Electrocatalytic activity of ligand-protected gold particles: formaldehyde oxidation

Tris(hydroxymethyl)phosphine oxide (THPO) and triphenyl phosphine oxide (PPh₃O) were introduced onto the surface of colloidal gold nanoparticles (Au NPs), and the effect of capping ligands on the catalytic electrooxidation of formaldehyde was studied voltammetrically by using colloidal Au-NP-modified glassy carbon electrodes (GCEs). This was compared with polycrystalline Au and another Au-NP-modified GCE without a capping molecule. We found that PPh₃O causes a larger decrease in the catalytic activity of the Au NPs in liquid than THPO does, indicating that the catalytic activity of the Au NPs is closely associated with the capping ligands. The effect of capping ligands is discussed based on the available surface ratio (ASR), which is defined as the ratio of the total surface area measured electrochemically to the calculated value based on the number and geometry of the Au NPs. These were determined to be 70.6?% for THPO and 0.23?% for PPh₃O, respectively. The significant blocking of formaldehyde is probably due to the structure and hydrophobicity of the benzene rings in the PPh₃O molecule, which is responsible for the decrease in catalytic activity of the Au NPs.