Light-Mediated Growth of Noble Metal Nanostructures (Au, Ag, Cu, Pt, Pd, Ru, Ir, Rh) From Micro- and Nanoscale ZnO Tetrapodal Backbones

Abstract

Micro- and nanoscale ZnO tetrapods provide an attractive support for metallic nanostructures since they can be inexpensively produced using the flame transport method and nanoparticle synthesis schemes can take advantage of a coupled response facilitated by the formation of a semiconductor-metal interface. Here, we present a light-mediated solution-based growth mode capable of decorating the surface of ZnO tetrapods with nanostructures of gold, silver, copper, platinum, palladium, ruthenium, iridium, and rhodium. It involves two coupled reactions that are driven by the optical excitation of electron-hole pairs in the ZnO semiconductor by ultraviolet photons where the excited electrons are used to reduce aqueous metal ions onto the ZnO tetrapod as excited holes are scavenged from the surface. For the most part, the growth mode gives rise to nanoparticles with a roundish morphology that are uniformly distributed on the tetrapod surface. Larger structures with irregular shapes are, however, obtained for syntheses utilizing aqueous metal nitrates as opposed to chlorides, a result that suggests that the anion plays a role in shape determination. It is also demonstrated that changes to the molarity of the metal ion can influence the nanostructure nucleation rate. The catalytic activity of tetrapods decorated with each of the eight metals is assessed using the reduction of 4-nitrophenol by borohydride as a model reaction where it is shown that those decorated with Pd, Ag, and Rh are the most active.

Assessment of synthesis approaches for tuning the photocatalytic property of ZnO nanoparticles

“…Alteration of photocatalytic properties may be achieved using different synthesis methods [1,18,19], which convey various morphologies of ZnO NPs, such as rods, spheres, tubes and others, with particle size as small as 2-10 nm [20][21][22][23]. However, care must be taken about the cost, complexity, feasibility and toxicity of the method opted for synthesis [24]. Ni et al [22] have demonstrated a cost-effective and simple hydrothermal process for the synthesis of ZnO nanorods.…”

Two Hybrid Au-ZnO Heterostructures with Different Hierarchical Structures: Towards Highly Efficient Photocatalysts

“…To overcome the aforementioned drawbacks, a workable solution to improve the optical absorption capacity and reduce charge recombination of ZnO is desired. It is well known that noble metals have desirable properties, such as surface plasmon resonance, straightforward reduction, chemical stability and bio-affinity 16–20 . Among them, Au nanoparticles show excellent SPR properties and charge storage capability 21 .…”

Engineering Charge Transfer Characteristics in Hierarchical Cu2S QDs @ ZnO Nanoneedles with p–n Heterojunctions: Towards Highly Efficient and Recyclable Photocatalysts

“…Until now, possible solutions have been tested. Metals doping (such as gold, silver, rhodium, or platinum) [22,23], metal ions doping (such as Bi or Al) [24], and nitrogen doping [25] are the most used techniques to give rise to visible light activity of the semiconductor materials, to extend their light absorption ability from UV to visible range and to feature good electron transport. Beyond that, heterojunctions, which can effectively capture the photo-generated charge carriers to improve the charge separation efficiency, decrease the surface reaction over potential, enhance apparent quantum efficiencies and provide active sites for surface redox reaction at two different reaction sites, are believed to be essential to achieving highly efficient photocatalytic performances [26,27,28,29,30,31,32,33,34,35,36,37].…”