Strain Engineering and Its Mechanism in the Detection of Responsivity to Cu²⁺ and Pb²⁺ Based on Two-Dimensional g-C₃N₄

Two-dimensional (2D) materials are widely used in heavy metal ion detection due to their high specific surface area and abundant active sites. Herein, we prepared highly selective and sensitive electrochemical sensors based on 2D graphitic-phase carbon nitride for the detection of Cu2+ and Pb2+ ions and investigated the effects of both tensile and compressive strains on the corresponding detection sensitivity, together with their mechanism. The prepared carbon nitride nanosheet sensors showed detection sensitivities of 3.63 and 0.41 μA·μM·cm–2, detection ranges of 0.2–100 and 6–100 μM, and detection limits of 0.0033 and 0.23 μM for Cu2+ and Pb2+, respectively. The induced compressive strain of −0.25% in the 2D CNNS significantly improved the sensitivity by 40.5% and 31.7%, while the tensile strain of +0.25% reduced the sensitivity by 41.9% and 43.9% in detecting Cu2+ and Pb2+ as compared to those at zero strain, respectively. Through DFT calculations, the corresponding compressive strain of −0.25% reduced the band gap from 1.21 eV under zero strain to 0.94 eV. On the contrary, the tensile strain of +0.25% increased the band gap from 1.21 to 1.45 eV, resulting from the contribution of orbitals of C-p and N-p. The declined and raised band gaps, respectively, result in increased and decreased electron transport rates, thereby improving and degrading the sensitivities of the sensors. Our research provides guidance on the design of flexible wearable sensors integrated into the construction of sensitive and reliable heavy ion detection systems.