Metallic-like boron-modified bio-carbon electrodes for simultaneous electroanalysis for Cd2+, Pb2+ and Cu2+: Theoretical insight into the role of CxBOy(H)

It still remains challenges to develop efficient, sensitive yet low-cost electrochemical sensing platforms for quantification of heavy metal ions. Herein, by combining experiments and theoretical calculations, a novel boron-modified bio-carbon (B-bioC) electrode material prepared by ultrasonic-assisted hot impregnation with cotton stalk and inexpensive boric acid and subsequent pyrolysis strategy is initially proposed for simultaneous electroanalysis of cadmium (Cd), lead (Pb) and copper (Cu) using differential pulsed anodic stripping voltammetry (DPASV). The physico-chemical characterizations together with electrochemical characterizations suggested that a higher graphitization level for B-bioC was obtained by the catalytic graphitization effect of metalloid boron, thus rendering lower impedance and faster electron-transfer rate compared with pristine bio-carbon. Also, stronger electrocatalytic activity was observed as a results of the introduction of various boron-bonding electroactive sites (CxBOy(H)). These combined unique advantages make a great role for the enhanced electroanalytical properties of the modified electrodes (B-bioC/MEDs) with a linear response of Cd2+, Pb2+, and Cu2+ concentration range of 0.25–40 μM, 0.06–4.8 μM, and 0.125–20 μM, with sensibility of 10.54, 509.96, and 22.38 μA μM−1 cm−2, and detection limit low to 54, 4, and 24 nM (S/N = 3), respectively, which are comparable to certain reported metal-modified bio-carbons. Finally, through DFT calculations, it was concluded that C-BO2 on B-bioC was the optimum active site over seven B-bonding configurations. This work throws light on the pivotal roles of B configurations in electrochemical sensing and provides theoretical support for deliberately designing ultrasensitive bio-carbon based electrochemical sensing platforms toward heavy metal ions of interest.