MoSe_xO_y‐Coated 1D TiO₂ Nanotube Layers: Efficient Interface for Light‐Driven Applications

Abstract

in the materials science community. [2] Apart from the generation of H 2 and O 2 gases, photocatalysis can be extended to other applications. The early works on the irradiation of TiO 2 for purification of water via photocatalytic decomposition of pollutants were demonstrated by Frank and Bard in late 1970s. [3][4][5] These initial works and many reports later have shown that photooxidation of inorganic and organic contaminants is a promising route for environmental remediation. [6][7][8][9][10][11][12] In fact, the key factors that determine the efficiencies of a photocatalyst include its light harvesting capability and reduced charge carriers recombination of the photo generated electron-hole pairs. [3,13] However, TiO 2 possesses rather wide bandgap energies between 3.0 and 3.2 eV, with high photo activity only in the UV region (λ ≤ 390 nm) equivalent to only ≈5% of the solar spectrum. [14,15] Nevertheless, owing to its nontoxicity, low-cost synthesis, chemical inertness, and resistance against photocorrosion, TiO 2 has been long studied and recognized as the most promising photocatalyst material. [13,16] In order to harness more from the abundant renewable energy source, that is, solar energy, tremendous efforts have been devoted to reduce the bandgap energy of TiO 2 and broaden its optical absorption to the visible region. [8,[13][14][15]17,18] Bandgap engineering has been extensively carried out Ultrathin molybdenum oxyselenide (MoSe x O y ) coatings are made first ever by atomic layer deposition (ALD) within anodic 1D TiO 2 nanotube layers for photoelectrochemical and photocatalytic applications. The coating thickness is controlled through varying ALD cycles from 5 to 50 cycles (corresponding to ≈1-10 nm). In the ultraviolet region, the coatings have enhanced up to four times the incident photon-to-current conversion efficiency (IPCE), and the highest IPCE is recorded at 32% at (at λ = 365 nm). The coatings notably extend the photoresponse to the visible spectral region and remarkable improvement of photocurrent densities up to ≈40 times is registered at λ = 470 nm. As a result, the MoSe x O y -coated-TiO 2 nanotube layers have shown to be an effective photocatalyst for methylene blue degradation, and the optimal performance is credited to a coating thickness between 2 and 5 nm (feasible only by ALD). The enhancement in photoactivities of the presented heterojunction is mainly associated with the passivation effect of MoSe x O y on the TiO 2 nanotube walls and the suitability of bandgap position between MoSe x O y and TiO 2 interface for an efficient charge transfer. In addition, MoSe x O y possesses a narrow bandgap, which favors the photoactivity in the visible spectral region.

Cyclic Silylselenides: Convenient Selenium Precursors for Atomic Layer Deposition

“…TMDs thin layers often show photocatalytic activity; MoSe 2 is a very promising candidate in this respect. It turned out to be very efficient photodegradation catalyst that may also replace Pt‐based catalysts used in electrochemically‐assisted hydrogen evolution techniques . The surface area may be further increased by ALD on nanotubes or nanoparticles, which generally lead to pronounced photocatalytic properties.…”

Atomic Layer Deposition of 2D Metal Dichalcogenides for Electronics, Catalysis, Energy Storage, and Beyond

“…Mo(CO) 6 + Se(SiMe 3 ) 2 167 1-10 nm films (amorp.) PEC, PC 2018 [230,231] MoCl 5 + Se(SiMe 3 ) 2 300 >10 nm rough films (50-100 nm) ? nm rough films (cryst.)…”

“…The deposited MoS 2 extended the activity of the catalyst from UV to visible range, up to a wavelength of ≈600 nm compared to 400 nm www.advmatinterfaces.de for TiO 2 (Figure 15d). In a similar manner, Ng et al [231] used the Mo(CO) 6 + Se(SiMe 3 ) 2 process to deposit films on TiO 2 nanotubes at 167 °C. The resulting films were characterized as amorphous MoSe x O y (on surface x ≈ 0.7, y ≈ 1.7), which implies insufficient reactivity of the ALD precursors and possibly instability of the films in air.…”

“…For gas-phase photocatalytic conversion of hexane to CO 2 , one cycle of MoS 2 performed the best, with a fivefold increase in conversion under 351 nm illumination compared to the bare TiO 2 nanotubes (Figure 15f). The amorphous MoSe x O y films deposited by Ng et al [231] were also used for photocatalytic degradation of methylene blue under 470 nm illumination, resulting in an increase of the rate constant by a factor of 75 compared to the bare TiO 2 nanotubes. The films in these two works were also used for PEC water splitting (Section 4.2.3)…”

Cu2O−Cu2Se Mixed‐Phase Nanoflake Arrays: pH‐Universal Hydrogen Evolution Reactions with Ultralow Overpotential

“…The Cu(I)−O species in the COCS NFs matrix is designated at 932.6 eV, and the apex at 931.8 eV implies the existence of hybrid phase. The binding energy of new peak in between Cu−Se and Cu−O bonds indicates formation of hybrid phase with Cu δ+ oxidation (1<δ<2) because O is significantly more electronegative than Se . Again, we investigated the Cu 2p 3/2 XPS spectrum of Cu 2 Se/NF (Figure S1c, d).…”