Preparation of Fe₃O₄-octadecyltrichlorosilane for removal of methyl orange and methylene blue: Influence of pH and ionic strength on competitive adsorption

Abstract

Fe₃O₄-octadecyltrichlorosilane (Fe₃O₄-OTS) was synthesized and used to remove dyes in a competitive system. Fe₃O₄-OTS was prepared by slow hydrolysis of OTS in cyclohexane on the surface of Fe₃O₄ obtained through coprecipitation method. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and contact angle analyzer (CA) were used to analyze the properties of Fe₃O₄-OTS. Methyl orange (MO) and methylene blue (MB) were selected as model molecules to study the influence mechanism of pH and ionic strength on competitive adsorption. The results of EDS and CA indicated that Fe₃O₄ was modified successfully with OTS on the surface. Silicon appeared and carbon content increased obviously on the surface of adsorbent. Contact angle of adsorbent increased from 0° to 107° after being modified by OTS. Fe₃O₄-OTS showed good separation for MO and MB in competitive system, which has potential to separate dyes in sewage. Separation factor (β _B ^O) changed from 18.724 to 0.017, when pH changed from 7 to 12, revealing that MO and MB could be separated almost thoroughly by Fe₃O₄-OTS. pH could change the surface charge of Fe₃O₄-OTS and structure of dyes, and thus change the interactions of competitive system indirectly. Even though hydrophobic interaction was enhanced, ionic strength reduced the difference of electrostatic interaction between dyes and Fe₃O₄-OTS. So it is unfavorable to separate dyes with opposite charges when ionic strength increases. These findings may provide theoretical guidances to separate two-component dye pollutants.

Keywords

Fe₃O₄-octadecyltrichlorosilane / competitive adsorption mechanism / pH / ionic strength / dye

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