Self‐Organized Arrays of Single‐Metal Catalyst Particles in TiO₂ Cavities: A Highly Efficient Photocatalytic System

Abstract

Peas in a pod: A highly aligned Au(np)@TiO2 photocatalyst was formed by self-organizing anodization of a Ti substrate followed by dewetting of a gold thin film. This leads to exactly one Au nanoparticle (np) per TiO2 nanocavity. Such arrays are highly efficient photocatalysts for hydrogen generation from ethanol.

Efficient Photocatalytic H2 Evolution: Controlled Dewetting–Dealloying to Fabricate Site‐Selective High‐Activity Nanoporous Au Particles on Highly Ordered TiO2 Nanotube Arrays

“…[9][10][11][12][13][14] Co-catalyst activity is not only determined by the material properties but also to a large extent by the size and distribution of the noble metal particles. [15] Photocatalytic M@TiO 2 systems have therefore been extensively studied in view of optimizing the efficiency of H 2 production from water (with or without the usage of sacrificial agents such as methanol or ethanol, among others).…”

“…[4,16] Nevertheless, another feature of the nanotube geometry is that it allows for an exceptionally defined self-ordered arrangement of catalyst particles on the surface. Conventionally, when M@TiO 2 systems are fabricated on compact or nanoparticulate TiO 2 films, the deposition of metal particles is fairly inhomogeneous, [15] and common techniques provide a relatively low degree of control for optimizing the geometry, size and distribution of the metal particles. In contrast, ordered TiO 2 nanotube layers represent an ideally corrugated platform which allows for conducting a welldefined dewetting process of a thin conformal metal layer (i.e., to split it up into highly uniform individual metal particles), and thus achieving a simple but effective control over size and distribution of the co-catalyst NPs.…”

“…[18] The morphology of the dewetted particles is strongly influenced by different parameters, which are precisely the metal film thickness, the film homogeneity, the dewetting atmosphere, the substrate morphology and its chemical nature. [12,15,[17][18][19][20][21][22][23][24][25] In general, the locations at which a thin metal film brake up (i.e., "hole formation") are random, but this process can be site-controlled by adopting regularly patterned substrate topographies.…”

“…As visible from the SEM images in Figure 1 and Au4d3 binding energies (Figure 3(c)). [15] In order to form precursors for alloyed layers (that later were dealloyed), we coated the Audecorated tubes by a second thin layer of Ag. Figure 1(d) shows an example after sputtering Ag (20 nm -labeled as Ag20) on the previously deposited Au film (step (3) in Scheme 1).…”

“…[15] If this done on a flat TiO 2 substrate, it leads to the formation of large metal particles of a broad size distribution, randomly spread on the TiO 2 surface ( Figure S2). On the contrary, by using the ordered TiO 2 nanotube stump array of Figure 1 Figure 2 shows that dewetting can be achieved, leading to a decoration of one particle at the tube bottom ("ground position") and/or to a selective decoration of the tube rims in the "crown position" (step 4 in Scheme 1).…”