Evaluation of Methylene Blue Adsorption onto Lignocellulosic Biomass (Raw Rumex Crispus L. Stem): Characterization, Kinetics, and Isotherms.

Worldwide water sources continue to be polluted daily by various additives, of which dyestuffs are a significant contributing factor. In the present study, Rumex Crispus L. (RCL) was used as a biomass bio-adsorbent, and the adsorption of methylene blue on RCL was investigated. RCL was characterized using Brauner–Emmett–Teller, Fourier transform infrared, X-ray diffraction, and scanning electron microscopy (SEM) analyses. The effects of the RCL amount (0.5–6 g/L), initial pH (3–10), concentration (40–200 mg/L), contact time (0–60 min), and temperature (293–313 K) on adsorption activities were investigated, and the point of zero charge value of the adsorbent was determined. Thermodynamic studies have shown that adsorption occurs spontaneously and exothermically (ΔG⁰ = − 2.19 to − 0.72 kJ/mol, ΔH⁰ = − 23.8 kJ/mol, ∆S⁰ = − 0.074 kJ/mol). Pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich kinetic models were tested, and the kinetic data were examined. The kinetic data showed that the pseudo-second-order kinetic model was the best fit (R² = 0.999). Tests were conducted using Langmuir and Freundlich models from the isotherm studies. Our data showed good agreement with the Langmuir isotherm model (R² = 0.998). The maximum adsorption capacity of the RCL monolayer was determined as 50 mg/g according to the Langmuir isotherm model. [ABSTRACT FROM AUTHOR]