Structural and Chemical Characterization of Carnauba Stalk Biochar (Copernicia prunifera) and Its Application in Methylene Blue Adsorption

The improper discharge of industrial effluents containing dyes, such as methylene blue, represents a serious environmental problem. The present study, therefore, aimed to evaluate the potential of biochar derived from carnauba stalks as an adsorbent for removing dyes from aqueous media. The raw stalks were subjected to carbonization under an inert atmosphere to yield biochar, and both materials were characterized by proximate and elemental analyses, SEM/EDS, PSD, XRD, FTIR, and thermal analyses. Batch adsorption experiments were monitored by UV-Vis spectrophotometry. Pyrolysis resulted in an increase in aromatic fixed carbon (+26.5%) and ash content (+23.8%), while simultaneously reducing volatile matter (−39.3%), moisture, and the atomic H/C (0.39) and O/C (0.07) ratios. Furthermore, thermal stability was enhanced without causing a significant alteration to the average particle size (~30 μm). Adsorption tests showed a maximum uptake of 32.5 mg∙g−1 at low dosage (2 mg), corresponding to 8.66% removal, while 27.83% removal was achieved at higher dosage (25 mg). Equilibrium data were best described by the Langmuir model (qm = 210.7 mg∙g−1; R2 = 0.971), with qm representing a theoretical fitting parameter. These findings of this study demonstrate the adsorption potential of carnauba stalk biochar and support its evaluation as a lignocellulosic material for dye removal applications.