Facile synthesis of carbon-coated layered double hydroxide and its comparative characterisation with Zn-Al LDH: application on crystal violet and malachite green dye adsorptionisotherm, kinetics and Box-Behnken design

The adsorption of crystal violet (CV) and malachite green (MG) dyes using carbon-coated Zn-Al-layered double hydroxide (C-Zn-Al LDH) was investigated in this work. The characterisation of both Zn-Al LDH and C-Zn-Al LDH was performed using XRD, SEM, TEM, EDX, XPS, FTIR, BET and TGA. The results indicated that carbon particles were effectively coated on Zn-Al LDH surface. The average total pore volume and pore diameter of C-Zn-Al LDH were observed as 0.007cc/g and 3.115nm. The impact of parameters like initial dye concentration, pH and adsorbent dosage on the dye removal efficiency was confirmed by carrying out Box-Behnken design experiments. Langmuir isotherm was well suited for both CV and MG adsorption among other isotherm models. The adsorption capacity was maximally obtained as 129.87 and 126.58mg/g for CV and MG respectively. Pseudo-second order fits the adsorption kinetics than any other kinetic models for both the dyes. The thermodynamic study indicates that the adsorption process of CV was exothermic, whereas for MG was endothermic. Electrostatic attraction, H-bonding, n- and - interactions were mainly influenced in the adsorption process. This study concludes that C-Zn-Al LDH is an efficient adsorbent for the CV and MG dye removal from aqueous solutions.