Methylene blue adsorption by wheat straw-based adsorbents: Study of adsorption kinetics and isotherms

Dyes are one of the major toxic pollutants discharged in large quantities into the hydrosphere. Among various dye removal methods, adsorption has a distinct position. In this study, wheat straw was used as a low-cost and renewable material to prepare two economical adsorbents through the facile production method. An adsorbent was prepared by alkaline hydrolysis of wheat straw. Then, another adsorbent was synthesized by carboxymethylation of the first adsorbent. The prepared adsorbents were characterized by various techniques, including Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD). A series of adsorption experiments were conducted in a batch adsorption system to study the effect of diverse parameters, such as solution pH, the initial dye concentration, and contact time, on the adsorption performance. Adsorption models and kinetic results indicated that the adsorption of methylene blue onto both adsorbents was more fitted to Langmuir isotherm and followed second-order kinetics. The maximum monolayer adsorption capacity of methylene blue on alkaline-modified wheat straw and carboxymethylated modified wheat straw reached 131.123 and 191.427 mg/g, respectively. Regarding their low cost and suitable adsorption potential, they can be cost-effective and promising adsorbents for wastewater treatment.