Structural Feature and Catalytic Performance of Cu Species Distributed over TiO2 Nanotubes

An Overview of Hydrothermally Synthesized Titanate Nanotubes: The Factors Affecting Preparation and Their Promising Pharmaceutical Applications

Recently, titanate nanotubes (TNTs) have been receiving more attention and becoming an attractive candidate for use in several disciplines. With their promising results and outstanding performance, they bring added value to any field using them, such as green chemistry, engineering, and medicine. Their good biocompatibility, high resistance, and special physicochemical properties also provide a wide spectrum of advantages that could be of crucial importance for investment in different platforms, especially medical and pharmaceutical ones. Hydrothermal treatment is one of the most popular methods for TNT preparation because it is a simple, cost-effective, and environmentally friendly water-based procedure. It is also considered as a strong candidate for large-scale production intended for biomedical application because of its high yield and the special properties of the resulting nanotubes, especially their small diameters, which are more appropriate for drug delivery and long circulation. TNTs' properties highly differ according to the preparation conditions, which would later affect their subsequent application field. The aim of this review is to discuss the factors that could possibly affect their synthesis and determine the transformations that could happen according to the variation of factors. To fulfil this aim, relevant scientific databases (Web of Science, Scopus, PubMed, etc.) were searched using the keywords titanate nanotubes, hydrothermal treatment, synthesis, temperature, time, alkaline medium, post treatment, acid washing, calcination, pharmaceutical applications, drug delivery, etc. The articles discussing TNTs preparation by hydrothermal synthesis were selected, and papers discussing other preparation methods were excluded; then, the results were evaluated based on a careful reading of the selected articles. This investigation and comprehensive review of different parameters could be the answer to several problems concerning establishing a producible method of TNTs production, and it might also help to optimize their characteristics and then extend their application limits to further domains that are not yet totally revealed, especially the pharmaceutical industry and drug delivery.

Copper nanoparticles encapsulated in zeolitic imidazolate framework-8 as a stable and selective CO2 hydrogenation catalyst

Metal-organic frameworks have drawn attention as potential catalysts owing to their unique tunable surface chemistry and accessibility. However, their application in thermal catalysis has been limited because of their instability under harsh temperatures and pressures, such as the hydrogenation of CO2 to methanol. Herein, we use a controlled two-step method to synthesize finely dispersed Cu on a zeolitic imidazolate framework-8 (ZIF-8). This catalyst suffers a series of transformations during the CO2 hydrogenation to methanol, leading to ~14 nm Cu nanoparticles encapsulated on the Zn-based MOF that are highly active (2-fold higher methanol productivity than the commercial Cu-Zn-Al catalyst), very selective (>90%), and remarkably stable for over 150 h. In situ spectroscopy, density functional theory calculations, and kinetic results reveal the preferential adsorption sites, the preferential reaction pathways, and the reverse water gas shift reaction suppression over this catalyst. The developed material is robust, easy to synthesize, and active for CO2 utilization.

Lewis Acidic Support Boosts C-C Coupling in the Pulsed Electrochemical CO2 Reaction

Copper-oxide electrocatalysts have been demonstrated to effectively perform the electrochemical CO₂ reduction reaction (CO₂RR) toward C₂₊ products, yet preserving the reactive high-valent CuO_x has remained elusive. Herein, we demonstrate a model system of Lewis acidic supported Cu electrocatalyst with a pulsed electroreduction method to achieve enhanced performance for C₂₊ products, in which an optimized electrocatalyst could reach ∼76% Faradaic efficiency for C₂₊ products (FE_C2+) at ∼-0.99 V versus reversible hydrogen electrode, and the corresponding mass activity can be enhanced by ∼2 times as compared to that of conventional CuO_x. In situ time-resolved X-ray absorption spectroscopy investigating the dynamic chemical/physical nature of Cu during CO₂RR discloses that an activation process induced by the KOH electrolyte during pulsed electroreduction greatly enriched the Cu^δ+O/Zn^δ+O interfaces, which further reveals that the presence of Zn^δ+O species under the cathodic potential could effectively serve as a Lewis acidic support for preserving the Cu^δ+O species to facilitate the formation of C₂₊ products, and the catalyst structure-property relationship of Cu^δ+O/Zn^δ+O interfaces can be evidently realized. More importantly, we find a universality of stabilizing Cu^δ+O species for various metal oxide supports and to provide a general concept of appropriate electrocatalyst-Lewis acidic support interaction for promoting C₂₊ products.

Cu-Co Co-Doped Microporous Coating on Titanium with Osteogenic and Antibacterial Properties

Titanium (Ti) and its alloys are widely used in bone surgery by virtue of their excellent mechanical properties and good biocompatibility; however, complications such as loosening and sinking have been reported post-implantation. Herein we deposited a copper-cobalt (Cu-Co) co-doped titanium dioxide (TUO) coating on the surface of Ti implants by microarc oxidation. The osteogenic and antimicrobial properties of the coating were evaluated by in vitro experiments, and we also assessed β-catenin expression levels on different sample surfaces. Our results revealed that the coating promoted the adhesion, proliferation, and differentiation of MG63 osteoblasts, and TUO coating promoted β-catenin expression; moreover, the proliferation of Staphylococcus aureus was inhibited. To summarize, we report that Cu-Co co-doping can enhance the osteogenic and antibacterial activities of orthopedic Ti implants, leading to potentially improved clinical performance.

Antiviral Effect of Visible Light-Sensitive CuxO/TiO2 Photocatalyst

Photocatalysis is an effective technology for preventing the spread of pandemic-scale viruses. This review paper presents an overview of the recent progress in the development of an efficient visible light-sensitive photocatalyst, i.e., a copper oxide nanoclusters grafted titanium dioxide (CuxO/TiO2). The antiviral CuxO/TiO2 photocatalyst is functionalised by a different mechanism in addition to the photocatalytic oxidation process. The CuxO nanocluster consists of the valence states of Cu(I) and Cu(II); herein, the Cu(I) species denaturalizes the protein of the virus, thereby resulting in significant antiviral properties even under dark conditions. Moreover, the Cu(II) species in the CuxO nanocluster serves as an electron acceptor through photo-induced interfacial charge transfer, which leads to the formation of an anti-virus Cu(I) species and holes with strong oxidation power in the valence band of TiO2 under visible-light irradiation. The antiviral function of the CuxO/TiO2 photocatalyst is maintained under indoor conditions, where light illumination is enabled during the day but not during the night; this is because the remaining active Cu(I) species works under dark conditions. The CuxO/TiO2 photocatalyst can thus be used to reduce the risk of virus infection by acting as an antiviral coating material.

Antibacterial and osteogenic activity of a multifunctional microporous coating codoped with Mg, Cu and F on titanium

As preferred materials for bone tissue repair and replacement, titanium (Ti) and its alloys have been widely applied in clinical practice. However, since these materials are bioinert, synostosis cannot occur between these materials and natural bone. Therefore, modifying the surface of Ti with bioactive elements has been the subject of intense research. In the present study, a magnesium-copper-fluorine (Mg-Cu-F) codoped titanium dioxide microporous coating (MCFMT) was prepared on the surface of Ti by micro-arc oxidation (MAO). The coating had a micro/nanoporous structure and was uniformly doped with Mg, Cu and F. In vitro, the MCFMT could promote the adhesion, proliferation, differentiation, mineralization and apoptosis of MC3T3-E1 osteoblasts. In addition, MCFMT could inhibit the growth of Staphylococcus, providing a good antibacterial effect. Further studies showed that MCFMT promoted MAPK expression and might promote osteogenesis through ERK1/2 signaling. Therefore, establishing an MCFMT coating on the Ti surface is a feasible and effective way to improve the biological activity of Ti. This study provides a new concept and method for improving the biological activity of Ti and thus has important theoretical significance and potential applications.

Surface deposited one-dimensional copper-doped TiO2 nanomaterials for prevention of health care acquired infections

Bacterial infections acquired in healthcare facilities including hospitals, the so called healthcare acquired or nosocomial infections, are still of great concern worldwide and represent a significant economical burden. One of the major causes of morbidity is infection with Methicillin Resistant Staphylococcus aureus (MRSA), which has been reported to survive on surfaces for several months. Bactericidal activity of copper-TiO2 thin films, which release copper ions and are deposited on glass surfaces and heated to high temperatures, is well known even when illuminated with very weak UVA light of about 10 μW/cm2. Lately, there is an increased intrerest for one-dimensional TiO2 nanomaterials, due to their unique properties, low cost, and high thermal and photochemical stability. Here we show that copper doped TiO2 nanotubes produce about five times more ·OH radicals as compared to undoped TiO2 nanotubes and that effective surface disinfection, determined by a modified ISO 22196:2011 test, can be achieved even at low intensity UVA light of 30 μW/cm2. The nanotubes can be deposited on a preformed surface at room temperature, resulting in a stable deposition resistant to multiple washings. Up to 103 microorganisms per cm2 can be inactivated in 24 hours, including resistant strains such as Methicillin-resistant Staphylococcus aureus (MRSA) and Extended-spectrum beta-lactamase Escherichia coli (E. coli ESBL). This disinfection method could provide a valuable alternative to the current surface disinfection methods.

Mesoporous TiO2 Embedded with a Uniform Distribution of CuO Exhibit Enhanced Charge Separation and Photocatalytic Efficiency

Mixed metal oxide nanoparticles have interesting physical and chemical properties, but synthesizing them with colloidal methods is still challenging and often results in very heterogeneous structures. Here, we describe a simple method to synthesize mesoporous titania nanoparticles implanted with a uniform distribution of copper oxide nanocrystals (CuO@MTs). By calcining a titanium-based metal-organic framework (MIL-125) in the presence of Cu ions, we can trap the Cu in the TiO₂ matrix. Removal of the organic ligand creates mesoporosity and limits phase separation so that tiny CuO nanocrystals form in the interstices of the TiO₂. The CuO@MTs exhibits superior performance for photocatalytic hydrogen evolution (4760 μmol h^-1) that is >90 times larger than pristine titania.

Uniformly active phase loaded selective catalytic reduction catalysts (V2O5/TNTs) with superior alkaline resistance performance

In this work, protonated titanate nanotubes was performed as a potential useful support and different vanadium precursors (NH₄VO₃ and VOSO₄) were used to synthesize deNO_x catalysts. The results showed that VOSO₄ exhibited better synergistic effect with titanate nanotubes than NH₄VO₃, which was caused by the ion-exchange reaction. Then high loading content of vanadium, uniformly active phase distribution, better dispersion of vanadium, more acid sites, better V⁵⁺/V⁴⁺ redox cycles and superior oxygen mobility were achieved. Besides, VOSO₄-based titanate nanotubes catalysts also showed enhanced alkaline resistance than particles (P25) based catalysts. It was strongly associated with its abundant acid sites, large surface area, flexible redox cycles and oxygen transfer ability. For the loading on protonated titanate nanotubes, active metal with cation groups was better precursors than anion ones. V₂O₅/TNTs catalyst was a promising substitute for the commercial vanadium catalysts and the work conducted herein provided a useful idea to design uniformly active phase loaded catalyst.

Synergistic activating effect of promoter and oxidant in single step conversion of methane into methanol over a tailored polymer-Ag coordination complex

Single-step conversion of methane to its oxygenated derivatives, such as methanol, is a challenging topic in C1 chemistry.

Selective catalytic reduction over size-tunable rutile TiO2 nanorod microsphere-supported CeO2 catalysts

Morphology and structure of TiO₂ supports impact NH₃-SCR performance of Ce/Ti catalysts significantly.

XANES, EXAFS and photocatalytic investigations on copper oxide nanoparticles and nanocomposites

CuO nanoparticles, Cu₂O/CuO and CuO/TiO₂ nanocomposites exhibit excellent photocatalyst properties toward the degradation of methyl-orange and potassium-dichromate under the visible light irradiation.

Titanium dioxide as a catalyst support in heterogeneous catalysis

The lack of stability is a challenge for most heterogeneous catalysts. During operations, the agglomeration of particles may block the active sites of the catalyst, which is believed to contribute to its instability. Recently, titanium oxide (TiO₂) was introduced as an alternative support material for heterogeneous catalyst due to the effect of its high surface area stabilizing the catalysts in its mesoporous structure. TiO₂ supported metal catalysts have attracted interest due to TiO₂ nanoparticles high activity for various reduction and oxidation reactions at low pressures and temperatures. Furthermore, TiO₂ was found to be a good metal oxide catalyst support due to the strong metal support interaction, chemical stability, and acid-base property. The aforementioned properties make heterogeneous TiO₂ supported catalysts show a high potential in photocatalyst-related applications, electrodes for wet solar cells, synthesis of fine chemicals, and others. This review focuses on TiO₂ as a support material for heterogeneous catalysts and its potential applications.

Zn-doped nanocrystalline TiO2 films for CdS quantum dot sensitized solar cells

Quantum dot-sensitized solar cells based on Zn-doped TiO(2) (Zn-TiO(2)) film photoanode and polysulfide electrolyte were fabricated. Zn-TiO(2) nanoparticles were obtained via a hydrothermal method and screen printed on the fluorine-doped tin oxide glass to prepare the photoanode. The structure, morphology and impedance of the Zn-TiO(2)/CdS film and the photovoltaic performance of the Zn-TiO(2)/CdS cell were investigated. It was found that the photovoltaic efficiency was improved by 24% when the Zn-TiO(2) film was adopted as the photoanode of CdS QDSSCs instead of only the TiO(2) layer. The improvement was ascribed to the reduction of electron recombination and the enhancement of electron transport in the TiO(2) film by Zn doping.

Facile assembly of cadmium sulfide quantum dots on titanate nanobelts for enhanced nonlinear optical properties

A facile route to assemble cadmium sulfide (CdS) quantum dots (QDs) uniformly on the surface of titanate nanobelts (TNBs) through electrostatic interactions is demonstrated. The photophysical properties of the resulting TNB-CdS nanostructured composite, including optical limiting properties, were studied using ultraviolet-visible absorption spectroscopy, photoluminescence spectroscopy, and the open aperture Z-scan technique in the nanosecond regime using a laser with a wavelength of 532 nm. The linear and nonlinear optical properties of this composite nanostructure were strongly influenced by a possible charge/energy transfer process between the QDs and TNBs. The as-prepared TNB-CdS composite offers an optical limiting effect that is superior to that of unmodified CdS QDs and TNBs. The main contributors to the enhanced optical limiting effect in the TNB-CdS composite were a combination of nonlinear scattering and increased nonlinear absorption resulting from efficient charge/energy transfer at the CdS/TNB interface.