Multi-functional nanoarchitectonics of allophane via addition reactions with acrylonitrile through C-O bond formation

Abstract

Organic functional groups, such as the cyano group (-CN), were introduced onto the Allophane (Allo) surface through addition reactions to achieve precise control over Allo surface properties. Polyacrylonitrile (PAN), Allo and surface-treated Allo were characterized using FT-IR, XRD, XPS and ²⁷Al NMR techniques. It was found that an additional reaction occurs between Allo and acrylonitrile (AN), forming a C-O covalent bond between the unsaturated carbon‑carbon bonds (C=C) of AN and the aluminum hydroxyl groups (Al-OH) on the Allo surface. This reaction constructs an (Al)O-C(C) structure, rearranging the electron density in the aluminum‑oxygen octahedral units, thereby affecting the short-range quasi-crystalline structure within Allo. Concurrently, -CN groups were attached to the Allo surface, while alkenes such as acrylic acid and sodium acrylate introduced organic functional groups like -COOH and -CONH₂ onto the Allo surface. This approach provides a new method for grafting functional groups onto the Allo surface and a novel strategy to modify the surface properties of Allo to obtain multifunctional, high-performance Allo nanocomposite materials.