Nanoporous TiO2 Research Articles

Fabrication and characterization of TiO2 deposited black electroless Ni-P solar absorber

Preparing a selective, efficient, and low-cost solar absorber is one of the main challenges in solar to thermal energy conversion. In this paper, black electroless NiP (ENi-P) solar absorber has been fabricated, and the effect of nanoporous TiO2 antireflection layer (ARL) on its optical and corrosion properties has been investigated. The optimum black coating was obtained by blackening in 9 M nitric acid solution at 50 °C for 40 s, in which a solar absorptance of 99.3% was achieved. Deposition of TiO2 ARL increased the solar absorptance of coating to 99.7% and addition of 0.8 g Pluronic F127 (F127) as pore former, further increased this value to 99.9% and solar-to-heat efficiency of the coating from 78.1 to 78.7%. F127 added coatings exhibited elongated and irregularly shaped pores with dimensions of a few tens of nanometers. Also, deposition of TiO2 ARL decreased the corrosion current density (icorr) of black ENi-P coating in 3.5 wt% NaCl solution from 20 to 4 μA/cm2. The results of this work indicate that the TiO2 deposited black ENi-P coating can be a suitable choice for black coating applications.

Gas response enhancement of VOCs sensor based on Sn doped nanoporous anatase TiO2 nanoparticles at a relative low operating temperature

In this paper, Sn-doped nanoporous anatase TiO2 nanoparticles were prepared via a hydrothermal method without surfactant or template modification. Various techniques were used to analyze the structure, morphology and specific surface area of the as-synthesized samples. The sensor responses for volatile organic compounds (acetone, ethanol, n-butanol and xylene) at the various concentrations under the different operating temperatures were studied. Under the operating temperature of 240 °C, the sensor has good response, linear correlation, repeatability and long-term stability. In particular, the 2.5% Sn/TiO2 nanoparticles show a high gas response with the highest response to 100 ppm VOCs (21.19). These values demonstrate the potential application of 2.5% Sn/TiO2 nanoparticles for VOCs detection. In addition, the mechanism related to advanced performance was studied and proposed.

Chemical-dealloying to fabricate nonconductive interlayers for high-loading lithium sulfur batteries

Lithium sulfur batteries have been recognized as a promising on-board energy-storage technology. One of the challenges in this system is the efficient inhibition of polysulfides shuttle with the low-cost sulfur hosts. In this work, we report the fabrication of nanoporous CeO2 and TiO2 by a novel chemical dealloying approach as a thin nonconductive interlayer to confine polysulfides in the cathodes. The abundant pores provide channels for the transportation of electrolyte, whereas the dissolved polysulfide species are chemically interacted with the metal oxides. Between the two interlayers, CeO2 demonstrates superior performance over TiO2, which is attributed to the appropriate redox window of the Ce3+/Ce4+ couple to in-situ catalyse the polysulfides. The cells with such a configuration exhibit significantly enhanced capacities and long-term stability. Even at a high sulfur loading of 6 mg cm−2, it is demonstrated stable capacities of ∼600 mAh g−1 over 120 cycles. These results suggest chemical dealloying is an efficient approach to prepare desired nanoporous interlayers to achieve practical cycling performance with a commercial sulfur host.

Another look at the role of trapped air in cell adhesion on superhydrophobic materials

Superhydrophobic materials have been widely applied in biomedical applications because of their ability to resist proteins/cells. But controversial results exist as some researches demonstrated enhanced cell adhesion on superhydrophobic materials and trapped air at the solid–liquid interface has been deemed to resist cell adhesion. However to date, the difficulty of keeping the solid–liquid interface from adsorbing air after air elimination hinders our understanding of the role of air in cell adhesion. To directly compare cell behavior on superhydrophobic materials with and without trapped air, an O-ring was fixed on the sample by metal paper clip and a certain amount of buffer was maintained on the surface after trapped air was removed by ultrasonication. The results revealed that the adsorption of BSA and serum proteins on superhydrophobic TiO2 nanopores (TNPs) only slightly increased when air was eliminated. There is no discernible difference in cell adhesion on superhydrophobic TNPs with and without trapped air, whereas cell adhesion was enhanced when basal media were utilized to replace serum-containing media. It implies that trapped air does not necessarily inhibit cell adhesion, whereas serum proteins dominate cell adhesion on superhydrophobic TNPs. The possible reason why air has no significant effect on cell adhesion is that the high adhesion force of superhydrophobic TNPs enables intimate contact of cell with the top of superhydrophobic TNPs and diminishes the effect of air inside naoporous structure.

Colorful nanostructured TiO2 film with superhydrophobic–superhydrophilic switchable wettability and anti-fouling property

Superhydrophobic nanostructured TiO2 film was successfully fabricated on the Ti plate by anodic oxidation and lauric acid modification. By varying the applied voltage, TiO2 films with various nanostructures and colors were prepared. The water contact angles (WCA) on the modified TiO2 film increased as the applied voltage increased, and the highest WCA on the TiO2 nanovesuvianite film was about 161.23°. When the applied voltage was 5 V and 20 V, the obtained TiO2 nanopores and TiO2 nanotubes could be used to build two improved Cassie models for designing superhydrophobic surface. Moreover, the superhydrophobic TiO2 film showed good anti-fouling property, particularly it could maintain superhydrophobicity both when immersed in and taken out from the organic solvents. The superhydrophobic film could be changed into superhydrophilic under ultraviolet (UV) irradiation, and the superhydrophilic film recovered to hydrophobic or superhydrophobic gradually at 60 °C in the dark. Additionally, the superhydrophilic film showed underwater superoleophobicity, which exhibited excellent anti-fouling property by degrading the oil under UV light.

Effect of vortex frictional drag reduction on ordered microstructures

The speed and energy consumption are important indices to evaluate the performance of surface and underwater vehicles. The frictional drag is a key factor influencing the speed and energy consumption of vehicles. We studied the flow field and the drag reduction for different transverse microstructures and found that vortices could be formed in the transverse structures, which reduced the frictional drag. We fabricated different apertures of nanoporous TiO2 films on smooth Ti foils by a two-step low-cost anodic oxidation process. Compared with smooth foils, the nanoporous with a depth of 100 nm and diameter 5.1 μm can decrease drag by 40% under the 1.5 m s−1 velocity condition. The results showed that sliding friction changes to rolling friction at the solid-liquid interface in the transverse grooves. The technology has practical application in drag reduction.

(Invited) Ordered Nanoporous Semiconductors with Controlled Geometrical Structures By Anodization Processes

For the preparation of functional nanodevices for efficient energy conversion, the use of the naturally occurring self-ordered structures is considered an effective process due to its capability of formation of precisely controlled fine nanostructures. To optimize the performance of the obtained devices, fabrication of precisely controlled geometrical structures of metals and semiconductors is essential. For example, the fabrication of highly ordered structures of metal and semiconductors contributes to the efficient absorption of the incident light and also enhance the charge separation in the interfaces. The anodization processes of metals have been widely applied to the fabrication of nanostructures of metal oxides. One advantageous point of this process is controllability of the geometrical structures of the obtained porous structures based on the anodization conditions. In addition, the ordered nanoporous structures can be obtained under the appropriate anodization conditions. In the present report, recent results concerning the preparation of nanoporous semiconductors with controlled geometrical structures and its applications are described. As a typical example, naturally ordered processes1 or pretexturing process2were applied to the preparation of nanoporous TiO2 with controlled geometrical structures. In addition, a high through-put process for the preparation of the through-hole membrane of TiO2 was also described. This process is based on the two-layer anodization used for the preparation of porous alumina through hole membranes3. The tow-layer anodization, which generates TiO2 layers with different solubility, and subsequent selective dissolution generate the through hole membrane of TiO2 4. Repetition of the process allows the high-throughput preparation of the ordered TiO2 through hole membranes. In addition to the self-ordered TiO2, preparation of the ideally ordered TiO2 through hole membranes is demonstrated. The obtained TiO2 through-hole membranes with controlled geometrical structures will be applied to various types of energy conversion devices. P. Roy, S. Berger, P. Schmuki, Angew. Chem. Int. Ed., 50, 2904 (2011).T. Kondo, S. Nagao, T. Yanagishita, N. T. Nguyen, K. Lee, P. Schmuki, H. Masuda, Electrochem. Commun., 50, 73 (2014).T. Yanagishita and H. Masuda, Electrochim. Acta, 184, 80 (2015).T. Yanagishita, H. Inada, T. Kondo, N. T. Nguyen, P. Schmuki, and H. Masuda, J. Electrochem. Soc., 165, E763 (2018).

Improving the photocatalytic performance of a sea-cucumber-like nanoporous TiO2 loaded with Pt Ag for water splitting

Abstract Nanoporous TiO2 loaded with Pt and Ag was prepared by the dealloyed Al Ti Ag Pt ribbons. The hydrogen generation rate via water splitting was measured for the photocatalytic performance. X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), UV–vis diffuse reflectance spectroscopy (UV–vis) and Raman spectroscopy were employed to analyze the synergy among TiO2, Pt and Ag. The results indicate that the synthetic TiO2 shows an anatase structure and that the size of the Pt-rich phase, Ag and Ag-rich phase particles are approximately 6–8 nm. An abundance of pores with about 5 nm in size are distributed on the surface of TiO2, and obtained samples exhibit a larger specific surface area. The hydrogen evolution rate was approximately 1.85 mmol/h/g under full-spectrum irradiation for the dealloyed Al92Ti7.86Pt0.04Ag0.1 ribbons, which was greatly improved compared with that of the dealloyed Al92Ti7.9Ag0.1 ribbons. The analyses indicate that Ag could promote the visible light absorption and that Pt serves as an electron sink for the effective electron-hole pairs separation. Moreover, the appropriate Schottky barrier, formed among the Pt-rich phase, Ag-rich phase and TiO2, effectively suppresses the recombination of electron-hole pairs and improves the utilization of photo-generated electrons.

Preparation of ZnO modified TiO2 nanoporous coatings and their photocatalytic properties

In the present work formation of active nanoporous TiO2 photocatalysts and their modification with ZnO were studied. TiO2 nanoporous coatings on Ti foil with surface area 100cm2 were prepared by using plasma electrolytic oxidation (PEO) method in 0.5M H2SO4 electrolyte and by using 160V DC voltage. For modification of TiO2 coatings with ZnO spray pyrolysis method where used. After preparation samples were dried and calcined at 400°C for 2h in air. Photocatalytic properties of obtained samples were tested by using degradation method of methylene blue (MB) solution under UV and VIS light illumination. Degradation rate of MB were measured by using spectrophotometer. From obtained results reaction constant (k) in the pseudo first order reaction were calculated. As prepared ZnO modified TiO2 nanoporous coating photocatalysts are with higher photocatalytic activity with respect to pure TiO2 nanoporous coating photocatalyst.

Nano-to-macroporous TiO2 (anatase) by cold sintering process

Cold Sintering Process (CSP) was applied on commercial nanopowders to produce nanostructured TiO2 anatase with nano-to-macro porosity. Nanoporous TiO2 based materials were obtained by applying CSP at 150 °C and pressures up to 500 MPa on three TiO2 nanopowders with different specific surface area (s.s.a. = 50, 90 and 370 m2/g), using water as transient aqueous environment. Although TiO2 is insoluble in water, a density of 68% and s.s.a. = 117 m2/g were achieved from the powder with the highest specific surface area. A post annealing process at 500 °C increased the density up to 73% with a s.s.a. = 59 m2/g, and the crystallites dimensions passed from 110 Å in the powder to 130 Å in CSP material and 172 Å after post annealing. Finally, macroporosity was produced by using thermoplastic polymer beads as sacrificial templates within TiO2 nanopowder during CSP, followed by a debonding at 500 °C.

Photo-Sensitive Pb5S2I6 crystal incorporated polydopamine biointerface coated on nanoporous TiO2 as an efficient signal-on photoelectrochemical bioassay for ultrasensitive detection of Cr(VI) ions

An ultrasensitive Visible light-triggered photoelectrochemical (PEC) sensor was designed based on ideal photoactive lead sulfoiodide (Pb5S2I6) as low band gap crystal, which hydrothermally synthesized rapidly at low temperature (160 °C) in hydrochloride acid media followed by its incorporation into polydopamine as reactive photo-biointerface, through a facile in situ electropolymerization method, coated on nanoporous TiO2 grown by anodization on Ti foil. The structure of as-prepared samples and their photoelectrochemical properties were fully characterized. This unique photo-sensitive Pb5S2I6 catalyst-based PEC bioassay was constructed for the detection of low-abundant Cr(VI) ion in real samples. Applying central composite design, individual and mutual interaction effects were evaluated to obtain optimized solution pH, applied potential and radiant light wavelength as operational factors influencing the PEC efficiency for Cr(VI) detection. At optimal condition, the proposed sensor due to effective suppress in electron–hole recombinations showed a very low detection limit of 3.0 nM, over a broad linear concentration range of 0.01–80 μM in addition to high sensitivity versus 1.9 μA/μM Cr(VI). Proposed PEC sensor displayed high selectivity, reproducibility and stability as well as improved excitation conversion efficiency, which make it highly applicable using solar energy. The potential applicability of the designed sensor was evaluated in water, tomato juice and hair color.

Quantum Dot-Sensitized Solar Cells via Integrated Experimental and Modeling Study

The solar energy is one of the potential renewable green energy source considering the availability of sunlight in abundance and the need for clean and renewable source of energy. Quantum dots are semiconductor nanocrystals having considerable interest in photovoltaic research areas. Cadmium sulfide-sensitized solar cells are synthesized by Chemical bath deposition and titanium nanowires were fabricated by hydrothermal method. The synthesized CdS quantum dots are sensitized to nanoporous TiO2 films to form quantum dots-sensitized solar cell applications. The introduction of TNWs enables the electrolyte to penetrate easily inside the film which increases the interfacial contact between the nanowires, the quantum dots and the electrolyte results in improvement in efficiency of solar cell. The goal of our research is to understand the fundamental physics and performance of quantum dot-sensitized solar cells with improved photoconversion efficiency at the low cost based on selection of TiO2 nanostructures, sensitizers and electrodes through an integrated experimental and modeling study.

Visible-light photoelectrochemical responses of dye-sensitized, compact TiO2 thin films deposited by electron beam evaporation

Organic dyes were adsorbed on a compact TiO2 thin film and nanoporous TiO2 film for use as a photosensitizer and their photoelectrochemical (PEC) water-splitting responses were compared under visible light illumination. The compact TiO2 thin film exhibited a much better PEC response than the nanoporous TiO2 film, even though the latter adsorbed a much higher amount of dye, due to its higher surface area. This can be attributed to the depletion layer formed in the compact film morphology, because its electric field suppresses the back transfer (or recombination rate) of the electrons photogenerated by the dye molecules.

COMPUTATIONAL SIMULATION MODEL FOR DYE ADSORPTION IN NANO TIO2 FILM FOR THE APPLICATIONS IN DYE SENSITIZED SOLAR CELLS

The theoretical and computational studies of dye sensitized solar cells (DSSCs) can contribute to a deeper understanding of these types of solar cells. The DSSCs are the novel design of solar cells which could be used as power producing windows or skylights. They represent a particular promising approach to a direct conversion of sunlight into electrical energy at low cost and with high efficiency. The light adsorption occurs in dye molecules adsorbed on a highly porous structure of TiO2 film. Despite the progress in the efficiency and stability of these solar cells, there is still a room of research on some of their operational aspects that are still not understood. One process, for which there is limited information, is the time taken to upload the dye on the TiO2 nanoporous film. The processes followed experimentally for dye uptake is by dipping the TiO2 semiconductor electrode into the dye solution for periods of several hours to several days. However, such long dipping times are not economical for industrial production of DSSCs. The factors controlling this process are not yet fully investigated. We propose a simple model based on the Langmuir isotherms to study and understand the diffusion and adsorption of the dye molecules in TiO2 films. Our computational modelling results show that the adsorption of dye into the TiO2 nanotubes film is controlled by the diffusion coefficient, the adsorption-desorption ratio and the initial dye concentration. Our results show that the initial dye concentration plays an important role on the surface coverage. It is also noted that for a higher concentration shorter immersion time is needed for the sufficient surface coverage. Furthermore, it is observed that for the large values of the adsorption-desorption ratio there is a delay in the diffusion of dye molecules on the surface.

Front Cover: Three‐Dimensional TiO2−Ag Nanopore Arrays for Powerful Photoinduced Enhanced Raman Spectroscopy (PIERS) and Versatile Detection of Toxic Organics (ChemNanoMat 1/2019)

TiO2 nanopore arrays decorated with plasmonic Ag nanoparticles have been fabricated as photo-induced enhanced Raman spectroscopy (PIERS) substrates. These hybrid nanostructures can achieve 8-fold PIERS enhancement over normal SERS due to the light-induced charge transfer from TiO2 to the Ag nanoparticles upon UV irradiation. Furthermore, this robust and recyclable PIERS substrate is versatile and can detect multiple toxic substances at trace levels. The PIERS technique may become an effective way to enhance Raman scattering, which has the great potential for practical portable Raman detection. More information can be found in the Communication by Maofeng Zhang, Jiaqin Liu et al. on page 55 in Issue 1, 2019 (DOI: 10.1002/cnma.201800389).

Two-dimensional TiO2 nanoflakes enable rapid SALDI-TOF-MS detection of toxic small molecules (dyes and their metabolites) in complex environments

High surface area (136 m2 g−1) nanoporous two-dimensional TiO2 nanoflakes are applied as an adsorbent and meanwhile a matrix for toxic small molecule analysis using positive-ion surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF MS). The TiO2 nanoflakes enable one-step enrichment and analysis, greatly simplifying the analysis technique. Due to the high enrichment efficiency and low background noise, small molecule organic contaminants at ppt or even sub-ppt concentrations such as malachite green (10 pg/mL), leucomalachite green (10 pg/mL), cetyltrimethylammonium bromide (0.001 pg/mL), rhodamine B (0.001 pg/mL), and crystal violet (0.1 pg/mL) were detected. In addition, malachite green and its metabolite leucomalachite green at ng/mL concentrations were successfully detected from fish blood and fish extracts, and crystal violet and its homologues at ng/cm2 concentrations were detected from inks on thermal receipt papers obtained from local supermarket.

High performance hydrogen sensor based on Pd/TiO2 composite film

Hydrogen sensors with fast response and recovery rate based on nanoporous palladium (Pd) and titanium dioxide (TiO2) composite films supported by anodic aluminum oxide (AAO) template have been demonstrated. Nanoporous TiO2 film was sprayed on the porous AAO templates, followed by Pd film deposited on TiO2 layer by DC magnetron sputtering. We have researched the detection performance of the hydrogen sensors depending on different thickness of TiO2 layer from 6 to 30 nm with keeping the thickness of Pd as 30 nm. The results have demonstrated the sensors with 10 nm thickness of TiO2 achieve the best performance with a response/recovery time as short as 4/8s at 0.8% and 0.4% hydrogen concentration, respectively. The sensors exhibited very good performance under hydrogen concentrations from 0.4% to 1.8%.

Electron transport improvement in CdSe-quantum dot solar cells using ZnO nanowires in nanoporous TiO2 formed by foam template

A facile in-situ modification of photoanode is proposed to construct a unique hierarchical TiO2/ZnO structure with the aim at suppressing charge recombination rate and enhancing light harvest efficiency. Foam is not only employed as the soft template to fabricate hierarchical porous TiO2 films but also as the carrier to realize in-situ growth of one dimensional ZnO nanowires among the TiO2 nanoparticles. The results revealed that the hierarchical porous TiO2 nanoparticles could provide both large surface areas and suitable porosity for the loading of quantum dots. In the meantime, ZnO nanowire can act as scattering centers for light absorption and offer direct pathways for electron transportation, thus decreasing the undesired charge recombination process. Consequently, the novel ZnO nanowires in-situ modified hierarchical porous TiO2 photoanode are used as photoanode material to boost the performances of CdSe sensitized solar cells by virtue of controlling the moderate growth of ZnO nanowires. As a result, a power conversion efficiency of 3.07% is obtained based on this modified photoanode, which manifests 39.5% improvement compared to that of the cells based on bare TiO2 hierarchical porous films (2.20%) due to the improved interconnections between TiO2 nanoparticles and FTO substrate caused by ZnO nanowires.

Single-Molecule Discrimination of Labeled DNAs and Polypeptides Using Photoluminescent-Free TiO2 Nanopores.

Multicolor fluorescence substantially expands the sensing capabilities of nanopores by complementing or substituting the resistive pulsing signals. However, to date single-fluorophore detection in multiple color channels has proven to be challenging primarily due to high photoluminescence (PL) emanating from the silicon nitride (SiN x) membrane. We hypothesize that the high bandgap of titanium oxide (TiO2) would eliminate the PL background when used as a substrate for a nanopore, and hence enable individual fluorophore sensing during the fast passage of biomolecules through the pore. Herein, we introduce a method for fabricating locally supported, free-standing, TiO2 membranes, in which solid-state nanopores can be readily drilled. These devices produce essentially no PL in the blue-to-red visible spectral range, even when excited by multiple lasers simultaneously. At the same time, the TiO2 nanopores exhibit low electrical noise comparable with standard SiN x devices. Importantly, the optical signal-to-background ratio (SBR) in single-molecule sensing is improved by an order of magnitude, enabling the differentiation among labeled DNA molecules of similar length based solely on their labeling scheme. Finally, the increased SBR of the TiO2 devices allows detection of single fluorophores conjugated to the lysine or cysteine residues of short polypeptides, thus introducing the possibility for optical based peptide/protein discrimination in nanopores.

Photo-Electrochemical Sensing of Dopamine by a Novel Porous TiO₂ Array-Modified Screen-Printed Ti Electrode.

In this paper, the development of a nanoporous TiO2 array-modified Ti electrode for photo-electrochemical (PEC) sensing of dopamine (DA) is reported. A porous TiO2 array-modified electrode was fabricated from the controlled anodic oxidation of a Ti working electrode of commercial screen-printed electrodes (SPE). The anodization process and the related morphological and microstructural transformation of the bare Ti electrode into a TiO2/Ti electrode was followed by scanning electron microscopy (SEM) and UV-visible reflectance spectroscopy (DR-UV-Vis). The modified electrode was irradiated with a low-power (120 mW) UV-Vis LED lamp (λ = 400 nm) and showed good performance for the detection of DA with a large linear response range, a sensitivity of 462 nA mM−1 cm−2, and a limit of detection of 20 µM. Moreover, it showed higher photocurrents in the presence of DA in comparison to some foreign species such as ascorbic acid, uric acid, glucose, K+, Na+, and Cl−. Thus, this proposed low-cost photo-electrochemical sensor, with the advantage of very simple fabrication, demonstrates potential applications for the determination of dopamine in real samples.