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Microwave irradiation used for all steps of pre-pillaring Al-montmorillonite

¹ Ege University, Chemical Engineering Department, 35100 Bornova, Izmir, Turkey,² CETMIC, Camino Centenario y 506, (1897) M. B. Gonnet, Argentina, ³ Institute of Functional Interfaces, Forschungszentrum Karlsruhe, Germany, and⁴ Competence Center for Material Moisture, University of Karlsruhe, Germany

^* E-mail: saadet.yapar{at}ege.edu.tr

(Received 24 March 2008; revised 25 February 2009)

In this study, a new procedure for the synthesis of pillared clays is proposed. Ageing processes and intercalation reactions were carried out using microwave irradiation in order to decrease the consumption of three industrially-important parameters; time, water consumption and energy. The effects of microwave irradiation, the amount of Al and the Al³⁺/clay ratio on the physicochemical properties of Al-pillared montmorillonites were investigated. The structural changes, depending on the intercalation and microwave irradiation, were characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) and scanning electron microscopy (SEM) analyses and by measuring the specific surface area and pore-size distribution. Additionally, simultaneous thermal analyses (STA) and zeta potential measurements were carried out to determine physicochemical properties. According to the XRD measurements, the d₀₀₁ value of microwave-irradiated samples is not affected by the amount of Al and the Al³⁺/clay ratio; microwave irradiation causes a 0.20 nm contraction in the d₀₀₁ value in comparison to that of a conventionally pillared sample. The results of FTIR analyses reveal that the intensity of peaks assigned to Keggin-OH and Keggin-H₂O stretches is diminished in the case of microwave-irradiated samples. The STA analyses indicate that the amount of water released during dehydroxylation is decreased in the case of microwave-irradiated samples. By considering the contraction in d₀₀₁ values and the decreases in Keggin-stretching bands and also in the amount of dehydroxylation water, it was concluded that microwave irradiation has a calcination effect.

KEYWORDS: STA, XRD, SEM, isoelectric point, FTIR, water-vapour adsorption