Covalently Linked Pigment@TiO2 Hybrid Materials by One-Pot Solvothermal Synthesis

Hybrid materials (HMs) combine the high diversity of functionalities of organic compounds with properties typical for inorganic materials, such as high mechanical strength or high thermal stability. Herein, HMs combining organic pigment molecules and TiO₂ as inorganic component, with covalently linked components, i.e., so-called class II HMs, are reported. The synthesis of such HMs is intrinsically challenging, as the apolar organic pigment component and the inorganic polar TiO₂ component require different conditions for their respective formation. Herein, we circumvent this issue by employing solvothermal synthesis in superheated isopropanol, which through temperature tunability of the solvent properties allows for both generating and linking both components in one-pot. First, it is shown that an organic benzimidazole-based pigment molecule designed for readily binding to Ti can be synthesized solvothermally. Second, new class II titanium-based HMs are generated from Ti(OⁱPr)₄ and pigment precursors in a solvothermal reaction. The pigment@TiO₂ HMs feature significant porosity and are structurally identified as layered structures of lepidocrocite-like TiO₂ linked via pigment molecules. These layered HMs assemble into hierarchical nanoflowers, and depending on the pigment segments, different interlayer spacings in between inorganic layers are observed. Third, the pigment@TiO₂ materials are shown to be usable as electrode materials in lithium-ion batteries.