Hierarchical TiO2 Nanostructures Research Articles

Cost-effective dye-sensitized solar cells based on rutile-phase three-dimensional TiO2 hierarchical nanostructures.

Specifically engineered three-dimensional (3D) and 1D morphologies are expected to play significant roles in the development of next-generation dye-sensitized solar cells. In this study, using a hydrothermal approach without a surfactant or template, we attempted to synthesize a 3D hierarchical rutile titanium dioxide (TiO2 ) architecture by varying the growth temperature and time. X-ray diffraction patterns of the synthesized TiO2 correlated well with rutile TiO2 . Scanning electron microscopy images exhibited different nanostructures, such as nanorods, aggregated nanorods, and 3D TiO2 microflowers comprised of nanorods at 100°C, 130°C, and 160°C, respectively, after growth for 6 h. A significantly improved efficiency was observed for the TiO2 microflowers. The TiO2 microflowers exhibited an efficiency of 1.16%, short-circuit current density of 12.8 mA cm-2 , open-circuit voltage of 0.692 V, and fill factor of 0.67.

Solvothermal synthesis of 3D hierarchical rutile TiO2 nanostructures for efficient dye-sensitized solar cells

3D hierarchical rutile TiO2 nanostructures were successfully prepared using the solvothermal method. X-ray diffraction (XRD) revealed the formation of the anatase phase. A high-resolution transmission electron microscope (HRTEM) shows that several hundred radially distributed nanofibers with a length of 1 μm were self-assembled to form a nanostructure. Current vs voltage (I-V) measurements for the cone-shaped nanostructure showed a short circuit current density (Isc) of 2.8 mA/cm2, an open circuit voltage (Voc) of 0.70 V, and the fill factor (FF) is 0.55. The efficiency obtained for cone-shaped hierarchical rutile TiO2 structures was 1.12 %.

In situ transformation of TiO2 hierarchical nanostructures toward efficient photoelectrochemical water splitting

TiO2 hierarchical nanomaterials have been intensively investigated as a very promising photoanode in photoelectrochemical water splitting due to its combined effects of large surface area and fast electron transfer. However, the TiO2 hierarchical nanostructures prepared by most prevailing synthesis methods currently are at distinct disadvantages such as complicated process, poor controllability, poor interfacial contact, excessive impurities and so on. Here we report a facile route to construct a well-defined TiO2 hierarchical nanostructure via in-situ transformation of TiO2 nanoparticles with highly exposed {001} facets in the tube wall of the pristine TiO2 nanotube arrays. The resulted TiO2 hierarchical nanostructures exhibit enhanced light harvesting, lowe recombination rate of photo-generated charger carrier. Upon these synergistic effects, the target hierarchical nanostructure shows significantly improved PEC performance and excellent photo-switching response with good reproducibility and stability. Corresponding photocurrent density and photon-to-current efficiency achieve 0.76 mA cm−2 and 0.50%, respectively, which show an enhancement of 1.70 and 1.32 times to those of the control one. This work provides a possible route for fabrication of TiO2 starting materials with decent efficiencies.

Space-Confined seeding and growth of ordered arrays of TiO2 hierarchical nanostructures

Here, we report a facile approach to fabricate large area ordered arrays of TiO2 hierarchical nanostructures through space-confined seeding and growth on inverted pyramid templates. The mechanisms of space-confined seeding and growth have been systematically explored and studied. The drying TiO2 seed precursor solution prefers to accumulate on the narrow structures including the centre and edges of the inverted pyramid structures, which facilitates to reduce the free energy of the precursor solution surface and form crystal seeds. Followed by hydrothermal treatment, selective growth of TiO2 hierarchical nanostructures on desirable locations, such as only on the centre, only on the edges, or on the entire surface of the inverted pyramid templates, can be achieved. In addition, the growth temperature, duration and solvents affect the morphology of TiO2 hierarchical nanostructures. This work may provide a universal approach to obtain ordered arrays of metal oxide (e.g. ZnO and MnO2, etc.) nanostructures for applications in optics, electrics, energy, and catalysis.

Ag3PO4-Deposited TiO2@Ti3C2 Petals for Highly Efficient Photodecomposition of Various Organic Dyes under Solar Light.

Two-dimensional Ti3C2 MXenes can be used to fabricate hierarchical TiO2 nanostructures that are potential photocatalysts. In this study, the photodecomposition of organic dyes under solar light was investigated using flower-like TiO2@Ti3C2, deposited using narrow bandgap Ag3PO4. The surface morphology, crystalline structure, surface states, and optical bandgap properties were determined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption analysis, and UV-Vis diffuse reflectance spectroscopy (UV-DRS). Overall, Ag3PO4-deposited TiO2@Ti3C2, referred to as Ag3PO4/TiO2@Ti3C2, demonstrated the best photocatalytic performance among the as-prepared samples, including TiO2@Ti3C2, pristine Ag3PO4, and Ag3PO4/TiO2 P25. Organic dyes, such as rhodamine B (RhB), methylene blue (MB), crystal violet (CV), and methylene orange (MO), were efficiently degraded by Ag3PO4/TiO2@Ti3C2. The significant enhancement of photocatalysis by solar light irradiation was attributed to the efficient deposition of Ag3PO4 nanoparticles on flower-like TiO2@Ti3C2 with the efficient separation of photogenerated e-/h+ pairs, high surface area, and extended visible-light absorption. Additionally, the small size of Ag3PO4 deposition (ca. 4–10 nm diameter) reduces the distance between the core and the surface of the composite, which inhibits the recombination of photogenerated charge carriers. Free radical trapping tests were performed, and a photocatalytic mechanism was proposed to explain the synergistic photocatalysis of Ag3PO4/TiO2@Ti3C2 under solar light.

Hierarchical TiO2 nanorods with a highly active surface for photocatalytic CO2 reduction

Photocatalytic carbon dioxide reduction reaction (CO2RR) has been considered as one of most effective ways to solve the current energy crisis and environmental problems. However, the practical application of photocatalytic CO2RR is largely hindered by lock of efficient catalyst. Here, hierarchical titanium dioxide (TiO2) nanostructures with a highly active {001} surface were successfully synthesized by a facile approach from metal Ti powders. The obtained hierarchical TiO2 nanostructures were composed of TiO2 nanorods, which have a diameter about 5–10 nm and a length of several micrometers. It is found that these nanorods have exposed {001} facets. On the other hand, these hierarchical TiO2 nanostructures have a good light-harvesting efficiency with the help of TiO2 nanorods component and large specific surface area. Therefore, these hierarchical TiO2 nanostructures exhibit a much better activity for photocatalytic CO2 reduction than that of commercial TiO2 (P25). This high activity can be attributed to the synergistic effects of active surface, efficient charge transfer along nanorods and good light harvesting in the nanorod-hierarchical nanostructures.

Carbon-incorporated, nitrogen-doped branch-like TiO2 nanostructure towards superior lithium storage performance

Hierarchical TiO2 nanostructures have shown a good prospect for energy storage and conversion. However, the intrinsic low conductivity and sluggish reaction kinetics greatly hamper their applications as the anode materials for lithium-ion batteries (LIBs). Herein, an eco-friendly route has been developed as a scalable strategy for preparing the anatase TiO2 nanostructures via a simple template-free hydrothermal process. The as-made TiO2 product has a high surface area of 146.3 m2 g−1 and a unique hierarchically branched nanostructure, which is constructed by the rigid trunk and flexible nanosheets. Significantly, the product demonstrates the uniform distribution of carbon/nitrogen in the TiO2 architecture. Benefiting from these unique structural features, the TiO2-400 electrode shows a superior electrochemical performance for reversible lithium storage, demonstrating a high reversible capacity of 268.2 mA h g−1 at 100 mA g−1 after 600 cycles and long cycling life. This study also opens a new window for rational design of hierarchical nanostructures with excellent properties by an environmentally benign technique.

Happy 5th Birthday, Advanced Materials Interfaces!

In February 2014, the very first issue of Advanced Materials Interfaces – a new journal for surfaces and interfaces from the Advanced journals family – came into the world. The number of submissions has been growing since its launch, and its increasing impact factor (currently 4.834) confirms a growing readership and citations, demonstrating the importance for this sister journal of Advanced Materials. Jeong Young Park and co-workers were featured on the front cover of the first edition with their work on “Enhanced H2 Generation of Au-Loaded, Nitrogen-Doped TiO2 Hierarchical Nanostructures under Visible Light” (Figure 1). We are proud of the journal's positive reception by the scientific community and, as it grows and develops, we are grateful for the company of our respected Advisory Board members, authors, reviewers, and readers. They continue to be the engine driving the success of the journal, and many of them have remained loyal to Advanced Materials Interfaces from the very beginning. This birthday issue is free to access and provides you with many interesting articles. We would particularly like to highlight these contributions from our Editorial Advisory Board members: The Progress Report by Qiang Zhang (Tsinghua University, China) and co-workers on “Sulfur Redox Reactions at Working Interfaces in Lithium–Sulfur Batteries: A Perspective” and a Research News article on “Bone-Adhesive Materials: Clinical Requirements, Mechanisms of Action, and Future Perspective” by Sander Leeuwenburgh (Radboud University, The Netherlands) and co-workers. In honor of our 5th anniversary, please also watch out for additional articles and posts related to our celebration on Advanced Science News. We hope you enjoy reading this edition and we are looking forward to further exciting submissions and contributions. Here is to many more successful years for Advanced Materials Interfaces! On behalf of the editorial team,

Fabrication of antireflective hierarchical TiO2 nanostructures by moth-eye patterning of anodic anodized nanotubes.

Herein, we report the fabrication and characterization of a hierarchical TiO2 structure that exhibits reduced surface reflection. The hierarchical structure, which is a moth-eye-shaped array containing nanotubes, was fabricated by dry-etching a TiO2 nanotube layer, by using colloidal lithography. The fabricated structure shows a reduced reflectance, compared with that of non-patterned TiO2 nanotubes. This is because of the graded refractive index of the moth-eye pattern. Furthermore, we investigated the optical properties of gold-decorated moth-eye TiO2 nanotubes and found that the absorption, which was caused by the plasmonic resonance of gold nanostructures, was further enhanced by coupling with the light-trapping effect.

Superhydrophilic and underwater superoleophobic Ti foam with fluorinated hierarchical flower-like TiO2 nanostructures for effective oil-in-water emulsion separation

In this work, a superhydrophilic Ti foam was designed and fabricated by applying a novel one-step hydrothermal approach to achieve highly efficient oil in water emulsion separation. Attributed to the synergistic effect of the surface roughness constructed by hierarchical flower-like TiO2 nanostructures and the surface hydrophilicity induced by titanium oxy-fluoride groups, the as-prepared Ti foam exhibited superhydrophilicity and underwater superoleophobicity. The formation of flower-like TiO2 nanostructures was studied and a possible “partial replacement” fluorinated process was proposed. Oil in water emulsion separation test showed that the superhydrophilic Ti foam could handle with various emulsions only under gravity with high separation efficiency over 99%. The separation efficiency remained high even after 20 times of reusing, demonstrating good reusability. More importantly, the superhydrophilic Ti foam could still maintain its wettability after immersed corrosive solutions for 48 h or stored under ambient atmosphere for three months, indicating excellent anti-corrosion property and long-term storage stability. We envision the methodology for the construction of a superhydrophilic surface by a simple and low-cost hydrothermal process will shed light on the Ti-based material design and also pave the way for applications in other fields such as liquid manipulation, fluidic devices and bioadhesion control.

Self-Reconstructed Formation of a One-Dimensional Hierarchical Porous Nanostructure Assembled by Ultrathin TiO2 Nanobelts for Fast and Stable Lithium Storage.

Owing to their unique structural advantages, TiO2 hierarchical nanostructures assembled by low-dimensional (LD) building blocks have been extensively used in the energy-storage/-conversion field. However, it is still a big challenge to produce such advanced structures by current synthetic techniques because of the harsh conditions needed to generate primary LD subunits. Herein, a novel one-dimensional (1D) TiO2 hierarchical porous fibrous nanostructure constructed by TiO2 nanobelts is synthesized by combining a room-temperature aqueous solution growth mechanism with the electrospinning technology. The nanobelt-constructed 1D hierarchical nanoarchitecture is evolves directly from the amorphous TiO2/SiO2 composite fibers in alkaline solutions at ambient conditions without any catalyst and other reactant. Benefiting from the unique structural features such as 1D nanoscale building blocks, large surface area, and numerous interconnected pores, as well as mixed phase anatase-TiO2(B), the optimum 1D TiO2 hierarchical porous nanostructure shows a remarkable high-rate performance when tested as an anode material for lithium-ion batteries (107 mA h g-1 at ∼10 A g-1) and can be used in a hybrid lithium-ion supercapacitor with very stable lithium-storage performance (a capacity retention of ∼80% after 3000 cycles at 2 A g-1). The current work presents a scalable and cost-effective method for the synthesis of advanced TiO2 hierarchical materials for high-power and stable energy-storage/-conversion devices.

Tuning the photoelectrochemical properties of hierarchical TiO2 nanostructures by control of pulsed laser deposition and annealing in reducing conditions

Nanostructured TiO2 films with hierarchical morphology were synthesized by Pulsed Laser Deposition (PLD) and tested as photoanodes for photoelectrochemical water splitting. The tuning of their photoresponse was addressed by employing oxygen-poor conditions both during the growth and the post-deposition annealing of the material: depositions were performed in different Ar/O2 background gas mixtures from both TiO2 and Ti targets, while thermal treatments, after standard air annealing for crystallization, were performed in a Ar/H2 mixture. By testing the double-annealed photoanodes in a three-electrode cell with solar simulator illumination, clear trends with optimal synthesis conditions for each target material appeared; for these conditions, also the effect of vacuum annealing was studied. The morphological, structural and optical properties were investigated by SEM, Raman spectroscopy and UV-visible-IR spectroscopy. From these observations, it emerged that the films deposited in the presence of oxygen do not show substantial differences in their morphology/structure, on the contrary of pure Ar-deposited films; thus, the trends in photoresponse can be related to differences in the defect concentration of the material, induced by depositions in the different Ar/O2 atmospheres and by annealing in Ar/H2 mixture or vacuum. In particular, the reported results suggest that some degree of oxygen shortage in the deposition process leads to a better photoelectrochemical performance, and a combination between improved charge transport and surface hydrogenation/reduction effect, leading to enhanced photoresponse, is suggested. This work elucidates the possibility of an accurate tuning of the material photoactivity by control of the deposition and annealing conditions.

CdSe x S1−x /CdS-cosensitized 3D TiO2 hierarchical nanostructures for efficient energy conversion

Three-dimensional TiO2 hierarchical nanostructures (3D-TiO2-HNs) containing TiO2 nanotrees and nest-like hollow spheres were synthesized and used as backbones for CdSe x S1−x quantum dot (QD) loading. These CdSe x S1−x QD-sensitized 3D-TiO2-HNs were then used as photoelectrodes in the preparation of quantum-dot-sensitized solar cells. As revealed by TEM images, the highly porous 3D-TiO2-HNs represent an excellent framework on which to deposit a large number of CdSe x S1−x QDs in order to form homogeneous and compact CdSe x S1−x -sensitized layers in photoelectrodes using a spin-assisted successive ionic layer adsorption and reaction method (spin-SILAR). Following careful adjustment of the molar ratio of Se2− to S2−, the number of spin-SILAR cycles, and the thickness of the CdS passivation layer used, the best-performing QDSC was shown to yield a short-circuit current density of 18.22 mA cm−2, an open-circuit voltage of 0.520 V, a fill factor of 0.510, and a power conversion efficiency of 4.83%. This high performance is possible because the device is able to absorb a relatively broad range of wavelengths and because charge recombination is suppressed in the device.

Facile one-pot synthesis of chain-like titanium dioxide nanostructure arrays for efficient ultraviolet sensing

Hierarchical TiO2 nanostructure arrays have been successfully synthesized on FTO glass by a facile one-pot hydrothermal method. The novel nanostructure arrays are composed of nanowire trunks and epitaxial nanobranches, and covered by interconnected nanosheets. The UV sensing performance is investigated by integrated them into a photoelectrochemical cell. Benefited from the efficient transport networks and large interface area provided by the novel nanostructure array, the assembled UV sensor exhibits a high responsivity of 0.11A/W, a fast response time of 20–40ms for current signal, as well as the self-powered, visible-blind characteristic and considerable spectral response under weak irradiation. Our work has provided an efficient strategy to improve the sensing performance of photoelectrochemical UV sensors by building hierarchical chain-like nanostructures with simple method.

Efficient quasi-mesoscopic perovskite solar cells using Li-doped hierarchical TiO2 as scaffold of scattered distribution

Circular plate like lithium doped hierarchical TiO2 (Li-hier-TiO2) nanostructures were synthesized and scattered on the compact TiO2 layer as a quasi-scaffold layer for perovskite solar cells (PSCs). The quasi-scaffold layer provides superior contact properties with perovskite layer and helps to form the high quality perovskite film with better crystallinity and less pin-holes. Simultaneously, Li-hier-TiO2 quasi-scaffold compared to pure hier-TiO2 quasi-scaffold exhibits superior electronic properties due to the reduced trap states together with better electron transport and extraction abilities. PSCs using Li-hier-TiO2 quasi-scaffold layer to host the CH3NH3PbI3 photoactive layer produce substantially higher PCE of 18.25% with suppressed hysteretic behavior, which is obviously higher than PCE (15.64%) of PSCs using pure hier-TiO2 quasi-scaffold layer.

Efficient photodegradation of organic dye using anatase TiO2 plants as catalyst

Anatase TiO2 hierarchical nanostructures with higher photocatalytic activity are of special importance in various applications. We have reported the synthesis of TiO2 as water chestnut plants like morphology via facile hydrothermal method, by using Titanium (IV) butoxide (TBOT) as a precursor solution. It is found that TiO2 nanoparticles work as seed and completely convert into water chestnut plants like structure or morphology, which are composed of crystallized anatase nanocrystals. X-ray diffraction spectra confirmed the presence of anatase phase of crystallized TiO2 plants (TPs). The average life time delay for generated charge carriers in TPs was calculated to be around 2.45 ns, which reflects slow recombination of charge carriers. The prepared TPs show excellent photocatalytic performance when applied in photo degradation of Rhodamine B organic dye. The unique features exhibited by TPs make them a promising candidate for vast potential applications in field such as solar cells, photocatalysis, supercapacitor, lithium ion batteries and some related fields. Open image in new window

Preparation and capacitance properties of Al-doped hierarchical TiO2 nanostructure by oxidation of Ti–8Al alloy

We reported a facile route for the fabrication of Al-doped TiO2 nanostructure for supercapacitor electrode materials through an in-situ oxidation of Ti–8Al alloy. Ti–8Al alloy was prepared through solidification route. After high-temperature oxidation, rod-like and wall-like Al-doped TiO2 composites were formed on the surface of Ti–8Al alloy flake. This kind of novel structure consisted of numerous nanorods and nanosheets, exhibiting large open space. When applied for supercapacitor, Al-doped TiO2 composites electrode materials exhibited excellent electrochemical performance. After oxidation at 650 °C for 100 h, the electrode can deliver the highest capacitance of 4650 μF cm−2 at the current density of 10 μA cm−2 as well as long-term cycling stability of 98.5% of the initial specific areal capacitance after 6000 cycles.

Enhanced Efficiency and stability of Perovskite Solar Cells using Porous Hierarchical TiO2 Nanostructures of Scattered Distribution as Scaffold

A type of quasi-mesoscopic perovskite solar cells (QM-PSCs) with porous hierarchical TiO2 (hier-TiO2) nanostructures of scattered distribution as scaffold was investigated. The porous hier-TiO2 nanostructures were synthesized by sintering MIL-125(Ti) of metal-organic frameworks (MOFs) at 500°C in air and which were partly inherited from the ordered porosity of MIL-125(Ti). The ordered hier-TiO2 nanostructures were scattered on compact TiO2 layer to form a quasi-mesoscopic scaffold of scattered distribution, which can offer enough growth space for perovskite grains and promote the ordered growth of perovskite grains. The QM-PSCs shows a power conversion efficiency (PCE) of 16.56%, much higher than PCE (11.38%) of PSCs with conventional small TiO2 nanoparticles (npt-TiO2) as scaffold and PCE (6.07%) of planar PSCs with compact TiO2 layer. The PCEs of PSCs with hier-TiO2 and npt-TiO2 remain 47% and 22% of the initial PCE values aging for 30days in air, indicating that PSCs with hier-TiO2 scaffold shown better stability and moisture resistance. The enhanced performance of QM-PSCs is primarily attributed to the superior wettability quasi-mesoscopic scaffold with ordered porous hier-TiO2 nanostructures, which help to form the high quality perovskite film with better crystillinity and less pin-holes, and improve the contact properties between perovksite and electron transport layer.

Effect of morphology evolution from nanotubes to concatenated nanoparticles of hierarchical TiO2 nanostructures on power conversion efficiency of dye-sensitized solar cells

Compared with TiO2 nanoparticles (TNPs) or TiO2 nanotubes (TNTs), the hierarchical TiO2 nanostructures with high porosity and direct charge pathway are desired for the fabrication of efficient TiO2-based devices for the dye-sensitized solar cells (DSSCs). The preparation methods applied so far to synthesize hierarchical TiO2 nanostructures are multi-step processes involving the control of many parameters and producing uneven nanoparticles and agglomeration on the decorated nanotubes. Herein, we report on the formation and morphology evolution of the hierarchical TiO2 nanostructures with tailored porosity in the absence of any template. The different hierarchical TiO2 nanostructures were obtained by thermal annealing at 450 °C for 1, 2, and 4 h of the free-standing TNT layers prepared by anodization. The hierarchical TiO2 nanostructures with pores formed on the TNT walls were obtained when the annealing time was set to 1 h, and a further increase in the annealing time led to the formation of larger concatenated nanoparticles of TiO2. The resulting hierarchically structured TiO2 nanotubes annealed for 1 h were subsequently exploited as a photoanode in the fabrication of the DSSCs, markedly enhancing the power conversion efficiency (PCE) of 7.24%. A 71.1% increase in the PCE was achieved in comparison to the device prepared by using pure anatase-TiO2 nanotubes (4.25%) due to the synergistic effect of higher capacity for dye loading because of a larger specific surface area, fast charge transport, and superior light scattering ability.

A novel hierarchical TiO2@Pt@mSiO2 hollow nanocatalyst with enhanced thermal stability

A novel hierarchical TiO2@Pt@mSiO2 hollow nanocatalyst with enhanced thermal stability has been synthesized successfully. The formation procedure involves a facile synthesis of SiO2@TiO2@Pt nanospheres and a subsequent solvothermal process. During the hydrothermal process, original TiO2 layer was transformed into a hierarchical nanostructure and, meanwhile, etch-released silica species redeposited on the surface of the in-situ grown TiO2 nanoplatelets. In the catalytic system, the in-situ grown TiO2 nanoplatelets were buried in the redeposited mSiO2 layers and the Pt NPs dispersed uniformly between TiO2 nanoplatelets and mSiO2 layers. Importantly, the redeposited mSiO2 layer provides a physical barrier to prevent Pt NPs from sintering up to 550 °C and the hierarchical TiO2 nanostructure shows an obvious co-catalysis effect in the reduction of 4-NP. Besides, the mSiO2 layer could also control the rapid crystallization process of TiO2 nanoplatelets effectively. In the high temperature reaction of propane dehydrogenation, HHN exhibits a lower deactivation parameter, indicating the excellent thermal stability.