Efficient dye removal using well-crystallized layered double hydroxides and their oxides: insights into kinetics, thermodynamics, isotherm and the memory effect.

Dyes are toxic organic compounds that can adversely affect living organisms, and their removal from wastewater is a critical environmental concern. This study primarily focuses on the synthesis and adsorption behavior towards both cationic and anionic dyes of well-crystallized Mg-Al layered double hydroxides (MAH), made using highly concentrated metal salts, and their thermally treated derivatives, Mg-Al layered double oxides (MAO). Whilst both MAH and MAO exhibit high adsorption capacities for the methyl orange (MO) and acid blue 113 (AB) dyes, MAO, however, demonstrates slightly greater adsorption efficiency due to its increased surface area resulting from calcination. The adsorption behavior of these nanocomposites was studied by varying parameters such as contact time, temperature, pH, ionic strength, initial dye concentration and adsorbent dosage. The adsorption kinetics were best described by a pseudo second order model. Thermodynamic parameters such as the enthalpy, entropy and Gibb's free energy were calculated and the negative value for the free energy confirms the spontaneity and feasibility of the process, while the negative value of Δ