Preparation of composite of bentonite clay and Azadirachta indica (neem) leaves powder for the removal of Congo red from an aqueous solution

In this study, a composite of bentonite clay and powdered neem leaf was used to investigate the adsorption of the anionic dye Congo red (CR) from an aqueous solution. The designed adsorbent was characterized through scanning electron microscopy and Fourier-transform spectroscopy. In order to estimate the percentage CR discharge, the impacts of several parameters, such as contact duration, adsorbent dose, initial dye concentration, pH and temperature were evaluated. Adsorption kinetics was investigated using nonlinear pseudo-first-order and pseudo-second-order models. Results indicated that CR adsorption onto composite fitted to nonlinear pseudo-second-order model. Experimental data of CR adsorption was subjected to several linear isotherm models. Attained results exhibited that CR adsorption fitted to linear Freundlich isotherm. Adsorption thermodynamic studies revealed that CR adsorption was an endothermic and spontaneous process. Moreover, the composite regeneration and removal of dye by column were also illustrated.