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Since the signing of the Minamata Convention in 2013, attempts have been primarily focused on reducing the emission of elemental mercury (Hg0) from coal-fired power plants (CFPPs). The most cost-effective measure for controlling the emission of mercury involves oxidizing Hg0 to mercury oxides, which are then removed using wet flue gas desulfurization (WFGD). Thus, novel photocatalysts with the best properties of photocatalytic ability and thermal stability need to be developed urgently. In this study, titanium dioxide (TiO2)-based photocatalysts were synthesized through the modification of three metal oxides: CuO, CeO2, and Bi2O3. All the photocatalysts were further characterized using X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence, and ultraviolet-visible spectrometry. The photocatalytic oxidation efficiencies of Hg0 were evaluated under an atmosphere of N2 + Hg0 at 100–200 °C. The photocatalytic reactions were simulated by kinetic modeling using the Langmuir–Hinshelwood (L–H) mechanism. The results showed that Bi2O3/TiO2 exhibited the best thermal stability, with the best oxidation efficiency at 200 °C and almost the same performance at 100 °C. L–H kinetic modeling indicated that photocatalytic oxidation reactions for the tested photocatalysts were predominantly physical adsorption. Additionally, the activation energy (Ea), taking into account Arrhenius Law, decreased dramatically after modification with metal oxides. [ABSTRACT FROM AUTHOR]

• Applying rGO-assisted catalysts to remove Hg and/or NO is systematically reviewed. • Advantages and characterization analysis of rGO-assisted catalysts are summarized. • Catalytic mechanisms of removing Hg0 and/or NO are reported and discussed. • Future perspective of rGO-assisted catalysts on Hg0 and/or NO removal is proposed. The escalating levels of electric power demand have created a lot of air pollution, especially from coal-fired power plants. Due to coal burning, this makes an urgent need for elemental mercury (Hg0) and nitric oxide (NO) treatment technologies. Among different approaches, heterogeneously oxidize Hg0 to HgO by using modified metal oxides-based selective catalytic reduction (SCR) catalysts and absorbing with wet flue gas desulfurization (WFGD) has emerged as a promising solution due to its remarkable economic value and high Hg0 removal efficiency. Although several modification researches have been reported, there are still technical gaps to improve the performance of the catalysts, including their activity and resistance in complex reaction conditions. We believe that graphene as a novel material has the potential to enhance the properties of traditional catalysts. However, there is still a lack of article focus on the removal of Hg0 and/or NO with graphene-based catalysts. This article thus summarizes the preparation method, characterization analysis, catalytic activity, and reaction mechanisms to reduce the knowledge barrier for developing novel graphene-modified catalysts. By conducting this study, we look forward to explaining the research progress of graphene-based catalysts and offering valuable suggestions to guide future modification. [ABSTRACT FROM AUTHOR]

[Display omitted] • rGO modified CeO 2 /TiO 2 was synthesized and explored the removal efficiency of Hg0. • The photothermal catalytic oxidation of Hg0 was dominated by physical adsorption. • S-scheme heterojunction rGO/CeO 2 /TiO 2 performed high redox ability. • The Hg0 oxidation efficiency of 5GCT was 1.5 times higher than CeO 2 /TiO 2 at 200 °C. This study explored the photothermal catalytic oxidation of Hg0 by using S-scheme heterojunction CeO 2 /TiO 2 modified by reduced graphene oxide (rGO) at 100-200 °C. The surface properties of self-prepared photothermal catalysts were characterized by BET, SEM, TEM, EDS, XRD, Raman, UV–Vis, XPS, EPR, and UPS. The crystal structure of TiO 2 was mainly anatase and the nano-sized CeO 2 /TiO 2 was uniformly distributed on the surface of the rGO sheet. The oxidation efficiency of Hg0 decreased with reaction temperature in the order of Ƞ 100 °C = Ƞ 150 °C > Ƞ 200 °C , implying that the oxidation of Hg0 was controlled by mass transfer governed by adsorption instead of photothermal catalytic reaction. Both photo- and thermos-catalytic reaction mechanisms were involved in the oxidation of Hg0 at 100–200 °C. Moreover, rGO-modified CeO 2 /TiO 2 could tolerate multi-pollutants (SO 2 and NO) except for 100 ppm NO, which slightly reduced the oxidation efficiency of Hg0. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu(II)O/TiO 2 as photothermal catalysts with were explored to remove Hg. • 5%Cu(II)O/TiO 2 has the greatest Hg0 oxidation performance. • NO and SO 2 could chemisorb on the surface of catalysts. • The influence of SO 2 and NO in the Hg0 oxidation reaction was clarified by DFT. This study aimed to apply sol–gel synthesized Cu(II)O doped TiO 2 to enhance the oxidation of gaseous elemental mercury (Hg0) in the flue gases containing NO and SO 2 at the temperatures of 120-180℃ under the irradiation of near-ultraviolet (near-UV). The influences of SO 2 and NO on the oxidation efficiency of Hg0 were investigated by in-situ diffuse reflection infrared spectroscopy (DRIFT) and density functional theory (DFT). Experimental results showed that an optimal 5 %Cu(II)O/TiO 2 had the oxidation efficiencies of Hg0 from 40 to 100 % at 120-180℃. The oxidation efficiencies of Hg0 were 85 and 70 % at 120℃, and 40 and 5 % at 180 °C, in the presence of solely SO 2 and NO, respectively. Surface characterization showed that Cu(II)O was evenly dispersed over the surface of TiO 2 catalysts. NO could inhibit the oxidation of Hg0 since it consumed the chemisorbed oxygen (O α) and compete with Hg0 at the surface active sites. In contrast, SO 2 could promote the oxidation efficiency of Hg0 due to the formation of HgSO 4 on the surface of Cu(II)O/TiO 2 catalysts. In the exposure of NO/SO 2 , NO and SO 2 can be adsorbed on the catalyst surface reacting with ̇OH. The photothermal oxidation reactivity of Hg0 was inhibited due to the competitive adsorption between NO/SO 2 and Hg0. The Langmuir-Hinshelwood (L-H) kinetic model successfully simulated the oxidation rate of Hg0. Moreover, DFT was further applied to estimate the binding energies of different gas molecules confirming the competence for active sites on the surface of Cu(II)O/TiO 2 between NO/SO 2 and Hg0. [ABSTRACT FROM AUTHOR]

This article reviews the fundamental theories and reaction mechanisms of photocatalytic technologies with the assistance of electrical field for degrading multi-phase pollutants. Photo(electro)catalysis including photocatalytic oxidation (PCO) and photoelectrocatalytic oxidation (PECO) have been a potential technologies applied for the treatment of organic and inorganic compounds in the wastewaters and waste gases, which has been treated as a promising technique by using semiconductors as photo(electro)catalysts to convert light or electrical energy to chemical energy. Combining photocatalytic processes with electrical field is an option to effectively decompose organic and inorganic pollutants. Although photocatalytic oxidation techniques have been used to decompose multi-phase pollutants, developing efficient advanced oxidation technologies (AOTs) by combining photocatalysis with electrical potential is urgently demanded in the future. This article reviews the most recent progress and the advances in the field of photocatalytic technologies combined with external electrical field, including the characterization of nano-sized photo(electro)catalysts, the degradation of multi-phase pollutants, and the development of electrical assisted photocatalytic technologies for the potential application on the treatment of organic and inorganic compounds in the wastewaters and waste gases. Innovative oxidation techniques regarding photo(electro)catalytic reactions with and without oxidants are included in this review article. [ABSTRACT FROM AUTHOR]