Au/TiO2 Photo(electro)catalysis: The Role of the Au Cocatalyst in Photoelectrochemical Water Splitting and Photocatalytic H2 Evolution
28 Oct 2015-Journal of Physical Chemistry C (American Chemical Society)-Vol. 119, Iss: 44, pp 24750-24759
TL;DR: In this paper, the role of Au nanoparticles as cocatalysts in photoelectrochemical thin-layer flow cells was explored by varying the Au loading and the light intensity, respectively.
Abstract: Photoelectrochemical water oxidation and photocatalytic H2 evolution on planar nanocrystalline Au/TiO2 catalyst film electrodes were studied by combined electrochemistry and online mass spectrometry, allowing for the detection and quantification of the volatile reaction products O2 and H2, and thus, by comparison with the photocurrent, to determine selectivities and to map out contributions from side reactions. The catalysts were prepared by a photodeposition method and deposited on conductive glass substrates, and measurements were performed under defined mass transport conditions in a photoelectrochemical thin-layer flow cell. The role of Au nanoparticles as cocatalysts in these reactions was explored by varying the Au loading and the light intensity, respectively. On the basis of these data, it is demonstrated that the Au nanoparticles affect the above reactions in different ways, by (i) catalyzing the recombination of photogenerated holes and electrons as well as parasitic side reactions (O2 reduction...
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TL;DR: In this article, the authors focus on the significant application based advances in neat and tailored nanostructures of noble metal-metal oxide nanohybrids and touched upon chalcogenides also.
Abstract: The skilful synthesis of nanohybrids composed of noble metals (Au, Ag, Pt and Pd, as well as AuAg alloy) and metal oxides (ZnO, TiO2, Cu2O, MnO2, Fe2O3, WO3 and CeO2) has received considerable attention for applications in photocatalysis, solar cells, drug delivery, surface enhanced Raman spectroscopy and many other important areas. The overall architecture of nanocomposites is one of the most important factors dictating the physical properties of nanohybrids. Noble metals can be coupled to metal oxides and metal chalcogenides to yield diverse nanostructures, including noble metal decorated-metal oxide nanoparticles (NPs), nanoarrays, noble metal/metal oxide core/shell, noble metal/metal oxide yolk/shell and Janus noble metal–metal oxide nanostructures. In this review, we focus on the significant application based advances in neat and tailored nanostructures of noble metal–metal oxide nanohybrids and touched upon chalcogenides also. The improvement in performance in representative energy conversion, electrochemical water splitting, photocatalytic hydrogen generation, photocatalytic CO2 reduction, photocatalytic degradation of organic pollutants and dye-sensitized solar cell (DSSCs) applications is discussed. Finally, we conclude with a perspective on the future direction and prospects of these controllable nanohybrid materials.
263 citations
TL;DR: Well-ordered TiO2 nanotube arrays (TNTAs) decorated with graphitic carbon nitride (g-C3N4) were fabricated by anodic oxidization and calcination process and served as an efficient and stable photoanode for photoelectrochemical water splitting.
Abstract: Well-ordered TiO2 nanotube arrays (TNTAs) decorated with graphitic carbon nitride (g-C3N4) were fabricated by anodic oxidization and calcination process. First, TNTAs were prepared via the anodic oxidation of Ti foil in glycerol solution containing fluorinion and 20% deionized water. Subsequently, g-C3N4 film was hydrothermally grown on TNTAs via the hydrogen-bonded cyanuric acid melamine supramolecular complex. The results showed that g-C3N4 was successfully decorated on the TNTAs and the g-C3N4/TNTAs served as an efficient and stable photoanode for photoelectrochemical water splitting. The facile deposition method enables the fabrication of efficient and low-cost photoanodes for renewable energy applications.
120 citations
TL;DR: In this article, small gold nanoparticles (Au-NPs) were used to modify the surface of titanium dioxide as visible-light absorbers and thermal redox active centers.
Abstract: Small gold nanoparticles (Au-NPs) were used to modify the surface of titanium dioxide as visible-light absorbers and thermal redox active centers. Au-NPs were synthesized on commercial TiO2 (P25) by reduction with tetrakis(hydroxymethyl)phosphonium chloride. The Au/P25 composites were characterized by different techniques including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). Time-resolved microwave conductivity (TRMC) was used to study the charge-carrier dynamics. The photocatalytic activity of Au/TiO2 was evaluated for the degradations of phenol, 2-propanol, and acetic acid and for H2 production from aqueous methanol solution. The modification of TiO2-P25 with Au-NPs with preferential localization on the anatase phase led to an increase in its photocatalytic activity under UV and visible-light. TRMC signals showed the injection of electrons from Au-NPs into the conduction band of TiO...
90 citations
TL;DR: By integrating CdS/α-Fe2O3/TiO2 ternary system, light absorption ability of the photoanode can be effectively improved with an obviously broadened optical-response to visible light region, and greatly facilitates the separation of photogenerated carriers, giving rise to the enhancement of PEC water oxidation performance.
Abstract: In this work, we demonstrate a facile successive ionic layer adsorption and reaction process accompanied by hydrothermal method to synthesize CdS nanoparticle-modified α-Fe2O3/TiO2 nanorod array for efficient photoelectrochemical (PEC) water oxidation. By integrating CdS/α-Fe2O3/TiO2 ternary system, light absorption ability of the photoanode can be effectively improved with an obviously broadened optical-response to visible light region, greatly facilitates the separation of photogenerated carriers, giving rise to the enhancement of PEC water oxidation performance. Importantly, for the designed abnormal type-II heterostructure between Fe2O3/TiO2, the conduction band position of Fe2O3 is higher than that of TiO2, the photogenerated electrons from Fe2O3 will rapidly recombine with the photogenerated holes from TiO2, thus leads to an efficient separation of photogenerated electrons from Fe2O3/holes from TiO2 at the Fe2O3/TiO2 interface, greatly improving the separation efficiency of photogenerated holes within Fe2O3 and enhances the photogenerated electron injection efficiency in TiO2. Working as the photoanodes of PEC water oxidation, CdS/α-Fe2O3/TiO2 heterostucture electrode exhibits improved photocurrent density of 0.62 mA cm− 2 at 1.23 V vs. reversible hydrogen electrode (RHE) in alkaline electrolyte, with an obviously negatively shifted onset potential of 80 mV. This work provides promising methods to enhance the PEC water oxidation performance of the TiO2-based heterostructure photoanodes.
75 citations
TL;DR: After thorough characterization, it was found that the hydrogenation treatment did not damage the flower-like architecture but distorted the anatase crystal structure and significantly changed the band structure of NHTA owing to the increased concentration of oxygen vacancies, hydroxyl groups, and Ti3+ cations.
Abstract: A facile two-step strategy was used to prepare black of hydrogenated/nitrogen-doped TiO2 nanoplates (NHTA) with a flower-like hierarchical architecture. In situ nitriding and self-assembly was realized by hydrothermal synthesis using tripolycyanamide as a N source and as a structure-directing agent. After thorough characterization, it was found that the hydrogenation treatment did not damage the flower-like architecture but distorted the anatase crystal structure and significantly changed the band structure of NHTA owing to the increased concentration of oxygen vacancies, hydroxyl groups, and Ti3+ cations. Under AM 1.5 illumination, the photocatalytic H2 evolution rate on the black NHTA was approximately 1500 μmol g−1 h−1, which was much better than the N-doped TiO2 nanoplates (≈690 μmol g−1 h−1). This improvement in the hydrogen evolution rate was attributed to a reduced bandgap, enhanced separation of the photogenerated charge carriers, and an increase in the surface-active sites.
74 citations
References
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TL;DR: Water photolysis is investigated by exploiting the fact that water is transparent to visible light and cannot be decomposed directly, but only by radiation with wavelengths shorter than 190 nm.
Abstract: ALTHOUGH the possibility of water photolysis has been investigated by many workers, a useful method has only now been developed. Because water is transparent to visible light it cannot be decomposed directly, but only by radiation with wavelengths shorter than 190 nm (ref. 1).
27,819 citations
TL;DR: In this article, the photocatalytic degradation of azo dyes containing different functionalities has been reviewed using TiO2 as photocatalyst in aqueous solution under solar and UV irradiation.
Abstract: The photocatalytic degradation of azo dyes containing different functionalities has been reviewed using TiO2 as photocatalyst in aqueous solution under solar and UV irradiation. The mechanism of the photodegradation depends on the radiation used. Charge injection mechanism takes place under visible radiation whereas charge separation occurred under UV light radiation. The process is monitored by following either the decolorization rate and the formation of its end-products. Kinetic analyses indicate that the photodegradation rates of azo dyes can usually be approximated as pseudo-first-order kinetics for both degradation mechanisms, according to the Langmuir–Hinshelwood model. The degradation of dyes depend on several parameters such as pH, catalyst concentration, substrate concentration and the presence of electron acceptors such as hydrogen peroxide and ammonium persulphate besides molecular oxygen. The presence of other substances such as inorganic ions, humic acids and solvents commonly found in textile effluents is also discussed. The photocatalyzed degradation of pesticides does not occur instantaneously to form carbon dioxide, but through the formation of long-lived intermediate species. Thus, the study focuses also on the determination of the nature of the principal organic intermediates and the evolution of the mineralization as well as on the degradation pathways followed during the process. Major identified intermediates are hydroxylated derivatives, aromatic amines, naphthoquinone, phenolic compounds and several organic acids. By-products evaluation and toxicity measurements are the key-actions in order to assess the overall process.
3,692 citations
TL;DR: Heterogeneous photocatalysis is a process in which the illumination of an oxide semiconductor, usually the anatase form of titanium dioxide, produces photoexcited electrons (e{sup {minus}}) and holes (h{sup +}). These can migrate to the oxide surface and participate in halfcell reactions that are part of a closed, catalytic cycle as mentioned in this paper.
Abstract: Heterogeneous photocatalysis is a process in which the illumination of an oxide semiconductor, usually the anatase form of titanium dioxide, produces photoexcited electrons (e{sup {minus}}) and holes (h{sup +}). These can migrate to the oxide surface and participate in half-cell reactions that are part of a closed, catalytic cycle. In the aqueous phase, the illuminated surface is widely regarded as a producer of hydroxyl radicals (e.g., h{sup +} + OH{sup {minus}} {yields} {center dot}OH), and these and other highly oxidizing initial products of this indirect photochemistry go on to attack oxidizable contaminants. This article highlights recent developments in photocatalysis that are applicable to water treatment. Topics discussed include the generality of photocatalysis for complete contaminant destruction (mineralization); some specific contaminant classes of interest (chlorinated aromatics, surfactants, herbicides, and pesticides); the use of solar versus artificial illumination; the influence of additional oxidants such as H{sub 2}O{sub 2}; catalyst forms (suspended vs. immobilized); and related potential applications of photocatalysis (metal recovery and total organic carbon (TOC) analyses).
1,115 citations
TL;DR: It is demonstrated that Au particles in the size range 3-30 nm on TiO₂ are very active in hydrogen production from ethanol, and the high hydrogen yield observed makes these catalysts promising materials for solar conversion.
Abstract: Catalytic hydrogen production from renewables is a promising method for providing energy carriers in the near future. Photocatalysts capable of promoting this reaction are often composed of noble metal nanoparticles deposited on a semiconductor. The most promising semiconductor at present is TiO₂. The successful design of these catalysts relies on a thorough understanding of the role of the noble metal particle size and the TiO₂ polymorph. Here we demonstrate that Au particles in the size range 3-30 nm on TiO₂ are very active in hydrogen production from ethanol. It was found that Au particles of similar size on anatase nanoparticles delivered a rate two orders of magnitude higher than that recorded for Au on rutile nanoparticles. Surprisingly, it was also found that Au particle size does not affect the photoreaction rate over the 3-12 nm range. The high hydrogen yield observed makes these catalysts promising materials for solar conversion.
1,053 citations
TL;DR: For the novel visible light photoactivity of Au/TiO(2), it has been determined that gold loading, particle size and calcination temperature play a role in the photocatalytic activity, the most active material being the catalyst containing 0.2 wt % gold with 1.87 nm average particle size.
Abstract: Gold nanoparticles supported on P25 titania (Au/TiO2) exhibit photocatalytic activity for UV and visible light (532 nm laser or polychromatic light λ > 400 nm) water splitting. The efficiency and operating mechanism are different depending on whether excitation occurs on the titania semiconductor (gold acting as electron buffer and site for gas generation) or on the surface plasmon band of gold (photoinjection of electrons from gold onto the titania conduction band and less oxidizing electron hole potential of about −1.14 V). For the novel visible light photoactivity of Au/TiO2, it has been determined that gold loading, particle size and calcination temperature play a role in the photocatalytic activity, the most active material (ΦH2 = 7.5% and ΦO2 = 5.0% at 560 nm) being the catalyst containing 0.2 wt % gold with 1.87 nm average particle size and calcined at 200 °C.
930 citations