Hydrothermal Synthesis And Photocatalytic Property Of Nano MoS₂

Photocatalytic oxidation is effective degradation technology of organic contaminants for wastewater treatment, and it reveals many advantages including high processing efficiency, simple process equipment, easy operating conditions and so on. Nevertheless, for current industrial photocatalytic materials, ultraviolet can only be utilized for catalytic reactions, resulting in very low light energy utilization rate. Mo S2 with a narrow band gap is an ideal visible-light-induced photocatalyst to utilize solar energy efficiently and Mo S2 nanomaterial is investigated here. For improving photocatalytic property of Mo S2 nanomaterial prepared via a facile hydrothermal method, effects of the hydrothermal temperature, reaction time and the ratio of S/Mo on the formation and photocatalytic properties of Mo S2 were investigated by using XRD, FESEM, EDS, HETEM, UV-vis, TG, DSC equipment and Materials studio analytical software. Growth mechanism and visible light catalytic mechanism of flower-like Mo S2 nanomaterial in the hydrothermal process was also explored.Crystal growth and microstructure results showed that the hydrothermal reaction couldn’t occur in the condition of low temperature(160℃) or short reaction time(4 h). With increasing reaction temperature and time, the grain size of Mo S2 nanomaterial increased fast. The kinetic grain growth exponent n = 1.9134 and the apparent activation energy Q = 50.462 k J/mol suggested that growth of the Mo S2 crystal strongly depended on both the hydrothermal temperature and reaction time. Therefore, appropriate hydrothermal temperature and reaction time were the key to synthesize Mo S2 with good crystallization and full growth. In the hydrothermal condition of 220℃ and 24 h, the grain size of the flower-like Mo S2 microspheres with mean diameter of 1~2 um was 53 nm.The effects of excess sulfur source on the formation showed that the excess sulfur affects the growth orientation of Mo S2 and promotes Mo S2 growing along(002) crystal direction with S/Mo ratio increases. As a result, more areas of the {100} facets which provided more active sites for the photocatalytic reaction were exposed on the crystal surfaces, and the thickness of thin nanosheets in the Mo S2 spheres increased to 30 nm when the S/Mo ratio was 2.75 and 3.Photocatalytic studies showed that with increasing hydrothermal temperature and reaction time, the photocatalytic properties of the products were improved. when the hydrothermal condition is 220℃ and 24 h, the product had the higher photocatalysis efficiency of 91.29%. With increasing S/Mo ratio, the photocatalysis efficiency of the Mo S2 first increased and then decreased slightly. As a result, the highest degradation rate constant of 3.833 × 10-2 min-1 and MB degradation rate of 95.61% under 90 min visible light irradiation was obtained at an S/Mo ratio of 2.75.Optical property characterization and simulation results showed that the Mo S2 nanomaterial had an indirect band gap of 1.5 e V. There was larger electrostatic potential between layers so that electrons and holes generated by light tend to move along the path([100] direction) in which the electrostatic potential fluctuation is small, gathering in and between layers of {100} faces, respectively. Thus, the {100} crystal plane has the higher photocatalytic reactivity.