Size-effects in TiO2 nanotubes: Diameter dependent anatase/rutile stabilization

Vibration Analysis of Porous Cu-Si Microcantilever Beams in Fluids Based on Modified Couple Stress Theory

The vibrations in functionally graded porous Cu-Si microcantilever beams are investigated based on physical neutral plane theory, modified coupled stress theory, and scale distribution theory (MCST&SDT). Porous microcantilever beams define four pore distributions. Considering the physical neutral plane theory, the material properties of the beams are computed through four different power-law distributions. The material properties of microcantilever beams are corrected by scale effects based on modified coupled stress theory. Considering the fluid driving force, the amplitude-frequency response spectra and resonant frequencies of the porous microcantilever beam in three different fluids are obtained based on the Euler-Bernoulli beam theory. The quality factors of porous microcantilever beams in three different fluids are derived by estimating the equation. The computational analysis shows that the presence of pores in microcantilever beams leads to a decrease in Young's modulus. Different pore distributions affect the material properties to different degrees. The gain effect of the scale effect is weakened, but the one-dimensional temperature field and amplitude-frequency response spectra show an increasing trend. The quality factor is decreased by porosity, and the degree of influence of porosity increases as the beam thickness increases. The gradient factor n has a greater effect on the resonant frequency. The effect of porosity on the resonant frequency is negatively correlated when the gradient factor is small (n<1) but positively correlated when the gradient factor is large (n>1).

Highly efficient visible-light-driven photocatalytic degradation of gaseous toluene by rutile-anatase TiO2@MIL-101 composite with two heterojunctions

The construction of heterophase junctions by rutile-anatase TiO2 is considered an effective strategy for toluene degradation, but the photogenerated electron utilization is still insufficient. In this study, the formation of type-II heterojunction by the encapsulation of Materials of Institut Lavoisier (MIL-101) by anatase is performed, and then the heterophase junction is further constructed to improve the catalytic performance of the photocatalyst. The enhancement of photocatalytic performance depends on the encapsulation of MIL-101 by anatase, the light absorption capacity of anatase, and the contact area of two heterojunctions. Photogenerated electrons are transferred to oxygen vacancies of anatase and promoting the generation of oxygen-containing radicals. The material certifies the synergistic effect of the heterophase junction and heterojunction design and provides a theoretical basis for application in the degradation of volatile organic compounds.

Biological Activity and Thrombogenic Properties of Oxide Nanotubes on the Ti-13Nb-13Zr Biomedical Alloy

The success of implant treatment is dependent on the osseointegration of the implant. The main goal of this work was to improve the biofunctionality of the Ti-13Nb-13Zr implant alloy by the production of oxide nanotubes (ONTs) layers for better anchoring in the bone and use as an intelligent carrier in drug delivery systems. Anodization of the Ti-13Nb-13Zr alloy was carried out in 0.5% HF, 1 M (NH₄)₂SO₄ + 2% NH₄F, and 1 M ethylene glycol + 4 wt.% NH₄F electrolytes. Physicochemical characteristics of ONTs were performed by high-resolution electron microscopy (HREM), X-ray photoelectron spectroscopy (XPS), and scanning Kelvin probe (SKP). Water contact angle studies were conducted using the sitting airdrop method. In vitro biological properties and release kinetics of ibuprofen were investigated. The results of TEM and XPS studies confirmed the formation of the single-walled ONTs of three generations on the bi-phase (α + β) Ti-13Nb-13Zr alloy. The ONTs were composed of oxides of the alloying elements. The proposed surface modification method ensured good hemolytic properties, no cytotoxity for L-929 mouse cells, good adhesion, increased surface wettability, and improved athrombogenic properties of the Ti-13Nb-13Zr alloy. Nanotubular surfaces allowed ibuprofen to be released from the polymer matrix according to the Gallagher-Corrigan model.

Size-Dependent Buckling and Post-Buckling Analysis of the Functionally Graded Thin Plate Al-Cu Material Based on a Modified Couple Stress Theory

Size-dependent functionally graded material thin plate buckling and post-buckling problems are considered using the framework of the MCST (Modified Couple Stress Theory). Based on modified couple stress theory and power law, the post-buckling deflection and critical buckling load of simply supported functionally graded material thin plate are derived using Hamilton's minimum potential energy principle. The analysis compares the simulation results of linear buckling and nonlinear buckling. Innovatively, a power-law distribution with scale effects is considered. The influences of scale effect parameters l and power-law index parameters k on buckling displacement, load, and strain energy of plates have been investigated. In this article, it is found that the critical buckling displacement, critical buckling load, and buckling strain energy increase with increases in the power-law index parameters k. The membrane energy decreases as the power-law index parameter increases. If the upper and lower layers are swapped, the opposite result is obtained. In comparison, the scale effect parameter is more influential than the power-law exponent. The critical buckling displacement in the x-direction is not affected by scale effects. The critical buckling load, the membrane energy, and buckling strain energy increase as the scale effect parameter increases. Scale effects increase material stiffness compared with traditional theory, and the power-law index parameters affect FGM properties such as elastic modulus, Poisson's ratio, density, etc. Both scale effects parameters and power-law index parameters have important effects on the mechanical behavior of materials.

Nanostructured photocatalysts for the abatement of contaminants by photocatalysis and photocatalytic ozonation: An overview

The water scarcity, the presence of different contaminants in the worldwide waters and wastewaters and their impacts should motivate their good elimination and water management. With this, photocatalysis and photocatalytic ozonation are strong solutions to obtain good quality reclaimed water, for different applications. Nanostructured supported photo-active catalysts, such as the TiO₂, WO₃ or ZnO can positively affect the performance of such technologies. Therefore, different semiconductors materials have been aroused the interest of the scientific community, mainly due to its functional properties as well as characteristics imposed by the different nanostructures. With this, this work overviews different works and perspective on the TiO₂ nanotubes and other semiconductors nanostructures, with the analysis of different works from 2001 to 2022. Aspects as the substrate effect, electrolyte nature, aspect ratio, electrolyte aging, and annealing treatment but also the effect of morphology, anodization time, applied voltage, temperature and viscosity are discussed. Modification of TiO₂ nanotubes is also presented in this paper. The main objective of this work is to present and discuss the key parameters and their effects on the anodization of different semiconductors, as well as the results obtained until today on the degradation of different contaminants by photocatalysis and photocatalytic ozonation, as well as their use on the treatment of real wastewater. TiO₂ nanotubes present unique properties and highly ordered configuration, which motivate their use on photo-driven technologies for the pollutant's abatement, even when compared to other nanostructures. However, photocatalysts with activity on the visible range and solar radiation, such as the WO₃, can present higher performance and can decrease operational costs, and must be an important source and a key to find efficient and cost-friendly solutions.

Recent Advances in TiO2-based Photoanodes for Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting has attracted a great attention in the past several decades which holds great promise to address global energy and environmental issues by converting solar energy into hydrogen. However, its low solar-to-hydrogen (STH) conversion efficiency remains a bottleneck for practical application. Developing efficient photoelectrocatalysts with high stability and high STH conversion efficiency is one of the key challenges. As a typical n-type semiconductor, titanium dioxide (TiO 2 ) exhibits high PEC water splitting performance, especially high chemical and photo stability. But, TiO 2 has also disadvantages such as wide band gap and fast electron-hole recombination rate, which seriously hinder its PEC performance. This review focuses on recent development in TiO 2 -based photoanodes as well as some key fundamentals. The corresponding mechanisms and key factors for high STH, and controllable synthesis and modification strategies are highlighted in this review. We conclude finally with an outlook providing a critical perspective on future trends on TiO 2 -based photoanodes for PEC water splitting.

Photocatalytic removal of pharmaceutical water pollutants by TiO2 - Carbon dots nanocomposites: A review

Pharmaceuticals are becoming increasingly more relevant water contaminants, with photocatalysts (such as TiO₂) being a promising approach to remove these compounds from water. However, TiO₂ has poor sunlight-harvesting capacity, low photonic efficiency, and poor adsorption towards organic pollutants. One of the emerging strategies to enhance the photocatalytic performance of TiO₂ is by conjugating it with fluorescent carbon dots. Herein, we performed a critical review of the development of TiO₂ - carbon dots nanocomposites for the photocatalytic removal of pharmaceuticals. We found that carbon dots can improve the photocatalytic efficiency of the resulting nanocomposites, mostly due to increasing the adsorption of organic pollutants and enhancing the absorption in the visible range. However, while this approach shows significant promise, we also identified and discussed several aspects that need to be addressed before this strategy could be more widely used. We hope that this review can guide future studies aiming to the development of enhanced photocatalytic TiO₂ - carbon dots nanocomposites.

Deciphering controversial results of cell proliferation on TiO2 nanotubes using machine learning

With the rapid development of biomedical sciences, contradictory results on the relationships between biological responses and material properties emerge continuously, adding to the challenge of interpreting the incomprehensible interfacial process. In the present paper, we use cell proliferation on titanium dioxide nanotubes (TNTs) as a case study and apply machine learning methodologies to decipher contradictory results in the literature. The gradient boosting decision tree model demonstrates that cell density has a higher impact on cell proliferation than other obtainable experimental features in most publications. Together with the variation of other essential features, the controversy of cell proliferation trends on various TNTs is understandable. By traversing all combinational experimental features and the corresponding forecast using an exhausted grid search strategy, we find that adjusting cell density and sterilization methods can simultaneously induce opposite cell proliferation trends on various TNTs diameter, which is further validated by experiments. This case study reveals that machine learning is a burgeoning tool in deciphering controversial results in biomedical researches, opening up an avenue to explore the structure-property relationships of biomaterials.

Electrical Transport and Magnetic Properties of Metal/Metal Oxide/Metal Junctions Based on Anodized Metal Oxides

In this paper, we describe magnetoelectric properties of metal/metal-oxide/metal junctions based on anodized metal oxides. Specifically, we use Ti and Fe metallic layers separated by the porous metal-oxides of iron or titanium formed by the anodization method. Thus, we prepare double junctions with at least one ferromagnetic layer and measure magnetoresistance, as well as their current-voltage and magnetic characteristics. We find that magnetoresistance depends on that junction composition and discuss the nature of differential resistance calculated from I-V characteristics. Our findings show that a top metallic layer and the interface between this layer and anodized oxide, where strong interatomic diffusion is expected, have the strongest influence on this observed behavior.

Enhanced photocatalytic degradation of gaseous toluene and liquidus tetracycline by anatase/rutile titanium dioxide with heterophase junction derived from materials of Institut Lavoisier-125(Ti): Degradation pathway and mechanism studies

Anatase/rutile titanium dioxide (TiO₂) with heterophase junction and large Brunauer-Emmett-Teller (BET) specific surface area (50.1 m² g^-1) is successfully synthesized by calcinating Materials of Institut Lavoisier-125(Ti) (MIL-125(Ti)) with 30% O₂/Ar at the temperature of 600 °C (M-O-600). Several techniques are used to examine the physicochemical, photoelectrochemical and optical properties of samples, and their photocatalytic performances are evaluated by photodegradation of gaseous toluene and liquidus tetracycline (TC) under visible light illumination. It is found that the calcination temperature has significant influence on the crystal structure and physicochemical parameters of TiO₂. The weight fractions of rutile and anatase TiO₂ of M-O-600 are approximately 0.7 and 0.3, which displays outstanding photocatalytic activity. Through the construction of heterophase junction, M-O-600 has better oxygen adsorption and higher density of localized states, which effectively promotes the generation of superoxide radical (·O₂^-) and hydroxyl radical (·OH) species. In-situ infrared spectra indicate that toluene is oxidized to benzyl alcohol, benzaldehyde and benzoic acid in turn and then oxidized to formic acid and acetic acid before eventually degraded into H₂O and CO₂. Gas chromatography-mass spectrometry (GC-MS) is also used to further investigate the degradation pathway of toluene. Degradation pathway and mechanism of TC are studied by liquid chromatography-tandem mass spectrometry (LC-MS). Moreover, three-dimensional excitation-emission matrix fluorescence spectroscopy (3D EEMs) and total organic carbon (TOC) show that TC can be effectively mineralized through a series of reactions by M-O-600 during photocatalysis.

Evaluation of annealed titanium oxide nanotubes on titanium: From surface characterization to in vivo assays

The entire route from anodic oxidation and surface characterization, including in vitro experiments and finally in vivo osseointegration assays were performed with the aim to evaluate nanotubular and crystalline annealed titanium oxides as a suitable surface for grade 2 titanium permanent implants. Polished titanium (T0) was compared with anodized surfaces obtained in acidic media with fluoride, leading to an ordered nanotubular structure of titanium oxide on the metal surface, characterized by tube diameter of 89 ± 24 nm (Tnts). Samples were thermally treated in air (TntsTT) to increase the anatase crystalline phase on nanotubes, with minor alteration of the structure. Corrosion tests were performed to evaluate the electrochemical response after 1, 14, and 28 days of immersion in simulated body fluid. Based on the in vitro results, heat-treated titanium nanotubes (TntsTT) were selected as a promissory candidate to continue with the osseointegration in vivo assays. The in vivo results showed no major improvement in the osseointegration process when compared with untreated Ti after 30 days of implantation and there also was a lower increase in the development of new osseous tissue.

Present applications of titanium dioxide for the photocatalytic removal of pollutants from water: A review

The evolution of modern technology and industrial processes has been accompanied by an increase in the utilization of chemicals to derive new products. Water bodies are frequently contaminated by the presence of conventional pollutants such as dyes and heavy metals, as well as microorganisms that are responsible for various diseases. A sharp rise has also been observed in the presence of new compounds heretofore excluded from the design and evaluation of wastewater treatment processes, categorized as "emerging pollutants". While some are harmless, certain emerging pollutants possess the ability to cause debilitating effects on a wide spectrum of living organisms. Photocatalytic degradation has emerged as an increasingly popular solution to the problem of water pollution due to its effectiveness and versatility. The primary objective of this study is to thoroughly scrutinize recent applications of titanium dioxide and its modified forms as photocatalytic materials in the removal and control of several classes of water pollutants as reported in literature. Different structural modifications are used to enhance the performance of the photocatalyst such as doping and formation of composites. The principles of these modifications have been scrutinized and evaluated in this review in order to present their advantages and drawbacks. The mechanisms involved in the removal of different pollutants through photocatalysis performed by TiO2 have been highlighted. The factors affecting the mechanism of photocatalysis and those affecting the performance of different TiO2-based photocatalysts have also been thoroughly discussed, thereby presenting a comprehensive view of all aspects involved in the application of TiO₂ to remediate and control water pollution.

Photoanodes based on TiO2and α-Fe2O3for solar water splitting – superior role of 1D nanoarchitectures and of combined heterostructures

Solar driven photoelectrochemical water splitting represents a promising approach for a sustainable and environmentally friendly production of renewable energy vectors and fuel sources, such as H₂.

Adherence of oral streptococci to nanostructured titanium surfaces

OBJECTIVES

Peri-implantitis and peri-mucositis pose a severe threat to the success of dental implants. Current research focuses on the development of surfaces that inhibit biofilm formation while not inferring with tissue integration. This study compared the adherence of two oral bacterial species, Streptococcus sanguinis and Streptococcus mutans to nanostructured titanium surfaces.

METHODS

The samples included TiO2 nanotubes formed by anodization of titanium foil of 100, 50 and 15nm diameter (NT15, NT50, NT100), a nanoporous (15nm pore diameter) surface and compact TiO2 control. Adherent surviving bacteria were enumerated after 1h in an artificial saliva medium containing bovine mucin.

RESULTS

Lowest numbers of adherent bacteria of both species were recovered from the original titanium foil and nanoporous surface and highest numbers from the Ti100 nanotubes. Numbers of attached S. sanguinis increased in the order (NT15<NT50<NT100), correlated with increasing percentage of surface fluoride. The lowest adhesion of S. sanguinis and S. mutans on TiO2 nanostructured surfaces was observed for small diameter nanoporous surfaces which coincides with the highest osteoblast adhesion on small diameter nanotubular/nanoporous surfaces shown in previous work.

SIGNIFICANCE

This study indicates that the adherence of oral streptococci can be modified by titanium anodization and nanotube diameter.

Anatase TiO2 nanotube powder film with high crystallinity for enhanced photocatalytic performance

We report on the synthesis of TiO2 nanotube (NT) powders using anodic oxidation and ultrasonication. Compared to free-standing NT array films, the powder-type NTs can be easily fabricated in a cost-effective way. Particularly, without the substrate effect arising from underlying Ti metals, highly crystallized NT powders with intact tube structures and pure anatase phase can be obtained using high-temperature heat treatment. The application of NTs with different crystallinity for the photocatalytic decomposition of methylene blue (MB) was then demonstrated. The results showed that with increasing annealing temperature, the photocatalytic decomposition rate was gradually enhanced, and the NT powder electrode annealed at 650°C showed the highest photoactivity. Compared to typical NTs annealed at 450°C, the rate constant increased by 2.7-fold, although the surface area was 21% lower. These findings indicate that the better photocatalytic activity was due to the significantly improved crystallinity of anatase anodic NTs in powder form, resulting in a low density of crystalline defects. This simple and efficient approach is applicable for scaled-up water purification and other light utilization applications.

Titanium dioxide nanotube films: Preparation, characterization and electrochemical biosensitivity towards alkaline phosphatase

Titania nanotubes (TNTs) were prepared by anodization on different substrates (titanium, Ti6Al4V and Ti6Al7Nb alloys) in ethylene glycol and glycerol. The influence of the applied potential and processing time on the nanotube diameter and length is analyzed. The as-formed nanotube layers are amorphous but they become crystalline when subjected to subsequent thermal treatment in air at 550°C; TNT layers grown on titanium and Ti6Al4V alloy substrates consist of anatase and rutile, while those grown on Ti6Al7Nb alloy consist only of anatase. The nanotube layers grown on Ti6Al7Nb alloy are less homogeneous, with supplementary islands of smaller diameter nanotubes, spread across the surface. Better adhesion and proliferation of osteoblasts was found for the nanotubes grown on all three substrates by comparison to an unprocessed titanium plate. The sensitivity towards bovine alkaline phosphatase was investigated mainly by electrochemical impedance spectroscopy in relation to the crystallinity, the diameter and the nature of the anodization electrolyte of the TNT/Ti samples. The measuring capacity of the annealed nanotubes of 50nm diameter grown in glycerol was demonstrated and the corresponding calibration curve was built for the concentration range of 0.005-0.1mg/mL.

A review of photocatalysis using self-organized TiO2 nanotubes and other ordered oxide nanostructures

Photocatalytic approaches, that is the reaction of light-produced charge carriers at a semiconductor surface with their environment, currently attract an extremely wide scientific interest. This is to a large extent due to the high expectations: i) to convert sunlight directly into an energy carrier (H(2)), ii) to stimulate chemical synthetic reactions, or iii) to degrade unwanted environmental pollutants. Since the early reports in 1972, TiO(2) has been the most investigated photocatalytic material by far; this originates from its outstanding electronic properties that allow for a wide range of applications. Not only the material, but also its structure and morphology, can have a considerable influence on the photocatalytic performance of TiO(2). In recent years, particularly 1D (or pseudo 1D) structures such as nanowires and nanotubes have received great attention. The present Review focuses on TiO(2) nanotube arrays (and similar structures) that grow by self-organizing electrochemistry (highly aligned) from a Ti metal substrate. Herein, the growth, properties, and applications of these tubes are discussed, as well as ways and means to modify critical tube properties. Common strategies are addressed to improve the performance of photocatalysts such as doping or band-gap engineering, co-catalyst decoration, junction formation, or applying external bias. Finally, some unique applications of the ordered tube structures in various photocatalytic approaches are outlined.