Titania Shell Research Articles

Probing the Nanonewton Mitotic Cell Deformation Force by Ion-Resonance-Enhanced Photonics Force Microscopy.

Mechanical forces are essential for regulating dynamic changes in cellular activities. A comprehensive understanding of these forces is imperative for unraveling fundamental mechanisms. Here, we develop a microprobe capable of facilitating the measurement of biological forces up to nanonewton levels in living cells. This probe is designed by coating the core of anatase titania particles with amorphous titania and silica shells and an upconversion nanoparticles (UCNPs) layer. Leveraging both antireflection and ion resonance effects from the shells, the optically trapped probe attains a maximum lateral optical trap stiffness of 14.24 pN μm-1 mW-1, surpassing the best reported value by a factor of 3. Employing this advanced probe in a photonic force microscope, we determine the elasticity modulus of mitotic HeLa cells as 1.27 ± 0.3 kPa. Nanonewton probes offer the potential to explore 3D cellular mechanics with unparalleled precision and spatial resolution, fostering a deeper understanding of the underlying biomechanical mechanisms.

Impact of Encapsulated Phase Change Material Additives for Improved Thermal Performance of Silicone Gel Insulation

Abstract Passive cooling through phase change materials (PCM) creates beneficial complimentary cooling techniques aimed at providing thermal gradient mitigation during device operation without additional power requirements. These have been well studied but are difficult to implement due to complications concerning effective enclosure of the liquid phase. Encapsulated PCM particles can be embedded in other materials to form composites with form stable solid–liquid phase transitions. This study characterizes a new composite of silicone gel and encapsulated phase change materials (ePCMs) for use as an encapsulant. The ePCMs contain a paraffin core and titania shell resulting in a self-contained solid–liquid phase transition producing an average of 132.9 J/g of latent heat capacity. The gel composites gain latent heat capacity as a linear function of ePCM concentration by weight. The 30% ePCM sample contains 41.0 J/g of latent heat capacity, approximately 30% of ePCM control samples. The specific heat capacity of the silicone gel without ePCMs is 1.539 J/g-° C and 2.825 J/g-° C for the ePCM particles. As the ePCM concentration increases, the specific heat capacity is increased toward the highest value of the pure ePCMs across all temperature ranges. The coefficient of thermal expansion of the composites is increased with ePCM concentration up to a maximum of 96% in the 20% ePCM concentration. The elastic modulus remains relatively constant across ePCM concentrations and temperatures. In the needle–needle breakdown voltage testing the 20% sample has a 6 kV/mm reduction in dielectric strength and higher than 20% ePCM samples show increased variability in strength due to the dispersed particles. Overall, the results from these material characterizations demonstrate the promise of dielectric composites containing ePCM particles to add passive cooling capability into electronics devices without complex structures.

Formation of authigenic titania during the alteration of volcanic glasses in modern deep-sea environments

Titanium (Ti), a typical rock-forming element, is traditionally considered to be lithophile, incompatible, and fluid-immobile, and is recognized as a significant proxy for understanding the oceanic environments, such as the content of terrestrial materials in modern marine sediments. However, recent investigations have revealed the production of various titania minerals through the alteration of volcanic rocks. Considering the occurrence of abundant volcanic rocks (e.g., volcanoclastics, seamounts, and oceanic crusts) in the oceanic environments, the activities of Ti may have been underestimated. Our study provides novel findings on the occurrence and growth mechanism of authigenic titania in the completely altered volcanic glasses collected from Line and Marshall seamounts by using multiple microanalytical methods. Both specimens primarily consist of mixed-layer illite/smectite (I/S), phillipsite, and carbonate-bearing fluorapatite, revealing that the volcanic glasses underwent palagonization processes. Scanning electron micrographs reveal numerous spherical Ti-rich shells with thicknesses of 450–1000 nm, enveloping spherical mixed-layer I/S aggregates with diameters of dozens to hundreds of microns. From the center to the edge of the spherule-shell structures, the concentration of Ti significantly increased. Further analysis using transmission electron microscopy confirms the presence of authigenic Fe-bearing titania particles within these Ti-rich shells. These titania shells likely form as a result of the migration of dissolved Ti(IV) ions and titania nanoparticles, which fill, nucleate, and aggregate at the interfaces of microspherules originally present in the volcanic glasses, ultimately coalescing into micron-sized particles through oriented attachment. Additionally, numerous titania nanoparticles, with aggregate sizes of 4–32 nm, were observed in the pore spaces of the mixed-layer I/S aggregates, likely be those trapped during Ti migration. Brookite is the dominant titania phase in both the titania shells and the smectite pores, with rutile and anatase occasionally present in the titania shells, implying the continuous mineral phase evolution during the growth of titania particles. The occurrence and distribution of titania suggest short-distance migration of Ti during palagonization processes. These findings offer new insight into the brookite formation and the Ti mobilization in basic and oxygen-rich marine environments, which is crucial for understanding the marine geochemical behaviors of Ti.

CeO2–TiO2 oxides with core-shell structure

A series of CeO2–TiO2 composites were synthesized using sol-gel method, and the structures were investigated by HR TEM, XRD, TG-DSC-MS, N2 adsorption-desorption isotherms. The titania coating layer consisting of fine crystallites contributes to properties of the CeO2@TiO2 nanocomposite. The development of the fast, simple, and facile route for the synthesis of novel CeO2@TiO2 core-shell nanocomposite particles was suggested. An approach to increase the shell thickness of titania is to increase the concentration of the precursor of titania, but it also observed the formation of a small amount of independent titania clusters. It is shown that an increase in the titania content leads to the formation of a larger proportion of the rutile phase and a decrease in the proportion of metastable anatase and brookite, while reducing the particle size of the initial ceria core and the specific surface area due to the contact of titania shells, caused by the closer connections between nanoparticles.

Antibacterial activity of core-shell CuxO@TiO2 photocatalyst under UV, vis and dark

The concept of a porous core@shell photocatalytic structure with less stable component as a core (CuxO) and a firm one (TiO2) as a shell having unique antimicrobial properties has been introduced in this study. The CuxO@TiO2 photocatalysts with different compositions (CuxO content from 1 to 50 wt.%), and thus various morphologies (a broad shell of titania composed of fine nanoparticles or incomplete coverage of CuxO core) and properties (oxidation states of elements, crystallite size, photoabsorption properties), have been prepared by water-in-oil microemulsion method. The materials have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS) and scanning transmission electron microscopy (STEM). The antibacterial tests have been performed via suspension method for Escherichia coli (E. coli) K12 in the dark and under UV (300–420 nm) or vis (> 420 nm) irradiation. It has been found that the morphology, which influences also other properties, e.g., surface charge and composition (being responsible for an efficient photocatalyst adsorption on the bacteria surface), is decisive for the overall antibacterial performance. The photocatalyst with the lowest content of copper (1%), and thus with a broad titania shell, exhibits the highest activity in the dark, probably due to the largest content of Cu2O. Interestingly, irradiation of this sample with any photons (UV or vis) is detrimental for antibacterial effect, probably due to the change of oxidation state of copper. In contrast, the irradiation significantly enhances the bactericidal activity of samples with larger content of CuxO (10 and 50%), and thus being not completely covered with titania, probably due to enhanced photocatalytic activity (Z-scheme mechanism) under UV irradiation, and electrostatic attractions between positively and negatively charged copper and bacteria, respectively, under vis light.

Silver nanoparticle-embedded titania nanobelts with tunable electronic band structures and plasmonic resonance for photovoltaic application

Metallic silver nanoparticle (NP)-embedded single-crystalline titania (Ag@TiO2) nanobelts have been prepared by a new process with use of sodium titanates sequentially from ion exchange, thermal hydrogenation to post-calcination. The structural transformation involved and their morphology were characterized. This work explored photovoltaic efficiency of these composite nanobelts as anode materials in dye-sensitized solar cells and their electronic and energy band properties, which correlate with the Ag content. Optical absorption and photoluminescence analyses reveal core Ag NP-induced localized surface plasmon resonance (LSPR) and mediated electron transfer within the titania shell. According to Mott-Schottky analysis, the Ag addition causes an increase in the donor density and an upshift in the flat-band potential of the oxide host. The investigated Ag@TiO2 cells produced higher photocurrents and open-circuit voltages than the bare TiO2 one, and the best performance was attained with a marked enhancement by 72% in the photovoltaic efficiency. As indicated by electrochemical impedance analysis, the Ag-added nanobelts are beneficial to rapid electron diffusion and electron lifetime, so that they promote charge collection efficiency. Synergistic combination of plasmonic resonance, electronic conduction and Fermi-level upshift is a plausible strategy to functionalize the one-dimensional core-shell Ag@TiO2 nanostructures for optoelectronic applications.

Low Concentration Acetone Sensing with ZnO-TiO2 Composites Nanoarrays: A Comparative Study Under Light Illumination

1.Introduction In the past decade, numerous efforts have been taken to develop one-dimensional nanomaterials with specific morphologies such as nanowires and/or NAs because of their large surface to volume ratio. These morphologies also offer a possibility for surface modification so their versatile material properties can be used for different applications. ZnO NAs has been widely used as a sensing layer but the major drawbacks of metal-oxide based sensitive layers are their lack of sensitivity at low operating temperatures. In this work, the ZnO NAs are coated with a thin TiO2 layer to form ZnO-TiO2 composite materials. The combination of ZnO and TiO2 has attained significant attention because of the synergistic advantages these materials could contribute [1]. Several studies have used ZnO-TiO2 composites as a gas sensing layer, however there is a void in the literature, especially in NAs structures for acetone sensing. Hence, this work centres on the investigation of tailored ZnO and TiO2 composites in NAs structures under light illumination for their sensing capability towards low concentrations of acetone (<100 ppm). 2.Experimental In this work ZnO-TiO2 based composite NAs were synthesised by coating a thin layer of (~50 nm) TiO2 using low-temperature CVD on the ZnO NAs grown by hydrothermal synthesis. The composition of TiO2 and ZnO added, the annealing temperature and time plays a crucial role in determining the crystal phase of the material [2]. The TiO2 coated ZnO NAs were annealed at 550 °C (1h, air) to form ZnO-TiO2 core-shell NAs and further annealed at 650 °C (1h, air) to form a mixed metal oxide, hence ZnTiO3 NAs. The surface morphology of the sensitive layers developed were studied using FEI Verios 460L SEM instrument. The acetone vapor sensing event included acetone exposure and recovery (under dry air) steps, each set at 5 minutes. All sensors developed were tested toward different acetone concentrations (ranging from 1.2 to 12.5 ppm). The acetone sensing performance was tested under operating temperatures 45 - 350 °C by applying a potential bias of 6 V DC. A UV light source with a wavelength of 365 nm (maximum intensity up to 2024 µW·cm-2) was used for light-assisted gas sensing. 3.Results and discussion The synthesis procedure schematic and the corresponding SEM images are presented in Figure. 1a-e. The ZnO NAs had an average length and diameter of 1.5 µm and ~30 nm, respectively. The images (Figure. 1d-e) suggest that the thicknesses of the NAs increased significantly after the ~50 nm TiO2 coating. The gas sensing performance of the developed sensors showed a poor dynamic range (Figure. 2a) at 85 °C in dark conditions. When illuminated with light, the sensors showed enhanced response magnitudes and dynamic range (Figure. 2b and 2c). The photo excitation of the sensitive layers has been shown to increase the electron carrier density of the layer, which in turn is hypothesized to facilitate the formation of oxygen ions on the surface of the sensor, which results in a significant increase in sensor response magnitude [3]. In comparison to the pristine ZnO control sensor, the ZnO-TiO2 composite NAs had much higher response magnitude. The annealing of the ZnO NAs coated with TiO2 initiates the diffusion of Ti from the titania shell to the zinc core and vice versa. The Zn2+ ions get substituted with Ti4+ ions in the core thereby the ZnO core becomes electron rich and also increases the affinity to adsorb more oxygen on the surface. The possible reason for the ZnO-TiO2 core-shell NAs to have higher response than the ZnO NAs could be the reactivity of TiO2 in tailored NAs morphology with high surface to volume ratio. Further, the formation of ZnTiO3 NAs introduces structural defects and oxygen deficiencies which results in higher oxygen adsorption on their surface in comparison to pure ZnO sensors. The LoD of the ZnO NAs, ZnO-TiO2 core-shell NAs and ZnTiO3 NAs sensors calculated to be 90, 70, 30 ppb respectively and the sensitivity, adsorption (t90-ads) and desorption (t90-des) time are presented in Table. 1. 4.Acknowledgements The support of the Australian Research Council Discovery Project DP150101939 is acknowledged. All authors acknowledge the RMIT Microscopy and Microanalysis Facility (RMMF) for their scientific and technical assistance and for providing access to their comprehensive infrastructure and research facilities.

Microfluidic Synthesis of Hybrid TiO2-Anisotropic Gold Nanoparticles with Visible and Near-Infrared Activity

Anisotropic gold nanoparticles (AuNPs), with their unique physical and optical properties, are emerging as smart and key nanomaterials and are being exploited in many crucial fields. To further improve their range of action, anisotropic AuNPs have been coupled with semiconductors, mainly TiO2 (titania), receiving great interest as powerful platforms both in biomedicine and in catalytic applications. Such hybrid nanoparticles show new properties that arise from the synergic action of the components and rely on NP size, morphology, and arrangement. Therefore, continuous advances in design and fabrication of new hybrid titania@gold NPs (TiO2@AuNPs) are urgent and highly desirable. Here, we propose an effective protocol to produce multibranched AuNPs covered by a controlled TiO2 thin layer, exploiting a one-pot microfluidic process. The proposed method allows the in-flow and reliable synthesis of titania-functionalized-anisotropic gold nanoparticles by avoiding the use of toxic surfactants and controlling the titania shell formation. TiO2@AuNPs have been fully characterized in terms of morphology, stability, and biocompatibility, and their activity in photocatalysis has been tested and verified.

Gold-core lithium-doped titania shell nanostructures for plasmon-enhanced visible light harvesting with photocatalytic activity

A simple sol-gel synthesis method has been developed to synthesize uniform nanospheres of gold lithium-doped titanium dioxide in anatase phase (Au/Li-TiO2) with a well-defined core-shell structure with the Li-doped titania as shell and Au nanoparticles as core. The resulting core-shell nanoparticles have a high surface area (~494 m2/g) and uniform pore size (~3.5 nm) for the anatase shell. The synthesis of the gold nanoparticles refers to the classical Turkevich synthesis, and the diameter can be regulated by adjusting the amount of HAuCl4. The gold nanoparticles were first covered with citrate group and subsequently removed by thermal treatment. The catalytic performance of Au/Li-TiO2 was investigated using the degradation of rhodamine B in water for a model reaction using UVb and visible light. The high surface area of the anatase shells provides direct access for the reactant molecules to diffuse and subsequently interact with the gold cores.

Low Concentration Acetone Sensing with ZnO-TiO2 Composites Nanoarrays: A Comparative Study Under Light Illumination

1.Introduction In the past decade, numerous efforts have been taken to develop one-dimensional nanomaterials with specific morphologies such as nanowires and/or NAs because of their large surface to volume ratio. These morphologies also offer a possibility for surface modification so their versatile material properties can be used for different applications. ZnO NAs has been widely used as a sensing layer but the major drawbacks of metal-oxide based sensitive layers are their lack of sensitivity at low operating temperatures. In this work, the ZnO NAs are coated with a thin TiO2 layer to form ZnO-TiO2 composite materials. The combination of ZnO and TiO2 has attained significant attention because of the synergistic advantages these materials could contribute [1]. Several studies have used ZnO-TiO2 composites as a gas sensing layer, however there is a void in the literature, especially in NAs structures for acetone sensing. Hence, this work centres on the investigation of tailored ZnO and TiO2 composites in NAs structures under light illumination for their sensing capability towards low concentrations of acetone (<100 ppm). 2.Experimental In this work ZnO-TiO2 based composite NAs were synthesised by coating a thin layer of (~50 nm) TiO2 using low-temperature CVD on the ZnO NAs grown by hydrothermal synthesis. The composition of TiO2 and ZnO added, the annealing temperature and time plays a crucial role in determining the crystal phase of the material [2]. The TiO2 coated ZnO NAs were annealed at 550 °C (1h, air) to form ZnO-TiO2 core-shell NAs and further annealed at 650 °C (1h, air) to form a mixed metal oxide, hence ZnTiO3 NAs. The surface morphology of the sensitive layers developed were studied using FEI Verios 460L SEM instrument. The acetone vapor sensing event included acetone exposure and recovery (under dry air) steps, each set at 5 minutes. All sensors developed were tested toward different acetone concentrations (ranging from 1.2 to 12.5 ppm). The acetone sensing performance was tested under operating temperatures 45 - 350 °C by applying a potential bias of 6 V DC. A UV light source with a wavelength of 365 nm (maximum intensity up to 2024 µW·cm-2) was used for light-assisted gas sensing. 3.Results and discussion The synthesis procedure schematic and the corresponding SEM images are presented in Figure. 1a-e. The ZnO NAs had an average length and diameter of 1.5 µm and ~30 nm, respectively. The images (Figure. 1d-e) suggest that the thicknesses of the NAs increased significantly after the ~50 nm TiO2 coating. The gas sensing performance of the developed sensors showed a poor dynamic range (Figure. 2a) at 85 °C in dark conditions. When illuminated with light, the sensors showed enhanced response magnitudes and dynamic range (Figure. 2b and 2c). The photo excitation of the sensitive layers has been shown to increase the electron carrier density of the layer, which in turn is hypothesized to facilitate the formation of oxygen ions on the surface of the sensor, which results in a significant increase in sensor response magnitude [3]. In comparison to the pristine ZnO control sensor, the ZnO-TiO2 composite NAs had much higher response magnitude. The annealing of the ZnO NAs coated with TiO2 initiates the diffusion of Ti from the titania shell to the zinc core and vice versa. The Zn2+ ions get substituted with Ti4+ ions in the core thereby the ZnO core becomes electron rich and also increases the affinity to adsorb more oxygen on the surface [4]. The possible reason for the ZnO-TiO2 core-shell NAs to have higher response than the ZnO NAs could be the reactivity of TiO2 in tailored NAs morphology with high surface to volume ratio. Further, the formation of ZnTiO3 NAs introduces structural defects and oxygen deficiencies which results in higher oxygen adsorption on their surface in comparison to pure ZnO sensors. The LoD of the ZnO NAs, ZnO-TiO2 core-shell NAs and ZnTiO3 NAs sensors calculated to be 90, 70, 30 ppb respectively and the sensitivity, adsorption (t90-ads) and desorption (t90-des) time are presented in Table. 1. 4.Acknowledgements The support of the Australian Research Council Discovery Project DP150101939 is acknowledged. All authors acknowledge the RMIT Microscopy and Microanalysis Facility (RMMF) for their scientific and technical assistance and for providing access to their comprehensive infrastructure and research facilities.

Magnetic titanium dioxide nanomaterial modified with hydrophilic dicarboxylic ligand for effective enrichment and separation of phosphopeptides and glycopeptides

A dual functionalized magnetic nanomaterial was fabricated by combining the magnetic core, titania shell, and hydrophilic molecules (denoted as Fe3O4@TiO2-IDA). Based on the mechanism of metal oxide affinity chromatography and hydrophilic interaction liquid chromatography, the sorbent shows excellent one-step separation capacity for both glycopeptides and phosphopeptides. For phosphopeptide enrichment, Fe3O4@TiO2-IDA exhibits high sensitivity and selectivity. The concentration of β-casein in the digests can be as low as 0.0125ngμL-1; the mass ratio of β-casein and BSA digest can reach 1:800. For glycopeptide enrichment, Fe3O4@TiO2-IDA also exhibits good performance. The concentration of horseradish peroxidase (HRP) in the digested sample can be as low as 0.04ngμL-1; the mass ratio of HRP and BSA digest can reach 1:100. Following the one-step enrichment, elution, and nano LC-MS/MS analysis, 550 unique phosphopeptides and 330 glycopeptides were identified from 100μg mouse brain sample through asingle run of LC-MS/MS. Graphical abstract Multipurpose Fe3O4@TiO2-IDA nanomaterials are employed in simultaneous enrichment and separation of glycopeptides and phosphopeptides.

Insight into enhanced visible light photocatalytic activity of Fe3O4–SiO2–TiO2 core-multishell nanoparticles on the elimination of Escherichia coli

A nano photocatalyst of Fe3O4–SiO2–TiO2 (FST) was produced, which can be used as a magnetic adsorbent in water treatment e.g. elimination of E.coli. Synthesis of shells on the initial Fe3O4 nanocores was carried out via the sol-gel technique. VSM, PSA, XRD, TEM, FE-SEM, EDS, FTIR and ZETA were analyses conducted for characterization. A 10-nm-passive layer of silica was formed between magnetic core and titania shell to inhibit direct contact of core and shell while superparamagnetic property was preserved. For TiO2 synthesis, it was found that the “concentration of water” and “mixing order of water and TBOT (Titanium butoxide)” had significant effect. Moreover, a minimum ratio of water to TBOT was required for TiO2 nucleation on Fe3O4–SiO2 (FS) seeds. Furthermore, an increment of water concentration to 3.8 M has led to 95% TiO2 coverage on FS nanoparticles. Results showed that FST nanoparticles were completely stable at pH = 7 and had acceptable zeta potential approximately −65 mV. Also, TiO2-coated magnetite nanoparticles (FT) were synthesized with the same condition of FST, but without silica midlayer, in order to observe th effect of SiO2 in nanostructure. Treatment of FST nanoparticles with E.coli showed 98% bacteria adsorption after 100 min, as well significant damage to bacteria cell membrane, was observed by SEM images. However, FT nanoparticles represented 82% bacteria removal with no harsh damage to the cells. This work demonstrated effective presence of SiO2 as a passive layer between Fe3O4 and TiO2 for photocatalytic efficiency improvement.

Facile preparation of polymer-grafted ZIF-8-modified magnetic nanospheres for effective identification and capture of phosphorylated and glycosylated peptides.

As a member of MOFs, Zn-MOFs (ZIF-8) are seldom used in phosphopeptide enrichment because ZIF-8 is soluble in acid solutions. Therefore, properly designing a novel strategy to overcome the defect of ZIF-8 is necessary. In this study, a novel multifunctional nanoprobe was designed by uniting magnetic core, titania shell and hydrophilic metal-organic frameworks (named as Fe3O4@PDA@mTiO2@PEI-g-ZIF-8). Integrating the strategies of hydrophilic interaction affinity chromatography (HILIC), immobilized metal ion affinity chromatography (IMAC) and metal oxide affinity chromatography (MOAC), the Fe3O4@PDA@mTiO2@PEI-g-ZIF-8 mesoporous microspheres can enrich phosphorylated peptides and glycosylated peptides simultaneously. Fe3O4@PDA@mTiO2@PEI-g-ZIF-8 has high selectivity (maximum molar ratio β-casein/HRP : BSA = 1 : 1000), low detection limit (2 fmol) towards phosphopeptides and glycopeptides. Besides, the Fe3O4@PDA@mTiO2@PEI-g-ZIF-8 also exhibited a fine performance in the actual sample detection. In the experiment, taking saliva as a sample, 16 phosphorylated peptides were identified, and from a human serum sample, 4 phosphorylated peptides were selectively identified. All in all, the materials show great potential in the future study of phosphoproteomics and glycoproteomics.

Hollow Au@TiO2 porous electrospun nanofibers for catalytic applications.

Catalytically active porous and hollow titania nanofibers encapsulating gold nanoparticles were fabricated using a combination of sol–gel chemistry and coaxial electrospinning technique. We report the fabrication of catalytically active porous and hollow titania nanofibers encapsulating gold nanoparticles (AuNPs) using a combination of sol–gel chemistry and coaxial electrospinning technique. The coaxial electrospinning involved the use of a mixture of poly(vinyl pyrrolidone) (PVP) and titania sol as the shell forming component, whereas a mixture of poly(4-vinyl pyridine) (P4VP) and pre-synthesized AuNPs constituted the core forming component. The core–shell nanofibers were calcined stepwise up to 600 °C which resulted in decomposition and removal of the organic constituents of the nanofibers. This led to the formation of porous and hollow titania nanofibers, where the catalytic AuNPs were embedded in the inner wall of the titania shell. The catalytic activity of the prepared Au@TiO2 porous nanofibers was investigated using a model reaction of catalytic reduction of 4-nitrophenol and Congo red dye in the presence of NaBH4. The Au@TiO2 porous and hollow nanofibers exhibited excellent catalytic activity and recyclability, and the morphology of the nanofibers remained intact after repeated usage. The presented approach could be a promising route for immobilizing various nanosized catalysts in hollow titania supports for the design of stable catalytic systems where the added photocatalytic activity of titania could further be of significance.

Morphology- and Crystalline Composition-Governed Activity of Titania-Based Photocatalysts: Overview and Perspective

Titania photocatalysts have been intensively examined for both mechanism study and possible commercial applications for more than 30 years. Although various reports have already been published on titania, including comprehensive review papers, the morphology-governed activity, especially for novel nanostructures, has not been reviewed recently. Therefore, this paper presents novel, attractive, and prospective titania photocatalysts, including zero-, one-, two-, and three-dimensional titania structures. The 1D, 2D, and 3D titania structures have been mainly designed for possible applications, e.g., (i) continuous use without the necessity of particulate titania separation, (ii) efficient light harvesting (e.g., inverse opals), (iii) enhanced activity (fast charge carriers’ separation, e.g., 1D nanoplates and 2D nanotubes). It should be pointed out that these structures might be also useful for mechanism investigation, e.g., (i) 3D titania aerogels with gold either incorporated inside the 3D network or supported in the porosity, and (ii) titania mesocrystals with gold deposited either on basal or lateral surfaces, for the clarification of plasmonic photocatalysis. Moreover, 0D nanostructures of special composition and morphology, e.g., magnetic(core)–titania(shell), mixed-phase titania (anatase/rutile/brookite), and faceted titania NPs have been presented, due to their exceptional properties, including easy separation in the magnetic field, high activity, and mechanism clarification, respectively. Although anatase has been usually thought as the most active phase of titania, the co-existence of other crystalline phases accelerates the photocatalytic activity significantly, and thus mixed-phase titania (e.g., famous P25) exhibits high photocatalytic activity for both oxidation and reduction reactions. It is believed that this review might be useful for the architecture design of novel nanomaterials for broad and diverse applications, including environmental purification, energy conversion, synthesis and preparation of “intelligent” surfaces with self-cleaning, antifogging, and antiseptic properties.

Structure, morphology and adsorption properties of titania shell immobilized onto cobalt ferrite nanoparticle core

A magnetic core-shell adsorbent was synthesized by immobilization of titanium dioxide nanoclusters on the cobalt ferrite nanoparticles. The synthesis was carried out using a modified Pechini sol-gel method with citric acid and ethylene glycol as chelating agents. The structure and morphology of reference TiO2, pristine CoFe2O4 and resulting nanocomposite CoFe2O4@TiO2 were thoroughly characterized using XRD, XRF, BET, SEM, IR spectroscopy and Mössbauer spectroscopy. The obtained spectral data indicate that a shift of electron density from titanium to oxygen atoms takes place. Antistructure modeling suggests that some titanium atoms are entered into the CoFe2O4 spinel structure resulting in defects of crystalline structure. In this way additional adsorption centers arise. The adsorption efficiency of the CoFe2O4@TiO2 nanocomposite was found to be more than twice as high as compared to TiO2 and CoFe2O4 alone. The observed synergistic effect is associated just with the formation of distorted titania nanocrystals. The obtained magnetic nanoadsorbent proved to be efficient in water purification from dichromate anions (83% removal) and Congo Red dye (61% removal).

Raspberry-Like Microspheres of Core-Shell Cr2 O3 @TiO2 Nanoparticles for CO2 Photoreduction.

To promote the interaction of p–n semiconductors, raspberry‐like microspheres of core–shell Cr2O3@TiO2 nanoparticles have been fabricated through a five‐step process. Raman spectroscopy of products calcined at various temperatures reveal that the titania shell causes crystal distortion of the Cr2O3 core, without changing the microstructures of the fabricated core–shell microspheres. In situ and time‐resolved synchrotron‐based powder XRD reveals the formation of monoclinic TiO2 in the fourth step, but these monoclinic TiO2 nanocrystals undergo a phase transition when the applied calcination temperature is above 550 °C. As a result, TiO2(B), a magnéli phase of Ti4O7 and Cr2Ti6O15 compounds, resulting from inner doping between Cr2O3 and TiO2, is formed. The close interaction of Cr2O3 and TiO2 forms a p–n junction that decreases the recombination of photogenerated electron–hole pairs, leading to enhanced production of CH4 by photocatalytic reduction of CO2.

UV-protection of cellulosic fabric prints using hyperbranched polyester-stabilized titania coating

This study approached a convenient method for the organic pigment coated with titania for attaining good UV-shielding properties. Hyperbranched polyesters (HBPs) included various HBPs; generation2 (HBPs16) and generation 4 (HBPs 64) are formulated for encapsulation of phthalocyanine pigments using liquid-phase separation method. The encapsulated pigments are then coated by titania via sol-gel process from n-butoxide (TBOT).Thermal gravimetric analysis (TGA), scanning/transmission electron microscope (SEM/TEM), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), X-ray diffraction pattern (XRD), and zeta potential analysis were examined to illustrate the coating performance of titania. The stabilized coated pigment nanocomposites are used for printing of cellulosic fabrics. UV shielding property of the pigment prints was systematically investigated. It is further demonstrated that the obtained titania shells of pigment prints can serve as an efficient protection against UV light and could obviously enhance the UV shielding property. The degree of protection depends on the numbers of functional hydroxyl end groups in hyperbranched polyesters. Besides, the titania coated pigment has no noticeable effect on the driving force for acceleration of pigment printing process under the unfavourable conditions.

One-Step Assembly of TiO2-Liposomes Based on Interfacial Sol-Gel Process within Lipid Bilayer.

There is a growing interest in the use of hybrid liposomes for various biochemical and biomedical applications. In this study, we report the first preparation and characterization of a class of TiO2-reinforced liposomes by a one-step assembly approach. The amphiphilic natural structure of lipids is exploited to localize a hydrophobic molecule, namely, precursor tetrabutyl titanate (TBOT), in the mid-plane of the liposomal bilayer assemblies in the aqueous phase. In situ TiO2 nanoshell formation is driven by subsequent interfacial hydrolysis of TBOT and the ensuing condensation within the hydrophobic interstices of the lipid bilayer. The core-shell structure, like cell and wall, is demonstrated by means of scanning electron microscopy and transmission electron microscopy images, and the formation of the TiO2 shell is confirmed using energy-dispersive X-ray spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. To study the structural evolution of the hybrid liposomes during titania formation, fluorescence probe technique and surface pressure versus molecular area (π- A) isotherms are designed. The results demonstrate that the incorporation of TBOT into the mid-membrane of the lipid and titania in the core of the membrane strengthened the assembly of the lipid bilayer. We further demonstrate that titania shell improved the stability and release property of liposomes. We expect that the reported new TiO2-coated liposomes by co-assembly will be valuable in designing hybrid liposomes, exhibiting integrative capacity for drug encapsulation, compartment reaction, and photocatalysis.

Ultrathin Amorphous Titania on Nanowires: Optimization of Conformal Growth and Elucidation of Atomic-Scale Motifs.

Due to its chemical stability, titania (TiO2) thin films increasingly have significant impact when applied as passivation layers. However, optimization of growth conditions, key to achieving essential film quality and effectiveness, is challenging in the few-nanometers thickness regime. Furthermore, the atomic-scale structure of the nominally amorphous titania coating layers, particularly when applied to nanostructured supports, is difficult to probe. In this Letter, the quality of titania layers grown on ZnO nanowires is optimized using specific strategies for processing of the nanowire cores prior to titania coating. The best approach, low-pressure O2 plasma treatment, results in significantly more-uniform titania films and a conformal coating. Characterization using X-ray absorption near edge structure (XANES) reveals the titania layer to be highly amorphous, with features in the Ti spectra significantly different from those observed for bulk TiO2 polymorphs. Analysis based on first-principles calculations suggests that the titania shell contains a substantial fraction of under-coordinated Ti4+ ions. The best match to the experimental XANES spectrum is achieved with a "glassy" TiO2 model that contains ∼50% of under-coordinated Ti4+ ions, in contrast to bulk crystalline TiO2 that only contains 6-coordinated Ti4+ ions in octahedral sites.