Simultaneous electrochemical sensing of heavy metal ions based on a g-C3N4/CNT/NH2-MIL-88(Fe) nanocomposite

Abstract

The presence of Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ in drinking-water can be harmful to human health, even if their concentration is fairly low. Hence, it is significant to detect these heavy metal ions in sewage to evaluate the quality of water. Herein, amino-functionalized metal–organic frameworks (NH₂-MIL-88(Fe)) embedded with graphitic carbon nitride (g-C₃N₄) nanosheets and acid-functionalized carbon nanotubes were prepared via a one-pot synthesis. The composite can be directly modified on the surface of glass carbon electrodes without the assistance of Nafion or other binders. The modified glass carbon electrodes can be used to simultaneously detect Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ in water via square wave stripping voltammetry. The doping of g-C₃N₄ in the composite, rich in N-containing functional groups, participates in the adsorption of metal ions on the surface of the electrodes. The porous composite provides accommodation room for metals generated by electro-reduction. The detection limit for Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ is 39.6 nM, 7.6 nM, 11.9 nM, and 9.6 nM, respectively. And the sensitivity for Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ is 0.0789 mA μM⁻¹ cm⁻², 0.4122 mA μM⁻¹ cm⁻², 0.2616 mA μM⁻¹ cm⁻², and 0.3251 mA μM⁻¹ cm⁻², respectively. This work not only enriches the functional design of Fe-MOF materials, but also develops a method for the determination of metal ions using the adsorption sites in g-C₃N₄.