Insight into the adsorption of tetracycline onto amino and amino-Fe3+ gunctionalized mesoporous silica: Effect of functionalized groups

Abstract

In order to study the influences of functionalized groups onto the adsorption of tetracycline, we prepared a series of amino and amino-Fe³⁺ complex mesoporous silica adsorbents with diverse content of amino and Fe³⁺ groups (named N,N-SBA15 and Fe-N,N-SBA15). The resulting mesoporous silica adsorbents were fully characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectrometer (FTIR) and N₂ adsorption/desorption isotherms. Furthermore, the effects of functionalized groups on the removal of TC were investigated. The results showed that the periodic ordered structure of SBA-15 was maintained after modification of amino/Fe³⁺ groups. The functionalized amino groups decreased the adsorption capacity while the coordinated Fe³⁺ increased the adsorption capacity. The adsorption kinetics of TC fitted pseudo-second-order model well and the equilibrium was achieved quickly. The adsorption isotherms fitted the Langmuir model well and with the Fe³⁺ content increased from 3.93% to 8.26%, the Q_max of the adsorbents increased from 102 to 188mmol/kg. The solution pH affected the adsorption of TC onto amino complex adsorbents slightly while influenced the adsorption onto Fe-amine complex adsorbents greatly. The adsorption of TC on SBA15 and N,N-SBA15 may be related to the formation of outer-sphere surface complexes, while the adsorption of TC onto Fe-N,N-SBA15 was mainly attributed to the inner-sphere surface complexes. This study could offer potential materials that have excellent adsorption behavior for environmental remediation and suggested useful information for the preparing other adsorbents in environmental applications.

Keywords: Adsorption; Amino groups; Fe(3+); Mesoporous silica; Tetracycline.