Multitechnique study of biochar and biochar–bentonite composite derived from the petiole of Carnauba (Copernicia prunifera) modified by high-energy ball milling for methylene blue removal.

Abstract

The escalating improper disposal of industrial effluents laden with synthetic dyes, such as methylene blue, constitutes a serious environmental hazard due to their high stability and recalcitrance to degradation. In this context, adsorption processes have gained prominence owing to their efficiency and operational simplicity, particularly when utilizing low‐cost and sustainable materials. Among these, biochar and clays exhibit significant potential, especially when combined into hybrid composites that integrate high surface area, structural stability, and a diversity of functional groups. Accordingly, this study proposes the utilization of the carnauba palm petiole (Copernicia prunifera), an abundant and underexploited biomass, to produce clay‐biochar composites for methylene blue removal. The biomass was pyrolyzed at 550 °C, producing a biochar (PB) with enhanced physicochemical properties, followed by modification through high‐energy ball milling, with and without sodium bentonite clay incorporation. The results indicated that carbonization process induced significant compositional and structural changes on PB, including a reduction in volatile matter (from 77.77% to 31.04%), an increase in fixed carbon (from 9.20% to 36.96%), ash content (from 3.63% to 27.45%), along with carbon enrichment (from 43.49% to 64.02%) and a decrease in H/C and O/C ratios. Multitechnique characterization (XRD, FTIR, SEM/EDS, and thermal analyses) revealed the formation of a disordered carbonaceous matrix containing crystalline mineral phases, resulting in a heterogeneous surface with multiple active sites. High‐energy ball milling significantly improved the adsorption capacity of biochar, reaching 72.39 mg∙g-1 under the most severe condition (PB406). Composite materials exhibited superior performance even without milling (95.50 mg∙g-1), while optimized milling conditions improved clay dispersion and accessibility of active sites. The best‐performing composite (B‐PB406) achieved near‐complete removal efficiency (99.17%) and a maximum adsorption capacity of 205.67 mg∙g-1, with excellent agreement with the Langmuir model. Thus, the results demonstrate that carnauba petiole‐derived biochar and its bentonite composites are efficient and sustainable adsorbents for methylene blue removal, where the combination of pyrolysis, mechanical activation, and clay incorporation effectively tailors’ material properties, enhancing adsorption through synergistic mechanisms.