A variety of organic and inorganic layered compounds are exfoliated into 2D nanomaterials in liquid phase. Improvement of exfoliation yield is a significant challenge for further applications of 2D nanomaterials. However, yield of transition-metal-oxide nanosheets is not so high, such as around 5% for 240 h and 15% for 120 h, in previous exfoliation methods. Here we show a new exfoliation approach to high-yield synthesis of nanosheets. A layered composite of cobalt hydroxide and guest quinone derivative was exfoliated into nanosheets through redox reactions of the interlayer guests in the yield 16–57% for 1 h under mild conditions. The redox reactions of the guest molecules on the layer facilitate efficient exfoliation through improvement of the affinity between the guest and dispersion medium. The present redox-mediated exfoliation approach can be applied to efficient synthesis of a variety of 2D nanomaterials from layered composites.
charge limits grafting and/or adsorption of the guest organic molecules in aqueous media. Designed surface of nanoparticles facilitates widening of the application range. [15][16][17] Therefore, versatile surface-functionalization methods are required for 2D nanosheets. Here we report on a new method for surface functionalization of monolayers through exchange of the surface-modified molecules coupled with exfoliation (Figure 1).The intercalation of organic molecules is regarded as the modification of the layer surface. In previous works, the surface-modified layers were exfoliated and dispersed in polymer matrices to obtain the composite materials with the characteristic properties, such as optical and mechanical properties. [18][19][20][21][22][23][24][25][26][27] A limited number of previous works showed the surface-functionalized monolayers with hydrophobic nature dispersible in nonpolar organic media. [28][29][30][31][32][33] In our previous reports, we developed a new exfoliation approach for synthesis of the surface-modified monolayers in nonpolar organic and aqueous media. [32][33][34][35] The precursor layered composites are synthesized by the intercalation of organic ions, such as longchain alkylammonium ions (C n NH 3 + ) and benzylammonium ions (RBA + ), in layered titanate, manganate, and tungstate. Exfoliation of the precursor layered composites proceeds with intercalation of nonpolar organic media, such as toluene, in the hydrophobic interlayer space. The hydrophobic nanosheets with surface modification by the C n NH 3 + are obtained in nonpolar organic media. However, the surface modification is only achieved by the initially intercalated molecules, such as C n NH 3 + , in the precursor layered composites. If the original surface molecules are exchanged to the other guest ones, the surface modification can be achieved by a variety of guest molecules. In the present work, the surface-functionalized titanate monolayers were prepared by the simultaneous exfoliation and surface modification in a nonpolar organic medium (Figure 1). The original surface mole cules on the monolayer were partially exchanged to the guest ones during the exfoliation process.The surface functionalization of semiconductor nanosheets has potentials for bandgap engineering. Our group found that the surface modification of the nanosheets induced the change of the bandgap energy. [32] Previous reports suggest that the surface modification of titanium-dioxide particles with catechol and phenol derivatives induces the visible-light Exfoliation of layered compounds generates nanosheets, such as mono layers and fewlayers. In general, it is not easy to control surface chemistry of the exfoliated nanosheets. Here, a new approach for surface function alization of titanate monolayer coupled with exfoliation is reported. The precursor layered composite is prepared by intercalation of longchain alkyl ammonium ion, such as stearylammonium ion (C 18 NH 3 + ), in the interlayer space of layered titanate. The layered composite of titanate...
Durch reduktive Alkylierung des Diamins (Ia) mit Glutaraldehyd bzw. 3‐Oxapentandial erhält man die Piperidin‐ und Morpholinderivate (Ib) und (lc), die durch Umsetzung mit den Anhydriden (II) bzw. (V) und anschließende Veresterung die Carbonsäureester (III) bzw. (VI) liefern, die zum Valerolacton (IV) bzw. Mevalolacton (VII) cyclisiert werden können.
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