Complicated and strict protocols are followed to tune the size of gold nanoparticles (GNPs) in chemical synthesis methods. In this study, we address the polarity of solvents as a tool for tailoring the size of GNPs in the chemical reduction method. The effects of varying polarity index of the reaction medium on synthesizing gold nanoparticles by chemical reduction method have been investigated. Ethanol as a polar solvent, ethanol-water mixture as reaction medium, L-ascorbic acid as reducing agent, and polyvinylpyrrolidone as stabilizer were used to synthesize GNPs. The polarity index of the reaction medium was adjusted by changing the volume ratio of ethanol to water. UV-Vis, dynamic light scattering (DLS), and transmission electron microscopy (TEM) characterizations reveal that the growth of nanoparticles was gradually increased (~22 to 219 nm hydrodynamic diameter) with decreasing value of polarity index of the reaction medium (~8.2 to 5.2). Furthermore, the high polarity index of the reaction medium produced smaller and spherical nanoparticles, whereas lower polarity index of reaction medium results in bigger size of GNPs with different shapes. These results imply that the mechanistic of the growth, assembly, and aggregation phenomena of ligand or stabilizer-capped GNPs strongly rely on the polarity of solvent molecules. Using the proposed methodology, wide size range of GNPs with different morphology sizes can be synthesized by simply modulating the volume percentage of organic solvent in the reaction medium.

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Reduced graphene oxide (rGO) combined with zeolitic imidazolate framework (ZIF), i.e., rGO-ZIF incorporated with polyetherimide (PEI) electrospun nanofiber, was produced using the electrospinning technique. The produced nanofibers had high porosity with enhanced conductivity. The ionic conductivity, porosity, morphology, and diameter of rGO-ZIF nanofiber were optimized by manipulating the weight percentage of rGO-ZIF and PEI in the electrospinning solution. Morphology, porosity, and contact angle analyses revealed that the 30 wt% PEI with 0.3 wt% of rGO-ZIF can produce nanofibers without beads with 136.3 ± 35 nm mean diameter and porosity of around 92.3%. Furthermore, electrochemical impedance spectroscopy (EIS) analysis revealed that with the addition of 0.3 wt% of rGO-ZIF, charge transfer resistance decreased, and the ionic conductivity of PEI nanofibers increased to 5.23 × 10–4 S/cm, nearly 200 times higher than the ionic conductivity of pure PEI nanofibers. The excellent ionic conductivity, low charge transfer resistance, and high porosity of electrospun rGO-ZIF/PEI-based composite nanofibers make them suitable for electrochemical sensing electrode applications.

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