Porous TiO2 Films Research Articles

Morphological and electrical study of porous TiO2 films with various concentrations of Pluronic F-127 additive

Porous TiO2 thin films were synthesized by dip-coating method on silicon substrates. Pluronic F-127 (F127), a structure-directing agent, was used to promote the evolution of pores during the synthesis of TiO2 thin films. The concentration of F127 was varied from 0.3 to 3.75 mM. FESEM micrograph has confirmed the presence of porous morphology, whereas XRD and Raman studies have revealed the formation of the anatase phase of the sample. Capacitance–voltage (C–V) measurement was carried out using TiO2 based metal oxide semiconductor (MOS) capacitor structure, where F127 was incorporated in the oxide layer. The oxide charge density was found to be increased with the concentration of F127 co-polymer. Interface trap density has a maximum value of 6.6 × 1012 eV−1 cm−2 after the addition of 3 mM of F127. It was found out that the 3 mM of F127 has better memory effect during the resistive switching study.

Porous TiO2 Film Immobilized with Gold Nanoparticles for Dual-Polarity SALDI MS Detection and Imaging.

Surface-assisted laser desorption/ionization (SALDI) mass spectrometry (MS) has become an attractive complementary approach to matrix-assisted laser desorption/ionization (MALDI) MS. SALDI MS has great potential for the detection of small molecules because of the absence of applied matrix. In this work, a functionalized porous TiO2 film immobilized with gold nanoparticles (AuNPs-FPTDF) was prepared to enhance SALDI MS performance. The porous TiO2 films were prepared by the facile sol-gel method and chemically functionalized for dense loading of AuNPs. The prepared AuNPs-FPTDF showed superior performance in the detection and imaging of small molecules in dual-polarity modes, with high detection sensitivity in the low pmol range, good repeatability, and low background noise compared to common organic MALDI matrixes. Its usage efficiently enhanced SALDI MS detection of various small molecules, such as amino acids and neurotransmitters, fatty acids, saccharides, alkaloids, and flavonoids, as compared with α-cyano-4-hydroxycinnamic acid, 9-aminoacridine, and the three precursor substrates of AuNPs-FPTDF. In addition, the blood glucose level in rats was successfully determined from a linearity concentration range of 0.5-9 mM, as well as other biomarkers in rat serum with SALDI MS. More importantly, the spatial distribution of metabolites from the intact flowers of the medicinal plant Catharanthus roseus was explored by using the AuNPs-FPTDF as an imprint SALDI MS substrate in dual-polarity modes. These results demonstrate wide applications and superior performances of the AuNPs-FPTDF as a multifunctional SALDI surface with enhanced detection sensitivity and imaging capabilities.

Carbon-coated porous TiO2 layers templated by core-shell polymer particles: Film processing and charge transfer resistance assessment

The performances of titanium dioxide (TiO2) thin films used in photoelectrochemical applications (solar cells, water splitting, photocatalysis, etc) highly depend on their morphology and interface. In this work, we describe a straightforward strategy for designing conductive carbon-coated TiO2 porous layers allowing for the tuning of interfacial charge transfers. Increased specific surface and improved conductivity are expected from the porosity and the carbon coating, respectively. In practice, polystyrene/polyacrylonitrile (PS-PAN) and polystyrene/polydopamine (PS-PDA) core-shell particles synthesized by emulsion polymerization are considered as templating agents for the production of carbon-coated and ordered porous TiO2 layers. After spin coating deposition of the particles, infiltration of the TiO2 precursor and calcination, voids are created in the film by thermal degradation of the PS cores whereas PAN and PDA produced carbon at the surface of the TiO2 inverse opal matrix. Uncoated PS particles are also considered as benchmark templating agents. Size and composition of the polymer particles as well as the morphology and electronic properties of the corresponding porous TiO2 films are evaluated. In particular, the charge transfer resistance of the films is investigated via Electrochemical Impedance Spectroscopy (EIS) as a preliminary assessment of these unprecedented carbon-coated porous TiO2 layers as semiconducting materials.

A novel regeneration method for deactivated commercial NH3-SCR catalysts with promoted low-temperature activities.

A novel route is developed for regeneration of deactivated commercial NH3-SCR catalysts, which includes an initial in situ construction of anatase TiO2 porous film, followed by loading of MnOx, CeOx, and Mn-Ce mixed oxides as active components. The regenerated catalysts present largely improved low-temperature denitrification performance due to the synergetic effect of MnOx and CeOx. The denitrification efficiency could reach a high value of 97% at 200°C and 100% at 250°C when the Ce-Mn mixed oxides are loaded at the optimized molar quantity ratio of 10:9 (Ce:Mn). Properties and reaction mechanisms of the regenerated catalysts are investigated with characterizations of X-ray photoelectron spectroscopy (XPS), NH3 temperature-programmed desorption (NH3-TPD), H2 temperature-programmed reduction (H2-TPR), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Our results demonstrate that the adsorption and oxidation of NO plays a crucial role for these three catalysts even though a difference exists on the reaction pathways. Graphical abstract.

Synthesis of nanocrystalline ZnS/TiO2 films for enhanced NO2 gas sensing

Highly porous nanocrystalline TiO2 films were sensitized with ZnS semiconductor nanocrystals by using a three-step facile strategy. The TiO2 matrices were firstly impregnated with the zinc bis(benzyl)thiol precursor that, unlike many other metal chalcogenides, is easily dispersible in the most common organic solvents. In the second step of the adopted synthetic strategy, the TiO2 impregnated with zinc thiolate was annealed at 250 °C in order to induce nucleation and growth of ZnS nanocrystals inside the porous matrices as well as on the film surface. A final cleavage in dichloromethane allowed us to remove all residual organic reagents and products. The size of the ZnS nanocrystals can be tuned by variation of the annealing time as shown by X-ray diffraction measurements, without changing the crystallographic phase structure (zincblende structure). Scanning electron microscopy analysis showed a random spatial dispersion of the ZnS nanocrystals and no remarkable aggregation was observed. The sensor device based on TiO2-ZnS nanocomposite was able to detect NO2 gas at 270 °C down to 1 ppm with negligible response towards reducing gases (CO, CH4). Compared to bare TiO2 film, the TiO2-ZnS nanocomposite shows higher sensitivity and lower recovery time towards an oxidant NO2 gas.

Ion-gated transistors based on porous and compact TiO2 films: Effect of Li ions in the gating medium

Ion-gated transistors (IGTs) are attractive for chemo- and bio-sensing, wearable electronics, and bioelectronics, because of their ability to act as ion/electron converters and their low operating voltages (e.g., below 1 V). Metal oxides are of special interest as transistor channel materials in IGTs due to their high mobility, chemical stability, and the ease of processing in air at relatively low temperatures (<350 °C). Titanium dioxide is an abundant material that can be used as a channel material in n-type IGTs. In this work, we investigate the role of the morphology of the TiO2 channel (porous vs compact films) and the size of the cations in the gating media ([EMIM][TFSI] and [Li][TFSI] dissolved in [EMIM][TFSI]) to study their role on the electrical characteristics of IGTs. We found that both the film morphology and the type of gating medium highly affect the electrical response of the devices.

Ni-Doped Titanium Dioxide Films Obtained by Plasma Electrolytic Oxidation in Refrigerated Electrolytes

Porous crystalline Ni-doped TiO2 films were produced using DC plasma electrolytic oxidation in refrigerated H2SO4 aqueous solutions containing NiSO4. The crystalline phase structure consisted of a mixture of anatase and rutile, ranging from ~30 to ~80 wt % rutile. The oxide films obtained at low NiSO4 concentration showed the highest photocurrent values under monochromatic irradiation in the UV-vis range, outperforming pure TiO2. By increasing NiSO4 concentration above a threshold value, the photoelectrochemical activity of the films decreased below that of undoped TiO2. Similar results were obtained using cyclic voltammetry upon polychromatic UV-vis irradiation. Glow discharge optical emission spectrometry (GD-OES) analysis evidenced a sulfur signal peaking at the TiO2/Ti interface. XPS spectra revealed that oxidized Ni2+, S4+ and S6+ ions were included in the oxide films. In agreement with photocurrent measurements, photoluminescence (PL) spectra confirmed that less intense PL emission, i.e., a lower electron-hole recombination rate, was observed for Ni-doped samples, though overdoping was detrimental.

Design, Molecular Modeling and Synthesis of Metal-Free Sensitizers of Thieno Pyridine Dyes as Light-Harvesting Materials with Efficiency Improvement Using Plasmonic Nanoparticles.

Considering the thiophene unit as an electron-rich heterocycle, it is investigated with the aim of elucidating its potential efficiency for solar cell application. With the introduction of active substituents such as COOEt, CONH2 and CN into the thiophene segment, three novel thieno pyridine sensitizers (6a–c), based on donor-acceptor D-π-A construction, are designed and synthesized. The effect of the anchoring groups is investigated based on their molecular orbital’s (MO’s) energy gap (Eg). The electrostatic interaction between the synthesized dyes and metal nanoparticles, namely gold, silver and ruthenium, is believed to improve their performance as organic sensitizers. The dye-sensitized solar cells (DSSCs) are manufactured using the novel diazenyl pyridothiophene dyes, along with their metal nanoparticles conjugates as sensitizers, and were examined for efficiency improvement. Accordingly, using this modification, the photovoltaic performance was significantly improved. The promising results of conjugate (6b/AgNPs), compared with reported organic and natural sensitizers (JSC (1.136 × 10−1 mA/cm2), VOC (0.436 V), FF (0.57) and η (2.82 × 10−2%)), are attributed to the good interaction between the amide, methyl, amino and cyano groups attached to the thiophene pyridyl scaffolds and the surface of TiO2 porous film. Implementation of a molecular modeling study is performed to predict the ability of the thiophene moiety to be used in solar cell applications.

Solution route to large area all-TiO2 one-dimensional photonic crystals with high reflectivity and different structural colors

In this paper, wafer-scale dense and meosoporous TiO2 films are fabricated via spin-coating and thermal treatment. A photo-curable resin, acrylated polytitanoxane tetramer (Ti-resin), is synthesized as the precursor of TiO2 to deposit dense films. The refractive index of TiO2 films at 500 nm is tuned from 2.17 (dense) to 1.49 (porous) by changing film porosity via adding different amount of polystyrene (PS) to the precursor solvent. A reactive compatibilizer containing one mercapto group and three benzyl rings is synthesized to reduce phase separation and prevent film crack of porous films during the calcinations. The deposition protocol is optimized to prevent infiltration of dense TiO2 layers into porous TiO2 layers. Film thicknesses of both dense and porous TiO2 films can be linearly tuned by changing deposition number. All-TiO2 1D photonic crystals with different structural colors are successfully fabricated on quartz and silicon wafers with reflectivity of at least 90%, covering the spectrum from 400 to 800 nm.

Titanium-dioxide nanostructures grown by dual DC/HiPIMS for dye-sensitized solar cell applications

This work reports how the solar conversion efficiency of dye-sensitized solar cells (DSSCs) depends on the crystalline structure of both the compact TiO2 blocking layer (BL) and homoepitaxially grown porous TiO2 mesoporous structure. The films were grown by simultaneous sputtering of titanium targets by DC magnetron and by high-power impulse magnetron systems (HiPIMS). The deposition conditions were managed to produce in situ dense BLs and porous TiO2 films. The only variable was the polarization of the BLs (0 to -200V). The polarization caused phase transformations from pure anatase phase through rutile-anatase mixed phases to rutile phase. The polarization results in decreasing intensity of the anatase (101) peak of the porous layers. The latter promptly decreased linearly the value of the short-current Isc and exponentially the open-circuit voltage Voc of the cells. Another inference is the surface energy of the BLs, which follows an exponential decay as a function of the film polarization. XPS study of the Ti 2p3/2 – Ti 2p1/2 doublet reveals an appearance of a shake-up satellite, whose area exponentially decreases as the polarization potential rises. This phenomenon is discussed and related with other physical aspects of the homo-epitaxially grown films with different texture. The anatase phase content and its purity predefined by the experimental conditions determine the quality of the DSSC, as well as other components such as the dye type, the electrolyte, and the electrode materials.

Effect of Synthesis Conditions on the Structural, Photocatalic, and Self-Cleaning Properties of TiO2 Nanoparticles

TiO2 nanoparticles were synthesized via the hydrothermal method. As-synthesized TiO2 properties were characterized by XRD, EDX, FESEM, FTIR, and UV-Vis spectroscopy. Indicated peaks in XRD patterns confirm formation of TiO2 nanoparticles with the anatase phase. Average crystallite sizes and strain were estimated from the XRD main peaks of all samples through Williamson–Hall method. Optical energy band gap of TiO2 was determined to be about 3.27–3.44 eV, which appeared higher than those of other researches for anatase TiO2 (3.20 eV). Also, increasing temperatures and aging times make the crystallite size increase and the energy band gap decrease. Photocatalytic activity of samples was examined by measuring rate of methylene blue (MB) decomposition. In photocatalytic process, MB was degraded by photocatalytic and adsorption processes. Aging temperature and time were significant in terms of the MB decolorization ability. The optimal synthesis condition of temperature and aging time was obtained at about 130°C and 16 h, respectively. TiO2 nanopowder prepared in the previous step was deposited by the spin-coating method on a glass substrate. Self-cleaning properties of the glass substrate coated with TiO2 nanoparticles were studied by measuring the water contact angle. TiO2 thin films have little photocatalytic activity because of their low area. To overcome this disadvantage, TiO2 porous thin films were deposited on glass substrates using polyethylene glycol (PEG) as a template pore-generating agent. TiO2 thin film with 20 wt % PEG showed better hydrophilic property and a better self-cleaning property. Enhancement of surface wettability due to UV-induced TiO2 hydrophilicity has been evidenced by contact angle measurements.

Efficiency and Stability Enhancement of Fully Ambient Air Processed Perovskite Solar Cells Using TiO2 Paste with Tunable Pore Structure

AbstractCrystallization and nucleation of the perovskite layer in the mesoscopic perovskite solar cells (PSCs) depend on the nucleation sites of the electron transport layer (ETL). The porosity optimization of TiO2 film as an efficient ETL plays an important role in the performance improvement of PSCs. In the present study, nontoxic carbon spheres synthesized with uniform morphology and controllable size under hydrothermal conditions and used as a template to generate the tunable porous TiO2 films. Furthermore, the effect of porosity modification of TiO2 on the formation of perovskite films with large grain size is studied in an ambient atmosphere with humidity higher than 50%. The best TiO2 film is produced with carbon spheres 8 wt% (C8), which results in the formation of a pinhole‐free, and compact‐packed perovskite layer. The fully air processed PSC device with the ETL made of C8 film exhibits an efficiency of 16.66% with reduced hysteresis, which is much superior in performance compared to the standard cell (11.72%). It is believed that this porosity optimization of TiO2 layer is a simple practical strategy for improved stability of fully air processed efficient perovskite solar cells and usable for the fabrication of reproducible compact perovskite layers in uncontrolled laboratories.

Comparison of In-Plane Stress Development in Sol-Gel- and Nanoparticle-Derived Mesoporous Metal Oxide Thin Films.

By using an evaporation-induced self-assembly (EISA) process, mesoporous metal oxide thin films are prepared via molecular precursors undergoing a sol-gel transition or by using nanoparticle dispersions as the starting materials. Both methods are employed together with PIB50-b-PEO45 as the structure-directing agent to produce porous TiO2 and ZrO2 thin films with spherical mesopores of around 14 nm in diameter. These nanoparticle- and sol-gel-derived films were investigated in terms of the intrinsic in-plane stress development during the heat treatment up to 500 °C to evaluate the impact of solvent evaporation, template decomposition and crystallization on the mechanical state of the film. The investigation revealed the lowest intrinsic stress for the nanoparticle-derived mesoporous film, which is assigned to the combination of the relaxing effects of the utilized diblock copolymer and the interparticular gaps between the precrystalline nanoparticles. Furthermore, the residual in-plane stress was studied after annealing steps ranging from 300 to 1000 °C and cooling down to room temperature. Here, TiO2 nanoparticle-derived mesoporous films possess a lower residual stress than the sol-gel-derived mesoporous films, while in the case of ZrO2 films, sol-gel-derived coatings reveal the smallest residual stress. The latter is based on the lower thermal expansion coefficient of the dominant monoclinic crystal phase compared to that of the silicon substrate. Hence, the present crystal structure has a strong influence on the mechanical state. The observation in this study helps to further understand the stress-related mechanical properties and the formation of mesoporous metal oxides.

Porous ceramic foam loading titanium dioxide for photocatalytic degradation of the methyl orange solution

Purpose The purpose of this paper is to provide an investigation on a new kind of photocatalytic material, namely, the porous ceramic foam loading titanium dioxide, which can make an effective photocatalytic degradation of the methyl orange (MO) solution in the wastewater. Design/methodology/approach The natural zeolite powder has been used as the primary raw material to produce a sort of lightweight porous ceramic foam by impregnating polymer foam in slurry and then sintering. With the sol-gel method, a kind of open-cell reticular porous ceramic foam loading TiO2 film was obtained having a good photocatalytic action, and the resultant porous composite product presents the bulk density of 0.3~0.6 g/cm3 to be able to float on water. Findings The MO could tend to be completely degraded in the solution with a certain concentration by the TiO2-loaded ceramic foam irradiated with ultraviolet light, and this composite foam was found to have high degradation efficiency for the MO solution in a wide range of pH. Originality/value This work presents a TiO2-loaded ceramic foam that can effectively photo-catalyze to degrade the MO in water, and the degradation efficiency were examined under different conditions of the MO solution with various pH values.

Effect of cadmium sulfide quantum dots prepared by chemical bath deposition technique on the performance of solar cell

Quantum dots are very tiny semiconductor particles used in solar cells; their optical and electronic properties differ from those of macro particles. They could improve the performance of solar cells if they are prepared in the suitable size. In this work, cadmium sulfide (CdS) quantum dot (QD) thin films were prepared on transparent conductive fluorine-doped tin oxide substrates. The formation and deposition of CdS QDs were optimized using the chemical bath deposition method under varied operating conditions (precursor concentration, and temperature). Chemical bath deposition is an effective method for the deposition of CdS on porous TiO2 films as QDs. The structural, morphological, and optical properties of the prepared CdS thin films were studied using X-ray diffraction, field-emission scanning electron microscopy, Raman spectroscopy and UV-Vis-near infrared spectroscopy. The particle size of the CdS QDs was calculated to be 3–7 nm from the observed X-ray diffraction pattern. The band gap was blue shifted in the UV-Vis absorption spectrum compared with that of bulk CdS, confirming the formation of CdS QDs.

Constructing micro-flower modified porous TiO2 photoanode for efficient quantum dots sensitized solar cells

TiO2 photoanode as the light harvest skeleton and electron transport material plays a critical role in the photovoltaic performance of the quantum dots sensitized solar cells (QDSSCs). In this paper, a bilayer-structured film with micro-flower TiO2 as an overlayer and hierarchical porous TiO2 as an underlayer is fabricated. The hierarchical porous TiO2 film is synthesized by the virtue of foam and the TiO2 micro-flower is introduced by spin-coating method. This TiO2 micro-flower supplies more adsorption sites for CdSe quantum dots, thus leading to the enhanced light harvesting efficiency. The staggered structure between the anatase nanoparticle and the rutile micro-flower will facilitate the separation of electron-hole pairs and promote the injection process of electron. Consequently, the photovoltaic performance of QDSSCs based on the TiO2 micro-flower modified photoanode is about 43% higher than that of the bare porous TiO2 photoanode.

Effect of Mesoporous TiO2 Thicknesses on the Performance of Solid-State Dye-Sensitized Solar Cells

We report the fabrication of solid-state dye-sensitized solar cells (ss-DSSCs), using a metal-free organic dye (D102) as a sensitizer. Mesoporous TiO2 acting as a photoanode, is prepared from TiO2 nanopaste followed by drafting light-absorbing dye molecules. Spiro-OMeTAD is used as a hole transport material (HTM), which has a potential role in the energy conversion process of solid-state dye-sensitized solar cells (ss-DSSCs). Here, TiO2 mesoporous films are used with three different thicknesses (∼ 1.5 μm, ∼ 1.7 μm and ∼ 2.0 μm) for the device fabrication. Various characterizations of optimum TiO2 porous film (with the thickness of ∼ 2.0 μm) are performed such as ultraviolet–visible (UV–Vis) transmission, x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and cross-section scanning electron microscopy (SEM). Transmittance analysis reveals that transparency of the TiO2 films ranges from 70% to 80%. The x-ray diffraction (XRD) pattern of TiO2 shows anatase as its major crystalline phase. The porous structure formation of the TiO2 film is confirmed by scanning electron microscopy (SEM) cross section analysis. Photovoltaic performance of the devices was examined in air. Higher power-conversion efficiency (PCE) of 3.5% is obtained with optimum device thickness (∼ 2.3 μm). The device stability test is performed under continuous illumination for 2 h, showing slightly good air and light stability.

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.

Reactivity of porous titanium oxide film and chitosan layer electrochemically formed on Ti-6Al-4V alloy in biological solution

Uniform porous TiO2 film on Ti-6Al-4V alloy was obtained by hard anodic oxidation and successfully the chitosan layer was electrodeposited. Surface morphology, compositional properties and diffraction patterns were analyzed by scanning electron microscopy with energy dispersive X-ray analysis system and X-ray diffraction. The reactivity of anodic porous TiO2 film in the presence or absence of chitosan layer was investigated by electrochemical methods in biological solution and compared with the reactivity with the unmodified Ti-6Al-4V alloy surface. The electrochemical impedance spectroscopy method was used to compare the response reactivity of the three surfaces. The combination of the high biocompatibility of chitosan and good mechanical characteristics of Ti-6Al-4V alloy make the obtained porous TiO2 film combined with chitosan a promising method to improve the reactivity of medical implants in biological solution.

Processing and Characterization of ZrO<sub>2</sub>-TiO<sub>2</sub> Porous Films by Dip Coating for Application as Environmental Sensors

The main objective of this work is to study and characterize porous ZrO2-TiO2 films on alumina substrates that will be used for the production of porous ceramic sensors for the monitoring of air humidity in environments subject to the incidence of solar radiation. For the production of the films the dip coating technique was adopted. A viscosity study was performed to obtain stable suspensions of ZrO2-TiO2 in isopropyl alcohol with the para-aminobenzoic acid deflocculant (PABA), at concentrations of 10, 12.5 and 15% by weight of solids. X-ray diffraction (XRD) characterizations were performed for the identification of crystalline phases, morphological analyzes by scanning electron microscopy (SEM) and chemical analyzes by energy dispersive X-ray spectroscopy (EDS). The results allowed to determine the minimum value of viscosity and amount of deflocculant to stabilize the suspension. The sensor elements in the form of 1:1 (weight) ZrO2 - TiO2 porous films showed great potential to be used as sensors for the measurement of relative humidity the size and distribution of desirable pores in the porous film for application as moisture sensors was obtained with 12.5 and 15 % by weight ZrO2-TiO2