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Weakened adsorption energy barrier by C–N bond elongation in graphitic carbon nitride enhances electrochemical detection of trace Cd(II)

Zhongyou Jiang,Shanshan Dong,Dingying He,Jiazheng Yang,Suqing Dai,Shuaitao Peng,Suhua Chen

Bonded nitrogen of lone pair electrons gives a chance for carbon-based substrates to complex with and consequently electrochemically analyze heavy metals, e.g., cadmium(II) (Cd(II)). However, the carbon atom bonded with nitrogen atom present positively charged and could electrostatically hinder Cd(II) adsorption, leading to a limited electroanalytical sensitivity. In this study, we adopted a sequential iron occupying and nitric acid etching strategy to elongate C–N bond in graphitic carbon nitride (CN), which could weaken the energy barrier for Cd(II) adsorption. Material characterizations show the iron occupying and nitric acid etching strategy successfully elongated C–N bond without damaging the skeletal structure of CN and significantly enhanced Cd(II) adsorption capacity. Experiments combined with first principle calculations verified the efficient and sensitive binding of Cd(II) with nitrogen in the elongated C–N. As a result, in comparison with pristine CN, the C–N elongated material (marked as EtCN–Fe 0.3 ) possessed a much higher sensitivity (22.34 vs. 16.92 μA ppb −1  cm −2 ) and a dramatically lower limit of detection (LOD) (0.29 vs. 2.22 ppb). The sensor demonstrates a broad linear range (1−500 ppb), exceptional reproducibility (relative standard deviation = 1.4 %), and long-term stability (only 1.1 % of sensitivity loss over 10 days). EtCN–Fe 0.3 electrode even showed high recovery rates (98.2−102.4 %) in various real waters, which were in agreement with Inductively coupled plasma-mass spectrometry (ICP-MS)/Atomic absorption spectrophotometry (AAS) methods. This study provides a facile strategy to activate carbon materials to electrochemically detect trace heavy metals with precision and cost-effectiveness.