Nitrogen-vacancy-rich manganese nitrides loaded on nitrogen-doped carbon nanotubes for sensitive and stable electrochemical detection of heavy metal ions

Abstract

The advancement of electrochemical sensing platforms designed for the precise detection of trace-level heavy metal ions (HMIs) is critically important in addressing the escalating environmental and public health challenges. This study presents a nitrogen-defect-enriched manganese nitride (Mn₂N_0.86) integrated onto nitrogen-doped carbon nanotube substrates (Mn₂N_0.86/N-CNTs), serving as a non-precious-metal-based system for voltametric quantification of Pb²⁺, Cd²⁺, Hg²⁺, and Cu²⁺ in aqueous environments. Morphological and structural characterizations conducted using SEM, TEM, XRD, XPS, and EPR revealed the presence of multiple valence states of manganese, nitrogen vacancies, as well as pyridinic-N, pyrrolic-N, and graphitic-N within the Mn₂N_0.86/N-CNTs material. The incorporation of nitrogen vacancies along with the redox mediation involving mixed-valence Mn²⁺/Mn³⁺ significantly enhanced both the adsorption capacity and catalytic performance of Mn₂N_0.86/N-CNTs, thereby improving its electroanalytical efficacy for HMIs. This platform achieved remarkable detection limits for Pb²⁺, Cd²⁺, Hg²⁺, and Cu²⁺ at concentrations as low as 5.3 nM, 4.5 nM, 15.9 nM, and 10.6 nM respectively. Furthermore, this electrode exhibits excellent stability, reproducibility, and anti-interference capabilities while enabling accurate detection in real water samples. This work establishes a paradigm for transition metal nitride-based sensors through vacancy engineering coupled with substrate optimization; offering an innovative strategy for environmental monitoring.