Synthesis of layered double hydroxides in W/O micro-emulsion: Influence of method of preparation on the physico-chemical
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1151-SS01-05
Synthesis of layered double hydroxides in W/O micro-emulsion: Influence of method of preparation on the physico-chemical and adsorption characteristics Sujata Mandal*1; Aniruddha S. Deshpande1; Aarti S. Harle2; S. Mayadevi1 1
Chemical Engineering and Process Development Division, National Chemical Laboratory,
Pune-411008, India. 2
Center for Materials Characterization, National Chemical Laboratory, Pune-411008, India.
ABSTRACT Zn/Al layered double hydroxide was synthesized in micro-emulsion system with the oil phase comprising of cyclohexane + TX100 (surfactant) + n-hexanol (co-surfactant). Aqueous NaOH solution was used as the precipitating agent. The XRD pattern showed Zincite as the primary and hydrotalcite as the secondary phase. The d003 diffraction peak corresponded to interlayer hydroxide ion. There was no interlayer NO3- ion. The synthesized LDH showed much higher BET surface area (116.3 m2/g) than similar LDH synthesized by conventional coprecipitation technique (4.2 m2/g). Well defined flaky nano-crystals having an average dimension of 5-20 nm were observed by HRTEM. INTRODUCTION Layered double hydroxides (LDHs) are synthetic inorganic clay materials consisting of flat two-dimensional structural network composed of different hydroxy layers of bivalent and trivalent metal ions. The positively charged layers of mixed metal hydroxides require the presence of interlayer anions to maintain the overall charge neutrality. They have the general formula [Mx2+ My3+ (OH)2(x+y)] Ay/nn-. mH2O, where M2+ is a bi-valent metal ion like Zn, Mg, Cu, Co, Ni, etc., M3+ is a tri-valent metal ion like Al, Fe, Cr, etc., and An- is the interlayer anion [1]. Over the past few years LDHs have attracted considerable attention due to their wide applications as catalysts, catalyst support, in industry, medicine and as adsorbent [2]. Traditionally, LDHs are synthesized by normal co-precipitation method in bulk aqueous solutions [2]. Some studies on hydrothermal synthesis of LDH are also reported [2]. But none other than Hu and O’Hare (2005) has reported LDH synthesis in reverse micro-emulsion system [3]. Considering the versatility of reverse micro-emulsions in controlled crystal formation, we were interested to study this effect on synthesis of LDH and its physico-chemical properties. The present communication reports synthesis of Zn/Al layered double hydroxide in reverse microemulsion of TX100 (surfactant) + n-hexanol (co-surfactant) + cyclohexane (oil phase). The LDH synthesized in W/O microemulsion system has been characterized by X-ray diffraction, Scanning electron microscopy and Transmission electron microscopy. The influence of synthesis procedure on the physico-chemical characteristics and fluoride adsorption capacity of the LDH have been examined. The results are compared with the properties of a similar LDH prepared by the traditional co-precipitation method.
EXPERIMENTAL DETAILS Reagents Al(NO3)3. 9H2O and Zn(NO3)2 .6H2O used for LDH synthesis were AR Grade Chemicals from SRL Chemicals Limited. AR Grade
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