Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University, Shanghai 200092, China.
Molecules. 2018 Jun 21;23(7):1502. doi: 10.3390/molecules23071502.
Concentration-gradient Fe₂O₃/SiO₂ aerogels were prepared by placing an MTMS (methyltrimethoxysilane)-derived SiO₂ aerogel on an iron gauze with an HCl atmosphere via one-dimensional diffusion, ammonia-atmosphere fixing, supercritical fluid drying and thermal treatment. The energy dispersive spectra show that the Fe/Si molar ratios change gradually from 2.14% to 18.48% with a height of 40 mm. Pore-size distribution results show that the average pore size of the sample decreases from 15.8 nm to 3.1 nm after diffusion. This corresponds well with TEM results, indicating a pore-filling effect of the Fe compound. In order to precisely control the gradient, diffusion kinetics are further studied by analyzing the influence of time and position on the concentration of the wet gel. At last, it is found that the diffusion process could be fitted well with the one-dimensional model of Fick’s second law, demonstrating the feasibility of the precise design and control of the concentration gradient.
浓度梯度 Fe₂O₃/SiO₂气凝胶是通过将 MTMS（甲基三甲氧基硅烷）衍生的 SiO₂气凝胶置于铁网上，并在 HCl 气氛中进行一维扩散、氨气氛固定、超临界流体干燥和热处理来制备的。能谱分析表明，Fe/Si 摩尔比从 2.14%到 18.48%逐渐变化，高度为 40mm。孔径分布结果表明，扩散后样品的平均孔径从 15.8nm 减小到 3.1nm。这与 TEM 结果吻合较好，表明 Fe 化合物具有填充孔的作用。为了精确控制梯度，通过分析时间和位置对湿凝胶浓度的影响进一步研究了扩散动力学。最后发现，扩散过程可以很好地符合菲克第二定律的一维模型，这证明了浓度梯度的精确设计和控制是可行的。
