Size-Dependent Electrophoretic Deposition of Catalytic Gold Nanoparticles

Abstract

Here we describe size-dependent electrophoretic deposition (EPD) of citrate-stabilized Au nanoparticles (NPs) onto indium-tin-oxide-coated glass (glass/ITO) electrodes as studied by linear sweep stripping voltammetry (LSSV) and scanning electron microscopy (SEM). LSSV allows both the determination of the Au NP coverage and NP size from the peak area and the peak potential, respectively. Two-electrode EPD in aqueous solutions of Au NPs plus HO reveal that a minimum potential of 1.5 V is needed for significant deposition of 4 nm diameter Au NPs as opposed to 2.0 V for 33 nm diameter Au NPs. EPD at 0.4 V in a solution of Au NPs prepared with a short 5 min reaction time led to the successful capture of 1-2 nm diameter Au NPs with appreciable coverage. In all cases, deposition did not occur in the absence of HO. Three-electrode experiments with a real reference electrode revealed the same size selective deposition with potential and that the amount of Au deposited depends on the deposition time and HO concentration. The deposition occurs indirectly by oxidation of HO, which liberates protons and neutralizes the citrate stabilizer, leading to precipitation of the Au NPs onto the glass/ITO electrode. Studies on pH stability show that larger Au NPs aggregate at lower pH compared to smaller Au NPs. More importantly, though, 4 nm diameter Au NPs are much more catalytic for HO oxidation, which is the main reason for the size selective deposition.

Improved Electrocatalysis and Electrophoretic Deposition due to the Strong Synergy between Au and Ag Nanoparticles.

“…[20] Zamborini's group recently shed light on the EPD mechanism by the use of proton liberating molecules (i. e.; peroxide or hydroquinone) capable of neutralizing the negatively-charged Au nanospheres (NSs) prior deposition on the electrode surface. [21,22] Allen et al [22] concluded that two mechanisms may interplay during EPD based on (a) destabilization of the negatively charged Au NSs by HQ and/or (b) lowering the z-potential of charged NS at the electrode as a consequence of local changes in pH. However, most relevant to the present work is that they demonstrated that smaller Au NSs required lower potentials to be deposited due to an improved electrocatalysis of the mediate molecule during the EPD process.…”

Potential of a sensitive uric acid biosensor fabricated using hydroxyapatite nanowire/reduced graphene oxide/gold nanoparticle

“…The change indicated the formation of Au clusters. The mixture solution was boiled for another 15 min and then cooled to room temperature under continuous stirring to obtain the AuNPs solution (Masitas, Allen, & Zamborini, 2016). The final AuNPs was characterized by TEM and UV.…”

Electrochemical determination of surface area-to-volume ratio for metal nanoparticle analysis.

“…Masitas and Allen recently reported the size-dependent electrophoretic deposition (EPD) of citrate-stabilized Au NPs. 187 EPD is a commonly used method for NS assembly on electrode surfaces for different applications. 188-189 During the course of those studies, they noticed higher Ep,ox values for NSs assembled by EPD versus chemical methods of assembly (aminefunctionalized silane linker) for the same size Au NSs.…”

“…These electrons interact with atoms in the sample which produces secondary and backscattered electrons that contain information about the surface topography of a sample. SEM provides useful information on morphology, [39][40] size [41][42] and aggregation 43 of NPs.…”