Kejian Deng

Selective aerobic oxidation of the biomass-derived precursor 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid under mild conditions over a magnetic palladium nanocatalyst

A new method for the selective aerobic oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) has been developed employing a magnetically separable [γ-Fe2O3@HAP-Pd(0)] catalyst. The catalyst was prepared by the exchange of Pd2+ with Ca2+ in γ-Fe2O3@HAP, followed by reduction of the Pd2+ to Pd(0) nanoparticles, and well characterized by TEM, XRD and XPS. The catalyst showed high activity in the oxidation of HMF to FDCA in water, with 97% HMF conversion and a 92.9% yield of FDCA under optimal reaction conditions. The method developed has demonstrated some advantages, including its sole requirement of a stoichiometric base, and high catalytic performance under atmospheric oxygen, even in air. More importantly, the γ-Fe2O3@HAP-Pd(0) catalyst was readily separated from the reaction solution using an external magnetic field and was successfully reused during five consecutive reaction runs while retaining its catalytic effectiveness. This study provides a green and sustainable method for the production of valuable chemicals from renewable resources.

(Bi, C and N) codoped TiO2 nanoparticles.

Bi, C and N codoped TiO2 photocatalysts were prepared by doping TiO2 with BiCl3 and KSCN in a sol-gel process (denoted as (Bi,SCN)-TiO2). The catalyst samples were then characterized by XRD, TEM, diffuse reflectance spectra (DRS), XPS, FT-IR and N2 sorption. Bi, C and N elements were detected both by XPS and elemental analysis, while S element was not found, suggesting that SCN- group may have decomposed during the sol-gel process. The effects of the doping on the properties and photocatalytic activity of the TiO2 were investigated. It was found that the cation and the anion affected the properties of TiO2 differently. The optical absorption onset of TiO2 red shifted in the presence of Bi3+, while long tail occurred in the presence of SCN-. The order of photoreactivity for TiO2 samples was as follow: (Bi,SCN)-TiO2>Bi-TiO2>undoped TiO2>p25 TiO2, whatever under UV or visible light illumination. The high photoreactivity of the doped TiO2 was also discussed.

Synergistic effects of hollow structure and surface fluorination on the photocatalytic activity of titania

To study the synergistic effects of hollow structure and surface fluorination on the photoactivity of TiO(2), TiO(2) hollow microspheres were synthesized by a hydrolysis-precipitate method using sulfonated polystyrene (PS) as templates and tetrabutylorthotitanate (TBOT) as precursor, and then calcined at 500 degrees C for 2h. The calcined samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N(2) sorption. Photocatalytic activity was evaluated using reactive brilliant red X3B, an anionic organic dye, as a model pollutant in water. The results show that the photocatalytic activity of TiO(2) hollow microspheres is significantly higher than that of TiO(2) nanoparticles prepared in the same experimental conditions. At pH 7 and 3, the apparent rate constants of the former exceed that of the latter by a factor of 3.38 and 3.15, respectively. After surface fluorination at pH 3, the photoactivity of hollow microspheres and nanoparticles further increases for another 1.61 and 2.19 times, respectively. The synergistic effect of surface fluorination and hollow structure can also be used to prepare other highly efficient photocatalyst.

Bin(Tu)xCl3n: a novel sensitizer and its enhancement of BiOCl nanosheets’ photocatalytic activity

Bismuth complexes, Bin(Tu)xCl3n, were found to be photosensitizers for the first time. BiOCl nanosheets with inner Bin(Tu)xCl3n were synthesized and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, UV-vis diffuse reflectance, Fourier transform infrared spectrometry, thermogravimetric analyses and photoluminescence. The as-synthesized BiOCl displayed high visible light (λ ≥ 420 nm) photocatalytic activity which was 112 and 13 times higher than P25 and BiOCl without Bin(Tu)xCl3n, for degrading RhB, respectively. The investigation of the photocatalytic mechanism demonstrated that Bin(Tu)xCl3n sensitized the BiOCl and resulted in unusually high visible light photocatalytic activity. The superoxide radical was the main active species in the photodegradation process. Furthermore, the concentration of the superoxide radical was quantized by the molecular probe nitroblue tetrazolium.

Transformation of TiOF2 Cube to a Hollow Nanobox Assembly from Anatase TiO2 Nanosheets with Exposed {001} Facets via Solvothermal Strategy

Hierarchical nanostructures have attracted increasing interest due to their exceptional properties and widespread potential applications. In this paper, anatase TiO2 hollow nanoboxes (TiO2-HNBs) are formed by assembly of nanosheets with exposed {001} facets by solvothermal treatment of TiOF2 cubes in alcohols (tert-butanol and ethanol) at 180 °C. It was found that phase transformation of TiOF2 to anatase TiO2 begins at corners and edges of TiOF2 cubes due to in situ hydrolysis of TiOF2, where water was produced by dehydration of alcohol molecules. With extension the reaction time, TiO2-HNB assemblies from nanosheets with exposed high-energy {001} facets were formed due to the steady inside-outside dissolution-recrystallization process. However, the resulting hierarchical TiO2-HNBs are unstable, which can decompose to discrete high-energy TiO2 nanosheets if the reaction time is further extended. The hierarchical TiO2-HNBs show higher photocatalytic activity than discrete high-energy TiO2 nanosheets and P25 TiO2 due to the unique structures of TiO2-HNBs.

High photocatalytic degradation activity of the polyvinyl chloride (PVC)-vitamin C (VC)-TiO2 nano-composite film.

A novel photodegradable polyvinyl chloride (PVC)-vitamin C (VC)-TiO(2) nano-composite film was prepared by embedding VC modified nano-TiO(2) photocatalyst into the commercial PVC plastic. The solid-phase photocatalytic degradation behavior of PVC-VC-TiO(2) nano-composite film under UV light irradiation was investigated and compared with those of the PVC-TiO(2) film and the pure PVC film, with the aid of UV-Vis spectroscopy, scanning electron microscopy (SEM), weight loss monitoring, and X-ray diffraction spectra (XRD). The results show that PVC-VC-TiO(2) nano-composite film has a high photocatalytic activity; the photocatalytic degradation rate of it is two times higher than that of PVC-TiO(2) film and fifteen times higher than that of pure PVC film. The optimal mass ratio of VC to TiO(2) is found to be 0.5. The mechanism of enhancing photocatalytic activity is attributed to the formation of a Ti(IV)-VC charge-transfer complex with five-member chelate ring structure and a rapid photogenerated charge separation is thus achieved.

Structures, photoluminescence and photocatalytic properties of three new metal–organic frameworks based on non-rigid long bridges

Three new metal–organic coordination polymers, [Cd3(5-NO2-bdc)2(5-NO2-bdcH)2(bpyo)2]n (1), [Mn(5-NO2-bdc)(bbim)]n (2) and {[Gd(5-NO2-bdc)(5-NO2-bdcH)](bpyo)0.5·2H2O}n (3) (5-NO2-bdcH2 = 5-nitro-1,3-benzenedicarboxylic acid; bpyo = 4,4′-bipyridine-N,N′-dioxide; bbim = 1,1′-(1,4-butanediyl)bis(benzimidazole)), were obtained under hydrothermal conditions and characterized structurally. The networks exhibit a variety of topologies and coordination modes at the metal centers. Complex 1 exhibits NaCl-type topology and contains the centrosymmetric trinuclear cluster SBU [Cd3(COO)4O2]. Complex 2 adopts CsCl-type topology based on bimetallic cores and is the first example of compounds containing a cis bbim bridge. Moreover, complex 3 possesses a 3D supramolecular framework by stronger contacts between 2D layers and non-rigid bpyo bridges. The thermal stabilities of 1–3, the photoluminescence properties of 1 as well as the photocatalytic performance of 3 were also examined, and the results indicated that 1 seems to be a good candidate for novel hybrid inorganic–organic photoactive materials, especially, compound 3 represents the rare example of coordination polymers with a 4f metal ion that exhibit good photocatalytic activity for dye degradation under UV light.

Oxidative degradation of dye pollutants over a broad pH range using hydrogen peroxide catalyzed by FePz(dtnCl2)4.

The oxidative degradation of rhodamine B (RhB) with hydrogen peroxide activated by iron(II) tetra-(5,6-dichloro-1,4-dithiin)-porphyrazine (abbreviated as FePz(dtnCl(2))(4)) was studied by means of UV-Vis spectra, GC-MS and TOC analysis, in which the effects of pH, light, concentration of hydrogen peroxide and the degraded products of the RhB were investigated. The results indicate that FePz(dtnCl(2))(4) was found to exhibit high catalytic activity to activate hydrogen peroxide for the oxidative degradation of RhB and good stability over a broad pH range under visible light irradiation (lambda>420 nm). The conversions of RhB in 80 min were 99%, 85%, 52% and the TOC removals in 240 min were 91%, 64%, 18% when the initial solutions pHs were 2, 7, 11, respectively. HO(.) radicals were testified to generate in the biomimetic catalytic system both at pH 2 and 7 by means of spin-trapping electron spin resonance. However, control experiment with scavenging of HO() radicals displayed the quite different results at pH 2 and 7. Based on experiment results together with theoretic deduction, a mechanism for RhB oxidation involving two kinds of reactive oxidizing species was proposed, the homolytic cleavage generating the HO(.) radicals and the heterolytic cleavage generating the Pz(.)(+)Fe(IV)=O radicals.

Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid Using O2 and a Photocatalyst of Co-thioporphyrazine Bonded to g-C3N4

Selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is one of the key reactions for producing chemical commodities from biomass and their derivatives. The challenge for this reaction is to develop an efficient catalytic process that can be conducted under mild conditions (room temperature and atmospheric pressure, using oxygen molecules in air as the oxidant) and a recyclable catalyst. Herein we report a photocatalyst of cobalt thioporphyrazine (CoPz) dispersed on g-C3N4 (abbreviated as CoPz/g-C3N4), which exhibits excellent catalytic activity toward the selective oxidation of HMF into FDCA under simulated sunlight using oxygen molecules in air as a benign oxidant. For example, an FDCA yield of 96.1% in an aqueous solution at pH = 9.18 is achieved at ambient temperature and air pressure. At lower pH (4.01), the product generated is 2,5-diformylfuran. Hence, it is possible to control the reaction outcome by control of the pH of the reaction system. g-C3N4 itself is not a suitable catalyst for the selective oxidation because under the experimental conditions g-C3N4 generates hydroxyl radicals that initiate processes that oxidize HMF directly to CO2 and H2O. CoPz on the other hand activates O2 to give singlet oxygen (1O2), which more controllably oxidizes HMF to FDCA albeit at a more moderate yield (36.2%). The strong interaction between the CoPz and g-C3N4 in the CoPz/g-C3N4 catalyst is experimentally evidenced, which not only improves accessibility of the CoPz sites and makes the catalyst recyclable but also disables the hydroxyl radical generation by g-C3N4 and promotes 1O2 generation on the CoPz sites, significantly enhancing the catalytic performance. This study demonstrates the potential for efficient non-noble metal photocatalysts for organic transformations driven by sunlight.

Effect of structure-directing agents on facile hydrothermal preparation of hierarchical γ-Al2O3 and their adsorption performance toward Cr(VI) and CO2.

Hierarchical flower-like and sphere-like mesoporous γ-Al2O3 microparticles were successfully prepared by a facile hydrothermal method followed by a calcination process using sodium aluminate as aluminum source, urea as precipitating agent, and Pluronic F127 (EO106PO70EO106), polyacrylic acid sodium (PAAS), and mixed F127-PAAS as structure-directing agents (SDAs), respectively. Effects of the SDAs on the phase structure, morphology, textural properties, surface alkaline, and the adsorption performance toward Cr(VI) and CO2 of the as-prepared samples were comparatively studied by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), N2 adsorption-desorption, CO2 temperature programmed desorption (CO2-TPD), and UV-Vis spectrophotometric method. The results indicate that the sphere-like γ-Al2O3 obtained by using F127 as the SDA shows the best adsorption performance toward Cr(VI) with a high adsorption rate of 95% and adsorption capacity of 5.7 mg/g when the adsorption reaches equilibrium for 4h at room temperature. However, the flower-like γ-Al2O3 obtained by using PAAS as the SDA has the biggest CO2 adsorption capacity of 1.04 mmol/g at room temperature. This work provides a simple and practical way to prepare potentially bifunctional γ-Al2O3 adsorbent for the removal of pollutants in water and air treatment from cheap sodium aluminate by using different SDAs.