Old wine and new bottles: Insights into traditional attapulgite adsorbents with functionalized modification strategies applied in efficient phosphate immobilization

Developing effective, economic and environmental-friendly phosphate adsorbents has attracted urgent attention due to the potential eutrophication caused by unnatural phosphate enrichment. In recent years, multifunctional materials prepared from traditional attapulgite clay have demonstrated excellent sorption potential due to their exclusive layered structure as well as moldable and easily-accessible properties. However, its electronegativity on the surface and the aggregation tendency of the one-dimensional nanorod crystals limit wider application for phosphate removal. Hence, various physicochemical modifications were investigated to endow attapulgite with nanoscale functional particles and specific groups. To date, few specialized works have comprehensively evaluated the progress and challenges for attapulgite-based adsorbents in efficient phosphate immobilization, leaving the structural evolution and application potential of the material to be further exploited. This review mainly summarizes the controllable modification strategies, dominant adsorption mechanisms, as well as their key influencing factors in phosphate removal of attapulgite-based adsorbents. Based on this summary, corresponding constructive recommendations such as in-depth adsorption mechanisms exploration, 3D structure development, intelligent recycling applications and machine learning are proposed to develop novel functional attapulgite-based phosphate adsorbents in a wider dimension.