SBA-15 mesoporous materials decorated with organic ligands: use as adsorbents for heavy metal ions

Abstract

When considering the importance of mesoporous materials as adsorbent for heavy metal ions, this study concerns on the preparation, characterization and application of a SBA-15 mesoporous silica material functionalized with a Schiff base ligand N-propylsalicylaldimine (SBA/SA). The properties of this adsorbent were compared with two SBA-15 mesoporous silica materials modified with aminopropyl (SBA/NH2) and ethylenediaminopropyl (SBA/En) groups. These materials were characterized by XRD, SEM, TEM, TGA techniques and FTIR spectroscopy. The potential of the prepared modified mesoporous materials, as metal ion adsorbents, was evaluated by their application for removal of Pb(II), Cd(II) and Ag(I) ions from aqueous solutions. The assessments were conducted by investigating the effect of sample aqueous pH, contact time, adsorbent dose and initial concentration of the metal ions in batch systems. Flame atomic absorption spectroscopy (FAAS) was used for metal ions measurements. It is found that after 4 h of mechanical agitation of the adsorbents and solution, under optimum conditions, lead ions can be quantitatively removed from 10 mg L−1 Pb(II) solution using 0.03 g of SBA/NH2, 0.005 g of SBA/En or 0.005 g of SBA/SA. Under same conditions, silver ions can be quantitatively removed from 10 mg L−1 Ag(I) solution using 0.04 g of SBA/SA. In addition, all the studied ions can be eliminated from solution (initial concentration 10 mg L−1) using 0.06 g of SBA/En adsorbent. Based on the calculated values from the Langmuir isotherm, the maximum adsorption capacities of the adsorbents SBA/NH2,SBA/En and SBA/SA for Pb(II), Cd(II) and Ag(I) were found to be 29.4, 111.1 and 100.0 mg g−1, 8.0, 14.0 and 5.6 mg g−1, and 7.3, 31.2 and 28.5 mg g−1, respectively. The equilibrium data were analyzed using the Langmuir and Freundlich isotherms. The proposed method was applied for removing Pb(II), Cd(II) and Ag(I) ions from real samples under selected experimental conditions.