Controlling nanoparticle placement in Au/TiO₂ inverse opal photocatalysts

Abstract

Gold-loaded titania (Au/TiO2) inverse opals are highly ordered three-dimensional photonic structures with enhanced photocatalytic properties. However, fine control over the placement of the Au nanoparticles in the inverse opal structures...

Colloidal Templating in Catalyst Design for Thermocatalysis

“…67 Other approaches involve coassembling templating colloids with nanocrystals to form 3DOM/IO structures templated entirely using nanocrystals. 68,69,71,72 The scalable wet chemical synthesis of high quality crack-free 3DOM/IO structures laid the foundation for incorporating catalytic NPs (e.g., Pt, Pd, Co, Fe, Ni, Cu, Au, Ag, bimetallic NPs, etc.) into these structures to exploit their high surface area and interconnected porosity for efficient mass transport in catalytic applications.…”

“…For instance, NP sintering, agglomeration, and/or dislodgement are common deactivation routes for such catalysts under typical thermocatalytic conditions of high temperatures, pressures, and mechanical agitation during catalytic evaluation. 3,72,76,83 Alternatively, templating colloids can be coassembled with support precursor(s) and NPs (or their metal precursors) during colloidal templating (Figure 3b). 84−86 The inclusion of NPs during templating is uncommon for catalytic applications as the resulting NPs are predominantly fully embedded within the formed support matrix (Figure 3b inset).…”

“…84,85,87 This structural attribute consequently confers a much higher degree of thermomechanical stability (compared to the first approach in Figure 3a), but severely limits NP accessibility to reactants. 72 Thus, this synthetic strategy is more frequently adopted in photonics 84,87 and energy storage 85 applications where NP exposure is not absolutely necessary and desirable NP−support interfacial interactions are maximized through near-complete NP embedding within the support.…”

“…22 While inducing NP nucleation on templating colloids is also synthetically feasible, 88 using preformed colloidal NPs presents an additional advantage of decoupling NP formation from the templating colloid's surface chemistry, 23 permitting fully independent preparation of precise and well-controlled designer NPs with specific desirable catalytic attributes (e.g., size, shape, composition, faceting, etc.). 44,45 Following evaporative self-assembly of the raspberry colloids into a colloidal crystal, infiltration with silica sol−gel 23,89 (noting that other support precursors in the sol− gel 90,91 or nanocrystal solution 68,69,72 forms, including mixed support precursors, 92 are similarly possible), and removal of templating colloids, the final RCT catalyst structure reveals NPs partially embedded at the exposed pore−support interface (Figure 3c inset, 3c1). 22 Here, we remark that the polymeric templating colloids used in most colloid-templated structures are removed either by calcination, 22,23,47 or by dissolution and depolymerization using an appropriate solvent mixture.…”

“…24,25,69,93 High temperature calcination typically leaves minimal carbonaceous residue due to the formation of gaseous combustion products but may result in appreciable NP sintering if the NPs are not stabilized within the support, such as when NPs are incorporated after colloidal templating. 72 Alternatively, solvent dissolution can be performed under milder and possibly, ambient conditions, to avoid NP sintering, 24,25,69 but may leave more carbonaceous residue from any incomplete dissolution of polymeric templates. Another difference between both methods is that calcination enables the complete polycondensation of the sol−gel precursor(s) to form more thermomechanically stable support structures and thus, a mild thermal treatment step is typically incorporated at the end if the solvent dissolution approach is used.…”