Hydrothermal Preparation And Modification Of Zinc Sulfide Based Photocatalysts And The Photocatalytic Activity

In order to improve the utilization of sunlight and inhibit the recombination of photogenerated electrons and holes, in this work we hydrothermally prepared a series of Zn S based photocatalysts by forming solid solution, ion doping and semiconductor compound. The structure and morphological properties of samples were investigated by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, particle size analyzer and X-ray photoelectron spectroscopy（XPS）, respectively. The photoabsorption property was measured by UV-vis diffused reflectance spectrophotometer and the photocatalytic activities of the samples for the hydrogen production were evaluated in the 200 ml aqueous solution system consists of 0.35 mol/L Na₂ S and 0.25 mol/L Na₂SO₃. Also, the mechanism of photocatalytic hydrogen production of samples was analyzed.The sub-micro sized spherical Zn_0.83Cd_0.17 S particles were prepared by hydrothermal method, which are mainly composed of cubic zinc-blended phase. The sample prepared at 180 oC is composed of sulfide solid solution and Zn S while the homogeneous sulfide solid solution can be formed when the hydrothermal temperature is no more than 160 oC. With the increase of temperature, the crystallization of the samples is improved and Cd content in the solid solution is increased, which enlarged the interplanar crystal spacing and resulted in a gradually red-shift of the absorption edges. Hydrothermal time has a little effects on the phase composition and morphology of samples, and with the prolonging of hydrothermal time, the crystallization and absorption edges of the samples firstly imcreases and then decreases, the sample prepared at 12 h has the best crystallization and the largest absorption edge than other samples. In addition, the amounts of the photocatalyst is an important factor to influence photocatalytic property. The best photocatalytic activity is obtained when the sample prepared at 160 oC and 12 h, and the amount of the sample is 0.03 g, with the H2 generation rate of 45.97 mmol·h^-1·g^-1.Two kinds of photocatalysts were prepared when adding different amounts of Ni2+ into hydrothermal reaction solution. Zn_1-x Ni_x S photocatalysts is formed when the content of Ni2+ is no greater than 0.1 by the incorporation of Ni2+ into lattice of Zn S. When the content of Ni2+ is higher than 0.1, Zn S/Ni_x Sy composites is formed. Both of Zn_1-x Ni_x S and Zn S/Ni_x Sy composites can improve the absorption intensity of samples in the visible light region as well as the photocatalytic hydrogen production activity of Zn S, and the former is superior to the latter. The optimized technology of Zn_0.98Ni_0.02 S b was obtained by changing the hydrothermal temperature and time: the hydrothermal temperature is 180 oC and the time is 12 h, and the prepared sample exhibits the best photocatalytic activity for H2 evolution with an intial rate of 457.11 μmol·h^-1·g^-1.By adding the hydrothermally prepared Mo S₂ nanosheets in the solution containing zinc salt, nickel salt and thiourea, Zn_0.98Ni_0.02S/Mo S₂ composites was prepared. The absorption edges of Zn_0.98Ni_0.02 S red-shift and the absorption intensity in the visible light region is enhanced after introducing the Mo S₂ nanosheets. When the hydrothermal time and amount of Mo S₂ nanosheets are 30 h and 0.02 g, respectively, the best photocatalytic activity with H2 generation rate of 887.40μmol·h^-1·g^-1 was obtained, which is more than twice of the samples without Mo S₂ nanosheets.