Photo-induced Hydrogen Evolution Properties of Sacrificial Reagents and Ta3N5/WO3

• Main Authors: Liu, Yuan, 劉 媛
• Other Authors: Perng, Tsong-Pyng
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/ueb9pz

碩士 === 國立清華大學 === 材料科學工程學系 === 105 === Many visible-light-driven photocatalysts with a narrow band gap and suitable band edge positions have been developed recently. However, the self-recombination of electrons and holes in a single photocatalyst is one of the main factors that leads to low efficiency of hydrogen production. To overcome this drawback, a Z-scheme system constructed of two photocatalysts has been developed. The aim of this work is to take the advantage of solar energy to achieve higher photocatalytic hydrogen production. In this work, Ta3N5, with a bandgap of 2.0 eV and suitable band structure for overall water splitting, was the main material to be investigated. When Ta3N5 and WO3 were combined in the presence of a shuttle redox mediator, the hydrogen production efficiency was greatly improved because electrons and holes were efficiently separated. WO3 powder was prepared by a simple sol-gel method followed by calcination, and Ta3N5 was prepared by directly annealing commercial Ta2O5 in NH3. SEM, XRD, and UV-vis absorption analyses were conducted to characterize the morphologies, crystalline phases and band gaps. The amounts of hydrogen production over Ta3N5/ WO3 with different molar ratios in deionized water were collected by gas chromatography, and the optimal molar ratios under visible-light and full spectrum irradiation were observed to be 0.75 and 0.5, respectively. The amount of hydrogen production over Ta3N5/WO3 with the optimal molar ratio under full spectrum irradiation was almost 80 times higher than that over single Ta3N5. Similarly, the Ta2O5/WO3 system also had better photocatalytic activity for water splitting than single Ta2O5, but the improvement was not as much as that of Ta3N5/WO3. Common sacrificial reagents, such as methanol, Na2SO3, and Na2S, had significant hydrogen production under full spectrum irradiation without the presence of photocatalyst. Our further research found that the interaction between a photocatalyst and a sacrificial reagent sometimes resulted in negative influence on the hydrogen production. Under full spectrum irradiation, the addition of Ta3N5 did not improve hydrogen production from methanol or Na2SO3 solution. Under visible-light irradiation, hydrogen production over Ta3N5/WO3 from methanol or Na2SO3 solution was even lower than that from deionized water. For better understanding of the behavior of sacrificial reagents, the influences of air and light on the hydrogen production from Na2SO3 solution during the storage were further investigated. The result showed that Na2SO3 was easily oxidized in air, and the hydrogen production decreased linearly with increasing storage time. Both oxygen and room light facilitated the oxidation of Na2SO3.