Preparation of MnS with Different Crystal Phases for Photocatalytic H2 Production from H2S

Cubic alpha-MnS and hexagonal gamma-MnS were successfully prepared by a one-pot solvothermal method. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and UV-Vis absorption spectrum were used to investigate the phase, microstructure, morphology, and optical property of the obtained samples. The photocatalytic H-2 production performances from H2S of alpha-MnS and gamma-MnS were evaluated both under visible light (lambda > 420 nm) and UV-Vis light irradiation. The results revealed that both alpha-MnS and gamma-MnS possess photo-splitting H2S activity under visible light, and the metastable state gamma-MnS showed better photocatalytic H2 evolution performance (23.38 mu mol/(g . h)) than the stable form alpha-MnS (4.24 mu mol/(g . h)). Comparing the photocatalytic activity under visible light, it was found that the hydrogen production rate of alpha,gamma-MnS under the full spectrum irradiation increased remarkably. A maximum H-2 production rate of 2272.69 mu mol/(g.h) was achieved over gamma-MnS under the full spectrum irradiation. It is noteworthy that during the process of 6 h photocatalytic testing, alpha, gamma-MnS displayed a good stability and resistance to the photocorrosion. In addition, the catalytic mechanism of alpha, gamma-MnS was investigated. Finally, the reason for the difference in photocatalytic activity between these two MnS phases was explored.