Heterostructure α-Fe2O3(0 0 1)/g-C3N4(0 0 2) adsorbent to remove As2O3 in simulated coal flue gas: Experimental and DFT study

Arsenic has strong migration and enrichment in flue gas and can produce serious arsenic pollution, so it is urgent to control the arsenic emission in flue gas. In this study, α-Fe2O3/g-C3N4 composites with heterostructure were prepared by hybrid calcination, which was innovatively used to combine As2O3(g) adsorption experiment and microscopic computational analysis. The experimental results show that FC2 (α-Fe2O3:g-C3N4 = 14%, Wt%) has a better As2O3(g) adsorption capacity within 400–500 °C. At 450 °C, FC2 has almost twice the adsorption capacity of As2O3(g) than α-Fe2O3 with an adsorption capacity of 2870.93 mg/kg. When the temperature rises to 500 °C, the adsorption amount of FC2 to As2O3(g) reaches 3450.80 mg/kg, which can be attributed to the more active points than α-Fe2O3. At the same time, with the increase of the adsorption time, the As(III) in the sample tends to be gradually oxidized to As(V). The results of density functional theory (DFT) show that in the heterostructure of α-Fe2O3(0 0 1)/g-C3N4(0 0 2), the electron transfers 0.614 e from g-C3N4 to α-Fe2O3, which establishes the electron transmission channel, thus enhancing the adsorption capacity of As2O3(g). Finally, the oxidation mechanism of As(III) is deduced, and the removal of As2O3 by α-Fe2O3/g-C3N4 can be understood as adsorption before catalysis. Firstly, As2O3(g) is adsorbed to Fe and O on the surface and generates chemical bonds, subsequently binding to the cleaved O2. Part of As(III) is oxidized to As(V), and the other part of As is still As(III) although the As-O bond is broken but combines with O of O2.