Characteristics and Applications of Aluminosilicate Clays: A Review

Abstract

Allophane, halloysite, and imogolite are aluminosilicate clays, whose structures mainly contain silicon and aluminum. However, their morphologies differ markedly: allophane occurs as hollow/porous nanospheres, imogolite as single-walled aluminosilicate nanotubes, and halloysite as multi-walled rolled nanotubes. These structural contrasts control surface hydroxyl chemistry, pH-dependent (variable) charge, porosity, and the accessibility of inner/outer surfaces, which in turn govern the performance of adsorption, catalysis/photocatalysis, enzyme immobilization, biomedical delivery, hydrogel, and membrane technologies. Here, we critically synthesize recent advances with an emphasis on structure–property–function relationships and on the transition from natural/synthesized extracts to engineered/functionalized nanohybrids. At the end of the review, we show that targeted control of morphology, surface charge, and surface functionalization consistently shifts selectivity and stability, enabling application-specific optimization. We also highlight priorities for future research and explain how they contribute to Sustainable Development Goals.