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Chemical reduction of three-dimensional silica micro-assemblies into microporous silicon replicas

机译：将三维二氧化硅微组件化学还原成微孔硅复制品

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The carbothermal reduction of silica into silicon requires the use of temperatures well above the silicon melting point (≥2,000 ℃). Solid silicon has recently been generated directly from silica at much lower temperatures (≤850℃) via electrochemical reduction in molten salts. However, the silicon products of such electrochemical reduction did not retain the microscale morphology of the starting silica reactants. Here we demonstrate a low-temperature (650℃) magnesiothermic reduction process for converting three-dimensional nanostructured silica micro-assemblies into microporous nanocrystalline silicon replicas. The intricate nanostructured silica microshells (frustules) of diatoms (unicellular algae) were converted into co-continuous, nanocrystalline mixtures of silicon and magnesia by reaction with magnesium gas. Selective magnesia dissolution then yielded an interconnected network of silicon nanocrystals that retained the starting three-dimensional frustule morphology. The silicon replicas possessed a high specific surface area (>500 m~2 g~(-1)), and contained a significant population of micropores (≤20 A). The silicon replicas were photoluminescent, and exhibited rapid changes in impedance upon exposure to gaseous nitric oxide (suggesting a possible application in microscale gas sensing). This process enables the syntheses of microporous nanocrystalline silicon micro-assemblies with multifarious three-dimensional shapes inherited from biological or synthetic silica templates for sensor, electronic, optical or biomedical applications.
机译：将二氧化硅碳热还原为硅需要使用远高于硅熔点（≥2,000℃）的温度。最近，通过熔融盐中的电化学还原，在较低的温度（≤850℃）下直接从二氧化硅中生成了固态硅。然而，这种电化学还原的硅产物没有保留起始二氧化硅反应物的微观形貌。在这里，我们演示了一种低温（650℃）镁热还原工艺，该工艺可将三维纳米结构的二氧化硅微组件转换为微孔纳米晶硅仿品。通过与镁气反应，将硅藻（单细胞藻类）的复杂的纳米结构二氧化硅微壳（壳）转化为硅和氧化镁的共连续纳米晶混合物。然后，选择性氧化镁溶解产生了硅纳米晶体的互连网络，该网络保留了初始的三维壳形状。硅复制品具有较高的比表面积（> 500 m〜2 g〜（-1）），并包含大量微孔（≤20A）。硅复制品是光致发光的，并且暴露于气态一氧化氮时阻抗快速变化（建议在微型气体传感中可能的应用）。该方法能够合成具有多种三维形状的微孔纳米晶体硅微组件，这些三维形状继承自用于传感器，电子，光学或生物医学应用的生物或合成二氧化硅模板。

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