Flat TiO2 Research Articles

Integration of Enzymes in Polyaniline-Sensitized 3D Inverse Opal TiO2 Architectures for Light-Driven Biocatalysis and Light-to-Current Conversion.

Inspired by natural photosynthesis, coupling of artificial light-sensitive entities with biocatalysts in a biohybrid format can result in advanced photobioelectronic systems. Herein, we report on the integration of sulfonated polyanilines (PMSA1) and PQQ-dependent glucose dehydrogenase (PQQ-GDH) into inverse opal TiO2 (IO-TiO2) electrodes. While PMSA1 introduces sensitivity for visible light into the biohybrid architecture and ensures the efficient wiring between the IO-TiO2 electrode and the biocatalytic entity, PQQ-GDH provides the catalytic activity for the glucose oxidation and therefore feeds the light-driven reaction with electrons for an enhanced light-to-current conversion. Here, the IO-TiO2 electrodes with pores of around 650 nm provide a suitable interface and morphology needed for the stable and functional assembly of polymer and enzyme. The IO-TiO2 electrodes have been prepared by a template approach applying spin coating, allowing an easy scalability of the electrode height and surface area. The successful integration of the polymer and the enzyme is confirmed by the generation of an anodic photocurrent, showing an enhanced magnitude with increasing glucose concentrations. Compared to flat and nanostructured TiO2 electrodes, the three-layered IO-TiO2 electrodes give access to a 24-fold and 29-fold higher glucose-dependent photocurrent due to the higher polymer and enzyme loading in IO films. The three-dimensional IO-TiO2|PMSA1|PQQ-GDH architecture reaches maximum photocurrent densities of 44.7 ± 6.5 μA cm-2 at low potentials in the presence of glucose (for a three TiO2 layer arrangement). The onset potential for the light-driven substrate oxidation is found to be at -0.315 V vs Ag/AgCl (1 M KCl) under illumination with 100 mW cm-2, which is more negative than the redox potential of the enzyme. The results demonstrate the advantageous properties of IO-TiO2|PMSA1|PQQ-GDH biohybrid architectures for the light-driven glucose conversion with improved performance.

Flexible Triboelectric Nanogenerator Based on High Surface Area TiO2 Nanotube Arrays

Triboelectric nanogenerators (TENGs) can harvest mechanical energy through coupling triboelectric effect and electrostatic induction. Typically, TENGs consist of organic materials, however on account of the potentially wide range of applications of TENGs as the self‐powered portable/wearable electronics, biomedical devices, and sensors; semiconductor metal oxide materials can be promising candidates to be incorporating in TENG structure. Here, flexible TENG based on self‐organized TiO2 nanotube arrays (TNTAs) is fabricated via anodization method. The introduced flexible large area nanotubular electrode is employed as the moving electrode in contact with Kapton film in vertical contact separation mode of TENG. The fabricated TENG can deliver output voltage of 40 V with the current density of 1 μA cm−2. To evaluate the role of nanostructured interface, its performance has been compared to the thin film flat compact TiO2 electrode. The results of extracted charge measurements under short circuit condition indicate that larger triboelectric charge density formed in TNTA‐based electrode (about 110 nC per cycle of press and release) is in comparison to 15 nC in flat TiO2 electrode. Due to the extensive range of applications of TiO2, the introduced structure can potentially be applicable in various types of self‐powered systems such as photo‐detectors and environmental gas and bio‐sensors.

Photocatalytic antimicrobial films on fluorinated contact lens polymers

Flat TiO2 thin films were dip coated on contact lens polymer substrates (fluorinated ethylene propylene copolymer, FEP) using a hybrid sol-gel and annealed for 12 h at ≤200 °C. The grain sizes were in the range 10–20 nm but extensive shrinkage cracking was present. The crystallinities of the films annealed at ≤150 °C increased with increasing temperature gradually but only to a limited extent, although the crystallinity at 200 °C was significant. Recrystallisation resulted in decreased transparency, increased reflectivity, and a red shift to lower band gap. The methylene blue (MB) degradation was in the order 25 °C < 200 °C < 100 °C < 150 °C, indicating that the photocatalytic performance was dominated by crystallinity and exposed surface area, the latter of which decreased at 200 °C owing to partial submergence in the softened polymeric substrate. The films indicated antimicrobial capacity since they exhibited a maximal level of S. aureus destruction (85%) following 5 h of UV irradiation. The films also appeared to be microstructurally stable following wash testing in contact lens washing solution.

What Controls Photocatalytic Water Oxidation on Rutile TiO2(110) under Ultra-High-Vacuum Conditions?

The photocatalytic O-H dissociation of water absorbed on a rutile TiO2(110) surface in ultrahigh vacuum (UHV) is studied with spin-polarized density functional theory and a hybrid exchange-correlation functional (HSE06), treating the excited-state species as excitons with triplet multiplicity. This system is a model for the photocatalytic oxidation of water by TiO2 in an aqueous medium, which is relevant for the oxygen evolution reaction and photodegradation of organic pollutants. We provide a comprehensive mechanistic picture where the most representative paths correspond to excitonic configurations with the hole located on three- and two-coordinate surface oxygen atoms (O3s and O2s). Our picture explains the formation of the species observed experimentally. At near band gap excitation, the O3s path leads to the generation of hydroxyl anions which diffuse on the surface, without net oxidation. In contrast, free hydroxyl radicals are formed at supra band gap excitation (e.g., 266 nm) from an interfacial exciton that undergoes O-H dissociation. The oxidation efficiency is low because the path associated with the O2s exciton, which is the most favored one thermodynamically, is unreactive because of a high propensity for charge recombination. Our results are also relevant to understand the reactivity in the liquid phase. We assign the photoluminescence measured for atomically flat TiO2(110) surfaces in an aqueous medium to the O3s exciton, in line with the proposal based on experiments, and we have identified a species derived from the O2s exciton with an activated O2s-Ti bond that may be relevant in photocatalytic applications in an aqueous medium.

Exposing high-energy surfaces by rapid-anneal solid phase epitaxy

The functional design of transition metal oxide heterostructures depends critically on the growth of atomically flat epitaxial thin films. Often, improved functionality is expected for heterostructures and surfaces with orientations that do not have the lowest surface free energy. For example, crystal faces with a high surface free energy, such as rutile (001) planes, frequently exhibit higher catalytic activities but are correspondingly harder to synthesize due to faceting transitions. Here we propose a broadly applicable rapid-anneal solid phase epitaxial synthesis approach for the creation of nanometer thin, high surface free energy oxide heterostructures that are atomically flat. We demonstrate its efficacy by synthesizing atomically flat epitaxial RuO2(001) and TiO2(001) model systems. The former have a superior oxygen evolution activity, quantified by their lower onset potential and higher current density, relative to that of more common RuO2(110) films.

Improvement of photoelectric conversion efficiencies of dye‐sensitized solar cells consisting of hemispherical TiO2 films

To improve the photoelectric conversion efficiency (PCE) of dye‐sensitized solar cells (DSSCs), we fabricated hemispherical TiO2 films using a poly(dimethylsiloxane) mold and improved the light harvesting efficiency in DSSCs by a large light‐scattering effect caused by the hemispherical structure. In addition, the amount of the adsorption density of the dye in TiO2 increased due to the larger surface area of the hemispherical structure. Consequently, the short‐circuit current of DSSCs containing hemispherical TiO2 film increased even though the open‐circuit voltage was not changed. As a result, the overall PCE value was improved to about 1.2 times larger than a DSSC containing a flat TiO2 film.In addition, polyethylene glycol‐doping in TiO2 effectively improved the DSSC performance comprised of hemispherical TiO2 films.

A better UV light and TiO 2 -PET sheet arrangement for enhancing photocatalytic decomposition of volatile organic compounds

Abstract Although the relative arrangement of a UV light source and immobilized TiO 2 is estimated to strongly affect the photocatalytic decomposition of volatile organic compounds (VOCs), no studies have been published regarding this matter. In the present study, reactor performances were compared between parallel arrangements, where UV lamps are placed in parallel to flat TiO 2 -PET sheets, and circular arrangements, where each glass tube has a UV lamp and a cylindrical TiO 2 -PET sheet closely attached to the inside surface of the tube. In the decomposition of isopropanol, acetone was released into air and decomposed after being readsorbed onto TiO 2 . In the decomposition of toluene, benzaldehyde remained on the surface and inhibited the decomposition. Parallel arrangement generated an area of low UV intensity on TiO 2 -PET sheets, leaving unconverted intermediates on the sheets. Circular arrangement made it possible to irradiate the whole surface of a TiO 2 -PET sheet with high intensity UV light and provided higher rates of VOC decomposition such that intermediates could be decomposed efficiently. To completely decompose VOCs including the intermediates, TiO 2 must be irradiated with strong UV light above a certain threshold that depends on the kind of VOC. The use of the circular arrangement is recommended for the VOC decomposition.

Engineering TiO2/Perovskite Planar Heterojunction for Hysteresis‐Less Solar Cells

Hybrid halide perovskite solar cells generally show differences in the power output depending on the voltage sweep direction, an undesired phenomenon termed hysteresis. Although the causes of this behavior have not yet been univocally determined, commonly, hysteresis heavily affects solar cells based on flat TiO2 as electron extracting layer. Herein, it is shown how perovskite material quality has a preeminent impact on hysteresis, and how combined deposition and post‐deposition engineered manufacturing could lead to highly efficient and hysteresis‐less solar cells, notwithstanding a planar TiO2‐based layout. This methodology relies on solvent engineering during the casting process, leading to an ultra‐flat, uniform, and thick film ensuring an optimal interface connection with the charge‐extracting layer combined with post‐deposition thermal and vacuum treatments, which merge the crystalline domains and cure the defects at the grain boundaries. This method allows obtaining perovskite active layer with superior optical properties, explaining the ideal device behavior and performances, therefore, a simple optimization of perovskite processing conditions can efficiently stem hysteresis targeting different device layouts. Power conversion efficiency of 15.4% and reduced hysteresis are achieved.

Adsorption of Dye Molecules on Single Crystalline Semiconductor Surfaces: An Electrochemical Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy Study

Adsorption of dye molecules on semiconductor surfaces dictates the interaction at and thus the electron transfer across the interface, which is a crucial issue in dye-sensitized solar cells (DSSCs). However, despite that surface enhanced Raman spectroscopy (SERS) has been employed to study the interface, information obtained so far is gathered from surfaces of irregularly arranged nanoparticles, which places complexities for precise attribution of adsorption configuration of dye molecules. Herein, we employ single crystalline rutile TiO2(110) for Raman spectroscopic investigation of TiO2–dye interfaces under electrochemical control by utilizing the enhancement of Au@SiO2 core–shell nanoparticles. FD-TD simulation is performed to evaluate the localized electromagnetic field (EM) created by the core–shell nanoparticles while Mott–Schottky measurements are used to determine the band structure of the semiconductor electrode. Comparative investigations are carried out on nanoporous P25 TiO2 electrodes. The potential-dependent Raman shift of ν(N═C═S) suggests that the binding of the SCN group of N719 to the TiO2 surface is the intrinsic nature of the TiO2–N719 interaction, after removing the possible bonding complexity by surface roughness. Nevertheless, hydrogen bonding between COOH and the TiO2 appears to be more favorable on the atomic flat rutile TiO2(110) surface than on the surface of nanoporous P25 nanoparticle as revealed by the stronger Raman shift of ν(C═O) (COOH) on the former. Electrochemical SERS (EC-SERS) results show that photoinduced charge transfer (PICT) occurs for both the P25 and rutile(110) TiO2 surfaces, and the potential to achieve PICT resonance depends on the band structure of the semiconductor. Our work demonstrates that EC-SERS can be applied to study the single crystalline semiconductor–molecule interfaces using core–shell based surface plasmonic resonance (SPR) enhancement strategy, which would promote fundamental investigations on interfaces of photovoltaic and photocatalytic systems.

Fabrication of a Contamination-Free Interface between Graphene and TiO2 Single Crystals.

The uniform and seamless interface between graphene and semiconductors, that is, without adsorbates or contamination in between, is of importance for optimizing the electronic and catalytic performances of the combined system. In this work, we try to synthesize graphene directly over atomically flat TiO2 single-crystal surfaces using chemical vapor deposition (CVD) with acetylene as the carbon source. The facile synthetic conditions facilitate the formation of ultrathin polycrystalline graphene films with nanosize domains, while reasonably maintaining the terrace-and-step morphologies of the TiO2 surfaces. The established recipe can thus lead to the construction of a contamination-free interface between graphene and reducible oxides and also provide a well-defined platform for further investigations into the physicochemical properties of the graphene–oxide complex system from an atomic/molecular level.

Gold Nanorods Coated Metallic Photonic Crystal for Enhanced Hot Electron Transfer in Electrochemical Cells

ABSTRACTWe recently demonstrated a sub-bandgap photoresponse with our wafer-scale Au/TiO2 metallic-semiconductor photonic crystals (MSPhC). The sub-bandgap energy with 590 nm peak could be absorbed in the form of hot electron and injected to TiO2, which provides 5.28 times more energy for photolysis than that of energy absorbed to flat TiO2. If the solar energy already absorbed above 700 nm could be injected to the catalyst, higher than 10 times improvement will be achieved, and above 20% solar to fuel efficiency will be feasible with the robust but inefficient TiO2 catalyst. In order to achieve photocurrent near and above 700 nm spectrum, we deposited gold nanorods on the surface of MSPhC to incur localized surface plasmon (LSP) modes absorption and subsequent injection to the TiO2 catalyst. We used electrophoretic deposition (EPD) method to deposit nanorods on the top, sidewall and bottom well surface of the photonic nanocavities. The deposition of nanorods was achieved reasonably uniform and sparse not to block the optical cavities of MSPhC. Flat gold surfaces were tested at 4 different suspension densities to get the optimum gold nanorods density. Under 10V applied electric field, positively charged gold nanorods at the concentration of 6.52×1013 #/mL could deposit MSPhC surface with the density of 230 #/µm2, which was reasonably uniform and sparse. Preliminary tests show an absorbance increase near 700 nm on flat device coated with gold nanorods. Photocurrent measurement is under way to demonstrate the enhanced hot electron transfer over full visible light and near-infrared solar spectrum.

Atomically flat reconstructed rutile TiO2(001) surfaces for oxide film growth

The availability of low-index rutile TiO2 single crystal substrates with atomically flat surfaces is essential for enabling epitaxial growth of rutile transition metal oxide films. The high surface energy of the rutile (001) surface often leads to surface faceting, which precludes the sputter and annealing treatment commonly used for the preparation of clean and atomically flat TiO2(110) substrate surfaces. In this work, we reveal that stable and atomically flat rutile TiO2(001) surfaces can be prepared with an atomically ordered reconstructed surface already during a furnace annealing treatment in air. We tentatively ascribe this result to the decrease in surface energy associated with the surface reconstruction, which removes the driving force for faceting. Despite the narrow temperature window where this morphology can initially be formed, we demonstrate that it persists in homoepitaxial growth of TiO2(001) thin films. The stabilization of surface reconstructions that prevent faceting of high-surface-energy crystal faces may offer a promising avenue towards the realization of a wider range of high quality epitaxial transition metal oxide heterostructures.

Localized committed differentiation of neural stem cells based on the topographical regulation effects of TiO2 nanostructured ceramics.

In this study, a porous-flat TiO2 micropattern was fabricated with flat and nanoporous TiO2 ceramics for investigating the effect of topography on neural stem cell (NSC) differentiation. This finding demonstrates that localized committed differentiation could be achieved in one system by integrating materials with different topographies.

Effect of glassy film micro/nanostructured topography on cell morphology

Effect of glassy film micro/nanostructured topography on cell morphology

Substrate-induced interfacial plasmonics for photovoltaic conversion.

Surface plasmon resonance (SPR) is widely used as light trapping schemes in solar cells, because it can concentrate light fields surrounding metal nanostructures and realize light management at the nanoscale. SPR in photovoltaics generally occurs at the metal/dielectric interfaces. A well-defined interface is therefore required to elucidate interfacial SPR processes. Here, we designed a photovoltaic device (PVD) with an atomically flat TiO2 dielectric/dye/graphene/metal nanoparticle (NP) interface for quantitatively studying the SPR enhancement of the photovoltaic conversion. Theoretical and experimental results indicated that the graphene monolayer was transparent to the electromagnetic field. This transparency led to significant substrate-induced plasmonic hybridization at the heterostructure interface. Combined with interparticle plasmonic coupling, the substrate-induced plasmonics concentrated light at the interface and enhanced the photo-excitation of dyes, thus improving the photoelectric conversion. Such a mechanistic understanding of interfacial plasmonic enhancement will further promote the development of efficient plasmon-enhanced solar cells and composite photocatalysts.

Correction to “Texture of MAPbI3 Layers Assisted by Chloride on Flat TiO2 Substrates”

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionCorrection to “Texture of MAPbI3 Layers Assisted by Chloride on Flat TiO2 Substrates”Giovanna Pellegrino, Silvia Colella, Ioannis Deretzis, Guglielmo G. Condorelli, Emanuele Smecca, Giuseppe Gigli, Antonino La Magna, and Alessandra Alberti*Cite this: J. Phys. Chem. C 2015, 119, 37, 21745Publication Date (Web):September 8, 2015Publication History Published online8 September 2015Published inissue 17 September 2015https://doi.org/10.1021/acs.jpcc.5b08573Copyright © 2015 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views284Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (108 KB) Get e-Alerts Get e-Alerts

Similar Structural Dynamics for the Degradation of CH3 NH3 PbI3 in Air and in Vacuum.

We investigate the degradation path of MAPbI3 (MA=methylammonium) films over flat TiO2 substrates at room temperature by means of X-ray diffraction, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The degradation dynamics is found to be similar in air and under vacuum conditions, which leads to the conclusion that the occurrence of intrinsic thermodynamic mechanisms is not necessarily linked to humidity. The process has an early stage, which drives the starting tetragonal lattice in the direction of a cubic atomic arrangement. This early stage is followed by a phase change towards PbI2 . We describe how this degradation product is structurally coupled with the original MAPbI3 lattice through the orientation of its constituent PbI6 octahedra. Our results suggest a slight octahedral rearrangement after volatilization of HI+CH3 NH2 or MAI, with a relatively low energy cost. Our experiments also clarify why reducing the interfaces and internal defects in the perovskite lattice enhances the stability of the material.

Multi-layering of a nanopatterned TiO2 layer for highly efficient solid-state solar cells

A facile process to prepare multi-layered nanopatterned photoanodes (MNPs) is presented with well-arrayed mesoporous inorganic oxide layers. The MNPs were prepared with multiple stacking of nanopatterned TiO2 layers using a sacrificial polystyrene (PS)-thin film layer, which not only guided the stacking TiO2 layer but also was removed completely by calcination without generating cracks. The prepared MNPs exhibited large enhancement of the light harvesting property by increasing the number of nanopatterned TiO2 layers, through multiple reflection of the incident light from the periodic embedded channels formed between the nanopatterned layers. The photovoltaic efficiency was optimized with a 3-layered nanopatterned photoanode exhibiting a 73% Jsc and a 65% power conversion efficiency enhancement compared with a cell with a flat TiO2 layer for I2-free solid-state dye-sensitized solar cells. Korean researchers have developed a multilayered, nanopatterned photoanode that traps significantly more light than conventional devices. Dye-sensitized solar cells based on titanium dioxide (TiO2) are an emerging low-cost photovoltaic technology, but efficiency gains must be made before they can be used in practical applications. Eunkyoung Kim and colleagues from Yonsei University in Seoul investigated ways to enhance light reflectivity in dye-sensitized solar cells by using a polydimethylsiloxane stamp to form nanoscale channels into a TiO2 paste. After removing the nanostamp and performing annealing, they coated the patterned TiO2 with a sacrificial polystyrene film that preserved the periodic channels when the stamping process was repeated. The team produced a three-layered TiO2 nanoarchitecture that captured light transmissions normally lost as waste, resulting in a 65% gain in photoconversion efficiency over flat TiO2 layers. A facile process to prepare multi-layered nanopatterned photoanodes (MNPs) is presented with well-arrayed mesoporous inorganic oxide layers. The MNPs were prepared by multiple stacking of nanopatterned TiO2 layers using a sacrificial polystyrene-thin film layer, which not only guided the stacking TiO2 layer but also was removed completely by calcination without generating cracks. The MNPs were applied to solid-state solar cells, to exhibit an enhancement of 73% and a 65% in Jsc and power conversion efficiency (PCE), respectively.

Texture of MAPbI3 Layers Assisted by Chloride on Flat TiO2 Substrates

In this paper, we use X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy to investigate the structural and morphological properties of methylammonium lead iodide (MAPbI3) thin films deposited on flat TiO2 substrates, as obtained with and without the use of chlorine precursors. We demonstrate that the presence of Cl precursors assists the growth of oriented MAPbI3 domains along a specific growth direction. Such features are attributed to the proximity of the Cl species to the interface with the TiO2 substrate.

Mechanistic Transition of Electron Transfer Kinetics from Quantum Electron Tunneling to Trap-Facilitated Hopping through TiO2 Films Grown By Atomic Layer Deposition on SnO2 Electrodes

The understanding of electron transfer (ET) phenomenon across semi-conductor interfaces is crucial for applications in photovoltaic systems and electrochemical heterogeneous catalysis . In order to probe ET mechanisms, we exploit atomic layer deposition (ALD) to conformally coat ultrathin films of TiO2 onto a lower conduction band (CB) SnO2 electrode. Between TiO2 film thicknesses of 1 to 10 Å, quantum tunneling through the insulating TiO2 layer is the kinetically preferred ET pathway. At films thicker than 10 Å, there is little change to the ET rate as a function of TiO2 thickness. To our surprise, annealing a 55 Å layer of TiO2 on SnO2, a 10x reduction in ET rate was observed compared to the as deposited TiO2. At potentials near the CB edge of SnO2, electrochemical impedance spectroscopy of nominally flat amorphous TiO2 indicated the presence of nearly double the density of states (DOS) with respect to their crystalline counterpart; the relationship between ET and DOS was studied in depth. These findings show the first observation of change in ET mechanism across semi-conductor interfaces, and demonstrates the ineffectiveness of thick layers films grown by ALD at completely shutting off electron transfer without annealing post film growth.