Formaldehyde electrochemical sensor using graphite paste-modified green synthesized zinc oxide nanoparticles

Abstract

• The ZnO NPs were synthesized via green synthesis route. • The ZnO NPs have irregular sponge-like shapes. • The GPE/ZnO NPs electrode performed a faster electron transfer rate. • The GPE/ZnO NPs is more accessible than other formaldehyde analytical methods. • The GPE/ZnO NPs was employed in formaldehyde electrochemical sensor in tofu sample. The green synthesis route of metal oxide nanoparticles using plant derivative extract has attracted the attention of researchers due to the simplicity, low cost, use less chemical reagents, produce less toxic waste, as well ready conducted in ambient conditions. In this study, zinc oxide nanoparticles (ZnO NPs) were successfully prepared via the facile green synthesis route using orange ( Citrus sinensis ) peel waste aqueous extract (OPE) as the bio-complexing agent. The prepared ZnO NPs showed a broad Ultra-Violet (UV) peak at around 358 nm, indicating the significant excitation binding energy of the ZnO NPs. Further characterization using Fourier-transform infrared (FTIR) confirmed that flavonoids in the OPE play the primary role in nanoparticle formation. Moreover, the scanning electrode microscopy-energy dispersive X-ray (SEM-EDX) and transmission electron microscopy (TEM) images showed that the prepared ZnO NPs have irregular sponge-like shapes, while the X-ray diffraction (XRD) confirmed the structure of ZnO was hexagonal wurtzite with a crystalline size of 11.58 nm. The electrochemical behavior study of the ZnO NPs-modified graphite paste electrode (GPE/ZnO NPs) using the ferro ferricyanide system was also performed, revealing that the ZnO NPs modification did not increase the mass transfer rate but successfully increased the electron transfer rate compared to the bare GPE. The cyclic voltammogram showed the optimum pH of 9 for the electrooxidation of formaldehyde (HCHO) on the GPE/ZnO NPs with an HCHO oxidation peak at 0.191 V vs. Ag/AgCl, while there was no reduction peak observed. Furthermore, in the phosphate buffer pH of 9 media, the linear correlation study between the square root of scan rate and the anodic peak current showed that the mass transfer of HCHO on the surface of GPE/ZnO NPs was mainly controlled by diffusion. The feasibility as the electrochemical sensor of HCHO is demonstrated by a limit of detection of less than 18 µM, linearity ranges from 0 to 100 mM, a ratio value of 0.38 of %relative standard deviation (RSD) to %RSD Horwitz, % recovery up to 103.9% in the real tofu sample, and the high selectivity toward HCHO instead of ethanol.