Bi-MOF-Derived Carbon Wrapped Bi Nanoparticles Assembly on Flexible Graphene Paper Electrode for Electrochemical Sensing of Multiple Heavy Metal Ions

Abstract

The development of nanohybrid with high electrocatalytic activity is of great significance for electrochemical sensing applications. In this work, we develop a novel and facile method to prepare a high-performance flexible nanohybrid paper electrode, based on nitrogen-doped carbon (NC) wrapped Bi nanoparticles (Bi-NPs) assembly derived from Bi-MOF, which are decorated on a flexible and freestanding graphene paper (GP) electrode. The as-obtained Bi-NPs encapsulated by an NC layer are uniform, and the active sites are increased by introducing a nitrogen source while preparing Bi-MOF. Owing to the synergistic effect between the high conductivity of GP electrode and the highly efficient electrocatalytic activity of Bi-NPs, the NC wrapped Bi-NPs (Bi-NPs@NC) modified GP (Bi-NPs@NC/GP) electrode possesses high electrochemically active area, rapid electron-transfer capability, and good electrochemical stability. To demonstrate its outstanding functionality, the Bi-NPs@NC/GP electrode has been integrated into a handheld electrochemical sensor for detecting heavy metal ions. The result shows that Zn²⁺, Cd²⁺, and Pb²⁺ can be detected with extremely low detection limits, wide linear range, high sensitivity, as well as good selectivity. Furthermore, it demonstrates outstanding electrochemical sensing performance in the simultaneous detection of Zn²⁺, Cd²⁺, and Pb²⁺. Finally, the proposed electrochemical sensor has achieved excellent repeatability, reproducibility, stability, and reliability in measuring real water samples, which will have great potential in advanced applications in environmental systems.

Keywords: Bi nanoparticles; electrochemical catalysis and sensing; flexible and freestanding graphene paper electrode; heavy metal ions detection; nitrogen-doped carbon.

Figure 1

Schematic illustration for the preparation process of Bi-NPs@NC/GP.

Figure 2

(A) SEM image of GO nanosheets; (B) photograph of GOP; (C) cross-section SEM image of GOP; (D) SEM image of Bi-BDC; (E) Bi-BDC/GOP; (F) Bi-NPs@NC assembly; (G) TEM; (H,I) HRTEM images; and (J) EDS elemental mapping images of Bi-NPs@NC/GP.

Figure 3

(A) XRD patterns of Bi-BDC, Bi-BDC/GOP, Bi-NPs/GP, and Bi-NPs@NC/GP; (B) XPS survey spectrum of Bi-NPs@NC/GP; XPS high-resolution (C) C 1s, (D) O 1s, (E) N 1s, and (F) Bi 4f spectrum of Bi-NPs@NC/GP.

Figure 4

(A) CV curves of Bi-BDC/GOP, Bi-NPs/GP, and Bi-NPs@NC/GP in 0.15 M KCl solution containing 5 mM [Fe(CN)₆]^3−/4−, scan rate: 50 mV s⁻¹; (B) EIS spectra of Bi-BDC/GOP, Bi-NPs/GP, and Bi-NPs@NC/GP in 0.15 M KCl solution containing 5 mM [Fe(CN)₆]^3−/4−, applied potential: 0.3 V vs. Ag/AgCl, frequency range: 0.01–10⁶ Hz; (C) SWASV curves of Bi-NPs/GP and Bi-NPs@NC/GP in 0.1 M ABS containing 400 ppb Cd²⁺.

Figure 5

(A) SWASV curves of different electrodes in ABS containing 400 ppb Zn²⁺. Effect of (B) pH of the buffer electrolyte, (C) deposition potential, and (D) deposition time on SWASV response of 400 ppb Pb²⁺, 400 ppb Cd²⁺, and 400 ppb Zn²⁺ in ABS at Bi-NPs@NC/GP.

Figure 6

SWASV response of the Bi-NPs@NC/GP for the individual analysis of (A) Zn²⁺, (B) Cd²⁺, and (C) Pb²⁺ with varying concentrations in a range of 10–1200 ppb, 0.5–1200 ppb, and 0.5–1500 ppb, respectively. The linear calibration curves of oxidation current versus concentrations of (D) Zn²⁺, (E) Cd²⁺, and (F) Pb²⁺. Data are presented as mean ± SD from three independent measurements.

Figure 7

(A) SWASV response of the Bi-NPs@NC/GP for simultaneous analysis of Zn²⁺, Cd²⁺, and Pb²⁺ with varying concentrations in a range of 1–1400 ppb; (B) effect of interfering species on the determination of 400 ppb Zn²⁺, Cd²⁺, and Pb²⁺. The concentration of K⁺, Ag⁺, Ca²⁺, Na⁺, Mg²⁺, Cl⁻, SO₄²⁻, Cu²⁺, DA, UA, and AA is 4 mg L⁻¹; (C) relative current response of the sensor stored over 30 days toward 400 ppb Zn²⁺, Cd²⁺, and Pb²⁺; (D) relative current response of seven sensors prepared under the same conditions toward 400 ppb Zn²⁺, Cd²⁺, and Pb²⁺.