Effective Capture and Immobilization of Hg0 from Flue Gas Using a Novel Selenium-Functionalized SrFeO3‑δ/HNTs Half-Metal Composite: Adsorption, Photocatalytic Oxidation, and Mechanism

One novel/multifunctional selenium-doped SrFeO3‑δ/HNTs composite was fabricated and used for immobilization of gaseous mercury. The composite showed excellent performances for Hg0 removal via adsorption coupled with photocatalytic oxidation in visible-light conditions. The adsorption capacity of 4271.15 μg·g–1, rate of 5.0 μg·g–1·min–1, and removal efficiency of ∼100% were obtained under N2+O2, which was further confirmed by reaction kinetics. SrFeO3‑δ was selenized into iron diselenide and a Se–Fe bond with high affinity toward Hg0. In addition, the yielding of •O2 – and the separation of photoexcited electrons and holes (h+) promoted the photocatalytic oxidation of mercury. The composite with intrinsic magnetism could be easily recycled for reuse by magnetic separation. Moreover, the composite possessed favorable tolerance to the complicated flue gas. An online lab-built thermal decomposition system demonstrated that the immobilized Hg was primarily HgSe, which exhibited very high stability and low toxicity. Density functional theory (DFT) calculations proved that the composite was half metal with magnetism, indicating that Hg on Se-SrFeO3‑δ/HNTs formed the stable structure releasing 1.055 eV. The doping of selenium promoted the charge transfer between O (2p) and Hg (6s), which also favored Hg0 removal. Se-SrFeO3‑δ/HNTs with recyclability possess great potentials for Hg0 efficient removal and immobilization/detoxification from flue gas.