Abstract
In the present work, a novel electrochemical sensor was developed for the detection of trace cadmium with high sensitivity and selectivity in an easy and eco-friendly way. Firstly, a glassy carbon electrode (GCE) was modified with nontoxic sodium carboxymethyl cellulose (CMC) by a simple drop-casting method, which was applied to detect cadmium by differential pulse anodic stripping voltammetry (DPASV) in a solution containing both target cadmium and eco-friendly bismuth ions, based on a quick electro-codeposition of these two metal ions on the surface of the modified electrode (CMC-GCE). Investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FT-IR), both CMC (with good film-forming ability) and bismuth (with well-defined stripping signal) were found to be well complexed with target cadmium, leading to vital signal amplification for cadmium detection at a sub-nanomolar level. Under the optimal conditions, the proposed sensor exhibited a good linear stripping signal response to cadmium (Ⅱ) ion, in a concentration range of 0.001 μmol/L–1 μmol/L with a limit of detection of 0.75 nmol/L (S/N = 3). Meanwhile, the results demonstrate that this novel electrochemical sensor has excellent sensitivity and reproducibility, which can be used as a promising detection technique for testing natural samples such as tap water.
Highlights
Nowadays, wide applications of heavy metal such as cadmium, chrome, lead, arsenic, and mercury, are causing serious problems including environmental pollution and risks to human health [1]
C, both cadmium and bismuth ions can be detected on the bare glassy carbon electrode (GCE) or carboxymethyl cellulose (CMC)-GCE surface, after electrodeposition has happened in NaAc/HAc buffer solution containing 0.2 μmol/L of Cd2+ and Bi3+ ; while on the CMC-GCE surface, more cadmium and bismuth ions can be observed. These results are consistent with those of scanning electron microscopy (SEM) analyses. Both SEM and energy dispersive spectroscopy (EDS) studies indicate that CMC has a good film-forming talent that is favorable for the smooth modification of GCE; it has a good adsorption/enrichment ability for better electrodeposition of both cadmium and bismuth ions
Bismuth ions will compete with cadmium ions for the active site on the electrode surface [43], so the further increase of Bi3+ concentration will in turn reduce the amount of cadmium ions that can be deposited upon the electrode surface, resulting in a decrease in the stripping signal of target Cd2+, as observed from 0.5 to 1.75 μmol/L
Summary
Wide applications of heavy metal such as cadmium, chrome, lead, arsenic, and mercury, are causing serious problems including environmental pollution and risks to human health [1]. Due to low toxicity as well as other merits such as easy preparation, well-defined stripping signal, and wide negative potential window, bismuth-based electrodes that can form a fused alloy with a heavy metal [23,24], have attracted much attention since first reported in 2000 as a desirable mercury-electrode substitute for the detection of heavy metal ions [25,26,27,28]. The successful fabrication of this new sensor based on Bi/CMC-GCE will develop an easy and quick, simple and sensitive, low-cost and eco-friendly electrochemical detection method for the analysis of trace cadmium residue in our surroundings. Strategy for the construction of the new cadmium electrochemical sensor based on synergetic effects of both CMC and bismuth on the enrichment and detection of cadmium ions
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