Structural characterization of hexadecyltrimethylammonium-smectite composites and their potentiometric electrode applications

Abstract Organosmectites were prepared by the intercalation of hexadecyltrimethylammonium cations at various ratios into interlayer of Unye smectite. Structural, thermal, morphological and textural properties of the synthesized organosmectites were characterized. Afterwards, a novel potentiometric PVC-membrane thiocyanate selective electrode was prepared based on the obtained hexadecyltrimethylammonium modified smectites as electroactive material. The basal spacing values of organosmectites were observed in the range of 15.61 and 35.50 A. Powder X-ray diffraction data show that the surfactant cations penetrated into the smectite layers with different molecular arrangements. Modification of smectite with hexadecyltrimethylammonium led to appreciable decreases in the intensities of the FTIR bands at 3402 and 1635 cm −1 and the new characteristic vibrational bands at 2927, 2850, 1472 and 722 cm −1 originating from the surfactant molecules appeared. The thermal analysis data showed that the decomposition of surfactant species occurred in the temperature range of 170–720 °C and the amount of dehydrated water gradually decreased with the increase in surfactant amount. The intercalation of surfactant species within the gallery spacing led gradually to smaller surface areas. In addition, the electrophoretic mobility values indicate that excess surfactant loadings also generate positive charges on the organosmectite surfaces. The most convenient membrane composition resulting in the best potentiometric performance was investigated. The optimum membrane composition was determined to have 20.0% (w/w) 2.5CEC.HDTMA-smectite, 26.0% (w/w) PVC, 54.0% (w/w) DBP The fabricated electrode exhibited a linear response over the thiocyanate concentration range of 1.0 × 10 −4 –1.0 × 10 −1 M ( R 2 = 0.9996) with a slope of −48.6 mV/decade. The detection limit, response time and pH working range were determined as 4.3 × 10 −5 M, ∼10 s and 4–8, respectively. The proposed electrode exhibited selective potentiometric response to thiocyanate comparable to most of the common anions.