Abstract
Acridine orange (AO) is a cationic fluorescent dye commonly used in DNA analyses. Extensive studies were conducted for its metachromasy under different solution concentrations and different amounts of AO sorbed on a solid surface. Meanwhile, for the safe disposal of wastewater, AO removal from water using different materials was also evaluated extensively. Clay minerals, due to their large specific surface area, high cation exchange capacity, and vast reserves, have been evaluated as potential sorbents for the removal of a variety of different types of contaminants, including color dyes. In this study, the sorption of AO on different types of clay minerals was contrasted. The sorption of co-presenting Zn2+ was much less than the sorption of AO, suggesting that clay minerals have higher affinities for AO in comparison to inorganic Zn2+. The desorption of exchangeable cations was linearly related to AO sorption, and the amounts of AO sorbed were close to the CEC values of the minerals, confirming that cation exchange is the dominating mechanism for AO sorption. Molecular dynamics simulation results showed that, under low and high AO loading levels, the sorbed AO formed monolayers and bilayers on the mineral surfaces of non-swelling clay minerals, except halloysite, as well as in the interlayer of swelling clay minerals, due to its relatively large dimer constant in solution. Overall, clay minerals are good candidates for the removal of cationic dyes from solution even in the presence of competing inorganic cations.
Highlights
Acridine orange (AO) is a cationic fluorescent dye commonly used in DNA analyses [1]
On SAz-1, AO sorption reached a capacity of 1.6 mmol/g, which is 30% higher than its cation exchange capacity (CEC) value, and cation exchange was considered the dominant mechanism at low AO loading levels up to 0.8 mmol/g, beyond which molecular association into a horizontal bilayer formed in the interlayer of MT [7]
The sorption of AO, a fluorescence dye used in DNA analyses, on nonswelling and swelling clay minerals was investigated
Summary
Acridine orange (AO) is a cationic fluorescent dye commonly used in DNA analyses [1]. On SAz-1 (a Ca-MT), AO sorption reached a capacity of 1.6 mmol/g, which is 30% higher than its CEC value, and cation exchange was considered the dominant mechanism at low AO loading levels up to 0.8 mmol/g, beyond which molecular association into a horizontal bilayer formed in the interlayer of MT [7]. A laponite was studied for AO dimer formation on its surface, and the dimers increased with more AO loading up to 50% of its CEC value, but the location of the AO on the surface or in the interlayer was not mentioned [9] In these studies, the AO used was in HCl form without co-presenting divalent cation Zn2+. For commercially available AO dyes, one will have ZnCl2 in the formula
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