TiO2 Nanoparticles Are Phototoxic to Marine Phytoplankton

Nanoparticulate titanium dioxide (TiO2) is highly photoactive, and its function as a photocatalyst drives much of the application demand for TiO2. Because TiO2 generates reactive oxygen species (ROS) when exposed to ultraviolet radiation (UVR), nanoparticulate TiO2 has been used in antibacterial coatings and wastewater disinfection, and has been investigated as an anti-cancer agent. Oxidative stress mediated by photoactive TiO2 is the likely mechanism of its toxicity, and experiments demonstrating cytotoxicity of TiO2 have used exposure to strong artificial sources of ultraviolet radiation (UVR). In vivo tests of TiO2 toxicity with aquatic organisms have typically shown low toxicity, and results across studies have been variable. No work has demonstrated that photoactivity causes environmental toxicity of TiO2 under natural levels of UVR. Here we show that relatively low levels of ultraviolet light, consistent with those found in nature, can induce toxicity of TiO2 nanoparticles to marine phytoplankton, the most important primary producers on Earth. No effect of TiO2 on phytoplankton was found in treatments where UV light was blocked. Under low intensity UVR, ROS in seawater increased with increasing nano-TiO2 concentration. These increases may lead to increased overall oxidative stress in seawater contaminated by TiO2, and cause decreased resiliency of marine ecosystems. Phototoxicity must be considered when evaluating environmental impacts of nanomaterials, many of which are photoactive

EPR as an analytical tool in assessing the mineral nutrients and irradiated food products-vegetables

EPR spectral investigations of some commonly available vegetables in south India, which are of global importance like Daucus carota (carrot), Cyamopsis tetragonoloba (cluster beans), Coccinia indica (little gourd) and Beta vulgaris (beet root) have been carried out. In all the vegetable samples a free radical corresponding to cellulose radical is observed. Almost all the samples under investigation exhibit Mn ions in different oxidation states. The temperature variation EPR studies are done and are discussed in view of the paramagnetic oxidation states. The radiation-induced defects have also been assessed by using the EPR spectra of such irradiated food products

EPR and Optical Studies of Vanady Ions in Alkali Lead Borotellurite Glasses

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of $VO^{2+}$ ions in different alkali lead borotellurite glasses have been studied. The spin-Hamiltonian parameters (g and A), bonding parameter $\beta_{2}.^{2}$ and Fermi contact interaction parameter k have been calculated. The values of spin-Hamiltonian parameters confirm that the vanadyl ions are present in the glasses as $VO^{2+}$ molecular ions in an octahedral site with a tetragonal compression. The number of spins (N) participating in resonance is calculated as a function of temperature (123-393 K) for 9 mol% of $VO^{2+}$ ions in lithium lead borotellurite glass sample. It is observed that N obeys the Boltzmann law. From EPR data, the paramagnetic susceptibility (\chi) is calculated at various temperatures and the Curie constant has been evaluated from $1/\chi$ graph. The optical absorption spectrum exhibits two bands characteristic of $VO^{2+}$ ions in tetragonal symmetry. The band gap $(E_{opt})$ and the Urbach energies $(\triangle E)$ have been determined from the ultraviolet absorption edges and are found to be dependant on the size of the alkali ion. The theoretical values of optical basicity $(A_{th})$ of these glasses have also been evaluated

Fe3+Fe^{3+} ions in alkali lead tetraborate glasses-an electron paramagnetic resonance and optical study

Glass systems of composition $90R_{2}B_{4}O_{7} + 9PbO + 1Fe_{2}O_{3}$ (R = Li, Na and K) and $90Li_{2}B_{4}O_{7} + (10-x)PbO + xFe_{2}O_{3}$ (x = 0.5, 1, 3, 4, 5, 7 and 9 mol%) have been investigated by means of electron paramagnetic resonance (EPR) and optical absorption techniques. The EPR spectra exhibit three resonance signals at g=6.0, 4.2 and 2.0. The resonances at g=6.0 and 4.2 are attributed to $Fe^{3+}$ ions in rhombic and axial symmetry sites, respectively. The g=2.0 resonance signal is due to two or more $Fe^{3+}$ ions coupled together with dipolar interaction. The EPR spectra of 1 mol% of $Fe_{2}O_{3}$ doped in lithium lead tetraborate glass samples have been studied at different temperatures (123-433 K). The intensity of g=4.2 resonance signal decreases and the intensity of g=2.0 resonance signal increases with the increase of temperature. The line widths are found to be independent of temperature. The EPR spectra exhibit a marked concentration dependence on iron content. A decrease in intensity for the resonance signal at g=4.2 with increase in iron content for more than 4 mol% has been observed in lithium lead tetraborate glass samples and this has been attributed to the formation of $Fe^{3+}$ ion clusters in the glass samples. The paramagnetic susceptibility (\chi) is calculated from the EPR data at various temperatures and the Curie constant (C) has been evaluated from 1/\chi versus T graph. The optical absorption spectrum of $Fe^{3+}$ ions in lithium lead tetraborate glasses exhibits three bands characteristic of $Fe^{3+}$ ions in an octahedral symmetry. The crystal field parameter Dq and the Racah interelectronic repulsion parameters B and C have also been evaluated. The value of interelectronic repulsion parameter B (825 $cm^{-1}$ obtained in the present work suggests that the bonding is moderately covalent

The effect of mixed alkalis on EPR and optical bandgap in Fe3+ ions doped xLi2O-(30-x)Na2O-70B2O3 glasses

Electron Paramagnetic Resonance (EPR) and optical absorption studies of iron doped mixed alkali borate glasses, xLi2O-(30-x)Na2O-70B2O3-0.5Fe2O3 (5 \leq x \leq 28) have been investigated as a function of alkali content to look for the 'mixed alkali effect' (MAE) on the spectral properties of the glasses. The EPR spectra of all the investigated samples exhibit resonance signals which are characteristic of the Fe3+ ions. The EPR spectrum exhibits an intense resonance signal at g = 4.20 ± 0.1, a moderately intense signal at g = 2.00 ± 0.1 and a shoulder in the region of g = 7.60 ± 0.5. The existence of the resonances at g = 4.20 and g = 7.60 have been attributed to Fe3+ ions in rhombic and axial symmetry sites respectively. The g = 2.00 resonance is due Fe3+ ions coupled by exchange interactions. The number of spins (N) participating in resonance and its paramagnetic susceptibility (\chi) have been evaluated. It is interesting to observe that N and \chi increase with x up to x = 20 and thereafter it decrease exhibiting a maximum at x = 20 showing the MAE effect. The EPR spectra have also been studied at different temperatures (123- 300 K). The number of spins participating in resonance is measured as a function of temperature and the activation energy is evaluated. It is observed that the temperature dependence of paramagnetic susceptibility (\chi) obeys Curie-Weiss law. From ultraviolet absorption edges, the optical bandgap and Urbach energies have been evaluated. It is interesting to observe that the optical band gap energy increases whereas the Urbach energy (\Delta E) decreases with x up to x = 25 showing the mixed alkali effect

Mixed Alkali Effect in Li2O−Na2O−B2O3Li_{2}O -Na_{2}O-B_{2}O_{3} Glasses Containing CuO-An EPR and Optical Study

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of 0.5 mol% CuO doped $xLi_{2}O-(30-x)Na_{2}O-{69.5}B_{2}O_{3}$ (5 \leq x \leq 25) mixed alkali glasses have been investigated. The EPR spectra of all the investigated samples exhibit resonance signals characteristic of $Cu^{2+}$ ions in octahedral sites with tetragonal distortion. It is found that the spin-Hamiltonian parameters do not vary much with x. It is interesting to observe that the number of $Cu^{2+}$ ions participating in resonance (N) and its paramagnetic susceptibility (χ) exhibits the mixed alkali effect with composition. It is observed that the temperature dependence of paramagnetic susceptibility (χ) obeys Curie–Weiss law. The paramagnetic Curie temperature $(\theta_p)$ is negative for the investigated sample, which suggests that the copper ions are antiferromagnetically coupled by negative super exchange interactions at very low temperatures. A broad band corresponding to the transition $(^{2}B_{1g}\longrightarrow^{2}B_{2g})$ in the optical absorption spectrum shows a blue shift with x. By correlating the EPR and optical absorption data, the molecular orbital coefficients $\alpha^{2}$ and $\beta^{2}_{2}$ have been evaluated. It is interesting to observe that the optical band gap $(E_{opt})$ and Urbach energies $(\Delta{E})$ exhibit the mixed alkali effect. The theoretical values of optical basicity $({\Delta}_{th})$ have also been evaluated

Electron paramagnetic resonance and luminescent properties of Mn2+:MgGa2O4Mn^{2+}:MgGa_{2}O_{4} phosphor

Electron-paramagnetic-resonance EPR and photoluminescence PL studies on magnesium gallate $(MgGa_{2}O_{4})$ phosphor activated with divalent manganese have been carried out. The EPR spectrum exhibits a six-line hyperfine structure centered at g=1.995, which is a characteristic of a $Mn^{2+}$ ion with a nuclear spin I=5/2. The spin-Hamiltonian parameters have been evaluated. The concentration and temperature 123-433 K dependences of EPR signals have been studied. The number of spins participating in resonance N with temperature obeys the Boltzman law and from the graph of log N versus 1/T the activation energy has been evaluated. The paramagnetic susceptibilities have been calculated from the EPR data at different temperatures and it is interesting to note that it obeys the Curie-Weiss behavior. The Curie constant has been evaluated from the 1/\chi versus T graph. A bright green photoluminescence according to the transition $^{4}T_{1} -> ^{6}A_{1}$ whose emission peak is located at 502 nm is observed from the phosphor under UV excitation when excited by 267-nm light. Such a stable luminescence performance is promising for use in the field of flat panel light-emitting devices. The mechanism involved in the generation of green emission has been explained in detail

Spectroscopic investigations of Mn2+Mn^{2+} ions doped polyvinylalcohol films

Electron paramagnetic resonance (EPR), luminescence and infrared spectral studies have been carried out on $Mn^{2+}$ ions doped in polyvinylalcohol (PVA) films. The EPR spectra at room temperature exhibit sextet hyperfine structure (HFS), centered at $g_{eff} \approx 2.0$ characteristic of Mn2+ ions in octahedral symmetry. The zero-field splitting parameter (D) at room temperature has been evaluated from the intensities of allowed hyperfine lines. The EPR spectra exhibit a marked concentration dependence. The EPR spectra have also been recorded at various temperatures. The number of spins participating in the resonance is measured as a function of temperature and the activation energy $(E_a)$ is calculated. The paramagnetic susceptibility (\chi ) is calculated from the EPR data at various temperatures. From the plot of $1/ \chi$ versus T, the Curie constant and Curie temperature have been evaluated. The emission spectrum of Mn2+ ions doped PVA film exhibits three bands centered at 390, 448 and 465 nm. The band at 448 nm is attributed to $^4T_{1g} \rightarrow ^6A_{1g}$ transition of $Mn^{2+}$ ions. The bands at 390 and 465 nm are attributed to the recombination of free charge carriers. The excitation spectrum exhibits two bands at 250 and 216 nm, which are attributed to host lattice absorption bands. The FT-IR spectrum exhibits few bands, which are attributed to $O-H$, $C-H$, $C=C$ and $C-O$ groups of stretching and bending vibrations

Incorporation of Cr3+ ions in tuning the magnetic and transport properties of nano zinc ferrite

Cost effective and low temperature synthesis methods namely solution combustion and hydrothermal methods were used to prepare chromium incorporated nanocrystalline zinc ferrites. The effect of incorporation of low concentration Cr3+ ions on the structural, morphological, magnetic and transport properties of the zinc ferrite compounds were investigated. The crystalline nature and size variation with chromium content were valid from powder x-ray diffraction. Particles size and crystallite size variation were valid from scanning electron microscopy and transmission electron microscopy respectively. With the increase in chromium incorporation, the crystallite and particles sizes were decreased. Fourier transform infrared spectroscopy (FTIR) studies confirmed the presence of strong metal-oxygen bonds. The elastic properties of the materials in both the methods were estimated by FTIR studies. Magnetic properties namely saturation magentization, remanent magnetization and coercivity values were decreased with increase in Cr3+ ions concentration. The dielectric properties of the samples decreased with increase in the Cr3+ ions. The dielectric constant was observed to be of the order of 10(6) at low frequency and almost 1 at higher frequency range. The activation energy estimated using Arrhenius plots was of the order of 0.182 eV and 0.368 eV respectively for the compounds prepared by solution combustion and hydrothermal methods. The emission spectra of the samples excited at 344 nm were reported using photoluminescence (PL) spectroscopy. Further, the approximate energy band gap(E-g) was estimated from PL studies. The E-g of the materials were lie in the range of 2.11-1.98 eV. (C) 2015 Elsevier B.V. All rights reserved