Abstract
For photocatalytic water splitting rate enhancement, it is said efficient to add oxidizing sacrifice agents to water, which can consume produced O2, in order to repress the reverse reaction, i.e. re-coupling of produced H2 and O2. From the viewpoint of carbon-neutral taking photosynthesis in nature into account, saccharides of foodstuffs are selected as experiementing oxidizing sacrifice agents. Additionally, a pyroligneous acid is also adopted as one of candidates of nonfood oxidizing sacrifice agents together with an acetic acid of its main component as a reference chemical. Since the most promising photocatalyst for water splitting is TiO2, that is clear from its electronic band structure, three commercial TiO2 are utilized after loading Pt. A simple batch vessel is employed as an apparatus since the purposes of this study are to clarify the fundamental characteristics of photocatalytic H2 production and to optimize the operating conditions. As the results, 0.10 wt%-Pt loaded P25 is realized to provide the highest H2 producing rate of 2.60 l/(m2 · h) from 50 g/l glucose aqueous solution. Though slightly higher efficiency can be obtained by regulating pH value, above-mentioned operating conditions with free pH are concluded superior from the viewpoint of consuming chemical for intending pH to efficiency increment. On the contrary to similar high photocatalytic H2 producing rates from solutions of monosaccharide (glucose and fructose) and disaccharide (sucrose), solution of polysaccharide (starch) shows remarkably slow H2 producing rate down to one-eighth of prescribed ones from monosaccharide and disaccharide, resulting in necessity of pretreating such macromolecules to unimolecules and/or micromolecules, controlling their adsorption to photocatalyst in order to adopt them as oxidizing sacrifice agents. A remarkably low H2 producing rate is recognized from a solution of nonfood pyroligneous acid. Therefore, searches for other natural oxidizing sacrifice agents remain as an indispensable future task.
