Senna Mamoru, Noda Hirotaka, Xin Yunzi, Hasegawa Hiroki, Takai Chika, Shirai Takashi, Fuji Masayoshi
Faculty of Science and Technology, Keio University Yokohama Japan
Advanced Ceramics Research Center, Nagoya Institute of Technology Tajimi Japan
RSC Adv. 2018 Oct 25;8(63):36338-36344. doi: 10.1039/c8ra07271j. eCollection 2018 Oct 22.
Metal oxides with an oxidation number lower than the highest often exhibit attractive functional properties. However, conventional chemical or thermal reduction of the stable oxides is often laborious and cannot be stopped at an appropriate level of reduction. Therefore, we here try to explore non-conventional reduction processes in a solid-state without external heating. Unique features of reduction processes of SiO toward suboxides, SiO (1 ≤ < 2), were made possible by milling fumed silica nanoparticles with polyolefins (POL), , polypropylene (PP) or polyethylene (PE) and a fluorine-containing one, polyvinylidene difluoride (PVDF). We mainly examined the electronic and coordination states of Si by Si2p XPS spectra and Si MAS NMR, respectively. They significantly differ from a similar commercial product obtained a thermal route. Judging from the chemical shift of Si MAS NMR as a criterion of the degree of reduction of SiO, the function of POL as a reductant is in the order PP ≈ PE > PVDF. Since the present solid-state reaction is free from the formation of unstable gaseous SiO as an intermediate, the products are free from the Si component in a Q state close to that of metallic Si. From these results we conclude that the present silicon suboxides obtained by co-milling silica with POL are closer to those defined as a random bonding model of SiO, than a random mixture model, the former being unachievable by a thermal process. The main mechanism of the present solid-state reduction is the oxygen abstraction from the SiO units by the polarized POL, with its simultaneous oxidative decomposition up to the state of carbon. The reaction process is simple and scalable so that it may offer a new affordable fabrication method of silicon suboxides.
氧化数低于最高氧化数的金属氧化物通常表现出引人注目的功能特性。然而，传统的对稳定氧化物进行化学或热还原的方法往往很费力，而且无法在适当的还原水平停止。因此，我们在此尝试探索在无外部加热的固态条件下的非常规还原过程。通过将气相二氧化硅纳米颗粒与聚烯烃（POL）、聚丙烯（PP）或聚乙烯（PE）以及含氟的聚偏二氟乙烯（PVDF）一起研磨，实现了SiO向低价氧化物SiO （1 ≤ < 2）还原过程的独特特性。我们主要分别通过Si2p XPS光谱和Si MAS NMR研究了Si的电子态和配位态。它们与通过热途径获得的类似商业产品有显著差异。以Si MAS NMR的化学位移作为SiO还原程度的标准来判断，POL作为还原剂的作用顺序为PP ≈ PE > PVDF。由于当前的固态反应不会形成不稳定的气态SiO作为中间体，所以产物中不存在接近金属Si的Q态的Si组分。从这些结果我们得出结论，通过将二氧化硅与POL共研磨得到的当前低价硅氧化物更接近由SiO的随机键合模型定义的那些，而不是随机混合模型，前者是热过程无法实现的。当前固态还原的主要机制是极化的POL从SiO单元中夺取氧，并同时将其氧化分解至碳的状态。该反应过程简单且可扩展，因此可能提供一种新的经济实惠的低价硅氧化物制备方法。
