TY - JOUR
T1 - Adsorption and interactions of methyl green with montmorillonite and sepiolite
AU - Rytwo, G.
AU - Nir, S.
AU - Crespin, M.
AU - Margulies, L.
PY - 2000/2/1
Y1 - 2000/2/1
N2 - The divalent organic cation, methyl green (MG), undergoes a slow transformation (6 h) to a monovalent cation, carbinol (MGOH+) upon dilution of its solution (10 mM), or in a buffer at neutral pH. Adsorption isotherms of MG on montmorillonite were determined by two procedures, both of which yield a final pH of suspensions between 7 to 7.4. When the amounts of MG in suspension were lower than the cation-exchange capacity (CEC) of the clay (0.8 mol(c)/kg clay), no measurable amount of MG remained in solution. The maximal amounts of MGOH+ adsorbed were larger than those of MG2+, being 1.15 and 0.75 mol MG/kg day, respectively, corresponding to 140% of the CEC in the first case. On a charge basis the adsorption of added MG2+ amounts to 185% of the CEC, which raises the possibility that a certain fraction of MG2+ transformed into the monovalent form during the incubation period, since other divalent organic cations previously studied only adsorbed up to the CEC (paraquat), or slightly above it (diquat). Adsorption of MG on sepiolite (CEC = 0.15 mol(c)/kg) further emphasizes the two patterns of its adsorption. The maximal adsorbed amounts of MG2+ and MGOH+ were 0.09 and 0.30 mol/kg day, respectively. X-ray diffraction measurements gave lower values for the basal spacings for montmorillonite-MG+ than for MGOH+, suggesting that MG2+ binds two clay platelets together, as in the case of other divalent cations. A competition for adsorption between MG and the monovalent organic cation, acriflavin (AF), gave lower adsorbed amounts of AF when competing with MG+, which is interpreted to be due to the smaller basal spacing in this case, which partially inhibits the entry of AF molecules into the interlammelar space. Spectra of montmorillonite-MG particles in the visible range exhibited significant differences between clay-MG and clay- carbinol. (C) 2000 Academic Press.
AB - The divalent organic cation, methyl green (MG), undergoes a slow transformation (6 h) to a monovalent cation, carbinol (MGOH+) upon dilution of its solution (10 mM), or in a buffer at neutral pH. Adsorption isotherms of MG on montmorillonite were determined by two procedures, both of which yield a final pH of suspensions between 7 to 7.4. When the amounts of MG in suspension were lower than the cation-exchange capacity (CEC) of the clay (0.8 mol(c)/kg clay), no measurable amount of MG remained in solution. The maximal amounts of MGOH+ adsorbed were larger than those of MG2+, being 1.15 and 0.75 mol MG/kg day, respectively, corresponding to 140% of the CEC in the first case. On a charge basis the adsorption of added MG2+ amounts to 185% of the CEC, which raises the possibility that a certain fraction of MG2+ transformed into the monovalent form during the incubation period, since other divalent organic cations previously studied only adsorbed up to the CEC (paraquat), or slightly above it (diquat). Adsorption of MG on sepiolite (CEC = 0.15 mol(c)/kg) further emphasizes the two patterns of its adsorption. The maximal adsorbed amounts of MG2+ and MGOH+ were 0.09 and 0.30 mol/kg day, respectively. X-ray diffraction measurements gave lower values for the basal spacings for montmorillonite-MG+ than for MGOH+, suggesting that MG2+ binds two clay platelets together, as in the case of other divalent cations. A competition for adsorption between MG and the monovalent organic cation, acriflavin (AF), gave lower adsorbed amounts of AF when competing with MG+, which is interpreted to be due to the smaller basal spacing in this case, which partially inhibits the entry of AF molecules into the interlammelar space. Spectra of montmorillonite-MG particles in the visible range exhibited significant differences between clay-MG and clay- carbinol. (C) 2000 Academic Press.
KW - Adsorption
KW - Clay minerals
KW - Methyl green
KW - Montmorillonite
KW - Organic cations
KW - Sepiolite
UR - http://www.scopus.com/inward/record.url?scp=0034141624&partnerID=8YFLogxK
U2 - 10.1006/jcis.1999.6595
DO - 10.1006/jcis.1999.6595
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AN - SCOPUS:0034141624
SN - 0021-9797
VL - 222
SP - 12
EP - 19
JO - Journal of Colloid and Interface Science
JF - Journal of Colloid and Interface Science
IS - 1
ER -