A Nanograss Boron and Nitrogen Co-Doped Diamond Sensor Produced via High-Temperature Annealing for the Detection of Cadmium Ions

Abstract

The high-performance determination of heavy metal ions (Cd²⁺) in water sources is significant for the protection of public health and safety. We have developed a novel sensor of nanograss boron and nitrogen co-doped diamond (NGBND) to detect Cd²⁺ using a simple method without any masks or reactive ion etching. The NGBND electrode is constructed based on the co-doped diamond growth mode and the removal of the non-diamond carbon (NDC) from the NGBND/NDC composite. Both the enlarged surface area and enhanced electrochemical performance of the NGBND film are achievable. Scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse anodic stripping voltammetry (DPASV) were used to characterize the NGBND electrodes. Furthermore, we used a finite element numerical method to research the current density near the tip of NGBND. The NGBND sensor exhibits significant advantages for detecting trace Cd²⁺ via DPASV. A broad linear range of 1 to 100 μg L^-1 with a low detection limit of 0.28 μg L^-1 was achieved. The successful application of this Cd²⁺ sensor indicates considerable promise for the sensitive detection of heavy metal ions.

Keywords: cadmium; co-doping; detection; diamond; electrochemical; nanograss.

Figure 1

SEM images of the (a) NGBND/NDC composite film deposited with a CH₄/H₂/B/N₂ flow rate of 20/200/2/1 sccm and the (b) NGBND film fabricated by etching the NDC phase (annealing in a quartz tube at 800 °C for 20 min in the air) from the composite. (c,d) are the images of (a,b), respectively, obtained at high magnification.

Figure 2

OES spectrum of the growth stage of the NGBND/NDC composite.

Figure 3

Raman spectra of the NGBND/NDC composite film and NGBND film.

Figure 4

(a) Entire XPS scanning spectrum of NGBND. XPS high-resolution survey scan of (b) B 1s, (c) C 1s, (d) N 1s, (e) O 1s, and (f) Si 2p of NGBND. The black, red, and blue line is the experimental data, overall fit and background line in the subfigures (b–f).

Figure 5

(a) CV curves of the NGBND/NDC composite and NGBND electrodes in 0.1 M acetate buffer at scan rates of 50 mV s⁻¹. (b) EIS of NGBND/NDC composite and NGBND electrodes tested in a 5 mM Fe(CN)₆^3−/4− solution containing 0.1 M KCl. The insert graph is a locally enlarged EIS image of NGBND.

Figure 6

(a) DPASV diagrams of Cd²⁺ with concentrations between 1 and 100 μg L⁻¹ on the NGBND electrode. (b) Calibration curve for Cd²⁺ detection. The error bars represent the relative standard deviations of triple measurements. The buffer used is 0.1 M acetate buffer (pH = 5.5).

Figure 7

Current density distributions on the surface of NGBND at the electrode tip, which increase as the tip radius decreases. The tip radius of the structure in each panel is (a) 5 nm, (b) 50 nm, and (c) 100 nm.