Occurrence and Evolution of Water in Attapulgite: From Structural Regulation to Functional Applications

Attapulgite is a natural one−dimensional nanomineral with a 2∶1 layered−chain crystal structure, which contains zeolite−like nanochannels and multiple forms of water. The occurrence forms of water in the mineral mainly include adsorbed water, zeolitic water, coordinated water, and structural hydroxyl groups. These water species play a critical role in maintaining the structural integrity, regulating surface chemical properties, influencing pore development, and determining the final functional characteristics of the mineral. This paper systematically summarizes the different occurrence states of water in attapulgite and their evolution during thermal treatment. It focuses on the crystal structure transformation, changes in surface chemical properties (including surface acidity, silanol group density, and charge characteristics), and the evolution of pore structure parameters (such as specific surface area, micropore volume, and mesopore distribution) induced by the progressive removal of various water species. Furthermore, this review discusses the mechanisms by which changes in water states affect the performance of attapulgite in applications such as adsorption, catalysis, and hybrid pigments. This review establishes a systematic understanding of the “water-structure-performance” relationship in attapulgite, providing a theoretical foundation for the rational design of attapulgite−based materials functional applications.