Dishun Zhao

Enhanced visible-light photocatalytic activity of active Al2O3/g-C3N4 heterojunctions synthesized via surface hydroxyl modification

Novel Al2O3/g-C3N4 heterojunction photocatalysts were fabricated through ultrasonic dispersion method. Al2O3, obtained via solution combustion, contained amorphous ingredient with lots of defect sites and was used as active component for transferring photo-induced electrons of g-C3N4. G-C3N4 was grafted surface hydroxyl groups in the presence of ammonia aqueous solution to combine with Al2O3 possessing positive charges via hydrogen bond. The XRD, SEM, element map, TEM, HRTEM, FT-IR, and XPS results indicate that these synthesized materials are two-phase hybrids of Al2O3 and g-C3N4 with interaction. The photocatalytic results for the degradation of rhodamine B (RhB) indicate that the most active heterojunction proportion is 60wt.% g-C3N4:40wt.% Al2O3, the visible light photocatalytic activity of which is 3.8 times that of a mechanical mixture. The enhanced performance is attributed to the high separation efficiency of photo-induced electrons from the LUMO of g-C3N4 injected into the defect sites of Al2O3, which is verified by photoluminescence spectroscopy (PL) and surface photovoltage (SPV) measurements. The electron paramagnetic resonance (EPR) signals and radical scavengers trapping experiments reveal holes (h(+)) and superoxide anion radical (O2(-)) are the main active species responsible for the degradation of RhB.

Desulfurization of dibenzothiophene by chemical oxidation and solvent extraction with Me3NCH2C6H5Cl·2ZnCl2 ionic liquid

Desulfurization of dibenzothiophene (DBT) by a combination of both chemical oxidation and solvent extraction was investigated. Me3NCH2C6H5Cl·2ZnCl2 ionic liquid was prepared from cheap starting materials and used as extractant for oxidative desulfurization of DBT in n-octane. DBT in oil phase was extracted into ionic liquid phase and then oxidized to its corresponding sulfone by H2O2 and equal volume of acetic acid. The desulfurization yield of DBT in n-octane was 94% at 30 min under the conditions of H2O2/DBT molar ratio at 6 and V (ionic liquid) : V (n-octane) = 1 : 5, which was remarkably higher than that by mere extraction with ionic liquid (28.9%). The Me3NCH2C6H5Cl·2ZnCl2 ionic liquid could be recycled six times without a significant decrease in activity. Kinetics of oxidative desulfurization of DBT by H2O2 and acetic acid was first-order with an apparent rate constant of 0.0842 min−1 and half-time of 8.23 min.

N-doped P25 TiO2–amorphous Al2O3 composites: One-step solution combustion preparation and enhanced visible-light photocatalytic activity

Nitrogen-doped Degussa P25 TiO2-amorphous Al2O3 composites were prepared via facile solution combustion. The composites were characterised using X-ray diffraction, high-resolution transmission microscopy, scanning electron microscopy, nitrogen adsorption-desorption measurements, X-ray photoelectron spectroscopy, UV-vis light-diffusion reflectance spectrometry (DRS), zeta-potential measurements, and photoluminescence spectroscopy. The DRS results showed that TiO2 and amorphous Al2O3 exhibited absorption in the UV region. However, the Al2O3/TiO2 composite exhibited visible-light absorption, which was attributed to N-doping during high-temperature combustion and to alterations in the electronic structure of Ti species induced by the addition of Al. The optimal molar ratio of TiO2 to Al2O3 was 1.5:1, and this composite exhibited a large specific surface area of 152 m2/g, surface positive charges, and enhanced photocatalytic activity. These characteristics enhanced the degradation rate of anionic methylene orange, which was 43.6 times greater than that of pure P25 TiO2. The high visible-light photocatalytic activity was attributed to synthetic effects between amorphous Al2O3 and TiO2, low recombination efficiency of photo-excited electrons and holes, N-doping, and a large specific surface area. Experiments that involved radical scavengers indicated that OH and O2- were the main reactive species. A potential photocatalytic mechanism was also proposed.

Ionic liquid self-combustion synthesis of BiOBr/Bi24O31Br10 heterojunctions with exceptional visible-light photocatalytic performances

Heterostructured BiOBr/Bi24O31Br10 nanocomposites with surface oxygen vacancies are constructed by a facile in situ route of one-step self-combustion of ionic liquids. The compositions can be easily controlled by simply adjusting the fuel ratio of urea and 2-bromoethylamine hydrobromide (BTH). BTH serves not only as a fuel, but also as a complexing agent for ionic liquids and a reactant to supply the Br element. The heterojunctions show remarkable adsorptive ability for both the cationic dye of rhodamine B (RhB) and the anionic dye of methylene orange (MO) at high concentrations, which is attributed to the abundant surface oxygen vacancies. The sample containing 75.2% BiOBr and 24.8% Bi24O31Br10 exhibits the highest photocatalytic activity. Its reaction rate constant is 4.0 and 9.0 times that of pure BiOBr in degrading 50 mg L(-1) of RhB and 30 mg L(-1) of MO under visible-light (λ > 400 nm) irradiation, respectively, which is attributed to the narrow band gap and highly efficient transfer efficiency of charge carriers. Different photocatalytic reaction processes and mechanisms over pure BiOBr and heterojunctions are proposed.

Deep extractive and oxidative desulfurization of dibenzothiophene with C5H9NO·SnCl2 coordinated ionic liquid

A new C5H9NO·SnCl2 coordinated ionic liquid (IL) was prepared by reacting N-methyl-pyrrolidone with anhydrous SnCl2. Desulfurization of dibenzothiophene (DBT) via extraction and oxidation with C5H9NO·SnCl2 IL as extractant, H2O2 and equal mol of CH3COOH as oxidants was investigated. The Nernst partition coefficients k(N) of C5H9NO·SnCl2 IL for the DBT in n-octane was above 5.0, showing its excellent extraction ability. During the oxidative desulfurization process, the optimal molar ratio of H2O2/DBT was six. Sulfur removal of DBT in n-octane was 94.8% in 30 min at 30 °C under the conditions of H2O2/DBT molar ratio of six and V (IL):V (oil)=1:3. Moreover, the sulfur removal increased with increasing temperature because of the high reaction rate constant, low viscosity, and high solubility of dibenzothiophene-sulfone in the IL. The kinetics of oxidative desulfurization of DBT was also investigated, and the apparent activation energy was found to be 32.5 kJ/mol. The IL could be recycled six times without a significant decrease in activity.

Structure Modification Function of g-C3N4 for Al2O3 in the In Situ Hydrothermal Process for Enhanced Photocatalytic Activity†

Heterojunctions of g-C3 N4 /Al2 O3 (g-C3 N4 =graphitic carbon nitride) are constructed by an in situ one-pot hydrothermal route based on the development of photoactive γ-Al2 O3 semiconductor with a mesoporous structure and a high surface area (188 m(2) g(-1) ) acting as electron acceptor. A structure modification function of g-C3 N4 for Al2 O3 in the hydrothermal process is found, which can be attributed to the coordination between unoccupied orbitals of the Al ions and lone-pair electrons of the N atoms. The as-synthesized heterojunctions exhibit much higher photocatalytic activity than pure g-C3 N4 . The hydrogen generation rate and the reaction rate constant for the degradation of methyl orange over 50 % g-C3 N4 /Al2 O3 under visible-light irradiation (λ>420 nm) are 2.5 and 7.3 times, respectively, higher than those over pristine g-C3 N4 . The enhanced activity of the heterojunctions is attributed to their large specific surface areas, their close contact, and the high interfacial areas between the components as well as their excellent adsorption performance, and efficient charge transfer ability.

Photocatalytic oxidative desulfurization of dibenzothiophene under simulated sunlight irradiation with mixed-phase Fe2O3 prepared by solution combustion

Mixed-phase Fe2O3 was prepared from Fe(NO3)3 and (C2H5)3NHCl via solution combustion. Photocatalytic oxidative desulfurization of dibenzothiophene (DBT) under simulated sunlight irradiation using mixed-phases of α- and β-Fe2O3 as catalysts was investigated. The DBT in the oil phase was extracted into water phase and then photooxidized to CO2 and SO42− by Fe2O3 and O2 dissolved in water. The Fe2O3 containing 36.6% β-Fe2O3 and 63.4% α-Fe2O3 exhibited the highest photocatalytic activity. Sulfur removal of DBT in n-octane was 92.3% for 90 min irradiation under the conditions of V(water) : V(n-octane) = 1 : 1, air flow rate at 150 mL min−1, and Fe2O3 addition at 0.05 g. The kinetics of photooxidative desulfurization of DBT was a pseudo-first-order with an apparent rate constant of 0.0287 min−1 and half-time of 24.15 min. The sulfur content of the actual diesel could be reduced from 478 μg mL−1 to 44.5 μg mL−1 after 90 min. The radical scavengers experiments and terephthalic acid fluorescence technique indicated that ˙OH and O2˙− were the main reactive species in the DBT photocatalytic degradation. A potential photocatalytic desulfurization mechanism using mixed-phase Fe2O3 was proposed.

Oxidative desulfurization of dibenzothiophene based on air and cobalt phthalocyanine in an ionic liquid

Cobalt phthalocyanines (CoPc(Cl)n) were synthesized by a microwave method and characterized by UV-Vis spectroscopy, FTIR, elemental analysis and ICP. Dibenzothiophene (DBT) was oxidized with air as the oxidant and cobalt phthalocyanines (CoPc(Cl)n) as catalysts in an ionic liquid at room temperature and atmospheric conditions. The removal ratio of DBT reached 90.0% at room temperature after 2 h, with 0.3 wt% of CoPc(Cl)16 in an ionic liquid, and the ratio of the ionic liquid to the model oil was 1.8 : 1 at room temperature. The effect of the substituents on the cobalt phthalocyanines on their catalytic activities was investigated. The results show that the catalytic activity of cobalt phthalocyanines with different substituents increases in the order CoPc(Cl)4 < CoPc(Cl)8 < CoPc(Cl)12 < CoPc(Cl)16, indicating that electron-withdrawing group substituents have a positive effect on the catalytic properties. The activity of CoPc(Cl)16 was kept unchanged after 5 runs of oxidation. The oxidation product detected by FTIR and mass spectrometry was single DBTO2. The desulfurization of different sulfur compounds and real gasoline was also investigated in this system. The sulfur removal ratio of five different sulfur compounds was over 80%. The sulfur content in real gasoline (1000 ppm) was decreased to 30 ppm after desulfurization.

Dissolution of cellulose in NaOH based solvents at low temperature

Three low-cost types of complex solvents systems were carried out to dissolve cellulose, which were NaOH/urea/acetamide, NaOH/urea/tetraethyl ammonium chloride, and NaOH/acetamide/tetraethyl ammonium chloride. As an effective dissolution, NaOH/acetamide/tetraethyl ammonium chloride behaved as the optimum system, and the solubility was 89 % under the conditions of: NaOH 8 wt%, acetamide 10 wt%, tetraethyl ammonium chloride 6 wt%, distilled water 76 wt%, and freezing temperature −5°C. With the analysis of Ubbelohde viscometer, infrared spectra (FTIR), wide-angle X-ray diffraction (XRD), and thermogravimetric analysis (TGA) for the original and regenerated cellulose samples, it was indicated that the viscosity-average molecular weight had no significant changes in the dissolution process, the crystalline structure of cellulose was converted to cellulose II from cellulose I in native cellulose, and the regenerated cellulose had a good thermal stability.

Photocatalytic Oxidation Kinetics of Thiophene with Nano-TiO2 as Photocatalyst

Photocatalytic oxidative kinetics of thiophene in n-octane/water extraction system was studied with nano-TiO₂ powders as photocatalyst and O₂ in air as oxidant. Influence of initial concentration of thiophene and addition of TiO₂ on reaction rate constant and half time were investigated. Kinetics equation was founded. The results showed that the approviate addition of TiO₂ was 0.1 g in 100 mL reaction system and the photooxidation kinetics of thiophene with TiO₂ was first-order with rate constant of 0.6405 h^-1 and half-time of 1.0822 h under the conditions with initial concentration of thiophene at 800 muLldrL^-1 and addition of TiO₂ at 0.1 g. The reaction rate constant increased with the decrease of initial concentration of thiophene.