Biochar from coffee husks: a green electrode modifier for sensitive determination of heavy metal ions.

Biochar is a carbon rich and low-cost material that has been used as electrode modifier due to the property of preconcentrate spontaneously both organic and inorganic species. In this work, a biochar from coffee husks is proposed for the first time to prepare a carbon paste modified electrode (BC-CPE), which was used for the simultaneous determination of Cd2+ and Pb2+ by differential pulse adsorptive stripping voltammetry (DPAdsV) as proof-of-concept. Different BC-CPE were prepared, characterized (by EIS, FTIR, SEM and SEM–EDS) and submitted to DPAdsV measurements in the presence of both metal ions. Using the optimized BC-CPE (25 wt% of BC pyrolyzed at 300 °C during 50 min) and optimal pre-concentration conditions (10 min under stirring in a solution at pH 7.0), good linear range and LOD's better than other BC-CPE from literature (1.7 and 0.2 µg L−1 for Cd2+ and Pb2+, respectively) were obtained, as well as stable responses (RSD < 4.5%; n = 5) and good inter-electrode reproducibility (RSD < 4.4%; n = 5). This optimized method was applied for the simultaneous determination of Pb2+ and Cd2+in water samples, being found good accuracy (recoveries between 81 and 122%). The good analytical features favor the determination of these and other heavy metal ions at trace levels using the proposed BC-CPE, due to the strong ion adsorption on biochar pyrolyzed from coffee processing residues, a novel eco-friendly, sustainable, and renewable biochar source. [ABSTRACT FROM AUTHOR]