Density functional theory study of adsorption of As₂O₃ on CeO₂ surface by Fe, La doping and oxygen defects

Density functional theory (DFT) was used to study the adsorption behavior of As₂O₃ (g) on iron and lanthanum doped CeO₂ (110) and oxygen-deficient LaCeO (110) surfaces, and the reasons for the arsenic adsorption capacity of LaCeO surface was significantly higher than that of FeCeO surface was explored. The results show that the adsorption effect of As₂O₃ (g) is closely related to the number of adsorption sites, adsorption energy, bond length and charge transfer amount. Ce and O atoms on the surface of pure CeO₂ are both active sites, and the adsorption is mainly chemisorption, the absolute adsorption energy is greater than −4.22 eV, and the charge transfer amount is (−0.19)−(−0.31) e. As₂O₃ has a negative charge and acts as a surface accepter, while CeO₂ loses electrons and has a positive charge on the surface, which acts as a surface donor. The number of free electrons in the CeO₂ conduction band gradually decreases, the conductivity decreases, and it is difficult to provide more electrons continuously, so the adsorption amount is small. Two adsorption sites are added on the surface of FeCeO (110): Fe top site and Bridge-2 Bridge site, where Fe top site is chemical adsorption and Bridge-2 Bridge site is physical adsorption. The gap doping of Fe changes the electron distribution and lattice structure on the surface of FeCeO, resulting in obvious deformation of the lattice and reducing the difficulty of bonding, thus increasing the configurational adsorption energy of some configurations. However, it does not change the charge transfer direction between As₂O₃ and FeCeO, thus not changing the surface adsorption form of As₂O₃. As₂O₃ is still adsorbed in the form of negative ions, which plays the role of surface acceptor, and the adsorption amount is small. LaCeO (110) has three new adsorption sites: La top site, Bridge-3 Bridge site and Hollow-2 vacancy, among which the La top site and Bridge-3 Bridge site are chemical adsorption. La doping changes the charge transfer direction between As₂O₃ and LaCeO, resulting in positive ion adsorption of As₂O₃ with electron loss and surface donor function. The electrons on the surface of LaCeO play the role of surface acceptor. With the progress of adsorption, the number of free electrons in the conduction band increases, and the conductivity increases. Therefore, the adsorption capacity of As₂O₃ on the surface of LaCeO increases. In the absence of O₂, the number of chemical bonds and bond energy formed on the surface of LaCeO (110) with single O defect are smaller than those on the surface of LaCeO and the charge transfer on the surface of the defect is less, so the adsorption energy decreases. In this case, As₂O₃ obtains electrons and acts as the surface donor, and the adsorption capacity is lower than that on the complete LaCeO surface. In the presence of O₂, the adsorption energy and charge transfer number increase in the ortho-configuration after O₂ supplementation with O defect. As₂O₃ is positively adsorbed in ionic form, and the adsorption energy is also higher than that on the intact LaCeO surface. The adsorption capacity of As₂O₃ is better than that on the LaCeO surface, indicating that O defect is conducive to the adsorption of As₂O₃ in the presence of O₂.