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

To advance the precise regulation and high-value utilization of halloysite nanotubes (HNTs), this work systematically investigated five treatment strategies, including calcination, acid treatment, alkali treatment, acid treatment of calcined HNTs, and alkali treatment of calcined HNTs, to modulate their structural and application properties. The structural characteristics, surface properties, and methylene blue (MB) adsorption capacity of HNTs under multiple treatments were systematically analyzed. Calcination at varying temperatures modified the crystal structure, morphology, and surface properties of HNTs, with higher calcination temperatures reducing their reactivity towards MB. Moderate acid treatment expanded the lumen and decreased the surface potential of HNTs, 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 their specific surface areas by leaching most of Al while maintaining the tubular structure, thereby maximizing MB adsorption. Alkali treatment of calcined HNTs destroyed the tubular structure and resulted in poor MB adsorption. HNTs pre-calcined at 600°C for 3 h and acid-treated at 60°C for 8 h exhibited an optimal specific surface area of 443 m²·g⁻¹ and an MB adsorption capacity of 190 mg·g⁻¹. Kinetic and Arrhenius equation fittings indicated that chemical reactions control interactions of acids and alkalis with HNTs. This study provides a comprehensive comparison and analysis of five treatment methods, offering insights into regulating the structures and surface properties of HNTs by controlling the treatment condition, thereby laying a foundation for their efficient utilization in practical applications.