Journal of Environmental Treatment Techniques 2021, Volume 9, Issue 2, Pages: 383-391 383 Mg-Cr Layered Double Hydroxide with Intercalated Oxalic Anion for Removal Cationic Dyes Rhodamine B and Methylene Blue Arini Fousty Badri 1 , Neza Rahayu Palapa 1 , Risfidian Mohadi 2 , Mardiyanto 3 , Aldes Lesbani 1* 1 Department of Chemistry, Faculty of Mathematics and Natural Sciences, Sriwijaya University, Jl. Palembang-Prabumulih, Km. 32, Ogan Ilir, South Sumatra, Indonesia 2 Department of Environmental Science, Graduate School, Sriwijaya University, Jl. Padang Selasa No. 524 Ilir Barat 1, Palembang-South Sumatra, Indonesia 3 Department of Pharmacy, Faculty of Mathematics and Natural Sciences, Sriwijaya University, Jl. Jl. Palembang-Prabumulih, Km. 32, Ogan Ilir 30662, South Sumatra, Indonesia Received: 12/09/2020 Accepted: 13/12/2020 Published: 20/06/2021 Abstract A MgCr-based layered double hydroxide (LDH) was synthesized by a coprecipitation method, followed by an intercalation process using an oxalic anion. The materials were characterized using X-ray diffraction analysis, FT-IR spectroscopy, and pH pzc measurement. The materials were then applied as adsorbents for removal of methylene blue (MB) and rhodamine B (RhB) from aqueous solution. Pristine Mg/Cr LDH exhibited RhB adsorption capacity of 32.154 mg g⁻ 1 , whereas the use of intercalated Mg/Cr LDH caused an increase in the capacity (139.526 mg g⁻ 1 ). Kinetic studies indicated that the dye adsorption using both LDHs followed a pseudo-second-order kinetic model; the K2 values of pristine and modified Mg/Cr LDH for RhB and MB were 6.970, 0.001, 0.426, and 2.056 g mg⁻ 1 min⁻ 1 , respectively. The thermodynamic study identified that the adsorption of both dyes onto the LDHs was a spontaneous process and can be classified as physical adsorption with adsorption energies of <40 kJ/mol. Moreover, the desorption and regeneration experiments indicated the high economic feasibility and reusability of the LDHs. By using HCl as the optimal solvent, the LDHs could desorb as much as 98% of the dye and could be used as adsorbents with high adsorption capacity over three cycles. Keywords: Layered double hydroxide, MgCr, rhodamine B, methylene blue, intercalation 1 Introduction 1 The contamination of water bodies due to dyes negatively affects the ecological system and human health [1]. Industrial activities such as production of textile, paper, and rubber use reactive synthetic dyes [2,3]. Such dyes are harmful organic pollutants because of their carcinogenic effects [3–5]. Dye contaminants are synthetic dyes that are non-biodegradable; therefore, it is recommended to remove such pollutants from wastewater before being discharged into natural water [6]. Several methods have been employed to remove dyes from wastewater, such as ion exchange, filtration, membrane separation, electrochemical degradation, and adsorption methods. Among these methods, adsorption is a suitable method to remove dyes from wastewater because of its low cost and high efficiency and because it involves a simple treatment. Moreover, adsorption efficiency depends on the adsorbent [7,8]. Various adsorbents have been used to remove dyes from wastewater such as bentonite [9], kaoline, activated carbon, zeolites, and hydrotalcite [10–12]. Hydrotalcite is a class of clay Corresponding author: Aldes Lesbani, Department of Chemistry, Faculty of Mathematics and Natural Sciences, Sriwijaya University, Jl. Palembang-Prabumulih, Km. 32, Ogan Ilir, South Sumatra, Indonesia. E-mail: aldeslesbani@pps.unsri.ac.id materials and serves as effective sorbents [13,14]. However, to achieve high efficiency for dye adsorption, hydrotalcite must be modified using an intercalating process with organic [15] or inorganic anions to increase its surface area [16]. Hydrotalcites have been extensively modified to impart high adsorption capacity and efficiency; such modification methods include development of LDH-MnFe2O4 hybrid materials [17] and intercalation of LDHs with aromatic acid anions [18]. Anionic synthetic clay layered double hydroxides (LDHs) consist of divalent and trivalent brucite-like layers that have a positive charge and an anion functioning as a counterion. These compounds have a general formula of [M II (1−x) M III x (OH)2] x+ (An − ) x/n ·mH2O, where An - is the intercalated anion [19– 21]. The anion in the interlayer of the LDH can be replaced, under suitable conditions, with inorganic ions such as nitrate, carbonate [22], and sulfate ions in order to enhance the interlayer. Modified LDHs have applications in various fields, especially in dye removal. According to Santos et al., calcined LDH was used to adsorb acid yellow 42 in aqueous solutions [23]. Deng et al. [24] J. Environ. Treat. Tech. ISSN: 2309-1185 Journal web link: http://www.jett.dormaj.com https://doi.org/10.47277/JETT/9(2)390