| The virtues of TiO2, including high photocatalytic activity and stability, cheapness,nontoxicity and none secondary pollution caused etc., have led it to be widely used inphotocatalytic water splitting since the first pioneering articles appeared in1972. Atthe same time, TiO2can only be excited under ultraviolet (UV) light, which occupiesonly4%~6%in the solar spectra. Compared to UV light, most photon flux fromsunlight ranges widely in visible(43%~46%) and infrared regions. This definitelyrestraint the widespread application of TiO2. So, we considered use dye-sensitizedTiO2to enhance its range of light response and improve its photocatalytic activity, inorder to use TiO2for water splitting under visible-light.Semiconductor photocatalyst, dye sensitizer and donors are the maincomponent of dye-sensitized photocatalytic system. In order to improve thephotocatalytic effect, some co-catalyst also will be added. Methanol is one of thecommonly used electron donors, and all the alcohol can be used as sacrificial agenttheoretically. We use TCPP as the dye sensitizer in our photocatalytic system. It hasa series advantages─strong absorption in the visible range, stable performance,long service life etc., but the electron transfer efficiency and adsorption firmnessbetween TCPP and the surface of a semiconductor will be strongly influenced by thepH value of the system. According to what we said above, the thesis focus on thephotocatalytic effect with Pt/TiO2photocatalyst under simulated visible-light,analysed the influenceing factors include different alcohol─methanol, ethanol,n-propanol, isopropanol, pH of solution. A certain quality of TCPP-TiO2-Pt in alcohol solution with different pH was testedfor H2evolution by water splitting. Through these work, the effect and donors werestudied. From our work we know that alkaline conditions make it difficult to thehappen of photocatalytic reaction. When we used the alcohol as donors for ourphotocatalytic system, higher dye desorption rate, the reduce of adsorption quantityof TCPP in TiO2nanoparticles surface and electron injection efficiency, decrease ofconduction band potential of TiO2, all these will be happened under alkalineconditions. At the same time, the value of pH is different when we got the bestphotocatalytic effect for the four alcohol solution: Methanol, n-propanol andisopropanol is pH=7, ethanol is pH=5. Those can be due to the change of absorptionability of TCPP to visible light, adsorption quantity of TCPP in TiO2nanoparticlessurface and electron injection efficiency.The maximum hydrogen yield of the photocatalytic system is changed withdifferent donors. Maximum hydrogen yield(about7.5×10-8mol) is basically the samewhen methanol, ethanol and n-propanol work as the donors. On the other side, themaximum hydrogen yield is only5.5×10-8mol when isopropanol was used as donor.Alougth adsorption quantity and capacity of TCPP in TiO2nanoparticles surface willdecreased with the sacrificial agent carbon chain growth, the efficiency that electronsreach the surface of TiO2is improving. For that reason the maximum hydrogen yieldof the system with n-propanol as donor is basically the same with the system withmethanol and ethanol as donor. The existence of branched structure of isopropanolled to the oxidation state of dye reduction rate becomes slow and lower electrontransfer efficency between photocatalyst and sacrificial agent. This is the reason thatthe system with isopropanol used as donor got lower maximum hydrogen yield. |
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