Environment Conservation and Energy Generation by Stratified Photocatalysts Using Sunlight

本课题的研究目的是通过含硫化合物在水溶液中的氧化还原反应，合成能够将太阳能转化为化学能的光催化剂，从而达到环境保护的目的。我们成功地合成了具有高效产氢性能的金属硫化物半导体光催化剂。光催化剂是以金属氧化物或氢氧化物为原料合成的。本课题采用新型湿法反应工艺合成的光催化剂具有纳米晶组成的“层状”结构，研究了层状结构与光催化能量转换活性之间的关系。结果发现，层状半导体形成胶囊与一个薄层的超细颗粒，并保持在这一层内的电位梯度，从形态观察的结果，通过透射电子显微镜和元素分布的分析，在半导体颗粒的能量色散X射线光谱。我们可以认为，光激发电子和空穴的有效分离是由于分层结构产生的电势梯度。我们还研究了以海水和含硫化合物为原料建立反应体系的研究。结果，我们成功地以硫化物的形式回收了各种金属离子，并发现了从海水中去除有害重金属离子和回收有用贵金属离子的可能性。我们将分层材料的合成工艺应用于各种化合物半导体材料，考虑到它们可以利用太阳光的可见光区域。实验结果表明，在此条件下得到了层状CdS。这些层状CdS粒子可以产生约7升/小时至1 m^2的阳光照射。

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.