Structural characteristics, surface properties, and methylene blue adsorption application of halloysite nanotubes regulated with controllable treatment processes

In this work, halloysite nanotubes (HNTs) were treated with calcination, acid, alkali, pre-calcination acid treatment, and pre-calcination alkali treatments to regulate their structural and application properties. The structural characteristics, surface properties, and methylene blue (MB) adsorption capacity of HNTs under multiple treatments were systematically analyzed and compared. Calcination at varying temperatures modified the crystal phase, morphology, and surface properties of HNTs, with higher calcination temperatures reducing its reactivity towards MB. Moderate acid treatment expanded the lumen and decreased surface potential, significantly enhancing MB adsorption capacity. In contrast, alkali treatment dispersed the multilayered walls of HNTs and raised surface potential, reducing MB affinity. Acid treatment of calcined HNTs effectively increased surface area by leaching most of Al while maintaining the tubular structure, maximizing MB adsorption. Alkali treatment of calcined HNTs leached 100% of Si but destroyed the tubular structure, resulting in poor MB adsorption. HNTs pre-calcined at 600°C and acid-treated at 60°C for 8 h exhibited an optimal specific surface area of 443 m2/g and an MB adsorption capacity of 190 mg/g. Kinetic fitting and Arrhenius equation analysis indicated that both acid and alkali reactions with HNTs were controlled by chemical reactions. This work provides a comprehensive comparison and analysis of five treatment methods, offering insights into regulating the structure and surface properties of HNTs, thereby laying a foundation for their efficient utilization in practical applications.