TiO2 Scaffold Research Articles

(Invited) Development of Ag- and Sn-Based Colloidal Quantum Dots for Near Infrared Photodetection

Low-cost photodetectors with sensitivity in the second near-infrared window (NIR-II, 1000–1700 nm) are highly demanded. Recently, we made the first demonstration of an Ag2Se colloidal quantum dots (QDs) photodiode with sensitivity up to 1200 nm. By employing secondary phosphine to elevate the precursor reactivity, the Ag2Se QDs with a distinct excitonic absorption peak was achieved. These nanocrystals were deposited from solution into a mesoporous TiO2 scaffold to increase the light absorption and charge separation and reduce the exciton diffusion length. By incorporating a suitable hole-transporting layer between the active layer and Ag anode, the resulting devices showed a responsivity of 4.17 mA/W at 1200 nm.1 Also, Ag2Te QDs are excellent for advancing the detection wavelength. Their synthesis with desired particle sizes, narrow size distribution and high photoluminescence quantum yield (PL QY) is challenging. We systematically investigate critical parameters affecting the synthesis in an organic phase. It shows that high Ag/Te feed ratio leads to smaller size and higher PL QY; under 4:1 Ag/Te feed molar ratio, addition of secondary phosphine leads to narrower size distribution and excellent colloidal stability; under 6:1 Ag/Te feed molar ratio, excess 1-dodecanethiol as a strong ligand slows the nucleation and results in fewer nuclei, leading to a broad size distribution and poor optical properties; additional n-trioctyl phosphine as a weak ligand provides better colloidal stability; and another weak ligand n-tributylphosphine improves Ag2Te QD colloidal stability, focuses size distribution, and enhances PL QY. After optimization relatively large Ag2Te QDs with distinct excitonic absorption peaks (~1050 – 1450 nm) and PL emission peak 1.3 – 1.7 µm (QY up to 6.2%) were obtained. NIR-II photodetection has been demonstrated with a responsivity of ~1.5 mA/W at 1400 nm.2 More recently, we have been developing Sn-based chalcogenide QDs and obtained preliminary photodetection results. These results demonstrate that Ag and Sn chalcogenide QDs offer a low-toxicity route for low-cost fabrication of NIR-II photodetection. Reference: [1] Graddage N, Ouyang J, Lu J, Chu TY, Zhang Y, Li Z, Wu X, Malenfant PRL, Tao Y. Near-Infrared-II Photodetectors Based on Silver Selenide Quantum Dots on Mesoporous TiO2 Scaffolds. ACS Applied Nano Materials 2020, 3: 12209–12217.[2] Ouyang J, Graddage N, Lu J, Zhong Y, Chu TY, Zhang Y, Wu X, Kodra O, Li Z, Tao Y, Ding J. Ag2Te Colloidal Quantum Dots for Near-Infrared-II Photodetectors. ACS Applied Nano Materials 2021, 4: 13587–13601. Keywords: Environmentally Friendly; Near Infrared; Quantum Dots; Photodetection.

Mechanical and Wear Response of TiO2 Scaffolds Processed via Powder Metallurgy

Mechanical and Wear Response of TiO2 Scaffolds Processed via Powder Metallurgy

Reticulated mesoporous TiO2 scaffold for self-cleaning surfaces

Interest in self-cleaning coatings is rising due to their potential to enhance comfort and quality of life in polluted urban environments, driving the search for materials with optimal physical properties. Convergent with this goal, this study investigates the wetting properties and photo-catalytic efficiency of reticulated TiO2 layers. It shows that these properties are significantly influenced by the topographical characteristics of the TiO2 surface, which can be precisely controlled through variations in pulverization pressure and low-temperature post-annealing treatments. Post-deposition annealing of the TiO2 layers achieves 100 % self-cleaning efficiency for both thick and thin films, with optical transmission ranging from approximately 60 %–80 % in the visible spectrum. Additionally, the TiO2 layers exhibited promising capabilities for eliminating pathogenic microorganisms and disinfecting surfaces. The underlying causal factors of these remarkable and technologically promising surface features are explored and discussed.

Metal-Halide Perovskite Submicrometer-Thick Films for Ultra-Stable Self-Powered Direct X-Ray Detectors

HighlightsSelf-powered direct X-ray detectors, based on FAPbBr3 255-nm-thick films deposited onto mesoporous TiO2 scaffolds, can withstand a 26-day uninterrupted X-ray exposure with negligible signal loss, demonstrating ultra-high operational stability.Bulk specific sensitivity is evaluated to be 7.28 C Gy−1 cm−3 at 0 V, an unprecedented value in the field of thin-film-based photoconductors and photodiodes for “hard” X-rays.Sensitivity of submicrometer-thick perovskite films to the X-rays produced by a medical linear accelerator used for cancer treatment is here demonstrated for the first time.

Enhanced efficiency and stability of inorganic CsPbBr3 perovskite solar cells based on carbon counter electrode by applying PbTiO3-coated TiO2 nanorod films as scaffold layers

The CsPbBr3 perovskite solar cells (PSCs) based on carbon counter electrode (CCE) are promising because of the advantages including fabrication simplicity and excellent stability, but their power conversion efficiencies (PCE) are low due to interfacial carrier recombination as the direct contact of the CsPbBr3 with electron transport materials (ETM). In this paper, PbTiO3 shells were grown onto TiO2 nanorods to form PbTiO3-coated TiO2 scaffold layer via a two-step method. The presence of PbTiO3 could promote crystallinity of the CsPbBr3 perovskite film and inhibits interface recombination at the CsPbBr3/TiO2 interface. Consequently, the carbon-based CsPbBr3 solar cells with PbTiO3/TiO2 scaffold layer achieves a high PCE of 7.28%, demonstrating an increase by 19.9% compared with the devices based on TiO2 NRs. Moreover, the champion devices exhibited excellent stability in ambient air, with the PCE value remaining at 93% over 28 days.

Aligned TiO2 Scaffolds in the Presence of a Galactopyranose Matrix by Sol-Gel Process.

In this work, titanium dioxide scaffolds were synthesized. Titanium isopropoxide (IV) was used as a precursor in its formation, using a polymeric network of galactopyranose as a template. The powder sample obtained was evaluated by scanning tunneling microscopy (STM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, and thermal gravimetric analysis (TGA-DTA). According to the results, it was found that these scaffolds can be successfully synthesized in solution using the sol-gel method. The synthesized scaffolds have diameters from 50 nm with porosity of approximately 0.3-10 nm. Important parameters, such as pH and the concentration of the metallic precursors, were optimized in this solution. The values of maximum average roughness R(max) and roughness value (Ra) were 0.50 and 1.45, respectively. XRD diffraction analysis shows the formation of crystalline phases in the TiO2 scaffold at 700 °C. The use of biological polymers represents an alternative for the synthesis of new materials at low cost, manipulating the conditions in the production processes and making the proposed system more efficient.

An investigation on the photo-catalytic oxidation of air pollutants via SiO2-supported TiO2

Persistence in the atmosphere of carbon dioxide (CO2) and volatile organic compounds (VOCs) represents a threat for human safety and health, both in the short and in the long term. Therefore, the removal, storage or, even better, utilization of these molecules is currently highly desirable. Photo-catalytic approaches aims to use the sunlight to afford this removal providing a limited or no further pollution. Wide band gap semiconductors are amongst the most studied and employed materials for this purpose. In this study, a crystalline (quartz) and an amorphous (SBA-15) type of silica were tested as TiO2 scaffolds in the photo-oxidation of VOCs. The photo-reduction of CO2 in presence of H2O was also considered as comparative reaction. Therefore, optical, chemical, and reflective properties of the synthesized materials were investigated. The two types of silica showed a different affinity and selectivity in both photo-reductive and photo-oxidative events. The light scattering properties of the scaffold were found to be effective as booster of the photo-catalytic performance of the active phase.

Osteoblasts in a Perfusion Flow Bioreactor-Tissue Engineered Constructs of TiO2 Scaffolds and Cells for Improved Clinical Performance.

Combining biomaterial scaffolds with cells serves as a promising strategy for engineering critical size defects; however, homogenous cellular growth within large scaffolds is challenging. Mechanical stimuli can enhance bone regeneration by modulating cellular growth and differentiation. Here, we compare dynamic seeding in a perfusion flow bioreactor with static seeding for a synthetic bone scaffold for up to 21 days using the cell line MC3T3-E1 and primary human osteoblast, confocal laser scanning microscopy, and real-time reverse transcriptase-polymerase chain reaction. The secretion of bone-related proteins was quantified using multiplex immunoassays. Dynamic culture improved cellular distribution through the TiO2 scaffold and induced a five-fold increase in cell number after 21 days. The relative mRNA expression of osteopontin of MC3T3-E1 was 40-fold enhanced after 7 and 21 days at a flow rate of 0.08 mL/min, and that of collagen type I alpha I expression was 18-fold after 21 days. A flow rate of 0.16 mL/min was 10-fold less effective. Dynamic culture increased the levels of dickkopf-related protein 1 (60-fold), osteoprotegrin (29-fold), interleukin-6 (23-fold), interleukin-8 (36-fold), monocyte chemoattractant protein 1 (28-fold) and vascular endothelial growth factor (6-fold) in the medium of primary human osteoblasts after 21 days compared to static seeding. The proposed method may have clinical potential for bone tissue engineering.

Operando Study of Structure Degradation in Solid‐State Dye‐Sensitized Solar Cells with a TiO2 Photoanode Having Ordered Mesopore Arrays

Via operando grazing‐incidence small‐angle X‐ray scattering, the degradation mechanisms of solid‐state dye‐sensitized solar cells (ssDSSCs) using two types of ordered mesoporous TiO2 scaffolds with different pore sizes, and an exemplary dye D205, are investigated. The temporal evolution of the inner morphology shows a strong impact on device performance. The photoinduced dye aggregation on the TiO2 surface leads to an increase in the domain radius but a decreased spatial order of the photoactive layer during the burn‐in stage. This dye aggregation on the TiO2 surface causes the short‐circuit current density loss, which plays a major role in the power conversion efficiency decay. Finally, it is found that a larger surface area in the small‐pore sample yields a faster short‐circuit current density decay as compared with the big‐pore sample. Therefore, a control of dye aggregation and the pore size of TiO2 photoelectrodes is crucial for the stability of TiO2‐based ssDSSCs.

Fabrication of CsPb1−x Mn x Br3−2x Cl2x (x = 0–0.5) quantum dots for near UV photodetector application

Abstract In this study, CsPb1–x Mn x Br3–2x Cl2x (x = 0–0.5) nanoparticles were synthesized directly in toluene solvents at high temperature. This approach results in small-size nanoparticles, which can be used in photoelectric components without adding a filtration process to eliminate high-temperature solvents such as octadecene. The high content Mn2+-incorporated CsPb(Cl/Br)3 host is observed by strongly wideband emission at 592 nm of manganese d-states spin and orbital forbidden transition. After infiltration into mesoporous TiO2, the Mn2+ ion receives energy from the CsPb(Cl/Br)3 host (irradiated 405 nm light-emitting diode source) and effectively transfers to the TiO2 scaffold layer. As a result, a metal/semiconductor/metal planar structure photodetector with m-TiO2/CsPb1–x Mn x Br3–2x Cl2x (x = 0–0.5) composite showed several figures of merit compared to bare m-TiO2 and m-TiO2/CsPbBr3 such as on/off ratio of 104 times, responsivity of 1.67 A·W−1, and detectivity of 4.42 × 109 Jones. The key factors contributing to the growth of the on/off ratio include the decreasing dark current and enhancing exciton energy and transportation due to the infiltration of CsPb1–x Mn x Br3–2x Cl2x (x = 0–0.5) perovskite quantum dots into mesopores of the m-TiO2 scaffold layer.

Photoelectrochemical hybrid cell for unbiased CO2 reduction coupled to alcohol oxidation

The reduction of CO2 to renewable fuels must be coupled to a sustainable oxidation process to devise a viable device that produces solar fuels. In photoelectrochemical cells, water oxidation to O2 is the predominant oxidation reaction and typically requires a pair of light absorbers or an applied bias voltage when coupled to CO2 reduction. Here, we report a bias-free photoelectrochemical device for simultaneous CO2 reduction to formate and alcohol oxidation to aldehyde in aqueous conditions. The photoanode is constructed by co-immobilization of a diketopyrrolopyrrole-based chromophore and a nitroxyl-based alcohol oxidation catalyst on a mesoporous TiO2 scaffold, which provides a precious-metal-free dye-sensitized photoanode. The photoanode is wired to a biohybrid cathode that consists of the CO2 reduction enzyme formate dehydrogenase integrated into a mesoporous indium tin oxide electrode. The bias-free cell delivers sustained photocurrents of up to 30 µA cm−2 under visible-light irradiation, which results in simultaneous aldehyde and formate production. Our results show that in the absence of an external bias, single light absorber photoelectrochemical cells can be used for parallel fuel production and chemical synthesis from CO2 and alcohol substrates.

Investigation and Optimization of Mxene Functionalized Mesoporous Titania Films as Efficient Photoelectrodes.

Three-dimensional mesoporous TiO2 scaffolds of anatase phase possess inherent eximious optical behavior that is beneficial for photoelectrodes used for solar energy conversion applications. In this regard; substantial efforts have been devoted to maximizing the UV and/or visible light absorption efficiency; and suppressing the annihilation of photogenerated charged species; in pristine mesoporous TiO2 structures for improved solar illumination conversion efficiency. This study provides fundamental insights into the use of Mxene functionalized mesoporous TiO2 as a photoelectrode. This novel combination of Mxene functionalized TiO2 electrodes with and without TiCl4 treatment was successfully optimized to intensify the process of photon absorption; charge segregation and photocurrent; resulting in superior photoelectrode performance. The photocurrent measurements of the prepared photoelectrodes were significantly enhanced with increased contents of Mxene due to improved absorption efficiency within the visible region; as verified by UV–Vis absorption spectroscopy. The anatase phase of TiO2 was significantly augmented due to increased contents of Mxene and postdeposition heat treatments; as evidenced by structural analysis. Consequently; an appreciable coverage of well-developed grains on the FTO surface was observed in SEM images. As such; these newly fabricated conductive mesoporous TiO2 photoelectrodes are potential candidates for photoinduced energy conversion and storage applications.

Photoelectrochemical IL-6 Immunoassay Manufactured on Multifunctional Catecholate-Modified TiO2 Scaffolds.

There is an increasing interest in using photoelectrochemistry for enhancing the signal-to-noise ratio and sensitivity of electrochemical biosensors. Nevertheless, it remains challenging to create photoelectrochemical biosensors founded on stable material systems that are also easily biofunctionalized for sensing applications. Herein, a photoelectrochemical immunosensor is reported, in which the concentration of the target protein directly correlates to a change in the measured photocurrent. The material system for the photoelectrode signal transducer involves using catecholate ligands to modify the properties of TiO2 nanostructures in a three-pronged approach of morphology tuning, photoabsorption enhancement, and facilitating bioconjugation. The catecholate-modified TiO2 photoelectrode is combined with a signal-off direct immunoassay to detect interleukin-6 (IL-6), a key biomarker for diagnosing and monitoring various diseases. Catecholate ligands are added during hydrothermal synthesis of TiO2 to enable the growth of three-dimensional nanostructures to form highly porous photoelectrodes that provide a three-dimensional scaffold for immobilizing capture antibodies. Surface modification by catecholate ligands greatly enhances photocurrent generation of the TiO2 photoelectrodes by improving photoabsorption in the visible range. Additionally, catecholate molecules facilitate bioconjugation and probe immobilization by forming a Schiff-base between their -COH group and the -NH2 group of the capture antibodies. The highest photocurrent achieved herein is 8.89 μA cm-2, which represents an enhancement by a factor of 87 from unmodified TiO2. The fabricated immunosensor shows a limit-of-detection of 3.6 pg mL-1 and a log-linear dynamic range of 2-2000 pg mL-1 for IL-6 in human blood plasma.

A Semi‐artificial Photoelectrochemical Tandem Leaf with a CO2‐to‐Formate Efficiency Approaching 1 %

AbstractSemi‐artificial photoelectrochemistry can combine state‐of‐the‐art photovoltaic light‐absorbers with enzymes evolved for selective fuel‐forming reactions such as CO2 reduction, but the overall performance of such hybrid systems has been limited to date. Here, the electrolyte constituents were first tuned to establish an optimal local environment for a W‐formate dehydrogenase to perform electrocatalysis. The CO2 reductase was then interfaced with a triple cation lead mixed‐halide perovskite through a hierarchically structured porous TiO2 scaffold to produce an integrated photocathode achieving a photocurrent density of −5 mA cm−2 at 0.4 V vs. the reversible hydrogen electrode during simulated solar light irradiation. Finally, the combination with a water‐oxidizing BiVO4 photoanode produced a bias‐free integrated biophotoelectrochemical tandem device (semi‐artificial leaf) with a solar CO2‐to‐formate energy conversion efficiency of 0.8 %.

A Semi-artificial Photoelectrochemical Tandem Leaf with a CO2 -to-Formate Efficiency Approaching 1 .

Semi-artificial photoelectrochemistry can combine state-of-the-art photovoltaic light-absorbers with enzymes evolved for selective fuel-forming reactions such as CO2 reduction, but the overall performance of such hybrid systems has been limited to date. Here, the electrolyte constituents were first tuned to establish an optimal local environment for a W-formate dehydrogenase to perform electrocatalysis. The CO2 reductase was then interfaced with a triple cation lead mixed-halide perovskite through a hierarchically structured porous TiO2 scaffold to produce an integrated photocathode achieving a photocurrent density of -5 mA cm-2 at 0.4 V vs. the reversible hydrogen electrode during simulated solar light irradiation. Finally, the combination with a water-oxidizing BiVO4 photoanode produced a bias-free integrated biophotoelectrochemical tandem device (semi-artificial leaf) with a solar CO2 -to-formate energy conversion efficiency of 0.8 %.

Highly porous Sr-doped TiO2 ceramics maintain compressive strength after grain boundary corrosion

Maintaining sufficient mechanical support during bone healing is an essential property for ceramic bone scaffolds. However, grain boundary (GB) dissolution may compromise the mechanical strength of polycrystalline ceramics in the physiological environment. Therefore, we investigated the GB formation and its impact on the compressive strength and corrosion behavior in TiO2 scaffolds doped with calcium and strontium. To alter the GB composition and densification process, sintering conditions were altered. Prolonged sintering times and increased sintering temperature led to improved densification and increased strength in Ca-doped scaffolds. However, dissolution of the resulting amorphous GBs caused a significant loss of compressive strength when exposed to an acidic environment. In contrast, a crystalline SrTiO3 GB phase present in Sr-doped scaffolds, for which increased sintering temperature combined with rapid cooling led to a significantly improved compressive strength. Formation of SrTiO3 crystals in the GBs maintained the strength for over 4 weeks in an acidic environment.

Fabrication of quantum dot-sensitized solar cells with multilayer TiO2/PbS(X)/CdS/CdSe/ZnS/SiO2 photoanode and optimization of the PbS nanocrystalline layer

In this work, two multilayer photoanode structures of TiO2/PbS(X)/CdS/ZnS/SiO2 and TiO2/PbS(X)/CdS/CdSe/ZnS/SiO2 were fabricated and applied in quantum dot-sensitized solar cells (QDSCs). Then, the effect of PbS QDs layer on the photovoltaic performance of corresponding cells was investigated. The sensitization was carried out by PbS and CdS QDs layers deposited on TiO2 scaffold through successive ionic layer adsorption and reaction (SILAR) method. The CdSe QDs film was also formed by a fast, modified chemical bath deposition (CBD) approach. Two passivating ZnS and SiO2 layers were finally deposited by SILAR and CBD methods, respectively. It was shown that the reference cell with TiO2/CdS/ZnS/SiO2 photoanode demonstrated a power conversion efficiency (PCE) of 3.0%. This efficiency was increased to 4.0% for the QDSC with TiO2/PbS(2)/CdS/ZnS/SiO2 photoelectrode. This was due to the co-absorption of incident light by low-bandgap PbS nanocrystalline film and also the CdS QDs layer and well transport of the charge carriers. For the CdSe included QDSCs, the PbS-free reference cell represented a PCE of 4.1%. This efficiency was improved to 5.1% for the optimized cell with TiO2/PbS(2)/CdS/CdSe/ZnS/SiO2 photoelectrode. The maximized efficiency was enhanced about 25% and 70% compared to the PbS-free reference cells with and without the CdSe QDs layer.

Solar-Powered Photodegradation of Pollutant Dyes Using Silver-Embedded Porous TiO2 Nanofibers.

Titanium dioxide (TiO2) nanomaterials have been ubiquitously investigated as a photocatalyst for organic contaminant treatment in wastewater due to their exemplary semiconductor properties. However, their huge band gap remains a barrier for visible light absorption, limiting their utility in practical applications. The incorporation of noble metals in the TiO2 scaffold would help mitigate the problem via plasmonic resonance enhancements. Silver (Ag) is the chosen noble metal as it is relatively cheap and has great plasmonic effects. In this study, the use of electrospun Ag-embedded TiO2 nanofibers as a photocatalyst is shown to be effective in decomposing rhodamine B and methyl orange dyes under a solar simulator in 3 h, which is more efficacious as opposed to pristine TiO2 nanofibers. This showcases the potential of a simple and economic wastewater treatment system for the removal of organic pollutants.

Construction of nacre-mimetic composites with a “brick-and-mortar” architecture based on structural defects in ice-templating

The construction of a hierarchically ordered “brick-and-mortar” structure with a high content of “brick” phase is a key challenge in the preparation of nacre-mimetic composites. Herein, inspired by the transverse cracks in the ceramic lamellae after freeze-drying caused by the secondary nucleation of ice crystals during directional freezing of water-based ceramic slurry, we propose a new idea to use these structural defects and an in-situ reaction to construct composites with a nacre-like “brick-and-mortar” structure and high hard-phase content. This uses ice-templating to first prepare lamellar TiO2 scaffolds with transverse cracks that separated the ceramic lamellae into “brick” whose size was controlled by adjusting the initial ceramic particle size (50, 300, and 700 nm). After the reactive infiltration, these cracks were filled with molten Al, leading to the formation of a “brick-and-mortar” structure with a high hard-phase content (86 vol%). The increasing ceramic particle size reduced the hard-phase content but significantly increased the aspect ratio (height/width) of the ceramic “brick” and the fracture toughness. The excellent damage tolerance was attributed to multiple toughening mechanisms, i.e., multiple cracking, crack deflection, and uncracked-ligament bridging of the metal layers. The existence of “mortar” increased the probability of the formation of multiple cracking.

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COVER ILLUSTRATION: The cover image is based on the Original Article Guided bone regeneration of chronic non-contained bone defects using a volume stable porous block TiO2 scaffold: An experimental in vivo study by Minh Khai Le Thieu et al., https://doi.org/10.1111/clr.13708.