The control of BN and BC bonds in BCN films synthesized using pulsed laser deposition

A novel chemical bond transformation from BN to BC was observed in BCN films synthesized using pulsed laser deposition (PLD). BCN film prepared by using green laser (λ=532 nm) induced two IR absorption at 1370 and 800 cm⁻¹. This film was dominated by amorphous carbon phase and sp² hybridized BN bonds. BCN film deposited using an ultraviolet (UV) laser (λ=266 nm ) induced an addition infrared (IR) absorption at 1250 cm⁻¹. As we deposit BCN film by deep-UV laser (λ=213 nm), the absorption at 1370 and 800 cm⁻¹ disappeared while the absorption at 1250 cm⁻¹ remained. According to X-ray photoelectron spectroscopy (XPS), BC bonds with a carbon rich composition were formed. The formation of BC bonds in BCN films was also sensitive to deposition gas pressure and substrate temperature. Reactive carbon and boron species were needed to enable BC bonds that hybridized the carbon and the BN phases. A low substrate temperature was required to avoid competition with sp² hybridized pure BN and pure carbon bonds.     

Towards osseointegration of bioinert ceramics: Can biological agents be immobilized on alumina substrates using self-assembled monolayer technique?

Immobilization of biological agents on inert alumina surfaces could promote bone growth and improve osseointegration. We hypothesize that functional groups on alumina surfaces can be used to link biological agents as a supporting factor e.g. for cell attachment. CH₂, OH, COOH, and NH₂ groups were linked to alumina surfaces using self-assembled monolayer technique (SAM). Subsequently, bovine serum albumin (BSA) was immobilized on each functionalized surface. Contact angle, bicinchoninic acid assay and immunofluorescence were used to detect immobilized BSA. The amount of BSA linked to functionalized surfaces increased in the following order CH₂ < OH < COOH = NH₂. The greatest amount, 26.1 μg/cm² of BSA was found on both, NH₂- and COOH-terminated surfaces. Cell tests confirmed cytocompatibility of all surfaces. The highest proliferation was detected on NH₂-terminated samples. Using the model protein, the results confirmed feasibility for immobilization of biological agents to inert alumina ceramic surfaces using SAM technique.     

Photodegradation of tetrahalobisphenol-A (X = Cl,Br) flame retardants and delineation of factors affecting the process

The photoassisted degradation (HPLC-UV absorption), dehalogenation (HPLC-IC) and mineralization (TOC decay) of the flame retardants tetrabromobisphenol-A (TBBPA) and tetrachlorobisphenol-A (TCBPA) were examined in UV-irradiated alkaline aqueous TiO₂ dispersions (pH 12), and for comparison the parent bisphenol-A (BPA, an endocrine disruptor) in pH 4–12 aqueous media to assess which factor impact most on the photodegradative process. Complete degradation (2.7–2.8 × 10⁻² min⁻¹) and dehalogenation (1.8 × 10⁻² min⁻¹) of TBBPA and TCBPA occurred within 2 h of UV irradiation, whereas only 45–60% mineralization (2.3–2.7 × 10⁻³ min⁻¹) was complete within 5 h for the flame retardants at pH 12 and ca. 80% for the parent BPA. Factors examined in the pH range 4–12 that impact the degradation of BPA were the point of zero charge of TiO₂ particles (pH_pzc; electrophoretic method), particle or aggregate sizes of TiO₂ (light scattering), and the relative number of OH radicals (as DMPO–OH adducts; ESR spectroscopy) produced in the UV-irradiated dispersion. Dynamics of BPA degradation (2.0–2.4 × 10⁻² min⁻¹) were pH-independent and independent of particle/aggregate size, but did correlate with the number of OH radicals, at least at pHs 4 to 8–9, after which the rates decreased somewhat at pH > 9 with decreasing adsorption owing to Coulombic repulsive forces between the very negative TiO₂ surface and the anionic forms of BPA (pK_as ca. 9.6–11.3), even though the number of OH radicals continued to increase at the higher pHs.     

Experimental and computational study of thaumasite structure

The structure of thaumasite has been studied experimentally by means of a single crystal X-ray diffraction and FTIR methods, and theoretically using density functional theory (DFT) method. Very good agreement was achieved between calculated and experimental structural parameters. In addition, calculations offered the refinement of the positions of the hydrogen atoms. The detailed analysis of the hydrogen bonds existing in the thaumasite structure has been performed. Several types of hydrogen bonds have been classified. The water molecules coordinating Ca^2 +cation act as proton donors in moderate OH⋯O hydrogen bonds formed with CO₃^2 −and SO₄^2 −anions. The multiple OH⋯O hydrogen bonds exist among water molecules themselves. Finally, relatively weak hydrogen bonds form water molecules with the OH groups from the coordination sphere of the Si(OH)₆^2 − anion. Further, calculated vibrational spectrum allowed complete assignment of all vibrational modes which are not available from the experimental spectrum that has a complex structure with overlapped bands, especially below 1500 cm^− 1.     

Transformation of hydroquinone to benzoquinone mediated by reduced graphene oxide in aqueous solution

The mediation effect of reduced graphene oxide (rGO) on the oxidative transformation of 1,4-hydroquinone (H₂Q) to 1,4-benzoquinone (BQ) in aqueous solution was investigated using a batch method and electron paramagnetic resonance. The results showed that the autoxidation of H₂Q was spin-restricted and extremely slow in acidic and neutral pH range, but this process can be dramatically accelerated when rGO was added. In the presence of 33.3 mg L⁻¹ rGO, more than 76.0% of H₂Q was oxidized to BQ within 36 h. The enhancement effects of rGO were attributed to the combined contribution of the high chemical reactivity of graphenic edges and defects on rGO and the high electron conductivity of graphene basal surface of rGO. It is proposed that dissolved oxygen reacted with graphenic edges and defects of rGO to produce surface-bound oxygen intermediates, which capture H atoms from the phenolic hydroxyl groups of H₂Q and facilitate the generation of semiquinone radical (SQ⁻). The generated SQ⁻ continued to transfer an electron to molecular oxygen to yield superoxide radical (O₂⁻) and BQ. As a chain-carrying radical, O₂⁻ further reacted with H₂Q to produce SQ⁻ and H₂O₂.     

New long-wavelength ethanolamino-substituted hypocrellin: photodynamic activity and toxicity to MGC803 cancer cell

To improve hydrophilicity and photoactivity of the new type of therapeutic agent, hypocrellin, a novel long-wavelength ethanolamino-substituted hypocrellin B (EAHB) was synthesized and its molecular structure was characterized by IR, NMR, MS, and UV–vis spectrometers, and EAHB had strong absorption at the phototherapeutic window (600–900 nm). Illumination of deoxygenated DMSO solution containing EAHB generated a strong electron paramagnetic resonance (EPR) signal, which was assigned to the semiquinone anion radical of EAHB (EAHB⁻). Absorption measurements displayed that the absorptive bands at 632 and 565 nm (shoulder) arose from the semiquinone anion radical (EAHB⁻) and the absorptive bands at 519 and 450 nm (shoulder) belonged to hydroquinone (EAHBH₂), which were formed via the decay of EAHB⁻ in water-contained solution. Superoxide anion radical (O₂⁻) was produced via electron transfer from EAHB⁻ (the precursor) to ground state oxygen. The presence of NADH, a bio-electron donor, significantly enhanced production of EAHB⁻ and O₂⁻. Singlet oxygen O₂ (¹Δ_g) could be produced via energy transfer from triplet EAHB to ground state oxygen molecules. The quantum yield of O₂ (¹Δ_g) and the relative quantum yield of O₂⁻ of EAHB were 0.15 and 0.76, respectively, with the parent compound hypocrellin B (HB) as the standard. It was inferred that Type I pathway was possibly a major photodynamic mechanism of EAHB. The study on photobiological action of EAHB on MGC803 cancer cells revealed that EAHB kept the same good phototoxic ability as HB but reduced 4 times cytotoxicity than HB, and also its photopotentiation factor increased 4-folds.     

Degradation of amoxicillin in aqueous solution using nanolepidocrocite chips/H2O2/UV: Optimization and kinetics studies

Degradation of amoxicillin (AMX) by nanolepidocrocite chips/H₂O₂/UV method as a new photo-Fenton like process was investigated and optimized by response surface methodology (RSM). The optimal conditions were initial AMX concentration of 10 mg l⁻¹ and initial H₂O₂ concentration of 60 mg l⁻¹ at pH of 2 under UV radiation for 120 min. The general photo-Fenton process mechanism was applied to propose a new kinetic model for AMX degradation. According to this model, the reaction constant between AMX and OH was obtained 4.55 × 10⁵ M⁻¹ s⁻¹. Also, nanolepidocrocite showed good catalytic activity even after four successive degradation cycles.     

Infrared spectroscopy of some carbon-based materials relevant in combustion: Qualitative and quantitative analysis of hydrogen

A detailed procedure for the quantitative analysis of aromatic and aliphatic hydrogen based on infrared spectroscopy was set up and implemented on some carbon-based materials produced from organic precursors (naphthalene pitch) and/or relevant in combustion field (asphaltenes, carbon particulate matter, carbon black), spanning in the H/C atomic ratio range from 0.1 to 1. The quantitative FT-IR analysis involved the spectral deconvolution in the CH vibrations regions and the calibration factors of diverse standard species having spectral characteristics suitable for the detailed peak-to-peak analysis of the CH stretching (3100–2800 cm⁻¹) and aromatic CH bending (900–700 cm⁻¹) regions. The good agreement between the H/C atomic ratio obtained by quantitative FT-IR analysis and elemental analysis showed a reasonable reliability of the procedure. The major value of the developed FT-IR quantitative technique relies also on the capacity of discriminating between the different kinds of aliphatic and aromatic hydrogen. The quantitative and detailed analysis of hydrogen in form of CH₃, CH₂ and CH groups and in form of solo, duo and trio/quatro aromatic hydrogens showed to be useful also for inferring the structure of the aromatic moieties constituting the CC backbone of carbon materials.     

The effect of Mg(OH)2 on furfural oxidation with H2O2

The oxidation of furfural in H₂O₂ and H₂O₂–Mg(OH)₂ system were systematically investigated and a rational explanation for the reaction mechanism was proposed. 2-formyloxyfuran, from selective oxidation of HCO group in furfural, was a crucial intermediate. The addition of Mg(OH)₂ suppressed the oxidation of furan ring of furfural and enhanced selectivities of 2(5H)-furanone (44.8%) and succinic acid (38.0%). FT-IR, Gaussian calculation and experimental results indicated that the process of furfural oxidation with H₂O₂ is homogeneous, and the synergy between dissolved Mg^2 + cations and OH⁻ ions facilitates the HOO⁻ attacking the carbon atom of HCO other than the CC bound of furan ring.     

Electrically conductive silicon carbide with the addition of TiNbC

The work deals with the preparation of dense SiC based ceramics with high electrical conductivity. SiC samples with different content of conductive TiNbSiCO based phase were hot pressed at 1820 °C for 1 h in Ar atmosphere under mechanical pressure of 30 MPa. The conductive phase is a mixture of 50 wt% TiNbC (molar ratio of Ti/NbC is 1:1.8) and 50 wt% eutectic composition of Y₂O₃SiO₂. Composite with 30% of conductive TiNbSiCO phase showed the highest electrical conductivity 28.4 S mm^?1, while the good mechanical properties of SiC matrix were preserved (fracture toughness K_IC = 5.4 MPa m^1/2 and Vickers hardness 17.8 GPa).The obtained results show that the developed additive system is suitable for the preparation of SiC-based composite with sufficient electrical conductivity for electric discharge machining.     

Adsorption of uranyl ions on kaolinite,montmorillonite, humic acid and composite clay material

Adsorption of uranyl ions onto kaolinite, montmorillonite, humic acid and composite clay material (both clays and humic acid) was studied by measuring the system response to clay suspensions (pre-equilibrated with or without uranyl) and to perturbations of the solution chemistry. Adsorption behavior of selected materials under the frame of batch experiments was tested at high uranyl concentrations (6–1170 μg/mL; 2.5 × 10^− 2 to 4.9 μM), whereas that under flow through continuous stirred reactor experiments was tested at low concentrations (1.00 × 10^− 4 to 1.18 × 10^− 4 M). Both experiments were developed at pH 4.5 and ionic strength 0.2 mM. The adsorption experiments follow a Langmuir isotherm model with a good correlation coefficient (R² > 0.97). The calculated amount of adsorbed and desorbed uranyl was carried out by numeric integration of the experimental data, whereas the desorption rates were determined from the breakthrough curve experiments. Kaolinite with highly disordered structure adsorbed less uranyl (3.86 × 10^− 6 mol/g) than well-ordered kaolinite (1.76 × 10^− 5 mol/g). Higher amount of uranyl was adsorbed by montmorillonite (3.60 × 10^− 5 mol/g) and only half of adsorbed amount was desorbed (1.85 × 10^− 5 mol/g). The molecular interactions between kaolinite, montmorillonite, humic acid, composite material and saturated uranyl ion solutions were studied by molecular fluorescence, infrared and X-ray photoelectron spectroscopy. The Stern–Volmer constant obtained for montmorillonite (2.6 × 10³ M^− 1) is higher than for kaolinite (0.3 × 10³ M^− 1). Molecular vibrations of SiO stretching and AlOH bending related to hydroxylated groups (SiOH or AlOH) of kaolinite and montmorillonite show structural changes when uranyl ions are adsorbed. X-ray photoelectron spectroscopy shows that the U 4f_7/2 core level signals occur at 380.5 eV in either kaolinite or montmorillonite that resulted from the interaction of aluminol surface sites with the (UO₂)₃(OH)₅⁺.     

Schiff pentadentate ligands based on an [ON2O2] core displaying structural isomerism and their coordination to dibutyltin moieties

Two tin compounds [Sn(ⁿBu)₂(Lⁿ)], where L¹{O(C₆H₄-2-NC(H)C₆H₄-2′-O)₂}^2 − and L²{O(C₆H₄-2-C(H)NC₆H₄-2′-O)₂}^2 − enclosing five electron donors in an [ON₂O₂] core, were synthesized and structurally characterized by infrared and NMR spectroscopy and by single crystal X-ray crystallographic studies at room temperature. The hepta-coordinate geometry around the Sn centers is achieved through the bonding of two monodentate n-butyl groups and the coordination of the pentadentate Lⁿ ligands, where the [ON₂O₂] core is forming a pentagonal base. The two types of oxygen atoms displayed different bonding situations around the Sn atom. DFT calculations with Gaussian 09 using PBEPBE/6-31G**/SDD level were carried out for both compounds. The topological analysis indicated that bond critical points are present along the SnO_ether direction.     

Measurement of the hydroxyl radical formation from H2O2, NO3−, and Fe(III) using a continuous flow injection analysis

Production of hydroxyl radical (OH) is of significant concern in engineered and natural environment. A simple in situ method was developed to measure OH formation in UV/H₂O₂, UV/Fe(III), and UV/NO₃^? systems using trapping of OH by benzoic acid (BA) and measuring fluorescence signals from hydroxylated products of BA. Method development included characterization of OH trapping mechanism and measurement of quantum yields (Φ_OH) for OH. The distribution of OHBA isomers was in the order of o-OHBA > p-OHBA > m-OHBA, although it changed with the H₂O₂ concentration and light intensity. This supports that OH attacks dominantly on the benzene rings. The quantum yields for OH formation in the UV/H₂O₂ process were 1.02 and 0.59 at 254 and 313 nm, which were in good agreement with the literature values, confirming that the method is suitable for the measurement of OH production from UV/H₂O₂ processes. Using the continuous flow method developed, quantum yields for OH in UV/H₂O₂, UV/Fe(III), and UV/NO₃^? systems were measured varying the initial concentration of OH precursors. The Φ_OH values increased with increasing concentrations of H₂O₂, Fe(III), and NO₃^? and approached constant values as the concentration increased. The Φ_OH values were 0.009 for H₂O₂ at 365 nm, showing that OH production is not negligible at such high wavelength. The Φ_OH values during the photolysis of Fe(OH)²⁺ (pH 3.0) and Fe(OH)₂⁺ (pH 6.0) at 254 nm were 0.34 and 0.037, respectively. The Φ_OH values for NO₃^? approached a constant value of 0.045 at 254 nm at the initial concentration of 10 mM.     

Trans,trans,trans-[ReO2I2(PPh3)2], a rare rhenium(VI) complex — Synthesis and DFT study

The heating of cis-[ReO₂I(PPh₃)₂] at reflux in benzene in air led to the isolation of the rhenium(VI) complex [ReO₂I₂(PPh₃)₂] (1). The compound is centrosymmetric around the octahedrally coordinated rhenium center, and the ReO bond length of 1.797(2) Å is longer than in typical trans-dioxorhenium(V) complexes. The asymmetric ReO stretching frequency occurs at 744 cm^− 1. Density functional theory has been used for the calculation of the vibrational spectrum density which confirms the experimental asymmetric ReO stretching frequency. DFT calculation within the polarizable continuum model shows that complex 1 is more stable in CH₂Cl₂ than in the gas phase. EPR spectroscopy confirms a single d electron in 1. The crystal structure was determined by X-ray single crystal diffraction. In addition, infra-red, redox and electronic properties are also reported.     

Direct conversion of citrus peel waste into hydroxymethylfurfural in ionic liquid by mediation of fluorinated metal catalysts

A new green technology was developed using citrus peel waste to produce hydroxymethylfurfual (HMF). FT-IR analysis of the waste showed 4 characteristic vibration modes (CH, CO, COH, and CO/COO^?), contributing to sugars. XRD and FESEM elucidated that the waste and its hydrolysate consist of highly amorphous clusters. HCl increased HMF yield by 1.4-fold. CrF₃ increased its yield by 1.7-fold. At 0.2 of the stoichiometric ratio value, HMF yield was highest. The highest HMF yield was achieved in the reaction mixture of 4 g [OMIM]Cl, 1 mL ethyl acetate, 0.1 g CrF₃, 5 mL 0.3 M HCl, and 0.5 g biomass.     

The effect of density functional and dispersion interaction on structure and bonding analysis of uranium(VI) nitride complex [NU{N(CH2CH2NSiMe3)3}]: A theoretical study

Geometry and bonding energy analysis of uranium(VI) nitride complex [NU{N(CH₂CH₂NSiMe₃)₃}] were investigated with the DFT, DFT-D3 and DFT-D3(BJ) methods using density functionals (BLYP, BP86, PW91, PBE, revPBE and TPSS). The BLYP functional yields a UN bond distance of 1.788 Å for the model complex [NU{N(CH₂CH₂NSiMe₃)₃}] which is in close agreement with the experimental value of the UN bond distance of 1.799(7) Å for [NU{N(CH₂CH₂NSiⁱPr₃)₃}]. The calculated Mayer bond order (2.95) and Gopinathan–Jug bond order (3.18) indicate that the UN bond in this complex is essentially UN triple bonds. The electrostatic interaction is significantly smaller than the covalent bonding. The bond dissociation energy (BDE) is largest for the functional PBE and smallest for the functional TPSS. The DFT-D3 dispersion corrections are 5.3 kcal/mol (BLYP) and 5.0 kcal/mol (TPSS).     

Extended X-ray absorption fine structure,X-ray diffraction and Raman analysis of nickel-doped Ba(Mg1/3Ta2/3)O3

Raman, X-ray diffraction and extended X-ray absorption fine structure (EXAFS) measurements of xBa(Ni_1/3Ta_2/3)O₃ + (1 − x)Ba(Mg_1/3Ta_2/3)O₃ samples with x = 0–0.03 were performed to reveal the nickel doping effect on the microwave properties. EXAFS result clearly shows that the nickel is located on the Mg lattice site. We also found that, as the nickel concentration increases, microwave dielectric constant decreases with the TaO and NiO bond distances. X-ray diffraction shows that the 1:2 ordered structure is degraded with the increasing of nickel concentration. The stretching phonon of the TaO₆ octahedra, that is A_1g(O) phonon near 800 cm⁻¹, are strongly correlated to the microwave properties of xBa(Ni_1/3Mg_2/3)O₃ + (1 − x)Ba(Mg_1/3Ta_2/3)O₃ samples. The large Raman shift and the large width of the A_1g(O) imply rigid but distorted oxygen octahedral structure, therefore, the effect of nickel doping lowers the dielectric constant and the Q × f value of Ba(Mg_1/3Ta_2/3)O₃ ceramic.     

Thermal properties of silicon carbide composites fabricated with chopped Tyranno® SiAlC fibres

Thermal diffusivity, a, and thermal conductivity, κ, between room temperature and 600 K were investigated for SiC composites containing 0–50 mass% of Tyranno^® SiAlC (SA) fibre (mean length: 394 μm) hot-pressed at 1800 °C for 30 min under a pressure of 31 MPa. The monolithic SiC specimen possessed κ of 32.1 W m⁻¹ K⁻¹ at room temperature; no significant changes were found for the SiC composite containing ≤20 mass% of SA fibre addition. However, further increases in the amount of SA fibre to 50 mass% improved κ to a maximum of 56.3 W m⁻¹ K⁻¹. The value of a for the SiC composite containing 40 mass% of SA fibre was 0.185 cm² s⁻¹ at room temperature and decreased to 0.120 cm² s⁻¹ at 600 K. In addition, SiC composites using 40 mass% of SA fibre with a carbon interface of approximately 100 nm were fabricated. The effect of this interface on a and κ was marginal.     

On the nature of “functional groups” in non-functionalized hypercrosslinked polystyrenes

The paper discusses the assignment of the absorbance band at 1700 cm⁻¹ in FTIR spectra of hypercrosslinked polystyrenes. This band is exceptionally intensive in the spectra of networks obtained by post-crosslinking styrene-0.5% DVB copolymer, swollen in ethylene dichloride, with monochlorodimethyl ether up to the maximum possible crosslinking degrees of 300%, 400% and 500% in the presence of non-oxidizing catalyst SnCl₄. Theoretically, in these networks each phenyl ring binds to neighboring phenyls through three, four or five methylene groups, respectively. Elemental analysis of the products seems to be deficient in C and H, thus allowing expectation of a surprisingly high percentage of oxygen. However, the traditional attribution of both the suspected high content of oxygen and the band at 1700 cm⁻¹ to aromatic carbonyl groups is incorrect. Treatment of hypercrosslinked polystyrenes with hydroxylamine, sodium bisulfite, ethyl orthoformiate or LiAlH₄ do not result in disappearance of the absorbance at 1700 cm⁻¹ in FTIR spectra and emergence of corresponding characteristic new bands. Solid state ¹³C NMR spectroscopy also confirms the absence of CO moieties in the above hypercrosslinked polystyrenes. The absorbance at 1700 cm⁻¹ disappears, while new bands in the range of 1670–1650 cm⁻¹ emerge, in the spectrum of the sample with 500% crosslinking degree after the reduction of its benzene rings via Birch reaction. This allows suggesting that the band at 1700 cm⁻¹ and its shoulders are caused by hindered vibrations of carbon–carbon bonds and valence angles in the aromatic fragments composing the rigid network with extremely high extent of mutual connectivity.     

Photocatalytic hydrogen production by Au–MxOy (MAg,Cu, Ni) catalysts supported on TiO2

Au–M_xO_y (MAg, Cu, Ni) nanoparticles supported on TiO₂–P25 were prepared by the deposition–precipitation method and were evaluated for the photocatalytic water splitting reaction for hydrogen production, using a mixture of water–methanol (1:1). The combinations of Au–Cu₂O/TiO₂ and Au–NiO/TiO₂ effectively increased the hydrogen production (2064 and 1636 μmol·h^− 1·g^− 1) obtained by Au/TiO₂ (1204 μmol·h^− 1·g^− 1). The higher photoactivities achieved by Au–Cu₂O and Au–NiO nanoparticles deposited on TiO₂ were attributed to an enhancement of the electron charge transfer from TiO₂ to the Au–M_xO_y systems and the effect of surface plasmon resonance of gold nanoparticles.