Study On TiO₂-based Photocatalyst For Hydrogen Production From Water

Energy shortage and environmental pollution are becoming two big problems facing humanity in nowadays society. In order to realize the sustainable development of energy, the search of clean and renewable energy is a problem urgently needed to be addressed. Photocatalytic water splitting for hydrogen evolution by the utilization of solar energy is considered to be the most ideal way to solve the contradiction between the energy and environment. Non-toxic, cost effectiveness, outstanding stability of chemical properties, and unusual optical and electronic properties make TiO₂ become widely employed photocatalyst. However, due to its wide bandgap of 3.2eV, single TiO₂ photocatalystis utilized only under UV light. Besides, the photogenerated electron-hole pairs are more likely to recombine. All of these limit the practical application of TiO₂. At present, the research hot spot is the modification of TiO₂, in order to improve its photocatalytic activity for hydrogen production under the visible light irridation. In this paper, our attention is focused on modifying TiO₂ with low-cost Cu component. Under visible light irridation, the photocatalytic activity for hydrogen production of CuO/TiO₂ and Cu₂O/TiO₂ is investigated. Besides, the effects of different catalyst fabrication method and scavengers on the activity of photocatalyst are compared and analyzed.At first, the CuO/TiO₂ photocatalysts were fabricated by six methods: simple wet impregnation（SWI）, ethanol impregnation（EI）, step impregnation（SI）, in situ sol-gel（SG）, chemical adsorption decomposition（CAD） and composite precipitation（CP）. The experimental results showed that the photocatalytic hydrogen evolution rate decreased in the sequence of CAD sample > CP sample > EI sample > SWI sample> SI sample > SG sample. The hydrogen evolution rate of the CAD sample was proved to be the highest among the samples and reached 3155.7μmol/（g·h）. But, its stability was poorer than EI sample.Secondly, photocatalytic hydrogen evolution was recorded using the 2.5-CuO/TiO₂ photocatalyst fabricated by CAD method, when different scavengers were added into the reaction system. These scavengers included alcohol（methanol, ethanol, ethylene glycol and glycerol）, aldehydes（formaldehyde, acetaldehyde） and acids（formic acid, acetic acid）. The experimental results indicated that, for the improvement of hydrogen evolutionh rate, scavengers of alcohol were better than aldehydes and acids. This was the result of synthetic action of many factors, such as the ratio of the number of carbon atoms and hydroxyl number in a scavenger molecule, molecular structure of scavenger molecule, the number of scavenger molecules in unit volume of reaction solution.At last, a series of Cu₂O/TiO₂ photocatalysts with different molar fraction of Cu2 O were prepared by a facile modified ethanol-induced approach. The influence of different loading amounts of Cu2 O on the photocatalytic activity of the photocatalyst was studied. The photocatalytic activity was significantly enhanced by the p-n heterojunction between p-type Cu2 O and n-type TiO₂, owing to the efficient separation of photogenerated electrons and holes. As a consequence, the prepared 2.5-Cu₂O/TiO₂ photocatalyst of which the loading molar fraction of Cu2 O was 2.5%, exhibited the highest photocatalytic activity for H2 evolution rate.