Localized SurfacePlasmon Resonance Increases PulseVoltammetry Detection of Nitrite by Noble-Metal Modified Zirconium-BasedMetal–Organic Frameworks: Fabrication and Mechanism

This study utilizes a noble-metal localized surface plasmon resonance-modified porous zirconium-based metal–organic framework (Zr-MOF, PCN-222) to increase pulse voltammetry as a sodium nitrite (NaNO₂) sensing electrode. Bipolar peak sensing electrodes can significantly improve electrochemical conductivity, linearity, and stability. Although PCN-222 with an organic and porous structure can be used as an excellent sensing electrode for nitrite, it has the disadvantage of poor conductivity of organic materials. Doping the electrode with gold and silver nanoparticles (Au and Ag NPs) was shown to increase conductivity and decrease impedance. The process follows two main steps: first is fabrication via the hydrothermal chemical synthesis of PCN-222. Various zirconium base content levels 92, 97, 102, and 107 mg were tested, and 97 mg was found to be optimal. The second step involved preparation of the Au and Ag NPs via chemical reaction. The synthesis particle sizes were confirmed by absorption spectra. The Au and Ag NPs were evenly coated on the surface of PCN-222 via Nafion dispersant. Cyclic voltammetry (CV), chronoamperometry (CA), and AC impedance were used to measure the sensitivity, charge transfer resistance (<i>R</i>_ct), linear fit, and coefficient of determination (<i>R</i>²) of the sensing electrode. Results showed that the Au and Ag NPs had bipolar peaks at 0.7 and 0.3 V during CV measurement, and the induced current intensity increased from 130 μA to 260 and 240 μA (a gain of 200 and 185%, respectively). During CA measurement, the induced current increased from 1 to 5 μA, a 5-fold gain. The current linearity increased from 0.06 to 0.48 and 0.46, and the <i>R</i>² also increased from 0.865 to 0.979 and 0.964, respectively. The <i>R</i>_ct dropped significantly from 246 to 33 and 48 kΩ, respectively. It is concluded that doping Au and Ag NPs successfully and significantly improves the performance of Zr-MOF detection electrodes.