Natural red clay nano-sorbent for methylene blue adsorption using response surface method of Box Behnken design approach

Environment friendly natural red clay nano-sorbent (NRC-ns) was investigated for removal of methylene blue (MB) dye from aqueous environment. The NRC-ns were prepared form less than 63 micron sieve (230 mesh sizes). Its chemical composition, functional groups, surface morphology, structure, and pH of Zero-point charge (pHpzc 5.5) were determined. Optimized operational parameters were adsorbent dosage (0.02–0.1 g), initial concentration (0.2–1.2ppm), pH (3–11), temperature (20–65°C) and contact time (10–70 minutes) using Response Surface Method (RSM)-Box Behnken Design (BBD). The maximum removal efficiency (%R) and adsorption capacity (qe) were 99.96% and 235.47 mg g−1 respectively. Pseudo-second-order and Freundlich isotherm were best fitting for this adsorption processes. Thermodynamic properties of the adsorption processes were found to be spontaneous, on 14.73 KJ mol−1 Gibb’s free energy (△Go), −1.79 kJ mol−1 enthalpy (ΔH°) and 0.05 KJ mol−1K−1 entropy (△S°), depicts desorption of MB dye on NRC-ns was spontaneous processes. Hence, positive ΔG° suggests adsorption at higher temperatures was favorable with randomness on adsorbent–adsorbate interface of positive ΔS). These imply a physic-sorption followed by a chemisorption process, enhancing the efficiency and feasibility of MB dye removal from wastewater.