Potential of functionalized SBA-15 mesoporous materials for decontamination of water solutions from Cr(VI), As(V) and Hg(II) ions

SBA-15 mesoporous materials modified with aminopropyl and N-propylsalicylaldimine groups abbreviated as SBA/NH2 and SBA/SA, respectively, were used for decontamination of aqueous solutions from Cr(VI), As(V) and Hg(II) ions. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used for metal ions measurements. It is shown that the functionalization enhances significantly the adsorption capacity of SBA-15 materials. Although an ion pair formation mechanism was deduced for the removal of Cr(VI) and As(V) ions, a cation exchange mechanism is proposed for the adsorption of Hg(II) ions. The influence of the parameters affecting the batch method efficiency such as pH of the aqueous solutions, contact time, adsorbent dose and initial concentration of the metal ions were assessed and discussed. Both adsorbents were shown to be selective toward Cr(VI) and As(V) at pH values lower than 2.5–3. It is found that, no significant decrease in the adsorbents efficiency was observed by using three times of SBA/NH2 and seven times of SBA/SA in adsorption–desorption processes. The applicability of the proposed method was assessed by testing the decontamination of some real samples. This selectivity was tuned toward Hg(II) ions at higher pH values. The evaluated thermodynamic parameters (ΔG°, ΔH° and ΔS°) show the processes are exothermic with negative entropy changes. The isotherms of the adsorption process were discussed in detail by applying the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich (D–R) isotherms. The kinetics of adsorption process of As(V) ions onto SBA/SA was examined by examined pseudo first-order, pseudo second-order and intra-particle diffusion models.