Environment Conservation and Energy Generation by Stratified Photocatalysts Using Sunlight

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The purposes of this research project are the synthesis of photocatalyst can convert from the solar-energy to the chemical energy and the environment conservation through the redox reactions of sulfur compounds in aqueous solutions. We had succeeded to synthesize the photocatalysts of metal sulfide semiconductors with high-efficiency of hydrogen generation. The photocatalysts were synthesized from metal oxides or hydroxides as starting material. Our photocatalysts synthesized by a novel wet-reaction process have the "stratified" structure composed by nano-crystals.In this project, we had researched the relationship between the stratified structure and the photocatalytic activity of the energy conversion. It was found that the stratified-semiconductors formed capsule with a thin layer by ultra fine particles and maintained a potential gradient within this layer, from the results of the morphology observation by transmission electron microscope and the analysis of elemental distribution in the semiconductor particle by energy dispersive x-ray spectroscopy. We can consider that the effective separation of the photoexcited electron and the hole was due to the potential gradient created by the stratified structure. We also researched the studies to establish the reaction system using sea water and sulfur compounds. As a result, we succeeded recovering of various metal ions as sulfides and found the possibilities of removing of harmful heavy metal ions and recovering of useful noble metal ions from sea water.We applied the synthesis process of stratified material to various compound semiconductor materials considered they can use visible region of sunlight. As the results of experiments, we found the stratified-CdS was obtained. These stratified-CdS particles can generate about 7 litters/hour to 1 m^2 of sunlight irradiation.