Abstract
The adsorption behavior of an organic dye, metanil yellow (My), from water using micro-nano silica particles (MNSPs) was investigated. MCM-41-like (Mobil Composition of Matter No. 41) MNSPs were synthesized using tetraethoxy orthosilicate as a silica source and hexadecyltrimethylammonium bromide (CTAB) as a surfactant under basic conditions. Comparative studies were performed to assess the adsorption behaviors of the organic dye using the as-synthesized MCM-41 before the removal of CTAB and MCM-41, either after one, two, and three times of chemical etching or after calcination. My was adsorbed more effectively from water on the as-synthesized MCM-41 without the removal of the surfactant than on MCM-41 after the removal of the surfactant by chemical etching or calcination. In addition, MCM-41 after removing the surfactant by one-time chemical etching in the presence of hydrochloric acid also showed better adsorption of My from water than MCM-41 after removing the surfactant by further two and three times of chemical etching or calcination. For comparison, other kinds of dye molecules with different chemical structures such as methylene blue (Mb) and rhodamine B (Rb) were also used to check the possibility of adsorption of various dyes by the CTAB-supported MNSPs. To better understand the reason behind the adsorption phenomena, detailed studies on the kinetics and thermodynamics of adsorption of the MNSPs were performed. Excellent adsorption of My was observed at concentrations up to 100 mg L-1 at 25 °C, whereas the adsorption was lower at higher concentrations of the My dye. Furthermore, enhanced My dye adsorption was observed at higher concentrations by increasing the adsorption temperature. It can be concluded that the MNSPs exhibited efficient adsorption of My, when the MNSPs are used without the removal of the surfactant and any further modifications, suggesting that the surfactant played key roles in the effective adsorption of the anionic dye. The as-synthesized MCM-41 was, however, not a good adsorbent for cationic dyes such as Mb and Rb.