Immobilization of Aspergillus niger xylanase A on Fe3O4-coated chitosan magnetic nanoparticles for xylooligosaccharide preparation

Aspergillus niger xylanase A (XylA) was immobilized onto Fe₃O₄-coated chitosan magnetic nanoparticles prepared by the layer-by-layer self-assembly approach. The Fe₃O₄-coated chitosan magnetic nanoparticles showed a high binding capacity of 162.2 mg ∙ g^− 1-particles and a recovery activity of 56.5% for XylA. The immobilized XylA showed improved thermostability and storage stability compared with free XylA. The immobilized XylA retained 87.5% activity after seven successive reactions by magnetic separation. Xylotriose and xylohexaose were the main products released from birchwood xylan and wheat bran insoluble xylan by immobilized XylA, respectively.     

Preparation of Y3Fe5O12 Microsphere Using Bead‐Milled Nanosize Powder for Embolization Therapy Application

Y₃Fe₅O₁₂ microspheres having a 20–32 μm diameter range were prepared by a spray dryer using a bead‐milled nanosize powder. The high heat generation ability in an AC magnetic field was obtained by the bead milling of a commercial powder. The yield of the 20–32 μm microspheres was 13.5% after sifting using 20 and 32 μm sieves. The heat generation ability of the microsphere sample was almost the same as that for the bead‐milled powder because the temperature enhancement mechanism was the Néel relaxation of the superparamagnetic material. Furthermore, the heat generation ability of the Y₃Fe₅O₁₂ microsphere was improved by calcination at low temperature. The heat ability increased as a function proportional to the square of the increasing magnetic field for the noncalcined sample and the samples calcined at 600°C. For the samples calcined at 650°C or higher, the heat generation ability increased as a function proportional to the cube of the increasing magnetic field because of the particle growth to form single‐domain ferrimagnetic particles. The sample calcined at 650°C showed the maximum heat generation ability(W/g) of 2.4·f·H³, where f and H are the frequency (kHz) and magnetic field (kA/m), respectively.     

Binuclear cyano-bridged complex derived from [MnIII(salpn)] and [FeIII(CN)6]: Synthesis,structure and magnetic properties

The reaction of the neutral [Mn(salpn)C(CN)₃(H₂O)] (salpn^2 − = N,N^′-1,3-propylenebis(salicylideneiminato) dianion) with [Fe^III(CN)₆]^3 − in the presence of strong oxidizer (NH₄)₂S₂O₈ yields a binuclear anion complex [NH₃CH₂CH₂CH₂NH₃]^2 +{[Mn^III(salpn)(H₂O)][Fe^III(CN)₆]}^2 − (1). Its structure, DC and AC susceptibility have been studied. Frequency dependence of the AC susceptibility characteristic for single-molecule magnets has been found.     

A novel 3D Co(II) coordination polymer with a considerable 2D channel: Synthesis,topological structure,magnetic and electrochemical properties

A novel 3D Co(II) complex [Co(Hhmt)(H₂O)∙H₂O] (1) (H₃hmt = 3,5-bis (hydroxymethyl)-1,2,4-triazole) has been hydrothermally synthesized. X-ray single crystal diffraction experiment reveals that each Hhmt^2 − ligand connects three Co(II) ions to form a 3D lvt topological framework with the (4² ∙ 8⁴) point symbol, especially for the existence of a considerable 2D channel. The magnetic and electrochemical properties of 1 are also discussed.     

Construction of a new 3D Zn(II) coordination polymer with (4,6)-connected topology: Synthesis,structure and luminescence

A new coordination polymer of {[Zn₂(odpa)(IP)]·4H₂O}_n (1) (H₄odpa = 3,3′,4,4′-oxydiphthalic acid and IP = 1-H-imidazo[4,5-f][1,10]-phenanthroline), is reported. The 3D (4,6)-connected {4⁴∙6²∙8⁸∙12}{4⁴∙6²} topology net is formed by IP and odpa ligands in 1. Interestingly, the IP ligand acts as a tridentate mode and extends the resulting 3D feature. The luminescence study indicates that the title compound emits bright red fluorescence.     

Synthesis of BaCeO3 and BaCe0.9Y0.1O3−δ from mixed oxalate precursors

An oxalate precipitation route is proposed for the synthesis of BaCe_1−xY_xO₃ (x = 0 and 0.1) after calcination at 1100 °C. The precipitation temperature (70 °C) was a determinant parameter for producing a pure perovskite phase after calcination at 1100 °C for 1 h. TG/DTA measurements showed that the co-precipitated (Ba, Ce and Y) oxalate had a different thermal behaviour from single oxalates. Despite a simple grinding procedure, sintered BaCe_0.9Y_0.1O_3−δ pellets (1400 °C, 48 h) presented 90.7% of relative density and preliminary impedance measurements showed an overall conductivity of around 2 × 10⁻⁴ S cm⁻¹ at 320 °C.     

Hidden value in low-cost inorganic pigments as potentially valuable magnetic materials

Inorganic pigments are substances that develop colour in organic solids such as ceramics and glazes, and are usually a complex mixture of oxides, and relatively low-cost. Their chromatic properties have been extensively studied, yet surprisingly the magnetic and electrical properties of these economic and common materials have been neglected, despite the fact many are based on ferrite spinels. Therefore, we investigated these properties in commercial black and brown pigments, to assess their potential as magnetic materials. The brown and black pigments were found to be spinel ferrites, with estimated formulas of Fe_1.34Cr_0.62Mn_0.66Zn_0.22Ni_0.10Co_0.06O₄ and Fe_1.02Cr_0.97Co_0.57Mn_0.23Ni_0.21O₄, respectively. The brown pigment also contained a higher amount of SiO₂ compared to the black pigment (~7 mol% vs. ~2 mol%), which appeared as a second phase of crystalline quartz, and adversely affected its porosity, magnetisation and electrical ac conductivity, compared to the black pigment. However, both were very magnetic and very soft ferrites. The brown pigment had M_s=11.7 A m² kg⁻¹ and H_c of 1.5 kA m⁻¹, with a high electrical conductivity (σ) of 4×10⁻⁴−7×10⁻³ Ω⁻¹ m⁻¹ between 100 Hz and 1 MHz. The black pigment was equally magnetically soft, but had a much greater magnetisation and lower electrical conductivity, with M_s=18.7 A m² kg⁻¹, H_c=2.4 kA m⁻¹, and σ=5×10⁻⁶−8×10⁻⁵ Ω⁻¹ m⁻¹ between 100 Hz and 1 MHz.This work has revealed the potential hidden value of low-cost commercial inorganic pigments based on spinel ferrites as magnetic materials. This demonstrates their potential at low-cost alternative materials for applications such as in power supply transformers, switching materials and sensors, where soft magnetisation is especially important.     

Magnetic,magnetostrictive, and AC impedance properties of manganese substituted cobalt ferrites

In this study, we investigated the effects of substituting Mn³⁺ for some Fe³⁺ in spinel lattice on the structure, magnetic properties, magnetostriction behavior, and AC impedance characteristics of cobalt ferrites. The manganese substituted cobalt ferrites (Co–Mn ferrites), CoMn_xFe_2−xO₄, with x varied from 0 to 0.3 in 0.1 increments, were prepared by solid-state reaction. XRD examination confirmed that all sintered Co-based ferrites had a single-phase spinel structure. The average grain size, obtained from SEM micrographs, increased from 8.2 μm to 12.5 μm as the Mn content (x) increased from 0 to 0.3. Both the Curie temperature and coercivity of Co-based ferrites decreased with greater amounts of Mn, while the maximum magnetization (at H=6 kOe) of Mn-substituted cobalt ferrites was larger than that of the pure Co-ferrite. Magnetostrictive properties revealed that the pure Co-ferrite had the largest saturation magnetostriction (λ_S), about −167 ppm, and the CoMn_0.2Fe_1.8O₄ sample exhibited the highest strain sensitivity (|dλ_⊥/dH|_m) of 2.23×10⁻⁹ A⁻¹m among all as-prepared Co-based ferrites. In addition, AC impedance spectra analysis revealed that the real part (Z′) of the complex impedance of Co–Mn ferrites was lower than that of pure Co-ferrite in the low frequency region, and the Co-based ferrites exhibited semiconductor-like behavior.     

Synthesis and characterization of an unprecedented 3D lanthanide coordination polymer assembled by cubane-like clusters and a flexible V-shaped dicarboxylate ligand

A lanthanide coordination polymer based on H₂sfdb ligand, namely [Tb₄(sdbc)₄(phen)₂(μ₃-OH)₄]_n ∙ 1.5nH₂O (1) (H₂sfdb = 4,4′-sulfonyldibenzoic acid, phen = 1,10-phenanthroline) has been hydrothermal synthesized and characterized. Compound 1 exhibits an unprecedented three-dimensional framework that comprised new cubane-like hydroxo clusters [Tb₄(μ₃-OH)₄]^8 + as the nodes and flexible (sfdb)^2 − ligands as the linkers. In 1, (sfdb)^2 − ligands display completely different four kinds of coordination modes. Interestingly, not only the carboxylate groups but also one oxygen atom of sulfonyl group of (sfdb)^2 − ligand are coordinated with Tb^III ions in 1, which is first found in the compounds based on H₂sfdb ligand. The luminescence experiments show that Tb^III compound exhibits the typical Tb^III-centered luminescence.     

Improved thermal conductivity of sintered reaction-bonded silicon nitride using a BN/graphite powder bed

Sintered reaction-bonded silicon nitride (SRBSN) with improved thermal conductivity was achieved after the green compact of submicron Si powder containing 4.22 wt% impurity oxygen and Y₂O₃-MgO additives was nitrided at 1400 °C for 6 h and then post-sintered at 1900 °C for 12 h using a BN/graphite powder bed. During nitridation, the BN/10 wt% C powder bed altered the chemistry of secondary phase by promoting the removal of SiO₂, which led to the formation of larger, purer and more elongated Si₃N₄ grains in RBSN sample. Moreover, it also enhanced the elimination of SiO₂ and residual Y₂Si₃O₃N₄ secondary phase during post-sintering, and thus induced larger elongated grains, decreased lattice oxygen content and increased Si₃N₄-Si₃N₄ contiguity in final SRBSN product. These characteristics enabled SRBSN to obtain significant increase (∼40.7%) in thermal conductivity from 86 to 121 W ∙ m⁻¹ ∙ K⁻¹ without obvious decrease in electrical resistivity after the use of BN/graphite instead of BN as powder bed.     

Construction and structural diversity of Cd-MOFs with pyrazole based flexible ligands and positional isomer of naphthalenedisulfonate

In the present communication, we have reported the construction of a series of Cd(II)-MOFs using conformationally flexible ligand (CFL); 3,3′,5,5′-tetramethyl-4,4′-bipyrazolyl (H₂BPz), flexible bent ligand (FBL); methylenebis-(3,5-dimethylpyrazole) (H₂MBPz) and positional isomer of naphthalene disulfonic acid salt ligands (1,5-NDS, 2,6-NDS). By using these ligands, four new coordination polymers namely [Cd(H₂MBPz)₂∙ 1,5-NDSA]_n (NDS-MOF-1), [Cd(H₂BPz)∙ 1,5-NDSA]_n (NDS-MOF-2), {[Cd(H₂MBPz)₂]^2 +∙ 2,6-NDSA^2 −}_n (NDS-MOF-3) and {[Cd(H₂BPz)₂]^2 +∙ 2,6-NDSA^2 −}_n (NDS-MOF-4) have been synthesized. The crystal structure analysis revealed that the employment of positional isomeric naphthalene disulfonic acid salts resulted in different architectures ranging from one dimensional chain to two dimensional grid network and further connected into a three dimensional supramolecular structure through intermolecular hydrogen bonds, π⋯π and C–H⋯π interactions. In addition, the photophysical properties and thermal stability studies for all the NDS-MOFs 1–4 were also investigated.     

A comparative study of the magnetic and microwave properties of Al3+ and In3+ substituted Mg–Mn ferrites

The effect of substitution of diamagnetic Al³⁺ and In³⁺ ions for partial Fe³⁺ ions in a spinel lattice on the magnetic and microwave properties of magnesium–manganese (Mg–Mn) ferrites has been studied. Three kinds of Mg–Mn based ferrites with compositions of Mg_0.9Mn_0.1Fe₂O₄, Mg_0.9Mn_0.1Al_0.1Fe_1.9O₄, and Mg_0.9Mn_0.1In_0.1Fe_1.9O₄ were prepared by the solid-state reaction route. Each mixture of high-purity starting materials (oxide powders) in stoichiometric amounts was calcined at 1100 °C for 4 h, and the debinded green compacts were sintered at 1350 °C for 4 h. XRD examination confirmed that the sintered ferrite samples had a single-phase cubic spinel structure. The incorporation of Al³⁺ or In³⁺ ions in place of Fe³⁺ ions in Mg–Mn ferrites increased the average particle size, decreased the Curie temperature, and resulted in a broader resonance linewidth as compared to un-substituted Mg–Mn ferrites in the X-band. In this study, the In³⁺ substituted Mg–Mn ferrites exhibited the highest saturation magnetization of 35.7 emu/g, the lowest coercivity of 4.1 Oe, and the highest Q×f value of 1050 GHz at a frequency of 6.5 GHz.     

Three d10 coordination polymers based on rigid ligands with flexible functional groups: Syntheses,structures and luminescence

Three coordination polymers, namely, {[Zn(L)(BPY)]·DMF·H₂O}_n (1), {[Zn(L)(TPY)]·0.5H₂BDC·H₂O}_n (2), {[Cd(L)(H₂O)₂]·DMF}_n (3), have been synthesized based on a rigid linear carboxylate ligand (H₂L = 2′,5′-dimethoxy-[1,1′:4′,1″-terphenyl]-4,4″-dicarboxylic acid) and different lengths of pyridine ligands (TPY = 4,3′:5′,4″-terpyridine; BPY = 4,4′-bipyridine). These complexes have been characterized by single crystal X-ray diffraction, infrared spectroscopy, thermogravimetry, elemental analysis, and powder X-ray diffraction measurements. Complex 1 is a 6-connected 3-fold interpenetrating pcu net with point symbol {4¹² ∙ 6³}, 2 and 3 can be simplified as 4-connected sql nets with point symbol {4⁴ ∙ 6²}. In addition, their photoluminescent properties are also investigated in detail.     

Hydrothermal synthesis,crystal structure and properties of a thermally stable dysprosium porphyrin with a three-dimensional porous open framework

A thermally stable dysprosium porphyrin with a three-dimensional (3D) porous open framework, [Dy(H₂TPPS)]_n∙ nH₃O∙2nH₂O (1) (H₂TPPS = tetra(4-sulfonatophenyl)porphyrin), has been synthesized via hydrothermal reactions and structurally analyzed by an X-ray single-crystal diffraction method. The 24-membered macrocyclic ring of H₂TPPS is exactly coplanar and the center is free from metal. The dysprosium ion is coordinated by eight O_sulfonic atoms from eight H₂TPPS moieties, forming a distorted square anti-prism geometry. Complex 1 shows a void space of 210 Å³, occupying 9.06% of the unit-cell volume. The 3D porous open framework of 1 is thermally stable up to 380 °C. Complex 1 exhibits a red fluorescence emission with a quantum yield and lifetime of 2.7% and 136 μs, respectively. CV result reveals one reductive peak at − 0.33 V and one quasi-reversible wave with E_1/2 = − 0.81 V.     

The composite material based on Dawson-type polyoxometalate and activated carbon as the supercapacitor electrode

A supercapacitor electrode assembled from activated carbon (AC) and (NH₄)₆[P₂Mo₁₈O₆₂]·14.2H₂O (P₂Mo₁₈) was fabricated for the first time, and showed remarkable electrochemical performance ascribed to the synergy of the double layer capacitance of AC and the pseudocapacitance of P₂Mo₁₈. The investigations indicate that the AC/P₂Mo₁₈ electrode exhibits a specific capacitance of 275 F g^− 1 at a high current density of 6 A g^− 1, which is substantially larger than the 182 F g^− 1 of the AC electrode. In addition, the AC/P₂Mo₁₈ electrode possesses a remarkable rate capability (89%) when the current density is increased from 2 to 6 A g^− 1.     

Electrogeneration of hydrogen peroxide in gas diffusion electrodes modified with tert-butyl-anthraquinone on carbon black support

Hydrogen peroxide (H₂O₂) is a versatile oxidizing agent that is synthesized commercially by the reduction of oxygen in organic medium. Electrochemical technology employing a modified gas diffusion electrode (MGDE) offers a viable alternative for the industrial-scale synthesis of the oxidant. Addition of 1% (w/w) of tert-butyl-anthraquinone (TBAQ) to carbon black deposited in the form of a microporous layer onto the disk of a rotating ring-disk electrode produced an increase in the ring current, which is directly related to H₂O₂ formation, and presented an efficiency of H₂O₂ generation of 89.6% compared with 76.6% for carbon black alone. No significant changes were detected in the number of electrons transferred in the presence of the catalyst suggesting an electrochemical/chemical mechanism for H₂O₂ formation. Analogous improvements in the generation of H₂O₂ were obtained with MGDEs comprising TBAQ on carbon black. The highest concentrations of H₂O₂ (301 mg L⁻¹) were produced at the fastest rate (5.9 mg L⁻¹ min⁻¹) with the lowest energy consumption (6.0 kWh kg⁻¹) when a potential of −1.0 V vs SCE was applied to a MGDE containing 1.0% of TBAQ on carbon black. It is concluded that the application of MGDEs comprising TBAQ on carbon black support offers considerable advantages in the electrogeneration of H₂O₂.     

Influence of Yb3+ doping on phase stability and thermophysical properties of (Y1-xYbx)3Al5O12 under high temperature

In this work, Yb³⁺ was selected to replace the Y³⁺ in yttrium aluminum garnet (YAG) in order to reduce its thermal conductivity under high temperature. A series of (Y_1-xYb_x)₃Al₅O₁₂ (x=0, 0.1, 0.2, 0.3, 0.4) ceramics were prepared by solid-state reaction at 1600 °C for 10 h. The microstructure, thermophysical properties and phase stability under high temperature were investigated. The results showed that all the Yb doped (Y_1-xYb_x)₃Al₅O₁₂ ceramics were comprised of a single garnet-type Y₃Al₅O₁₂ phase. The thermal conductivities of (Y_1-xYb_x)₃Al₅O₁₂ ceramics firstly decreased and subsequently increased with Yb ions concentration rising from room temperature to 1200 °C. (Y_0.7Yb_0.3)₃Al₅O₁₂ had the lowest thermal conductivity among investigated specimens, which was about 1.62 W m⁻¹ K⁻¹ at 1000 °C, around 30% lower than that of pure YAG (2.3 W m⁻¹ K⁻¹, 1000 °C). Yb had almost no effect on the coefficients of thermal expansion (CTEs) of (Y_1-xYb_x)₃Al₅O₁₂ ceramics and the CTE was approximate 10.7×10⁻⁶ K⁻¹ at 1200 °C. In addition, (Y_0.7Yb_0.3)₃Al₅O₁₂ ceramic remained good phase stability when heating from room temperature to 1450 °C.     

Novel nonaqueous precipitation synthesis of alumina powders

Alumina powders were prepared via a novel nonaqueous precipitation method with aluminum powders as aluminum source and anhydrous acetic acid as precipitant. The thermal decomposition and phase transformation of crystal precipitate and the influence of precipitate aging were investigated via TG-DTA-MS, XRD, TEM, BET, FE-SEM and performance tests of sintered bodies. The results show crystal precipitate C₄H₇AlO₇ transforms to amorphous Al₂O₃ at 300 °C, and then to γ-Al₂O₃ at 950 °C, and finally to α-Al₂O₃ at 1050 °C. The particle size of α-Al₂O₃ prepared at 1100 °C is 50–100 nm with BET surface area of 25.98 m²∙g⁻¹. FE-SEM morphology of sintered sample at 1400 °C shows excellent sinterability of the α-Al₂O₃ powders. Aging eliminates aggregation, and leads to highly homogenized and densified particles. It also affects the densification behaviour during sintering and further influences density, thermal expansion coefficient, flexural strength, volume resistivity and electric breakdown strength of sintered bodies     

Reversible water inclusion in a porous magnetic material synthesized from copper(II) incorporated metal-organic framework showing alternate ferro- and antiferromagnetic interactions

X-ray structural analysis shows that {[Cu₂(CTA) (H₂O)] · 5 H₂O}_n constitutes infinite one-dimensional parallel chains along the c-axis with water columns running down the crystallographic a-axis. The inclusion of water molecules is reversible and is confirmed by X-ray powder diffraction studies. The magnetic data (2–300 K) reveal that there are alternate ferro- (J = 0.29 cm⁻¹) and antiferromagnetic (J = −2.5 cm⁻¹) interactions.     

Synthesis,structure and magnetic properties of spinel ferrite (Ni,Cu, Co)Fe2O4 from low nickel matte

Spinel ferrite (Ni, Cu, Co)Fe₂O₄ was synthesized from the low nickel matte by using a co-precipitation-calcination method for the first time. The influences of the added amount of NiCl₂·6H₂O, calcination temperature and time on the structure and magnetic properties of the as-prepared ferrites were studied in detail by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Raman spectroscopy, and Vibrating sample magnetometer (VSM). It is indicated that pure (Ni, Cu, Co)Fe₂O₄ with cubic phase could be obtained under the experimental conditions (NiCl₂·6H₂O added amount of 3.0: 100 g mL⁻¹, calcination temperature from 800 to 1000 °C and calcination time from 1 to 3 h). With increasing calcination temperature and time, saturation magnetization (M_S) of the synthesized (Ni, Cu, Co)Fe₂O₄ increased and the coercivity (H_C) decreased. Under the optimum conditions (i.e. NiCl₂·6H₂O added amount of 3.0: 100 g mL⁻¹, 1000 °C, 3 h), the M_S and H_C values of the product were approximately 46.1 emu g⁻¹ and 51.0 Oe, respectively, which were competitive to those of other nickel ferrites synthesized from pure chemical reagents. This method explores a novel pathway for efficient and comprehensive utilization of the low nickel matte.