Highly Sensitive Electrochemical Detection of Paraquat in Environmental Water Samples Using a Vertically Ordered Mesoporous Silica Film and a Nanocarbon Composite

Abstract

Herein, we demonstrate a sensitive and rapid electrochemical method for the detection of paraquat (PQ) using a glassy carbon electrode (GCE) modified with vertically ordered mesoporous silica films (VMSF) and a nanocarbon composite. The three-dimensional graphene-carbon nanotube (3DG-CNT) nanocarbon composite has a 3D network structure, a large electroactive area and oxygen-containing groups, promoting electron transfer between PQ and the underlying electrode and providing a suitable microenvironment for the stable growth of VMSF. This VMSF/3DG-CNT nanocomposite film could be prepared on the GCE's surface by a two-step electrochemical method with good controllability and convenience. Owing to the synergistic effect of the electrocatalytic ability of 3DG-CNT and the electrostatically enriched capacity of VMSF, the proposed VMSF/3DG-CNT/GCE has superior analytical sensitivity compared with the bare GCE. Furthermore, VMSF has excellent anti-fouling ability that makes the fabricated sensor exhibit satisfactory performance for direct analysis of PQ in environmental water samples.

Keywords: carbon nanotubes; electrochemical detection; electrochemically reduced graphene oxide; paraquat; vertically ordered mesoporous silica films.

Scheme 1

Illustration of the preparation of VMSF/3DG-CNT/GCE and the direct detection of PQ in complex environmental samples.

Figure 1

(a,b) The XPS C1s spectra of the GO (a) and ErGO (b). (c,d) SEM images of the 3DG-CNT network electrodeposited under a potential of −1.2 V for 300 s.

Figure 1

(a,b) The XPS C1s spectra of the GO (a) and ErGO (b). (c,d) SEM images of the 3DG-CNT network electrodeposited under a potential of −1.2 V for 300 s.

Figure 2

(a) Top-view TEM image of the VMSF. The inset is the corresponding magnified image. (b) CV curves obtained for different electrodes in a 0.05 M KHP solution containing 0.5 mM [Ru(NH₃)₆]³⁺.

Figure 3

(a) CV curves of bare GCE (black) and VMSF/3DG-CNT/GCE (red) in PBS (0.1 M, pH = 6). The inset depicts the normalized electroactive surface area of each electrode. (b) Relationship between the peak currents and the square root of the scan rate derived from the CV curves of bare GCE in 0.05 M KHP containing 0.5 mM K₃[Fe(CN)₆].

Figure 4

(a) CV and (b) DPV curves obtained with different electrodes in 0.1 M PBS (pH = 6) containing a 10 μM PQ solution.

Scheme 2

Schematic diagram of PQ’s reaction process.

Figure 5

(a) DPV curves of the VMSF/3DG-CNT/GCE obtained in PBS (0.1 M, pH = 6) containing different concentrations of PQ. The inset is the magnified view of the DPV curves in the low concentration region. (b) The calibration curve for PQ. The inset in (b) shows the calibration lines in the low concentration range. The error bars represent the standard deviation (SD) of three measurements.

Figure 6

Normalized oxidation peak current ratio of the VMSF/3DG-CNT/GCE and 3DG-CNT/GCE towards PQ (1 μM). I and I₀ represent the currents obtained in the present and absence of 20 μg/mL of SDS (a), BSA (b), starch (c) or HA (d) in 0.1 M PBS (pH = 6). The insets are the corresponding DPV curves obtained for the 3DG-CNT/GCE and VMSF/3DG-CNT/GCE in the absence and presence of the fouling species.