Nanocomposite of ZIF-67/reduced graphene oxide as sensing element for voltammetric detection of silver(I) ion: optimizing operational conditions by half-fraction central composite design

In this work, a sensing platform founded on the immobilization of ZIF-67 and rGO nanocomposite (ZIF-67/rGO) by Nafion on the glassy carbon electrode surface was fabricated and used for probing silver by differential pulse anodic stripping voltammetry (DPASV) procedure. The half-fraction central composite design (HF-CCD) was utilized for optimizing the experimental variables (weight percentage of composite: 8%; pre-concentration time and applied potential: 240 s, −1.3 V; scan rate of DPASV: 100 mV s⁻¹; pre-concentration solution pH: 6). The detection limit was 4.0 × 10⁻¹¹ mol/dm³. The repeatability (relative standard deviation) of the measurements using a single sensor was approximately 4% (n = 5, 1.0 × 10⁻⁸ mol/dm³ Ag(I)). One of the advantages of the proposed sensor is its high selectivity, which is based on the size-selective property of the ZIF-67 toward silver, and it causes the interference of other species, especially mercury, to be absent. Also, the use of Nafion immobilizes a large amount of composite on the surface of the electrode, and on the other hand, the synergistic effect related to the high conductivity of rGO and the high porosity of the ZIF-67 causes effective pre-concentration of silver by the composite, and these two factors strengthen the sensor signal, increase sensitivity and cause reaching the appropriate detection limit. In this research, an attempt has been made to overcome the challenges of using ZIF-67 in the construction of an electrochemical sensor, and its results can be used to build electrochemical platforms based on MOFs.

Graphical abstract