Sodium-ion batteries are a promising alternative to lithium-ion devices, but the development of proper negative electrode materials is still challenging. Here, the properties of a low-voltage sodium ...titanate material are evaluated. Sodium titanate nanotubes (NTO) were produced by an alkalyne alkaline hydrothermal treatment with TiO2 and consisted of a hydrated Na1.4H0.6Ti3O7 with a surface area of 128 m2 g−1. NTO electrode kinetics were studied by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic intermittent titration techniques. The (de)intercalation of Na+ ions involved two redox pairs at 0.3/0.5 V and 1.0/1.2 V, associated with the present mixture of nanotubes and nanosheets. Surface processes had a 95% coulombic efficiency and a high contribution even at low scan rates, accounting for 47% of the total capacity at 0.5 mV s−1. Upon Na+ removal, the electronic resistance and the semiconductor capacitance increased. Battery tests performed on Na|NTO half-cells showed a reversible capacity of 90 mA h g−1 at 10 mA g−1 and near 100% coulombic efficiency at current rates ranging from 10 mA g−1 to 10 A g−1. Additionally, NTO presented a good capacity retention of 92% after 170 cycles at 100 mA g−1.
•Surface process contribution is 47% at 0.5 V s−1 with 95% efficiency.•Finite-space diffusion model to fit EIS data considering particle-size distribution.•(Semi)conductive properties of NTO change with (de)sodiation.•Electrode capacity of 93 mA h g−1 at 10 mA g−1•92% capacity retention after 170 cycles at 100 mA g−1
Abstract Objective To evaluate the strength and ion release of experimental composites containing TEGDMA-functionalized calcium phosphate particles. Methods Seven composites containing equal parts ...(in mols) of BisGMA and TEGDMA and 60 vol% of fillers were manipulated. Filler phase was constituted by silanized barium glass and 0% (control), 10% or 20% (volume) of dicalcium phosphate dihydrate (DPCD) particles, either non-functionalized or functionalized with two different TEDGMA contents. DCPD particles were synthesized and characterized by X-ray diffraction (XRD), elemental analysis, surface area and dynamic light scattering. Composites were tested for degree of conversion (DC) by near-FTIR. Biaxial flexural strength (BFS) was determined after 24 h and 28 days in water. Calcium and phosphate release after 7 days was assessed using inductively coupled plasma optical emission spectrometry (ICP-OES). Data were analyzed by ANOVA/Tukey test (alpha:5%). Results XRD confirmed the crystalline structure corresponding to DCPD. Elemental analysis revealed particles with zero, 14% or 22% TEGDMA, with similar D50 (around 19 μm) and surface areas from 3.5 to 11.4 m2 /g. The presence of DCPD did not reduce DC. After 24 h, functionalization (both 14% and 22% TEGDMA) improved composite strength in comparison to non-functionalized DCPD, both at 10% and 20% levels. After 28 days, BFS of materials containing 10% functionalized DCPD were statistically similar to the control containing only barium glass. Among composites containing 10% DCPD, particle functionalization with 14% TEGDMA did not jeopardize ion release. Significance At 10 vol%, the use of TEGDMA-functionalized CaP particles improved composite strength in relation to non-functionalized particles, while maintaining similar ion release levels.
This study describes the synthesis of brushite nanoparticles (CaHPO4·2H2O) functionalized with triethylene glycol dimethacrylate (TEGDMA) and their application in dental restorative composites with ...remineralizing capabilities.
Nanoparticles were synthesized, with TEGDMA being added to one of the precursor solutions at three different molar ratios (0:1, 0.5:1 and 1:1, in relation to the ammonium phosphate precursor). Then, they were added (10 vol%) to a photocurable dimethacrylate matrix containing 50 vol% of reinforcing glass particles. The resulting composites were tested for degree of conversion, biaxial flexural strength and elastic modulus (after 24h and 28days in water), and ion release (over a 28-day period). Commercial composites (one microhybrid and one microfilled) were tested as controls.
The final TEGDMA content in the functionalizing layer was modulated by the molar ratio added to the precursor solution. Functionalization reduced nanoparticle size, but did not reduce agglomeration. Improved mechanical properties were found for the composite containing nanoparticles with higher TEGDMA level in comparison to the composite containing non-functionalized nanoparticles or those with a low TEGDMA level. All brushite composites presented statistically significant reductions in strength after 28 days in water, but only the material with high-TEGDMA nanoparticles retained strength similar to the microhybrid commercial control. Overall, ion release was not affected by functionalization and presented steady levels for 28 days.
Though agglomeration was not reduced by functionalization, the improvement in the matrix-nanoparticle interface allowed for a stronger material, without compromising its remineralizing potential.
•Temperature and reactant concentration interacted to define the precipitated phase.•DCPD/OCP mixtures (22 °C) and HAP (45 °C) were obtained under low concentration.•DCPD (22 °C) and DCPD/OCP (45 °C) ...precipitated under medium and high concentrations.•Particle hydrodynamic radius was not strongly affected by the tested variables.•Surface area results reflected differences in particle morphology among phases.
Calcium orthophosphates (CaP) constitute an important group of biomaterials used in bone repair and tooth remineralization. In some applications, controlling particle surface area and/or dimensions is important to fine-tune ion release kinetics. This study evaluated the interaction between synthesis temperature (22 °C or 45 °C) and reactant concentration (“Low”: 0.1 mol.L−1, “Medium”: 0.5 mol.L−1 or “High”: 1.0 mol.L−1) on phase formation, particle morphology, size and surface area. Calcium and phosphate precursor solutions (Ca/P = 1.0, initial pH: 7.9–8.1) were mixed and the precipitate was obtained after 24 h. DCPD (CaHPO4·2H2O) was the only phase identified by X-ray diffraction at 22 °C/Medium and 22 °C/High, with large plate crystal morphology, while DCPD/OCP (Ca4H(PO4)3·2.5H2O, as agglomerates of sub-micron crystals) mixtures were observed at 22 °C/Low, 45 °C/Medium and 45 °C/High. Small-plate, low-crystallinity HAP (Ca5OH(PO4)3) was obtained at 45 °C/Low. In spite of the different morphologies, particle hydrodynamic radius (as determined by laser light scattering) was not affected by the tested variables (median: 10–20 μm). Surface area, on the other hand, varied according to particle morphology (37–135 m2/g). In conclusion, temperature and reactant concentration interacted to define the precipitated phases, each of them with a characteristic morphology. Thermodynamically more stable phases (OCP or HAP) were found in syntheses conducted at 45 °C due to accelerated DCPD hydrolysis.
To synthesize and characterize brushite particles in the presence of acidic monomers (acrylic acid/AA, citric acid/CA, and methacryloyloxyethyl phosphate/MOEP) and evaluate the effect of these ...particles on degree of conversion (DC), flexural strength/modulus (FS/FM) and ion release of experimental composites.
Particles were synthesized by co-precipitation with monomers added to the phosphate precursor solution and characterized for monomer content, size and morphology. Composites containing 20 vol% brushite and 40 vol% reinforcing glass were tested for DC, FS and FM (after 24 h and 60 d in water), and 60-day ion release. Data were subjected to ANOVA/Tukey tests (DC) or Kruskal–Wallis/Dunn tests (FS and FM, alpha: 5%).
The presence of acidic monomers affected particle morphology. Monomer content on the particles was low (0.1–1.4% by mass). Composites presented similar DC. For FS/24 h, only the composite containing DCPD_AA was statistically similar to the composite containing 60 vol% of reinforcing glass (without brushite, “control”). After 60 days, all brushite-containing materials showed similar FS, statistically lower than the control composite (p<0.01). Composites containing DCPD_AA, DCPD_MOEP or DCPD_U (“unmodified”) showed statistically similar FM/24 h, higher than the control composite. After prolonged immersion, all composites were similar to the control composite, except DCPD_AA. Cumulative ion release ranged from 21 ppm to 28 ppm (calcium) and 9 ppm to 17 ppm (phosphate). Statistically significant reductions in ion release between 15 and 60 days were detected only for the composite containing DCPD_MOEP.
Acidic monomers added to the synthesis affected brushite particle morphology. After 60-day storage in water, composite strength was similar among all brushite-containing composites. Ion release was sustained for 60 days and it was not affected by particle morphology.
•The presence of acidic monomers in the synthesis affected DCPD particle morphology.•Monomer retention on particles was low.•DCPD morphology did not influence composite strength after aging.•Overall, composite modulus was not compromised by DCPD after aging.•At 60 days, ion release was higher for the composite with the smallest particles.
TiO2-based nanotubes are a very promising material with many applications in solar cells, biomedical devices, gas sensors, hydrogen generation, supercapacitors, and lithium batteries, among others. ...Nanotube thickness is a very important property since it is related to electronic and surface mechanics. In this sense, transmission electron microscopy (TEM) can be used. However, it can be difficult to acquire a good TEM image because the transversal section of the nanotubes needs to be visible. In this work, TiO2-based nanotubes obtained via hydrothermal synthesis were studied using X-ray line profile analysis. Scherrer and Single-Line methods provided consistent results for the thickness of the nanotubes (≃ 5 nm) when compared with TEM. Additionally, Single-Line method was also applied to estimate the microstrain. The advantage of using XRD is given by the fact that it is a quick and statistically significant analysis when compared with TEM. The results show that XRD can be used as a rapid and reliable alternative for the thickness estimation of nanotubes.
Low temperature synthesis of CdSiO3 nanostructures Santana, Leonardo P.; Almeida, Erick S. de; Soares, Jones L. ...
Journal of the Brazilian Chemical Society,
10/2011, Letnik:
22, Številka:
10
Journal Article
Recenzirano
Odprti dostop
We report the synthesis of single-phase, crystalline CdSiO3 nanostructures at 580ºC; to the best of our knowledge, this is the lowest temperature at which this material is reported to form. The ...desired phase does not form below 580ºC, since the diffraction peaks are shifted to lower angles in the material treated at 570ºC when compared to JDPDS Card No. 85-0310. The source of silicon has strong influence on the product morphology: Na2SiO3 yields single-phase CdSiO3 in needle-shaped nanostructures, while high surface area mesostructured SiO2 yields coralloid-shaped particles. Low angle X-ray diffractometry reveals that the mesostructured nature of the silica precursor is not maintained in the resulting CdSiO3. Scanning electron microscopy suggests that in this case a transition occurs between the spherical morphology of the precursor and the needle-shape morphology of the material prepared from Na2SiO3. The surface area of the silica precursor has a strong influence in the reaction, since the use of commercial silica with a lower surface area does not yield the desired product.
In this paper we describe how the conductivity of a mesoporous TiO2 membrane is strongly affected by the chemistry of the pore walls. We have studied the effect of site density, state of surface ...protonation, and surface modification in samples with a fixed pore structure. Pore structure was kept fixed by firing all samples at the same temperature. Changing the surface site density (number of water molecules per square nanometer) from 5.5 to 5.7 leads to an increase in conductivity from 8.00 × 10-3 to 1.00 × 10-2 Ω-1 cm-1 at 25 °C and 81% relative humidity (RH). The effect of the state of protonation was studied by pretreating wafers at pH 1.5 and equilibrating them with solutions at pH 2.5 and 4.0. This variable (protonation state of the material) was found to have an even stronger effect on conductivity. Surface modification was achieved by adsorbing phosphate anions from solutions with different pH. It was observed that even a very small degree of phosphate loading (0.71 ions/nm2) leads to an increase in conductivity from 8.27 × 10-3 to 9.66 × 10-3 Ω-1 cm-1 at pH 2.5. The conductivity of our materials, especially those treated at pH 1.5, is very close to that of Nafion, a polymeric material used as a proton conducting membrane in fuel cell systems. The lower cost and higher hydrophilicity of our materials make them potential substitutes for costlier hydrophobic polymeric membranes in fuel cells.
Titania ceramic materials modified with 5% antimony and 5% tungsten were prepared by the sol–gel method. For the antimony-modified material, a treatment with H
2O
2 was also performed, in order to ...obtain antimonic acid. The electric conductivity of the xerogels was measured at 25 °C in the relative humidity (RH) range 33–81%. At 25 °C, the electrical conductivity of the “as prepared” 5% Sb ceramic varies from 2.02×10
−5 S cm
−1 at 33% RH to 1.12×10
−2 S cm
−1 at 81% R.H. For the material treated with H
2O
2, the conductivity varies from 1.56×10
−5 to 2.37×10
−2 S cm
−1 for 33% and 81% R.H., respectively. For the tungsten-modified material, the conductivity varies from 1.02×10
−5 to 2.66×10
−3 S cm
−1 for 33% and 81% R.H., respectively. The activation energies observed for proton conduction were 23.5 kJ mol
−1 for TiO
2/W 5%, 22.9 kJ mol
−1 for TiO
2/Sb 5% and 20.6 kJ mol
−1 for the material treated with H
2O
2. The highest activation energy was observed for untreated TiO
2:24.8 kJ mol
−1.
The conductivity values for the Sb-modified ceramics are superior to those reported previously for antimonic acid films, and approach the values reported for proton-conducting polymers, such as Nafion®, making them a potential candidate for application as electrolytes in fuel cell systems.
The water content, water properties and proton conductivity in nanoporous TiO2 materials fabricated by the sol-gel route were studied. TiO2 nanoparticles with a primary particle size < 5 nm were ...packed into xerogels at room temperature and at 50 C. The resulting xerogels were fired at 200, 300 and 400 C to alter the structural properties of these materials. Further alteration in the surface chemistry of the pore walls of these materials are made by equilibrating these porous wafers at pH 1.5 and 4.0 using nitric acid. Porosity, pore size, and surface area were evaluated by N2 adsorption. Water content was calculated using TG and water adsorption isotherms. Proton conductivity was measured by impedance spectroscopy. Of all variables affecting water content, water structure, and proton conductivity, the pH of pre-equilibrating the fired xerogels is the most important. However, porous structures of TiO2 arising from the open packing of nanoparticles, that have less tortuosity, are substantially different in the uptake of water with relative humidity than samples obtained from the close-packing of these same particles regardless of firing temperature. Also, the material with the smallest pore size (a close-packed structure fired at 200 C) has the highest proton conductivity when measured between 20-60% relative humidity, making this system the most favourable in terms of proton exchange membrane systems. It is noted that the density of water in these pores can vary between 1.2 and 1.6 g/l which is different from the 1.0 g/l of bulk water, probably due to a combination of surface charge and surface roughness that affects the structure of interfacial water. These findings are important not only for proton exchange membrane systems but also for other membrane technologies, cements, sensors, fabrication of wetting surfaces and in other areas that might benefit from the use of nanoporous materials. 20 refs.
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