SYNTHESIS AND CHARACTERIZATION OF HYDROCALUMITE: INFLUENCE OF AGING CONDITIONS ON THE STRUCTURE, TEXTURAL PROPERTIES, TH
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SYNTHESIS AND CHARACTERIZATION OF HYDROCALUMITE: INFLUENCE OF AGING CONDITIONS ON THE STRUCTURE, TEXTURAL PROPERTIES, THERMAL STABILITY, AND BASICITY THIAGO M. ROSSI, JUACYARA C. CAMPOS, AND MARIANA M. V. M. SOUZA * 1
Escola de Química, Universidade Federal do Rio de Janeiro (UFRJ), Centro de Tecnologia, Bloco E, Sala 206, Rio de Janeiro, RJ CEP 21941-909, Brazil
Abstract—Hydrocalumite (HC) is a type of synthetic layered double hydroxide (LDH) that has many important industrial uses and is commonly synthesized by a co-precipitation method in a water:ethanol (2:3) mixture; however, atmospheric carbon dioxide interferes with the synthesis by decreasing the solubility of other gases in the reaction medium. The aim of the present study was to vary the temperature and aging time used in the coprecipitation method in order to mitigate the adverse effects of carbon dioxide. The water/ ethanol mixture (2:3) was able to prevent atmospheric carbon dioxide contamination of the sample, as it decreased the solubility of the gas in the reaction mixture. Aging time (9–36 h) and temperature (35–95°C) were varied to modify the hydrocalumite structure, textural properties, thermal stability, and basicity. The characterization of the samples was performed using X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), nitrogen physisorption, thermogravimetric analysis (TGA), and CO2 temperature-programmed desorption (TPD-CO2) techniques. The aging time of 9 h and temperature of 95°C provided the most crystalline sample with the largest mean crystallite size (49 nm). The variation of the synthesis conditions also provided changes in the surface area (6.5–20.2 m2 g–1), pore diameter (116–148 Å), and pore volume (0.0147–0.0499 cm3 g–1). The temperature ranges for thermal decomposition of structural water and carbonate varied among the samples, indicating different thermal stabilities. The basicity (basic sites quantified by TPD-CO2) was also affected by the change in aging conditions; the sample aged for 9 h at 65°C presented the greatest basicity (1557 μmol g–1), whereas that aged for 36 h at 35°C had the least basicity (337 μmol g–1). Keywords—Aging . Hydrocalumite . Lamellar double hydroxide . Synthesis INTRODUCTION Hydrocalumite-like compounds (HLCs) are anionic clays that are part of the layered double hydroxide (LDH) family. LDHs bear a positive surface charge which attracts anionic species between the layers, where the layers contain two types of metals (Roy et al. 1992). The general formula of the HLCs is [Ca2M3+(OH)6]+[(An–)(1/n).mH2O]– where An– = NO3–, SO42–, or CO32– and M3+ = Al3+, Fe3+, Ga3+, and/or Sc3+ (Leroux et al. 2002; Guo and Tian 2013; Barrado 2015; Sánchez-Cantú et al. 2015). The c lattice parameter varies with the size and charge of the interlayer anion, while the isomorphic substitution between calcium and aluminum is associated with the a lattice parameter (Pérez-Barrado et al. 2013). The chemical and/or physical properties of LDHs differ from those of their individual
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