Controlling Au Photodeposition on Large ZnO Nanoparticles

Abstract

This study investigated how to control the rate of photoreduction of metastable AuCl2(-) at the solid-solution interface of large ZnO nanoparticles (NPs) (50-100 nm size). Band-gap photoexcitation of electronic charge in ZnO by 370 nm UV light yielded Au NP deposition and the formation of ZnO-Au NP hybrids. Au NP growth was observed to be nonepitaxial, and the patterns of Au photodeposition onto ZnO NPs observed by high-resolution transmission electron microscopy were consistent with reduction of AuCl2(-) at ZnO facet edges and corner sites. Au NP photodeposition was effective in the presence of labile oleylamine ligands attached to the ZnO surface; however, when a strong-binding dodecanethiol ligand coated the surface, photodeposition was quenched. Rates of interfacial electron transfer at the ZnO-solution interface were adjusted by changing the solvent, and these rates were observed to strongly depend on the solvent's permittivity (ε) and viscosity. From measurements of electron transfer from ZnO to the organic dye toluidine blue at the ZnO-solution interface, it was confirmed that low ε solvent mixtures (ε ≈ 9.5) possessed markedly higher rates of photocatalytic interfacial electron transfer (∼3.2 × 10(4) electrons·particle(-1)·s(-1)) compared to solvent mixtures with high ε (ε = 29.9, ∼1.9 × 10(4) electrons·particle(-1)·s(-1)). Dissolved oxygen content in the solvent and the exposure time of ZnO to band-gap, near-UV photoexcitation were also identified as factors that strongly affected Au photodeposition behavior. Production of Au clusters was favored under conditions that caused electron accumulation in the ZnO-Au NP hybrid. Under conditions where electron discharge was rapid (such as in low ε solvents), AuCl2(-) precursor ions photoreduced at ZnO surfaces in less than 5 s, leading to deposition of several small, isolated ∼6 nm Au NP on the ZnO host instead.

Size- and density-controlled photodeposition of metallic platinum nanoparticles on titanium dioxide for photocatalytic applications

“…The expected reaction between a metal in solution and TiO 2 is reductive photodeposition: 26 M n+1 (aq) + ne À / M(s), where oxygen vacancies in the semiconductor substrate act as traps for the photogenerated electrons 55 allowing the adsorption of positive metal ions to the TiO 2 surface and their subsequent reduction 49 to a solid phase. This basic reaction can therefore be supported by either encouraging the creation of oxygen vacancies, or favoring the attraction between the substrate and the metallic ions.…”

“…The photodeposition time, instead, affects the size of the deposited particles 45 as the metallic particles become favorable sites for further deposition. 46,47 The presence of oxygen vacancies increments with the concentration of sacricial donors in the solution: the donors scavenge the photogenerated holes from the semiconductor, 48 resulting to a longer lifetime for the electrons, 49 which are now more likely to participate in the reductive photocatalysis. A high concentration of the sacricial donor also yields lower valence states for platinum, favoring the deposition of metal rather metal oxide.…”

“…1b, and this sampling scheme is called an orthogonal array. The choice of the processing parameters is discussed in the introduction and it was based on literature 26,33,[42][43][44][45][46][47][48][49][50][51][52][53][54] and on experimental tests that explored subsets of parameters in order to ascertain the lack of relative inuence and the conditions that would lead to a successful photodeposition. The concentration values chosen for the methanol reagent are based on the study by Pan et al 52 in order to aim for a methanol content three orders of magnitude larger than the chloroplatinic acid, thus obtaining a solution rich in donor electrons.…”

Metal/semiconductor interfaces in nanoscale objects: synthesis, emerging properties and applications of hybrid nanostructures

“…clusters result (when the reaction conditions favor charge accumulation). 63 The main drawback of the photodeposition approach discussed thus far is its non-selective nature. This work also demonstrates another limitation, which is the nonepitaxial nature of the formed heterostructure.…”

Localized photodeposition of catalysts using nanophotonic resonances in silicon photocathodes

“…However, current catalysts are simply randomly placed on semiconductor photo-electrodes with an optimized average density [20,24–25]. Photodeposition of the catalytic material with photogenerated charges from excited semiconductors has been also achieved but without a good control over the deposition sites [26–31]. An exception is the work of Li et al [27], where charge separation was achieved at different crystal facets of BiVO 4 nanocrystals for selective photodeposition of metal and metal oxide catalytic nanoparticles.…”