Optimized dispersion of nanoparticles for biological in vitro and in vivo studies

Background

The aim of this study was to establish and validate a practical method to disperse nanoparticles in physiological solutions for biological in vitro and in vivo studies.

Results

TiO₂ (rutile) dispersions were prepared in distilled water, PBS, or RPMI 1640 cell culture medium. Different ultrasound energies, various dispersion stabilizers (human, bovine, and mouse serum albumin, Tween 80, and mouse serum), various concentrations of stabilizers, and different sequences of preparation steps were applied. The size distribution of dispersed nanoparticles was analyzed by dynamic light scattering and zeta potential was measured using phase analysis light scattering. Nanoparticle size was also verified by transmission electron microscopy. A specific ultrasound energy of 4.2 × 10⁵ kJ/m³ was sufficient to disaggregate TiO₂ (rutile) nanoparticles, whereas higher energy input did not further improve size reduction. The optimal sequence was first to sonicate the nanoparticles in water, then to add dispersion stabilizers, and finally to add buffered salt solution to the dispersion. The formation of coarse TiO₂ (rutile) agglomerates in PBS or RPMI was prevented by addition of 1.5 mg/ml of human, bovine or mouse serum albumin, or mouse serum. The required concentration of albumin to stabilize the nanoparticle dispersion depended on the concentration of the nanoparticles in the dispersion. TiO₂ (rutile) particle dispersions at a concentration lower than 0.2 mg/ml could be stabilized by the addition of 1.5 mg/ml albumin. TiO₂ (rutile) particle dispersions prepared by this method were stable for up to at least 1 week. This method was suitable for preparing dispersions without coarse agglomerates (average diameter < 290 nm) from nanosized TiO₂ (rutile), ZnO, Ag, SiO_x, SWNT, MWNT, and diesel SRM2975 particulate matter.

Conclusion

The optimized dispersion method presented here appears to be effective and practicable for preparing dispersions of nanoparticles in physiological solutions without creating coarse agglomerates.     

Pro-inflammatory adjuvant properties of pigment-grade titanium dioxide particles are augmented by a genotype that potentiates interleukin 1β processing

Background

Pigment-grade titanium dioxide (TiO₂) particles are an additive to some foods (E171 on ingredients lists), toothpastes, and pharma?/nutraceuticals and are absorbed, to some extent, in the human intestinal tract. TiO₂ can act as a modest adjuvant in the secretion of the pro-inflammatory cytokine interleukin 1β (IL-1β) when triggered by common intestinal bacterial fragments, such as lipopolysaccharide (LPS) and/or peptidoglycan.Given the variance in human genotypes, which includes variance in genes related to IL-1β secretion, we investigated whether TiO₂ particles might, in fact, be more potent pro-inflammatory adjuvants in cells that are genetically susceptible to IL-1β-related inflammation.

Methods

We studied bone marrow-derived macrophages from mice with a mutation in the nucleotide-binding oligomerisation domain-containing 2 gene (Nod2 ^m/m), which exhibit heightened secretion of IL-1β in response to the peptidoglycan fragment muramyl dipeptide (MDP). To ensure relevance to human exposure, TiO₂ was food-grade anatase (119?±?45 nm mean diameter?±?standard deviation). We used a short ‘pulse and chase’ format: pulsing with LPS and chasing with TiO₂ +/? MDP or peptidoglycan.

Results

IL-1β secretion was not stimulated in LPS-pulsed bone marrow-derived macrophages, or by chasing with MDP, and only very modestly so by chasing with peptidoglycan. In all cases, however, IL-1β secretion was augmented by chasing with TiO₂ in a dose-dependent fashion (5–100 μg/mL). When co-administered with MDP or peptidoglycan, IL-1β secretion was further enhanced for the Nod2 ^m/m genotype. Tumour necrosis factor α was triggered by LPS priming, and more so for the Nod2 ^m/m genotype. This was enhanced by chasing with TiO₂, MDP, or peptidoglycan, but there was no additive effect between the bacterial fragments and TiO₂.

Conclusion

Here, the doses of TiO₂ that augmented bacterial fragment-induced IL-1β secretion were relatively high. In vivo, however, selected intestinal cells appear to be loaded with TiO₂, so such high concentrations may be ‘exposure-relevant’ for localised regions of the intestine where both TiO₂ and bacterial fragment uptake occurs. Moreover, this effect is enhanced in cells from Nod2 ^m/m mice indicating that genotype can dictate inflammatory signalling in response to (nano)particle exposure. In vivo studies are now merited.

     

Empagliflozin Attenuates Non-Alcoholic Fatty Liver Disease (NAFLD) in High Fat Diet Fed ApoE(-/-) Mice by Activating Autophagy and Reducing ER Stress and Apoptosis

Aims/hypothesis: SGLT-2 inhibitors (SGLT-2i) have been studied as potential treatments against NAFLD, showing varying beneficial effects. The molecular mechanisms mediating these effects have not been fully clarified. Herein, we investigated the impact of empagliflozin on NAFLD, focusing particularly on ER stress, autophagy and apoptosis. Methods: Five-week old ApoE^(-/-) mice were switched from normal to a high-fat diet (HFD). After five weeks, mice were randomly allocated into a control group (HFD + vehicle) and Empa group (HFD + empagliflozin 10 mg/kg/day) for five weeks. At the end of treatment, histomorphometric analysis was performed in liver, mRNA levels of Fasn, Screbp-1, Scd-1, Ppar-γ, Pck-1, Mcp-1, Tnf-α, Il-6, F4/80, Atf4, Elf2α, Chop, Grp78, Grp94, Χbp1, Ire1α, Atf6, mTor, Lc3b, Beclin-1, P62, Bcl-2 and Bax were measured by qRT-PCR, and protein levels of p-EIF2α, EIF2a, CHOP, LC3II, P62, BECLIN-1 and cleaved CASPASE-8 were assessed by immunoblotting. Results: Empagliflozin-treated mice exhibited reduced fasting glucose, total cholesterol and triglyceride serum levels, as well as decreased NAFLD activity score, decreased expression of lipogenic enzymes (Fasn, Screbp-1c and Pck-1) and inflammatory molecules (Mcp-1 and F4/80), compared to the Control group. Empagliflozin significantly decreased the expression of ER stress molecules Grp78, Ire1α, Xbp1, Elf2α, Atf4, Atf6, Chop, P62(Sqstm1) and Grp94; whilst activating autophagy via increased AMPK phosphorylation, decreased mTOR and increased LC3B expression. Finally, empagliflozin increased the Bcl2/Bax ratio and inhibited CASPASE-8 cleavage, reducing liver cell apoptosis. Immunoblotting analysis confirmed the qPCR results. Conclusion: These novel findings indicate that empagliflozin treatment for five weeks attenuates NAFLD progression in ApoE^(-/-) mice by promoting autophagy, reducing ER stress and inhibiting hepatic apoptosis.     

A glass-ceramic approach to prepare porous TiO2 with self-supported nano-flakes: The phase evolution and the thermal stability of the product

A porous TiO₂ material consisting of self-supported nano-flakes with mixed anatase/rutile phases was prepared by acid-etching of a glass-ceramic derived from 20MgO?24CuO?32TiO₂?24P₂O₅ phosphate glass frit. The analysis showed that selective dissolution of components of CuO, Mg₃(PO₄)₂, MgTi₄(PO₄)₆ in the crystallized sample first occurred, followed by the growth of TiO₂ nano-flakes and the formation of Ti(HPO₄)₂?2H₂O phase due to the supply of Ti⁴⁺ and [PO4]^3- released form the dissolved crystallites. The sample acid-treated for 17 h had the best crystallization of anatase and rutile phases, and the smallest band gap. In addition, the porous skeleton showed excellent thermal stability and a large surface area. The present study provided a new method which could be used for the scale-up production of porous TiO₂.     

Genotoxicity of nano/microparticles in in vitro micronuclei, in vivo comet and mutation assay systems

Background

Recently, manufactured nano/microparticles such as fullerenes (C₆₀), carbon black (CB) and ceramic fiber are being widely used because of their desirable properties in industrial, medical and cosmetic fields. However, there are few data on these particles in mammalian mutagenesis and carcinogenesis. To examine genotoxic effects by C₆₀, CB and kaolin, an in vitro micronuclei (MN) test was conducted with human lung cancer cell line, A549 cells. In addition, DNA damage and mutations were analyzed by in vivo assay systems using male C57BL/6J or gpt delta transgenic mice which were intratracheally instilled with single or multiple doses of 0.2 mg per animal of particles.

Results

In in vitro genotoxic analysis, increased MN frequencies were observed in A549 cells treated with C₆₀, CB and kaolin in a dose-dependent manner. These three nano/microparticles also induced DNA damage in the lungs of C57BL/6J mice measured by comet assay. Moreover, single or multiple instillations of C₆₀ and kaolin, increased either or both of gpt and Spi^- mutant frequencies in the lungs of gpt delta transgenic mice. Mutation spectra analysis showed transversions were predominant, and more than 60% of the base substitutions occurred at G:C base pairs in the gpt genes. The G:C to C:G transversion was commonly increased by these particle instillations.

Conclusion

Manufactured nano/microparticles, CB, C₆₀ and kaolin, were shown to be genotoxic in in vitro and in vivo assay systems.     

Enhancement of photocatalytic disinfection of surface modified rutile TiO<Subscript>2</Subscript> nanocatalyst

We demonstrate a facile modification of rutile TiO₂ and its anti-bacterial activity under solar irradiation. The modification of rutile TiO₂ was done by microwave-assisted hydrothermal process with hydrogen peroxide (H₂O₂) as a solvent. The structural properties were analyzed by using XRD and Raman studies. The modified rutile TiO₂ shows no change either crystalline phase or crystalline size. The formation of Ti-OH was observed in Raman study. The TEM analysis shows modification on the surface of rutile TiO₂. The photocatalytic disinfection of Escherichia coli (E. coli) under solar irradiation shows double-times better performance by modified rutile TiO₂ compared to rutile TiO₂. The enhancement of anti-bacterial activity was attributed surface modification and Ti-OH.     

Fabrication of nanostructured non-stoichiometric TiO2-x by spark plasma sintering for enhancing its thermoelectric properties

In this study, nanostructured non-stoichiometric TiO_2-x compacts were prepared by the in-situ reduction of rutile titanium oxide (TiO₂) powder with urea powder via spark plasma sintering (SPS). The crystal structure and particle size of the prepared compacts were examined. The XRD patterns revealed that TiO₂ could be reduced easily by the urea powder to obtain non-stoichiometric TiO_2-x, and the compacts still possessed rutile crystal structures. The average particle sizes of the compacts were less than 250 nm, successfully obtaining the non-stoichiometric TiO_2-x with uniform nanostructures at the sintering temperature of 1073 K. In addition, nanostructured TiO_2-x compacts with Magnéli phase Ti_nO_2n-1 (n = 2, 4, 8) were fabricated by varying the volume fraction of Ti powder in a urea environment via SPS. The results suggested that addition of Ti powder contributed to the formation of Magnéli phases Ti_nO_2n-1, and the value of n decreased with an increase in the volume fraction of the Ti powder. Furthermore, the thermoelectric properties of the compacts sintered with and without Ti powder were both investigated. The TiO₂–U13.3-Ti10 compact displayed the highest power factor of 5.04 μWcm⁻¹K⁻² at 973 K. A lower thermal conductivity was achieved by TiO₂–U13.3-Ti10 compact in the temperature range of 373–973 K, approximately 3 Wm⁻¹K⁻¹, due to the nanostructures and Magnéli phases. The highest ZT value of 0.146 was obtained for the TiO₂–U13.3-Ti10 compact at 973 K, achieving a reasonable enhancement of thermoelectric properties.     

One-step preparation of size-defined aggregates of TiO2 nanocrystals with tuning of their phase and composition

One-step route based on the thermal decomposition of the double salt (NH₄)₂TiO(SO₄)₂ (ammonium titanyl sulfate, ATS) is presented to prepare size-defined aggregates of Ti-based nanoparticles with structural hierarchy. The component of Ti-based networks is tunable from anatase/rutile TiO₂, nitrogen-doped TiO₂, TiN_xO_1−x, to TiN depending on the atmospheres and reaction temperatures. The as-prepared Ti-based powders were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS), and BET surface area techniques. It is found that TiO₂ in the predominant rutile phase could be achieved by the thermal decomposition of ATS in flowing Ar gas. Furthermore, the nitrogen-doped TiO₂, TiN_xO_1−x solid solution and TiN were prepared by the thermal decomposition of ATS in flowing NH₃ gas by varying the temperatures. The network of anatase TiO₂ with a specific surface area up to 64 m² g⁻¹ contains large mesopores with a mean diameter of ca. 15 nm, and the large pore size allows more accessible surface and interface available for the photocatalytic degradation of large-molecule dyes. The photocatalytic activity of the prepared TiO₂ and nitrogen-doped TiO₂ under UV–vis light irradiation is compared to Degussa P-25 using the photocatalytic degradation of methylene blue (MB) as a model reaction. The anatase TiO₂ nanoparticles derived from one-step route show the highly efficient photocatalytic activity for the degradation of MB in comparison with Degussa P-25. The presence of large-sized rutile in the TiO₂ powder decreases the specific surface area and thus the powder exhibits a lower photocatalytic activity.     

Lung inflammation and genotoxicity following pulmonary exposure to nanoparticles in ApoE-/- mice

Background  

The toxic and inflammatory potential of 5 different types of nanoparticles were studied in a sensitive model for pulmonary effects in apolipoprotein E knockout mice (ApoE^-/-). We studied the effects instillation or inhalation Printex 90 of carbon black (CB) and compared CB instillation in ApoE-/- and C57 mice. Three and 24 h after pulmonary exposure, inflammation was assessed by mRNA levels of cytokines in lung tissue, cell composition, genotoxicity, protein and lactate dehydrogenase activity in broncho-alveolar lavage (BAL) fluid.     

Synthesis, Crystal Structures and Luminescence of Organic-Lanthanide Complexes with Nicotinic Acid and Adipic Acid Ligands

Two new lanthanide coordination polymers, [Sm₂(nic)₃(ad)_0.5(H₂O)(μ₃-O)₂] (1), [Pr(nic)(ad)]·2H₂O (2) (nic?=?nicotinic acid, ad?=?adipic acid) have been synthesized hydrothermally from the self-assembly of the lanthanide ions (Ln³⁺) with rigid nicotinic acid and the flexible adipic acid. They were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. Structural analyses reveal that both of the complexes crystallize in triclinic, space group P-1 and have different framework characterization. Because of different coordination modes of nicotinate, complexes 1 and 2 exhibit 2D and 3D framework structure, respectively. In 1, the Sm1 and Sm2 atoms and their corresponding centrosymmetric atoms are connected by bridging oxygen atoms to form a 1D Sm₂(μ₃ -O)₂ polymeric chain along [010] direction. The photoluminescent properties of 1 and thermogravimetric analysis of 1 and 2 are discussed in detail.     

NanoTIO2 (UV-Titan) does not induce ESTR mutations in the germline of prenatally exposed female mice

Background

Particulate air pollution has been linked to an increased risk of cardiovascular disease and cancer. Animal studies have shown that inhalation of air particulates induces mutations in the male germline. Expanded simple tandem repeat (ESTR) loci in mice are sensitive markers of mutagenic effects on male germ cells resulting from environmental exposures; however, female germ cells have received little attention. Oocytes may be vulnerable during stages of active cell division (e.g., during fetal development). Accordingly, an increase in germline ESTR mutations in female mice prenatally exposed to radiation has previously been reported. Here we investigate the effects of nanoparticles on the female germline. Since pulmonary exposure to nanosized titanium dioxide (nanoTiO₂) produces a long-lasting inflammatory response in mice, it was chosen for the present study.

Findings

Pregnant C57BL/6 mice were exposed by whole-body inhalation to the nanoTiO₂ UV-Titan L181 (~42.4?mg UV-Titan/m³) or filtered clean air on gestation days (GD) 8?C18. Female C57BL/6?F1 offspring were raised to maturity and mated with unexposed CBA males. The F2 descendents were collected and ESTR germline mutation rates in this generation were estimated from full pedigrees (mother, father, offspring) of F1 female mice (192 UV-Titan-exposed F2 offspring and 164?F2 controls). ESTR mutation rates of 0.029 (maternal allele) and 0.047 (paternal allele) in UV-Titan-exposed F2 offspring were not statistically different from those of F2 controls: 0.037 (maternal allele) and 0.061 (paternal allele).

Conclusions

We found no evidence for increased ESTR mutation rates in F1 females exposed in utero to UV-Titan nanoparticles from GD8-18 relative to control females.     

Asbestos, carbon nanotubes and the pleural mesothelium: a review of the hypothesis regarding the role of long fibre retention in the parietal pleura, inflammation and mesothelioma

Background

Increasing environmental and occupational exposures to nanoparticles (NPs) warrant deeper insight into the toxicological mechanisms induced by these materials. The present study was designed to characterize the cell death induced by carbon black (CB) and titanium dioxide (TiO₂) NPs in bronchial epithelial cells (16HBE14o- cell line and primary cells) and to investigate the implicated molecular pathways.

Results

Detailed time course studies revealed that both CB (13 nm) and TiO₂(15 nm) NP exposed cells exhibit typical morphological (decreased cell size, membrane blebbing, peripheral chromatin condensation, apoptotic body formation) and biochemical (caspase activation and DNA fragmentation) features of apoptotic cell death. A decrease in mitochondrial membrane potential, activation of Bax and release of cytochrome c from mitochondria were only observed in case of CB NPs whereas lipid peroxidation, lysosomal membrane destabilization and cathepsin B release were observed during the apoptotic process induced by TiO₂ NPs. Furthermore, ROS production was observed after exposure to CB and TiO₂ but hydrogen peroxide (H₂O₂) production was only involved in apoptosis induction by CB NPs.

Conclusions

Both CB and TiO₂ NPs induce apoptotic cell death in bronchial epithelial cells. CB NPs induce apoptosis by a ROS dependent mitochondrial pathway whereas TiO₂ NPs induce cell death through lysosomal membrane destabilization and lipid peroxidation. Although the final outcome is similar (apoptosis), the molecular pathways activated by NPs differ depending upon the chemical nature of the NPs.     

Significantly improved dielectric properties of TiO2 ceramics through acceptor-doping and Ar/H2 annealing

The acceptor-doped rutile TiO₂ ceramics, x mol% M₂O₃-(1-x) mol% TiO₂ (M = Al³⁺, Ga³⁺, and In³⁺), were prepared by solid state reaction method. The influence of Ar/H₂ annealing on the structural and dielectric properties of the ceramics were systematically investigated. Our results reveal that the dielectric properties of the ceramics can be significantly improved by the Ar/H₂ annealing. Ga³⁺ is found to be the most suitable dopant with the best doping level of 5 mol%. Excellent dielectric properties of colossal and flat dielectric permittivity (~1.2 × 10⁵ (@1 kHz and 25 °C), low dielectric loss (~0.1), and good frequency stability were achieved over the temperature range of -70–150 °C in the Ar/H₂-annealed 5 mol% Ga₂O₃-95 mol% TiO₂ ceramic. This approach of acceptor-doping and Ar/H₂ annealing leads to two thermally activated relaxations in the sample. The low-temperature relaxation is argued to be a Maxwell-Wagner relaxation caused by frozen electrons, while the high-temperature relaxation is a glass-transition-like relaxation associated with the freezing process of the electrons. This work highlights that engineering low-temperature Maxwell-Wagner relaxation paves a new way other than the frequently used acceptor-donor dual doping to design superior dielectric properties in the TiO₂ system.     

Photocatalytic mineralization of phenol catalyzed by pure and mixed phase hydrothermal titanium dioxide

The photocatalytic mineralization of phenol catalyzed by pure (anatase, rutile) and mixed phase hydrothermal TiO₂ was studied in aqueous solution employing different oxidative agents, H₂O₂ and O₂. In the case of H₂O₂, rutile particles, having large dimensions and high aspect ratio (size: 30–70 nm × 150–350 nm), display the highest catalytic activity due to their low tendency to recombine electrons and holes generated by UV irradiation. By using water dissolved gaseous O₂, the catalytic TiO₂ activity generally decreases and rutile displays the lowest efficacy. In fact, oxygen preferentially chemisorbs at the surface of the nanosized particles of anatase (5–15 nm) and acts as effective electron scavenger, inhibiting the electron-hole recombination. The number of electron and hole traps (Ti³⁺, O₂⁻ and O⁻) and the rate of formation of the short-lived hydroxyl radicals OH under UV irradiation, were evaluated by electron paramagnetic resonance (EPR). A correlation was suggested among the amount of the charge carrier centers, the rate of formation of OH radicals and the catalyst photoactivity. This confirms that the photocatalytic properties depend on the possibility that electrons and holes separately interact with the oxidative agents at the TiO₂ surface, inducing the formation of OH radicals.     

Ca–O Binding of Poly[1-carboxylate-2-(N-t- butylcarbamoyl)ethylene-alt-ethylene] and Calcium Carbonate Composites

A novel poly(carboxylate) ligand was synthesized as a ligand for a crystalline CaCO₃-organic composite. Poly[1-carboxylate-2-(N-t-butylcarbamoyl)ethylene-alt-ethylene] has a 7-membered ring with an intramolecular NH·O hydrogen bond between the carboxylate group and the neighboring amide NH proton in the anionic carboxylate form. The configuration of the polymer ligand was estimated with polymer repeat-unit models, (S,S)- or (R,R)-2-(N-t-butylcarbamoyl)-cyclohexanecarboxylic acid ((S,S)- or (R,R)-TBCA) and (S,R)- 2-(N-t-butylcarbamoyl)-cyclohexanecarboxylic acid ((S,R)-TBCA). The proton NMR spectum of the carboxylate anion of (S,S)- or (R,R)-TBCA exhibits a non-hydrogen bonded NH signal at 7.31 ppm in Me₂SO-d ₆. (S,R)-TBCA shows a strongly NH·O hydrogen-bonded NH signal at 8.50 ppm. The observation of one strongly NH·O hydrogen bonded NH signal at 11.3 ppm indicates that the polymer anion has a threo-form in the zigzag polymer main chain. Moreover, a polymer ligand-CaCO₃ composite was synthesized. The composite was characterized by ¹³C cross polarization/magic angle spinning (CP/MAS) and scanning electron microscopy (SEM). The polymer ligand stabilizes the Ca–O (carboxylate) bond in the CaCO₃ composite. This prevents dissociation due to pK_a shifts of the NH·O hydrogen bond and controls the crystal growth toward metastable vaterite.     

Controlled synthesis of TiO2 nanorod arrays immobilized on ceramic membranes with enhanced photocatalytic performance

In this work, TiO₂ nanorod arrays (NRAs) were synthesized directly on flat sheet Al₂O₃ ceramic membrane (CM) substrates by a two-step hydrothermal method. The effects of the addition of anions and cations and the preparation parameters in the second step on the morphology and size of TiO₂ were investigated in detail, and the photocatalytic activities of the as-synthesized TiO₂-loaded ceramic membranes were investigated by the degradation of methylene blue (MB) under UV light. The results highlighted that the growth of TiO₂ on the CM strongly depended on the synthesis conditions. The anions of Cl^- and Br^- were favorable for the further growth of TiO₂ nanorods, while the anions of SO₄^2- and PO₄^3- with larger ionic radius and higher charge number could retard the growth of TiO₂ nanorods. The SO₄^2- and PO₄^3- could accelerate the formation of nanospheres or nanosheets, respectively. The cation like Na⁺, K⁺, Mg²⁺ and Ca²⁺ had no obvious impact on the formation of TiO₂ NRAs. TiO₂ nanorods exhibited the highest photocatalytic activity, as about 2.2 and 1.9 times larger than those of TiO₂ nanosheets and TiO₂ nanospheres, respectively. More importantly, the as-synthesized TiO₂ NRAs-loaded ceramic membrane could be easily reused and exhibited better photocatalytic stability. These findings would aid the development of TiO₂ photocatalytic materials with high performance.     

Stable anatase phase with a bandgap in visible light region by a charge compensated Ga–V (1:1) co-doping in TiO2

A series of charge compensated Ga–V co-doped TiO₂ samples (Ti_(1-x)(Ga_0.5V_0.5)_xO₂) have been synthesized by a modified sol-gel process. X-ray diffraction pattern shows that the anatase to rutile (A→R) onset temperature (T_O) shifts to a higher temperature, whereas the complete phase transformation temperature (T_C) shifts to a low-temperature region as compared to pure TiO₂, due to Ga–V incorporation. Ga–V co-doping helps in the transformation of some smaller sized Ti⁴⁺ to a relatively larger Ti³⁺. In the anatase phase, oxygen content also increases with increasing doping concentration, which along with the larger size of Ti³⁺ results in lattice expansion and thereby delays the T_O. In the rutile phase, oxygen vacancy increases with increasing doping concentration, which results in lattice contraction and accelerates phase transition. Grain growth process is hindered in the anatase phase (crystallites size reduces from ~15 nm (x = 0.00) to 8 nm (0.10)), whereas it is accelerated in the rutile phase as compared to pure TiO₂. In both phases bandgap (E_g) reduces to the visible light region (anatase: E_g = 3.16 eV (x = 0.00) to 2.19 eV (x = 0.10) and rutile: 3.08 eV (x = 0.00) to 2.18 eV (x = 0.10)) in all co-doped samples. The tail of the absorption edge reveals lattice distortion and increase of Urbach energy proofs the same due to co-doping. All these changes (grain growth, phase transition, and optical properties) are due to lattice distortion created by the combined effect of substitution, interstitials, and oxygen vacancies due to Ga–V incorporation in TiO₂.     

Photoelectro-Fenton combined with photocatalytic process for degradation of an azo dye using supported TiO2 nanoparticles and carbon nanotube cathode: Neural network modeling

In this work, treatment of an azo dye solution containing C.I. Basic Red 46 (BR46) by photoelectro-Fenton (PEF) combined with photocatalytic process was studied. Carbon nanotube-polytetrafluoroethylene (CNT-PTFE) electrode was used as cathode. The investigated photocatalyst was TiO₂ nanoparticles (Degussa P25) having 80% anatase and 20% rutile, specific surface area (BET) 50 m²/g, and particle size 21 nm immobilized on glass plates. A comparison of electro-Fenton (EF), UV/TiO₂, PEF and PEF/TiO₂ processes for decolorization of BR46 solution was performed. Results showed that color removal follows the decreasing order: PEF/TiO₂ > PEF > EF > UV/TiO₂. The influence of the basic operational parameters such as initial pH of the solution, initial dye concentration, the size of anode, applied current, kind of ultraviolet (UV) light and initial Fe³⁺ concentration on the degradation efficiency of BR46 was studied. The mineralization of the dye was investigated by total organic carbon (TOC) measurements that showed 98.8% mineralization of 20 mg/l dye at 6 h using PEF/TiO₂ process. An artificial neural network (ANN) model was developed to predict the decolorization of BR46 solution. The findings indicated that artificial neural network provided reasonable predictive performance (R² = 0.986).     

Preparation,characterization, and giant dielectric permittivity of (Y3+ and Nb5+) co–doped TiO2 ceramics

The microstructure and giant dielectric properties of Y³⁺ and Nb⁵⁺ co–doped TiO₂ ceramics prepared via a chemical combustion method are investigated. A main rutile–TiO₂ phase and dense ceramic microstructure are obtained in (Y_0.5Nb_0.5)_xTi_1-xO₂ (x = 0.025 and 0.05) ceramics. Nb dopant ions are homogeneously dispersed in the microstructure, while a second phase of Y₂O₃ particles is detected. The existence of Y³⁺, Nb⁵⁺, Ti⁴⁺ and Ti³⁺ as well as oxygen vacancies is confirmed by X–ray photoelectron spectroscopy and X–ray absorption near edge structure analysis. The sintered ceramics exhibit very high dielectric permittivity values of 10⁴–10⁵ in the frequency range of 40–10⁶ Hz. A low loss tangent value of ≈0.08 is obtained at 40 Hz. (Y_0.5Nb_0.5)_xTi_1-xO₂ ceramics can exhibit non–Ohmic behavior. Using impedance spectroscopy analysis, the giant dielectric properties of (Y_0.5Nb_0.5)_xTi_1-xO₂ ceramics are confirmed to be primarily caused by interfacial polarization.     

Anatase-rutile transformation in Fe/TiO2, Th/TiO2 and Cu/TiO2 catalysts and its possible role in metal-support interaction

Based onin-situ Mössbauer and X-ray diffraction studies, it is shown that in the Fe/TiO₂ catalyst, the anatase-rutile transformation of the TiO₂ support is facilitated by the Fe²⁺ ions formed during the reduction. The transformation occurs at lower temperatures in Th/TiO₂ and Cu/TiO₂ compared to pure TiO₂. In general, the transformation of anatase to rutile seems to occur at or below the temperature (770 K) at which strong-metal-support-interaction manifests itself.Contribution No. 718 from the Solid State and Structural Chemistry Unit.