FeOOH were higher than those on α-Fe2O3 and α-FeOOH. Furthermore, EXAFS analysis revealed that Sb formed an inner-sphere complex with the iron oxides in A-nZVI through the bidentate mononuclear edge-sharing structure (2E). Therefore, A-nZVI showed higher affinity and long-term stability toward Sb(III) remediation.
危险品化学品经营许可证（带存储）