Borate Materials Research Articles

Strain-Driven Polarized Electric Field-Promoted Photocatalytic Activity in Borate-Based CsCdBO3 Bulk Materials.

Piezoelectrically polarized electric field can provide a strong driving force for the separation of the photoinduced charge carriers that has attracted a wide attention in the field of photocatalysis. In this paper, a new type of piezoelectric borate material CsCdBO3 exhibits a high efficiency for the degradation of typical organic pollutants under the synergistic effects of strain and light conditions. The oxidation rate constant of the synergistic effect is 0.653 min-1, which is 3.77 times that of just under visible light irradiation. Further, the material shows a higher efficiency when treated both under the clockwise stirring direction and a high stirring speed. A characteristic piezoresponse hysteresis loop was detected using the piezoresponse force microscopy (PFM) approach. The strain-driven polarized electric field facilitates to promote the photoinduced electron-hole pair separation, thus enhancing the photocatalytic activity. The present work provides a new direction of the borate with a noncentrosymmetric structure in the environmental remediation.

FeBO3 as a low cost and high-performance anode material for sodium-ion batteries

The research of borate materials as sodium-ion batteries (SIBs) anode is still in the early stages, but the boron polyoxoanions are attracting intense interest due to their low atomic weight and high electronegative features. In this work, FeBO3 was prepared with low-cost raw materials and evaluated as SIBs anode. The FeBO3 shows a high reversible capacity of 328 mAh/g at the current density of 0.4 A/g. In addition, the electrochemical performance of FeBO3 can be improved by carbon coating. The prepared carbon-coated FeBO3 composite has a reversible capacity of 426 mAh/g (at 0.4 A/g) and an outstanding rate capability of 272 mAh/g (at 1.6 A/g). Furthermore, the sodium storage mechanism of FeBO3 was studied by in-situ XRD and ex-situ XPS.

Evaluation of MgB4O7:Ce, Li and Ce-doped 80MgB2O4–20MgB4O7 as alternative OSL materials for use in quality assurance of 6 MV photon beams

We investigated the potential use of two new borate matrices for quality assurance (QA) tests in radiotherapy. Both matrices, MgB4O7:Ce, Li (MBO) and Ce-doped 80MgB2O4–20MgB4O7 (80-20MBO), were doped with 0.5% cerium oxide. The following dosimetric properties of these materials prepared as pellets were tested: optically stimulated luminescence (OSL) sensitivity, dose response, fading, reproducibility, and the supralinearity index. Subsequently, the pellets were exposed to a 6 MV photon beam, and the percentage depth dose (PDD) curve, OSL response to different dose rates, and radiation field size dependencies were compared with those obtained with a reference detector (ionization chamber, I.C.) used in QA. The results indicated a higher OSL sensitivity of 80–20MBO as compared with MBO, on the order of 6- to 8-fold. The dose response of MBO presented a linear behavior within the range evaluated (20 mGy–2 Gy), unlike 80-20MBO, which had a supralinear behavior. The OSL signal of 80–20MBO was also marked by 60% fading within 5 h post irradiation; afterwards, the OSL signal stabilized. A better reproducibility of 80–20MBO compared with MBO was also observed. No dose rate dependence of the OSL response was observed; moreover, a maximum 5% standard deviation was seen in this test. For the field size tests, the pellets over-responded by 3.1% (80-20MBO) and 3.4% (MBO), in a 3 × 3 cm2 field, compared with the I.C. For the PDD, a high deviation was observed if compared with the I.C. data at the build-up region (at a depth d ≤ 2 cm), maximum 4.3% and 7.8% for 80-20MBO and MBO, respectively, and beyond this value, good agreement among detectors was seen. Our preliminary results indicate the potential utility of these pellets in QA for radiotherapy.

Sea urchin-like calcium borate microspheres and synergistic action with cholinesterase-inhibiting insecticides for ecofriendly Spodoptera littoralis control

The development of nanoagrochemicals has attracted much attention in the last decade to overcome the recent agricultural and environmental challenges associated with the intensive usage of insecticides. Herein, nanostructured calcium borate materials with hierarchical sea urchin-like microspheres and microblocks have been synthesized by a facile hydrothermal method. The insecticidal activity of CaB2O4 and its synergistic combination with cholinesterase-inhibiting insecticides are explored against Spodoptera littoralis (S. littoralis) for the first time via a feeding bioassay protocol. The insecticidal efficacy of sea urchin-like microspheres (CB-A) is estimated to be LC50 = 207 mg L-1 which is two-fold higher than that of microblocks (CBM-A) with LC50 = 406 mg L-1 after eleven days of exposure. The synergistic combination of the CB-A sample with methomyl and chlorpyrifos increases the toxicity to 2.4 and 2.6-fold higher than that of the individual insecticides, respectively. Significantly, sea urchin-like CaB2O4 microspheres cause physical damage to the external insect's cuticle layer, which consequently enhances the uptake of organic insecticides. Our results revealed that calcium borate micro-/nano-structures can be employed as a multifunctional nanoagrochemical in various agricultural programs for S. littoralis control and decrease the usage of cholinesterase-inhibiting insecticides.

Physical, mechanical, and radiation attenuation properties of serpentine concrete containing boric acid

Serpentine and boric acid are effective materials to produce the radiation-shielding concrete (RSC) for attenuating the fast and thermal neutrons, respectively. Therefore, this study investigates the effect of boric acid (0, 1, and 3% by cement weight) on the physical, mechanical, microstructural, and radiation shielding properties of serpentine concrete. The results showed that the addition of boric acid hindered the hydration of cement through the generation of amorphous borate material, which encapsulates the cement phases and retards their transformation into hydration products. Such a retardation process negatively influenced the mechanical properties of boric acid-bearing concrete and contributed to the thicker and less condensed interfacial transition zone. Furthermore, unlike total γ-rays, boric acid enhanced the attenuation properties of serpentine concrete against thermal and fast neutrons favoring the former. There was a satisfying agreement between the theoretical and measured values of fast neutron attenuation parameters. However, negligible variations in the theoretical values of photon interaction parameters showed that porosity was the principal reason for the reduction in gamma-ray attenuation as a result of boric acid addition.

New Cf-252 neutron source shielding design based Monte Carlo simulation using material combination

Neutron shielding has been a worldwide concern for decades and appropriate methods in nuclear reactors and associated facilities for shielding have been developed. Light materials such as paraffin and water cannot be used in neutron radiography due to structural and fire concerns, and a material in the solid form is needed for effective neutron shielding. Therefore, the present study developed a new neutron shielding design for fixed industrial radiography facilities with solid structures based on material combination. Different materials were investigated to find the most appropriate combination design to shield the spontaneous neutron emitted from a Cf-252 source (with an energy in the range from several keV up to 20 MeV). The combination of iron, graphite, boron (or borate materials), and lead in this order, respectively, were found to be the most appropriate shielding structure for an open Cf-252 source used in fixed industrial radiography. As iron is characterized by a high removal cross section, its use in shielding the californium spontaneous neutron source is the key outcome of the present study. These results were confirmed with the Monte Carlo simulation-based particle and heavy ion transport code system.

Crystal Chemistry of High-Temperature Borates.

In recent years borate-based crystals has attracted substantial interest among the research community. The overall importance of this family of materials is reflected in miscellaneous articles and several reviews that have been published over the years. Crystalline borate materials exhibit numerous interesting physical properties, which make them promising for further practical applications. Diversity of functional characteristics results from their high structural flexibility caused in the linkage of planar/non–planar BO3 groups and BO4 tetrahedra, which can occur as isolated or condensed structural units. This report is a brief review on crystal chemistry and structure features of anhydrous/high-temperature borates. Polymorphism of boron-oxygen radicals has been considered basing on cations’ nature and synthesis conditions. Analysis of the laws governing borates structures and general principles of their systematics was discussed. As a result, an alternative classification of anhydrous compounds has been considered. It is based on four orders of their subdivision: (1) by the variety of anion formers, (2) by the cation charge, (3) by the N = NM:NB, i.e., ratio of metal atoms number to the ratio of boron atoms number (N-factor) value indicating the borate structural type (if it is known), (4) by the cation type and size.

Influence of matrix on the luminescence properties of Eu2+/Eu3+ doped strontium borates: SrB4O7, SrB2O4 and Sr3(BO3)2, exhibiting multicolor tunable emission

Three complex strontium borate matrices, i.e. Sr3(BO3)2, SrB2O4 and SrB4O7 doped with Eu2+/Eu3+ ions, were prepared by the solid state reaction method in the air. X-ray and SEM analyses confirmed that all these samples are pure phase micro-sized materials. The luminescence properties of the Eu2+ and Eu3+ doped compounds were investigated in detail, i.e. excitation and emission spectra, including luminescence decay curves and determined lifetimes. Furthermore, the effects of the strontium borate matrices on the luminescence properties of the Eu2+/Eu3+ ions were discussed. The intensity ratio of Eu2+/Eu3+ emission varies significantly in different matrices. The products obtained exhibited tunable multicolor luminescence from violet-blue to orange-red, depending on the excitation wavelength applied and the host matrix used.

BaB2 O3 F2 : A Barium Fluorooxoborate with a Unique [B2 O3 F]- Layer and Short Cutoff Edge.

Substitution of oxygen by fluorine in the borate group offers a materials platform from which intriguing structure and functionality may arise. Herein, we report a new fluorooxoborate, BaB2 O3 F2 , synthesized by introducing the F atoms into the BaO-B2 O3 system. BaB2 O3 F2 exhibits a unique oxyfluoride layer [B2 O3 F]- and a deep-ultraviolet cutoff edge below 180 nm. The effect of the introduction of F atoms on the structure and optical property of the borate group has been investigated; this should be useful to further expand borate chemistry and materials.

Diffuse-reflectance and luminescence study of the reduction of samarium in lead borate

Trivalent samarium has been observed for the first time to be reduced to samarium(II) in lead borate matrices fired under an air atmosphere. Air-firing of equivalent masses of co-precipitated samarium(III):lead(II) borate and boric acid at 650 °C resulted in the reduction of a portion of the trivalent samarium to the divalent state. The diffuse reflectance spectrum characteristic of the sample as well as the low-temperature emission spectrum both provided confirmation of the reduction of samarium. The diffuse reflectance spectrum indicated a nearly complete reduction of the samarium ion, however, an immensely strong emission from residual trivalent samarium appeared to overwhelm the divalent samarium emission. Divalent samarium emission appears to be quenched at room temperature, but becomes apparent when cooled to 77K.

Changing emission of divalent samarium doped into barium octoborate as a function of firing time

Barium octoborate has been synthesized by air firing of co-precipitated borates with additional boric acid. During the firing process, samarium ions doped into the matrix are reduced to the divalent state. Two different divalent samarium emission spectra have been observed from the material as a function of the firing history, even though the structure, as identified by powder X-ray diffraction remained consistent. A minor barium pentaborate impurity, in conjunction with significant thermal variability in the strength of the divalent samarium emission generated by the different sites in the two borate materials, appears to give rise to this phenomenon.

Studies on pelletised lithium magnesium borate TL material for eye lens dosimetry

Recent epidemiological studies in various cohorts confirm that radiation induced cataract may occur at a threshold dose as low as 0.5 Gy. ICRP has recognised the higher radiosensitivity of eye lens and recommended to reduce annual eye lens dose limit from 150 to 20 mSv. Present dosimetry for eye lens is largely based on LiF based dosimeters. The present work is an attempt towards using near tissue equivalent lithium borate material namely lithium magnesium borate doped with terbium (LMB:Tb) in eye lens dosimetry. The material in powder form was synthesised using solid state sintering method and pelletised using poly tetra fluoro ethylene (PTFE) as binding agent. It was observed that 130 mg of 1 mm thick LMB:Tb pellet bound with PTFE showed stable glow curve structure and attractive dosimetric features in terms of sensitivity, fading, linearity, reusability etc. A proposal of 1.5 mm Teflon encapsulation corresponding to tissue equivalent thickness of 3 mm was put forward for an ideal dosimeter for the measurement in terms of Hp(3). Energy and angular dependence studies based on FLUKA simulations suggest a flat response for the prototype design. In addition to PTFE, various tissue equivalent encapsulations such as polyimide, polyamide 6 and PMMA were also evaluated using FLUKA code.

Densification of lightweight aluminum borate ceramics by direct sintering of milled powders

ABSTRACTDense aluminum borate (Al18B4O33) materials were processed by simple milling-sintering of aluminum borate powders obtained by reacting calcined alumina and fine boric acid at temperatures of around 600–800ºC. The effect of milling on the grain size and sintering behavior of the aluminum borate powders was also determined. Sintering began at around 1000°C and was limited by the thermal decomposition (T > 1300 °C) of the borate in to alumina and boron oxide, which volatilize at this temperature. Sub-angular and medium spherical sintered grain microstructures were developed. A hardness of 6 GPa and bulk density below 2.5 g/cm3 were achieved. The results are accomplished encouraging the structural applications of borate materials.

Thermally stimulated luminescence of Li2B4O7:Cu,Ag,P+PTFE

Lithium borate is one of the most important materials for thermoluminescent dosimetry of ionizing radiation due to its human tissue equivalence. This work presents results of thermoluminescent studies of an improved lithium borate material doped with copper, silver and phosphate ions embedded in PTFE, under exposure to 60Co gamma radiation. Results show that the sensitivity of this new material is around 30% that of commercial TLD-100 (LiF:Mg,Ti) dosimeter and about 120 times greater than that of TLD-800. The TL response of this new material is linear over the extensive dose range 0.001–100 Gy. Its minimal detecting dose is 0.09 mGy, the coefficient of variability for 10 cycles consisting of annealing, irradiation and readout, is ± 3.5% and the dosimetric glow peak shows general-order kinetics. In addition, a morphological, structural and photoluminescent characterization of this TL detector was performed. Results show that this new detector may be appropriate for dosimetry applications.

Two Novel Deep‐Ultraviolet Nonlinear Optical Crystals with Shorter Phase‐Matching Second Harmonic Generation than KBe2BO3F2: A First‐Principles Prediction

In this work, we propose a strategy to design new deep‐ultraviolet (deep‐UV) nonlinear optical (NLO) materials through the combination of borate and phosphate NLO material genome. Accordingly, a series of borophosphates are predicted with very large energy bandgaps, strong second harmonic generation (SHG) effects, and moderate birefringence in the deep‐UV region. In particular, two novel fluoride borophosphates, PBO3F2 and PB3O6F2, are able to achieve the deep‐UV SHG laser output with shorter phase‐matching wavelengths (≈155 and 137 nm) than that of KBe2BO3F2 (KBBF, ≈161 nm). Further calculations show that these two structures are dynamically and thermodynamically stable, thus triggering possible synthesis, growth, and applications of them. The results attest that the proposed strategy is instructive and pave a comprehensive road map for us to discover new NLO crystals, especially in the borophosphate catalog with excellent deep‐UV phase‐matching capabilities beyond KBBF.

Influence of boric acid/Sr2+ ratio on the structure and luminescence properties (colour tuning) of nano-sized, complex strontium borates doped with Sm2+ and Sm3+ ions

Several complex strontium borate matrices (Sr3(B2O6), Sr2(B2O5), SrB2O4, SrB4O7, SrB6O10 and SrB8O11) doped with Sm2+/3+ ions were prepared using a modified Pechini method, with increasing Sr2+/boric acid ratio and a two-step annealing process. The Sm3+ ions were transformed into Sm2+ ones without additional reducing agents during the syntheses performed in the air atmosphere. The obtained crystal structures were investigated using powder X-ray diffraction (XRD) method. The use of 300% molar excess of boric acid during the synthesis process (Sr:B ratio 1:3), resulted in the formation of pure SrB2O4: Sm2+ nanoparticles, whose morphology was investigated with the use of transmission electron microscopy (TEM). Luminescence properties of the Sm2+ and Sm3+ doped compounds, i.e. excitation and emission spectra, including luminescence decay curves and determined lifetimes, were investigated. The obtained doped strontium borates show strong emission from Sm2+ and Sm3+ ions, in the range from 550 to 780 nm, after UV–Vis excitation. Depending on the λex used four characteristic bands of the Sm3+ ions, i.e. 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2 → 6H9/2, 4G5/2 → 6H11/2, and a series of split, very narrow bands typical of the Sm2+ ions, i.e. 5D0→7F0, 5D0→7F1, 5D0→7F2, 5D0→7F3, were clearly observed in the spectra. Chromaticity coordinates (CIE diagram) were calculated for different Sr:B ratios, showing a colour tuneable luminescence of the products synthesized.

Synthesis, structure characterization, photoluminescence properties and TD-DFT calculations for two new borates.

Due to their rich structural chemistry and wide variety of applications, borate materials have provided a rich area of research. In a continuation of this research, diethylammonium bis(2-oxidobenzoato-κ2O1,O2)borate, C4H12N+·BO4(C7H4O)2-, (1), and propylammonium bis(2-oxidobenzoato-κ2O1,O2)borate, C3H10N+·BO4(C7H4O)2-, (2), have been synthesized by the reaction of boric acid with salicylic acid under ambient conditions. In both structures, the B atom exhibits a slightly distorted tetrahedral environment formed by the bidentate coordination of two salicylate anions via the O atoms of the central carboxylate and oxide groups. In the crystals of salts (1) and (2), mixed cation-anion layers lying parallel to the (101) plane are formed through N-H...O, C-H...O and C-H...π/N-H...O hydrogen-bonding interactions, resulting, in each case, in a two-dimensional supramolecular architecture in the solid state. The photoluminescence properties of the salts were studied using the as-synthesized samples and reveal that salts (1) and (2) both display a strong blue-light emission, with maxima at 489 and 491 nm, respectively. In DFT/TD-DFT (time-dependent density functional theory) studies, the blue emission appears to be derived from an intramolecular charge transfer (ICT) excited state. In addition, IR and UV-Vis spectroscopies were used to investigate the title salts.

Copper-doped lithium triborate (LiB3O5) crystals: A photoluminescence, thermoluminescence, and electron paramagnetic resonance study

When doped with copper ions, lithium borate materials are candidates for use in radiation dosimeters. Copper-doped lithium tetraborate (Li2B4O7) crystals have been widely studied, but little is known thus far about copper ions in lithium triborate (LiB3O5) crystals. In the present investigation, Cu+ ions (3d10) were diffused into an undoped LiB3O5 crystal at high temperature. These ions occupy both Li+ and interstitial positions in the crystal. A photoluminescence (PL) band peaking near 387nm and a photoluminescence excitation (PLE) band peaking near 273nm verify that a portion of these Cu+ ions are located at regular Li+ sites. After an irradiation at room temperature with x rays, electron paramagnetic resonance (EPR) spectra show that Cu+ ions at Li+ sites have trapped a hole and converted to Cu2+ ions (3d9) while Cu+ ions at interstitial sites have trapped an electron and converted to Cu0 atoms (3d104s1). Two distinct Cu2+ trapped-hole spectra are formed by the x rays: one due to isolated Cu2+ ions with no nearby defects and the other due to perturbed Cu2+ ions. When the x-ray-irradiated crystal is heated above room temperature, a thermoluminescence (TL) peak appears at 120°C with a maximum in the emitted light near 630nm. EPR shows that this TL peak occurs when trapped electrons are thermally released from interstitial Cu0 atoms. Thermal quenching above room temperature prevents the electron-hole recombination at Cu2+ ions from contributing to the TL emission.

Radiological properties of plastics and TLD materials its application in radiation dosimetry

In the current study, we evaluated the tissue equivalency of nine different commonly used thermoluminescence compounds and six plastic materials over the photon energy range of 15 KeV to 20 MeV. Our result confirmed that the ratio of number of electrons per gram, electron density of the entire TLD compounds and plastic materials to ICRU-44 soft tissue was lesser than unity, except in the case of polypropylene plastics. The effective atomic number ratio of all the plastic materials was also <1 excluding Poly-vinyl-chloride, and for TLD lithium borate material, it was <1 others which showed the deviation with respect to photon energy. Mass attenuation coefficient (µ/ϼ), mass absorption coefficient (µen/ρ) was calculated and the results are discussed in this paper.

Enhanced electrochemical performance of LiMnBO3 with conductive glassy phase: a prospective cathode material for lithium-ion battery

LiMnBO3 has been identified as a promising cathode material for next-generation lithium-ion batteries. In this study, LiMnBO3 along with glassy lithium borate material (LiMnBO3 (II)) is synthesized by sol-gel method. X-ray diffraction (XRD) analysis depicts the existence of LiBO2 glassy phase along with m-LiMnBO3 phase. Transmission electron microscopy (TEM) analysis confirms the presence of LiBO2 glassy phase. An enhanced electrical conductivity of 3.64 × 10−7 S/cm is observed for LiMnBO3 (II). The LiBO2 glassy phase is found to promote the Li reaction kinetics in LiMnBO3 (II). The synthesized LiMnBO3 (II) delivers a first discharge capacity of 310 mAh g−1 within a potential window of 1.5–4.5 V at C/10 rate. Further, a discharge capacity of 186 mAh g−1 at the 27th cycle shows a better cycle performance. The enhanced capacity is due to the presence of LiBO2 glassy phase and more than one Li-ion transfer in the lithium-rich stoichiometry of LiMnBO3 (II). Density functional theory calculation reveals the exact electronic structure of m-LiMnBO3 with a band gap of 3.05 eV. A charge transfer mechanism is predicted for delithiation process of m-LiMnBO3.