Raman and Phosphide Studies on Gold Phosphide

Gold phosphide is a crystalline metastable phase at macroscale. In earlier studies of bulk polycrystalline gold phosphides, several phases were detected, including multiple compositions. However, the only metastable phase is Au2P3. It has attracted considerable interest in fundamental research.

For the first time, a Raman study of Au2P3 thin films was carried out. This method enabled the characterization of the vibrational properties of the gold phosphide phase. The X-ray crystallographic structure was subsequently confirmed.

The first-principles Raman spectra indicate that Au2P3 is a narrow band indirect semiconductor. First-principles Raman calculations also reveal that the P vibrations occur at higher frequencies.

As a result of the phosphidation reaction, the domains of the metal nanoparticles are enlarged, which results in robust nanoparticles. The domains shield the ligand from ligand exchange.

The surface capping ligand of the precursors of the gold nanoparticles plays an important role in the purity of the Au2P3 phase. The phosphido-bridged AuCl2 was formed from N-heterocyclic carbenes. A simple synthesis route was used to produce the nanoparticles.

Afterward, a selective phosphidation reaction was performed on the gold nanoparticles. White phosphorus (P4) was used as a soluble phosphorus donor. Besides, the tertiary phosphine PPh(C(O)Ph)2 was isolated from the AuCl complex.

Compared with the polycrystalline gold, the Au2P3 nanoparticles showed a significant activity towards the hydrogen evolution reaction. These results suggest the potential of the colloidal hybrid nanoparticles containing metal phosphide domains for solar hydrogen generation and photocatalysis.

To understand the fundamental mechanisms of the phosphidation reaction, a first-principles Raman spectroscopic study of the metal phosphide was conducted. Interestingly, the PbS conduction band is close to the work function of the metal phosphides.

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