Synthesis of a novel green biopolymer-based composites beads for removal of methylene blue from aquatic medium: isotherm, thermodynamic and kinetic investigation

The increase in the world population and the decrease in clean water resources increase people's interest in water purification technologies. Many industries, such as the textile industry, leather industry, cosmetics and food industry, color their products with substances such as dyes and pigments. In this study, a cheap, useful, innovative, environmentally friendly, and sustainable adsorbent was developed for the removal of Methylene Blue (MB), one of the dyes that is harmful to the environment. In fruit tree cultivation, in addition to the product, very high amounts of by-products/waste (branches, bark, leaves, fruit seeds, fruit shells, etc.) are produced. In this direction, walnut tree and olive tree wastes were immobilized with chitosan, made magnetic (m-WCH and m-OCH), and the adsorption of MB on the developed adsorbents was examined in a batch system. Characterization of the synthesized biocomposite adsorbents was performed by FT-IR, SEM, EDX and XRD analyzes. It has been thoroughly described how the pH solution of the MB dye compares to the pH PZC of the adsorbent surface. The pH PZC values for m-WCH and m-OCH were 5.2 and 5.5 respectively. MB adsorption of biocomposites depends on the pH of the environment (3–8), amount of adsorbent (2–10 gL −1 ), contact time (5–360 min), temperature (25–55 °C) and initial dye concentration (10–250 ppm) was examined as a function. The obtained data were evaluated with kinetic and isotherm models. Using adsorption equilibrium data obtained from MB adsorption studies using m-WCH and m-OCH biocomposite adsorbents, their suitability to Langmuir, Freundlich, Stachard, Dubinin–Radushkevich and Temkin models was examined. The empirical data of MB adsorption by m-WCH and m-OCH showed agreement with the Langmuir isotherm model. The maximum adsorption capacity for MB by m-WCH and m-OCH was estimated to be 85.47 mg g −1 and 53.48 mg g −1 , respectively. The result showed that a higher adsorption selectivity on m-WCH compares to m-OCH. Among the kinetic models applied, the pseudo-second-order kinetic model was identified with the highest regression coefficients. In the light of these results, it was determined that there are new promising adsorbents of natural origin, with higher adsorption capacity, lower cost, and alternatives to commercially used adsorbents in the removal of MB from aqueous media. Graphical abstract