Ternary ANTs@ZIF-8@ZIF-67 hybrid nanocomposite for ultra high dye adsorption.

Synthetic dyes from textile and related industries are discharged in large volumes; the discharged dyes persist in aquatic environments, causing long-term ecological and health risks. Among them, crystal violet (CV) is particularly hazardous dye due to its toxicity, recalcitrance, and widespread industrial use, necessitating advanced treatment solutions. In this work, a hybrid ternary nanocomposite was constructed by sequentially coating alumina nanotubes (ANTs) with ZIF-8 and ZIF-67 to form ANTs@ZIF-8@ZIF-67 nanostructure, and its performance for CV removal from water was systematically evaluated at different conditions (i.e., dye initial concentration, contact time, pH, and temperature ranging from 5 to 500 mg/L, 0-96 h, 4-10, and 283-328 K, respectively). Crystallinity, functional groups, morphology, and textural properties of the synthesized tertiary nanocomposite and its constituents were thoroughly investigated by XRD, FTIR, XPS, SEM, and N2-sorption analyses. The performance of the tertiary nanocomposite in removing CV from synthetic wastewater samples was benchmarked to those of its constituents (i.e., ANTs, ZIF-8, ZIF-67, ANTs@ZIF-8, ANTs@ZIF-67) as well as of the other tertiary nanocomposite (i.e., ANTs@ZIF-67@ZIF-8), and the obtained results revealed the superiority of ANTs@ZIF-8@ZIF-67. Equilibrium data of CV adsorption onto the ANTs@ZIF-8@ZIF-67 nanocomposite were best described by the Langmuir isotherm model, while kinetics followed a pseudo-second-order rate law. Thermodynamic parameters revealed that the adsorption process is endothermic and spontaneous in nature. The hybrid ANTs@ZIF-8@ZIF-67 nanocomposite preserved 85% of its initial CV uptake after five adsorption-desorption cycles, demonstrating good reusability. In addition, machine-learning algorithms (MLP, SVM, Extra Trees) reliably predicted adsorption capacity with R2 up to 0.93, supporting data-driven evaluation of adsorbent performance. These findings establish ANTs@ZIF-8@ZIF-67 nanocomposite as a robust, regenerable, and effective platform for efficient remediation of dye-laden wastewater.