Activated biochar: Preparation, characterization and electroanalytical application in an alternative strategy of nickel determination

This work reports for the first time the use of chemically activated biochar as electrode modifier for nickel determination. The biochar activation was performed by refluxing with HNO3, which promoted a higher nickel preconcentration compared to unmodified and modified biochar precursor electrodes. Morphological and structural characterization revealed the increase of surface acid groups, surface area and porosity of biochar after activation. Nickel determination was investigated adopting an alternative voltammetric methodology based on monitoring the Ni(II)/Ni(III) redox couple. In the proposed method, it was not necessary to use a complexing agent and the biochar itself was responsible for the analyte preconcentration. A linear response for Ni(II) concentration range from 1.0 to 30 μmol L−1 and a limit of detection of 0.25 μmol L−1 were obtained. The method was successfully applied for Ni(II) determination in spiked samples of bioethanol fuel and discharge water, with recoveries values between 103 and 109%. [Display omitted] •Alternative electroanalytical strategy for determination of nickel ions in alkaline medium.•Activated biochar as an electrode modifier for determination of nickel ions samples in bioethanol fuel and discharge water.•A simple chemical route way to improve the adsorption ability of biochar towards nickel ions.•Comparative morphological and structural characterization of treated and untreated biochar.•Nickel ions as an electroactive probe for investigation of surface properties of biochar.