An electrochemical sensor based on copper-based metal-organic framework-reduced graphene oxide composites for determination of 2,4-dichlorophenol in water

Abstract

In the present work, we reported the fabrication of a novel electrochemical sensing platform to detect 2,4-dichlorophenol (2,4-DCP) by using a copper benzene-1,3,5-tricarboxylate-graphene oxide (Cu-BTC/GO) composite. The sensor was prepared by drop-casting Cu-BTC/GO suspension onto the electrode surface followed by electrochemical reduction, leading to the generation of an electrochemically reduced graphene oxide network (ErGO). By combining the large specific area of the Cu-BTC matrix with the electrical percolation from the graphene network, the number of accessible reaction sites was strongly increased, which consequently improved the detection performance. The electrochemical characteristics of the composite were revealed by cyclic voltammetry and electrochemical impedance spectroscopy. For the detection of 2,4-DCP, differential pulse voltammetry was used to emphasize the faradaic reaction related to the oxidation of the analyte. The results displayed a low detection limit (83 × 10^-9 M) and a linear range from 1.5 × 10^-6 M to 24 × 10^-6 M alongside high reproducibility (RSD = 2.5% for eight independent sensors) and good stability. Importantly, the prepared sensors were sufficiently selective against interference from other pollutants in the same electrochemical window. Notably, the presented sensors have already proven their ability in detecting 2,4-DCP in real field samples with high accuracy (recovery range = 97.17-104.15%).

Fig. 1. XPS survey (a) and high-resolution C 1s (b), O 1s (c), Cu 2p (d) of Cu–BTC/GO powder.

Fig. 2. XRD patterns of GO, Cu–BTC and Cu–BTC/GO sample.

Fig. 3. SEM and TEM images of (a and b) GO and (c and d) of Cu–BTC/GO samples.

Fig. 4. N₂ adsorption–desorption isotherms of GO and Cu–BTC/GO.

Fig. 5. Nyquist diagrams of GCE, Cu–BTC/GO/GCE and Cu–BTC/ErGO/GCE in the solution containing 5 mM Fe(CN)₆^3−/4− and 0.1 M KCl. Parameters as follow: frequency range from 0.01 Hz to 10000 Hz, initiative potential: 0.23 V amplitude: 10 mV and quiet time of 5 s. Its equivalent circuit is in inset.

Fig. 6. CVs of 2,4-DCP 48 μM in PBS pH 7 recorded on Cu–BTC/ErGO/GCE at different scan rates (ν): 10, 20, 50, 100, 200, 400 and 500 mV s⁻¹. Inset: relationship between anodic peak currents and scan rate (a); peak position and scan rate (b).

Fig. 7. DPVs of 2,4-DCP on Cu–BTC/ErGO/GCE in PBS pH 7 with different pH: 6.0; 6.5; 7.0; 7.5; 8.0 (a), currents varied by pH (b) and relationship between potentials and pH (c).

Fig. 8. Voltammograms acquired from 2,4-DCP in the concentration range from 1.5 to 24 μM (a) and the variations of peak intensities according to the concentration change using both modified and bare GCE (b).