A physico-chemical study of the cationic surfactants adsorption on montmorillonite

Abstract

O objetivo deste trabalho é o estudo da adsorção de brometo de cetiltilmetilamônio (CTA) e de cloreto de cetilpiridínio (CP) em argilas do tipo montorilonita (MMT) ricas em sódio. Um método isotacoforético (ITP) específico foi desenvolvido visando à determinação rápida e simultânea dos surfatantes catiônicos (CS) adsorvidos. A fim de reduzir os limites de detecção, o método isotacoforético foi conjugado com a técnica de eletroforese capilar. Para determinar o arranjo dos surfatantes catiônicos (CS) adsorvidos na superfície das argilas foi efetuada a avaliação do balanço molar entre os surfatantes e os cátions metálicos juntamente com as isotermas de adsorção. A maior adsorção do CP comparada a do CTA pode ser entendida não só pela ação das forças eletrostáticas, mas também por outras interações, tais como, interação hidrofóbica cauda-cauda e/ou interações entre anéis piridínicos formando bicamadas incompletas e/ou monocamadas condensadas, respectivamente.The adsorption of cetyltrimethylammonium (CTA) bromide and cetylpyridinium (CP) chloride on Na + -rich montmorillonite (MMT) was studied. An ad hoc isotachophoretic (ITP) method was developed for the simultaneous and rapid determination of the cationic surfactants (CSs) adsorbed. In order to decrease the detection limits, ITP was on-line coupled with capillary zone electrophoresis. Adsorption data were analysed by their fitting with adsorption isotherms. The adsorption of CP is well described by the Langmuir isotherm. It indicates the monolayer arrangement of CP on the MMT surface. In case of the CTA data, the best fitting LangmuirFreundlich model with the power constant r<1 was found. It can be explained by the CTA interactions because of its intercalation into the MMT interlayer space.

Adsorption and bioactivity studies of albumin onto hydroxyapatite surface

“…The Langmuir model can be described by the equation: a = a m Kc e /(1 + Kc e ), where a (mmol g −1 ) and c e (mmol L −1 ) are the equilibrium concentration of adsorbate on an adsorbent surface and the adsorbate concentration in solution, respectively. The constant K is the equilibrium constant that represents the affinity between adsorbate and adsorbent and a m is the maximum amount adsorbed on surface (mg m −2 ) [21]. The Freundlich model can be expressed by the equation: a = Kc e 1/p in which K is the equilibrium constant and p is a power parameter.…”

“…The equation for this isotherm is: a = a m (Kc e ) r /[1 + (Kc e ) r ], where c e is the adsorbate concentration in equilibrium, K is the affinity constant that includes contribution from surface binding to monomer, monomer-dimer, and more highly associated forms of proteins. The Langmuir-Freundlich coefficient number r represents the cooperativity present in the binding interaction (r = 1 represents no interacting site, r > 1 a positive cooperativity and 0 < r < 1 a negative cooperativity) and a m represents the maximum binding sites or amount of protein adsorbed if each available adsorption site is occupied by a protein molecule [21]. It is known that there are dimmers and hexamers of BSA on aqueous solutions and this quaternary structure is probably involved during the adsorption process at high concentration [4].…”

Adsorption of chlorhexidine on synthetic hydroxyapatite and in vitro biological activity

“…4), was fitted with Langmuir-Freundlich and Langmuir functions that describe adsorption processes with and without molecule-molecule interactions, respectively. Langmuir equation is described by a = a m ·K.c e /(1 + K.c e ), where a is the CHX equilibrium concentration on HA surface, K is the equilibrium constant, a m is the maximum amount of CHX adsorbed on HA surface and c e is the CHX concentration in solution [41]. The Langmuir-Freundlich isotherm is describe by a = a m (K.c e ) r /[1 + (K.c e ) r ], where r is a cooperativity factor that express the molecule-molecule binding interaction (r = 1 for non-interacting site, r > 1 a positive cooperativity and 0 < r < 1 a negative cooperativity) [41].…”

Adsorption of Cationic Dyes from Aqueous Solution by Termite Feces, a Non‐Conventional Adsorbent

“…The combination of Langmuir and Freundlich models gives the Langmuir–Freundlich isotherm model, also known as Sips isotherm 22, 23, represented by Eq. (3): where K LF is the Langmuir–Freundlich adsorption constant (L mg −1 ).…”

“…At low dye concentrations, this model reduces to the Freundlich isotherm; while at high concentrations, it characterizes a Langmuir‐type isotherm. When the heterogeneity factor is 1, the model assumes the Langmuir model, when c > 1, positive cooperativity adsorption is expected, and values of 0 < c < 1 indicate a negative adsorption cooperativity 23.…”