Magnetic coconut shell biochar/sodium alginate composite aerogel beads for efficient removal of methylene blue from wastewater: Synthesis, characterization, and mechanism.

The challenges of recovering powdered biochar and its limited adsorption capacity are major obstacles to the application of agricultural waste in dye adsorption. To address these issues, this work fabricates FeO-modified coconut shells biochar (mCSB)/sodium alginate (SA) aerogel beads using an in-situ crosslinking-gelation method and freeze-drying technology for methylene blue (MB) removal from wastewater. The spherical mCSB/SA aerogel beads with good magnetic properties (12.8 emu·g) can be easily separated from aqueous solutions, thereby completely avoiding the hazard of secondary pollution and device obstruction associated with powdered adsorbents. The absorption capability of MB by mCSB/SA aerogel beads was analyzed and optimized at different conditions. Furthermore, the maximum adsorption capacity of mCSB/SA aerogel beads is 625 mg·g for MB, following the Langmuir isotherm model (R = 0.9997). Additionally, the adsorption process of MB on mCSB/SA aerogel beads is found to be spontaneous and endothermic, following the pseudo-second-order kinetic (R = 0.9991). Encouragingly, the adsorption efficiency of mCSB/SA aerogel beads remains above 95 % even after 5 times of reusability cycles, demonstrating excellent regeneration ability. This work proposes a straightforward and scalable fabrication strategy to convert agricultural waste into efficient adsorbents for wastewater treatment, adhering to the principles of sustainable development.