Nickel-Doped CaO to Improve Its Antisintering Property and Electron-Transfer Ability for the Removal of As2O3 from Flue Gas: Experiments and DFT Simulations

CaO, as a relatively inexpensive and readily available adsorbent, has been widely used in areas such as the removal of heavy metal pollutants, but CaO produces sintering with an increasing temperature, which seriously influences its adsorption capacity. This work uses the urea-assisted Pechini sol–gel technique and innovatively combines As2O3 (g) adsorption experiments with theoretical calculations to prepare sintering-resistant Ni/CaO adsorbents. The experimental results showed that the Ni/Ca-2 (Ni doping mass ratio is 2%) adsorbent exhibited excellent adsorption performance, and its adsorption of arsenic reached 602.56 mg/kg at 700 °C, which is 2.89 times higher compared to that of pure CaO. The unique structure formed by trace Ni doping effectively prevented the sintering phenomenon of CaO, significantly enlarged the specific surface area of the adsorbent, added more adsorption sites, and also helped the system to convert the lattice oxygen into chemisorbed oxygen. In addition, the adsorption of As2O3 on Ni/CaO adsorbent was simulated by using a density functional theory approach. The results showed that the main active adsorption sites of Ni/CaO were the O sites in NiO and CaO, and the presence of Ni atoms enhanced the As2O3 adsorption energy on the CaO surface. The reason for this is that Ni undergoes strong orbital hybridization with the O atoms in the system, and the Ni atoms provide more free electrons to the O atoms, which contribute to the electron redistribution on the CaO (001) surface. This also suggests that Ni acts as a kind of bridge for electron transfer during the reaction. The Ni/CaO adsorbent proposed in this article provides a useful guide for the development of composite adsorbent materials.