Modification Strategies of Kapok Fiber Composites and Its Application in the Adsorption of Heavy Metal Ions and Dyes from Aqueous Solutions: A Systematic Review

Kapok fiber (Ceiba pentandra) belongs to a group of natural fibers that are mainly composed of cellulose, lignin, pectin, and small traces of inorganic compounds. These fibers are lightweight with hollow tubular structure that is easy to process and abundant in nature. Currently, kapok fibers are used in industry as filling material for beddings, upholstery, soft toys, and nonwoven materials. However, kapok fiber has also a potential application in the adsorptive removal of heavy metal ions and dyes from aqueous systems. This study aims to provide a comprehensive review about the recent developments on kapok fiber composites including its chemical properties, wettability, and surface morphology. Effective and innovative kapok fiber composites are analyzed with the help of characterization tools such as scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller analysis. Different pre-treatment methods such as alkali and acid pre-treatment, oxidation pre-treatment, and Fenton reaction are discussed. These techniques are applied to enhance the hydrophilicity and to generate rougher fiber surfaces. Moreover, surface modification and synthesis of kapok fiber-based composites and its environmental applications are examined. There are various methods in the fabrication of kapok fiber composites that include chemical modification and polymerization. These procedures allow the kapok fiber composites to have higher adsorption capacities for selective heavy metal and dye removal.