Mesoporous TiO2 Films Research Articles

Improved electrochromic device based on mesoporous TiO2 and NiO films

Fabrication of electrochromic films with micro/nanostructures is one of the most feasible ways to improve their properties for high-performance electrochromic devices (ECDs). In this work, mesoporous TiO2 and NiO electrochromic films are prepared by sol-gel technique with an auxiliary solvent of F108 (PEO[Formula: see text]PPO[Formula: see text]PEO[Formula: see text]). By adjusting the content of F108 and heat treatment temperature, the transparent and uniform mesoporous films are successfully prepared. The TiO2 and NiO films are composed of inter-connected nanoparticles with a size of about 20 nm. The thicknesses of the films are about 300 nm and the mesoporous sizes are about 13 nm. The films have a short response time during the electrochromic process. When supplied with positive/negative voltages for 50 s, the coloring/bleaching times of TiO2 and NiO mesoporous films are 15/13 and 17/12 s, respectively. The ECD fabricated with TiO2 and NiO mesoporous films shows good electrochromic properties: short response time (14/19 s, for bleaching/coloring time), wide transmittance modulation range ([Formula: see text]37.21% at 540 nm), high coloration efficiency (CE) (100.6 cm2/C at 540 nm) and outstanding cycle stability (800 cycles). These are attributed to the mesoporous channels of films, which can increase reaction activity site, shorten ions transport path, and thus improve electrochromic reaction.

Electrodeposited mesoporous TiO2 thin films and their application as the scalable electron transport layer for perovskite solar modules

In this study, we present the utilization of electrodeposited TiO2 mesoporous film (ED-MS-TiO2) as the electron transport layer (ETL) for perovskite solar cells, especially marking the first report of its application in perovskite solar modules. In the first part of this paper, we refine the electrodeposition process to enhance the porosity of the ED-MS-TiO2 thin film by elevating the ED temperature from room temperature to a mild 60 °C. Notably, the ED-MS-TiO2 ETL fabricated at 60 °C demonstrates comparable charge extraction capability and conversion efficiency to the benchmark ETL produced via the widely adopted spin-coating technique, achieving a remarkable 20.5 %. Furthermore, we demonstrate the immense superiority of the ED process in achieving uniformity in the preparation of large-area ETLs. Our current findings reveal that ED-MS-TiO2 exhibits exceptional uniformity control, with a thickness distribution of 122.69 ± 8.39 nm on a 100 cm² substrate, while its spin-coated counterpart exhibits poor thickness control, measuring 135.72 ± 50.72 nm. Moreover, perovskite solar modules (5 cm × 5 cm) employing the optimized ED-MS-TiO2 ETL attain an impressive efficiency of 15.63 %, surpassing counterparts utilizing spin-coated TiO2 ETLs, which achieve only 9.70 %.

Probe Beam Deflection study of Au Nanoparticles Supported into TiO2 Mesoporous Films

Mesoporous thin films modified with nanoparticles of metal (Au) have been used for the fabrication of an ultra‐microelectrode array (UMEA). For the first time, UMEAs were studied using probe beam deflection (PBD) and cyclic voltammetry. The study was carried out using the [Fe(CN)6]3‐/ [Fe(CN)6]4‐ couple as a redox probe. The electrochemical response is that of an array of nanoelectrodes. The effects of scan rate on the current and PBD signal profiles are discussed in the context of mass transport within the pores and at the solution‐electrode interface. The study suggests that the combination of PBD and CV allows a better understanding on the mass transport phenomena in this type of UMEAs of complex architecture.

Spectroelectrochemical determination of the conduction band level of mesoporous titanium dioxide semiconductor in diverse reaction media

AbstractThe conduction band edge (ECB) energy levels of a mesoporous TiO2 film were investigated in aprotic dimethylformamide (DMF) and aqueous media to explore the influence of various proton additives and electron donors. Spectroelectrolysis (SE) technique was employed to measure the ECB in non‐aqueous solvents, revealing a significantly negative ECB in dry non‐aqueous solvents compared to values obtained in aqueous solvents. In non‐aqueous DMF, the ECB of TiO2 was found to be highly dependent on the proton‐donating additive due to the establishment of a proton adsorption–desorption equilibrium, reaching –(1.42–1.94) V versus SCE. The introduction of a well‐known electron donor, 1,3‐dimethyl‐2‐phenyl‐1,3‐dihydrobenzimidazole (BIH) led to a slight positive shift in the TiO2 ECB, indicating that the electron donor contributes to the to the CB energetics of the mesoporous TiO2 films. Under aqueous conditions and in the presence of various electron donors (TEA, TEOA, ascorbic acid, EDTA•2Na, and sodium ascorbate), the proton‐donating/accepting capacity of the additive significantly influenced the pH of the aqueous solvent, causing changes in the TiO2 ECB across the electrolyte solution. This study emphasizes the crucial role of proton additives and electron donors in influencing the CB energetics of mesoporous TiO2 electrodes and aims to determine the extent to which the ECB of TiO2 can shift as a result of the adsorption and intercalation of protons on its surface. The findings obtained herein contribute to the understanding of the energy efficiency of TiO2‐mediated photocatalytic systems in various solvent environments.

Highly efficient photoelectrochemical aptasensor based on CdS/CdTe QDs co-sensitized TiO2 nanoparticles designed for thrombin detection.

A photoelectrochemical (PEC) sensor for the sensitive detection of thrombin (TB) was established. Co-sensitized combination of TiO2 nanoparticles combined with modified cadmium sulfide and cadmium telluride quantum dots (CdS/CdTe QDs) was utilized as a photoactive material. Successful growth of CdS/CdTe quantum dots on mesoporous TiO2 films occuredby successive ion-layer adsorption and reaction. This interesting formation of co-sensitive structure is conducive to enhancing the photocurrent response by improving the use rate of light energy. Additionally, the step-level structure of CdS/CdTe QDs and TiO2 NPs shows a wide range of visible light absorption, facilitating the dissociation of excitons into free electrons and holes. Consequently, the photoelectric response of the PEC analysis platform is significantly enhanced. This constructed PEC aptasensor shows good detection of thrombin with a low detection limit (0.033pM) and a widelinear range (0.0001-100nM) in diluted actual human serum samples. In addition, this PEC aptasensor also has the characteristics of good stability and good reproducibility, which provides a novel insight for the quantitative measurement of other similar analytes.

Study of chlorophyll dye from peppermint (mentha spicata) used as a sensitizer in TiO2 solar cells

Abstract Chlorophyll from peppermint (mentha spicata) was evaluated as a natural dye sensitizer in TiO2 solar cells. The final photoconversion efficiency depended on the solvent used as chlorophyll dispersant and the technique used to sensitize the mesoporous TiO2 film. Evaluated sensitization techniques included pipetting, immersion, and electrophoresis. Best solar cell performance was obtained using methanol as solvent simultaneously with electrophoresis. A short circuit current density (J sc) of 0.174 mA/cm2 and an open circuit voltage (V oc) of 0.508 V were obtained. The photoconversion efficiency reached 0.39 %. However, sensitizing by the pipetting technique allowed a photoconversion efficiency of 0.35 % with better reproducibility.

Insights into the Interfacial Charge Transfer Dynamics in Semiconductor–Molecular Catalyst Assemblies for Photo–Induced CO2 Reduction

AbstractThis mini–review summarises examples of photo and photoelectrochemical CO2 reduction reactions (CO2RR) using semiconductor–molecular catalyst–based hybrid assemblies in which studies of charge transfer dynamics were also performed. In these catalysts, the grand challenges are controlling ultra–fast one–electron charge separation and simultaneously governing its impact on the efficiency and product selectivity in the multielectron and multi–proton–assisted CO2RR. In practice, several unwanted electron recombination processes occur in the femtosecond to millisecond timescale range impacting the overall catalysis efficiency. Titanium di‐oxide (TiO2) nanoparticle, mesoporous TiO2 film, copper indium sulphide (CuInS2) quantum dots were used as semiconductor materials, in turn rhenium (I) bipyridine, cobalt (II) terpyridine, cobaloxamine complex, and iron (III) porphyrins were investigated as molecular catalysts. The results of the charge transfer dynamic studies operating in such hybrid systems shed light on their charge accumulation processes, their rate constants for the intramolecular charge transfer processes and the decay lifetimes of the different excited state species that are produced. Moreover, a comprehensive understanding of the catalysts’ charge transfer dynamics is crucial to identifying detrimental charge recombination pathways. These undesired pathways can be used as rational basis for improving the design of future multi–redox–driven hybrid catalysts.

Laser processing of Li-doped mesoporous TiO2 for ambient-processed mesoscopic perovskite solar cells

A rapid and scalable laser-assisted process to manufacture Li-doped mesoporous TiO2 films for ambient-processed perovskite solar cells.

Colloidal TiO2-Modified Mesoporous Electron Transport Layer in Perovskite Solar Cells

The electron transport layer (ETL) is a crucial part in perovskite solar cells (PSC) as it specifically governs the charge extraction at the perovskite/ETL interface. In this study, methylammonium lead iodide-based PSCs with an n-i-p structure were fabricated and modified by adding colloidal TiO2 into the mesoporous TiO2 film as ETL. The effect of the colloidal TiO2 addition on the PSC performance was investigated for ETL comprising different types of TiO2 particles, i.e. P25 and anatase TiO2. Despite producing lower performance than the PSC made with commercial paste, the power conversion efficiency of the PSCs could be improved with the introduction of colloidal TiO2 solution. An optimum condition was observed depending on the type of TiO2 particle, where the best performing device was achieved with colloidal TiO2 of 0.4 and 0.2 mL for P25 and anatase TiO2, respectively. The amount of colloidal TiO2 in samples with P25 overall had less impact than the samples with anatase TiO2.

Nanoscale Phase Separations for Versatile Synthesis of Centimeter‐Sized Hierarchically Mesoporous Metal‐Oxide Films

Hierarchically porous metal‐oxide materials have immense potential for many fields, which are highly desired to tackle the limitations of mono‐porous architectures, and to combine the advantages of different pore scales. Herein, a simple small‐molecule‐assisted interfacial assembly strategy, which elegantly combines the mesoscale block copolymers (BCPs)‐directed coassembly and nanoscale phase separations of dicyandiamide (DCDA), is developed for the synthesis of centimeter‐sized inorganic metal‐oxide films with multiscale porosity. The synthetic approach is versatile and can be broadly applied for the fabrication of hierarchically mesoporous metal‐oxide films with single (TiO2, ZrO2, Al2O3) or binary components (TiO2–ZrO2 and TiO2–Al2O3) on various substrates ranging from 1D to 3D. The as‐prepared films possess ordered structures, uniform thickness, interconnected pores, highly crystallized frameworks, and high surface areas (>200 m2 g−1). As a proof of concept, the photoelectric device assembled by the hierarchically mesoporous TiO2 films (denoted as H–TiO2) shows excellent performance, including a high photocurrent of 0.68 mA cm−2 and outstanding stability. The presented method may provide new insight into the controllable synthesis of hierarchically porous materials.

X-ray photoelectron spectroscopy of surface-treated TiO2 mesoporous film by 500 eV argon ion beam

The surface sensitivity profiling feature of x-ray photoelectron spectroscopy (XPS) regularly calls for sample surface treatment through irradiation with beam of argon ion. The beam potentially ensures surface cleanliness against contaminations under ultra-high vacuum conditions for elemental identification. This work systematically and elegantly employs an argon ion (Ar+) beam to create oxygen vacancies in TiO2 mesoporous film at different time of radiation exposure. Survey spectra acquired from XPS compositionally indicates the presence of oxygen (O 1s), titanium (Ti 2p) and carbon (C 1s). Three peaks were detected in the spectra of O 1s at high-resolution XPS which can be linked to oxygen vacancy, lattice oxygen and adsorbed oxygen while increase in radiation exposure time leads to increase in oxygen vacancy concentration. The presence of Ti3+ was observed in Ti 2p spectra analysis and indicates the creation of oxygen vacancies due to Ti4+ reduction. The potential of Ar+ to induce oxygen vacancies in TiO2 mesoporous film as demonstrated in this work would facilitate photocatalytic activity enhancement of TiO2 semiconductor films for different applications.

Enhanced photoelectrochemical performance of mesoporous TiO2 photoanode prepared by multi-step evaporation-induced self-assembly method

Mesoporous TiO2 films are promising in photocatalysis and photoelectrochemistry for energy and environment applications, because of its high specific surface area and regular mesopore structure. However, the performances of mesoporous TiO2 films are still limited by low catalyst loading due to the damage during the preparation process. In this study, a multi-step evaporation-induced self-assembly method is proposed to develop a mesoporous TiO2 photoanode with high catalyst loading. The prepared mesoporous TiO2 photoanodes possess not only high catalyst loading without damage but also large specific surface area, which provides more active sites. Moreover, regular mesopore structure is remained to benefit mass transport. Because of these merits, the mesoporous TiO2 photoanode prepared by the multi-step evaporation-induced self-assembly method exhibits superior performance than does conventional nanoparticles-packed TiO2 photoanode. The superiority of the mesoporous TiO2 photoanode prepared by this multi-step evaporation-induced self-assembly method is also demonstrated by incorporating it into a photocatalytic fuel cell. The short circuit current density and maximum power density increase by 90.9% and 25.0%, respectively. The present work provides a new way to prepare high-performance mesoporous TiO2 films for various photocatalytic and photoelectrochemical applications.

Excitation-Wavelength-Dependent Charge Injection and Hole Localization in Diblock Oligomers Anchored to TiO2.

A series of diblock oligomers containing oligothiophene (Tn, n = 4, 5) and 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadizole (TBT) segments, functionalized with carboxylic acid anchoring groups, were prepared and anchored to mesoporous TiO2 films to study wavelength-dependent interfacial electron transfer mechanisms. Thin films of the surface-anchored diblock oligomers contained two absorption bands centered at 400 and 500 nm, corresponding to the Tn and TBT blocks, respectively. Pulsed-laser excitation of the oligomer-sensitized films yielded local excited-states that promoted electron injection into TiO2. The injection pathway was dependent on the excitation wavelength, as electron injection occurred from the oligomer block that was locally excited. Recombination between the injected electron and the oxidized oligomer was sensitive to the bridging unit that separates the oligomer conjugated segments (-C≡C- vs trans-Pt(PBu3)2-). When the bridge facilitated strong coupling between the two blocks (-C≡C- bridge), the excitation wavelength had no effect on the recombination pathway, as the hole was delocalized over the entire oligomer. However, in the weak coupling case (Pt(PBu3)2- bridge), selective excitation resulted in wavelength-dependent hole localization that persisted to the μs time scale, providing control over the recombination pathway by varying the excitation wavelength. Dye-sensitized solar cells (DSSCs) were fabricated by using the diblock oligomers as sensitizers. The photocurrent action spectra were measured, and the absorbed photon-to-current efficiency (APCE) provided further insight into the electron-transfer mechanisms that are operative under continuous illumination.

Synthesis of TiO2 mesoporous film with the effect of 200 eV argon ion beam on its surface chemistry

This work presents an elegant and systematic method to study the effect of a 200 eV Ar ion beam on TiO2 semiconductor mesopores film. Argon ion beam (Ar+) of 200 eV energy was irradiated on the prepared TiO2 film (thickness ∼ 20 μm) at different irradiation times of 0, 150, 250, 350, and 450 s. The irradiated samples were subsequently characterized using x-ray photoelectron spectroscopy (XPS). The survey spectrum reveals the presence of elemental composition of titanium (Ti 2p), oxygen (O 1s), and carbon (C 1s). The compositional ratio of Ti3+/Ti4+ increases and lattice oxygen/Ti 2p decreases with an increase in irradiation time which confirms the creation of oxygen vacancy as the irradiation time progresses. The demonstrated oxygen vacancy induction potentials would be highly meritorious in enhancing the photocatalytic activity of the semiconductor under visible light for various applications.

2000-eV argon ion beam induced formation of multiple chemical states in titanium dioxide mesoporous film

Oxygen vacancies were created on the surface of TiO2 mesoporous film after exposure to a 2000 eV argon ion beam. Confirmation of the presence of the vacancies was conducted through x-ray photoelectron spectroscopy analysis which reveals Ti 2p, O 1s, C 1s, and Ar 2p chemical states at different binding energies. Ti 2p spectra show five distinct peaks corresponding to Ti2+ 2p1/2, Ti3+ 2p3/2, Ti4+ 2p3/2, Ti3+ 2p1/2, and Ti4+ 2p1/2 states while the Ti4+ continuously reduced to Ti3+ and Ti2+ as the irradiation time of Ar+ increases. The Ar+ irradiation leads to the lower binding energy of the Ti 2p state with an increase in irradiation time while the binding energy of O 1s becomes higher with irradiation time. The peaks correspond to lattice oxygen; oxygen vacancy and adsorbed oxygen were observed in high-resolution O 1s spectra while the peak area ratio of oxygen vacancy with lattice oxygen increases with irradiation time. The atomic percentage of C 1s decreases with irradiation time while that of Ti 2p, O 1s, and Ar 2p increases with irradiation time. An increase in irradiation time leads to insignificantly shifting of the valence band edge towards the conduction band. The observed response of the prepared nano-particle TiO2 after 2000 eV Ar+ exposure which conveniently creates oxygen vacancies in the crystallographic structure of the semiconductor could be a versatile approach to enhancing the photocatalytic activity of the semiconductor for various industrial and technological applications.

Electrochemical Properties of Silver Nanoparticles in Mesoporous Silica and Titania Films: Specific Behavior of Titania Composite.

Electrochemical behavior of silver nanoparticles in mesoporous oxides electrodes is investigated. Mesoporous SiO2 and TiO2 films deposited on FTO (fluorine-doped tin oxide) and containing Ag nanoparticles (NPs) are used as electrodes. The study of voltammetric curves (CVs) and the diffusion of Ag+ ions out of the films highlight the importance of the retention of Ag+ ions by the TiO2 films. By varying several factors such as the speed rate or the initial potential, we observe the existence of the two potentials' anodic peaks. These are explained by the nature of two silver NP populations created in two distinct areas in the film and with different size distributions, as shown by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. The size distributions of the two NP populations allow the position and shape of each of the oxidation peaks in the CVs to be adequately simulated.

Tuning the oxidation state of titanium dioxide mesoporous film by 1000 eV argon ion beam irradiation

This work proposes the creation of oxygen vacancies on the surface of TiO2 mesoporous film using a 1000 eV argon ion (Ar+) beam. After X-ray photoelectron spectroscopic characterization, the survey spectra of TiO2 nano-particles reveal the presence of oxygen (with chemical state O 1s), titanium (with chemical state Ti 2p), carbon (with chemical state C 1s) and argon (with chemical state Ar 2p) while the concentrations of each chemical states vary with an irradiation time of the Ar+ beam. The acquired Ti 2p spectra show five peaks at high resolution which correspond to Ti4+ 2p3/2, Ti4+ 2p1/2, Ti3+ 2p3/2, Ti3+ 2p1/2, and Ti2+ 2p1/2. The concentrations of Ti2+ and Ti3+ increase with irradiation time while the concentrations of Ti4+ decrease as the irradiation time increases. Three peaks characterize high-resolution spectra of O 1s which correspond to lattice oxygen, oxygen vacancy, and adsorbed oxygen. The peak area of lattice oxygen decreases with irradiation time while that of oxygen vacancies increases with irradiation time which shows the creation of oxygen vacancies at the expense of contaminant removal due to Ar+ exposure. Valence spectra analysis shows an insignificant effect on the valance band as the sample exposure to Ar+ increases. This proposed method of oxygen vacancy creation would facilitate the effective utilization of TiO2-based semiconductors in addressing many photo-catalytic challenges and widening the sunlight absorption capacity of the semiconductor.

Electro- and Photoinduced Interfacial Charge Transfers in Nanocrystalline Mesoporous TiO2 and TiO2/Iron Porphyrin Sensitized Films under CO2 Reduction Catalysis.

Electro- and photochemical CO2 reduction (CO2R) is the quintessence of modern-day sustainable research. We report our studies on the electro- and photoinduced interfacial charge transfer occurring in a nanocrystalline mesoporous TiO2 film and two TiO2/iron porphyrin hybrid films (meso-aryl- and β-pyrrole-substituted porphyrins, respectively) under CO2R conditions. We used transient absorption spectroscopy (TAS) to demonstrate that, under 355 nm laser excitation and an applied voltage bias (0 to -0.8 V vs Ag/AgCl), the TiO2 film exhibited a diminution in the transient absorption (at -0.5 V by 35%), as well as a reduction of the lifetime of the photogenerated electrons (at -0.5 V by 50%) when the experiments were conducted under a CO2 atmosphere changing from inert N2. The TiO2/iron porphyrin films showed faster charge recombination kinetics, featuring 100-fold faster transient signal decays than that of the TiO2 film. The electro-, photo-, and photoelectrochemical CO2R performance of the TiO2 and TiO2/iron porphyrin films are evaluated within the bias range of -0.5 to -1.8 V vs Ag/AgCl. The bare TiO2 film produced CO and CH4 as well as H2, depending on the applied voltage bias. In contrast, the TiO2/iron porphyrin films showed the exclusive formation of CO (100% selectivity) under identical conditions. During the CO2R, a gain in the overpotential values is obtained under light irradiation conditions. This finding was indicative of a direct transfer of the photogenerated electrons from the film to absorbed CO2 molecules and an observed decrease in the decay of the TAS signals. In the TiO2/iron porphyrin films, we identified the interfacial charge recombination processes between the oxidized iron porphyrin and the electrons of the TiO2 conduction band. These competitive processes are considered to be responsible for the diminution of direct charge transfer between the film and the adsorbed CO2 molecules, explaining the moderate performances of the hybrid films for the CO2R.

Self-cleaning application of mesoporous ZnO, TiO2 and Fe2O3 films with the accommodation of silver nanoparticles for antibacterial activity

BackgroundThe infections spread in healthcare circumstances is a growing and persistent issue worldwide, motivated by the development of microbial durability to disinfectants and antibiotics. Self-cleaning or disinfecting is one of the most attractive and promising technologies for glass windows, buildings, operating rooms, and hospitals. MethodThe transparent films of mesoporous TiO2, ZnO and Fe2O3 with different layers were synthesized and coated with silver nanoparticles through the sol-gel technique. The contact angles of the Ag/ZnO, Ag/TiO2 or Ag/Fe2O3 films were found to be less than 10°, indicating the obtained films were superhydrophilic. These films were tested for their disinfection ability for different bacteria species under direct light illumination. Significant FindingsResults have shown that Ag/TiO2 exhibited strong anti-bactericidal performances, and the Ag/TiO2 1-layer (1L), 2-layer (2L) and 3-layer (3L) films were the best of all treatments producing consistently higher antibacterial activity with Vibrio parahaemolyticus, Aeromonas hydrophila, and Bacillus subtilis in the reducing order of efficacy. The exposure time of 3 h was sufficient to reduce the cell counts of bacterial strains. The reason behind the higher antibacterial activity of Ag/TiO2, Ag/ZnO and Ag/Fe2O3 films compared with pristine ZnO, Fe2O3 and TiO2 films might be the surface plasmon resonance of Ag nanoparticles. The small Ag clusters create sinks for electrons, thus expediting the photoinduced electron- holes separation and enhancing the antibacterial activity. Therefore, the highest antibacterial activity observed for the Ag/TiO2 films was referred to as the most effective separation of charge carriers during the fast charge transfer.

Effects of hydrothermal treatment of cellulose nanocrystal templated TiO2 films on their photodegradation activity of methylene blue, methyl orange, and rhodamine B

Transparent mesoporous TiO2 films with enhanced photocatalytic degradation efficiency were systematically synthesized. The films were prepared using a mixed sol containing a cellulose nanocrystal (CNC) template that was spin-coated onto an ITO substrate, followed by calcination at 400 °C for 1 h. Subsequently, the fabricated films were subjected to hydrothermal treatment in a pure aqueous medium for various periods of time (1, 2, and 4 h) and at different temperatures (150 and 250 °C). The surface area and crystallite size of the prepared TiO2 film were increased and decreased from 76.7 m2/g and 12.78 nm (without the template) to 127.3 m2/g and 9.95 nm (with the template), and then to 233.4 m2/g and 4.43 nm (1 h and 150 °C) with hydrothermal treatment, respectively. Hydrothermal treatment plays an important role in enlarging the surface area, and decreasing the crystallite size. Furthermore, the optimized TiO2 film exhibits exceptional photodegradation activity towards organic dyes with performance nearly equal to that of the standard photocatalyst. Because of the exceptional properties of the prepared optimized TiO2 film, the adsorption of organic dyes on its surface increases, which promotes the photocatalytic degradation efficiency during light irradiation.