Correlating the excited state relaxation dynamics as measured by photoluminescence and transient absorption with the photocatalytic activity of Au@TiO₂core–shell nanostructures

Abstract

The spectroscopic and photocatalytic properties of a series of Au@TiO(2) core-shell nanostructures are characterized. The crystallinity of the TiO(2) shells was varied by changing the etching and calcination conditions. Measurements of the photoluminescence, transient absorption, and H(2) production rate permit us to look for correlations between the spectroscopic and catalytic behaviors. We found that there is a strong effect of crystallinity on the H(2) production rate and also the stretched exponential lifetime of the photoluminescence created by short-wavelength (266 and 300 nm) photoexcitation. As the TiO(2) crystallinity is increased, the photoluminescence lifetime increases from 22 to 140 ps in a 1 ns detection window, while the H(2) production rate increases by a factor of ~4. There is no discernible effect of crystallinity on the photoluminescence dynamics excited at 350 or 430 nm, or on the electronic dynamics measured by femtosecond transient absorption after excitation at 300 nm. We hypothesize that high-energy photons create reactive and emissive charge-separated states in parallel, and that both species are subject to similar electron-hole recombination processes that depend on sample crystallinity. Based on our observations, it can be concluded that the photoluminescence dynamics may be used to evaluate the potential performance of this class of photocatalysts.

Promotion of atomic hydrogen recombination as an alternative to electron trapping for the role of metals in the photocatalytic production of H 2

“…A recent study from our laboratory using well-defined Au@Void@TiO 2 yolk-shell nanostructures identified clear correlations among the lifetime of the fluorescence decay, the rate at which hydrogen is produced in photocatalysis, and the crystallinity of the titania shells: the more crystalline catalysts display both longer fluorescence lifetimes and higher hydrogen production rates (Fig. S1) (19). Surprisingly, however, similar fluorescence decay kinetics were seen here with Au@Void@TiO 2 versus Void@TiO 2 samples [ Fig.…”

Au nanoparticle-embedded SiO2–Au@SiO2 catalysts with improved catalytic activity, enhanced stability to metal sintering and excellent recyclability

“…18,30,31,34,39 Since smaller metal particles can provide larger specic active sites, we synthesized Au NPs with 3-5 nm diameter by NaBH 4 reduction method using Au precursor (HAuCl 4 ) with weak capping agent (TSC). 18,30,31,34,39 Since smaller metal particles can provide larger specic active sites, we synthesized Au NPs with 3-5 nm diameter by NaBH 4 reduction method using Au precursor (HAuCl 4 ) with weak capping agent (TSC).…”

“…Although TSC-stabilized Au NPs (Au NPs-TSC) can be dispersed in DI water, Au NPs-TSC can be easily aggregated by changing the solution environment. 18,34,43,45 The reddish color of the PVP-treated Au NPs (Au NPs-PVP) solution was maintained and the UV-Vis absorption peak shi of the Au NP solution was negligible even aer adding NaBH 4 solution, indicating the well maintained stability (Fig. S1(a), † the original reddish color of the as-synthesized Au NPs-TSC solution was changed to dark violet by adding NaBH 4 solution (which is similar to the conditions of catalytic 4-NP reduction), indicating the instability of the Au NPs and their irreversible aggregation.…”

“…11,12 As the diameter of the Au particle continuously deceases to less than a specic size, it eventually loses its bright, shiny gold color and gains different colors, indicating a change in its chemical and optical properties. [17][18][19][20][21][22] Over the past decade, intensive efforts have focused on synthesizing nanoscale materials and remarkable progress has been achieved on the fabrication of novel nanomaterials. [11][12][13] However, since Haruta et al rst demonstrated the exceptional reactivity of small Au nanoparticles (NPs) dispersed on suitable substrates, [14][15][16] numerous reports have been published on Au catalysis for the promotion of a variety of chemical reactions.…”

Prolonged Electron Lifetime in Ordered TiO2 Mesophyll Cell‐Like Microspheres for Efficient Photocatalytic Water Reduction and Oxidation

“…[24a] All the three TiO 2 films' PIA show ultrafast rise indicating the highly efficient trapping of photoexcited electrons. The decay of the PIA signal is attributed to electron‐hole recombination . As the recombination is rate‐limited by a distribution of trap states, we fit the dynamics within 1 ns delay using a stretched exponential decay function (with an offset B to account for the long‐lived recombination extending beyond the measurement window.…”