Synthesis and characterization of CTAB-silica nanocapsules and its adsorption behavior towards Pd(II) ions in aqueous solution

The silica nanocapsules (SiNC) with CTAB (SiNC-CTAB) and free CTAB (SiNC-FREE) were prepared by the microemulsion polymerization process, in which the cetyltrimethylammonium bromide (CTAB) was used as a structure directive as well as a cationic functionalized agent. The structure and properties of these adsorbents were characterized by a field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), nitrogen adsorption–desorption (NAD) analyzer, Fourier transform infrared (FTIR) spectrophotometer, thermogravimetric analyzer (TGA) and pH at point zero charges (pHpzc) determination. The adsorbents were then characterized for their adsorption behavior towards Pd(II) ions in aqueous solution performed in a batch adsorption experiment. The maximum adsorption capacity of Pd(II) ions onto SiNC-CTAB obtained from the adsorption isotherm was 124.50 mg g-1, which was over 2.4 times higher than that of the SiNC-FREE (51.28 mg g-1). The diffusion modeling analysis by the Weber Morris model indicated that the film diffusion is the controlling step, while the chemical reaction modeling obeyed the pseudo-second order kinetic model. The SiNC-CTAB was found to be reusable in which a good adsorption performance of up to 4 adsorption cycles was observed