Enhancing the photothermal catalytic efficiencies of Hg0and NO with Bi2O3/TiO2modified by reduced graphene oxide (rGO)

This study aimed to develop novel photothermal catalysts to simultaneously remove Hg0and NO at lower temperatures of 100–200 °C. A new type of photothermal catalysts incorporating reduced graphene oxide (rGO) and bismuth (Bi) modified TiO2(rGO/Bi2O3/TiO2) was developed and further investigated the optimal mass ratio of rGO to Bi-modified TiO2. The surface characterizations of Bi2O3/TiO2and rGO/Bi2O3/TiO2were further performed by using various physical and chemical analytical instruments. A continuous-flow photothermal catalytic reaction system was established to explore the simultaneous catalytic efficiencies of Hg0and NO and to ascertain the optimal operating parameters in this study. Experimental results indicated that the catalytic oxidation efficiency of Hg0decreased with reaction temperature, following the order of η(100 ℃)> η(150 ℃)> η(200 ℃). Among them, 3%Bi2O3/TiO2exhibited better thermal stability and higher catalytic oxidation efficiency of Hg0. Therefore, the photothermal catalysts were further modified with rGO to form 4%rGO/3%Bi2O3/TiO2(4G3BT), which made the catalytic oxidation efficiency of Hg0went up to 80%. The ratio of the intensities of D band to G band (ID/IG) in rGO was about 1.25, indicating significant adsorption effects of rGO. Further simulating with Langmuir-Hinshelwood (L-H) kinetic model, it was determined that, with the increase of reaction temperature, the reaction rate constant (k) tended to increase, while the reaction equilibrium constant (KHg0) decreased. It suggested that the photocatalytic reaction of Hg0was primarily dominated by physical adsorption.