Síntese e caracterização de biocarvões a partir do coco verde (Cocos nucifera L.) para potencialidade eletroanalítica

Abstract

The growth of the agro-industry has intensified the generation of lignocellulosic waste, whose improper disposal represents an environmental and economic challenge, while also highlighting the need for sustainable strategies for its valorization. In this context, the conversion of this waste into functional materials emerges as a promising alternative. Given this problem, this research proposed the sustainable use of agro-industrial waste using green coconut mesocarp to produce cbiochars via pyrolysis and chemical activation, with the aim of developing carbonaceous materials with high porosity and electrical conductivity applicable in electrochemical sensors. Different activation methods (pre- and post-pyrolysis) using phosphoric acid and potassium hydroxide were evaluated, resulting in porous and thermally stable structures. Morphological and structural characterizations were performed using elemental analysis, FT-IR, TG, EDX, XPS, SEM/EDS, TEM/EDS, and N2 adsorption, with statistical processing through Principal Component Analysis. The synthesized biochars exhibited high thermal stability, significant modifications in lignocellulosic structure, and adsorption properties directly related to surface area and pore distribution, highlighting their potential as functional platforms. The produced biochars were applied to modify electrodes for the detection of heavy metals and emerging contaminants. In the first application, the electrode modified with activated biochar with orthophosphoric acid showed excellent performance in the simultaneous detection of Cd2+, Pb2+, and Hg2+ by differential pulse voltammetry, with sensitivities of 42.75 µA L µmol-1 (Cd2+), 38.96 µA L µmol-1 (Pb2+), and 8.07 µA L µmol-1 (Hg2+), as well as very low detection limits, particularly for Cd2+ (1,4 nmol L-1 ). The sensor showed satisfactory selectivity and reproducibility, with recovery values between 89% and 106% in real samples (sewage, tap water, and cosmetics), confirming its practical feasibility, low cost, and sustainable nature. In a second application, the activated biochar with potassium hydroxide was functionalized with bimetallic Au@Pd nanoparticles, yielding the CMB500-Au@Pd electrode, which was used for the determination of the synthetic hormone 17α-ethinylestradiol (EE2). The sensor displayed a linear response in the range of 0.05-5.0 µM (R2= 0.9993), a detection limit of 2.53 nmol L -1 , and a quantification limit of 8.43 nmol L-1 , approximately 2,000 times lower than those obtained by HPLC. Reproducibility tests showed intra-day and inter-day RSDs of 5.77% and 8.14%, respectively. Selectivity studies indicated significant interference only for structurally related compounds (17β-estradiol and ascorbic acid), while urea, NaCl, and caffeine produced negligible effects. The method was successfully validated in real and simulated samples (groundwater, artificial breast milk, synthetic urine, saline solution, and contraceptive tablets), with recoveries ranging from 58.20% to 133.65%. Overall, the results prove the high potential of biochars derived from green coconut mesocarp as functional materials for sustainable electrochemical sensors. The developed electrodes combine high sensitivity, selectivity, and stability, representing cost-effective and environmentally responsible alternatives for monitoring toxic metals and hormonal contaminants in diverse matrices.