Optimization, characterization, reversible thermodynamically favored adsorption, and mechanistic insights into low-cost mesoporous Fe-doped kapok fibers for efficient caffeine removal from water

• Published in: Separation science and technology Vol. 60; no. 13; pp. 1643 - 1658
• Main Authors: Latiza, Rich Jhon Paul, Mustafa, Adam, Delos Reyes, Keno, Nebres, Kharl Laurence, Abrogena, Stephany Lera, Rubi, Rugi Vicente
• Format: Journal Article
• Language: English
• Published: Taylor & Francis 02.09.2025
• Subjects: Adsorption; caffeine; Fe-Kapok; natural adsorbent; optimization; regeneration
• ISSN: 0149-6395; 1520-5754
• DOI: 10.1080/01496395.2025.2514953

This study explores the use of innovative Fe-Kapok fiber as an adsorbent to address persistent caffeine contamination in water. Kapok, a naturally abundant yet underutilized biomass, was modified with Fe particles to enhance its adsorption capacity. This study aimed to optimize the adsorption process by Box-Behnken Design, evaluate the performance of the material through isotherm, kinetic, and thermodynamic studies, and assess its regeneration potential and adsorption mechanism. The optimization revealed that the maximum caffeine removal (94.32%) was achieved under pH 5, a caffeine concentration of 50 mg/L, a contact time of 5 minutes, and an adsorbent dosage of 0.5 g/L. The adsorption process was best described by the Langmuir model (R 2  = 0.9993) with a monolayer capacity of 9.1429 mg/g at 40°C and followed pseudo-second-order kinetics (R 2  = 0.9999), indicating chemisorption. Thermodynamic analysis confirmed the process to be not spontaneous and endothermic, with positive entropy changes. Mechanistic insights suggest a multi-modal adsorption process involving key interactions such as electrostatic attraction, hydrogen bonding, π-π interactions, and coordination with Fe sites. Regeneration studies demonstrated durability of the Fe-Kapok, retaining 90.64% of its initial capacity after five cycles. The findings highlight efficiency and sustainability of Fe-Kapok as an adsorbent for caffeine removal.