Irradiated TiO2 Research Articles

Gamma irradiated Cu-doped TiO2 nanoparticles for selective ammonia sensing

In this research, the effect of gamma ray doses on volatile organic compound (VOC) sensing properties of Cu doped TiO2 nanoparticles are studied to further improve the VOC sensing performance. Pure and Cu doped TiO2 nanoparticles have been prepared by sol-gel technique on Au interdigitated plexiglas substrate and irradiated by gamma-rays with doses varying from 1 to 150 KGy. The irradiation was performed by using 60Co as gamma source. The structural, morphology and modifications were analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM), and Atomic Force Microscopy (AFM) techniques. The sensing performance of these films toward ethanol, methanol, 2-propanol, benzene, toluene, xylene and ammonia vapors has been tested. It was observed that no remarkable sensor response to any vapors except ammonia was observed at room temperature. Changes in sensor’ ammonia sensitivity have been correlated with the gamma radiation dose and Cu doping ratio. Maximum sensing performance was observed with 3% Cu doped TiO2 exposed to gamma radiation dose of 150 kGy.

Nitrate radicals generated by TiO2 heterogeneous photocatalysis: Application to the cleavage of C=C double bond to carbonyl compounds

The oxidative cleavage of alkenes represents a relevant chemical process with immense potential for the synthesis of partially oxidized compounds. Several methodologies have been proposed for achieving oxidative cleavage of alkenes, aiming to obtain carbonyl products. However, none of these approaches have been successfully scaled up for industrial applications beyond the laboratory scale. In this study, we report the selective photocatalytic oxidative cleavage of limonene to limononaldehyde using irradiated TiO2 suspensions in the presence of silver nitrate under ambient conditions. Results demonstrate that within one hour of irradiation, a notable conversion and selectivity of 60% towards limononaldehyde can be achieved. The investigation reveals that the oxidation process is primarily driven by nitrate radicals, generated through hole-induced oxidation of nitrate ions. Notably, this selective photocatalytic approach shows potentials that bode well for its application to other olefinic substrates in addition to limonene. These results present a promising pathway for the scalable industrial synthesis of partially oxidized compounds through selective photocatalytic oxidation of alkenes.

TiO2-based photocatalytic hydrogen production: How to transfer it to an applicable approach?

Global industrial development and increased energy demand are key contributors to the rise in CO2 emissions and global climate change. It is therefore necessary to build a sustainable energy infrastructure that would be based on hydrogen from renewable energy sources. Herein, we first introduce the different methods for H2 generation, including photocatalysis with TiO2 as one of the most widely used photocatalysts. The various processes occurring on irradiated TiO2 and their contribution to photocatalytic H2 efficiency are discussed. The next part deals with the best techniques for material engineering, including self-doping, loading with co-catalysts, doping with metals and non-metals, and heterojunction structures. The last part displays the effects of external conditions that positively influence photocatalytic H2 production, especially thermo- and mechanically-assisted photocatalysis. As part of this special issue, this mini-review summarizes most of the investigations carried out in this field by the groups led by Prof. Bahnemann.

Effectiveness of metal–EDTA-polluted water treatment and metal recovery at drop-casted films of TiO2 under UV-LED irradiation: A photoelectrochemical study

EDTA is an important metal sequestering agent in industrial processes and household products, but also an emerging pollutant and a challenge for wastewater treatment due to its high resistance to biodegradation. Conventional strategies for recovering metals from the metal chelates require a previous oxidation step. Herein, P25 TiO2 photocatalyst was applied to assemble nanoparticulate films on gold (model conducting substrate) with highly reproducible photocatalytic activity toward EDTA and Cu(II)-EDTA (model chelate) UVA-photooxidation. Films were obtained from P25 suspensions in acidic medium by a quick cold drop-casting method without thermal annealing. The involved TiO2 agglomerates were characterized by Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), voltammetric DC techniques and zero-current chronopotentiometry. Photocatalytic treatment of Cu(II)-EDTA solutions and electrochemical essays were accomplished in a thin layer-type cell coupled with a 365 nm UV-LED. Synthetic samples of the chelate at stoichiometric ratio or with EDTA in excess were exposed to the irradiated TiO2 film to promote the photooxidation of the ligand, and recovery of copper mainly by direct (photo)electrodeposition on gold. Three potential programs were tested during UV-irradiation: open circuit potential (OCP), +0.5 V and –0.3 V vs Ag/AgCl. Overall best results were obtained at –0.3 V, showing that it is more effective to favor in-situ metal reduction rather than collecting photogenerated electrons via +0.5 V biasing to diminish electron/hole (exciton) recombination. Nevertheless, operation without external biasing, i.e., at OCP, is nearly as effective since the substrate is spontaneously driven to circa –0.7 V by photogenerated electrons plus electrons injected into photoholes by EDTA, as it oxidizes. The Cu(II)-EDTA treatment can be abbreviated by coupling both redox processes at the same photoelectrode, thus, avoiding the transport of Cu(II) from the photoanode to the cathode, conceivably with risk of rechelation, like in conventional photoelectrochemical cells. Similar results were obtained with the TiO2 drop-casted on other conducting substrates including carbon, a relevant finding for a forthcoming scale-up of the treatment process.

Localized thermal spike driven morphology and electronic structure transformation in swift heavy ion irradiated TiO2 nanorods

Irradiation of materials by high energy (∼MeV) ions causes intense electronic excitations through inelastic transfer of energy that significantly modifies physicochemical properties. We report the effect of 100 MeV Ag ion irradiation and resultant localized (∼few nm) thermal spike on vertically oriented TiO2 nanorods (∼100 nm width) towards tailoring their structural and electronic properties. Rapid quenching of the thermal spike induced molten state within ∼0.5 picosecond results in a distortion in the crystalline structure that increases with increasing fluences (ions per cm2). Microstructural investigations reveal ion track formation along with a corrugated surface of the nanorods. The thermal spike simulation validates the experimental observation of the ion track dimension (∼10 nm diameter) and melting of the nanorods. The optical absorption study shows direct bandgap values of 3.11 eV (pristine) and 3.23 eV (5 × 1012 ions per cm2) and an indirect bandgap value of 3.10 eV for the highest fluence (5 × 1013 ions per cm2). First principles electronic structure calculations corroborate the direct-to-indirect transition that is attributed to the structural distortion at the highest fluence. This work presents a unique technique to selectively tune the properties of nanorods for versatile applications.

Electron and Energy Transfer Mechanisms: The Double Nature of TiO2 Heterogeneous Photocatalysis.

Photocatalytic chemical transformations in the presence of irradiated TiO2 are generally considered in terms of interfacial electron transfer. However, more elusive energy-transfer-driven reactions have been also hypothesized to occur, mainly on the basis of the indirect evidence of detected reaction products whose existence could not be justified simply by electron transfer. Unlike in homogeneous and colloidal systems, where energy transfer mechanisms have been investigated deeply for several organic syntheses, understanding of similar processes in heterogeneous systems is at only a nascent level. However, this gap of knowledge can be filled by considering the important achievements of synthetic heterogeneous photocatalysis, which bring the field closer to industrial exploitation. The present manuscript summarizes the main findings of previous literature reports and, also on the basis of some novel experimental evidences, tentatively proposes that the energy transfer in TiO2 photocatalysis could possess a Förster-like nature.

TRIBOLOGICAL CHARACTERISTICS OF ‘STEEL – CERAMICS-IRRADIATED-BY-HELIUM-IONS’ PAIR

Facility for the tribological characteristics studying of a metal – ceramics pair and parameters of ceramic samples irradiation on the helium ions linear accelerator with energies 0.12 and 4 MeV are resulted. Profiles of damageability and occurrence of target atoms along of helium ions range are calculated for the irradiated TiO2 and Al2O3. Sputtering ratios and dependence of the sputtered atoms quantity on samples thickness are received. Calculations on density change of the irradiated samples are made. Experimental results of a sliding friction factor measurement depending on cycle’s quantity, temperature and irradiation doses are presented. On the basis of microscopic researches and calculation data conclusions are drawn about irradiation influence on interacting pair’s tribological characteristics.

Assessment of irradiated TiO2 nanoparticles on the growth and nutritional components of broccoli

Broccoli is highly tremendously as it is enriched with healthy promoting phytochemicals. This research was undertaken to study the feedback of broccoli to different concentrations of un-irradiated and irradiated (50 kGy of gamma rays) titanium dioxide nanoparticles (TiO2NPs). Un-irradiated and irradiated titanium dioxide characterization was accomplished by FT-IR, XRD, TGA, SEM and TEM. Foliar spray of titanium dioxide was applied to the broccoli in regards to the results of the characterizations. The growth traits; plant height, leaves No. per plant as well as stem diameter of plants and physical quality of heads were measured. Also, nutritional components of heads were determined. The results detailed that vegetative growth and physical quality of heads positively responded to foliar application of titanium dioxide compared to those obtained from control and 50 ppm from irradiated titanium dioxide (ITiO2NPs) gave the highest values of all traits. Regarding to nutritional components of heads, the efficiency of photosynthesis increased by using TiO2 (un-irradiated and irradiated) specially, 50 ppm ITiO2NPs. Application of Ti significantly increased the osmolytes concentrations such as proline, total free amino acids and soluble sugars as well as the extracts of heads sprayed with TiO2NPs concentrations displayed a prospective DPPH free radical scavenging action. Likewise, absorption of other nutrient elements and amino acids pool increased by spraying TiO2NPs. It was found that there are several phytochemical constituents identified by GC-MS that contribute to the biological activity of the methanol extract of broccoli heads that were affected by the use of TiO2NPs. It is clear that from above results, the using of ITiO2NPs specially; 50 ppm stimulated growth, resulting in improved quality of broccoli heads which is ultimately reflected in productivity.

Reduction of dopant ions and enhancement of magnetic properties by UV irradiation in Ce-doped TiO2

We report the experimental observation of and theoretical explanation for the reduction of dopant ions and enhancement of magnetic properties in Ce-doped TiO2 diluted magnetic semiconductors from UV-light irradiation. Substantial increase in Ce3+ concentration and creation of oxygen vacancy defects in the sample due to UV-light irradiation was observed by X-ray and optical methods. Magnetic measurements demonstrate a combination of paramagnetism and ferromagnetism up to room temperatures in all samples. The magnetization of both paramagnetic and ferromagnetic components was observed to be dramatically enhanced in the irradiated sample. First-principle theoretical calculations show that valence holes created by UV irradiation can substantially lower the formation energy of oxygen vacancies. While the electron spin densities for defect states near oxygen vacancies in pure TiO2 are in antiferromagnetic orientation, they are in ferromagnetic orientations in Ce-doped TiO2. Therefore, the ferromagnetically-oriented spin densities near oxygen vacancies created by UV irradiation are the most probable cause for the experimentally observed enhancement of magnetism in the irradiated Ce-doped TiO2.

Evolution of structural and magnetic properties of Ar2+ ion irradiated TiO2 thin films annealed under argon atmosphere

In this report, the evolution of structural as well as magnetic state of 900 °C annealed TiO2 films under argon (Ar) environment have been examined before and after irradiating with the Ar2+ ions of energy 500 keV. The pristine film stabilized with Magneli phase (Ti4O7), the film retains its crystallinity but phase get transformed to anatase TiO2, irradiating with the lowest fluence, 1 × 1014 ions/cm2. After rising up to 5 × 1016 ions/cm2 ion fluence, film again stabilize with the Magneli phase (Ti4O7). In the previous report, we have demonstrated an unusual phase change from anatase TiO2 to brookite, where films are annealed in O2 atmosphere. In contrast to that here we have obtained TiO2 from Ti4O7 at lowest fluence but at highest fluence again Ti4O7 is obtained. The energy deposited by the ion beam passed to the lattice and collision cascades are formed which brings atomic displacement in the lattice, results the structural transformation. Surface topography is not affected much after the irradiation as observed from atomic force microscopy (AFM). Interesting, ferromagnetic behavior at room temperature stems in all the films as a consequence of the controlled introduction of anionic defects (oxygen vacancies).

Degradation of Direct Blue 1 through Heterogeneous Photocatalysis with TiO2 Irradiated with E-Beam

Most dyes used in the textile industry are chemically stable and poorly biodegradable, therefore, they are persistent in the environment and difficult to degrade by conventional methods. An alternative treatment for this kind of substance is heterogeneous photocatalysis using TiO2, so, in this work, it is proposed to degrade Direct Blue 1 (DB1) using microparticulate TiO2 irradiated with e-beam at three different doses: 5, 10 and 20 kGy (J/kg). The DB1 degradation was implemented in a batch reactor (DB1 initial concentration = 50 mg L−1, pH 2.5, TiO2 concentration = 200 mg L−1). We have demonstrated that the photocatalytic power of TiO2, when irradiated with e-beam (5, 10, 20 kGy), varies slightly, with minor effects on photodegradation performance. However, the dose of 10 kGy showed a slightly better result, according to the DB1 photodegradation rate constant. Adsorption process was not affected by irradiation; its isotherm was fitted to Freundlich’s mathematical model. The DB1 photodegradation rate constants, after one hour of treatment, were: 0.0661 and 0.0742 min−1 for irradiated (10 kGy) and nonirradiated TiO2, respectively. The degradation rate constant has an increase of 12.3% for irradiated TiO2. Finally, there was no evidence of mineralization in the degradation process after 60 min of treatment. According to the results, the irradiation of microparticulate TiO2 with e-beam (10 kGy) slightly improves the photodegradation rate constant of DB1.

Features and application of coupled cold plasma and photocatalysis processes for decontamination of water

Dielectric barrier discharge plasma and photocatalysis have been proposed as tools for decontamination of process water, especially in food industry. The present investigation aims to redefine and identify the features of coupling the two technologies in terms of degradation efficiency of a model compound. Results show that, when the process is carried out in plasma activated water in the presence of irradiated TiO2, the efficiency of the integrated process is lower than the sum of the two processes acting separately. It is proposed that afterglow species, e.g. hydrogen peroxide and/or peroxynitrites could be activated by UVA light irradiation producing hydroxyl radicals in the liquid phase. Even if TiO2 limits this additional effect by acting as UVA screen barrier material, its decontamination efficiency under certain conditions results higher than that obtained with plasma systems. These results open the route to chlorine-free decontamination processes and redefine the application framework of this integrated approach.

Synthesis of chitosan-acrylic acid/multiwalled carbon nanotubes composite for theranostic 47Sc separation from neutron irradiated titanium target

A simple and efficient separation method of carrier-free 47Sc from neutron irradiated titanium target using a novel chitosan-acrylic acid/multiwalled carbon nanotubes (CS-AA/MWCNTs) composite was established. The synthesis of the CS-AA/MWCNTs composite was achieved using gamma radiation-induced template polymerization. The grafting efficiency (GE%) of AA on CS onto the surface of f-MWCNTs reached a maximum of~84% under the optimized conditions (30 wt% CS, 1.0 wt% AA, 0.15 wt% f-MWCNTs, >0.2 wt% N,N′-Methylenebisacrylamide (NMBA), and irradiation dose ~25 kGy). Different analyses (FT-IR, SEM, TGA and DTA) were examined for confirming the structural morphology and mechanical properties of the new synthesized composite. Interestingly, the CS-AA/MWCNTs composite depicted a selective adsorption of Sc(III) rather than Ti(IV) ions at pH 5 with adsorption efficiency of ~93.93%. The ionic exchange separation of no-carrier-added (NCA)47Sc(III) from irradiated TiO2 target on CS-AA/MWCNTs composite packed column efficiently eluted 47Sc(III) by 91 ± 0.8% using 1 M HCl solution. The quality control tests (radionuclidic, radiochemical, and chemical purities) for the eluted 47Sc(III) clarified its high purity and validity for cancer theranostics.

Dynamic Surface evolution and scaling studies on TiO2 thin films by Ti ion implantation

The surface dynamics of TiO2 thin films, evolving under the implantation of 50 keV Ti ions, have been investigated. The morphological evolution, as investigated with atomic force microscopy, delineates a surface smoothening by ion implantation.The nanoscale structures at surfaces also undergo a size reduction. Scaling formalism has been applied to understand this temporal and spatial dynamics by estimating the scaling exponents (α,β and γ) via Height-height correlation function (HHCF) and power spectral density (PSD) investigations. The roughness exponent α (0.5 < α < 1) indicates these ion irradiated surfaces to be of self affine nature. Also, they evolve into locally smoother surfaces with increasing fluence. Negative growth exponent (β) also delineates surface smoothening. Exponent, γ, is observed to increase from ~2 at lower ion fluences to 2.5 at the highest fluence. This behavior suggests that diffusion is predominantly controlling the dynamical evolution of the ion irradiated TiO2 surfaces at the highest fluence, similar to that in the bulk case.

Structural and optical properties of γ-ray irradiated TiO2 single crystals

The effects of γ-ray irradiation on structural and optical properties of TiO2 were investigated. γ-ray irradiation was skillfully used to induce oxygen vacancy (VO) in rutile TiO2. Photoluminescence (PL) and Electron Spin-Resonance (ESR) methods employed to characterize VO defects. Optical properties characterized by UV–Vis spectra, the optical bandgap decreased with the increase in irradiation dose. To verify this phenomenon, the CASTEP module was used to calculate the microstructural and optical properties of VO, 2VO, and 3VO in rutile TiO2. VO could induce defects state and new defects levels, which decrease the bandgap and expand the absorption in visible light. Theoretical results agree well with the experimental data.

Interaction between SO2 and NO in their adsorption and photocatalytic conversion on TiO2

The simultaneous adsorption and photocatalytic conversion of SO2 and NO on P25–TiO2 were studied. In particular, the interaction of SO2 and NO on each other’s adsorption and photocatalytic oxidation was discussed. The adsorption of NO on P25 was negligible when comparing to that of SO2, while with the coexistence of NO and SO2 in flue gas, both the adsorption of SO2 and NO were improved. In the presence of water and oxygen, the photocatalytic oxidation efficiency of NO with an efficiency of >69% was observed on irradiated TiO2 surface, which lasted for at least 1000 min. Oxygen was found to have much more important effect than water on the photocatalytic oxidation of NO. In the presence of SO2 however, the photocatalytic process of NO was largely reshaped. The whole process was controlled by the photocatalytic oxidation of SO2. A dramatic efficiency decease (breakthrough of the catalyst bed) was observed for both NO and SO2 due to the catalyst deactivation caused by the poisoning of SO2 oxidation products. Before the breakthrough, the photocatalytic conversion efficiency of NO increased with increasing the SO2 concentration, which was mainly due to the improved NO adsorption in the presence of SO2.

Room temperature ferromagnetism in D-D neutron irradiated rutile TiO2 single crystals.

Room temperature ferromagnetism (RTFM) was observed in unirradiated rutile TiO2 single crystals prepared by the floating zone method due to oxygen vacancy (VO) defects. D–D neutrons mainly collide elastically with TiO2, producing VO, titanium vacancies (VTi) and other point defects; the density and kind of defect is related to the neutron irradiation fluence. D–D neutron irradiation is used to regulate the concentration and type of defect, avoiding impurity elements. As the irradiation fluence increases, the saturation magnetization (Ms) first increases, then decreases and then increases. To verify the origin of RTFM, the CASTEP module was used to calculate the magnetic and structural properties of point defects in TiO2. VO induces a 2.39 μB magnetic moment, Ti3+ and F+ induce 1.28 μB and 1.70 μB magnetic moments, respectively, while VTi induces a magnetic moment of ∼4 μB. Combining experimental and theoretical results, increases in VO concentration lead to Ms increases; more VO combine with electrons to form F+, inducing a smaller magnetic moment. VO and VTi play a key role and Ms changes accordingly with larger fluence. VO, F+ and VTi are the most likely origins of RTFM.

Oxygen Vacancy-Induced Room Temperature Ferromagnetism in Rutile TiO2

As oxygen vacancies play an important role in ferromagnetism of rutile TiO2, a method of γ-ray irradiates rutile TiO2 single crystals was subtly proposed to study the effect of oxygen vacancies on magnetic properties. Remarkably, room temperature ferromagnetism was observed in γ-ray irradiated rutile TiO2 single crystals, and the saturation magnetization is the strongest when dose is 4 × 104 Gy which assigned to ESR results. Since the displacement threshold energy of Ti atom is much bigger than that of O atom, the defects produced by γ-irradiation are mainly oxygen vacancies. After irradiation, XPS, PL spectra indicate the presence of oxygen vacancies(VO), Ti3+, and VO-Ti3+ composite defects.

Synthesis and characterization of black TiO2 nanoparticles by pulsed laser irradiation in liquid

Modified TiO2 (black TiO2) nanoparticles (NPs) produced by different methods showed enhanced visible light absorption than ordinary white TiO2 NPs. Pulsed laser ablation in liquid (PLAL) is a promising technique for synthesizing nanostructures due to its simplicity, less usage of toxic reagents and absence of costly vacuum systems. In the present study, black TiO2 NPs synthesized by pulsed laser irradiation is examined for their structure, morphology and optical properties. Nanoparticles of modified TiO2 were prepared by pulsed laser ablation in liquid technique by irradiating white TiO2 powder in water using an Nd:YAG laser (532 nm, 10 ns, 10 Hz). Characterization of morphology of the nanoparticles by scanning electron microscopy (SEM) showed a change in morphology by laser irradiation for TiO2 nanoparticles. Crystalline structure was determined by X-ray diffraction (XRD) in which the major anatase phase in white TiO2 was changed to rutile during irradiation and for longer irradiation, rutile became the major phase. Most of the vibrational peaks for TiO2 were identified in Raman spectra. Ti 2p and O 1s binding energy analysis by X-ray photoelectron spectroscopy (XPS) for black TiO2 (90 min) showed changes of 0.5 eV and 0.7 eV respectively compared to the white TiO2 due to their change in chemical states. Optical absorption and band gap evaluation were done using the diffuse reflectance spectra measurements that showed enhanced absorption in the visible range for all the laser irradiated nanoparticles and a decrease in the bandgap from 2.98 eV of white TiO2 to 1.84 eV for black TiO2. Synthesis of black TiO2 at normal atmospheric conditions by irradiation of TiO2 in liquid using 532 nm laser output which is a very common Nd:YAG wavelength is reported for the first time.

Synergistic effect of TiO2-CuWO4 on the photocatalytic degradation of atrazine.

In this work, CuWO4 is prepared and its effect of improving photocatalytic degradation of atrazine by TiO2 as well as the synergetic mechanism is studied. Results show that the addition of CuWO4 (50mg/L) into the reaction system can significantly enhance the efficiency of atrazine degradation, resulting in an increased degradation efficiency of 92.1% after 270min, which is 1.94 times higher than that of the single TiO2. As the sintering temperate of CuWO4 was increased, the degradation efficiency of atrazine increased initially and then deceased after reaching a maximum at 500°C. The origin of the synergistic effect of TiO2-CuWO4 is attributed to the introduction of solid CuWO4. The photochemical test results indicate that the photogenerated electrons transfer from irradiated TiO2 to CuWO4, which is beneficial to the O2 reduction and H2O2 formation in aqueous solution thus promoting the photocatalytic activity of TiO2. These observations unveil the importance of improving photocatalytic activity of TiO2 with Cu-bearing semiconductors.