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71.
Rare earth Ce, Eu, Gd and Dy doped Ti/Sb-SnO2 electrodes were prepared by thermal decomposition and the performance of electrodes for the electro-catalytic decomposition of a model pollutant (phenol) was investigated. Phenol degradation and TOC removal followed pseudo-first-order kinetics in the experimental range, with the maximum rate achieved using Gd-doped electrode and the minimum rate obtained by Ce-doped electrode. Electrodes were characterized by cyclic voltammetry, X-ray diffraction, electron dispersive spectrometry, and X-ray photoelectron spectroscopy. It was suggested that the enhanced performance of the Gd-doped Ti/Sb-SnO2 electrode arose from the increased adsorption capacity of hydroxyl radicals on the electrode surface and the lower mobility of oxygen atoms in SnO2 lattice. The redox couple of Ce4+/Ce3+ on Ce-doped Ti/Sb-SnO2 electrode surface functioned as mediators in the electrochemical oxidation process, allowing oxygen transfer in the SnO2 lattice, and lowered the electro-catalytic ability of the electrode on phenol mineralization. 相似文献
72.
Catalytic efficiency, stability and environmental applicability of five iron(III) oxide nanopowders differing in surface area and crystallinity were tested in degradation of concentrated phenolic aqueous solutions (100 g/L) at mild temperature (30 °C), initially almost neutral pH and equimolar ratio of hydrogen peroxide and phenol. The catalyst properties were easily controlled by varying in reaction time during isothermal treatment of ferrous oxalate dihydrate in air at 175 °C. Although the catalytic efficiency clearly increases with the surface area of the nanopowders, it is not due to the solely heterogeneous catalytic mechanism as would be expected. The amorphous Fe2O3 nanopowders possessing the largest surface areas (401 m2 g−1, 386 m2 g−1) are the most efficient catalysts evidently due to their highest susceptibility to leaching in acidic environment arising as a consequence of phenol degradation products. Thus, these amorphous samples act partially as homogeneous catalysts, which was confirmed by a high concentration of leached Fe(III) ions in the solution (19 ppm). The crystalline hematite (α-Fe2O3) samples, varying in surface area between 337 m2 g−1 and 245 m2 g−1, are generally less efficient when compared to the amorphous powders, however their catalytic action is almost exclusively heterogeneous as only 3 ppm of leached Fe(III) was found in the reaction systems catalyzed by nanohematite samples. A significant difference in relative contributions of heterogeneous and homogenous catalysis was definitely established in buffered reaction systems catalyzed by amorphous Fe2O3 and nanocrystalline hematite. The nanohematite sample exhibiting the highest heterogeneous action was tested at decreased initial phenol concentration (10 g/L), which is closer to the real contents of phenol in waste waters, and at different hydrogen peroxide/phenol molar ratios to consider its environmental applicability. At the hydrogen peroxide/phenol ratio equal to 5, no traces of the leached iron were detected and the phenol conversion of 84% was reached. Moreover, such a high degree of conversion is accompanied by a decrease of the chemical oxygen demand (COD) from the initial value of 11.23 g/L to 4.22 g/L after 125 min. This fact indicates that the considerable fraction of primary reaction products was totally degraded. 相似文献
73.
Mohammad S. Yalfani Sandra Contreras Francesc Medina Jesus Sueiras 《Applied catalysis. B, Environmental》2009,89(3-4):519-526
The recent reported pathway using oxygen and formic acid at ambient conditions has been utilized to generate hydrogen peroxide in situ for the degradation of phenol. An alumina supported palladium catalyst prepared via impregnation was used for this purpose. Almost full destruction of phenol was carried out within 6 h corresponding to the termination of 100 mM formic acid at the same time. In addition, a significant mineralization (60%) was attained. A simulated conventional Fenton process (CFP) using continuous addition of 300 ppm H2O2 displayed maximum 48% mineralization. Study of different doses of formic acid showed that decreasing the initial concentration of formic acid caused faster destruction of phenol and its toxic intermediates. The catalytic in situ generation of hydrogen peroxide system demonstrated interesting ability to oxidize phenol without the addition of Fenton's catalyst (ferrous ion). Lower Pd content catalysts (Pd1/Al and Pd0.5/Al) despite of producing higher hydrogen peroxide amount for bulk purposes, did not reach the same efficiency as the Pd5/Al catalyst in phenol degradation. The later catalyst showed a remarkable repeatability so that more than 90% phenol degradation along with 57% mineralization was attained by the used catalyst after twice recovery. Higher temperature (45 °C) gave rise to faster degradation of phenol resulting to almost the same mineralization degree as obtained at ambient temperature. Meanwhile, Pd leaching studied by atomic adsorption proved excellent stability of the catalysts. 相似文献
74.
Jaime S. Valente Francisco Tzompantzi Julia Prince Jose G.H. Cortez Ricardo Gomez 《Applied catalysis. B, Environmental》2009,90(3-4):330-338
Mg–Zn–Al layered double hydroxides (LDHs) with varying amounts of zinc were prepared by the coprecipitation method. Solids were analyzed by XRD and N2 physisorption, confirming the formation of pure LDH phase; and the production of mixed oxides with high specific surface areas (182–276 m2 g−1) after calcination. Band gap energy was also determined, presenting the expected decreasing tendency on increasing zinc amounts. These mixed oxides were tested both for the adsorption of 2,4 dichlorophenoxiacetic acid (2,4-d) and for the photocatalytic degradation of 2,4-d and phenol. Nearly total (97%) degradation of initial 1.45 mmol L−1 of 2,4-d, with 1 g calcined LDH per liter, was accomplished in 9 h, while phenol half-life was as short as 3.5 h, with the catalyst with lowest zinc amount (5 wt.%). Langmuir adsorption isotherms are presented. Solids were also characterized by XRD and FTIR analysis after photocatalytic and adsorption activity, to determine the presence of 2,4-d. The versatility of LDH decomposition products in the elimination of different contaminants by different mechanisms puts them forward as a viable alternative for environmental remediation. 相似文献
75.
76.
A Cu(II)-catalyzed ortho-selective amination of simple phenols with O-benzoylhydroxylamines has been developed, which provides access to 2-aminophenols under mild conditions. Various functional groups on the phenol and electrophilic amine are compatible, and the protocol typically delivers the products in moderate to good yields. The mechanistic detail of this process are discussed. 相似文献
77.
78.
Facile synthesis of nano-TiO2/stellerite composite with efficient photocatalytic degradation of phenol 总被引:1,自引:0,他引:1
Xiaolong Hu Zhiming Sun Junying Song Guangxin Zhang Shuilin Zheng 《Advanced Powder Technology》2018,29(7):1644-1654
In this paper, we report a kind of nano-TiO2/stellerite composite with enhanced photoactivity, which was synthesized by a typical homogeneous precipitation method followed by a calcination crystallization process using natural stellerite as support. The as-prepared composites were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption-desorption, high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The results showed that TiO2 loading amounts and calcination temperatures had significant influence on the adsorption and photocatalytic degradation properties of phenol. Moreover, it was indicated that the TiO2 nanoparticles (NPs) with smaller grain size (around 12.0?nm) and narrower size distributions were uniformly deposited on the surface of stellerite as a layer of film. Compared with commercial P25, the received composite exhibited more superior photocatalytic degradation performance towards phenol. The enhanced photocatalytic degradation performance should result from the better dispersibility of TiO2 NPs and higher separation efficiency of photogenerated electron-hole pairs. This work may set foundation for the practical application of this new composite photocatalyst in the field of wastewater treatment. 相似文献
79.
The kinetics of the extraction of phenol from the aqueous phase by sulfuric acid salts of trioctylamine (TOA salts) in kerosene and the stripping of phenol from the organic phase by sodium hydroxide solution were studied using a constant interfacial area cell. Measurements of the extraction and stripping rates were made by measuring the time-dependent phenol concentrations in the aqueous phase. It is found that the extraction rate of phenol is strongly dependent on the initial concentration of phenol in the aqueous phase and on the initial concentration of TOA salts in the organic solvent. However, the effect of the total sulfate concentration and the acidic concentration on the extraction rate are not significant. The stripping rate is only a function of the initial concentration of phenol in the TOA salt-organic phase. By analyzing the experimental data, it was recognized that the extraction of phenol occurs at the interface, rather than in the bulk of the solution. The diffusion resistance, rather than the resistance of chemical reaction, is the rate-controlling step for the phenol extraction. Based on the experimental data, simple expressions of the extraction rate and stripping rate of phenol were obtained. 相似文献
80.
A multi-section method was proposed to describe the batch adsorption system under intraparticle diffusion-controlled kinetics with a nonlinear adsorption isotherm. The intraparticle diffusivity of phenol on the anion exchange resins determined by using the proposed method was compared with the values determined from D-K and modified D-K methods. It was found that the intraparticle diffusivity determined in this study was reasonable. 相似文献