Enhanced photoelectrochemical performance of multi-leg TiO2 nanotubes through efficient light harvesting
TL;DR: In this paper, a model has been presented for light trapping and scattering ability on the basis of the graded refractive index behavior associated with multi-leg nanotubes, leading to a greater scattering of light into the nanotube structure.
Abstract: Multi-leg TiO2 nanotubes have been synthesised by electrochemical anodisation of Ti foils with suitable optimisation of the electrolyte (containing NH4F and HF) composition and concentration. As a result, multi-leg nanotube morphology shows a 4-fold enhancement in photocurrent density compared with that of compact tubes of comparable length under UV-VIS (320–500 nm) light illumination. We attribute this enhancement in photocurrent to efficient light scattering within the multi-leg morphology and the availability of a large contact area with the electrolyte compared to that of compact nanotubes. A model has been presented for light trapping and scattering ability on the basis of the graded refractive index behaviour associated with multi-leg nanotubes. Such graded refractive index behaviour is found to reduce specular reflectance, leading to a greater scattering of light into the nanotube structure. The diffused reflectance spectra confirm higher scattering in the multi-leg nanotube arrays, which indicates greater light harvesting by the multi-leg nanotube arrays.
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TL;DR: This review attempts to bridge the knowledge gap between individual layered oxide types by summarizing recent developments in all important 2D oxide systems including supported ultrathin oxide films, layered clays and double hydroxides, layered perovskites, and novel 2D-zeolite-based materials.
Abstract: 2D oxide nanomaterials constitute a broad range of materials, with a wide array of current and potential applications, particularly in the fields of energy storage and catalysis for sustainable energy production. Despite the many similarities in structure, composition, and synthetic methods and uses, the current literature on layered oxides is diverse and disconnected. A number of reviews can be found in the literature, but they are mostly focused on one of the particular subclasses of 2D oxides. This review attempts to bridge the knowledge gap between individual layered oxide types by summarizing recent developments in all important 2D oxide systems including supported ultrathin oxide films, layered clays and double hydroxides, layered perovskites, and novel 2D-zeolite-based materials. Particular attention is paid to the underlying similarities and differences between the various materials, and the subsequent challenges faced by each research community. The potential of layered oxides toward future applications is critically evaluated, especially in the areas of electrocatalysis and photocatalysis, biomass conversion, and fine chemical synthesis. Attention is also paid to corresponding novel 3D materials that can be obtained via sophisticated engineering of 2D oxides.
91 citations
TL;DR: In this article, a novel photocatalyst composed of TiO2 nanotube arrays sensitized with electrodeposited graphene quantum dots (GQDs) is presented.
Abstract: TiO2 nanotube arrays (TNT) offer an exciting prospect as a photocatalytic material architecture due to the combined properties of high surface area, 1-D vectorial charge transfer, and reduced photogenerated charge recombination. However the TiO2 band gap (≈3.2 eV) limits light absorption to the UV region, which comprises but a small fraction of the solar spectrum energy. Graphene is known to effectively absorb visible light, and due to its high conductivity promote efficient charge transfer. Herein, we present a novel photocatalyst composed of TNTs sensitized with electrodeposited graphene quantum dots (GQDs). GQDs electrodeposition-duration is varied to optimize photocatalytic performance of the resulting nanostructured graphene-TNT (G-TNT) films. Under solar spectrum illumination we find optimal G-TNT samples promote a CO2 to CH4 photocatalytic conversion rate of 1.98 ppm cm−2 h−1, with carbon origin confirmed by 13CO2 isotopic test.
77 citations
TL;DR: In this paper, the authors proposed a simple and novel route for the preparation of Ti3+-TiO2, which would facilitate the preparation and application of TiO2 photocatalyst.
Abstract: In this work, we have shown that aluminium acetylacetonate (Al(acac)3) can be used as the catalyst to synthesize Ti3+ self-doped TiO2 (Ti3+-TiO2) by sol–gel method in air. Ti3+-TiO2 can be obtained directly and Al(acac)3 is removed during the annealing process. Ti3+ concentrates in the surface layer of powders, making a homojunction between Ti3+-TiO2 in the surface layer and TiO2 in the bulk. Based on the scheme of Zielger-Natta catalysts and the characterization of the sols and gels of samples, the synthesis mechanism of Ti3+ is proposed as the combination of steric hindrance effect, Lewis acid-base reaction and crystal field effect and Al(acac)3 acts as the catalyst in the reaction. Charge generation, charge transport and interface reactions, all of the three crucial strategies of photocatalytic are improved through the self-doped Ti3+, resulting in enhanced photocatalytic and photoelectrochemical activities. Compared with the reported methods, this work proposes a simple and novel route for the preparation of Ti3+-TiO2, which would facilitate the preparation and application of TiO2 photocatalyst.
55 citations
TL;DR: In this paper, a unique composite architecture of graphene-oxide wrapped TiO2 nanotubes for the photocatalytic reduction of CO2 has been developed for the reduction of adsorbed CO2 molecules.
53 citations
TL;DR: In this article, the authors make use of alloyed multipodal Ti-Nb-Zr-O nanotubes (MPNTs) annealed under different atmospheres: Air, O2, and H2 for enhanced photoelectrochemical water splitting.
36 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 paper, the progress of the scientific research on TiO2 photocatalysis as well as its industrial applications are reviewed, and future prospects of this field mainly based on the present authors' work.
Abstract: Photocatalysis has recently become a common word and various products using photocatalytic functions have been commercialized. Among many candidates for photocatalysts, TiO2 is almost the only material suitable for industrial use at present and also probably in the future. This is because TiO2 has the most efficient photoactivity, the highest stability and the lowest cost. More significantly, it has been used as a white pigment from ancient times, and thus, its safety to humans and the environment is guaranteed by history. There are two types of photochemical reaction proceeding on a TiO2 surface when irradiated with ultraviolet light. One includes the photo-induced redox reactions of adsorbed substances, and the other is the photo-induced hydrophilic conversion of TiO2 itself. The former type has been known since the early part of the 20th century, but the latter was found only at the end of the century. The combination of these two functions has opened up various novel applications of TiO2, particularly in the field of building materials. Here, we review the progress of the scientific research on TiO2 photocatalysis as well as its industrial applications, and describe future prospects of this field mainly based on the present authors' work.
3,008 citations
TL;DR: This review attempts to cover all aspects, including underlying principles and key functional features of TiO(2), in a comprehensive way and also indicates potential future directions of the field.
Abstract: TiO(2) is one of the most studied compounds in materials science. Owing to some outstanding properties it is used for instance in photocatalysis, dye-sensitized solar cells, and biomedical devices. In 1999, first reports showed the feasibility to grow highly ordered arrays of TiO(2) nanotubes by a simple but optimized electrochemical anodization of a titanium metal sheet. This finding stimulated intense research activities that focused on growth, modification, properties, and applications of these one-dimensional nanostructures. This review attempts to cover all these aspects, including underlying principles and key functional features of TiO(2), in a comprehensive way and also indicates potential future directions of the field.
2,735 citations
TL;DR: Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection were used in this paper, where the authors proposed a method to eliminate the reflection in optical thin-films.
Abstract: Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection
1,153 citations
TL;DR: It is demonstrated that the wall thickness and length of the nanotubes can be controlled via anodization bath temperature and this hydrogen generation rate is the highest reported for a titania-based photoelectrochemical cell.
Abstract: In this study highly ordered titania nanotube arrays of variable wall thickness are used to photocleave water under ultraviolet irradiation. We demonstrate that the wall thickness and length of the nanotubes can be controlled via anodization bath temperature. We find that the nanotube wall thickness is a key parameter influencing the magnitude of the photoanodic response and the overall efficiency of the water-splitting reaction. For 22 nm inner pore diameter nanotube arrays, those fabricated in a 5 °C anodization bath, 224 nm length and 34 nm wall thickness produced a photoanodic response that was thrice that of a nanotube array fabricated in a 50 °C anodization bath, 120 nm length and 9 nm wall-thickness. At high anodic polarization, above 1 V, the quantum efficiency under 337 nm illumination was greater than 90%. For the 5 °C anodization bath samples (22 nm pore-diameter, 34 nm wall thickness), upon 320−400 nm illumination at an intensity of 100 mW/cm2, hydrogen gas was generated at the power−time norm...
1,098 citations