Layer-by-layer loading iron onto mesoporous silica surfaces: Synthesis, characterization and application for As(V) removal

Iron-bearing minerals have been used as adsorbents for arsenic anions for many decades, but both the small surface area and the poorly defined pore structure limit their performance in removal of arsenic from aqueous systems. Herein, we report a sonochemical layer-by-layer (LBL) loading process for depositing of ferric species onto mesoporous silicas (i.e., MCM-41, SBA-15, and KIT-6). The surface area, pore size and volume, as well as the iron loading of these mesoporous silicas can be tailored and optimized with increasing in loading cycle via a LBL protocol. The surface functioned materials were characterized by X-ray diffraction (XRD), N-2 physisorption, transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectrometry and zeta potential measurement. Their performance in As(V) adsorption was also tested. The results indicate that the iron-loaded mesoporous silicas retained their ordered pore structure as well as the large surface area, which enable them a good kinetic performance in uptake of As(V) anions. When iron loading is as much as 10 wt.%, two representative iron-loaded silicas Fe10MCM-41 and Fe10KIT-6, exhibited the best performance in trapping the As(V) anions, with an Fe/As molar ratio of about 5.77 and 5.10, respectively. The Fe/As molar ratio implies they belong to the iron-containing adsorbents with the highest adsorption performance for As(V), and therefore could be used as alternative adsorbents for As(V) adsorption. (C) 2012 Elsevier Inc. All rights reserved.