Fabrication of polyacrylonitrile-coated kapok hollow microtubes for adsorption of methyl orange and Cu(II) ions in aqueous solution

Abstract

Polyacrylonitrile (PAN)-coated kapok hollow microtubes were synthesized using a facile surfactant-assisted method. Cetyltrimethylammonium bromide (CTAB) was employed to assist in polymer deposition and arrangement. The kapok fibers retained its hollow microtube structure after PAN coating. A drastic decrease in water contact angle from 133.43 to 0° was also determined. Generally, thicker and more uniform PAN coating was achieved at higher concentration of CTAB. On the other hand, addition of larger amount of AN resulted in thicker PAN coating. Batch experiments were utilized to investigate the effect of contact time and temperature on the adsorption efficiency of methyl orange dye and Cu(II) from aqueous solution. Isotherm studies revealed that removal of methyl orange and Cu(II) follow the Langmuir isotherm model, with maximum adsorption capacity of 34.72 and 90.09 mg/g, respectively. This suggests that Cu(II) is preferentially adsorbed on the PAN-kapok fibers over methyl orange. Kinetic studies show that the adsorption of methyl orange and Cu(II) on PAN-kapok follow a pseudo-second order kinetic model, indicating chemisorption as the rate-determining step. Based on thermodynamic data, both Cu(II) and methyl orange adsorption is spontaneous and endothermic.