Near-Infrared-DrivenSelective Photocatalytic Removalof Ammonia Based on Valence Band Recognition of an α-MnO2/N-Doped Graphene Hybrid Catalyst

摘要

Near-infrared (NIR)-response photocatalysts are desired to make use of 44% NIR solar irradiation. A flower-like α-MnO2/N-doped graphene (NG) hybrid catalyst was synthesized and characterized by X-ray diffraction spectroscopy, transmission electron microscopy, Raman spectroscopy, UV–vis–NIR diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The flower-like material of α-MnO2/NG was oval-shaped with the semi major axis of 140 nm and semi minor axis of 95 nm and the petal thickness of 3.5–8.0 nm. The indirect band gap was measured to be 1.16 eV, which is very close to 0.909 eV estimated by the first-principles calculation. The band gap can harvest NIR irradiation to 1069 nm. The coupling of α-MnO2 with NG sheets to form α-MnO2/NG can significantly extend the spectrum response up to 1722 nm, improving dramatically the photocatalytic activity. The experimental results displayed that the α-MnO2/NG hybrid catalyst can recognize ammonia in methyl orange (MO)–ammonia, rhodamine B (RHB)–ammonia, and humic acid–ammonia mixed solutions and selectively degrade ammonia. The degradation ratio of ammoniareached over 93.0% upon NIR light irradiation in the mixed solutions,while those of MO, RHB, and humic acid were only 9.7, 9.4, and 15.7%,respectively. The products formed during the photocatalytic processwere followed with ion chromatography, gas chromatography, and electrochemistry.The formed nitrogen gas has been identified during the photocatalyticprocess. A valence band recognition model was suggested based on theselective degradation of ammonia via α-MnO2/NG.