Tianyong Zhang

Enhancement of photocatalytic activity of nano-scale TiO2 particles co-doped by rare earth elements and heteropolyacids

Nano-scale TiO(2) photocatalysts co-doped by rare earth ions (La(3+), Ce(3+)) and heteropolyacids were designed and prepared by sol-gel method to probe synergistic effect on photocatalytic elimination of organic compounds, and their physicochemical properties were characterized by X-ray diffraction (XRD), specific surface area and porosity (BET and BJH), high resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), and X-ray photoelectron spectroscopy (XPS) as well as Raman spectroscopy. The photocatalytic activity of prepared catalysts was evaluated by the degradation of methylene blue (MB) in water under UV-light irradiation. The results showed that the co-doping of the rare earth ions and heteropolyacids can significantly improve the photocatalytic activity of prepared composite photocatalysts due to the efficient inhibition of the recombination of photogenerated electron-hole pairs. The enhancement mechanism of co-doping of the rare earth ions and heteropolyacids on TiO(2) is also discussed.

Preparation and photocatalytic activity of La3+ and Eu3+ co-doped TiO2 nanoparticles: photo-assisted degradation of methylene blue

Rare earth ions La3+ and Eu3+ co-doped TiO2 photocatalyst (La-Eu/TiO2) was prepared by sol-gel method, and characterized by various techniques such as X-ray diffraction (XRD), specific surface area and porosity (BET and BJH), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the La-Eu/TiO2 was evaluated by the degradation of methylene blue (MB) under UV light irradiation. The catalyst had a relatively uniform particle diameter distribution in the range of 40–60 nm. When calcining at 600°C, the XRD patterns of La-Eu/TiO2 indicated the anatase phase, while the XPS patterns showed the Ti4+, La3+ and Eu3+ ions existence. The DRS spectra showed red shift in the band-gap transition. The experimental results of MB degradation demonstrated that the photocatalytic activity of La-Eu/TiO2 was significantly enhanced due to better separation of photogenerated electron-hole pairs.

Synthesis, characterization, electrochemical properties and catalytic reactivity of N-heterocyclic carbene-containing diiron complexes

(μ-dmedt)[Fe(CO)3]2 (I, dmedt = 2,3-butanedithiol) was chosen as the parent complex. A series of new model complexes, N-heterocyclic carbene (NHC) substituted (μ-dmedt)[Fe–Fe]–NHC (II, (μ-dmedt)[Fe(CO)2]2[IMe(CH2)2IMe], IMe = 1-methylimidazol-2-ylidene; III, {(μ-dmedt)[Fe2(CO)5]}2[IMe(CH2)2IMe]; IV, (μ-dmedt)[Fe2(CO)5]IMes, IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; V, (μ-dmedt)[Fe2(CO)5]IMe, IMe = 1,3-dimethylimidazol-2-ylidene) as mimics of the [Fe–Fe]–H2ase active site were synthesized from I and characterized using solution IR spectroscopy, NMR spectroscopy, elemental analysis and single-crystal X-ray diffraction. The electrochemical properties of complexes I–V, with and without the addition of HOAc, were investigated by cyclic voltammetry in the coordinating solvent CH3CN to evaluate the effects of different NHC ligands on the redox properties of the iron atoms of the series of complexes. It was concluded that all the new complexes are electrochemical catalysts for proton reduction to hydrogen. The symmetrically substituted cisoid basal/basal coordination complex II displays the most negative reduction potential owing to the stronger δ-donating ability of the NHC and the orientation of the NHC donor carbon as a result of the constraints of the bridging bidentate ligands. A new application for the [Fe–Fe]–NHC model complexes in the direct catalytic hydroxylation of benzene to phenol was also studied. Under the optimized experimental conditions (II, 0.01 mmol; benzene, 0.1 mL; CH3CN, 2.0 mL; H2O2, 6.0 mmol; 60 °C, 3 h), the maximal phenol yield was 26.7%.

Photocatalytic Conversion of Naphthalene to α-Naphthol Using Nanometer-Sized TiO2

Abstract The effects of various parameters (co-solvents, electron acceptors, and surface modification) on the direct synthesis of α-naphthol from naphthalene using photocatalytic processes were investigated. The OH radicals generated on UV-illuminated TiO 2 photocatalysts led to the direct hydroxylation of naphthalene to α-naphthol. The addition of Fe 3+ , Fe 2+ , Fe 3+ + H 2 O 2 , and Fe 2+ + H 2 O 2 greatly increases the conversion of naphthalene and the yield of α-naphthol in TiO 2 suspensions. The addition of Fe 3+ + H 2 O 2 to a TiO 2 suspension increased the yield to 22.2%. Surface modified-TiO 2 had a significant influence on the hydroxylation reaction. La-Eu/TiO 2 , La-Y/TiO 2 , H 3 PW 12 O 40 /TiO 2 , H 3 PMo 12 O 40 /TiO 2 , Fe/TiO 2 , Ag/TiO 2 , Cu/TiO 2 , and N/TiO 2 enhanced the conversion and yield more than TiO 2 . Fe/TiO 2 has the highest photocatalytic efficiency among these species.

Water-mediated promotion of direct oxidation of benzene over the metal–organic framework HKUST-1

Pretreatment of a HKUST-1 catalyst with water significantly accelerated the catalytic oxidation of benzene to phenol and hydroquinone with hydrogen peroxide as an oxidant. The corresponding oxygenates had a yield of 36.5%, and the selectivity to phenol and hydroquinone was 53.2% and 35.5%, respectively. The turnover frequency (TOF) was 35.1 h−1. Comparatively, the product yield was only 2.7% over the original HKUST-1, and the TOF was 2.6 h−1. Moreover, water treatment protected HKUST-1 from decomposition due to formation of a new oxidation mode. Therefore, the catalytic system in the presence of water opened a new door towards a facile and efficient preparation of phenol and hydroquinone.

Direct synthesis of phenol by novel [FeFe]-hydrogenase model complexes as catalysts of benzene hydroxylation with H2O2

Three new [FeFe]-hydrogenase model complexes, μ-(SCH(CH2CH3)CH2S)–Fe2(CO)6 (complex 1), μ-(SCH(CH2CH3)CH2S)–Fe2(CO)5PCy3 (complex 2) and μ-(SCH(CH2CH3)CH2S)–Fe2(CO)5PPh3 (complex 3) were prepared. The structures of complexes 1–3 were characterized by FT-IR, UV-vis, 1H, 13C, 31P NMR spectra and single-crystal analyses. The electron density of these model complexes was studied by IR spectra, UV spectra and electrochemical analysis and evaluated against their respective catalytic performances. The CV (cyclic voltammetry) study of complex 2 showed a less positive oxidation event at 0.6 V and a more negative reduction event at −1.94 V, which is in accordance with the enlargement of electron density at diiron centers when CO were substituted by better electron donor ligands. Of all these three complexes, complex 2 exhibited the best catalytic activity, with a yield of phenol of up to 24.6% and selectivity up to 92%, which is consistent with its higher electron density of the Fe–Fe bond. This study revealed the correlations between the electron density of the catalytic site of catalysts and their performance in catalytic hydroxylation of benzene. Based on these experimental results, a catalytic oxidation mechanism via an Fe2+–μ-O–Fe2+ intermediate as oxygen transfer reagent has been proposed.

Synthesis, structural characterization, and chemical properties of pentacoordinate model complexes for the active site of [Fe]-hydrogenase

Based on the synthesis of two new hexa-coordinate N-heterocyclic carbene (NHC) substituted precursors FeI2(CO)3(NHC) with NHC = IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) (2) and NHC = SIPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylide) (3) and two known complexes FeI2(CO)3SIMes, SIMes = (1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylide) (1) and FeI2(CO)3IMe IMe = 1,3-bismethylimidazol-2-ylidene (4), four new mononuclear [Fe]-hydrogenase model complexes Fe(CO)2(NS)(NHC) (NS = aminothiophenol; 5, NHC = SIMes; 6, NHC = IPr; 7, NHC = SIPr; 8, NHC = IMe) were prepared by substitution of two iodine ligands with the help of dipotassium-aminothiophenol salt and subsequently the absence of a CO ligand. New complexes 2, 3 and 5–8 were fully structurally characterized by infrared spectroscopy (IR), elemental analysis, NMR spectroscopy, and X-ray crystallography. IR spectroscopy studies show that complexes 5–8 exhibit similar IR patterns and absorption wavelengths in terms of ν(CO) with the active site of [Fe]-hydrogenase. The facile protonation/deprotonation of the NS ligand of complexes 6 and 7 was disclosed with the assistance of IR spectroscopy. The NS ligand accepts a proton reversibly as an internal base, generating two protonated species, [Fe(CO)2IPr(H-NS)]+ and [Fe(CO)2SIPr(H-NS)]+, which play the same role with the intrinsic cysteine thiolate ligand in [Fe]-hydrogenase. DFT results showed that the N atom of the NS ligand is the thermodynamically active proton acceptor in acetone while the NS ligand is prone to be dually protonated first in the N atom and then the S atom in the gas phase. Complex 5 exhibited simultaneous protonation and the combination of CO, forming a new mer-tricarbonyl species in the presence of CO and HBF4. It showed easy reversible deprotonation and deprivation of CO with the assistance of t-BuOK or Et3N. Also, the electrochemical properties of these new pentacoordinate model complexes were explored through cyclic voltammetry, which enabled us to identify the contributions of different NHC ligands to the complexes redox properties.

Synthesis, characterization and catalytic reactivity of pentacoordinate iron dicarbonyl as a model of the [Fe]-hydrogenase active site

Abstract Two mono iron complexes Fe(CO) 2 PR 3 (NN) (R = Cy ( 3 ), Ph ( 4 ), NN = o -phenylenediamine dianion ligand, N 2 H 2 Ph 2– ) derived from the ligand substitution of Fe(CO) 3 I 2 PR 3 by the NN ligand were isolated and structurally characterized by single crystal X-ray diffraction. They have a similar first coordination sphere and oxidation state of the iron center as the [Fe]-hydrogenase active site, and can be a model of it. IR demonstrated that the effect of the NN ligand on the coordinated CO stretching frequencies was due to its excellent electron donating ability. The reversible protonation/deprotonation of the NN ligand was identified by infrared spectroscopy and density functional theory computation. The NN ligand is an effective proton acceptor as the internal base of the cysteine thiolate ligand in [Fe]-hydrogenase. The electrochemical properties of complexes 3, 4 were investigated by cyclic voltammograms. Complex 3 catalyzed the transfer hydrogenation of benzoquinone to hydroquinone effectively under mild conditions.

Biomimetic synthesis of micro/nanostructured tubular TiO2 photocatalyst: adjusting the shape of the outer tube wall from nanoparticles to interlaced nanofibers and nanobelts

In this study, hierarchical micro/nanostructured tubular TiO2 photocatalysts were fabricated with the fluff of the chinar tree (FCT) as a biological template and titanium tetrachloride (TiCl4) as a precursor through an impregnation–calcination method. The structure, morphology and optical properties were extensively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption–desorption, Fourier-transform infrared spectroscopy (FTIR), UV-vis diffused reflectance spectroscopy (UV-vis) and photoluminescence (PL) spectra. The results indicated that the FCT played pivotal roles as a template and inducer to assemble the tubular micro/nanostructure. Interestingly, the morphologies and structures of the outer tube wall of the obtained materials could be controlled and tailored by adjusting the dosages of TiCl4. In addition, the structures of the outer tube wall of the samples could be tuned from cross-linked nanobelts to interlaced nanofibers, and then spherical-likely nanoparticles by adjusting the dosages of TiCl4. Moreover, the as-prepared TiO2 material exhibited a 99.8% photocatalytic degradation rate for 15 mg L−1 rhodamine B (RhB) in 30 min under a 300 W mercury lamp. Compared with P25, the obtained TiO2 had superior photocatalytic activity. Furthermore, the hierarchical micro/nanostructured tubular TiO2 was easily recycled and had excellent photocatalytic stability.

Ferrocene particles incorporated into Zr-based metal–organic frameworks for selective phenol hydroxylation to dihydroxybenzenes

UiO-66 with high dispersibility and a cuboctahedron morphology was synthesized by an improved solvothermal method. The morphology of UiO-66 was adjusted using benzoic acid as a modulator. UiO-66 with a regular morphology was then used as the support to load ferrocene (Fc). A series of Fc@UiO-66 composites were prepared via a facile impregnation method. The composites were characterized by powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), SEM/EDX mapping, FT-IR, UV/vis, TG analysis, N2 adsorption–desorption, and X-ray photoelectron spectroscopy (XPS). The results showed that Fc was incorporated into UiO-66, thus preventing the agglomeration of Fc particles in water. The Fc@UiO-66 composites with a Fc loading of 5% (FU-5) exhibited the highest catalytic activity for hydroxylation of phenol with H2O2 at room temperature in water, which gave a phenol conversion of 38.5% and 87.4% selectivity for dihydroxybenzenes (DHB). UiO-66 played a crucial role in the enhancement of catalytic performance compared with conventional supports such as γ-Al2O3, etc. A hydroxyl radical mechanism was proposed for this catalytic hydroxylation process and the high selectivity was attributed to the interaction between Fc particles and UiO-66.