Boric Acid Flux Research Articles

A Mini Review on Borate Photocatalysts for Water Decomposition: Synthesis, Structure, and Further Challenges.

The development of novel photocatalysts, both visible and UV-responsive, for water decomposition reactions is of great importance. Here we focused on the application of the borates as photocatalysts in water decomposition reactions, including water splitting reaction, hydrogen evolution half-reaction, and oxygen evolution half-reaction. In addition, the rates of photocatalytic hydrogen evolution and oxygen evolution by these borate photocatalysts in different water decomposition reactions were summarized. Further, the review summarized the synthetic chemistry and structural features of existing borate photocatalysts for water decomposition reactions. Synthetic chemistry mainly includes high-temperature solid-state method, sol-gel method, precipitation method, hydrothermal method, boric acid flux method, and high-pressure method. Next, we summarized the crystal structures of the borate photocatalysts, with a particular focus on the form of the B-O unit and metal-oxygen polyhedral in the borates, and used this to classify borate photocatalysts, which are rarely mentioned in the current photocatalysis literature. Finally, we analyzed the relationship between the structural features of the borate photocatalysts and photocatalytic performance to discuss the further challenges faced by the borate photocatalysts for water decomposition reactions.

Casparian strips prevent apoplastic diffusion of boric acid into root steles for excess B tolerance.

Casparian strips are ring-like structures consisting of lignin, sealing the apoplastic space between endodermal cells. They are thought to have important functions in controlling radial transport of nutrients and toxic elements in roots. However, Arabidopsis mutants with a defective Casparian strip structure have been found to maintain nutrient homeostasis in ranges supportive of growth under standard laboratory conditions. In this study, we investigated the function of Casparian strips under excess boron (B) conditions using sgn3 and sgn4 mutants with defective Casparian strip development but which do not exhibit excessive deposition of suberin, another endodermal diffusion barrier. The growth of sgn3 and sgn4 mutants did not differ significantly from that of wild-type (WT) plants under different B conditions in plate cultures; however, they were highly sensitive to B excess in hydroponic culture, where transpiration drives the translocation of boric acid toward the shoot. In hydroponic culture with sufficient to excess boric acid, B accumulation in shoots of the sgn3 and sgn4 mutants was higher than that in the WT. A time-course tracer study using 10B-enriched boric acid at a sufficient or slightly excessive concentration showed higher translocation of B into shoots of the sgn3 and sgn4 mutants. Furthermore, a genetically encoded biosensor for boric acid expressed under a stele-specific promoter (proCIF2:NIP5;1 5'UTR : Eluc-PEST) visualized faster boric acid flux into the mutant steles. Collectively, our results demonstrate the importance of Casparian strips in preventing apoplastic diffusion of boric acid into the stele under excess supply.

Flux synthesis, crystal structure, and characterization of a gamma-vanadate selenite polymorph

Our exploration in vanadate selenites by using boric acid flux method has successfully lead into a new phase, namely, γ-V2Se2O9. Single crystal X-ray diffraction indicates its a new structure which crystallizes in monoclinic space group P21/c with a lattice parameter of a ​= ​7.4857 (12) Å, b ​= ​7.4388 (8) Å, c ​= ​13.042 (2) Å, β ​= ​106.619 (9)°. Its crystal structure features novel 2D electroneutral [V2Se2O9] layers composed of 1D [V2SeO9]4- chains that are further bridged by Se (1)O3 triangular pyramids. [V2SeO9]4- chain consist corner-sharing of VO6 and tridentate Se (2)O3. Unlike previously reported α- and β-V2Se2O9 with isolated [V4O18]16− tetramers, corner-sharing of VO6 octahedra lead into a 1D [V2O9]8- chain in γ-V2Se2O9. X-ray powder diffraction and thermal behavior analysis were performed to study its phase purity and thermal stability. Optical diffuse reflectance spectra associated with Tauc's fitting indicates a direct bandgap semiconductor with an energy value of 2.34 ​eV, which consistent with the theoretical prediction. As a compare, the electronic bandgaps of three polymorphs were studied and shows a sequence of α-V2Se2O9<β-V2Se2O9<γ-V2Se2O9. Density of states were also calculated to reveal the origin of the bandgaps and bond interactions.

La1-xEuxB4O6(OH)2Cl (0 ≤ x ≤ 0.54): Strong 4f-4f excitations due to the noncentrosymmetric and oxychloride coordination of Eu3+

A strategy to utilize the nonlinear optical borate as the photoluminescent host is proposed in order to gain enhanced 4f-4f transitions because there exists a high probability of Eu3+ locating in a noncentrosymmetric coordination, serving as the near ultraviolet LED pumped red phosphor. With such a rationale, La1-xEuxB4O6(OH)2Cl have been prepared by boric acid flux method, which transfer to TD-α-La1-xEuxB3O6 by high temperature annealing. In the meantime, HS-α-La1-yEuyB3O6 (y ​= ​0, 0.075, 0.15, 0.3, 0.4) are synthesized directly by high temperature solid state reactions. The Eu3+-dependent cell volume is employed to obtain equation (1): V1 ​= ​421.0(3)-26(1)y. Accordingly, the x values of TD-α-La1-xEuxB3O6 can be deduced and the cell volume of La1-xEuxB4O6(OH)2Cl can be simulated into equation (2): V2 ​= ​695.1(1)-37.9(8)x. In the following, all the x values for 11 samples of La1-xEuxB4O6(OH)2Cl are determined. The noncentrosymmetric coordination as well as the mix-coordination atoms lead to strong 4f-4f transitions of Eu3+, and only a slight concentration quenching effect is observed despite the existence of hydroxyl groups. Once combined with a 395 ​nm LED chip, it emits a bright pink light, and the thermal stability is satisfied according to the in-situ high temperature photoluminescent study.

Synthesis, characterization and standard molar enthalpies of formation of two zinc borates: 2ZnO·2B2O3·3H2O and ZnB4O7

The standard mole enthalpy of formation is an essential feature of chemical compounds, which is critical for assessing the thermal effects of chemical reactions with their participation. In this paper, two pure phases of zinc borates, 2ZnO·2B2O3·3H2O and ZnB4O7, have been synthesized by hydrothermal and boric acid flux methods, respectively. They were characterized by XRD, FT-IR and TGA. The molar enthalpies of solution of 2ZnO·2B2O3·3H2O (s) and ZnB4O7 (s) in 1 mol·dm−3 HCl (aq) were measured at T = 298.15 K, respectively, by the use of an isothermal microcalorimeter. In accordance with Hess’ law, the standard molar enthalpies of formation of the two zinc borates 2ZnO·2B2O3·3H2O (s) and ZnB4O7 (s) were calculated to be −(4177.02 ± 3.3) kJ·mol−1 and −(2971.1 ± 3.3) kJ·mol−1, respectively, by the use of standard molar enthalpies of formation for ZnO (s), H3BO3 (s) and H2O (l) based on the two designed thermochemical cycles.

Photoluminescence of complete solid solutions α-Y1-xEuxB5O9 by sol-gel synthesis and thermal decomposition from Y1-xEux[B6O9(OH)3

Completed solid solutions of Y1-xEux[B6O9(OH)3] were prepared by boric acid flux method and the structure of Eu[B6O9(OH)3] was determined by single crystal X-ray diffraction (XRD). The successful cationic doping was supported by the linear change of unit cell parameters obtained by Le Bail fitting on powder XRD. Thermal treatments on Y1-xEux[B6O9(OH)3] will lead to the dehydration, re-crystallization into TD-α-Y1-xEuxB5O9, and decomposition to α-Y1-xEuxB3O6 eventually. For comparison, the sol-gel method was also applied to prepare SG-α-Y1-xEuxB5O9. Rietveld refinements on powder XRD was applied to obtain the crystallographic data for α-YB5O9. PL investigation indicated that the existence of hydroxyl groups weakened the Eu3+ charge transfer (CT) in Y1-xEux[B6O9(OH)3]. In α-Y1-xEuxB5O9, an intense CT absorption was detected and a bright right emission was observed. Moreover, both series of phosphors exhibited a right shift of CT maximum wavelength due to the expansion of unit cell and the delayed concentration at x = 0.6.

Removal of nuclides and boric acid from simulated radioactive wastewater by forward osmosis

In this paper, the removal of nuclides and boric acid from the simulated borate-containing radioactive wastewater was studied using forward osmosis (FO) process. The effect of membrane materials and their orientation, as well as borate concentration on the flux and retentions of nuclides and boric acid was determined. The results indicated that cellulose triacetate with embedded polyester screen support (CTA-ES) membrane had highest Co2+ retention (99.62–99.69%) and Sr2+ retention (96.90–97.85%) when boric acid concentration increased from 0 to 2400 mg L−1 and the active layer facing feed solution (AL-FS) mode was used. Cellulose triacetate with a cast nonwoven support (CTA-NW) and CTA-ES membranes had equivalently high Cs+ retention (∼95%). Thin-film composite with embedded polyester screen support (TFC-ES) membrane had lowest Cs+ retention (below 40%). For both CTA membranes at AL-FS mode, the nuclide retentions did not change obviously with borate concentration. However, the nuclide retention for TFC-ES membrane was affected by borate concentration. Borate retention was lower than 37% for three membranes. For both CTA membranes, borate concentration had no obvious influence on the trans-membrane osmotic pressure, water flux and reverse NaCl flux. CTA-ES membrane has potential for the treatment of borate-containing radioactive wastewater due to its highest nuclide retention, boric acid flux and water flux.

A Novel Cesium Pentaborate with Ribbon-Type Anionic Radical

A novel hydrated cesium hydroxypentaborate is synthesized from boric acid flux at 180°С, and its crystal structure is determined by X-ray diffraction. The compound crystallizes in the triclinic system, sp. gr. P $$\bar {1}$$ , with the parameters a = 7.8107(5) A, b = 9.1929(8) A, c = 12.3553(11) A, α = 98.98(1)°, β = 106.32(1)°, γ = 91.10(1)°, V = 839.1(1) A3, Z = 4. The structure is refined to R1 = 5.8% with anisotropic displacement parameters for all nonhydrogen atoms, with allowance for the non-merohedral twinning by a twofold axis coinciding with the b axis. The twin components were 0.546(1) and 0.454(1). The features of the hydrogen bonds in Cs[B5O7(OH)2] · 0.5H2O are analyzed in comparison with isostructural rubidium analogue. The unit-cell parameters a and c of A[B5O7(OH)2] · 0.5H2O pentaborates are found to systematically increase with an increase in the radius of A cation in the NH4 → Rb → Cs series; the small variation in the b parameter is due to the rigidity of the pentaborate chains elongated along this direction.

Crystal chemistry and physical properties of the A2M3(H2O)2[B4P6O24(OH)2] (A = Cs, Rb; M = Ni, Cu, (Ni, Fe)) borophosphate family.

Three new transition metal borophosphates, Cs2Cu3(H2O)2[B4P6O24(OH)2] (denoted (I)), Cs2Ni3(H2O)2[B4P6O24(OH)2] (II) and mixed Rb2Ni2.5Fe0.5(H2O)2[B4P6O24(OH)2] (III), were synthesized by a boric acid flux method at 473-493 K. X-ray single-crystal diffraction study confirms their isotipy with (Cs/Rb)2Co3(H2O)2[B4P6O24(OH)2] borophosphates crystallizing in the orthorhombic space group Pbca. The crystal structures of all compounds are based on 3D frameworks made from corrugating borophosphate layers [B4P6O24(OH)2] and trimers of MO4(H2O)2 and two MO6 edge-sharing octahedra. The negative charge of the framework is compensated by alkali metal cations, Rb+ or Cs+. Structural analysis reveals the flexibility of mixed anionic frameworks of the described structural type. The Cu-member demonstrates a strong distortion of the unit cell due to the Jahn-Teller effect of the d9 configuration of the Cu2+ cation. The possibility of a solid solution between different transition metals (Fe and Ni) with the formation of crystals with mixed structural positions is confirmed by an example of the (III) phase. It is shown that Fe2+ cations prefer to occupy the M2 position with more distorted oxygen environment, as compared to the M1O6 octahedra. Magnetic studies of (I), (II) and (III) prove that all compounds are paramagnets down to the lowest temperatures of measurements, 2 K. (I) and (II) compounds are thermally stable up to 500 °C. Different mechanisms of their thermal decomposition are discussed. The possibility of a wide isomorphous substitution at the transition metal sites of the title structure type opens the way to the modification of the properties in the discussed series of borophosphates.

Thermometry of red nanoflaked SrAl12O19:Mn4+ synthesized with boric acid flux

This paper presents the luminescence properties and potential of red SrAl12O19:Mn4+ (SAO:Mn4+) phosphor for optical thermometry application. The SAO crystal consisted of a spinel block along with two mirror-like blocks. The Al3+/Sr2+ molar ratio of the precursor solution affected the crystalline-phases, morphology, and photoluminescence of the phosphor. The addition of flux H3BO3 promoted the growth of hexagonal-nanoflakes and enhanced the external quantum efficiency of phosphor 2.6-fold. The absolute sensitivity Sa and relative sensitivity Sr of SAO:Mn4+ showed a linear function of the temperature. The value of Sa was 4.17 × 10−3 K−1, and the maximum Sr was 2.70 × 10−3 K−1 at 393 K. A stable emission color was observed even with a change in temperature and a bright red light was seen in both daylight and a darkroom.

Boron transfer during desalination by electrodialysis

Effective boron rejection is challenging, particularly in seawater reverse osmosis (SWRO). Fortunately, electrodialysis (ED) provides a feasible alternative. This study was targeted at a mechanistic understanding of the transfer of boron in ED by systematically evaluating the effects of the chief parameters of solution pH, salinity, boron concentration, current and membrane type. Diffusion and additional transfer are key mechanisms for boron transfer in ED, and the additional transfer is governed by convection for boric acid and migration for borate. Four key results are highlighted. Firstly, boric acid (i.e., at pH = 6.1) transfer was greater than borate (i.e., at pH = 10.8) transfer, giving the permeability and additional transfer coefficient of the former of respectively an order-of-magnitude and twofold that of the latter. Secondly, while changes in salt concentrations had negligible impact on boric acid flux, borate flux decreased with NaCl concentration due to increased competition with the chloride ions. Thirdly, boron permeability was greater for the RO membranes than the ion-exchange membranes (IEMs) due to different membrane properties, and boron permeability decreased with pH for both the RO membranes and IEMs due respectively to electrostatic repulsion and competition for charge carriers. Fourthly, the percentage of boric acid transferred decreased with current, which suggests enhanced boron rejection as current increased. Collectively, results indicate that ED is promising for boron removal, and is possibly more effective than RO in boron rejection both because of the different membrane properties and transfer mechanisms.

Small amount of water induced preparation of several morphologies for InBO3:Eu3+ phosphor via a facile boric acid flux method and their luminescent properties

Four kinds of morphologies for InBO3:Eu3+ phosphor have been prepared via a facile boric acid flux method only by adjusting the small amount of added water. The prepared samples have been characterized by XRD, FT-IR, and SEM. It was found that the size and morphology of the samples could be effectively controlled by adjusting reaction temperature, reaction time, especially the small amount of added water, which plays an extremely critical role in the controlling morphology. The possible growth mechanisms for microsphere and flower-like morphologies were further discussed on the basis of time-dependent experiments. Furthermore, the luminescence properties of prepared InBO3:Eu3+ samples have been investigated by photoluminescence (PL) spectra. The results show that the InBO3:Eu3+ phosphors show strong orange emissions under ultraviolet excitation at 237 nm. The monodisperse microsphere sample possesses the highest PL intensity among above four morphologies, which can be used as a potential orange luminescent material.

Effects of boric acid on structural and luminescent properties of BaAl2O4:(Eu2+, Dy3+) phosphors

Eu2+/Dy3+-codoped BaAl2O4 phosphors were prepared by conventional solid-state reaction with boric acid flux. The effects of boric acid on structural and luminescent properties of BaAl2O4:(Eu2+, Dy3+) were investigated. The crystallinity of BaAl2O4 improved with increasing amount of H3BO3. Incorporation of Eu2+ and Dy3+ ions into effective lattice sites was promoted by H3BO3 addition. As a result, Eu2+ emission in BaAl2O4 was greatly enhanced by H3BO3, and the duration of persistent luminescence increased with the amount of H3BO3. However, the decay lifetime of persistent luminescence was not strongly influenced by the amount of H3BO3.

ChemInform Abstract: A New Type of KYP2O7 Synthesized by the Boric Acid Flux Method and Its Luminescence Properties.

AbstractSingle crystals of a new phase of KYP2O7, r‐KYP2O7, are prepared by a low‐temperature H3BO3 flux method using a 1:1:8 molar mixture of YF3, H3BO3, and KH2PO4 (autoclave, 573 K, 3 d; cooling to 453 K at a rate of 1 K/h).

Potassium uranyl borate 3D framework compound resulted from temperature directed hydroborate condensation: structure, spectroscopy, and dissolution studies.

The equatorial coordination nature of the uranyl unit has resulted in only three uranyl borate 3D framework compounds reported so far formed from boric acid flux reactions conducted at 190 °C while all others are 2D layers. Here in this work, by increasing the reaction temperature to 250 °C, a new potassium uranyl borate K[(UO2)B6O10(OH)] (KUBO-4) framework compound is synthesized that shares the same layer topology with the previously reported 2D layered KUBO-1. The 3D structure of KUBO-4 is achieved by interlayer hydroborate condensation. The KUBO-4 was further characterized with single crystal XRD, SHG and fluorescence spectra, and TG/DSC measurements. A deep understanding regarding the dissolution behaviours of uranyl borate is achieved via solubility studies of the KUBO-1 and KUBO-4 performed using a combination of ICP-MS, powder XRD, and fluorescence spectroscopy techniques. The results confirm the lack of stability of borates in aqueous solutions with the presence of coordinating ligands in the environment regardless of the structure types.

A new type of KYP2O7 synthesized by the boric acid flux method and its luminescence properties

A new type of KYP2O7 was prepared by the low-temperature H3BO3 flux method. Different from the known ɑ and β phase of KYP2O7, this new r-KYP2O7 (P21/m, a = 7.052 Å, b = 5.660 Å, c = 8.930 Å, β = 108.5°) has a polyhedral assembly of 4- and 6-membered rings and K+ ions locating in the voids. By the doping of rare earth ions such as Ce3+, Tb3+ and Eu3+, a series of r-KYP2O7:RE3+ with different luminescent properties were also investigated. The results indicate that the boric acid flux method is a promising way to develop new phosphors, which may open a gate for the further exploration of novel luminescent substances.

PKU-3: An HCl-Inclusive Aluminoborate for Strecker Reaction Solved by Combining RED and PXRD.

A novel microporous aluminoborate, denoted as PKU-3, was prepared by the boric acid flux method. The structure of PKU-3 was determined by combining the rotation electron diffraction and synchrotron powder X-ray diffraction data with well resolved ordered Cl(-) ions in the channel. Composition and crystal structure analysis showed that there are both proton and chlorine ions in the channels. Part of these protons and chlorine ions can be washed away by basic solutions to activate the open pores. The washed PKU-3 can be used as an efficient catalyst in the Strecker reaction with yields higher than 90%.

Synthesis of Divalent Europium Borate via in Situ Reductive Techniques

A new divalent europium borate, Eu[B8O11(OH)4], was synthesized by two different in situ reductive methodologies starting with a trivalent europium starting material in a molten boric acid flux. The two in situ reductive techniques employed were the use of HI as a source of H2 gas and the use of a Zn amalgam as a reductive, reactive surface. While both of these are known reductive techniques, the title compound was synthesized in both air and water which demonstrates that strict anaerobic conditions need not be employed in conjunction with these reductive methodologies. Herein, we report on the structure, spectroscopy, and synthetic methodologies relevant to Eu[B8O11(OH)4]. We also report on a europium doping study of the isostructural compound Sr[B8O11(OH)4] where the amount of doped Eu(2+) ranges from 2.5 to 11%.

ChemInform Abstract: Field‐Induced Spin‐Flop‐Like Metamagnetism in α‐CoB4O7.

AbstractPure α‐CoB4O7 is synthesized by a boric acid flux method from a mixture of Co(OAc)2 and H3BO3 (autoclave, 220 °C, 5 d) followed by step‐wise annealing of the resulting new cobalt polyborate up to 800 °C.

Boric acid flux synthesis, structure and magnetic property of MB12O14(OH)10 (M=Mn, Fe, Zn)

Three new borates MB12O14(OH)10 (M=Mn, Fe, Zn) have been synthesized by boric acid flux methods, which are isotypic to NiB12O14(OH)10. Single-crystal XRD was performed to determine the crystal structures in detail. They all crystallize in the monoclinic space group P21/c. The size of MO6 (M=Mg, Mn, Fe, Co, Ni, Zn) octahedron shows a good agreement with the Shannon effective ionic radii of M2+. Magnetic measurements indicate MnB12O14(OH)10 is antiferromagnetic without a long-range ordering down to 2 K. The values of its magnetic superexchange constants were evaluated by DFT calculations, which explain the observed magnetic behavior. The UV–vis diffuse reflectance spectrum of ZnB12O14(OH)10 suggests a band gap ∼4.6 eV. DFT calculations indicate it has a direct band gap 4.9 eV. The optical band gap is contributed by charge transfers from the occupied O 2p to the unoccupied Zn 4s states.