Insights into Efficient Removal of Gaseous Hg⁰ using AgIO₃-Modified BiOI/CoFe₂O₄ Composites through Photocatalytic Oxidation

Abstract

A series of AgIO3 modified BiOI/CoFe2O4 heterojunction photocatalysts synthesized by a solvothermal and subsequent deposition–precipitation method were utilized to remove gaseous Hg0 from simulated flue gas under fluorescent light irradiation. The effects of AgIO3 content, photocatalyst dosage, solution temperature, fluorescent lamp irradiation, pH value, inorganic anions, and SO2 and NO on Hg0 removal performances were investigated in detail. Moreover, the ternary AgIO3–BiOI/CoFe2O4 composites were characterized by XRD, magnetic hysteresis, N2 adsorption–desorption, SEM, TEM, XPS, DRS, ESR, and photocurrent analyses. The results indicated that the AgIO3–BiOI/CoFe2O4 materials possessed enhanced visible-light-driven photocatalytic activities for Hg0 removal, which were much higher than those for AgIO3 and BiOI, and the Hg0 removal efficiency by optimum AgIO3(7%)/BC can reach as high as 99%. The AgIO3 content, solution temperature, FSL irradiation, and SO2 all exhibited significant effects on Hg0 removal. AgIO3(7%)/BC showed good stability and remained highly efficient after four runs. The characterization suggested that AgIO3 was tightly anchored onto the BiOI/CoFe2O4 surface to form a AgIO3–BiOI/CoFe2O4 heterojunction photocatalyst, and the presence of a small amount of AgI might play a vital role for enhanced activity of AgIO3–BiOI/CoFe2O4 photocatalysts. The scavenging experiments of reactive species demonstrated that the superoxide radicals (•O2 –) and holes (h+) were the main oxidant for efficient removal of Hg0.

Intimate Coupling AgI/AgIO3 Heterojunction Photocatalysts with Excellent Visible-Light-Driven Photocatalytic Activity

“…where X is photocatalyst electronegativity (6.71 eV for AgIO 3 ) and E c is the energy of free electrons on the hydrogen scale (4.44 eV), respectively. 27 Consequently, the E CB and E VB for AgIO 3 are estimated to be 0.66 and 3.88 eV, respectively.…”

“…The value of the band gap ( E g ) of AgIO 3 was calculated by the virtue of the classical Tauc method to be 3.22 eV (Figure S5). Moreover, the following empirical equation can be used to determine the conduction band (CB) position ( E CB ) and the valence band (VB) position ( E VB ) for semiconductor photocatalysts: E CB = X – E c – 0.5 E g , E VB = E CB + E g , where X is photocatalyst electronegativity (6.71 eV for AgIO 3 ) and E c is the energy of free electrons on the hydrogen scale (4.44 eV), respectively . Consequently, the E CB and E VB for AgIO 3 are estimated to be 0.66 and 3.88 eV, respectively.…”

Olive Mill Wastewater Remediation: From Conventional Approaches to Photocatalytic Processes by Easily Recoverable Materials

“…Zhou et al [193] studied ternary magnetic Ag 2 WO 4 /BiOI/CoFe 2 O 4 hybrid compounds, evaluating their photocatalytic activity towards toxic elemental mercury Hg(0) removal. In addition, BiOI/CoFe 2 O 4 composites modified with AgIO 3 [194] and Ag 2 CO 3 [195] were found to be highly efficient in the photocatalytic reduction of Hg(0).…”

Mercury Removal Based on Adsorption and Oxidation by Fly Ash: A Review

“…Mercury (Hg), a typical heavy metal with hypertoxicity, volatility, persistence, and bioaccumulation, − has attracted much attention in recent years. , The source of Hg can be divided into natural sources including volcano eruption and forest fires, anthropogenic sources including coal combustion for industrial or domestic utilization, as well as Hg reemission from natural surfaces. , Among different anthropogenic Hg sources, coal combustion in power plants is a major source. − As shown in Figure , during the process of coal combustion, almost all the Hg in coal will release and enter into the flue gas in the form of Hg 0 . − With the cooling of the flue gas, a part of Hg 0 undergoes a series of homogeneous and heterogeneous reactions to transform into the oxidized Hg (Hg 2+ ), and some of the Hg 2+ adsorbs on the surface of fly ash to transform into the particulate-associated Hg (Hg p ), which mainly refers to HgCl 2 , HgO, HgSO 4 , and HgS. , The content of Hg in fly ash can be measured using a specific Hg analyzer. , The identification of Hg species in fly ash can be accomplished by the method of H 2 -TPD through classifying the decomposition peaks against temperature. Hg species identified and corresponding temperature ranges are HgCl 2 (134–142 °C) < HgS (293–317 °C) < HgO (277–476 °C) < HgSO 4 (575–591 °C) .…”