J. Chil. Chem. Soc., 63, Nº 2 (2018) 3950 ANTACID EVALUATION OF CARBONATED HYDROCALUMITES: A COMPARISON OF AGING METHODS CARLOS F. LINARES *, a , JOEL MOSCOSSO a , VÍCTOR ALZURUTT a , FREDDY OCANTO a , PABLO BRETTO a , GEMA GONZÁLEZ b a Unidad de Síntesis de Materiales y Metales de Transición. Facultad de Ciencias y Tecnología. Departamento de Química. Universidad de Carabobo. Valencia. Edo. Carabobo. Venezuela. Apartado Postal 3336. Fax:+582418678243 b Laboratorio de Materiales, Centro Tecnológico, Instituto Venezolano de Investigaciones Científicas(IVIC), Carretera Panamericana Km 11 Altos de Pipe, Los Teques, Venezuela. ABSTRACT The synthesis of carbonated hydrocalumites could be troublesome because the carbonate anions can precipitate as calcium carbonate, therefore the aging times should be reduced. In this paper, carbonated hydrocalumites were synthesized using an unique gel divided in two portions: a part was aging to temperature room for 30 min, and the other one, by microwave radiations for 2 min. Samples were characterized by different techniques such as: Fourier-transformed infrared spectroscopy, X-ray diffraction, BET surface measurements, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Then, they were tested as antacid using a synthetic gastric juice. Results showed that carbonated hydrocalumites aging by microwave radiations were more flawless than those obtained by the conventional method. Moreover, using microwave radiations, the aging times were notably reduced and the purity of carbonated hydrocalumites was improved. The antacid properties were similar for hydrocalumites synthesized by different ways. However, they showed they showed better antacid properties with higher antacid capacity than commercial antacid. Keywords: carbonated hydrocalumite; microwave radiation; antacid; carbonate calcium; aging times 1. INTRODUCTION Hydrocalumites are a close family of hydrotalcites-type (LDH) materials. They are classified as anionic clays. The general formula has been described as [Ca 2 M 3+ (OH) 6 ](A n- ) 1/n .mH 2 O], where M 3+ is often a Al 3+ cation. The hydrocalumite structure is constructed by the periodical stacking of positively charged Ca 2+ octahedral layers related to brucite-like mineral and negatively charged interlayers consisting of diverse anions (A n- ) and water molecules. The Ca 2+ /Al 3+ ratio is fixed in two. These structures are seven and sixfold coordinated. The seventh ligand of the Ca 2+ -polyhedron corresponds to water molecules from the interlayer 1, 2. Due to its basic properties, they have been used in several reactions such as: oil castor bean and rapeseed oil transesterifications 1,3 , isomerization 4 , glycerol etherification 5 , aldolic condensation 6 , 2-cyclohexen-1-one catalytic epoxidation 7 , catalytic transfer hydrogenation of citral 8 , biodiesel 9 and recently as antacid 10 . The synthesis of hydrocalumites is often carried out by the co-precipitation method using calcium and aluminum salts which are added to a basic solution containing sodium hydroxide and sodium nitrate or chloride salts. Reaction conditions for the precipitation are: temperatures between 60 and 80 °C under magnetic agitation for 12-48 h. Other methods such as: sol-gel and homogeneous precipitation with urea have also been applied 11 . However, new routes of hydrocalumites synthesis should be formulated when carbonate ions are hoped in the hydrocalumite´s structure because the presence of this anion in the reactant gel is frequently precipitated as calcium carbonate. So, large aging times favor the formation of calcium carbonate. The microwave radiation is known as a novel alternative when short aging times are required for the synthesis of materials. In addition, this method allows obtaining more homogeneous materials, modifying some properties and consequently, energy saving. The microwave radiation has been applied in the synthesis of chloride hydrocalumites to obtain higher crystalline samples using relatively short aging times compared to conventional aging times 12 . In this sense, Granados-Reyes et al. 13 , synthesized nitrated hydrocalumites by the microwave radiation method, and found really small crystals. The aim of this paper was to synthesized carbonated hydrocalumites using two different aging ways: by microwave radiations and using an aging conventional method (room temperature, atmospheric pressure and stirring for 30 min). Synthesized carbonated hydrocalumites were characterized by different techniques such as X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), BET specific surface area measurements, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Then, these synthesized carbonated hydrocalumites were tested as antacid materials in vitro using a synthetic gastric juice. Antacids are substances able to increase the stomach’s pH until an ideal pH when the organism cannot normally do it. Heartburn is caused under certain conditions such as stress, inadequate nutrition or several diseases 14 . 2. EXPERIMENTAL 2.1. Synthesis of carbonated hydrocalumites (HC) The carbonated hydrocalumite gel was synthesized by the co-precipitation method previously reported by López-Salinas et al 4 . Two gels were prepared: in a general procedure, a calcium and aluminum solution was prepared dissolving Al(NO 3 ) 3 ·9H 2 O (3.8235 g) and Ca(NO 3 ) 2 ·4H 2 O (3.3475 g) in distilled water (25 mL). This solution was added dropwise to 50 mL of a solution containing NaOH (4.0745 g) and Na 2 CO 3 (0.2672 g), this gel was aging under microwave radiation. On the other hand, a similar gel as above mentioned, was prepared using Na 2 CO 3 (1,0776 g). This gel was aging at room temperature for 30 min under agitation. After the gel preparations, the gel corresponding to the microwave radiation was placed in a Teflon recipient inside domestic microwave (120 V and 60 Hz of power consumption) with operating power of 1250 W and a frequency of 2450 MHz for 2.5 min. The microwave power was controlled by adjustable independent channels. The synthesis was carried out using the first channel. By using the conventional method, the gel was magnetically stirring at room temperature and atmospheric pressure for 30 min. After aging, a white precipitate was obtained. Solids were filtered from the mixture, washed with abundant distilled water and dried at 100 ºC for 18 h. To ascertain the effectiveness of the carbonated hydrocalumites as antacid, its behavior was compared with a commercial antacid containing hydrotalcite as active agent. 2.1. Characterization of hydrocalumites Solids were characterized by different techniques such as: powder X-ray diffraction (XRD), BET specific surface area measurements, Fourier transformed infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). XRD studies were conducted in a Phillips PW 3442 diffractometer with a CuKa radiation (1,54060 Å) for crystalline phase detection between 5 and 85º (2q), and obtained patterns were compared with JCPDS data files. Physisorption measurements were performed with a Beckman Coulter SA 3100 instrument; BET specific surface areas were done using the N 2 adsorption at -196 ºC. The presence of functional groups and evaluation of purity of solids were achieved by FT-IR; spectra were recorded e-mail: clinares@uc.edu.ve