Removal of elemental mercury by photocatalytic oxidation over La2O3/Bi2O3 composite

Non-radical activation of persulfate with Bi2O3/BiO1.3I0.4 for efficient degradation of propranolol under visible light

Non-radical activation of persulfate (PS) by photocatalysts is an effective approach for removing organic pollutants from aqueous environments. In this study, a novel Bi2O3/BiO1.3I0.4 heterojunction was synthesized using a facile solvothermal approach and used for the first time for non-radical activation of PS to degrade propranolol (PRO) in the presence of visible light. The findings found that the degradation rate of PRO in the Bi2O3/BiO1.3I0.4/PS system was significantly increased from 19% to more than 90% within 90 min compared to the Bi2O3/BiO1.3I0.4 system. This indicated that the composite system exerted an excellent synergistic effect between the photocatalyst and the persulfate-based oxygenation. Quenching tests and electron paramagnetic resonance demonstrated that the non-radical pathway with singlet oxygen as the active species played a major role in the photocatalytic process. The existence of photo-generated holes during the reaction could also be directly involved in the oxidation of pollutants. Meanwhile, a possible PRO degradation pathway was also proposed. Furthermore, the impacts of pH, humic acid and common anions on the PRO degradation by the Bi2O3/BiO1.3I0.4/PS were explored, and the system's stability and reusability were also studied. This study exhibits a highly productive catalyst for PS activation via a non-radical pathway and provides a new idea for the degradation of PRO.

Photo- and thermo-catalytic mechanisms for elemental mercury removal by Ce doped commercial selective catalytic reduction catalyst (V2O5/TiO2)

The elemental mercury was catalytically removed by V₂O₅/TiO₂ and Ce doped V₂O₅/TiO₂ catalysts under the UV irradiation at 30-160 °C to determine whether the catalysts could simultaneously have both thermo- and photo-catalytic activities. The physicochemical properties of catalysts were characterized by XRD, SEM, EDX, BET, XPS, UV-visible, PER and EIS. The experimental results demonstrated that V₂O₅/TiO₂ and Ce-doped catalysts possessed both thermo- and photo-catalytic reactivities. A suitable reaction temperature (120 °C) and UV light had promoting effects on mercury removal efficiency. In addition, owing to the high oxidation capability as well good oxygen storage performance of Ce⁴⁺, Ce doping could greatly improve the mercury removal properties of the catalyst, reduce the inhibition of SO₂ and make NO the component with enhanced effect. Ce doping also had the capability of enhancing the light absorption intensity in the UV region as well as the separation rate of photoinduced carriers. Finally, DFT calculations of V-Ti and Ce-V-Ti for Hg⁰ removal were investigated to further verify the experimental conclusion.

Enhanced photocatalytic Hg0 oxidation activity of iodine doped bismuth molybdate (Bi2MoO6) under visible light

The application of photocatalytic Hg⁰ oxidation under visible light is an up-and-coming method to solve the problem of energy shortage and environmental pollution. In this work, iodine doped Bi₂MoO₆ nanomaterials were prepared by one-step solvothermal method. The photocatalytic oxidation efficiency was greatly improved by iodine doping from 35.5% to 95.2% in the N₂ + 4% O₂ atmosphere under visible light. The main reason was that iodine doping decreased the band gap of the catalyst, expanded the optical response range and intensity, sped up the separation rate of photoinduced carriers and reduced the recombination rate. In addition, the flue gas components of SO₂ and NO played a promoting role in mercury removal. Iodine doped Bi₂MoO₆ had good stability and still maintained high mercury removal efficiency after 5 cycles. Density functional theory (DFT) calculations and experiments demonstrated that iodine doping changed the valence band and conduction band of the catalyst, making superoxide ions, hydroxyl radicals and photoinduced hole become the active species of the catalytic reaction.