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.     

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.     

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.     

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.     

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.     

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.     

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.     

Bridge-splitting of trans-[PtCl2(η2-CH2CH2)]2 by weak nucleophiles: Crystal and molecular structure of trans-[PtCl2(η2-CH2CH2)(MeCN)]

Bridge-splitting of trans-[PtCl₂(η²-CH₂CH₂)]₂, 1, by L in dichloromethane yields trans-[PtCl₂(η²-CH₂CH₂)(L)] (L = THF, 2, or MeCN, 3) with bridge-splitting equilibrium constants of 0.0289 ± 0.0007 and 3601 ± 215 mol^?1 dm³, respectively, as determined by UV/Vis measurements. The reaction of 3 in MeCN with Cl^? is essentially quantitative. The crystal structure of trans-[PtCl₂(η²-CH₂CH₂)(CH₃CN)] is reported.     

Synthesis,X-ray structure,spectroscopic properties,and theoretical investigations of dinuclear imidazole molybdenum(VI) complex with long MoO bands

One new dinuclear multioxomolybdenum(VI) complex containing long MoO bands with imidazole, [Mo₂O₆(imi)₄] (1) (imi = imidazole), has been prepared and characterized, and the geometric structure, electronic structure and spectroscopic properties, investigated experimentally and theoretically. The rarely observed long MoO bonds in 1 (ca. 0.15 Å longer than documents previously) are analysed by orbital structure analysis. The electronic origins of the optical transitions are also mainly related to the MoO groups with ligand-to-metal charge transfer (LMCT) nature (P_terminal-oxo → d_Mo).     

Synthesis,pyrolysis of a novel liquid SiBCN ceramic precursor and its application in ceramic matrix composites

SiBCN ceramic precursor, polyborosilazane, was synthesized through a novel method which used sodium borohydride as boron source. Vinyl silazane with SiCl was converted to vinyl silazane with SiH structure, followed by hydroboration reaction and subsequent high-temperature reaction to form soluble polyborosilazane liquid. The process of precursor-to-ceramic conversion was almost completed before 800 °C and the cross-linked polyborosilazane precursor exhibited higher ceramic yield 75.6% at 1200 °C. The SiBCN ceramic annealed at 1400 °C contained BN, SiN and SiC bonds with smooth and dense surface and still retained principally amorphous structure up to 1600 °C. In addition, the viscosity of the polyborosilazane was 65 mPa.s, which can efficiently prepare ceramic matrix composite by means of precursor infiltration and pyrolysis (PIP). The density of as-obtained ceramic matrix composite (CMC) was 1.82 g/cm³, and the average bending strength, bending modulus and tensile strength were 265.2 MPa, 37.5 GPa and 158.6 MPa, respectively.     

Thermally stable pseudo-third-generation Grubbs ruthenium catalysts with pyridine–phosphinimine ligand

The ligand precursors 2-(R₃PN)CH₂Py (R = Ph(1a), Cy(2a)) were prepared from reaction of pyridine azide with various phosphine ligands. Reaction of 1a or 2a with RuCl₂(CHPh)(Py)₂(H₂IMes) (Py = pyridine) afforded the ruthenium alkylidene complex RuCl₂(CHPh)(PyCH₂(NPR₃))(H₂IMes) (R = Ph(1), Cy(2)). Both catalysts showed good thermal stability and latent behavior toward RCM and ROMP reactions.     

Deposition of carbon nitride films using an electron cyclotron wave resonance plasma source

Hydrogenated amorphous carbon nitride (a-C:N:H) has been synthesised using a high plasma density electron cyclotron wave resonance (ECWR) technique using N₂ and C₂H₂ as source gases, at different ratios and a fixed ion energy (80 eV). The composition, structure and bonding state of the films were investigated and related to their optical and electrical properties. The nitrogen content in the film rises rapidly until the N₂/C₂H₂ gas ratio reaches 2 and then increases more gradually, while the deposition rate decreases steeply, placing an upper limit for the nitrogen incorporation at 30 at%. For nitrogen contents above 20 at%, the band gap and sp³-bonded carbon fraction decrease from 1.7 to 1.1 eV and ∼65 to 40%, respectively. The transition is due to the formation of polymeric CN, CN and NH groups, not an increase in CH bonds. Films with higher nitrogen content are less dense than the original hydrogenated tetrahedral amorphous carbon (ta-C:H) film but, because they have a relatively high band gap (1.1 eV), high resistivity (10⁹ Ω cm) and moderate sp³-bonded carbon fraction (40%), they should be classed as polymeric in nature.     

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.     

Degradation of mechanical and electrical properties after long-term oxidation and corrosion of non-oxide structural ceramic composites

This work summarizes the results related to the influence of the starting composition and of microstructure on properties degradation, due to oxidation and corrosion, relatively to the following structural ceramics: Si₃N₄TiN, Si₃N₄MoSi₂, AlNSiCMoSi₂, AlNSiC.The effects of: (i) long-term oxidation in air (100 h), in the temperature range 600–1500 °C and (ii) of long-term corrosion (400 h) in acid or basic aqueous solution at RT, 40 and 70 °C, on the electrical resistivity and mechanical strength of the composites are analysed and compared. The degradation of the properties are related to the characteristics of the surface and sub-surface damage after oxidation and corrosion treatments.     

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.     

Microwave dielectric properties of mineral sillimanite obtained by conventional and cold sintering process

The sillimanite (Al₂SiO₅) mineral has been sintered by conventional ceramic route and by cold sintering methods. The mineral has very poor sinterability and transformed to mullite on sintering above 1525 °C. The dielectric properties of sillimanite mineral (Al₂SiO₅) are investigated at radio and microwave frequency ranges. The mineral sintered at 1525 °C has low ε_r of 4.71 and tanδ of 0.002 at 1 MHz and at microwave frequency ε_r = 4.43, Q_u × f = 41,800 GHz with τ_f = −17 ppm/°C. The sintering aid used for cold sintering Al₂SiO₅ is sodium chloride (NaCl). The Al₂SiO₅NaCl composite was cold sintered at 120 °C. XRD analysis of the composite revealed that there is no additional phase apart from Al₂SiO₅ and NaCl. The densification of the Al₂SiO₅NaCl composite was confirmed by using microstructure analysis. The Al₂SiO₅NaCl composite has ε_r of 5.37 and tanδ of 0.005 at 1 MHz whereas at microwave frequency it has ε_r = 4.52, Q_u × f = 22,350 GHz with τ_f = −24 ppm/°C. The cold sintered NaCl has ε_r = 5.2, Q_u × f = 12,000 GHz with τ_f = −36 ppm/°C.     

Low-temperature synthesized nitrogen-doped iron/iron carbide/partly-graphitized carbon as stable cathode catalysts for enhancing bioelectricity generation

Low efficiency of oxygen reduction reaction (ORR) across cathode interfaces constitutes an obstacle to the bioelectricity generation in microbial fuel cells (MFCs). Advances in the property of carbon-based catalysts for ORR will have far-reaching implications for MFCs. Melamine is used as both carbon and nitrogen sources for preparing nitrogen-doped Fe-species/partly-graphitized carbon (Fe-species/NPGC) catalysts at relatively low temperature (640–700 °C). Main crystalline phases in Fe-species/NPGC-x (x = 640, 650, 660 and 700) change from iron carbide (Fe₃C) to α-Fe as temperature increases. The OCO groups and structurally-bonded nitrogen (Fe-bonded N, pyridinic N and pyrrolic N) in PGC skeleton are favorable for improving electrical conductivity and catalytic activity. Single chamber MFCs with Fe/Fe₃C/NPGC-650 generate power density of 1323 mW m⁻², which is higher than those of Fe-species/NPGC-x (x = 640, 660 and 700) and Pt/C (1191 mW m⁻²). Minimum power density decline (1.75%) is achieved by Fe/NPGC-660, which is far lower than that (17.11%) of Pt/C. The highest coulombic efficiency (30%) is obtained by Fe/Fe₃C/NPGC-650 due to the sufficient active-sites (embedded Fe₃C or FeN species) and easy charge transport across the triphase interfaces, which are conducive to “capture–consume” the electrons for catalyzing ORR.     

Etherification reactions of propargylic alcohols catalyzed by a cationic ruthenium allenylidene complex

The cationic ruthenium allenylidene complex R_RuR_ax −[Ru(indenyl)L(PPh₃)CCCPh₂]⁺PF₆ catalyzes the etherification of secondary and tertiary propargylic alcohols in a formal nucleophilic substitution reaction utilizing primary and secondary alcohols as the nucleophiles. At a catalyst loading of only 1.1 mol%, the corresponding propargylic ether products were obtained in 9 to 73% isolated yields (18 h reaction time at 100 °C); no further additives are required. The reaction exhibits an induction period; as shown by a control reaction, the high reaction temperature may chemically change the allenylidene complex to be employed as the catalyst but does not lead to catalyst deactivation.     

Carbothermal synthesis of β-sialon from mechanochemically activated precursors

Reaction mixtures of halloysite clay and fine carbon for carbothermal reduction and nitridation (CRN) synthesis of β-sialon were ground in a planetary ball mill under flowing nitrogen for varying periods before being converted to sialon by heating in nitrogen at 1200–1400 °C. After 4 h grinding the XRD reflections of the halloysite were destroyed and some of the octahedrally-coordinated Al was converted to four- and five-fold coordination. ²⁷Al and ²⁹Si MAS NMR gave no evidence of the formation of AlN or SiN bonds upon grinding. Upon subsequent heating in nitrogen, the ground samples show significant differences from the unground control, the intermediate compound mullite being replaced by β-sialon (z ≈ 2) a temperature at least 100 °C lower, but the formation of corundum (α-Al₂O₃) also occurs at a lower temperature and is more persistent than in the unground control. MAS NMR spectroscopy shows that the products from the ground mixtures contain relatively less AlON units and that the formation of SiC (a transient reaction intermediate) is also facilitated by grinding. The optimum grinding time for this system was found to be 12 h.     

Synthesis and proton conductivity of a new two-dimensional layered aluminophosphate [C9H14N]8[H2O]4·[Al8P12O48H4]

A new two-dimensional layered aluminophosphate [C₉H₁₄N]₈[H₂O]₄·[Al₈P₁₂O₄₈H₄] (denoted as AlPO-CJ70) has been synthesized by using N,N-dimethylbenzylamine as the template under solvothermal conditions at 403 K. Single-crystal X-ray diffraction analysis reveals that the structure of AlPO-CJ70 consists of AAAA-stacked Al₂P₃O₁₂^3 − layers made of alternating AlO₄ and PO₄ (PO₃(O) and PO₂(O)(OH)) tetrahedra, forming 1D 8-ring channels along the [100] direction. The inorganic layer exhibits a new type of 4 × 6 × 8 sheets with the Al/P ratio of 2/3. Protonated N,N-dimethylbenzylamine cations are located between the layers compensating the negative charge of the anionic framework. The existence of guest water and extensive H-bonds in the structure endows AlPO-CJ70 with proton conduction properties, as elucidated by impedance studies of the powder sample.