Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay Note The simultaneous anionic and cationic dyes removal with ZneAl layered double hydroxides Starukh H. a, ⁎ , Levytska S. b a Chuiko Institute of Surface Chemistry of the National Academy of Sciences of Ukraine, 17 General Naumov Str., Kyiv 03164, Ukraine b Institute for Sorption and Problems of Endoecology of the National Academy of Sciences of Ukraine, 13 General Naumov Str., Kyiv 03164, Ukraine ARTICLE INFO Keywords: Layered double hydroxides Adsorption Dyes removal Intercalation ABSTRACT ZnAl layered double hydroxides (LDH) as-synthesized and in calcined forms with a cationic ratio of 2–4 were applied for the study of anionic indigo carmine (IC) and cationic methylene blue (MB) dyes removal from aqueous media in batch mode. The highest adsorption of IC was observed for ZnAl LDH calcined at 600 °C with Zn: Al ratio 2. The adsorption of IC on calcined ZnAl LDH was accompanied by the reconstruction of the layered structure. The sorption capacity of calcined ZnAl LDH to cationic dye MB was extremely low in single dye solutions. The highly efective removal of MB with calcined ZnAl LDHs was achieved from the solutions that contained MB and IC dyes. The optimal IC: MB molar ratio for the total removal of both dyes was found to be 2:1. IC - modifed ZnAl LDH demonstrated high activity for the removal of MB from its solutions. The total removal of both dyes was 930 and 320 mg/g for IC and MB, correspondingly. 1. Introduction Facing the ever-growing demand for eco-safety and health concerns, research is now extensively devoted to the search for environmentally benignant and non-toxic bioresource products for regaining popularity in diferent spheres of our lives. In particular, the scientists discover new opportunities for industry to replace harmful synthetic dyes with natural ones, obtained from plants, insects/animals and minerals, that are renewable and sustainable bioresource products with minimum environmental impact and known since antiquity for their use (Shahid et al., 2013). Despite this, the extensive use of synthetic dyes, in both dye-manufacturing and dye-consuming industries, continues to be detrimental efects on the environment and associated allergic, harmful, carcinogenic toxic responses. The synthetic textile dyes have complex aromatic molecular structures that make them difcult to biodegrade when discharged in the ecosystem. Synthetic organic dyes are a great class of pollutants in an environmental, and it is necessary to develop efective methods for textile wastewater treatment. The bio- logical and physicochemical methods of the polluted water treatment have extensively been studied (Paz et al., 2017). Biological treatment usually includes a combination of anaerobic and aerobic processes, which are successively carried out to efectively degrade azo-dye ef- fuents. But the application of biological method alone generally does not allow the efective decolorization wastewaters containing water- soluble dyes; hence a chemical treatment is a necessary primary stage (Punzi et al., 2015). Adsorption is an efective and practical method of the treatment of dyes polluted water due to its high efciency, sim- plicity and the availability of many adsorbents (Gisi et al., 2016). The selection of the adsorbent is based on the nature of dyes, the level of contamination and the eco-friendly way of treatment. Although the use of naturally occurring adsorbents is the general direction of research (Duman et al., 2015; Zhou et al., 2019). Natural mineral clay posses high hydrophilicity and negative character of their surfaces that make them very good adsorbents for cationic and highly-polar dyes (Demirbas, 2009; Gil et al., 2011), whereas their adsorption capacity for anionic and highly hydrophobic dyes is usually small. A great at- tention is now paid to layered double hydroxides (LDH) because of their tunable charge density and large chemical versatility (Lei et al., 2014). LDH or hydrotalcite-like materials are a class of ionic lamellar com- pounds made up of positively charged brucite-like layers [M 2+ 1−x M 3+ x (OH) 2 x+ ] with M 3+ -for-M 2+ substitution, and an interlayer region containing charge compensating anions and solvation molecules. The chemical composition of LDH is expressed by the general formula [M 2+ 1−x M 3+ x (OH) 2 ][A n− ] x/n ·zH 2 O, where M 2+ may be common; Mg 2+ , Zn 2+ ,orNi 2+ ,andM 3+ may be common; Al 3+ ,Ga 3+ ,Fe 3+ ,orMn 3+ . A n− is a nonframework charge compensating inorganic or organic anion, e.g. CO 3 2− , Cl − , SO 4 2− , RCO 2 − , and x is normally between 0.2 and 0.4 (Cavani et al., 1991). The high adsorption ability of LDH to https://doi.org/10.1016/j.clay.2019.105183 Received 27 December 2018; Received in revised form 3 June 2019 ⁎ Corresponding author. E-mail address: starukh_halyna@isc.gov.ua (H. Starukh). Applied Clay Science 180 (2019) 105183 0169-1317/ © 2019 Elsevier B.V. All rights reserved. T