期刊
CRYSTALS
卷 11, 期 6, 页码 -出版社
MDPI
DOI: 10.3390/cryst11060708
关键词
dimers; interactions; mechanism; palygorskite; sepiolite; toluidine blue
资金
- National Natural Science Foundation of China [41403083]
- Key Project of Science and Technology of Hubei Provincial Department of Education [D20141305]
- Science Foundation of Education Commission of Hubei Province of China [T2020008]
- SPARK grant from Wisys
The interactions between cationic dyes and negatively charged mineral surfaces, specifically palygorskite and sepiolite, were investigated in this study. It was found that the dimer molecules formed on the surface of the minerals contributed to the higher TB uptake in addition to cation exchange. Palygorskite was shown to be a better carrier for cationic dyes due to its limited SSA and large CEC values, while sepiolite had a loosely dimeric formation due to its large SSA and limited CEC values.
Interactions between cationic dyes and negatively charged mineral surfaces have long attracted great attention from clay mineralogists, environmental scientists, and chemical engineers. In this study, the interactions between a cationic dye toluidine blue (TB) and palygorskite and sepiolite were investigated under different experimental conditions. The results showed that in addition to cation exchange, the specific surface area (SSA) of the minerals, particularly the formation of dimer molecules on the surface of both minerals, also accounted for the much higher TB uptake in comparison to their cation exchange capacities (CEC). The TB molecules were sorbed to the external surfaces, as no d-spacing expansion was observed in X-ray diffraction analyses. FTIR analyses showed strong interactions between the C=N or N-(CH3)(2) group and the mineral surfaces, suggesting net electrostatic interactions if either of these functional groups bears a positive charge. Results from molecular dynamic simulations suggested dense monolayer TB formation on palygorskite because of its limited SSA and large CEC values. In comparison, a loosely dimeric formation was revealed on sepiolite for its large SSA and limited CEC values. Therefore, palygorskite is a better carrier for the sorption of cationic dyes, as evidenced by Maya blue paintings.
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