Facile synthesis of ternary AgBr/BiOI/Bi2O2CO3 heterostructures via BiOI self-sacrifice for efficient photocatalytic removal of gaseous mercury

Ternary AgBr/BiOI/Bi2O2CO3 heterojunction materials, which were synthesized by BiOI self-sacrifice and deposition-precipitation method, were explored for photocatalytic removal of Hg-0 from simulated flue gas. Numerous analytical techniques were used to characterize the properties of photocatalysts. The AgBr content, photocatalyst dosage, solution temperature, pH value, fluorescent lamp (FSL) irradiation, SO2 and NO were also implemented to evaluate Hg0 removal performance in detail. The results indicated that AgBr-BiOI/Bi2O2CO3 was successfully prepared with the sacrifice of BiOI and AgBr was uniformly loaded onto the surface of BiOI/ Bi2O2CO3. The Hg-0 removal efficiency by optimum 2 %AgBr-BiOI/Bi2O2CO3 could reach about 97%, which was 1.38, 1.49 and 3.59 times that of pure AgBr, Bi2O2CO3 and BiOI, respectively. FSL irradiation was essential for an efficient mercury removal and the supply of SO2 significantly exerted inhibition of mercury removal activity. According to the density functional theory (DFT) calculations, a double Z-scheme heterojunction was constructed among AgBr, Bi2O2CO3 and BiOI materials, in which the photo-induced electrons in Bi2O2CO3 combined with holes from AgBr and BiOI, tremendously inhibiting the combination of carriers. According to trapping experiments and electron spin (ESR) test, superoxide radical (O-2(-)) and hole (h(+)) were testified to make major contributions in the process of an efficient Hg-0 removal.