Synthesis, characterization, and mercury removal application of surface modified kapok fibers with dopamine (DA): investigation of bidentate adsorption

The present work evaluated a mercury adsorption from its aqueous solution through chemically enhanced kapok fiber with the self-polymerization of the dopamine (DA) on the surface of the kapok fiber. The adsorption capacity of mercury ions was greatly improved with the DA coated kapok fiber (235.7 mg/g), compared with the raw kapok fiber (39.9 mg/g). The kinetic and isotherm studies were established, and the most fitting pseudo-first-order reaction and the Langmuir model indicated that the homogenous chemisorption occurred on the surface of the chemically modified kapok fiber with the equilibrium time of 80 min. According to the FTIR and XPS spectra analyses, the bidentate adsorption of mercury ions was illustrated with hydroxyl groups induced by three-dimensional (3-D) polymerization of DA. The optimum pH was at 8 for the adsorption with the dopamine-coated kapok fiber and the high adsorption efficiency was still maintained after three recycle times, extending its application to treating a number of industrial wastewater streams.