Recent advances and mechanism of plasmonic metal-semiconductor photocatalysis.

Benefiting from the unique surface plasmon properties, plasmonic metal nanoparticles can convert light energy into chemical energy, which is considered as a potential technique for enhancing plasmon-induced semiconductor photocatalytic reactions. Due to the shortcomings of large bandgap and high carrier recombination rate of semiconductors, their applications are limited in the field of sustainable and clean energy sources. Different forms of plasmonic nanoparticles have been reported to improve the photocatalytic reactions of adjacent semiconductors, such as water splitting, carbon dioxide reduction, and organic pollutant degradation. Although there are various reports on plasmonic metal-semiconductor photocatalysis, the related mechanism and frontier progress still need to be further explored. This review provides a brief explanation of the four main mechanisms of plasmonic metal-semiconductor photocatalysis, namely, (i) enhanced local electromagnetic field, (ii) light scattering, (iii) plasmon-induced hot carrier injection and (iv) plasmon-induced resonance energy transfer; some related typical frontier applications are also discussed. The study on the mechanism of plasmonic semiconductor complexes will be favourable to develop a new high-performance semiconductor photocatalysis technology.

Correction: Direct Z scheme-fashioned photoanode systems consisting of Fe2O3 nanorod arrays and underlying thin Sb2Se3 layers toward enhanced photoelectrochemical water splitting performance.

Correction for 'Direct Z scheme-fashioned photoanode systems consisting of Fe2O3 nanorod arrays and underlying thin Sb2Se3 layers toward enhanced photoelectrochemical water splitting performance' by Yong Zhou et al., Nanoscale, 2019, DOI: 10.1039/c8nr08292h.

Direct Z scheme-fashioned photoanode systems consisting of Fe2O3 nanorod arrays and underlying thin Sb2Se3 layers toward enhanced photoelectrochemical water splitting performance.

An elegant Z-scheme-fashioned photoanode consisting of Fe2O3 nanorod arrays and underlying thin Sb2Se3 layers was rationally constructed. The photocurrent density of the Sb2Se3-Fe2O3 Z-scheme photoanode reached 3.07 mA cm-2 at 1.23 V vs. RHE, three times higher than that of pristine Fe2O3 at 1.03 mA cm-2. An obvious cathodic shift of the photocurrent onset potential of about 200 mV was also observed. The transient photovoltage response demonstrates that the suitable band edges (ECB ∼ -0.4 eV and EVB ∼ 0.8 eV) of Sb2Se3, match well with Fe2O3 (ECB ∼ 0.29 eV and EVB ∼ 2.65 eV), permitting the photoexcited electrons on the conduction band of the Fe2O3 to transfer to the valence band of Sb2Se3, and recombine with the holes therein, thus allowing a high concentration of holes to collect in the Fe2O3 for water oxidation. The transient absorption spectra further corroborate that the built-in electric field in the p-n heterojunction leads to a more effective separation and a longer lifetime of the charge carriers.

Boosted Water Oxidation Activity and Kinetics on BiVO4 Photoanodes with Multihigh-Index Crystal Facets.

The crystal facet of the BiVO4 photoanode has potential influence on its charge-transfer and separation properties as well as water oxidation kinetics. In the present work, a BiVO4 polyhedral film with exposed {121}, {132}, {211}, and {251} high-index facets was synthesized by a facile Bi2O3 template-induced method and investigated as a photoanode for water oxidation. In comparison with the normal BiVO4 film with a {121} monohigh-index facet, the BiVO4 film with multihigh-index crystal facets shows higher activity and faster kinetics for photoelectrochemical water oxidation. Specifically, a higher photocurrent density of 1.21 mA/cm2 was achieved on the multihigh-index facet BiVO4 photoanode at 1.23 V versus reversible hydrogen electrode (RHE) in 0.1 M Na2SO4, which is about 200% improved over the normal BiVO4 photoanode (0.61 mA/cm2 at 1.23 V vs RHE). In addition, a negative shift of 300 mV onset potential for water oxidation was observed on the as-prepared BiVO4 photoanode (0.22 V vs RHE) relative to the normal BiVO4 photoanode (0.52 V vs RHE) in 0.1 M Na2SO4. Although the UV-vis absorbance property and water oxidation pathway not be changed, the charge-transfer and separation properties as well as the overall water oxidation kinetics on the multihigh-index facet BiVO4 film were boosted obviously. Theory calculations reveal that the adsorption of H2O molecules on BiVO4{121} and {132} high-index facets is energetically favorable for subsequent dissociation and oxidation relative to that on {010} and {110} low-index facets. Furthermore, the water oxidation limiting step on {121} and {132} high-index facets of BiVO4 is changed to the step of two protons reacting with •O to form •OOH species (•O + H2O(l) + 2H+ + 2e- → •OOH + 3H+ + 3e-), which is different from the limiting step on {010} and {110} low-index facets that corresponds to the dissociation of H2O to •OH (2H2O(l) + • → •OH + H2O(l) + H+ + e-). In addition, the overpotential of water oxidation limiting step on BiVO4{121} and {132} high-index facets is lower than that on {010} and {110} low-index facets.

Integration of FexS electrocatalysts and simultaneously generated interfacial oxygen vacancies to synergistically boost photoelectrochemical water splitting of Fe2O3 photoanodes.

Integration of FexS electrocatalysts and simultaneously generated interfacial oxygen vacancies (VO) was designed to promote the water splitting performance of Fe2O3 photoanodes, in which a synergistic effect remarkably reduces the carrier recombination, increases the number of active sites, and facilitates the photogenerated holes to participate in water oxidation.

Quasi-Topotactic Transformation of FeOOH Nanorods to Robust Fe2O3 Porous Nanopillars Triggered with a Facile Rapid Dehydration Strategy for Efficient Photoelectrochemical Water Splitting.

A facile rapid dehydration (RD) strategy is explored for quasi-topotactic transformation of FeOOH nanorods to robust Fe2O3 porous nanopillars, avoiding collapse, shrink, and coalescence, and compared with a conventional treatment route. Additionally, the so-called RD process is capable of generating a beneficial porous structure for photoelectrochemical water oxidation. The obtained RD-Fe2O3 photoanode exhibits a photocurrent density as high as 2.0 mA cm-2 at 1.23 V versus reversible hydrogen electrode (RHE) and a saturated photocurrent density of 3.5 mA cm-2 at 1.71 V versus RHE without any cocatalysts, which is about 270% improved photocurrent density over Fe2O3 with the conventional temperature-rising route (0.75 mA cm-2 at 1.23 V vs RHE and 1.48 mA cm-2 at 1.71 V vs RHE, respectively). The enhanced photocurrent on RD-Fe2O3 is attributed to a synergistic effect of the following factors: (i) preservation of single crystalline nanopillars decreases the charge-carrier recombination; (ii) formation of long nanopillars enhances light harvesting; and (iii) the porous structure shortens the hole transport distance from the bulk material to the electrode-electrolyte interface.

Low-temperature liquid phase reduced TiO2 nanotube arrays: synergy of morphology manipulation and oxygen vacancy doping for enhancement of field emission.

The partially reduced TiO(2) nanotube arrays (TNAs) are prepared via an uncomplicated and low-cost liquid phase reduction strategy using NaBH(4) as the reducing agent. By controlling and adjusting the reduction temperatures from 30 to 90 °C, the reduction treatment can not only change their surface morphology but also introduce oxygen vacancies into them, resulting in an optimized morphology, elevated Fermi-level, reduced effective work function and improved conductivity of the TNAs. Meanwhile, the thermal and long-term stability of oxygen vacancy are also investigated, indicating that the oxygen vacancies retain long-term stability from room temperature up to 150 °C. More interesting, partially reduced TNAs show drastically enhanced field emission (FE) performances including substantially decreased turn-on field from 18.86 to 1.53 V µm(-1), a high current density of 4.00 mA cm(-2) at 4.52 V µm(-1), and an excellent FE stability and repeatability. These very promising results are attributed to the combination of the optimized morphology and introduced oxygen vacancies, which can increase FE sites, reduce effective work function and increase conductivity.

Enhancement of the field emission from the TiO2 nanotube arrays by reducing in a NaBH4 solution.

A mass of oxygen vacancies are successfully introduced into TiO2 nanotube arrays using low-cost NaBH4 as a reductant in a liquid-phase environment. By controlling and adjusting the reduction time over the range of 0-24 h, the doping concentration of the oxygen vacancy is controllable and eventually reaches saturation. Meanwhile, the thermal stability of oxygen vacancies is also investigated, indicating that part of the oxygen vacancies remain stable up to 250 °C. In addition, this liquid-phase reduction strategy significantly lowers the requirements of instruments and cost. More interesting, reduced TiO2 nanotube arrays show drastically enhanced field emission performances including substantially decreased turn-on field from 25.01 to 2.65 V/µm, a high current density of 3.5 mA/cm(2) at 7.2 V/µm, and an excellent field emission stability and repeatability. These results are attributed to the oxygen vacancies obtained by reducing in NaBH4 solution, resulting in a reduced effective work function and an increased conductivity.