TiO2 Nanomaterials Research Articles

(Invited) Anodic TiO2 Nanotube Layers: Efficient Photocatalyst

The self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 15 years motivated by their possible range of applications including photocatalysis, solar cells, hydrogen generation and biomedical uses [1,2]. The synthesis of these 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheet.Among other TiO2 nanomaterials, these nanotube layers stand out due to their directionality, tunability of dimensions, ability to absorb significant amount of incident light and the possibility to utilize nanotube interiors and exteriors for decoration-coating of secondary materials.One of the most significant applications of TiO2 nanomaterials is photocatalysis, which is very effective to decompose various pollutants (e.g. dyes) and kill bacteria [3,4].The presentation will focus on the utilization of the nanotube layer for photocatalytic removal of various species in the liquid phase [5, 6] as well as gas phase [7]. We will demonstrate the photocatalytic performance of recently developed single-wall TiO2 nanotubes and single-tube TiO2 powders [8]. We will also show that various modifications of nanotube ssecondary materials have a positive influence on photo-electrochemical properties of nanotube layers [9,10]. Experimental details and some recent photocatalytic results will be presented and discussed.

How Can the Introduction of Zr4+ Ions into TiO2 Nanomaterial Impact the DSSC Photoconversion Efficiency? A Comprehensive Theoretical and Experimental Consideration.

A series of pure and doped TiO2 nanomaterials with different Zr4+ ions content have been synthesized by the simple sol-gel method. Both types of materials (nanopowders and nanofilms scratched off of the working electrode’s surface) have been characterized in detail by XRD, TEM, and Raman techniques. Inserting dopant ions into the TiO2 structure has resulted in inhibition of crystal growth and prevention of phase transformation. The role of Zr4+ ions in this process was explained by performing computer simulations. The three structures such as pure anatase, Zr-doped TiO2, and tetragonal ZrO2 have been investigated using density functional theory extended by Hubbard correction. The computational calculations correlate well with experimental results. Formation of defects and broadening of energy bandgap in defected Zr-doped materials have been confirmed. It turned out that the oxygen vacancies with substituting Zr4+ ions in TiO2 structure have a positive influence on the performance of dye-sensitized solar cells. The overall photoconversion efficiency enhancement up to 8.63% by introducing 3.7% Zr4+ ions into the TiO2 has been confirmed by I-V curves, EIS, and IPCE measurements. Such efficiency of DSSC utilizing the working electrode made by Zr4+ ions substituted into TiO2 material lattice has been for the first time reported.

Cost Effective Solvothermal Method to Synthesize Zn-Doped TiO2 Nanomaterials for Photovoltaic and Photocatalytic Degradation Applications

Titanium dioxide (TiO2) is a commonly used wide bandgap semiconductor material for energy and environmental applications. Although it is a promising candidate for photovoltaic and photocatalytic applications, its overall performance is still limited due to low mobility of porous TiO2 and its limited spectral response. This limitation can be overcome by several ways, one of which is doping that could be used to improve the light harvesting properties of TiO2 by tuning its bandgap. TiO2 doped with elements, such as alkali-earth metals, transition metals, rare-earth elements, and nonmetals, were found to improve its performance in the photovoltaic and photocatalytic applications. Among the doped TiO2 nanomaterials, transition metal doped TiO2 nanomaterials perform efficiently by suppressing the relaxation and recombination of charge carriers and improving the absorption of light in the visible region. This work reports the possibility of enhancing the performance of TiO2 towards Dye Sensitised Solar Cells (DSSCs) and photocatalytic degradation of methylene blue (MB) by employing Zn doping on TiO2 nanomaterials. Zn doping was carried out by varying the mole percentage of Zn on TiO2 by a facile solvothermal method and the synthesized nanomaterials were characterised. The XRD (X-Ray Diffraction) studies confirmed the presence of anatase phase of TiO2 in the synthesized nanomaterials, unaffected by Zn doping. The UV-Visible spectrum of Zn-doped TiO2 showed a red shift which could be attributed to the reduced bandgap resulted by Zn doping. Significant enhancement in Power Conversion Efficiency (PCE) was observed with 1.0 mol% Zn-doped TiO2 based DSSC, which was 35% greater than that of the control device. In addition, it showed complete degradation of MB within 3 h of light illumination and rate constant of 1.5466×10−4s−1 resembling zeroth order reaction. These improvements are attributed to the reduced bandgap energy and the reduced charge recombination by Zn doping on TiO2.

A novel solar radiation absorption enhancement of TiO2 nanomaterial by a simple hydrogenation method

A novel solar radiation absorption enhancement of TiO2 nanomaterial by a simple hydrogenation method

Single-step synthesis of TiO2/WO3−x hybrid nanomaterials in ethanoic acid: Structure and photoluminescence properties

In this paper, we report the one-step synthesis of the TiO2/WO3−x hybrid nanomaterials in ethanoic acid using the tungsten hexachloride (WCl6) and titanium butoxide precursors. The characterization results indicate that the WO3−x incorporation in TiO2 nanomaterials leads to the morphology conversion of TiO2 nanomaterials from the nanoparticles to the nanowire beams. The conversion mechanism is based on enhancing the nucleation rate of TiO2 and the viscosity of the solution containing the mixed WCl6 powder and titanium butoxide precursors. The photoluminescence (PL) studies reveal that the as-synthesized TiO2/WO3−x hybrid nanomaterials generate the UV, blue, green and red light, and these emissions are related to the band-band transition, surface states, oxygen vacancies and the transition between the gap state and valence band, respectively. Furthermore, WO3−x also leads to the PL quenching due to the oxygen vacancy migration and charge transfer across the TiO2/WO3−x interfaces and the enhancement of nonradiative recombination centers. Finally, the application of the as-synthesized hybrid nanomaterials in the area of photocatalysis was explored.

Recent Advances in the Synthesis of Polymer-Grafted Low-K and High-K Nanoparticles for Dielectric and Electronic Applications.

The synthesis of polymer-grafted nanoparticles (PGNPs) or hairy nanoparticles (HNPs) by tethering of polymer chains to the surface of nanoparticles is an important technique to obtain nanostructured hybrid materials that have been widely used in the formulation of advanced polymer nanocomposites. Ceramic-based polymer nanocomposites integrate key attributes of polymer and ceramic nanomaterial to improve the dielectric properties such as breakdown strength, energy density and dielectric loss. This review describes the “grafting from” and “grafting to” approaches commonly adopted to graft polymer chains on NPs pertaining to nano-dielectrics. The article also covers various surface initiated controlled radical polymerization techniques, along with templated approaches for grafting of polymer chains onto SiO2, TiO2, BaTiO3, and Al2O3 nanomaterials. As a look towards applications, an outlook on high-performance polymer nanocomposite capacitors for the design of high energy density pulsed power thin-film capacitors is also presented.

Facile synthesized TiO2 with excellent electrochemical performances for lithium-oxygen batteries

Benefited from the super-high theoretical energy storage density, the rechargeable lithium–oxygen batteries (LOBs) are perceived as a shiniest energy conversion and storage devices with the highest potential. To gain the stable and long-life cycle performance and high-efficiency energy storage device, developing of non-toxic, environmental protection and price moderate cathode catalyst is a vital component to the application of the LOBs. Here, TiO2 nanomaterials, as low cost, environmentally friendly and effective cathode catalyst had been synthesized with a facile hydrothermal method and followed calcination processes. The structure, surface morphology and the growth mechanism of the as synthesized TiO2 nanotubes, TiO2 nanofibers were studied in detail. When they were applied as cathode materials for LOBs, TiO2 nanotubes exhibits better electrochemical performance and good cycling stability for over 132 cycles accompanied by a fixed capacity of 600 mAh g−1 at a current density of 200 mA g−1, which is better than the TiO2 nanofibers. The good performances could be originated from the high specific surface area and the large amounts of oxygen vacancy in the TiO2 nanotubes samples.

Multigenerational Exposure to Nano‐TiO2 Induces Ageing as a Stress Response Mitigated by Environmental Interactions

Despite their ubiquity in personal care products, the health implications of titanium dioxide (TiO2) nanomaterials (NMs) are under strenuous investigation for their potential as a carcinogen, whereas other evidence has shown links with premature ageing. Both potential hazards are manifested after chronic exposure. To explore the chronic effects of TiO2 NMs in the environment, a multigenerational study using the model test species Daphnia magna is conducted. Phenotypical characteristics associated with ageing are observed (loss or shortening of tails and lipid accumulation) with increased expression of highly conserved key stress response genes involved in inflammatory responses and oxidative stress. These responses are visible in continuously exposed daphnids over four generations and in daphnids removed from maternal exposure even three generations later. However, exposure to the “aged” variants of these NMs at the same concentrations significantly reduced these effects, and exposure in medium containing natural organic matter is less severe than in salt‐only medium.

Innovative Polymeric Hybrid Nanocomposites for Application in Photocatalysis.

The immobilization of inorganic nanomaterials on polymeric substrates has been drawing a lot of attention in recent years owing to the extraordinary properties of the as-obtained materials. The hybrid materials, indeed, combine the benefits of the plastic matter such as flexibility, low-cost, mechanical stability and high durability, with them deriving from their inorganic counterparts. In particular, if the inorganic fillers are nanostructured photocatalysts, the originated hybrid systems will be able to utilize the energy delivered by light, catalysing chemical reactions in a sustainable pathway. Most importantly, since the nanofillers can be ad-hoc anchored to the macromolecular structure, their release in the environment will be prevented, thus overcoming one of the main restrictions that impedes their applications on a large scale. In this review, several typologies of hybrid photocatalytic nanomaterials, obtained by using both organic and inorganic semiconductors and realized with different synthetic protocols, were reported and discussed. In the first part of the manuscript, nanocomposites realized by simply blending the TiO2 or ZnO nanomaterials in thermoplastic polymeric matrices are illustrated. Subsequently, the atomic layer deposition (ALD) technique is presented as an excellent method to formulate polymeric nanocomposites. Successively, some examples of polyporphyrins hybrid systems containing graphene, acting as photocatalysts under visible light irradiation, are discussed. Lastly, photocatalytic polymeric nanosponges, with extraordinary adsorption properties, are shown. All the described materials were deeply characterized and their photocatalytic abilities were evaluated by the degradation of several organic water pollutants such as dyes, phenol, pesticides, drugs, and personal care products. The antibacterial performance was also evaluated for selected systems. The relevance of the obtained results is widely overviewed, opening the route for the application of such multifunctional photocatalytic hybrid materials in wastewater remediation.

Tuning crystal structure of iridium-incorporated titanium dioxide nanosupport and its influence on platinum catalytic performance in direct ethanol fuel cells

Titanium dioxide (TiO2) has recently been used as a promising support for platinum (Pt)-based catalysts; however, its very low electrical conductivity and understanding the effect of the TiO2 structure on Pt electrocatalytic performance for ethanol electro-oxidation reaction (EOR) are major challenges in direct ethanol fuel cells. This study reports an easy and green approach to control the crystal structures of a robust iridium-incorporated TiO2 nanomaterial and its effect on the Pt electrocatalytic performance for EOR. A green hydrothermal route is used to fabricate iridium-modified TiO2 nanosupports with different structures by controlling the reaction temperature and time as well as solution pH without using further calcination, followed by the anchoring of Pt nanoparticles (NPs) via a surfactant-free modified reduction route. The experimental results indicate that the pure structure of the iridium-modified TiO2 nanosupport can easily be obtained by controlling the solution pH. In terms of EOR, all prepared catalysts show more effective performance than the commercial Pt/C catalyst. Among the prepared catalysts, the Pt anchored on the rutile iridium-incorporated TiO2 exhibits higher EOR performance than on the anatase iridium-incorporated TiO2 nanosupport, with negative onset potential, high current density, and electrochemical stability. The enhancement is assigned to the great adsorption and desorption ability as well as the high natural resistance to metal NPs ripening on (110) facets of the rutile structure compared with the (101) facets of the anatase structure. This exploration can offer an efficient route for tuning the structure of metal oxides and understanding the effect of the structure of the TiO2-based support on the Pt catalytic performance.

Carbon-doped titanium dioxide nanoparticles for visible light driven photocatalytic activity

This work reports tuning of the band gap of the titanium dioxide (TiO2) nanoparticles by carbon doping during sol-gel synthesis. Herein, polydiallyldimethylammonium chloride (PDADMAC), a cationic polymer has been used as the carbon source. The band gap, microstructure and the phase of the synthesized TiO2 can be engineered by controlling the concentration of PDADMAC. A significant reduction in the band gap energy from 2.96 eV to 2.37 eV was observed upon carbon doping. Phonon Confinement Model was employed to investigate the material properties. Theoretical calculations based on Density Functional Theory have also suggested the reduction of band gap as a result of significant interaction between carbon, titanium and oxygen atoms in the lattice. These studies have also proved that structural modifications also occurred due to doping of carbon atom in TiO2 nanomaterial. Carbon-doping resulted in a more efficient photocatalytic activity of the TiO2 nanoparticles. The kinetics and thermodynamics of photodegradation of methylene blue was investigated in detail.

Crystal Phase-Related Toxicity of One-Dimensional Titanium Dioxide Nanomaterials on Kidney Cells.

One-dimensional (1D) nanomaterials are widely used in different fields, and the increased application of 1D nanomaterials has drawn concerns about their unknown toxicity. 1D titanium oxide (TiO2) nanomaterials in different crystal phases are commonly applied in environmental remediation and solar energy conversion fields, but these materials pose a threat to human health, especially to the kidneys, an organ with abundant blood flow. To systematically evaluate the cytotoxicity to the kidneys, TiO2 nanofibers with TiO2(B), anatase, and rutile phases, as well as nanorods with anatase and rutile phases were synthesized and added to the culture medium of HK2 cells. Cell counting kit-8 assay, 2',7'-dichlorofluorescin diacetate assay, Hoechst 33342 staining experiments, and quantitative real-time reverse transcription polymerase chain reaction tests were used to explore the renal effects of the as-prepared TiO2 nanomaterials in the short term or long term. In the short-term evaluation, all the added TiO2 nanomaterials were toxic to HK2 cells, and the cytotoxicity was dose-dependent. Rutile TiO2 can widely attach to the cell surface and displays the most serious cell-killing and proapoptotic ability, while anatase induces the most serious oxidative stress. In long-term evaluation, all the as-prepared TiO2 nanomaterials led to epithelial mesenchymal transition (EMT), a mechanism of renal fibrosis. Consistent with the short-term results, rutile induced the most serious EMT. This study indicated that the renal toxicity of 1D TiO2 nanomaterials is crystal phase-dependent and that rutile induced the most significant renal cell injury. Oxidative stress is a crucial but not the only contributor to the renal toxicity of TiO2 nanomaterials in the short term.

Solid State Reaction Synthesis and Characterization of Cu doped TiO2 Nanomaterials

In this work, copper-doped titanium dioxide (TiO2) nano-powder with of different doping concentration, weights were successfully fabricated with a classical method. This method authorizes obtaining pellets from powder in nonmetric scale with a small quantity. The best conditions for fabrication these pellets are acquired. Different quantities of Cu concentrations (0%, 3%, 5%, and 7%) are mixed with TiO2 (NPs) nano-particles. Then, the mixed powders are transformed into pellets using hydraulic press and sintered by a traditional furnace at temperature of about 1100 °C. The following apparatus demonstrates the structural, morphological, mechanical, optical properties and the composition of elements of materials for those as-prepared samples: X-ray diffraction (XRD), optical microscope, scanning electronic microscope (SEM), Shore D hardness instrument, roughness test Instrument, Lee’s Disc, Fourier-transform infrared spectroscopy (FTIR) and Energy-dispersive X-ray spectroscopy (EDS) respectively. The effects of Cu doped concentrations on the properties of TiO2 NPs based on the above instruments are examined. Crystalinality of these materials revealed by XRD patterns and have a grain size between (20-30) nm. A roughness measurement points that TiO2 NPs values decreases with the addition of Cu weights because of hardness values of the samples. Moreover, results showed that the thermal conductivity increased with the increasing the weight fraction of Cu element. The main goal of the present research is to demonstrate the annealing temperature dependent behavior of the broadening parameter and the properties of Cu doped TiO2 NPs.

Probing Acid–Base Properties of Anatase TiO2 Nanoparticles with Dominant {001} and {101} Facets Using Methanol Chemisorption and Surface Reactions

In the present study, we investigate the surface acid–base properties of anatase TiO2 nanomaterials with dominant {101} and {001} facets via methanol titrations. Two anatase nanoparticles, TiO2(101...

Gemini surfactant assisted synthesis of mesoporous Mn/Mg bimetal doped TiO2 nanomaterial: characterization and photocatalytic activity studies under visible light irradiation

The present work mainly aimed to synthesize different weight percentages (0.25–1.00 wt%) of Manganese (Mn2+) and Magnesium (Mg2+) bimetal ions doped TiO2 nanomaterial assisted with different weight percentages (5–15 wt%) of Gemini surfactant (GS) using sol-gel method. The bimetal doped and undoped TiO2 photocatalysts were characterized by X-ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, Fourier Transform Infrared Spectroscopy (FT-IR), UV-Visible Diffused Reflectance Spectroscopy, Transmission Electron Microscopy, Brunauer-Emmett-Teller surface area analyzer, and Photoluminescence Spectroscopy. Characterization results revealed that mesoporous multi-particle anatase TiO2 nanoparticles with a narrowed band gap, small particle size, and high surface area were formed due to the combined effect of Mn2+/Mg2+ bimetal ions doping and effective encapsulation of GS over the initially formed TiO2 nanoparticles. The surface elemental composition of the 0.25 wt% Mn2+ and 1.00 wt% Mg2+ bimetal doped TiO2 in the presence of 10 wt% of GS (after calcination) revealed the presence of both the metal dopants Mn2+ and Mg2+ along with the Ti and O and their chemical interactions were further confirmed by FT-IR results. The photocatalytic activity of these catalysts was assessed by the degradation of Methyl Red using visible light irradiation. To understand the effect of different reaction parameters on the photocatalytic activity of the nanocatalysts such as the dopant concentration, surfactant concentration, catalyst dosage, solution pH, and initial dye concentration were investigated and optimized to achieve the best performance. The photoluminescence results conclude that OH radicals are the crucial reactive species responsible for oxidative photocatalytic degradation of Methyl Red.

Substoichiometric titanium oxide Ti2O3 exhibits greater efficiency in enhancing hydrolysis of 1,1,2,2-tetrachloroethane than TiO2 nanomaterials

Oxygen-deficient substoichiometric titanium oxides, or “titanium suboxides,” are produced incidentally from coal combustion and are environmentally abundant. Additionally, titanium suboxide nanomaterials are promising new materials with likely future environmental release. How these materials may affect contaminant fate differently than stoichiometric TiO2 (nano)materials is largely unknown. Here, we show that Ti2O3 (selected as a model titanium suboxide) exhibits significantly greater efficiency in enhancing the hydrolysis of 1,1,2,2-tetrachloroethane (TeCA), a common groundwater contaminant, than the stoichiometric anatase and rutile TiO2. At environmentally relevant pH (6.5–7.5), the surface area-normalized pseudo-first-order hydrolysis rate constant in the presence of Ti2O3 is approximately an order of magnitude higher than those associated with TiO2. The superior catalytic efficiency of Ti2O3 can be attributed to both its higher surface hydrophobicity, which renders higher adsorption affinity for TeCA, and its higher concentration of Lewis acid sites (mainly the Ti3+ and the five-coordinated Ti4+). Particularly, the deprotonated hydroxyl groups attached to Ti3+ (a weaker Lewis acid than Ti4+) exhibit higher basicity and thus, are more effective in catalyzing the base-promoted hydrolysis reaction. The findings call for further understanding of the environmental implications of titanium suboxide (nano)materials, which may not be readily predictable based on the knowledge acquired for TiO2.

Free-standing nitrogen-doped TiO2 nanorod arrays with enhanced capacitive capability for supercapacitors

TiO2 nanomaterials have attracted desirable attention as advanced electrode materials in supercapacitors, but they suffer from poor conductivity and low capacitance. Herein, we developed an effective approach to dramatically boost the capacitive capability of TiO2 nanorods by controlling the morphology of TiO2 and introducing N dopants upon nitridation process. The nitrided TiO2 with different morphologies are facilely synthesized by a seed-assisted hydrothermal method with different concentrations of nanosize TiO2 as seeds and subsequent nitridation. Without seeding, TiO2 nanorods are assembled into porous microflowers, while the introduction of seeds can induce the vertical growth of TiO2 nanorods. The results also show that the morphology of TiO2 can affect the doping degree of nitrogen. Owing to the improved charge transport and unique free-standing nanorod structure, the optimized nitrided TiO2 electrode obtains a remarkable areal capacitance of 177.1 mF cm−2 at 4 mA cm−2, which is much larger than nitrided TiO2 electrode without seeding (16 mF cm−2). This provides a general method for increasing the areal capacitance of nanomaterials by adjusting the seed solution concentration of the seed-assisted method.

Large-Scale Synthesis Route of TiO2 Nanomaterials with Controlled Morphologies Using Hydrothermal Method and TiO2 Aggregates as Precursor.

TiO2 of controlled morphologies have been successfully prepared hydrothermally using TiO2 aggregates of different sizes. Different techniques were used to characterize the prepared TiO2 powder such as XRD, XPS, FEGSEM, EDS, and HRTEM. It was illustrated that the prepared TiO2 powders are of high crystallinity with different morphologies such as nanobelt, nanourchin, and nanotube depending on the synthesis conditions of temperature, time, and additives. The mechanism behind the formation of prepared morphologies is proposed involving nanosheet intermediate formation. Furthermore, it was found that the nanoparticle properties were governed by those of TiO2 nanoparticles aggregate used as a precursor. For example, the size of prepared nanobelts was proven to be influenced by the aggregates size used as a precursor for the synthesis.

The Role of Adsorption in the Photocatalytic Decomposition of Dyes on APTES-Modified TiO2 Nanomaterials

This work investigated for the first time the role of adsorption in the photocatalytic degradation of methylene blue and Orange II dyes in the presence of 3-aminopropyltriethoxysilane (APTES)-modified TiO2 nanomaterials. It has been demonstrated that the decrease in adsorption has a detrimental effect on photocatalytic activity. APTES/TiO2 photocatalysts were successfully prepared by solvothermal modification of TiO2 in a pressure autoclave, followed by heat treatment in an inert gas atmosphere at the temperature range from 300 °C to 900 °C. It was observed that functionalization of TiO2 via APTES effectively suppressed the anatase-to-rutile phase transformation, as well as the growth of crystallites size during calcination, and reduction of specific surface area (APTES modification inhibits sintering of crystallites). The noted alterations in the adsorption properties, observed after the calcination, were generally related to changes in the surface characteristics, mainly surface charges expressed by the zeta potential. Positively charged surface enhances adsorption of anionic dye (Orange II), while negatively charged surface was better for adsorption of cationic dye (methylene blue). The adsorption process substantially affects the efficiency of the photocatalytic oxidation of both dyes. The methylene blue decomposition proceeded according to the pseudo-first and pseudo-second-order kinetic models, while the degradation of Orange II followed the zero, pseudo-first, and pseudo-second order kinetic models.

Different physiological responses of C3 and C4 plants to nanomaterials.

Several studies have previously reported that nanomaterial uptake and toxicity in plants are species dependent. However, the differences between photosynthetic pathways, C3 and C4, following nanomaterial exposure are poorly understood. In the current work, wheat and rice, two C3 pathway species are compared to amaranth and maize, which utilize the C4 photosynthetic mechanism. These plants were cultured in soils which were spiked with CuO, Ag, TiO2, MWCNT, and FLG nanomaterials. Overall, the C4 plant exhibited higher resilience to NM stress than C3 plants. In particular, significant differences were observed in chlorophyll contents with rice returning a 40.9-54.2% decrease compared to 3.5-15.1% for maize. Fv/Fm levels were significantly reduced by up to 51% in rice whereas no significant reductions were observed in amaranth and maize. Furthermore, NM uptake in the C3 species was greater than that in C4 plants, a trend that was also seen in metal concentration. TEM results showed that CuO NPs altered the chloroplast thylakoid structure in rice leaves and a large number of CuO NPs were observed in the vascular sheath cells. In contrast, there were no significant changes in the chloroplasts in the vascular sheath and no significant CuO NPs were found in maize leaves. This study was the first to systematically characterize the effect of metal and carbon-based nanomaterials in soil on C3 and C4 plants, providing a new perspective for understanding the impact of nanomaterials on plants.