Muramatsu Keisuke, Hayashi Shiori, Kuroda Yoshiyuki, Oka Yuya, Wada Hiroaki, Shimojima Atsushi, Kuroda Kazuyuki
Department of Advanced Science and Engineering, Faculty of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan.
Department of Applied Chemistry, Faculty of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan.
Inorg Chem. 2020 May 4;59(9):6110-6119. doi: 10.1021/acs.inorgchem.0c00192. Epub 2020 Mar 18.
Layered double hydroxides (LDHs) have occupied an important place in the fields of catalysts, electrocatalysts, and fillers, and their applicability can be greatly enhanced by interlayer organic modifications. In contrast to general organic modification based on noncovalent modification using ionic organic species, this study has clarified in situ interlayer covalent modification of LDH nanoparticles (LDHNPs) with the tripodal ligand tris(hydroxymethyl)aminomethane (Tris-NH). Interlayer-modified CoAl LDHNPs were obtained by a one-pot hydrothermal treatment of an aqueous solution containing metal salts and Tris-NH at 180 °C for 24 h. Tris-NH was covalently bonded on the interlayer surface of LDHNPs. Interlayer-modified NiAl LDHNPs were also similarly synthesized. Some comparative experiments under different conditions indicate that the important parameters for interlayer modification are the number of bonding sites per a modifier, the electronegativity of a constituent divalent metal element, and the concentration of a modifier; this is because these parameters affect the hydrolytic stability of alkoxy-metal bonds between a modifier and a layer of LDHNPs. The synthesis of interlayer-modified MgAl LDHNPs was achieved by adjusting these parameters. This achievement will enable new potential applications because modification of only the outer surface has been achieved until now. Interlayer-modified LDHNPs possessing CO in the interlayer space were delaminated into monolayers under ultrasonication in water. The proposed method provides a rational approach for interlayer modification and facile delamination of LDHNPs.
层状双氢氧化物（LDHs）在催化剂、电催化剂和填料领域占据重要地位，通过层间有机修饰可大大提高其适用性。与基于离子有机物种的非共价修饰的一般有机修饰不同，本研究阐明了用三脚架配体三（羟甲基）氨基甲烷（Tris-NH）对LDH纳米颗粒（LDHNPs）进行原位层间共价修饰。通过在180°C下对含有金属盐和Tris-NH的水溶液进行24小时的一锅水热处理，获得了层间修饰的CoAl LDHNPs。Tris-NH共价键合在LDHNPs的层间表面上。层间修饰的NiAl LDHNPs也以类似方式合成。不同条件下的一些对比实验表明，层间修饰的重要参数是每个改性剂的键合位点数、二价金属元素成分的电负性以及改性剂的浓度；这是因为这些参数会影响改性剂与LDHNPs层之间的烷氧基-金属键的水解稳定性。通过调整这些参数实现了层间修饰的MgAl LDHNPs的合成。这一成果将带来新的潜在应用价值，因为到目前为止仅实现了外表面的修饰。层间空间中含有CO的层间修饰的LDHNPs在水中超声处理下会分层为单层。所提出的方法为LDHNPs的层间修饰和简便分层提供了一种合理的方法。
