In this work, industrial waste hexafluorosilicic acid (H₂SiF₆ or FSA) has been proven to be a low-cost alternative to silicate esters for the synthesis of high-quality MCM-41 (high surface area, high degree of order, narrow pore size distribution, high thermal stability) through a head-to-head comparison between the most common silica precursor, tetraethylorthosilicate (TEOS), and FSA. The effect of different parameters such as temperature, time, hydrothermal treatment, and the presence of ethyl acetate has been explored by studying the textural, structural, and morphological features. On the most promising samples, thermal and hydrothermal stability has been assessed, indicating a higher thermal stability for the FSA-derived sample, due to the thicker walls, and comparable hydrothermal stability. The mother solution treatment has allowed the obtainment of nanostructured fluorite as an additional valuable product and a CTAB-rich ammonia solution for successive synthesis with FSA. Recovery processes for the templating agent entrapped in the MCM-41 mesostructure have also been explored for both FSA- and TEOS-derived samples, showing an easier removal in the case of FSA-MCM-41. Moreover, mesostructured silica derived from FSA has also been proven to be an ideal support to design efficient and regenerable mesostructured iron oxide-based sorbents for H₂S removal from syngas, showing similar performance to that of the corresponding nanocomposite prepared from TEOS.

中文翻译：

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六氟硅酸（FSA）：从危险废物到宝贵资源，以获得高附加值的介孔结构二氧化硅

在这项工作中，工业废料六氟硅酸（H ₂ SiF ₆或FSA）已被证明是从头到尾合成高质量MCM-41（高表面积，高有序度，窄孔径分布，高热稳定性）的硅酸酯的低成本替代品最常见的二氧化硅前体，原硅酸四乙酯（TEOS）和FSA之间的对比分析。通过研究质地，结构和形态特征，探索了不同参数（例如温度，时间，水热处理和乙酸乙酯的存在）的影响。在最有前途的样品上，已评估了热稳定性和水热稳定性，表明由于壁厚较厚，FSA衍生的样品具有更高的热稳定性，并且具有相当的水热稳定性。母液处理允许获得纳米结构萤石，作为额外的有价值的产品，以及富含CTAB的氨溶液，用于与FSA的连续合成。对于FSA和TEOS衍生的样品，也已经探索了MCM-41介孔结构中截留的模板剂的回收方法，在FSA-MCM-41的情况下，回收过程更容易。此外，从FSA衍生而来的介孔结构二氧化硅也被证明是设计高效，可再生的介孔氧化铁基吸附剂的理想选择从合成气中去除₂ S，显示出与从TEOS制备的相应纳米复合材料相似的性能。