Gallic and salicylic acid-functionalized Mg/Al hydrotalcite as highly effective materials for reductive adsorption of AuCl4

• Published in: Applied surface science Vol. 507; p. 145115
• Main Authors: Santosa, Sri Juari, Fitriani, Dyah, Aprilita, Nurul Hidayat, Rusdiarso, Bambang
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30-03-2020
• Subjects: AuCl4; Functionalization; Gallic acid; Magnesium aluminum hydrotalcite; Reductive adsorption; Salicylic acid; Magnesium aluminum hydrotalcite; Salicylic acid; Reductive adsorption; Gallic acid; Functionalization; AuCl4
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2019.145115

Mono deprotonated gallic acid attached on the protonated hydroxyl group of Mg and Al at the edge of Mg/Al hydrotalcit.
Schematic illustration of AuCl4− removal by gallic acid-functionalized Mg/Al hydrotalcite.
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•Functionalization of Mg/Al hydrotalcite (Mg/Al HT) with gallic and salicylic acids has been performed.•Functionalization occurred through hydrogen bonding between deprotonated carboxyl group of acids with protonated hydroxyl group of metal ions at the edges of hydrotalcite’s particles.•Functionalization enhanced significantly the removal performance of Mg/Al HT for AuCl4−.•Hydroxyl group of the functionalized Mg/Al HT played its central role on the removal of AuCl4−.•The removal of AuCl4− by the functionalized Mg/Al HT was exothermic and governed by adsorption and reduction to Au metal.
Two materials as the functionalization products of magnesium aluminum hydrotalcite (Mg/Al HT) with gallic and salicylic acids have been prepared and their application to effectively remove AuCl4− has been examined. Functionalization was carried out through immobilization in which deprotonated carboxyl group of gallic and salicylic acids was the responsible functional group for the immobilization. Immobilization of both acids was optimum at pH 5.0 and matched better in Langmuir isotherm model than the Freundlich one with capacity of immobilization was 7.22 and 7.18 × 10−4 mol/g for galic and salicylic acids, respectively. In spite of both acids were immobilized at comparable amount, but gallic-acid-functionalized Mg/Al HT (Mg/Al-GA HT) had higher ability in removing AuCl4− than the salicylic-acid-functionalized Mg/Al HT (Mg/Al-SA HT). The removal capacity of Mg/Al-GA HT and Mg/Al-SA HT for AuCl4− at temperature 25 °C was 3.10 and 2.08 × 10−4 mol/g and it was 8.16 and 5.47 time-fold higher than that of Mg/Al HT. The removal of AuCl4− by Mg/Al-GA HT and Mg/Al-SA HT was exothermic and involved OH group and this functional group was responsible for not only the adsorption of AuCl4− but also reduction of AuCl4− to Au metal.