Effects of Photodeposited Gold vs Platinum Nanoparticles on N,F-Doped TiO₂ Photoactivity: A Time-Resolved Photoluminescence Investigation

Abstract

The time-resolved photoluminescence (PL) in the nanosecond time scale of TiO2 materials undoped or codoped with nitrogen and fluorine (N,F-doping) and modified by noble metals (NM, i.e. Au or Pt) nanoparticles (NPs) photodeposition has been systematically investigated in relation to their photocatalytic activity in hydrogen production. The main aim of the study is to elucidate the origin of the NM-dependent synergistic effects in photoactivity produced by N,F-doping of TiO2 and NM NPs deposition on the oxide surface. While TiO2 doping with fluorine and nitrogen introduces new stabilized luminescent defective trap states below the conduction band revealed by long-living PL components, the presence of NM NPs on the TiO2 surface produces a PL intensity suppression, which is more relevant for Au- rather than for Pt-NPs containing materials. Time-resolved PL analysis indicates that the electron transfer occurring at the TiO2/metal interface is affected by both the defective structure of anatase N,F-doped TiO2 and the type of NM (Au or Pt). In particular, Au rather than Pt NPs appear to strongly interact with the charge carriers trapped at surface defect sites, gold NPs being expected to preferentially grow on such sites during photodeposition. Furthermore, plasmonic gold NPs excitation upon PL light absorption is evidenced by the PL spectral shape variation observed only in the case of Au/TiO2. Thus, the larger synergistic effect on photocatalytic hydrogen production observed upon Au NPs photodeposition on N,F-doped TiO2 results from the opening of a new efficient electron transfer path from luminescent defective trap states on doped TiO2 to Au NPs, where proton reduction occurs.

Mechanistic Considerations on the H2 Production by Methanol Thermal‐assisted Photocatalytic Reforming over Cu/TiO2 Catalyst

“…Thus, higher efficiencies are achieved by avoiding the electron-hole recombination processes. [4,5,6] Alternatively to noble metals, transition metals such as Cu, Fe, Co or Ni have been proposed as a promising cheaper option in comparison to noble metals . [1,3,7,8] Particularly, copper based catalysts have attracted much attention not only for H 2 reduction but also for CO 2 reduction process.…”

Sensitizing effects of BiVO4 and visible light induced production of highly reductive electrons in the TiO2/BiVO4 heterojunction

“…However, its relatively high energy band gap of 3.2 eV (anatase phase) makes it active only under UV light, which is only 3% of the solar spectrum incoming on the earth [18]. In this context, many strategies have been employed to make TiO 2 visible light-active [19][20][21], in particular through the insertion of dopant species [17,22,23], which may extend light absorption through the introduction of defective sites, and dye sensitization [24]. However, an excess of dopant impurities, acting as charge recombination centres, can have detrimental effects on TiO 2 photoefficiency [22], while organic dye sensitizers are known to undergo photodegradation over time [21].…”

Plasmon-enhanced photocatalytic overall water-splitting over Au nanoparticle-decorated CaNb2O6 electrospun nanofibers

“…The reduced PL intensity reveals either a faster transfer process with a shorter lifetime or a slower recombination process with a longer lifetime of the photoinduced electrons. 57 To further understand the reason for the PL quenching of the above noble-metal NP-decorated CaNb 2 O 6 NFs, TRPL spectroscopy measurement was carried out, and the corresponding results are given in Fig. 7D.…”