Use of statistical design of experiments to evaluate the sorption capacity of 1,4-diazoniabicycle[2.2.2]octane/silica chloride for Cr(VI) adsorption

1,4-Diazabicycle[2.2.2]octane (dabco) silica prepared by grafting (GR-dabco) and sol–gel (SG-dabco) methods were used for removal of Cr(VI) species from aqueous solutions. Full 23 factorial designs with two pseudo-central points were carried out in order to achieve the best conditions of batch adsorption procedure for the Cr(VI) anion uptake by the adsorbents. In order to continue the optimizations, central composite surface design was also employed. These two independent statistical designs of experiments leaded to the following conditions: m = 30.0 mg of adsorbent; pH 6.0; t of contact of 180 min to guarantee the equilibration at higher adsorbate concentration. After achieving the best conditions for Cr(VI) adsorption, isotherms of this adsorbate on using the chosen adsorbents were obtained, which were fitted to non-linear Langmuir, Freundlich, and Sips isotherm models. The maximum sorption capacity for Cr(VI) anion adsorption was 63.86 and 79.82 mg g−1 for using GR-dabco and SG-dabco, respectively.