Benzalkonium chloride adsorption surface sites on two raw montmorillonites and their organo-clay

FEDERICO MANUEL FLORES; FLORENCIA YARZA; ROBERTO CANDAL; ELSA GABRIELA LÓPEZ LOVEIRA; ROSA MARÍA TORRES SANCHEZ

Kosice

Congreso; 8th Mid-European Clay Conference; 2016

Benzalkonium chloride (BAC) is a cationic surfactant with bactericidal and fungicidal properties and relatively low toxicity to human beings. These properties allow it to be used as an active ingredient in pharmaceutical or cosmetic formulations, public health areas, food and feed areas as well as wood preservatives. The addition of cationic surfactant exchanged montmorillonites (Mt) (denoted nano-Mt) to certain polymers allowed to improve mechanical properties [1] and transfer the surfactant bactericidal activity [2] to the final product. The aim of this work was to evaluate the surface adsorption sites involved when BAC was used to obtain nano-Mt. To attain this objective BAC (C0= 0.01 and 1.25 mM), was adsorbed on two raw Mt (commercial Cloisite, MCloi and Argentine raw Mt, MCas) and a nano-Mt (MCas-ODTMA and MCloi-30B exchanged 100 % CEC with octadecyltrimethyl-ammonium bromide and methyl, tallow, bis-2-hydroxyethyl ammonium chloride, respectively). The products were characterized by XRD and Zeta potential (ζ) measurements, to study inner and outer surfaces, respectively.BAC adsorption at the nano-Mt interlayer space increased the basal space from 1.9 to 2.0 nm indicating a surfactant rearrangement. In the cases of MCloi and MCas, BAC adsorption increased the basal space in two steps: from 1.1 to 1.4 and to 1.75 nm, as BAC concentration increased from 0.01 to 0.1 mM. This phenomenon is assigned to monolayer to bilayer BAC arrangement in the interlayer. The ζ curves vs pH indicated a decrease of negative surface charge only with higher concentration of BAC (C0= 1.25 mM) for raw Mt. In the case of nano-Mt a gradual increase of positive surface charge was found as BAC concentration increased. Particularly, for raw Mt with adsorbed BAC, an edge isoelectric point (IEP) at pH 4 was found. This value is similar to others IEP reported with different cations [3]. Indicating that for raw Mts, interlayer sites were preferred for BAC adsorption, whereas up to attain a certain BAC concentration the outer surface sites were also occupied. For, nano-Mt samples BAC adsorption mainly occurred at the outer surface, due to interlayer space already occupied by the respective surfactants.