Abstract
Boron-doped carbon nanowalls (B:CNW) versus boron-doped diamond (BDD) materials were investigated for the effective electrochemical detection of highly toxic herbicide paraquat (PQ). Depending on the surface morphology and functional groups of BDD and B:CNWs, the electrochemical absorption and detection of the target analyte PQ revealed different detection mechanisms. The surface absorption mechanism was mainly observed for BDD, while for B:CNWs, both surficial and edge absorption were observed due to the sharp edges of carbon nanowalls. This effectually drives the high heterogenous electron transfer kinetics at absorption sites. Detection of PQ was carried out in phosphate buffer solution with an optimized pH of 10 and parameters of the square-wave voltammetry. Comparative studies show higher voltammetric current peak heights for B:CNWs (∼90.5 μA) than BDD (∼7.5 μA) at a much lower PQ concentration of 4 μM. B:CNWs show a higher sensitivity of 11 μA/μM/cm2 than BDD of 2.23 μA/μM/cm2, hence BDD shows a LOD of 1.8 μM, whereas B:CNWs have a much lower LOD of 0.47 μM. Density functional theory calculations (DFT) show a higher propensity of the B:CNW models toward electrocatalytic reduction of the PQ. Moreover, the proposed two-step detection mechanism is strongly supported by the distribution of the PQ electrostatic potential in different oxidation states in conjunction with the slab surfaces. The higher the sensitivity, the lower the LOD, and the excellent performance of B:CNWs in the detection of PQ in real water samples also suggests its potential for use in the environmental monitoring and assessment of emerging pollutants.
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