Solvents mediated-synthesis of 3D-BiOX (X = Cl, Br, I) microspheres for photocatalytic removal of gaseous Hg~0 from the zinc smelting flue gas

摘要

Three-dimensional (3D-BiOX (X = Cl, Br, I)) microspheres were fabricated by a facile solvothermal method with ethylene glycol (EG) as the solvent. The as-prepared microspheres compounds BiOX were characterized by XRD, SEM, BET, UV-vis DRS, FT-IR and XPS techniques and employed as a photocatalyst to photocatalytic oxidize elemental mercury (Hg-0) from a smelting flue gas. Results showed that the band gaps values of 3.12, 2.69 and 1.77 eV were obtained for the direct electronic transition of BiOCl, BiOBr and BiOI samples, respectively. The specific surface area and surface hydroxyl groups are the two crucial factors affecting the photocatalytic oxidation of Hg-0 BiOI microsphere possesses the maximum of the surface hydroxyl groups, largest BET specific surface area (35.8964 m(2)/g), strongest optical absorption properties, narrowest band gap width (1.77 eV) and the highest photocatalytic activity (eta(oxi) = 96.83%) under UV-vis irradiation. The photogenerated holes (h(+)) produced in the Valence Band (VB) can react with surface-bonded H2O ((ad)) or OH-, I- to produce hydroxyl radicals (center dot OH) and I-2, respectively. The photogenerated electrons (e(-)) produced in the Conduction Bands (CB) can react with adsorbed dissolved oxygen to form super-oxide radicals (center dot O-2(-)). In addition, for the BiOBr reaction system, the center dot OH, h(+) and center dot O-2(-) could play key roles in the formation of HgO, while in BiOI photocatalytic system, except for center dot OH, center dot O-2(-) and h(+), I-2 could also be an important species for the generation of HgO and HgI2 species.