The water is a non-wetting liquid for kapok fiber due to the formation of large contact angle (>90°) between water and kapok fiber. Therefore, the water is not accessible to the large lumen of kapok fiber. Then, the kapok fiber should experi­ence a chemical or physical pretreatment to be hydrophilic for further application as the adsorbent for removing different kinds of pollutants from aqueous solution. Wang et al. (2012b) found that after NaClO2 treatment, the water drop can form a large spreading radius on the corresponding fiber surface, suggesting that by NaClO2 treatment, the surface of kapok fiber has been transformed from intrinsic hydrophobic-oleophilic to hydrophilic. In addition, NaClO2 treatment can lead to the de-esterification of kapok fiber, thus reducing the aggregate structure and expanding the proportion of amorphous region in kapok fiber (Wang et al. 2012a). In this case, Liu et al. (2012a) investigated the adsorption behaviors of a cationic dye methylene blue from aqueous solution using NaClO2-treated kapok fiber as the adsorbent. In order to alter the hydrophobicity to hydrophilicity, a series of chemical modifications on the kapok fibers via the combination processes of chlorite — periodate oxidation have also been carried out (Chung et al. 2008). When treated with NaClO2 for lignin degradation and NaIO4 for sugar degradation, the chemi­cally oxidized kapok fibers retained their hollow tube shape and evidenced elevated ability to adsorb heavy metal ions, with the adsorption rates of 93.55 %, 91.83 %, 89.75 %, and 92.85 % for Pb, Cu, Cd, and Zn ions, respectively. This enhanced adsorption of heavy metal ions onto the chemically oxidized kapok fibers can be attributed to the generation of — COOH groups during the oxidation process. When the kapok fiber is washed with dichloromethane to remove the botanic wax and further treated with NaOH solution, the resultant fiber can be modified with diethy — lenetriamine pentaacetic acid (DTPA). The resultant kapok-DTPA shows a fast adsorption for the metal ions with the adsorption equilibrium being reached within 2 min for Pb2+ and Cd2+, and 5 min for Cu2+ . Maximum adsorption capacities of kapok-DTPA are 310.6 mg/g for Pb2+. 163.7 mg/g for Cd.+. and 101.0 mg/g for Cu2+, respectively (Duan et al. 2013).