Effect of CeO2 doping on catalytic activity of Fe2O3/gamma-Al2O(3) catalyst for catalytic wet peroxide oxidation of azo dyes

In order to find a catalyst with high activity and stability for catalytic wet peroxide oxidation (CWPO) process under normal condition, with Fe(2)O(3)/gamma-Al(2)O(3) and Fe(2)O(3)-CeO(2)/gamma-Al(2)O(3) catalysts prepared by impregnation method, the effect of CeO(2) doping on the structure and catalytic activity of Fe(2)O(3)/gamma-Al(2)O(3) for catalytic wet peroxide oxidation of azo dyes at 25 degrees C and atmospheric pressure is evaluated using BET, SEM, XRF, XRD, XPS and chemical analysis techniques, and test results show that, better dispersion and smaller size of Fe(2)O(3) crystal can be achieved by adding CeO(2), and the content of chemisorbed oxygen can also be increased on the surface of catalyst. CWPO experimental results indicate that azo dyes in simulated wastewater can be efficiently mineralized and the catalytic activity of Fe(2)O(3)-CeO(2)/gamma-Al(2)O(3) can be increased by about 10% compared with that of Fe(2)O(3)/gamma-Al(2)O(3) because of the promotion of the structural and redox properties of the ferric oxide by ceria doped. Leaching tests indicate that Fe(2)O(3)/gamma-Al(2)O(3) and Fe(2)O(3)-CeO(2)/gamma-Al(2)O(3) are stable with a negligible amount of irons found in the aqueous solution after reaction for 2h. It can therefore be concluded from results and discussion that in comparison with Fe(2)O(3)/gamma-Al(2)O(3), Fe(2)O(3)-CeO(2)/gamma-Al(2)O(3) is a suitable catalyst, which can effectively degrade contaminants at normal temperature and atmospheric pressure.     

Humic acid coated Fe3O4 magnetic nanoparticles as highly efficient Fenton-like catalyst for complete mineralization of sulfathiazole

Humic acid coated Fe(3)O(4) magnetic nanoparticles (Fe(3)O(4)/HA) were prepared for the removal of sulfathiazole from aqueous media. Fe(3)O(4)/HA exhibited high activity to produce hydroxyl (OH) radicals through catalytic decomposition of H(2)O(2). The degradation of sulfathiazole was strongly temperature-dependent and favored in acidic solution. The catalytic rate was increased with Fe(3)O(4)/HA dosage and H(2)O(2) concentration. When 3 g L(-1) of Fe(3)O(4)/HA and 0.39 M of H(2)O(2) were introduced to the aqueous solution, most sulfathiazole was degraded within 1h, and >90% of total organic carbon (TOC) were removed in the reaction period (6h). The major final products were identified as environmentally friendly ions or inorganic molecules (SO(4)(2-), CO(2), and N(2)). The corresponding degradation rate (k) of sulfathiazole and TOC was 0.034 and 0.0048 min(-1), respectively. However, when 3 g L(-1) of bare Fe(3)O(4) were used as catalyst, only 54% of TOC was eliminated, and SO(4)(2-) was not detected within 6h. The corresponding degradation rate for sulfathiazole and TOC was 0.01 and 0.0016 min(-1), respectively. The high catalytic ability of Fe(3)O(4)/HA may be caused by the electron transfer among the complexed Fe(II)-HA or Fe(III)-HA, leading to rapid regeneration of Fe(II) species and production of OH radicals.     

Kinetics of Fe(3)O(4)-CoO/Al(2)O(3) catalytic ozonation of the herbicide 2-(2,4-dichlorophenoxy) propionic acid

The presence of Fe(3)O(4)-CoO/Al(2)O(3) can improve degradation efficiency significantly during the ozonation of the herbicide 2-(2,4-dichlorophenoxy) propionic acid (2,4-DP). The main factors affecting degradation efficiency, such as pH, the catalyst concentration and addition of the scavenger, were investigated. The kinetics of the catalytic ozonation are also discussed. The results indicate that two factors, the oxidation after adsorption of 2,4-DP and the oxidation of hydroxyl radicals (OH), lead to a great enhancement in ozonation efficiency during the catalytic ozonation of 2,4-DP in the presence of Fe(3)O(4)-CoO/Al(2)O(3), in which the oxidation of the OH plays an important role. Under controlled conditions, the apparent reaction rate constants for the degradation of 2,4-DP were determined to be 2.567 × 10(-4)s(-1) for O(3) and 1.840 × 10(-3)s(-1) for O(3)/Fe(3)O(4)-CoO/Al(2)O(3). The results from the analysis of the reaction kinetics using the relative method showed that O(3)/Fe(3)O(4)-CoO/Al(2)O(3) possessed a larger R(ct) (R(ct) is defined as the ratio of the ·OH exposure to the O(3) exposure, R(ct) = ∫C(t)(OH) dt/C(t)O(3)dt) than O(3), indicating that O(3)/Fe(3)O(4)-CoO/Al(2)O(3) produced more hydroxyl radicals.     

Novel active heterogeneous Fenton system based on Fe3-xMxO4 (Fe, Co, Mn, Ni): the role of M2+ species on the reactivity towards H2O2 reactions

In this work, the effect of incorporation of M2+ species, i.e. Co2+, Mn2+ and Ni2+, into the magnetite structure to increase the reactivity towards H2O2 reactions was investigated. The following magnetites Fe3-xMnxO4, Fe3-xCoxO4 and Fe3-xNixO4 and the iron oxides Fe3O4, gamma-Fe2O3 and alpha-Fe2O3 were prepared and characterized by M?ssbauer spectroscopy, XRD, BET surface area, magnetization and chemical analyses. The obtained results showed that the M2+ species at the octahedral site in the magnetite strongly affects the reactivity towards H2O2, i.e. (i) the peroxide decomposition to O2 and (ii) the oxidation of organic molecules, such as the dye methylene blue and chlorobenzene in aqueous medium. Experiments with maghemite, gamma-Fe2O3 and hematite, alpha-Fe2O3, showed very low activities compared to Fe3O4, suggesting that the presence of Fe2+ in the oxide plays an important role for the activation of H2O2. The presence of Co or Mn in the magnetite structure produced a remarkable increase in the reactivity, whereas Ni inhibited the H2O2 reactions. The obtained results suggest a surface initiated reaction involving Msurf2+ (Fe, Co or Mn), producing HO radicals, which can lead to two competitive reactions, i.e. the decomposition of H2O2 or the oxidation of organics present in the aqueous medium. The unique effect of Co and Mn is discussed in terms of the thermodynamically favorable Cosurf3+ and Mnsurf3+ reduction by Femagnetite2+ regenerating the active species M2+.     

Constructing carbon-coated Fe₃O₄ microspheres as antiacid and magnetic support for palladium nanoparticles for catalytic applications

Fe?O? microsphere is a good candidate as support for catalyst because of its unique magnetic property and large surface area. Coating Fe?O? microspheres with other materials can protect them from being dissolved in acid solution or add functional groups on their surface to adsorb catalyst. In this paper, a carbon layer was coated onto Fe?O? microspheres by hydrothermal treatment using polyethylene glycol as the connecting agents between glucose and Fe?O? spheres. Through tuning the added amounts of reactants, the thickness of the carbon layer could be well-controlled. Because of the abundant reductive groups on the surface of carbon layer, noble metal ions could be easily adsorbed and in situ reduced to nanoparticles (6-12 nm). The prepared catalyst not only had unique antiacid and magnetic properties, but also exhibited a higher catalytic activity toward the reduction of methyl orange than commercially used Pd/C catalyst.     

A novel nanoscale catalyst system composed of nanosized Pd catalysts immobilized on Fe(3)O(4)@SiO(2)-PAMAM

This study reports the syntheses of Fe(3)O(4)@SiO(2)-Gn-PAMAM-Pd(0) composites and their applications as magnetically recoverable catalysts for the hydrogenation of allyl alcohol. The controlled growth of polyamidoamine (PAMAM) dendrimers with different generations on Fe(3)O(4)@SiO(2) surfaces was monitored by FT-IR spectra. Subsequently, Pd nanoparticles with diameters of about 2.5?nm were stabilized homogeneously on the surface of Fe(3)O(4)@SiO(2)-Gn-PAMAM (n = 1-4), investigated by thermogravimetry (TG) and transmission electron microscopy (TEM) measurements. The?Fe(3)O(4)@SiO(2)-Gn-PAMAM-Pd(0) have high catalytic activity for the hydrogenation of allyl alcohol and the rate of the reaction can be controlled by changing the generation of PAMAM. In particular, the composites made of superparamagnetic Fe(3)O(4) nanocrystals with diameters of about 10?nm are very suitable as catalyst supports for catalyst separation under a relatively low external magnetic field and catalyst re-dispersion after removing the external magnetic field.     

Photodegradation mechanism and kinetics of methyl orange catalyzed by Fe(III) and citric acid

In this study, the photodegradation process of methyl orange (MO) catalyzed by Fe(III) and citric acid and the reaction kinetics were investigated in detail at pHs from 2 to 8. The results show that the photodegradation of MO is slow in the presence of Fe(III) or citric acid alone. However, it is markedly enhanced when Fe(III) and citric acid coexist. High initial citric acid or initial Fe(III) concentrations lead to increased photodegradation of MO. And Fe(III) citrate mediated photodegradation of MO is optimized at pH 6. The photoproduction of hydroxyl radicals (·OH) in different catalytic systems was determined by HPLC. And the concentrations of Fe(II) and citric acid concentration in the process of the reaction were analyzed. The photodegradation of MO obeys to pseudo-zero order kinetics with respect to MO and the degradation reaction occurs in two phases. At the initial initiation stage, degradation rate is relatively slow, and significantly increases at a later acceleration stage.     

In situ modifying of carbon tube-in-tube nanostructures with highly active Fe(2)O(3) nanoparticles

A novel in situ method based on a liquid membrane templated self-assembly process is employed to modify carbon tube-in-tube nanostructures (TTCNTs) with Fe(2)O(3) nanoparticles. The as-obtained Fe(2)O(3) modified TTCNTs (Fe(2)O(3)/TTCNTs) nanocomposites are well constructed and the Fe(2)O(3) nanoparticles are well dispersed and decorated on the outer, inner and intramolecular surfaces of TTCNTs. In addition, the Fe(2)O(3)/TTCNTs nanocomposites are employed as catalysts for selective catalytic reduction (SCR) of NO with NH(3) and show high SCR catalytic activity, indicating that the novel multiple intramolecular channels and unique surface chemistry of the TTCNTs should play an important role in improving the properties of?TTCNTs.     

Preparation and characterization of magnetically separable photocatalyst (TiO2/SiO2/Fe3O4): effect of carbon coating and calcination temperature

TiO2/SiO2/Fe3O4 composite was synthesized by sol-gel technique for silica and titania coatings on magnetite core to enable recovery after photocatalytic degradation. Carbon coating was also carried out by calcination of TiO2/SiO2/Fe3O4 under nitrogen atmosphere in presence of PVA as a source of carbon to enhance the adsorption of organic compounds on catalyst surface and to get better activity. All prepared samples were characterized using EDX, CN analyzer, XRD, BET and SEM. Degradation of methyl orange dye was used to assess the photocatalytic performance of the prepared samples. Calcination temperature was found to affect rate of reaction because of the formation of rutile phase at high calcination temperature. Carbon coated samples unexpectedly exhibited lower rate of reaction at almost all calcination temperatures.     

Magnetic SiO(2)/Fe(3)O(4) colloidal crystals

We proposed a novel technique to fabricate colloidal crystals by using monodisperse SiO(2) coated magnetic Fe(3)O(4)(SiO(2)/Fe(3)O(4)) microspheres. The magnetic SiO(2)/Fe(3)O(4) microspheres with a diameter of 700?nm were synthesized in the basic condition with ferric sulfate, ferrous sulfate, tartaric acid and tetraethyl orthosilicate (TEOS) in the reaction system. Monodisperse SiO(2)/Fe(3)O(4) superparamagnetic microspheres have been successfully used to fabricate colloidal crystals under the existing magnetic field.     

Bonding MnO2/Fe3O4 shell-core nanostructures to catalyze H2O2 degrading organic dyes

Shell-core nanostructures with both high catalytic activation and recyclability have been becoming hot property in nano-catalysis. By respectively using co-precipitation method, sol-gel method, and homogeneous precipitation method we manufactured shell-core nano-particles of Fe3O4 core and MnO2 shell. The Bonding mechanism of the composite is discussed in detail, and the efficiency and nature of the particles to degrade methyl orange by catalyzing H2O2 is also demonstrated. We show that by using homogeneous precipitation method one can obtain morphologically uniform nano-particles of about 5-6 nm MnO2 shell and 13-14 nm Fe3O4 core. The characteristic peak of Fe3O4 in the Infrared spectra of the composite particles was blue shifted, and a novel peak appears at 775.68 cm(-1) referring to occurrence of new bond. X-ray Photoelectron Spectroscopy analysis showed that the bonding energy of Fe2p and Ols was increased due to the combination of the MnO2 shell and the Fe3O4 core, suggesting a new bond of Fe-O-Mn occurred in the composite. The MnO2 shell has abundant hydroxyl radicals and exhibits high chemical activity in catalyzing H2O2 and degrading methyl orange with a degree of greater than 95%. On the other hand, the shell-core nanostructures are super-paramagnetic, and the saturated magnetization reaches 33.5 eum/g, which is sufficient for the catalyst to be recycled.     

Oxidation and isomerization of cyclohexane catalyzed by SO42-/Fe2O3-CoO under mild condition

SO(4)(2-)/Fe(2)O(3)-CoO solid catalyst was prepared and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transfer infrared (FT-IR) spectroscopy. Its catalytic activities in oxidation and isomerization of cyclohexane in air under mild condition were studied by UV, GC/MS and XPS. The results suggested that isomerization and oxidation of cyclohexane under mild conditions can synchronously performed and the catalytic activity of the catalyst can be improved by promotion of Co element into the sulfated iron. The high catalytic activities of catalysts may be related to the shift of the asymmetric stretching frequency of the SO bonds of sulfate species. Finally, the possible mechanism was also proposed.     

Heterogeneous Fenton-like discoloration of methyl orange using Fe3O4/MWCNTs as catalyst: process optimization by response surface methodology

Fe₃O₄/MWCNTs nanocomposites were prepared by chemical oxidation coprecipitation method and developed as highly efficient heterogeneous Fenton-like catalyst. XRD results revealed that Fe₃O₄ nanoparticles deposited onto MWCNTs surface remained the inverse spinel crystal structure of cubic Fe₃O₄ phase. The FTIR characteristic peaks of MWCNTs weakened or disappeared due to the anchor of Fe₃O₄ nanoparticles and Fe–O peak at 570 cm^–1 was indicative of the formation of Fe₃O₄. TEM observation revealed that Fe₃O₄ nanoparticles were tightly anchored by MWCNTs. The Fenton-like catalytic activity of Fe₃O₄/MWCNTs nanocomposites for the discoloration of methyl orange (MO) was much higher than that of Fe₃O₄ nanoparticles. The process optimization of this heterogeneous Fenton-like system was implemented by response surface methodology (RSM). The optimum conditions for MO discoloration were determined to be of 12.3 mmol/L H₂O₂ concentration, 2.9 g/L catalyst dosage, solution pH 2.7 and 39.3 min reaction time, with the maximum predicted value for MO discoloration ratio of 101.85%. The corresponding experimental value under the identical conditions was obtained as 99.86%, which was very close to the predicted one with the absolute deviation of 1.99%.     

Mn、Fe和Cu氧化物在低温等离子体催化氧化甲苯体系中的活性比较

采用等体积浸渍法制备了MnOx/γ-Al2O3、FeOx/γ-Al2O3和CuOx/γ-Al2O3催化剂,测定了不同催化剂在低温等离子体场内分解甲苯的活性,用X射线衍射(XRD)、氢气程序升温还原(H2-TPR)技术对催化剂进行表征。结果表明催化剂分解甲苯的活性的顺序是MnOx/γ-Al2O3>FeOx/γ-Al2O3>CuOx/γ-Al2O3。催化剂分解臭氧的实验表明,不同催化活性组分对臭氧的催化分解性能顺序与对甲苯的分解性能顺序是一致的。MnOx/γ-Al2O3催化剂的Mn负载量对其催化活性有明显影响,Mn的含量为1%(质量分数)时,催化剂的活性最高,当能量密度为19J/L时,其对甲苯催化氧化的转化率接近100%。催化剂表征结果表明当Mn含量为1%(质量分数)时,氧化锰在载体γ-Al2O3上最接近单层分散量,此时活性组分与载体表面的相互结合力最强,在载体上有很好的分散性,从而表现出对甲苯分解的最好性能。     

玻璃微珠-Cu/Cu_2O复合镀层的制备及其光催化降解甲基橙的研究

采用化学镀铜和水热氧化法制备了玻璃微珠-Cu/Cu2O复合镀层,采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)等方法对样品结构和形貌进行了分析和表征,在日光灯照射下降解一定浓度的甲基橙溶液,研究其对甲基橙溶液的降解效果。研究了催化剂用量、pH值和甲基橙初始浓度对甲基橙降解率的影响以及催化剂在重复使用中的稳定性。     

Synthesis of N-doped nano TiO2 using guanidine nitrate: an excellent visible light photocatalyst

An excellent visible light active nitrogen-rich TiO2 nanocatalyst has been synthesized by using guanidine nitrate as the nitrogen source. The catalytic efficiency of the catalyst has been demonstrated by the decomposition of the dye, methyl orange (MO), and the pollutant, 2,4 dichlorophenol (DCP), under common household lightbulbs as well as sunlight. The reactions proceed faster on exposure to solar light (less than 1 h for MO and 4 h for DCP) compared with the commercial light bulbs (3 h for MO and 6 h for DCP). The catalyst could be used up to five times without loss of activity and regenerated for further use just by washing and drying at 200 degrees C.     

Possible weak ferromagnetism in pure and M (Mn, Cu, Co, Fe and Tb) doped NiGa2O4 nanoparticles

We report on the structural and magnetic properties of nanoparticles of NiGa2O4 and 5 at.% M doped (M = Mn2+, Cu2+, Co2+, Fe3+ and Tb3+) at Ga site of NiGa2O4, synthesized by gel-combustion method. The particle size, as investigated by X-ray diffraction and transmission electron microscopy, could be fine tuned by a controlled annealing process. Weak ferromagnetism becomes significant, when the particles are in the nano regime (5-7 nm). The magnetization becomes insignificant at larger particle size ( 150 nm). Cu2+ and Tb3+ doped NiGa2O4 nanoparticles showed relatively large room temperature ferromagnetism compared to other doped (Fe, Mn and Co) and undoped NiGa2O4 samples. The weak ferromagnetism observed in the nanoparticles of NiGa2O4, which is antiferromagnetic in the bulk, is due to the surface disordered states with uncompensated spins.     

Simple and effective synthesis of methoxy-dimethylbenzene from electrochemical oxidation of p-xylene in methanol solvent catalyzed by SO(4)(2-)/ZrO(2)-M(x)O(y)

A series of composite solid superacid catalysts SO(4)(2-)/ZrO(2)-M(x)O(y) (M=Ti, Ni, Si) were prepared and investigated by means of Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). All catalysts exhibit good catalytic activity in the electrochemical reaction of p-xylene with methanol assisted with a pair of porous graphite plane electrodes and the selectivity of main products higher than 90% were observed. In particular, SO(4)(2-)/ZrO(2)-SiO(2) catalyst exhibited excellent catalytic activity. According to the experimental results, a possible free radical reaction mechanism confirmed by XPS and ultraviolet-visible (UV-vis) spectra was proposed. It may be concluded that a simple and feasible electrochemical catalytic oxidation reaction at room temperature and standard atmosphere may be possible.     

磁性La3+掺杂TiO2的制备及性能

利用溶胶-凝胶法,在室温条件下,以钛酸四丁酯、硝酸镧为主要原料,无水乙醇为溶剂,冰醋酸为抑制剂,浓硝酸为催化剂制得稳定的掺La3+TiO2溶胶,陈化后的凝胶经不同温度煅烧3h后制得不同掺La3+量的TiO2。通过XRD对不同煅烧温度及不同掺La3+量的TiO2进行了表征;以紫外光为光源,研究了掺La3+-TiO2对甲基橙溶液的光降解效果。用化学共沉淀法制备了具有强磁性的Fe3O4水基磁流体,再与La3+掺杂TiO2进行复合,制备了Fe3O4负载量不同的磁性La3+掺杂TiO2,研究了Fe3O4负载量不同的La3+掺杂TiO2对甲基橙的光催化降解效果、磁分离回收率的影响。结果表明,掺La3+量及煅烧温度对TiO2的晶型、各晶型TiO2的相对含量及对甲基橙的光降解效果均有影响。La3+掺杂TiO2比纯TiO2显示出更强的光催化性能,掺La3+量2%,热处理温度450℃的La3+掺杂TiO2光催化活性最高。Fe3O4负载量为10%的Fe3O4/La3+-TiO2对甲基橙的降解率8h时为99.4%;磁分离回收率达97.39%。     

碳纳米管负载Fe2O3催化剂的制备及其乙苯脱氢催化活性

采用FeSO4-H2O2体系对碳纳米管氧化修饰的同时,氢氧化铁被吸附在碳纳米管管壁上,然后分别通过氢气、氮气、空气在723K下处理2h,制备了碳纳米管负载的γ-Fe2O3催化剂、γ-Fe2O3和α-Fe2O3复合催化剂和非晶态Fe2O3催化剂。采用XRD、TEM和TG-DSC表征了催化剂结构,采用连续流动乙苯气相脱氢生成苯乙烯反应对催化剂性能进行评价,结果表明：热处理条件对催化剂乙苯脱氢的催化性能影响明显,碳纳米管负载的晶态Fe2O3纳米催化剂对乙苯脱氢具有高的活性与选择性。