Adsorption behavior and mechanism of reactive brilliant red X-3B in aqueous solution over three kinds of hydrotalcite-like LDHs

Three kinds of layered double hydroxides (LDHs), including Ni/Al-LDH, Mg/Al-LDH and Co/Al-LDH, were adopted in this research to study the adsorption process of reactive brilliant red X-3B. Factors affecting adsorption such as contact time and temperature were investigated. The adsorption kinetic data fit well into the pseudo-second-order model, while the adsorption isotherm followed the Langmuir model. The thermodynamic tests indicated spontaneous and exothermic nature of X-3B adsorption. In order to examine the adsorption mechanism, pH effect was investigated and adsorbents and adsorption products of Ni/Al- and Mg/Al-LDHs were characterized further by several physicochemical techniques in view of their relative large capacity. The pH effect tests illustrated that electrostatic reaction and hydrogen bonding between dye molecules and LDH layers may be the major mechanisms involved in adsorption. The FT-IR analysis revealed that there was ion exchange during the adsorption process. The XPS, TG, and NMR experiments further proved that the hydrogen bonding between the adsorbent and adsorbate played the dominant role in this process and the -SO3 was the interaction site.