Abstract

Eggshell membrane (ESM), an abundant biowaste, was converted into biochar-derived carbon materials through carbonization at 800 degrees C under a nitrogen atmosphere using two heating rates: 10 degrees C/min (CESM10) and 30 degrees C/ min (CESM30). Next, multistage activation and oxidation treatments were applied to tailor the surface chemistry and porous structure, yielding CESM10-OX and CESM30-OX materials. Comprehensive physicochemical characterization established clear relationships between processing conditions, morphology, porosity, and surface functionality. A lower heating rate preserved a porous, crosslinked fibrillar structure and enabled a higher accessible surface area upon oxidation, whereas higher heating rates produced more compact structures. The oxidation protocol promoted the incorporation of oxygenated functional groups, particularly carboxylic acids, and induced a selective transformation of nitrogen functionalities. As proof of concept, the functionalized biochar was evaluated as a sensing platform for the electrochemical detection of carbendazim. The optimized GCE/ CESM10-OX electrode exhibited enhanced electrochemical performance, attributed to the combined effects of surface carboxylation, favorable nitrogen speciation, and improved textural accessibility. Differential pulse voltammetry measurements yielded three linear dynamic ranges from 0.082 to 400 mu M and a limit of detection of 0.025 mu M. These results demonstrate that controlled thermal processing and post-treatment strategies enable the rational design of sustainable biochar-based materials for electrochemical sensor applications.