用动态核极化NMR、漫反射红外傅里叶变换光谱和X射线光电子能谱学研究焙烧的苯基桥周期性介孔有机硅酸盐的官能度和酸性
Probing Functionalities and Acidity of Calcined Phenylene-Bridged Periodic Mesoporous Organosilicates Using Dynamic Nuclear Polarization NMR, Diffuse Reflectance Infrared Fourier Transform Spectroscopy, and X-ray Photoelectron Spectroscopy
摘要：
周期性介孔有机硅（PMO）材料具有高比表面积、高稳定性和疏水性，是环境友好型水化学反应的理想催化载体。我们在这里研究如何煅烧PMO材料与苯连接（PMOB）允许其功能化。常规和动态核极化（DNP）增强NMR光谱、漫反射红外傅里叶变换光谱和X射线光电子能谱学证明，在450 °C下煅烧导致亚苯基桥氧化成（聚）酚，但也氧化成羧酸。还观察到酮、醛以及烯丙基和脂肪醇官能团，但它们的量远低于羧酸。煅烧还裂解Si-C键。然而，N2吸附脱附测量、粉末X射线衍射和透射电子显微镜表明，煅烧至600 °C的PMOB材料仍然表现出有序的中孔。我们表明，在450 °C下煅烧的PMOB的酚和羧酸官能团在室温下使1-（3-氨丙基）咪唑（API）在水中的NH 2基团质子化，但没有检测到API和煅烧的PMOB官能团之间形成共价键。
英文摘要：
Owing to their high surface area, their high stability, and their hydrophobicity, periodic mesoporous organosilica (PMO) materials represent promising catalytic support for environmentally friendly chemical processes in water. We investigate here how the calcination of PMO material with benzene linkers (PMOB) allows its functionalization. Conventional and dynamic nuclear polarization (DNP)-enhanced NMR spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy prove that calcination at 450 °C results in the oxidation of phenylene bridges into (poly)phenols but also into carboxylic acids. Ketone, aldehyde, as well as allyl and aliphatic alcohol functionalities are also observed, but their amount is much lower than that of carboxylic acids. The calcination also cleaves the Si-C bonds. Nevertheless, N2 adsorption desorption measurements, powder X-ray diffraction, and transmission electron microscopy indicate that the PMOB materials calcined up to 600 °C still exhibit ordered mesopores. We show that the phenol and carboxylic acid functionalities of PMOB calcined at 450 °C protonate the NH2 group of 1-(3-aminopropyl)imidazole (API) in water at room temperature, but no formation of a covalent bond between API and the calcined PMOB functionalities has been detected.
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