Bentonite-layered double hydroxide composite for enhanced aqueous adsorption of Eriochrome Black T

This work reports on layered double hydroxide (LDH) based nanocomposites synthesized via a co-precipitation method with the incorporation of bentonite. The produced bentonite-supported CoAl-LDH (B-CoAl) was employed as an adsorbent for removal of Eriochrome Black T (EBT) dye in aqueous solutions in batch mode experiments. The B-CoAl exhibited superior affinity towards EBT adsorption which yielded significant enhancement of EBT adsorption capacity of up to 675.67 mg/g from 361.01 mg/g of its parent material (i.e., CoAl). Pseudo second-order models (R² = 0.998–0.999) describe the kinetics of adsorption of EBT while the adsorption mechanism was controlled by external mass transfer as well as intra-particle diffusion. A Freundlich isotherm model provided a better fit of the B-CoAl EBT adsorption data than a Langmuir isotherm model, indicating a multi-layered adsorption phenomenon. The thermodynamic analysis showed that EBT adsorption onto B-CoAl was spontaneous and exothermic in nature. The improved adsorption affinity of EBT removal onto the B-CoAl is attributed to multiple adsorption interaction mechanisms dominated by electrostatic, surface adsorption and chemical interaction between EBT molecules with the additional oxygen-containing functional groups on the B-CoAl composite. This study demonstrates the potentials of environmental applications of bentonite supported LDH as a promising adsorbent removal of organic contaminants from aqueous solutions.