Tannic acid adsorption on amino-functionalized magnetic mesoporous silica

Amino-functionalized magnetic mesoporous silica (magMCM-41-NH2) was prepared and adsorption of organic pollutant tannic acid (TA) from aqueous solution on the resulting material was investigated. The adsorbent was characterized by elemental analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption, IR spectroscopy, Zeta potential measurements and vibration sample magnetometer (VSM). Characterization results showed that magMCM-41-NH2 had ordered mesoporous structure with amino group content of 4.57 wt%, BET surface area of 668 m2/g and the pore volume of 0.525 cm3/g. Batch adsorption tests indicated that magMCM-41-NH2 adsorbent exhibited high adsorption affinity towards aqueous TA with a maximum adsorption capacity of 510.2 mg/g. The Freundlich model could fit the adsorption isotherm of TA over magMCM-41-NH2 very well, implying that adsorption process is heterogeneous. TA adsorption on magMCM-41-NH2 could be well described by the pseudo-second-order kinetics. Adsorption of TA on the adsorbent was found to be strongly dependent on pH and ionic strength, suggesting that electrostatic interaction played a crucial role in TA adsorption. X-ray photoelectron spectroscopy (XPS) analysis confirmed the formation of complex compound between TA and surface amino groups of magMCM-41-NH2 upon adsorption.