Microwave-Assisted Acid Activation of Clays Composed of 2:1 Clay Minerals: A Comparative Study

Abstract

The effect of the microwave-assisted acid treatment (MAT) on the structure and texture of dioctahedral (montmorillonite) and trioctahedral (saponite) smectites, kerolitic clays and sepiolites were studied by scanning electron microscopy, nitrogen adsorption, X-ray fluorescence, X-ray diffraction and Fourier transform infrared spectroscopy. This study shows that in the smectite group of minerals the effectiveness of MAT is notably influenced by the chemical composition of the octahedral sheet, whereas in kerolitic clays it is influenced by the proportion of the expandable phase in the mixed layer sequence. On the other hand, the reactivity of sepiolites depends on the width of the natural fibres. With these treatments, extremely high specific surface area (SSA) increments are achieved in just 16 min. The SSA increments reach values up to 231 m2/g (%ΔSBET = 80) in sepiolites, 198 m2/g (%ΔSBET = 155) in Mg-smectites, and 161 m2/g (%ΔSBET = 61) in kerolitic clays.

Adsorption of Carvone and Limonene from Caraway essential oil onto Tunisian montmorillonite clay for pharmaceutical application

“…These data reveal that the partial removal of calcite and quartz in the purification step causes a slight increase of the surface area. In any case, the S BET values are in the same range of those achieved for other raw smectites such as montmorillonite or saponite in previous studies 46,47 . The analyses of the pore volume reveal that the purification treatment improves the micro-and mesoporosity.…”

Magnetron sputtering technique for analyzing the influence of RF sputtering power on microstructural surface morphology of aluminum thin films deposited on SiO2/Si substrates

“…Furthermore, the bands in the range of 1300-1516 cm −1 are assigned to the Si-O-Si stretching bands of low "crystallinity" phases, mainly amorphous silica [38]. In addition, in the higher frequency region, the absorption bands at approximately 3554 cm −1 , 3616 cm −1 and 3741 cm −1 are attributed to the OH stretching modes of Al (OH) Si [42] and (Al Al) O-OH [43] Si-OH groups, respectively. The observation of OH stretching modes in all the samples may be due to the presence of silicate in the substrate.…”

Acid Activated Smectite Clay as Pozzolanic Supplementary Cementitious Material

“…4 shows the FTIR spectra of AAS samples. The -OH stretching region in the raw as-received sample only shows a weak band at 1635 cm −1 , associated to the -OH stretching modes of Al(OH)Si groups, [26]. It was observed that the -OH band weakened in 1D sample and disappeared in 8H90 due to the leaching of octahedral cations Al 3+ and Mg 3+ , and protons penetrating into the smectite layers attacking the structural OH groups [24].…”