Smooth TiO Research Articles

Cover Picture: Bisphosphonates on Smooth TiO2: Modeling and Characterization (ChemistrySelect 19/2022)

The cover picture shows different aspects related to the work. Characterization data (CHADA) and modeling data (MODA) representations foster interdisciplinary understanding and facilitate standardized communication of material-specific interphase characteristics. Adsorbed molecules of the three studied bisphosphonates are displayed on a TiO2 surface at the center. The linear structure of the bisphosphonates is represented in the background. The cover was illustrated by Giseli Sina. More information can be found in the Research Article by Leonardo F. G. Dias et al. (DOI: 10.1002/slct.202200286).

Bisphosphonates on Smooth TiO2: Modeling and Characterization

AbstractThis paper presents insights into surfaces properties of sputter‐deposited titania modified with bisphosphonates, including zeta potential measurements in a pH range. Functionalization was investigated through simulation and experimental approaches to model the adsorbate and evaluate structure‐response relationships. Molecules of etidronic, alendronic, and risedronic acids were investigated through density functional theory. The molecules vary their reactivity through similar structures considering different scenarios. X‐ray photoelectron spectroscopy of titania/BP systems demonstrated that functionalization occurs in a short time and resulted in a predominantly “side‐on” adsorbate configuration after two hours of immersion. Zeta potential showed the predominancy of negative charges deprotonated free phosphonates. Water contact angle demonstrated that titania surfaces are hydrophilic after overnight functionalization. Atomic force measurements of bisphosphonates layers suggested that the molecular anions follow the surface topography, unchanging the surface roughness.

TiO2 nanoparticles via simple surface modification as cathode interlayer for efficient organic solar cells

Cathode interlayers (CILs) play important roles in promoting high-performance organic solar cells (OSCs). Among the commonly used CILs, metal oxides, such as ZnO, TiO 2 and SnO 2 , display suitable work function and high conductivity. However, they are usually processed under high temperature and in most cases, they are adopted in the inverted OSCs. Since high-performing non-fullerene OSCs are usually fabricated with conventional configuration, it is interesting to explore the potential application of these metal oxide materials as CIL in these cells. An efficient strategy is to use metal oxide nanocrystals as CIL to deposit onto photoactive layers. However, the as-synthesized nanocrystals have the difficulty to form smooth and dense films due to the serious aggregation. In this work, we developed a method via the surface modification of TiO 2 nanoparticles by using 4-dimethylamino benzoic acid to reduce the aggregation, so that smooth TiO 2 –N film can be formed on top of the photoactive layer. Besides, TiO 2 –N displays lower work function, which is helpful for better energy levels alignment. All these factors contribute to the improved charge generation and transport, leading to the power conversion efficiencies enhanced from 13.68% to 15.90% for PM6:BTP-4Cl solar cells. • Metal oxide nanocrystals are applied as cathode interlayer deposited onto the photoactive layer in organic solar cells. • The method via the surface modification on the TiO 2 nanoparticles by using polar acid ligand is facile. • TiO 2 –N displays lower work function, leading to better energy level alignment. • The TiO2–N based interlayer results in the PCE enhancement of PM6:BTP-4Cl type OSC from 13.68% to 15.90%.

Modulation of Volmer step for efficient alkaline water splitting implemented by titanium oxide promoting surface reconstruction of cobalt carbonate hydroxide

The sluggish water dissociation (Volmer step) is a rate-limiting step slowing down alkaline hydrogen evolution reaction (HER), and therefore hinders the efficient industrial production of clean hydrogen resource. In this work, we report that the Volmer step can be facilitated by in-situ surface reconstruction on a composite between cobalt carbonate hydroxide and titanium oxide (TiO 2 @CoCH), and the resultant activated structure turns to be a highly efficient electrocatalyst for alkaline HER. Experimental characterization and density functional theory calculation evidence that under HER potential the smooth TiO 2 @CoCH surface is roughened and Co interstitial defects in TiO 2 are formed, which are energetically favorable for Volmer step. The activated composite exhibits an overpotential of 99 ± 6 mV for a current density of 20 mA cm −2 and 187 ± 21 mV for 100 mA cm −2 , suggesting that TiO 2 @CoCH is one of promising non-precious metal electrocatalysts for HER in alkaline media. • The combination of two inert component resulted in a highly active electrocatalyst for alkaline hydrogen evolution reaction. • Titanium oxide promoted the surface reconstruction of cobalt carbonate hydroxide during hydrogen evolution reaction. • The Volmer step of hydrogen evolution reaction was significantly promoted after surface reconstruction. • The surface reconstruction of cobalt carbonate hydroxide during hydrogen evolution reaction was evidenced.

Synthesis and growth mechanism of multilayer TiO2 nanotube arrays

High-aspect-ratio TiO(2) nanotube arrays formed by anodic oxidation have drawn extensive attention due to their easy fabrication and various excellent optical, electrical and biomedical properties. In contrast to conventional single-layer TiO(2) nanotubes prepared via constant-voltage anodization, we synthesize multilayer TiO(2) nanotube arrays with high surface area by using alternating-voltage anodization steps. This work presents synthesis and growth mechanisms of single-layer smooth TiO(2) nanotubes, bamboo-type nanotubes and double-layer nanotubes, by tuning various parameters such as voltage, time, and water content in the electrolyte. It is found that ion diffusion inside the nanotubes dominates growth of these three structures. A stable pH and ion-diffusion profile allows the steady growth of smooth TiO(2) tubes in NH(4)F-containing ethylene glycol (EG). The addition of a low-voltage anodization step reduces the pH and ion-diffusion gradient in the nanotubes and induces formation of bamboo-type nanotubes and double-layer nanotubes when a second high-voltage anodization is conducted. Ion diffusion through a nanotube takes time; thus formation of lower-layer TO(2) nanotubes costs more time if longer nanotubes are grown in the upper layer, since ions diffuse through these longer nanotubes. This ion-diffusion controlled growth mechanism is further confirmed by tailoring the water content (0-20 vol%) in the electrolyte and the voltage gaps to control the time needed for initiation of lower-layer TiO(2) nanotube arrays. The fundamental understanding of the growth characteristics of double-layer TiO(2) nanotubes presented in this paper offers us more flexibility in engineering morphology, tuning dimensions and phase compositions of multilayer TiO(2) nanotubes. In addition, we synthesize double-layer TiO(2) nanotube arrays composed of one layer of anatase phase and another layer of amorphous phase.

Non-linear electric field response of permittivity of atomically smooth TiO2(rutile) single crystals studied by an electrochemical approach

Electric field-dependent permittivity of n-TiO2 (rutile) along different crystallographic axes was investigated by an electrochemical impedance spectroscopy (EIS) measurement. The C−2 versus U plots were fitted with a quadratic function of U, derived from a model that adds the effects of electric field dependent permittivity to the conventional Mott–Schottky equation. Only when atomically flat n-TiO2 single crystal electrodes were used, could the intrinsic behavior of the electric field dependent permittivity be observed. The principal components of permittivity in the ab-plane exhibited a weak electric field dependence, while a strong electric field dependence was confirmed along the c-axis direction. By taking the electric field dependent permittivity into account, we were able to evaluate accurately the flat-band potential and the donor density. Different photocurrent behavior between (110), (100), and (001) electrodes is discussed in terms of the electric field strength at the surface and the depletion layer width within TiO2.

Photoelectrochemical Performance of Smooth TiO2Nanotube Arrays: Effect of Anodization Temperature and Cleaning Methods

The formation of self-organized titanium dioxide (TiO2) nanotube arrays without bundling or clustering is essential for their high efficiency in photoelectrochemical (PEC) application. The present paper reports on the use of different temperatures to control the specific architecture of nanotube arrays and effective cleaning techniques to ensure the formation of clean TiO2nanotube surface. The wall thickness of nanotube arrays could be controlled from 12.5 nm to 37.5 nm through different anodization temperature ranging from 10°C to 80°C. Furthermore, ultrasonic cleaning combined with acetone showed the high-ordered TiO2nanotube arrays without morphological disorder, bundling, and microcrack problems. Based on the results obtained, a higher PEC response of 1 mA/cm2and a photoconversion efficiency of 1.3% could be achieved using a wall thickness of 12.5 nm and defect-free TiO2nanotube arrays for low charge transfer resistance.

Wettability Conversion from Superoleophobic to Superhydrophilic on Titania/Single-Walled Carbon Nanotube Composite Coatings

Superoleophobic surfaces were demonstrated on perfluorosilane-rendered titania (TiO(2))/single-walled carbon nanotube (SWNT) composite coatings. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations revealed that SWNTs play a key role in the formation of overhanging structures and the nanoscale roughness on the coating surface, which compose the two critical morphologic factors for a superoleophobic surface. The wettability conversion from superoleophobic to superhydrophilic of the composite coatings was realized by the gradual decomposition of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) on the coating surface using UV irradiation. Contact angle measurement on both smooth TiO(2) surface and rough composite coating surface under different UV irradiation time revealed that the wetting behavior of the liquids on the composite coating surface passes from the Cassie to the Wenzel and finally to the inversed-Cassie regime. Different liquids show different irradiation time for the wetting state change. By controlling the UV irradiation dose, liquids with surface tension difference smaller than 5 mN/m can exist in completely converse wetting states on the same coating surface, that is, superphobic for one liquid while superphilic for another with lower surface tension. Mixed organic liquids with different surface tension can be completely separated through a coated grid using this wettability tuning technique.

High Efficiency Dye-Sensitized Solar Cells Based on Hierarchically Structured Nanotubes

Dye-sensitized solar cells (DSSCs) based on hierarchically structured TiO(2) nanotubes prepared by a facile combination of two-step electrochemical anodization with a hydrothermal process exhibited remarkable performance. Vertically oriented, smooth TiO(2) nanotube arrays fabricated by a two-step anodic oxidation were subjected to hydrothermal treatment, thereby creating advantageous roughness on the TiO(2) nanotube surface (i.e., forming hierarchically structured nanotube arrays-nanoscopic tubes composed of a large number of nanoparticles on the surface) that led to an increased dye loading. Subsequently, these nanotubes were exploited to produce DSSCs in a backside illumination mode, yielding a significantly high power conversion efficiency, of 7.12%, which was further increased to 7.75% upon exposure to O(2) plasma.

Carbon-doped mesoporous TiO 2 film and its photocatalytic activity

A visible-light-active C-doped mesoporous TiO 2 film was prepared by sol–gel process combined with hydrothermal treatment. Glucose was used as carbon source and structure-directing agent. The structure and physicochemical properties of the film were characterized by X-ray diffraction (XRD), N 2 adsorption–desorption isotherms, scanning electron microscopy (SEM), Fourier transform-infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectrum (DRS) and photoluminescence (PL). The results indicated that oxygen sites in the TiO 2 lattice were substituted by carbon atoms and an O–Ti–C bond was formed. The C-doped mesoporous TiO 2 film had a high surface area of 283 m 2 g −1. The film was about 10 μm thick and was composed of anatase TiO 2 particles. The prepared C-doped TiO 2 film exhibited excellent photocatalytic activity in the degradation of dye Reactive Brilliant Red X-3B (C.I. reactive red 2) under UV and visible light irradiation compared with that of the smooth TiO 2 film and P25 film. The recycle ability of the C-doped mesoporous TiO 2 film was also investigated. The degradation ratio which was still higher than 87% after 5 cycles, decreased by 3% compared to the first cycle.

Development of mesoporous TiO 2 microspheres with high specific surface area for selective enrichment of phosphopeptides by mass spectrometric analysis

In this study, mesoporous TiO 2 microspheres were synthesized by simple hydrothermal reaction, and successfully developed for phosphopeptides enrichment from both standard protein digestion and real biological sample such as rat brain tissue extract. The mesoporous TiO 2 microspheres (the diameter size of about 1.0 μm) obtained by simple hydrothermal method were found to have a specific surface area of 84.98 m 2/g, which is much larger than smooth TiO 2 microspheres with same size. The surface area of mesoporous TiO 2 microspheres is almost two times of commercial TiO 2 nanoparticle (a diameter of 90 nm). Using standard proteins digestion and real biological samples, the superior selectivity and capacity of mesoporous TiO 2 microspheres for the enrichment of phosphorylated peptides than that of commercial TiO 2 nanoparticles and TiO 2 microspheres was also observed. It has been demonstrated that mesoporous TiO 2 microspheres have powerful potential for selective enrichment of phosphorylated peptides. Moreover, the preparation of the mesoporous TiO 2 microspheres obtained by the hydrothermal reaction is easy, simple and low-cost. These mesoporous TiO 2 microspheres with the ability of large scale synthesis can widely be applied for phosphorylated proteomic research.

Comparative evolved gas analyses of crystalline and amorphous titanium(IV)oxo-hydroxo-acetylacetonates by TG-FTIR and TG/DTA-MS

Decomposition of crystalline and amorphous titanium(IV)oxo-acetylacetonate chemicals have been studied in situ up to 800 °C in flowing air by simultaneous thermogravimetric and differential thermal analysis coupled online with quadrupole mass spectrometer (TG/DTA-MS) and FTIR spectrometric gas cell (TG-FTIR) for the analysis of evolved gases (EGA) in order to get more information about pyrolytic processes taking place at elevated temperatures during smooth TiO 2 layer processing. Crystalline samples (characterized by XRD, PDF 00-35-1778 reference pattern) are releasing acetylacetone (acacH) vapors already from 140 °C onwards. At 245 °C, after an acceleration of this release process, a huge and sharp exothermic heat effect also occurs and results in additional evolution of acetic acid, CO 2, H 2O, and CO. Minute amount of unidentified volatile species with ion fragments not higher than m/ z = 152 are also detected up to 285 °C. The remaining organic residues are burning out from the solid phase in two further exothermic stages until 500 °C. While an amorphous hydrated sample (with low acetylacetonate content) releases first 6.6% of water vapor until 140 °C, then acetone and acetylacetone up to 300 °C. Between 215 and 385 °C, some acetic acid, CO 2, and CO is also evolved. Formation of CO 2 is detected till 650 °C. At 800 °C, the anatase: rutile TiO 2-ratio were 11:89 and 84:16 for the well-crystallized and the amorphous sample, respectively.

Fabrication of TiO 2 μ-donuts by sol–gel spin coating using a polymer mask

TiO 2 μ-donuts have been fabricated on glass and silicon substrates using polymer masks in combination with a sol–gel technique. Cylindrical poly(methyl methacrylate) (PMMA) nanopillars have been created using a composite polymer of polystyrene (PS) and PMMA followed by careful removal of the PS. Atomic force microscopy (AFM) analyses show that the height and diameter of the PMMA cylinders used as the mask are 440 ± 5 nm and 2.1 ± 0.2 μm, respectively. The cylindrical PMMA nanopillars have been coated with the sol of the TiO 2 precursor by a spin coating technique and annealed in air at elevated temperature to remove the PMMA mask. Removal of the PMMA mask has resulted in the formation of well ordered μ-donuts of TiO 2 on silicon surfaces. The interior and exterior heights of the TiO 2 μ-donuts are found to be 373 ± 152 nm and 457 ± 136 nm, respectively; and the interior and exterior diameters of the TiO 2 μ-donuts are found to be 1.33 ± 0.63 μm and 2.82 ± 0.50 μm, respectively. X-ray photoelectron spectroscopy (XPS) spectra of the TiO 2 μ-donuts as well as the smooth TiO 2 thin film showed signals from Ti and O confirming the presence of TiO 2 with Ti 2p 3/2 and O 1s peaks at 458.8 eV and 530.4 eV, respectively. The O 1s peak of the TiO 2 μ-donuts shows another peak at binding energy 532.0 eV due to SiO 2, as during annealing, the PMMA evaporates and the Si substrate is exposed. The X-ray diffractometer (XRD) pattern of the smooth TiO 2 thin film indicates that the anatase phase is present, with the characteristic peaks observed at 2 θ values of 25.4°, 37.4°, and 48° corresponding to (1 0 1), (0 0 4), and (2 0 0) planes, respectively. UV–vis absorption spectra of TiO 2 μ-donuts on glass showed an unusual absorption of light in the visible region at ∼524 nm in addition to the usual UV absorption at ∼337 nm.

The influence of surfactants on the roughness of titania sol–gel films

Substrate dipping in a composite sol–gel solution was used to prepare both smooth and rough thin films of titanium dioxide (TiO 2) on commercial fiberglass. The deposition of a composite film was done in a beaker using a solution of titanium (IV) isopropoxide as the sol–gel precursor and cetyltrimethyl ammonium bromide as the surfactant. In order to establish a correlation between experimental conditions and the titanium oxide produced, as well as the film quality, the calcined samples were characterized using Raman spectroscopy, UV–vis spectrophotometry, scanning electron microscopy and atomic force microscopy. One of the most important results is that a 61-nm TiO 2 film was obtained with a short immersion of fiberglass into the sol–gel without surfactant. In other cases, the deposited film consisted of a titanium precursor gel encapsulating micelles of surfactant. The gel films were converted to only the anatase phase by calcining them at 500 °C. The resulting films were crystalline and exhibited a uniform surface topography. In the present paper, it was found that the TiO 2 films prepared from the sol–gel with a surfactant showed a granular microstructure, and are composed of irregular particles between 1.5 and 3 μm. Smooth TiO 2 films could have useful optical and corrosion-protective properties and, on other hand, roughness on the TiO 2 films can enhance the inherent photocatalytic activity.