Silver nanoparticles synthesis using H2 as reducing agent in toluene–supercritical CO2 microemulsion

• A new technique to synthesize silver nanoparticles with controllable size was developed using toluene–scCO2 microemulsion.
• Hydrogen was used as reducing agent in the synthesis process.
• The relationship between the wavelength of maximum absorption and size of AgNPs was discussed, which was consistent with the MIE theory.

A new technique to synthesize silver nanoparticles (AgNPs) with controllable size was developed using hydrogen as reducing agent in toluene–supercritical carbon dioxide (toluene–scCO2, the mixture ratio of toluene:CO2 is about 20%, v/v) microemulsion. The method involves both process of AgNPs formation (nucleation and crystal growth) at high pressure and thermal incubation at ordinary pressure in the micro-water pool of the microemulsion. Silver ions were reduced by hydrogen (H2) in the micro-reactor of toluene–scCO2 microemulsion, and the size of AgNPs can be controlled by adjusting molar ratio of water to surfactant. The size and morphology of AgNPs were characterized by DLS, TEM and AFM. The AgNPs capped with surfactant were proved by the ATR-FTIR. The relationship between the wavelength of maximum absorption and size of AgNPs was discussed, which was consistent with the MIE theory. This method is better than traditional microemulsion method to synthesize AgNPs by comparing AgNPs prepared using different methods. This method is not only able to obtain AgNPs with controllable size, but also avoids use of fluorinated reagents and reducing agent residual.

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