Tuning enhanced dielectric properties of (Sc3+-Ta5+) substituted TiO2 via insulating surface layers.

In this study, we achieved significantly enhanced giant dielectric properties (EG-DPs) in Sc3+-Ta5+ co-doped rutile-TiO2 (STTO) ceramics with a low loss tangent (tanδ ≈ 0.05) and high dielectric permittivity (ε' ≈ 2.4 × 104 at 1 kHz). We focused on investigating the influence of insulating surface layers on the nonlinear electrical properties and the giant dielectric response. Our experimental observations revealed that these properties are not directly correlated with the grain size of the ceramics. Furthermore, first-principles calculations indicated the preferred formation of complex defects, specifically 2Ta diamond and 2ScVo triangular-shaped complexes, within the rutile structure of STTO; however, these too showed no correlation. Consequently, the non-Ohmic properties and EG-DPs of STTO ceramics cannot be predominantly attributed to the grain boundary barrier layer capacitor model or to electron-pinned defect-dipole effects. We also found that the semiconducting grains in STTO ceramics primarily arise from Ta5+, while Sc3+ plays a crucial role in forming a highly resistive outer surface layer. Notably, a significant impact of grain boundary resistance on the nonlinear electrical properties was observed only at lower co-dopant concentrations in STTO ceramics (1 at%). The combination of low tanδ values and high ε' in these ceramics is primarily associated with a highly resistive, thin outer-surface layer, which substantially influences their non-Ohmic characteristics.

Significantly Enhanced Dielectric Properties of Ag-Deposited (In1/2Nb1/2)0.1Ti0.9O2/PVDF Polymer Composites.

The enhanced dielectric permittivity (ε') while retaining a low loss tangent (tanδ) in silver nanoparticle-(In1/2Nb1/2)0.1Ti0.9O2/poly(vinylidene fluoride) (Ag-INTO/PVDF) composites with different volume fractions of a filler (fAg-INTO) was investigated. The hybrid particles were fabricated by coating Ag nanoparticles onto the surface of INTO particles, as confirmed by X-ray diffraction. The ε' of the Ag-INTO/PVDF composites could be significantly enhanced to ~86 at 1 kHz with a low tanδ of ~0.044. The enhanced ε' value was approximately >8-fold higher than that of the pure PVDF polymer for the composite with fAg-INTO = 0.5. Furthermore, ε' was nearly independent of frequency in the range of 102-106 Hz. Therefore, filling Ag-INTO hybrid particles into a PVDF matrix is an effective way to increase ε' while retaining a low tanδ of polymer composites. The effective medium percolation theory model can be used to fit the experimental ε' values with various fAg-INTO values. The greatly increased ε' primarily originated from interfacial polarization at the conducting Ag nanoparticle-PVDF and Ag-INTO interfaces, and it was partially contributed by the high ε' of INTO particles. A low tanδ was obtained because the formation of the conducting network in the polymer was inhibited by preventing the direct contact of Ag nanoparticles.

High-Performance Giant Dielectric Properties of Cr3+/Ta5+ Co-Doped TiO2 Ceramics.

The effects of the sintering temperature on microstructures, electrical properties, and dielectric response of 1%Cr3+/Ta5+ co-doped TiO2 (CrTTO) ceramics prepared using a solid-state reaction method were studied. The mean grain size increased with an increasing sintering temperature range of 1300-1500 °C. The dielectric permittivity of CrTTO ceramics sintered at 1300 °C was very low (ε' ∼198). Interestingly, a low loss tangent (tanδ ∼0.03-0.06) and high ε' (∼1.61-1.9 × 104) with a temperature coefficient less than ≤ ±15% in a temperature range of -60 to 150 °C were obtained. The results demonstrated a higher performance property of the acceptor Cr3+/donor Ta5+ co-doped TiO2 ceramics compared to the Ta5+-doped TiO2 and Cr3+-doped TiO2 ceramics. According to a first-principles study, high-performance giant dielectric properties (HPDPs) did not originate from electron-pinned defect dipoles. By impedance spectroscopy (IS), it was suggested that the giant dielectric response was induced by interfacial polarization at the internal interfaces rather than by the formation of complex defect dipoles. X-ray photoelectron spectroscopy (XPS) results confirmed the existence of Ti3+, resulting in the formation of semiconducting parts in the bulk ceramics. Low tanδ and excellent temperature stability were due to the high resistance of the insulating layers with a very high potential barrier of ∼2.0 eV.

Enhanced solar water disinfection using ZnO supported photocatalysts.

Nano-structured ZnO photocatalysts on cellulose and polyester supports were developed for enhancing solar water disinfection (SODIS). The photocatalysts were fabricated by a two-step hydrothermal method, in which ZnO nanoparticles were synthesized and deposited on a cellulose or polyester support as a seed layer, followed by the growth of one-dimensional ZnO nanorods on the seed layer in a liquid bath containing zinc nitrate and hexamethylenetetramine as sources of precursors. The morphologies and phase compositions of the synthesized ZnO nanorods from different growth conditions were investigated with field emission scanning electron microscope and X-ray diffraction (XRD), respectively. The crystallinity size of the ZnO nanorods was in the range of 17-30 nm and increased with the precursor concentration. The XRD patterns also revealed that higher growth solution concentrations led to higher intensity of XRD peaks, indicating higher crystallinity. Additionally, to test for SODIS enhancement, experiments using 200-mL transparent polyethylene bags as SODIS reactors, with ZnO photocatalysts inside, and water samples containing 106 CFU of Escherichia Coli were conducted in a laboratory UVA setup. The photocatalyst with a polyester support resulted in a 15% higher disinfection efficiency than that of the one with a cellulose support. Moreover, a field test of enhanced SODIS was conducted in actual sunlight, using specially designed SODIS reactors containing ZnO photocatalysts with a polyester support. Nearly total disinfection (97-98% efficiency) was achieved within the first 15 min of every test. The treated water was also tested for zinc contents, which could be released from the photocatalysts, by ICP-OES. The results were lower than 2 mg/L.

Safety and durability of low-density polyethylene bags in solar water disinfection applications.

Solar water disinfection (SODIS) is a simple point-of-use process that uses sunlight to disinfect water for drinking. Polyethylene terephthalate (PET) bottles are typically used as water containers for SODIS, but a new SODIS container design has recently been developed with low-density polyethylene (LDPE) bags and can overcome the drawbacks of PET bottles. Two nesting layers of LDPE bags are used in the new design: the inner layer containing the water to be disinfected and the outer one creating air insulation to minimize heat loss from the water to the surroundings. This work investigated the degradation of LDPE bags used in the new design in actual SODIS conditions over a period of 12 weeks. The degradation of the LDPE bags was investigated weekly using a scanning electron microscope, Fourier transform infrared spectroscopy, ultraviolet-visible spectrophotometer, and tensile strength tester. It was found that the LDPE bags gradually degraded under the sunlight due to photo-oxidation reactions, especially in the outer bags, which were directly exposed to the sun and surroundings, leading to the reduction of light transmittance (by 11% at 300 nm) and tensile strength (by 33%). In addition, possible leaching of organic compounds into the water contained in the inner bags was examined using gas chromatography-mass spectrometer. 2,4-Di-tert-butylphenol was found in some SODIS water samples as well as the as-received water samples, in the concentration range of 1-4 µg/L, which passes the Environmental Protection Agency Drinking Water Guidance on Disinfection By-Products.

Dithizone nanofiber-coated membrane for filtration-enrichment and colorimetric detection of trace Hg(II) ion.

Dithizone nanofiber-coated membranes (dithizone membranes), which are useful for sensitive and selective determination of Hg(II), were fabricated. Simply by filtration of the aqueous dispersion of dithizone nanofiber through a cellulose ester membrane filter, a dithizone nanofiber layer of less than 500 nm thickness was coated firmly and uniformly over the membrane filter surface. The steel blue color of the membrane remained unchanged for more than three months when fabricated in the presence of ascorbic acid and stored with an oxygen absorber in an evacuated aluminium bag. Determination at the parts per billion level of Hg(II) was achieved by filtration-enrichment of a sample solution and simultaneous colorimetric analysis using a TLC scanner (500 nm). Consequently, Hg(II) ion was concentrated in the dithizone layer as reddish brown complexes by filtration of a sample solution at pH 2.7. More than 90% of 10 ppb Hg(II) was retained in the dithizone layer at the filtration rate of 1.3-9.3 ml min(-1). The presence of Na+ (10,000 ppm), K+ (5000 ppm), Ca(II) (5000 ppm), Cu(II) (6.4 ppm), Fe(II) (100 ppm), Zn(II) (100 ppm), Pb(II) (100 ppm) and Cd(II) (10 ppm) by using 2.5 x 10(-4) M of ethylenediamine tetraacetic acid (EDTA) as a masking reagent did not interfere with the detection of Hg(II) (10 ppb). Most of anions did not interfere with the determination of Hg(II). The present method was tested for the detection of simulated wastewater, river water and seawater spiked with 10 ppb of Hg(II).