Optimizing methylene blue adsorption conditions on hydrothermally synthesized NaX zeolite through a full two-level factorial design

Abstract

Besides being hazardous to humans and aquatic organisms, dyes present in water reservoirs limit sunlight's availability to aquatic plants and animals, making significant impact on their growth and development. Herein, the adsorptive removal of methylene blue (MB) dye from aqueous solution using type X (NaX) zeolite by full experimental design 2ⁿ was studied. The physical and chemical properties of NaX zeolite were identified using various characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray (SEM-EDS), Fourier transform infra-red (FT-IR), and Brunauer–Emmett–Teller (BET) surface area analyses. Results confirmed that NaX zeolite had a cubic shaped crystalline structure with 2–4 μm size and high (375 m² g⁻¹) specific surface area, having 90% optimal adsorption efficiency. Langmuir and Elovich isotherm models were best fitted to adsorption experimental data and a pseudo-second-order kinetic model describes well the adsorption kinetic data. Akaike information criteria (AIC) was used to assess the best fitted models on the experimental data. A thermodynamic study reveals that the MB adsorption onto NaX was exothermic, spontaneous, and feasible.