Research PaperEffect of the operating conditions on the colloidal and microemulsion synthesis of Pt in aqueous phase

- Comprehensive study of methods and variables for the synthesis of Pt NPs.
- Colloidal synthesis yielded Pt NPs in the 3-6 nm range.
- Higher flexibility to tailor Pt NP size for microemulsion synthesis (1-7 nm).
- Larger Pt NPs obtained with NaBH4 than with N2H4 in microemulsion synthesis.
- Highly stable Pt NPs for both colloidal and microemulsion synthesis.

The syntheses of platinum nanoparticles (Pt NPs) using colloidal and microemulsion methods and different reducing agents (methanol, NaBH4, and N2H4) have been compared systematically. The colloidal synthesis was based on polyvinylpyrrolidone (PVP) as capping agent and water and methanol-water mixtures as reaction media. The microemulsion syntheses were carried out using the water-in-oil (w/o) system formed by dioctyl sulfosuccinate sodium salt (AOT), n-heptane and water. The influence of PVP/Pt, reducing agent/Pt and water/AOT molar ratios was studied. The Pt NPs prepared were characterized by transmission electron microscopy (TEM) and X-ray diffractometry (XRD). Both colloidal and microemulsion syntheses resulted in globular shaped NPs consisting mainly of a single crystal domain with fcc structure. Colloidal synthesis with methanol and NaBH4, yielded very stable NPs suspensions with small mean particle size (3-6 nm) and distributions extending from 2 to 10 nm. Narrower size distributions were obtained with NaBH4, whereas the use of N2H4 led to oversized particles. The most important synthesis variable was the PVP/Pt ratio. In the case of the microemulsion method, a broader range of NPs mean size was obtained (1-7 nm). A better tailoring of the properties of the NPs was achieved varying the type of reducing agent, the reducing agent/Pt ratio and water/AOT ratio. The conditions for the synthesis of NPs suspensions with well differentiated mean size and distribution were identified.

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