Photocatalytic Hydrogen Evolution From NaCl Saltwater In The Presence Of Electron Donors

Hydrogen is an ideal green energy in the new century. But hydrogen does not exist in the atmosphere, it largely exists in all kinds of waters. The amount of water on earth is extremely rich, but the distribution of wate in water circle is uneven, most of the waters store in low-lying sea, while fresh water only accounted for 2.53% in the total water.Moreover, the sunshine in western China is adequate, and there are many salt lakes, so photocatalytic hydrogen production from seawater and salt water by solar energy will be of great significance. As NaCl is the major component of seawater and salt lake, In this thesis, we studied photocatalytic hydrogen evolution in the presence of electron donors over Pt/TiO2, ZnS1-x-0.5yOx(OH)y-ZnO from NaCl saltwater. The research work is composed of two parts:1. The effects of electrolyte NaCl on photocatalytic hydrogen evolution in the presence of electron donors over Pt/TiO2 have been investigated. The adsorption performance and surface reaction of electrolyte NaCl and the electron donors on TiO2 have been characterized by electrophoretic analysis and in situ attenuated total reflectance infrared spectroscopy. Under acidic condition Cl- ions are adsorbed on TiO2, while under neutral and basic condition Na+ ions are adsorbed on TiO2. In the case of ethanol as an electron donor, the activity of photocatalytic hydrogen evolution over Pt/TiO2 increases when concentration of NaCl< 0.10 mol L-1, while the activity decreases when the concentration> 0.10 mol L-1. At different pH values, the activity decreases in the order:basic> neutral> acidic. In the cases of formic acid and oxalic acid as electron donors, the activities decrease with increase of NaCl concentration. The Na+ ions can affect adsorption performance of ethanol on TiO2. Possible reaction mechanisms were discussed.2. Photocatalytic hydrogen production was investigated over ZnS1-x-0.5yOx(OH)y-ZnO using sulfide ion (Na2S-Na2SO3) as an electron donor from NaCl saltwater. NaCl can affect markedly the activity for photocatalytic hydrogen production, depending on NaCl concentration. When NaCl concentration is lower, the activity is lower than that in pure water, whereas when NaCl concentration is higher, the activity is higher than that in pure water. The activity at 3.0 mol L-1 NaCl is 1.72 times as high as that at 0 mol L-1 NaCl. This suggests that with the photocatalyst and electron donor, a high-efficient reaction system of saltwater can be constructed, which is very important to practical application. NaCl decreases not only the surface charge of ZnS1-x-0.5yOx(OH)y-ZnO but also the surface hydration. These two factors can markedly influence the activity of ZnS1-x-0.5yOx(OH)y-ZnO. The impregnated photocatalyst (with Na2S-Na2SO3) exhibits much higher activity than non-impregnated one. This can be attributed the fact that ZnO is partly transformed into ZnS.