Sorption study of an anionic dye – benzopurpurine 4B – on calcined and uncalcined Mg–Al layered double hydroxides

In this paper, the elimination from aqueous solution of the pollutant benzopurpurine 4B by Mg–Al–CO 3 hydrotalcite and its modified form Mg–Al–500 has been studied. Mg–Al–CO 3 2− layered double hydroxide with an Mg/Al molar ratio of 2.0 was synthesized by the co-precipitation method, and its modification was carried out by calcination. The affinity of these materials with a mixture of benzopurpurine 4B was studied as a function of dye–adsorbent contact time, initial pH of the solution, initial dye concentration and temperature. The results indicate that HDLs were effective in removing benzopurpurine 4B anionic dye. Their saturated adsorption capacities are very high, particularly for the calcined material Mg–Al–500 compared to the standard one Mg–Al–CO 3 2−. The characterisation of the solid Mg–Al–500, both fresh and after removal of the dye by X-ray diffraction and infrared spectroscopy, shows that the benzopurpurine 4B adsorption on this calcined phase is enhanced by reconstruction of a matrix hydrotalcite intercalated by the dye, with basal spacing of 23.77 Å, which is larger than that of Mg–Al–CO 3 2− LDHs (7.57 Å).