Boronic acid-functionalized porous polycarbazoles: preparation,adsorption performance,and heterogeneous catalysts for selective oxidation

Boronic acid-functionalized porous polycarbazoles (PCBA-1 and PCBA-2) which possess special functions as well as permanent porosity have been synthesized by oxidative coupling polymerization, followed by characterization of their chemical structure and porosities. The Brunauer–Emmett–Teller (BET) specific surface area value scope of PCBA-1 and PCBA-2 is from 868 to 768 m² g^?1 and the related dominant pore sizes are centered at about 1.0 nm. PCBA-1 and PCBA-2 exhibit potential adsorption for vapor solvent and small gas molecules. Their adsorption capacity for methanol measured at saturated vapor pressure and room temperature is 534 and 430 mg g^?1, respectively. They also show moderate uptake capacity (15.3 and 14.0 wt%) for CO₂ at 1.0 bar and 273 K. Also, the obtained porous polymers as effective heterogeneous catalysts can promote transformation of 1,2-diols into α-hydroxy ketones accordingly by selective oxidation.     

Synthesis and characterization of novel AZO chromophore with multi hydroxyl groups

Novel organic second order nonlinear optical chromophore with 4,4′-(5-(bis(2-hydroxyethyl)amino)-1,3-phenylene)bis(oxy)dibutan-1-ol as electron donor and azo thiophene as π-electronic bridge was synthesized and characterized by ¹H NMR spectra and mass spectra. After the introduction of four hydroxyl groups to the electron donor, the solubility of chromophore Z1 in water was improved greatly (0.5 g). Else, the solubility of chromophore Z1 in common organic solvents was still very good. The thermal decomposition temperature was above 250 °C, which was high enough for its application in both the preparation of optoelectronic devices and Second harmonic generation imaging. Electro-optical films prepared by chromophore Z1 showed us the largest second-order nonlinear optical coefficient was about 85 pm/V, which was large enough for the detection of second harmonic generation signal in water solution. Else, the photochemical stability of chromophore Z1 was also studied; the advantage of chromophore with azo bond was very obvious for improving the photochemical stability of organic second order nonlinear optical chromophores.     

Anionic NbO-type copper organic framework decorated with carboxylate groups for light hydrocarbons separation under ambient conditions

Light hydrocarbons are important raw materials for industrial products and fine chemicals. The storage and separation of C₁–C₃ hydrocarbons are vital to their practical use. Here, we report efficient C₁–C₃ hydrocarbon adsorption and separation with a NbO-type anionic copper metal–organic framework with uncoordinated –COO^? groups ([Cu₂(L)·(H₂O)₂]·2H₂O·3DMA·(CH₃)₂NH₂) (1). Complex 1 exhibited large C₂H₂ (190 cm³ g^?1), C₂H₄ (147 cm³ g^?1), C₂H₆ (156 cm³ g^?1), C₃H₆ (170 cm³ g^?1), and C₃H₈ (173 cm³ g^?1) uptakes and high selectivities for C₂H₂/CH₄ (32.3), C₃H₆/CH₄ (152), and C₃H₈/CH₄ (127) under ambient conditions. The excellent cycling performance of the material was reflected by only 9.2 and 10.9% losses of the C₂H₂ and C₃H₆ storage capacities even after ten cycles of adsorption–desorption tests. First-principles calculations and Grand canonical Monte Carlo simulations further revealed that not only the open metal sites but also the –COO^? groups played a key role in the high C₂–C₃ hydrocarbon uptakes. The results obtained in this study suggest that anionic 1 is a promising candidate for light hydrocarbon adsorption and natural gas purification at room temperature.     

A biogenic TiO<Subscript>2</Subscript>-C-O nanohybrid grown from a Ti<Superscript>4+</Superscript>-polymer complex in green tissues of chilis,interface bonding,and tailored photocatalytic properties

A nanostructured a-TiO₂ (anatase) is well known to be a promising material for harvesting photocatalysis in ultraviolet–visible light for its applications. In this article, we report a simple biosynthesis of a stable compound a-TiO₂-C-O of small core–shells by a hydrothermal reaction of titanium tetrabutoxide in small tissues (proteins, lipids, or carbohydrates) of green chili (hot) at moderate temperature followed by burning out the organics in a flame in camphor in open air. In a proposed microscopic model, the a-TiO₂ is shown to be growing preferentially in support of an inbuilt biogenic 2D layer C–sp ² (template) in the coherent (101) facets in a controlled shape of small cuboids (8–15 nm sizes), with a joint C–sp ² charge/spin layer in an a-TiO₂-C-O hybrid composite phase. A thin residual ‘Ti⁴⁺ -O-C’ surface layer lasts, with a rocking of a ‘C-O cage’ on the Ti⁴⁺ ions of 285 cm^?1 frequency, in the samples heated at ≤ 600 °C in air. It is found to be promoting a markedly enhanced photocatalytic response in degrading methylene blue dye and 2-chlorophenol under a visible light irradiation. The results are described with N₂ sorption hysteresis, microscopic images, Raman/XPS (X-ray photoelectron spectroscopy) bands, and ultraviolet–visible light absorption/emission spectra in the samples prepared of varied microscopic surface layers.     

Preparation of yolk–shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@N-doped carbon nanocomposite particles as anode in lithium ion batteries

The yolk–shell-structured Fe₃O₄ nanocomposite particles (Fe₃O₄@Void@C–N NPs) with Fe₃O₄ as the yolk and N-doped carbon as the shell were prepared by using melamine formaldehyde resin as the N and C sources. When used as anode material for lithium ion battery, the yolk–shell structure could not only afford adequate void to accommodate the large volume change during charge/discharge process but also improve structural stability and electrical conductivity. The anode material demonstrated superior long-term and high-rate performance because of the novel structure and the N-doped carbon shell with mesopore. Thus, Fe₃O₄@Void@C–N NPs exhibited a high reversible capacity of 1530 mAh g^?1 after 300 cycles at a current density of 500 mA g^?1, which were approximately 1.5 and 6 times higher than Fe₃O₄@C–N NPs and pure Fe₃O₄ particles, respectively. Even at the higher current density of 2000 mA g^?1, the reversible capacity remained at 651 mAh g^?1 after 500 cycles.     

Ultrasensitive leak detection

The objective of this investigation was to develop a method of detecting leaks to a sensitivity of 1.0 × 10^?13 std cm0^?3 s^?1 in vacuum devices and to develop a qualifiable standard leak to provide system calibration at this leak rate. The development work demonstrated that minimum detectable leak rates of 6.5 × 10^?14 and 5.5 × 10^?15 std cm^?3 s^?1 are possible for respective analog and digital measurement modes.     

Metal nanoparticle-loaded porous carbon hollow spheres by twin polymerization

The formation of silver and gold nanoparticle-encapsulated hollow carbon spheres (HCS) by twin polymerization is reported. Therefore, silica spheres with different diameters (Aerosil^® AS90, d = 20 nm; Aerosil^® OX50, d = 40 nm; Stöber particles, d = 200 nm) were coated with the metal carboxylates [AgO₂C(CH₂OCH₂)₃H] (1) or [(PPh₃)AuO₂C(CH₂OCH₂)₃H] (2). Thermal treatment of the as-produced templates gave the respective metal nanoparticle-functionalized systems, which were characterized by powder X-ray diffraction (PXRD) and transmission electron microscopy. The plasmon resonance of the surface-bonded particles was determined by using UV–Vis spectroscopy showing absorptions at 412 nm for silver and 524 nm for gold. The metal nanoparticle-modified templates were then coated with a twin polymer layer as result of the acid-catalyzed twin polymerization of 2,2′-spiro-bi[4H-1,3,2-benzodioxasiline] (3). This coating consists of a phenolic resin and in situ formed silicon dioxide nanoclusters. After carbonization and removal of the SiO₂ phase by refluxing with a NaOH solution, the appropriate metal-loaded HCS were obtained. The thus prepared carbon materials were characterized by PXRD, electron microscopy and nitrogen adsorption–desorption isotherms. Mainly micro-porous materials (IUPAC type I) were obtained with a surface area between 910 and 1110 m²/g. These HCS materials were used for the catalytic reduction of methylene blue and 4-nitrophenol proving the accessibility of the incorporated M-NPs. A size-dependent influence of the used carbon hull was found.     

Synthesis and structural features of Np(VI) and Pu(VI) isophthalates

New An(VI) isophthalate complexes [PuO₂(C₈H₄O₄)] (I), Cs₂[(NpO₂)₂(C₈H₄O₄)₃]·4H₂O (II), [H₃O]₂[(NpO₂)₂(C₈H₄O₄)₃]·nH₂O (III), and [H₃O][NpO₂(C₈H₄O₄)(C₈H₅O₄)]·2H₂O (IV) with the An(VI): Lig ratios of 1: 1 (I), 1: 1.5 (II, III), and 1: 2 (IV) were synthesized and studied by single crystal X-ray diffraction. In complex I, the coordination polyhedron of the Pu(1) atom is a pentagonal bipyramid whose equatorial plane is formed by the oxygen atoms of four [C₈H₄O₄]^2– anions. The coordination capacity of the ligand in complex I is maximal among compounds I–IV and equal to 5, with each [C₈H₄O₄]^2– anion binding four PuO₂²⁺ cations into electrically neutral layers. In the structures of II and III, the coordination polyhedra of the Np(1) atoms are hexagonal bipyramids whose equatorial planes are formed by the oxygen atoms of three [C₈H₄O₄]^2– anions. Two crystallographically independent [C₈H₄O₄]^2– anions exhibit the coordination capacity equal to 4, each binding two NpO₂²⁺ cations in the chelate fashion. As a result, doubled anionic layers are formed in the crystals of II and III. Outer-sphere cations influence the packing of doubled layers in the crystals: Complex II crystallizes in the monoclinic system, and complex III, in the orthorhombic system. In the structure of IV, the coordination polyhedron of the Np(1) atom is a hexagonal bipyramid whose equatorial plane is formed by the oxygen atoms of two [C₈H₄O₄]^2– anions and one [C₈H₅O₄]^– anion. The crystallographically independent bridging anion [C₈H₄O₄]^2– exhibits the coordination capacity equal to 4 and binds in the chelate fashion two NpO₂²⁺ cations to form chains, and the independent hydrogen isophthalate anion [C₈H₅O₄]^– binds one neptunyl(VI) cation in the chain in the chelate fashion, exhibiting the coordination capacity equal to 2.     

Ternary alloy nanocatalysts for hydrogen evolution reaction

Cu–Fe–Ni ternary alloys (size ～55–80 nm) with varying compositions viz. CuFeNi (A1), CuFe ₂ Ni (A2) and CuFeNi ₂ (A3) were successfully synthesized using microemulsion. It is to be noted that synthesis of nanocrystalline ternary alloys with precise composition is a big challenge which can be overcome by choosing an appropriate microemulsion system. High electrocatalytic activity towards HER in alkaline medium was achieved by the formation of alloys of metals with low and high binding energies. A high value of current density (228 mA cm ² ) at an overpotential of 545 mV was obtained for CuFeNi (A1), which is significantly high as compared to the previously reported Ni _{5 9} Cu _{4 1} alloy catalyst.     

In-situ construction of 2D direct Z-scheme g-C<Subscript>3</Subscript>N<Subscript>4</Subscript>/g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> homojunction with high photocatalytic activity

Constructing all-solid-state Z-scheme junction is a very effective strategy to design highly active photocatalysts for solar energy conversion and environmental purification. We herein firstly construct 2D g-C₃N₄/g-C₃N₄ Z-scheme homojunction by using a bottom-up approach, during which the supramolecular complex is initially formed, followed by a facile thermal polycondensation. Based on the active species trapping experiments, Mott–Schottky test and band edge position analysis, the prepared 2D nanosheet g-C₃N₄/g-C₃N₄ homojunctions are found to be Z-scheme type, different from those available reported ones with a type-II energy alignment. Benefiting from the specific 2D morphology with large exposed surface area and Z-scheme junction with efficient separation and high redox abilities of the photoinduced electrons and holes, the obtained 2D g-C₃N₄/g-C₃N₄ homojunctions are much more active than the conventional g-C₃N₄/g-C₃N₄ homojunction (CN-MT) and bulk g-C₃N₄ (CN-M) under visible light irradiation, validating by the high rhodamine degradation rate of 0.833 h^?1, which is about 3.9 and 15.4 times higher than that of CN-MT (0.214 h^?1) and CN-M (0.054 h^?1), respectively. The present work sheds light on design of novel Z-scheme photocatalysts with specific morphology and thus further application in the field of environment or energy.     

Synthesis and Structure of Mixed-Cation Salts with [PuO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]<Superscript>3–</Superscript> Anions

Mixed-cation salts of the composition NaM₂[PuO₄(OH)₂]·4H₂O, where M = Rb (I) and Cs (III), and NaRb₅[PuO₄(OH)₂]₂·6H₂O (II) were synthesized and structurally characterized. The central Pu atom in [PuO₄(OH)₂]^3– anions has oxygen surrounding in the form of a tetragonal bipyramid with oxygen atoms of hydroxide ions in apical positions. The hydrated Na⁺ cations have oxygen surrounding in the form of a distorted octahedron. In the structure of I, there are two independent Rb⁺ cations with 10- and 12-vertex coordination polyhedra (CPs), and in the structure of II, three independent Rb⁺ cations with the 12-, 11-, and 13-vertex CPs. In the structure of III, the Cs⁺ cation has a 12-vertex CP. Frameworks of large Rb⁺ or Cs⁺ cations can be distinguished in the structure. The CPs of the Pu and Na atoms (I, III) sharing a common edge or the isolated CPs of the Pu and Na atoms (II) are incorporated in these frameworks. Hydrogen bonds influence the crystal packing and the geometric characteristics of the [PuO₄(OH)₂]^3– anions.     

Electrical and dielectric properties of bismuth holmium cobalt titanate (BiHoCoTiO<Subscript>6</Subscript>): a complex double perovskite

A lead-free bismuth holmium cobalt titanate multiferroic(BiHoCoTiO₆) was synthesized at high temperatures by a solid-state reaction (a mixed oxide) route. Structural analysis of the compound is performed using X-ray diffraction data and an orthorhombic crystal system is suggested for the material. Study of room temperature scanning electron microigrapgh exhibited better morphology for the material. The uniform distribution of the small rod-type of grains with dimension of 1–2 µm length and 0.2–0.3 µm diameters was visible. Analysis of temperature-frequency dielectric data exhibited two dielectric anomalies or phase transitions: first transition temperature(t_c1) at 175?°C and the second one at 325?^°C. Study of frequency and temperature dependence of resistive characteristics (performed using complex impedance spectroscopy) has shown significant contributions of grains and grain boundaries, which in turn, helps in understanding the electrical conduction mechanism and microstructure behaviour of the material in a better way. The impedance or Nyquist plots were modelled with an equivalent circuit containing capacitance, resistance and related parameters due to grain (bulk), grain boundaries and capacitance. The transport properties, AC conductivity and electrical modulus of the material were also investigated and reported here.     

Synthesis and Structure of Mixed-Cation Salts with [NpO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]<Superscript>3–</Superscript> Anions

Mixed-cation salts of the general composition NaM₂[NpO₄(OH)₂]·4H₂O, where M = Rb (I, II) and Cs (III), were synthesized and structurally characterized. The compounds differ from each other in the structural organization. The Np central atom in [NpO₄(OH)₂]^3– anions has oxygen surrounding in the form of a tetragonal bipyramid with the O atoms of hydroxide ions in the apical positions. The hydrated Na⁺ cations have oxygen surrounding in the form of a distorted octahedron. In the structure of I, there are two independent Rb cations with 10- and 12-vertex coordination polyhedra, and in the structures of II and III the framework of large cations is built of 12-vertex Rb and Cs polyhedra. The coordination polyhedra of the Np and Na atoms, sharing a common edge (I, III), or chains of the coordination polyhedra of the Np and Na atoms, sharing common vertices (II), are accommodated in the channels of the frameworks. Hydrogen bonds influence the crystal packing and the geometric characteristics of the [NpO₄(OH)₂]^3– anions.     

Synthesis and crystal structure of An(VI) complexes with cyclobutanecarboxylic acid anions and 2,2′-bipyridine [An(VI) = U,Np, Pu]

New complexes of hexavalent U, Np, and Pu of the composition [UO₂(bipy)(cbc)₂] (I) and [AnO₂(bipy)(cbc)₂]·0.5(bipy) [An = Np (II) and Pu (III)] with cyclobutanecarboxylic acid anions C₄H₇COO^– and 2,2′-bipyridine (bipy) were synthesized, and their structures were studied. The An atoms in I–III have the coordination surrounding in the form of distorted hexagonal bipyramids with the О atoms of AnO₂²⁺ cations in the apical positions. The equatorial plane of the bipyramids is constituted by the O atoms of two C₄H₇COO^– anions and N atoms of bipy.     

Fabrication of stable Ni–Al<Subscript>4</Subscript>Ni<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> superhydrophobic surface on aluminum substrate for self-cleaning,anti-corrosive and catalytic performance

A stable Ni–Al₄Ni₃–Al₂O₃ superhydrophobic surface (SHS) was fabricated on aluminum (Al) substrate via etching, subsequent replacement deposition and then annealing. The water contact angle of the SHS could reach to 155°, and the water sliding angle was less than 2°. The morphology and chemical composition of the samples were characterized using scanning electron microscopy, X-ray diffraction pattern, energy-dispersive spectroscopy and X-ray photoelectron spectroscopy. Anti-corrosion behaviors of the samples were investigated via Tafel extrapolation and electrochemical impedance, and the SHS showed a better corrosion resistance than that of pure Al. In addition, when the water drops impinged on the SHS, the drops could fully bounce, exhibiting exquisite self-cleaning property. The catalytic property of the samples was evaluated by the reduction of 4-nitrophenol (4-NP) at room temperature, in which the SHS served as the hydrogen generator as well as a catalyst. The degradation rate of 4-NP at the existence of the superhydrophobic samples in NaOH aqueous solution was 97%. And the reaction rate constant of 4-NP at the existence of the superhydrophobic samples was 9.51 × 10^?2 s^?1, which was about twice as large as that at the existence of pure Al. This work offers an effective strategy to fabricate SHSs and expands industrial applications for Al and its alloys.     

Synthesis and Structure of the Np(VII) Complex with Guanidinium,Li[C(NH<Subscript>2</Subscript>)<Subscript>3</Subscript>]<Subscript>2</Subscript>[NpO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]·6H<Subscript>2</Subscript>O

The previously unknown Np(VII) compound Li[C(NH₂)₃]₂[NpO₄(OH)₂]·6H₂O (I), containing organic cations, was synthesized and studied by single crystal X-ray diffraction. In contrast to the relatively numerous structurally characterized salts of [NpO₄(OH)₂]^3– anions with Na⁺, K⁺, Rb⁺, and Cs⁺ cations, which were prepared only from strongly alkaline media, crystals of I were isolated from solutions with a very low concentration of OH^– ions (about 0.1 M). The compound is relatively stable in storage in the dry form, but is strongly hygroscopic. In the structure of I, there are two independent Np(VII) atoms with the oxygen surrounding in the form of tetragonal bipyramids. In contrast to the other salts of the [NpO₄(OH)₂]^3– anions with singlecharged alkali metal cations, the C(NH₂) ₃ ⁺ ions and hydrated Li⁺ ions in I interact with the oxygen surrounding of Np(VII) only via hydrogen bonds of types O_w–H···O and N–H···O with the formation of a three-dimensional H-bond network.     

Synthesis and Crystal Structures of New Layered Uranyl Compounds Containing Dimers [(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>O<Subscript>8</Subscript>] of Edge-Linked Pentagonal Bipyramids

Two new U(VI) compounds, [((CH₃)₂CHNH₃)(CH₃NH₃)][(UO₂)₂(CrO₄)₃] (1) and [CH₃NH₃][(UO₂)· (SO₄)(OH)] (2), were prepared by combining hydrothermal synthesis with isothermal evaporation. Compound 1 crystallizes in the monoclinic system, space group Р2₁, a = 9.3335(19), b = 10.641(2), c = 9.436(2) Å, β = 94.040(4)°. Compound 2 crystallizes in the rhombic system, space group Рbca, a = 11.5951(8), b = 9.2848(6), c = 14.5565(9) Å. The structures of the compounds were solved by the direct methods and refined to R₁ = 0.041 [for 5565 reflections with Fo > 4σ(Fo)] and 0.033 [for 1792 reflections with Fo > 4σ(Fo)] for 1 and 2, respectively. Single crystal measurements were performed at 296 and 100 K for 1 and 2, respectively. The crystal structure of 1 is based on [(UO₂)₂(CrO₄)₃]^2– layers, and that of 2, on [(UO₂)(SO₄)(OH)]^– layers. Both kinds of layers are constructed in accordance with a common principle and are topologically similar. Protonated isopropylamine and methylamine molecules are arranged between the layers in 1, and protonated methylamine molecules, in 2. Compound 1 is the second known example of a U(VI) compound templated with two different organic molecules simultaneously.     

Complexes of An(VI) with Cyclobutanecarboxylic Acid Anions and Outer-Sphere Alkali Metal Cations

New complexes of hexavalent actinides with cyclobutanecarboxylic acid (Hcbc) anions, Na₄[NpO₂· (cbc)₃]₄·H₂O (I), K[NpO₂(cbc)₃] (II), Cs[NpO₂(cbc)₃] (III), and Cs[PuO₂(cbc)₃] (IV), cbc = C₄H₇(COO)^–, were synthesized and studied by single crystal X-ray diffraction. The structures of I–IV are based on the anionic complexes [AnO₂(cbc)₃]^– surrounded by alkali metal cations. The AnO ₂ ²⁺ cation in the anionic complex is bonded with three chelating C₄H₇COO^– anions, and the coordination polyhedron (CP) of An is a hexagonal bipyramid with the O atoms of the AnO ₂ ²⁺ cations in apical positions. The coordination number (CN) of the alkali metal cations in the structures of II–IV is the same and equal to 6; the coordination surrounding of the K⁺ and Cs⁺ cations is constituted by the O atoms of six C₄H₇COO^– anions. The crystal structures of II–IV are examples of cubic 3-connected networks (10,3) built of alkali metal and actinide cations. In the structure of I, there are four kinds of crystallographically different NpO ₂ ²⁺ and Na⁺ cations. The coordination surrounding of the NpO ₂ ²⁺ cations differs only in the conformational characteristics of the C₄H₇COO^– ligands. Four independent Na⁺ cations differ from each other in the structure of the coordination surrounding. The CPs of the Na(1) and Na(4) atoms can be described as distorted octahedra (CN 6); that of Na(3), as a trigonal prism (CN 6); and that of Na(2), as a tetragonal pyramid (CN 5) with one of the basal vertices occupied by the Ow(1) atom of a water molecule. In the structure of I, the configuration of the network formed by the Na and Np cations differs from the cubic 3-connected network found in the structures of II–IV.     

Microwave absorption characteristics of CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>PbI<Subscript>3</Subscript> perovskite/carbon nanotube composites

The CH₃NH₃PbI₃ (MAPbI₃) and CH₃NH₃PbI₃/carbon nanotube (MC) composite have been successfully synthesized by a facile in situ solution method, which are investigated as the microwave absorption materials. For the MAPbI₃ particles, the minimum reflection loss is only ?4.9 dB around 16.4 GHz due to the poor relative complex permittivity. Then, the relative complex permittivity of MC composites could be adjusted by changing the mass fraction of CNTs in composite, which is a vital role for the dielectric loss. The reflection loss of MC-5 composite (MAPbI₃/CNT, 5:1 wt%) can be improved to ?35.7 dB with thickness of 1.3 mm at 13.1 GHz. When the thickness is <3.0 mm, the microwave absorption bandwidth of MC-5 is 11.8 GHz (5.0–16.8 GHz) under the reflection loss lower than ?20 dB. The quarter-wavelength (λ/4) matching model is used to discuss the microwave absorption mechanism of MC composites. These results indicate that MC-5 composite could be used as the microwave absorption materials with strong reflection loss, lightweight and broad bandwidth.     

Real time calibration for ultrasensitive leak detection

A variable reference leak rate system is developed for real time calibration of ultrasensitive leak detection. It is based on the molecular flow characteristics of the platinum wire-glass leak element combined with a helium pressure adjustable device. Helium reference leak rate range from 10⁻¹⁴ to 10⁻¹⁰ Pa m³/s is provided and has been used for real time calibration of ultrasensitive mass spectrometer leak detection system.