Improvement in Efficiency of Dinitrogen Fixation Using Conducting Polymer/Titanium Oxide Junction System

研究了温和条件下白色光驱动的固氮系统。典型的体系由二氧化钛（TiOx）和聚（3-甲基噻吩）（P3 MeT）组成，它们的异质结在20℃和40%RH的空气中暴露于白色光下时产生铵盐晶体（NH_4ClO_4）。本研究的目的是收集实验数据，阐明固定机理，并研究提高固定率和固定产率的物质条件。前一种方法揭示了固定过程包括在连接界面处形成氨并将其转化为聚合物本体中的铵盐。后一种方法给出的数据表明，二氧化钛表面的氧空位起到了吸附、活化和还原二氮的作用。其次，我们研究了影响固定产率和固定率的物质条件。结果表明，聚咔唑膜的使用导致定影产率的提高，并且使用在磷酸水溶液中电化学制备的氧化钛提高定影速率。前一种改进由聚咔唑中掺杂剂阴离子物质的高浓度（即，高掺杂密度），后者是通过在磷酸中合成的高密度氧缺陷的氧化钛表面。

Nitrogen fixation systems driven by white light under mild conditions was investigated. The typical system consists of titanium oxide(TiOx) and poly(3-methylthiophene)(P3MeT), and their heterojunction is previously shown to produce ammonium salt crystals (NH_4ClO_4) when exposed to white light in air at 20℃ and 40%RH. The aims of this study have been directed to the collection of experimental data which would allow us to elucidate the fixation mechanism and to the investigation of material conditions for increasing the fixation rate and the fixation yield.First, the mechanistic study was performed by the chemical and physical approaches. The former approach revealed that the fixation process consists of the formation of ammonia at the junction interface and its conversion to ammonium salt in the polymer bulk. The latter approach gave the data suggesting that the oxygen vacancy on the titanium oxide surface plays the role of a site for the adsorption, activation, and reduction of dinitrogen.Secondly, we investigated the material conditions to affect the fixation yield and the fixation rate. The results indicated that the use of polycarbazole films leads to the enhancement in the fixation yield and that the use of titanium oxide prepared electrochemically in aqueous phosphoric acid increases the fixation rate. The former improvement was explained by the high concentration of dopant anion species in the polycarbazole (i.e., high doping density), and the latter by the high density of oxygen deficiency on the titanium oxide surface synthesized in phosphoric acid.