Native TiO2 Research Articles

Unraveling the influence of deposited layers on Ti/RuO2 anodes to define the electroactivity of oxygen evolution and active chlorine reactions

Ti/RuO2 were synthesized using Pechini method with 4, 8 and 16-RuO2 layers, to account for the influence of their physical properties upon their behavior towards reactive oxygen evolution (OER) and active chlorine reaction (CER). Rietveld refinement conducted using X-Ray diffraction (XRD) measurements confirmed the formation of TiO2 (P42/mnm) and RuO2 (P42/mnm, poor rutile-type), which grew on a thin native TiO2 layer forming a solid solution. This analysis corroborated that the smaller RuO2 crystallite size was obtained using 4-layers, unlike the trend of increasing sizes with more layer’s numbers. This situation is not conducive to accessing reactive sites and electronic conduction issues. Interestingly, exchange current densities (j0) in NaCl(aq) presence were higher than Na2SO4(aq) for 4 and 8-layers, evidencing an inhibition of OER to catalyze CER due to RuO2. This behavior is not related to the electroactive area, since this property decreased by rising the number of layers. The 4-layers anode showed the largest production of CER after 20 min of electrolysis, but the lower accelerated lifetime (ALT). Thus, the stacking of more RuO2 layers creates a higher resistance for charge transfer. Likewise, Ti substrate is important to define the CER catalysis, whence a low coverage of RuO2 will be more catalytic than a high coverage of this oxide. The electrode activity was assessed through the removal of 132 µmol L−1 Acetaminophen (ACM), revealing that 93, 80, and 50 % was removed using 4, 8 and 16-layers of RuO2 coating respectively, at 10 mA and 0.1 molL−1 NaCl. Density functional theory (DFT) and high-performance liquid chromatograph coupled to a mass spectrometer (HPLC-MS) were used to propose a reaction mechanism for ACM degradation. Four byproducts with m/z ACM-I-1 (C8H5Cl4NO3) 304, ACM-I-2 (C8H6Cl3NO3) 274, ACM-I-3 (C6H4Cl3NO2) 227, and ACM-I-4 (C6H3Cl3O3) 229 were identified corresponding to the addition of chlorine in the amide group and aromatic ring, as a susceptible site to electrophilic attack.

ELECTROCHEMICAL REDUCTION DOPING OF TiO2 NANOTUBES TO INCREASE THE EFFICIENCY OF PHOTOELECTROCHEMICAL WATER SPLITTING

TiO2 films being a 1D nanotube structure were obtained by electrochemical anodic oxidation of titanium foil. Electrochemical reduction activation of electrodes based on TiO2 nanotubes was carried out using the method of cyclic voltammetry (CV). The activated electrodes showed significantly higher current density and quantum efficiency of the photoelectrochemical water splitting compared to native TiO2 nanotubes. Electrochemical treatment of electrodes by the CV method leads to an increase in the photocurrent density from 4 to 14 times, depending on both the wavelength used and the applied potential. The analysis of electrochemical impedance spectra showed that the increase in the photoelectrochemical process performance is due to an increase in the charge transfer rate at the semiconductor/electrolyte interface, as well as improved electronic conductivity of the oxide layer, which contributes to better charge carrier separation and a decrease in their recombination rate.

Enhanced Effect of Metal Sulfide Doping (MgS-TiO2) Nanostructure Catalyst on Photocatalytic Reduction of CO2 to Methanol

The conversion of CO2 gas from the global emission to methanol can be a route to look at in addressing greenhouse gas (GHG) issues. Photocatalysis has been attracting attention in the conversion of CO2 to methanol, as it is seen to be one of the most viable, economic, and sustainable strategies. The biggest hindrance to the use of metal oxide photocatalysts was the poisoning by sulfur content in the CO2 gas feedstock. Therefore, in the development of photocatalysts using metal oxide-based additives, the metal needs to be in the form of metal sulfides to avoid catalyst poisoning due to the presence of H2S. The magnesium sulfide-based TiO2 (MgS-TiO2) photocatalyst has not been synthesized and studied for its photocatalytic potential. In this study, a novel MgS-TiO2 photocatalyst was synthesized using a combination of wet impregnation and hydrothermal method and characterized to determine the physical and chemical properties of the photocatalyst. Characterization results have shown the presence of MgS on the native TiO2 photocatalyst. The optimization of MgS-TiO2 formulation was conducted, wherein the MgS and TiO2 ratio of 0.5 wt % has been shown to give the highest methanol yield of 229.1 μmol/g·h. The photocatalytic parameter optimization results showed that temperature and catalyst loading were the most important factors that impacted the photocatalytic process. In contrast, reaction time had the least significant effect on the CO2 photocatalytic reduction to methanol. This concludes that the MgS-TiO2 photocatalyst has potential and can be used for the photocatalytic reduction of CO2 to methanol.

Influence of different pretreatments on the adhesion of nanodiamond composite films on Ti substrates via coaxial arc plasma deposition

In this study, we report on the novel growth of nanodiamond composite (NDC) films on titanium (Ti) substrates using the coaxial arc plasma deposition (CAPD) at room temperature, which offers several advantages over conventional growth techniques. CAPD employs a unique coaxial arc plasma gun structure that provides a supersaturated condition of highly energetic carbon ions (C+) for ultrafast quenching on the substrate, promoting the growth of nanodiamond grains. This allows for NDC films’ growth on diverse substrates without the need for initial seeding or substrate heating. However, the growth of NDC films on Ti substrates at room temperature is challenging due to the native oxide layer (TiO2). Here, we grew NDC films on Ti substrates using three different pretreatments: (i) hydrofluoric acid (HF) etching, (ii) insertion of a titanium carbide (TiC) intermediate layer, and (iii) in situ Ar+ plasma etching. The morphology and structure of the grown NDC films were examined by 3D laser, high-resolution scanning electron microscopies (HR-SEM), Raman, and x-ray photoelectron (XPS) spectroscopies. Our results demonstrate that in situ Ar+ plasma etching is the most effective pretreatment method for completely removing the native TiO2 layer compared to the other two ex situ pretreatments, in which re-oxidation is more likely to occur after these pretreatments. Furthermore, NDC films grown using the hybrid Ar+ ion etching gun (IG) and CAPD exhibit the highest sp 3 content (63%) and adhesion strength (16 N).

A Nanohybrid Containing Cyan‐Emitting Copper Nanoclusters and TiO2 Nanoparticles: Tuning of Optoelectronic Properties

AbstractNanohybrid materials are designed to cover up the weaknesses of individual components. In this current work, an environment‐friendly synthesis was used to produce a cyan‐emitting copper nanocluster (Cu NC) with a quantum yield of 8.7 %. This negatively charged nanocluster was successfully used to make a nanohybrid with anatase titanium dioxide mesoporous nanoparticles having Lewis‐acidic pores. The nanohybrid formation was characterized by time‐correlated single‐photon counting studies (TCSPC), solid‐state UV‐visible absorption spectroscopy and valence band X‐ray photoelectron spectroscopy. A systematic increase of Cu NC loading on the TiO2 showed an increase of current from a range of 10−7 A (in native TiO2) to 10−4 A (1 : 10 Cu NC‐TiO2 hybrid). Interestingly, the photocurrent response of TiO2 also dramatically improved from 8.9×10−3 mA to 4.1 mA in1 : 10 Cu NC−TiO2 hybrid. Systematic variation of their weight ratio vividly demonstrated that 10 % w/w TiO2−Cu NC hybrid was the most effective current generator, keeping the semiconducting and photovoltaic nature intact. The increase in photocurrent can be attributed to the long‐lived electron‐hole separation in the nanohybrid system.

Enhanced photoelectrochemical activity of WO3-decorated native titania films by mild laser treatment

The effectiveness of the electrochemical WO3-modification as a method for improving the photoactivity of native air-formed TiO2 layers was assessed. The way in which a mild laser treatment influences the photoelectrochemical performances of the thus obtained WO3/TiO2 systems was also investigated. At laser-treated electrodes (L-WO3/TiO2), the melting-solidification process induced by the treatment led to a smaller size of the deposited WO3 particles and to their better dispersion on the surface. The treatment also enhanced the surface oxygen deficiency and ensured better relative absorptivity of the oxygenated species on the surface. These features, together with the intrinsic narrower bandgap of the WO3-TiO2 composites, the higher donor density and the lower flat band potential of L-WO3/TiO2 enabled faster kinetic of the oxygen photoanodic evolution. Importantly, the same process exhibited a cathodic shift of its onset potential. The laser treatment also strongly enhanced the photoelectrocatalytic performances for UV-assisted methanol anodic oxidation.

Synthesis of an oxygen-permeable block copolymer with catechol groups and its application in polymer-ceramic pressure-sensitive paint

An oxygen-permeable block copolymer, poly (2,2,2-trifluoroethyl-co-isobutyl methacrylate)-b-poly (N-acryloyldopamine) (FEM-b-PDOPA), in which the PDOPA segment acts as an adhesive section to attach TiO2 nanoparticles, was successfully synthesized via RAFT polymerization followed by a post-polymerization modification with dopamine. Conjugates of FEM-b-PDOPA with TiO2 nanoparticles were prepared by mixing them in chloroform and methanol. IR and solid-state CP-MAS 13C NMR spectroscopies clearly indicated the presence of FEM on the TiO2 nanoparticles. Thermogravimetric analysis of the resulting nanoparticles indicated that FEM-b-PDOPA, rather than FEM alone, was tightly bound to the TiO2 nanoparticles, and that the weight fraction was 2.5 wt%. Polymer-ceramic pressure-sensitive paint was prepared by mixing a luminescent dye, FEM, and TiO2 treated with either FEM-b-PDOPA or native TiO2. In comparison with the coating prepared using native TiO2, the pretreatment of TiO2 with FEM-b-PDOPA effectively reduced the photodegradation of the luminescent dye without deterioration in pressure and temperature sensitivity or dynamic response performance.

Self-reduction of the native TiO2 (110) surface during cooling after thermal annealing \u2013 in-operando investigations

We investigate the thermal reduction of TiO2 in ultra-high vacuum. Contrary to what is usually assumed, we observe that the maximal surface reduction occurs not during the heating, but during the cooling of the sample back to room temperature. We describe the self-reduction, which occurs as a result of differences in the energies of defect formation in the bulk and surface regions. The findings presented are based on X-ray photoelectron spectroscopy carried out in-operando during the heating and cooling steps. The presented conclusions, concerning the course of redox processes, are especially important when considering oxides for resistive switching and neuromorphic applications and also when describing the mechanisms related to the basics of operation of solid oxide fuel cells.

Improved suitability as catalyst support and more efficient charge carrier separation of native air-formed TiO2 films by mild laser treatment

The possibility of using native air-formed TiO2 films (N–TiO2) as substrate for platinum deposition and the extent to which the effectiveness of such Pt/TiO2 systems can be improved by a mild laser treatment of the TiO2 support was investigated. Laser-treated titania (LT-TiO2) exhibited homogeneous rough surface and allowed much efficient separation of photogenerated charge carriers. Both N–TiO2 and LT-TiO2 were used as substrates for platinum electrochemical deposition and it was found that the use of the latter enables more uniform distribution and much lower average size of the Pt particles, leading to an enhancement of the electrochemically active specific surface area of ca. 75%. Moreover, the use of a laser-treated titania substrate not only facilitates methanol anodic oxidation overall process but also improves the resistance of the electrocatalyst to deactivation by strong adsorption of intermediates. Upon UV irradiation, Pt/LT-TiO2 electrodes exhibit a strong enhancement of the methanol oxidation current and, importantly, a much better resistance to poisoning.

Surface grafting modification of titanium dioxide by silane coupler KH570 and its influences on the application of blue light curing ink

A series of reactive TiO2 pigments with olefinic double-bonds were prepared by grafting modification of silane coupler KH570 to be covalently anchored in the blue-light curing film, which improved the color fastness to crocking of the printed fabrics significantly. Effects of KH570 concentrations on particle size, surface wettability and dispersing stability of KH570-TiO2 pigments, photo-polymerization of KH570-TiO2 bule-light curing inks and tensile properties of curing films were investigated. Color fastness to crocking of KH570-TiO2 pigment on cotton fabric was explored. Results showed that compared to the native TiO2, all the properties of KH570-TiO2 improved. With the increases of KH570 concentrations, the grafting degrees of KH570-TiO2 had gradual increase. The surface hydrophobicity and dispersion stability of KH570-TiO2 pigments, photo-polymerization of KH570-TiO2 blue-light curing ink and tensile properties of curing films enhanced, especially those of 12∼20KH570-TiO2 the best. Within the concentrations of KH570 12–20 wt %, the printed fabrics had dry/wet color fastness to crocking no less than 4 grades.

Two-step biocompatible surface functionalization for two-pathway antimicrobial action against Gram-positive bacteria.

The use of indwelling devices has emerged as a frequent and often life-saving medical procedure. However, infection in prosthetic surgery is one of the most important and devastating complications. Once the biofilm has been formed, its eradication is extremely difficult, due to an increased resistance to host defense and conventional antimicrobials. Thus, the design of novel strategies for inhibiting the bacterial adhesion on implantable devices is a key point for successful surgical procedures. In this work, the development of a simple two-step protocol to prepare surfaces able to prevent the bacterial growth was successfully achieved. The surface-modification design includes a combined approach involving the multi-functionalization of Ti surfaces with silver nanoparticles (AgNPs) and/or ampicillin (AMP). The surface chemistry involved in AMP adsorption on titanium and silver surfaces was elucidated for the first time, thus establishing the basis for the further anchoring of other antibacterial compounds having similar functional groups. Our results show that the antibiotic binds to the titanium surface through covalent interactions between the COOH groups in AMP and the OH groups of the native TiO2 on the surface, although electrostatic interactions between protonated AMP and negatively charged TiO2 can also contribute to the antibiotic anchoring to the surface. The AMP immobilization on the AgNPs is carried out by thiolate-like bonds. The β-lactam ring functionality is preserved after the adsorption process, since the Ti-AgNPs-AMP surface was able to decrease the bacterial viability in more than 80%. Moreover, the antimicrobial capacity is maintained over time due to a two-pathway antibacterial mechanism: death by contact (AMP) and death by release (AgNPs). The effect of AMP prevails on AgNPs at early stages of bacterial adhesion, while AgNPs are responsible for sustaining the relatively low but steady release of Ag(I), preserving the bacteriostatic activity of the surface over time. This effect would contribute to prevent infections due to sessile cells on indwelling devices, powering the action of the immune system and the conventional antibiotics usually dosed in implanted patients.

Sulfur-Doped TiO2: Structure and Surface Properties

A comprehensive study on the sulfur doping of TiO2, by means of H2S treatment at 673 K, has been performed in order to highlight the role of sulfur in affecting the properties of the system, as compared to the native TiO2. The focus of this study is to find a relationship among the surface, structure, and morphology properties, by means of a detailed chemical and physical characterization of the samples. In particular, transmission electron microscopy images provide a simple tool to have a direct and immediate evidence of the effects of H2S action on the TiO2 particles structure and surface defects. Furthermore, from spectroscopy analyses, the peculiar surface, optical properties, and methylene blue photodegradation test of S-doped TiO2 samples, as compared to pure TiO2, have been investigated and explained by the effects caused by the exchange of S species with O species and by the surface defects induced by the strong H2S treatment.

Ag films deposited on Si and Ti: How the film-substrate interaction influences the nanoscale film morphology

Submicron-thick Ag films were sputter deposited, at room temperature, on Si, covered by the native SiO2 layer, and on Ti, covered by the native TiO2 layer, under normal and oblique deposition angle. The aim of this work was to study the morphological differences in the grown Ag films on the two substrates when fixed all the other deposition parameters. In fact, the surface diffusivity of the Ag adatoms is different on the two substrates (higher on the SiO2 surface) due to the different Ag-SiO2 and Ag-TiO2 atomic interactions. So, the effect of the adatoms surface diffusivity, as determined by the adatoms-substrate interaction, on the final film morphology was analyzed. To this end, microscopic analyses were used to study the morphology of the grown Ag films. Even if the homologous temperature prescribes that the Ag film grows on both substrates in the zone I described by the structure zone model some significant differences are observed on the basis of the supporting substrate. In the normal incidence condition, on the SiO2/Si surface a dense close-packed Ag film exhibiting a smooth surface is obtained, while on the TiO2/Ti surface a more columnar film morphology is formed. In the oblique incidence condition the columnar morphology for the Ag film occurs both on SiO2/Si and TiO2/Ti but a higher porous columnar film is obtained on TiO2/Ti due to the lower Ag diffusivity. These results indicate that the adatoms diffusivity on the substrate as determined by the adatom-surface interaction (in addition to the substrate temperature) strongly determines the final film nanostructure.

Shape Transition of TiO2 Nanocube to Nanospindle Embedded on Reduced Graphene Oxide with Enhanced Photocatalytic Activity

In this study, we report a facile synthetic route for the transition of anatase TiO2 nanocube to nanospindle with coexposed {001} and {101} facets on a reduced graphene oxide (rGO) platform. Initially, a TiO2 nanocubes/graphene oxide suspension in an ethanol–water solvent mixture was hydrothermally treated at 180 °C for various reaction durations to perform the in situ growth of TiO2 and simultaneous reduction of graphene oxide to rGO. All composites resulted in the formation of anatase TiO2 with a surface heterojunction formed by coexposed {101} and {001} facets embedded on an rGO sheet. Interestingly, it was observed that 4 h of hydrothermal treatment resulted in the formation of a TiO2 nanospindle with enhanced {001} high energy facet % embedded on an rGO sheet. The photocatalytic performance of the products was evaluated for the photodegradation of malachite green under simulated solar irradiation. All TiO2@ rGO composites exerted enhanced activity as compared to the native TiO2 cube owing to enhanced...

Effect of Low-Concentration Alloying in Titanium on Reduction Reaction Kinetics in Alkaline Environments

The electrochemical behavior of oxides of three Ti-based binary alloys, Ti99Co1, Ti99Sn1, and Ti99Cr1, are investigated using electrochemical impedance spectroscopy, Mott-Schottky analysis and cyclic voltammetry. It is found that native amorphous TiO2 can be doped in order to change the oxide's electronic properties and thereby reduce oxygen reduction rates in an alkaline solution, with the greatest reduction seen for the Ti99Sn1 alloy.

Low-temperature fabrication of brown TiO2 with enhanced photocatalytic activities under visible light.

Here we report a facile one-step low-temperature solution-based method to treat native TiO2 with NaH. The NaH treatment effectively induces the Ti(iii) species and oxygen vacancies into the TiO2 host lattice, and enables the absorption edge of TiO2 to be conveniently adjusted from the UV region to the red end of the visible spectrum.

Preparation and Characterization of Surface Photocatalytic Activity with NiO/TiO₂ Nanocomposite Structure.

This study achieved a nanocomposite structure of nickel oxide (NiO)/titanium dioxide (TiO2) heterojunction on a TiO2 film surface. The photocatalytic activity of this structure evaluated by decomposing methylene blue (MB) solution was strongly correlated to the conductive behavior of the NiO film. A p-type NiO film of high concentration in contact with the native n-type TiO2 film, which resulted in a strong inner electrical field to effectively separate the photogenerated electron-hole pairs, exhibited a much better photocatalytic activity than the controlled TiO2 film. In addition, the photocatalytic activity of the NiO/TiO2 nanocomposite structure was enhanced as the thickness of the p-NiO film decreased, which was beneficial for the migration of the photogenerated carriers to the structural surface.

Biological effect of food additive titanium dioxide nanoparticles on intestine: an in vitro study.

Titanium dioxide nanoparticles (TiO2 NPs) are widely found in food-related consumer products. Understanding the effect of TiO2 NPs on the intestinal barrier and absorption is essential and vital for the safety assessment of orally administrated TiO2 NPs. In this study, the cytotoxicity and translocation of two native TiO2 NPs, and these two TiO2 NPs pretreated with the digestion simulation fluid or bovine serum albumin were investigated in undifferentiated Caco-2 cells, differentiated Caco-2 cells and Caco-2 monolayer. TiO2 NPs with a concentration less than 200 µg ml(-1) did not induce any toxicity in differentiated cells and Caco-2 monolayer after 24 h exposure. However, TiO2 NPs pretreated with digestion simulation fluids at 200 µg ml(-1) inhibited the growth of undifferentiated Caco-2 cells. Undifferentiated Caco-2 cells swallowed native TiO2 NPs easily, but not pretreated NPs, implying the protein coating on NPs impeded the cellular uptake. Compared with undifferentiated cells, differentiated ones possessed much lower uptake ability of these TiO2 NPs. Similarly, the traverse of TiO2 NPs through the Caco-2 monolayer was also negligible. Therefore, we infer the possibility of TiO2 NPs traversing through the intestine of animal or human after oral intake is quite low. This study provides valuable information for the risk assessment of TiO2 NPs in food.

Photoelectrochemical Studies on High Specific Capacitance-Photoactive Interfaces Based on Poly 3,4- Ethylenedioxythiophene/Metal Oxides Assemblies

Inorganic/organic interfaces (IOI) consist of TiO2/PEDOT (poly 3,4-ethylenedioxythiophene) and (PMo12O40 )3− or MoO3/PEDOT were subject to photoelectrochemical studies in both aqueous nano- suspensions and in thin solid films. The effects PEDOT modifier caused on the photoelectrochemi- cal behavior of the IOI were investigated using (Fe(CN)6) 4− as the photoactive hydrated electron donor agent. Results show that native PEDOT or PEDOT doped with MoO3 thin films increased charge storage capability evident by the high capacitive current. In the case of nano suspensions composed of TiO2/PEDOT the adsorption process of (Fe(CN)6) 3− (photolysis product) control of the photoactivity outcome of the IOI assemblies. TiO2/PEDOT shows a lower heterogeneous photo- chemical response than native TiO2 in short term photolysis times. At longer photolysis times the IOI shows photoactivity greater than that of native TiO2. The interface activities were explained by analyzing the IOI junction characteristics, such as electron affinity, work function and hole/elec- trons barrier heights. The aqueous nano-systems retained moderate stability as indicated by the reproducibility of their photocatalytic activities. Both (Fe(CN)6)4− and PEDT contributed to the stability of native TiO2 surfaces.

Electronic structure and optical properties of C doped rutile TiO2: the first-principles calculations

The lattice parameters and band-gap of native rutile TiO2 are investigated by the first-principles calculations of local density approximation+U method with different U values for Ti-3d (0 U 9 eV). The electronic structures and optical properties of different content C doped rutile TiO2 systems are also studied by the same method with appropriate U values. The calculations results show that the lattice parameters and band-gaps of TiO2 increase with the increase of U and the U =3 eV is fitted for the corrected band-gap. For the doped systems, the impurity energy level is introduced due to the coupling between O-2p and C-2p, which can increase the TiO2 absorption edge to the visible region, and therefore enlarge the absorption region of TiO2. Moreover, the 8.3% C is an optimal doped density, which can lead to the red-shift of optical absorption edge obviously and increase the coefficient of light absorption, therefore facilitate the enhancement of the photocatalytic efficiency.