Efficient Fe(III)/Fe(II) cycling triggered by MoO2 in Fenton reaction for the degradation of dye molecules and the reduction of Cr(VI)

There is a relatively low efficiency of Fe(III)/Fe(II) conversion cycle and H₂O₂ decomposition (<30%) in conventional Fenton process, which further results in a low production efficiency of OH and seriously restricts the application of Fenton. Herein, we report that the commercial MoO₂ can be used as the cocatalyst in Fenton process to dramatically accelerate the oxidation of Lissamine rhodamine B (L-RhB), where the efficiency of Fe(III)/Fe(II) cycling is greatly enhanced in the Fenton reaction meanwhile. And the L-RhB solution could be degraded nearly 100% in 1 min in the MoO₂ cocatalytic Fenton system under the optimal reaction condition, which is apparently better than that of the conventional Fenton system (～50%). Different from the conventional Fenton reaction where the OH plays an important role in the oxidation process, it shows that ¹O₂ contributes most in the MoO₂ cocatalytic Fenton reaction. However, it is found that the exposed Mo⁴⁺ active sites on the surface of MoO₂ powders can greatly promote the rate-limiting step of Fe³⁺/Fe²⁺ cycle conversion, thus minimizing the dosage of H₂O₂ (0.400 mmol/L) and Fe²⁺ (0.105 mmol/L). Interestingly, the MoO₂ cocatalytic Fenton system also exhibits a good ability for reducing Cr(VI) ions, where the reduction ability for Cr(VI) reaches almost 100% within 2 h. In short, this work shows a new discovery for MoO₂ cocatalytic advanced oxidation processes (AOPs), which devotes a lot to the practical water remediation application.     

Photoassisted degradation of dye pollutants in aqueous TiO2 dispersions under irradiation by visible light

The photoassisted degradation of two dye compounds, erythrosine and rhodamine B, has been investigated in an aqueous TiO₂ dispersion under irradiation by visible light. The compounds can be easily decomposed photochemically by visible light, which provides possibly a new approach for the treatment of dye pollutants in wastewater.     

Synthesis of mono- and binuclear dioxomolybdenum(VI) complexes derived from N(4)-substituted thiosemicarbazones: X-ray crystal structures of [(MoO2L)2], [MoO2Lpy] and [MoO2Lpy]

Four molybdenum(VI) thiosemicarbazonato complexes have been synthesized and characterized. The dinuclear complexes [(MoO₂L¹)₂] (1) and [(MoO₂L²)₂] (3) have been prepared by the reaction of [MoO₂(acac)₂] with 2-hydroxyacetophenone N(4)-cyclohexyl (H₂L¹) and N(4)-phenyl (H₂L²) thiosemicarbazones in alcoholic medium. Mononuclear dioxomolybdenum(VI) complexes of the type [MoO₂L¹py] (2) and [MoO₂L²py] (4) have been prepared by the reaction of 1 or 3 with pyridine (py) in alcoholic medium. In all the complexes, molybdenum is coordinated by two terminal oxo-oxygen atoms, (O_t), oxygen, nitrogen and sulfur atoms from the principal ligand and by an oxygen atom from the second unit in 1, and by a nitrogen atom from pyridine in complexes 2 and 4. All complexes have been spectroscopically characterized. The molecular structures of complexes 1, 2 and 4 have been determined by the single crystal X-ray diffraction method.     

Sonophotocatalytic activity of methyl orange over Fe(III)/TiO2

TiO₂ doped with Fe³⁺ was prepared by an impregnation technique and its sonophotocatalytic activity over methyl orange (MO) was investigated. The Fe/TiO₂ surface presented red shift to longer wavelength, resulting in a lower energy band gap. Fe loading of 0.1 wt% on TiO₂ provided the optimum degradation. The MO degradation rate constant under sonophotocatalytic conditions was 2.5 times higher than under photocatalytic conditions.     

Molybdenum pentachloride (MoCl5) or molybdenum dichloride dioxide (MoO2Cl2): advanced catalysts for thioacetalization of heterocyclic, aromatic and aliphatic compounds

A new, convenient and mild method for thioacetalization of heterocyclic, aromatic and aliphatic compounds catalyzed by MoCl₅ or MoO₂Cl₂ is described. This novel method is important for the synthesis of the difficult to prepare heterocyclic thioacetals such as the pterin thioacetals and it offers significant advantages such as high conversion, short reaction times and simplicity in operation.     

Synthesis of N-TiO2@NH2-MIL-88(Fe) Core-shell Structure for Efficient Fenton Effect Assisted Methylene Blue Degradation Under Visible Light

Core-shell TiO₂-based photocatalysts with specific composition, morphology, and functionality have attracted considerable attention for their excellent degradation properties on organic pollutants via a photocatalytic oxidation process. Herein, a N-TiO₂@NH₂-MIL-88(Fe) core-shell structure was prepared by coating NH₂-MIL-88(Fe) on nitrogen-doped TiO₂(N-TiO₂) nanoparticles. Introduction of heteroatom nitrogen to pure TiO₂ expands the spectral response range, leading to enhanced quantum efficiency of photocatalyst. Furthermore, loading NH₂-MIL-88(Fe) on N-TiO₂ improved the adsorption ability of the nanocomposites due to the porous tunnels of NH₂-MIL-88(Fe). The resulted core-shell N-TiO₂@NH₂-MIL-88(Fe) nanocomposites realized the transfer of photo excited electrons from N-TiO₂ to NH₂-MIL-88(Fe) rapidly, partially reduced Fe³⁺ to Fe²⁺ in NH₂-MIL-88(Fe), and further enhanced the Fenton effect on efficiently degrading methylene blue dye(MB) under visible light(λ ≥ 420 nm) with the assistance of H₂O₂.     

Direct Mannich reaction mediated by Fe(Cp)2PF6 under solvent-free conditions

Fe(Cp)₂PF₆ (5 mol %) efficiently catalyzed Mannich reaction of aldehydes, anilines, and ketones under solvent-free condition to give β-amino-ketones in high yield (up to 94%) within 30 min with anti-isomer in excess. Simple experimental conditions and product isolation procedure makes this protocol potential for the development of clean and environment-friendly strategy for the synthesis of β-amino-ketones.     

Enhanced Water Oxidation Activity on Ni,Co-Doped Fe2O3 (0001) Surface

Fe based oxides are considered as a promising catalyst for the oxygen evolution reaction (OER) due to their low cost and high stability. Here, based on density functional theory calculations, the electrocatalytic behaviors of pure and metal (Ni, Co) doped Fe-terminated Fe₂O₃(0001) are investigated. The potential-limiting step for OER is determined as the formation of O^* by dehydrogenating surface hydroxyl and it is suggested that the doping enhances the catalytic activity of Fe₂O₃(0001) by reducing the free energy change of rate limiting step on doped Ni or Co atom. Especially, the calculated over-potential of Co-doped Fe₂O₃ (0001) surface is about 0.63 eV on Co site, which is comparable with the theoretical over-potential of 0.56 eV for RuO₂.     

Zeolite-encapsulated Cr(III), Fe(III), Ni(II), Zn(II) and Bi(III) salpn complexes as catalysts for the decomposition of H2O2 and oxidation of phenol

Cr(III), Fe(III), Bi(III), Ni(II) and Zn(II) complexes of N,N′-bis(salicylidene)propane-1,3-diamine (H₂salpn) encapsulated in Y-zeolite were prepared by flexible ligand method. These complexes were characterized by chemical and thermal analyses, FT-IR and electronic spectral studies and their XRD pattern. The encapsulated materials are active catalysts for the decomposition of hydrogen peroxide and for the oxidation of phenol using H₂O₂ as oxidant with good selectivity.     

Micellar effects on photoinduced redox reactions of Fe(bpy)2(CN)2

Excitation of solutions of Fe(bipy)₂(CN)₂ by a 266-nm laser pulse produces a hydrated electron and the oxidized complex, Fe(bipy)₂ (CN)₂⁺, in the primary photochemical step, in homogeneous aqueous solution as well as in aqueous solutions containing cetyltrimethylammonium bromide (CTAB) or sodium dodecyl sulfate (SDS) micelles. In all cases nascent hydrated electrons react with ground state Fe(bipy)₂(CN)₂ to form Fe(bipy)₂(CN)₂⁻, and comparison of the decay constants in the three media (H₂O: k = 2.8 × 10¹⁰ M⁻¹ s⁻¹; CTAB: k = 2.9 × 10¹⁰ M⁻¹ s⁻¹; SDS: k = 5.5 × 10⁹ M⁻¹ s⁻¹), shows that the reaction is essentially unaffected by CTAB micelles but is much slower in SDS solution. Similar micellar effects were found for the back reaction between e_aq⁻ and Fe(bpy)₂(CN)₂⁺. Rate constants for the scavenging of the photogenerated hydrated electrons by methyl viologen (MV²⁺) cations and NO₃⁻ anions were measured in the three systems, and the results indicate that for scavenging by MV²⁺ the rate constants are decreased in the micelle systems (k in H₂O, 8.4 × 10¹⁰; CTAB, 3.5 × 10¹⁰ and SDS, 1.58 × 10¹⁰ M⁻¹ s⁻¹), whereas for NO₃⁻ the CTAB micelle decreases while the SDS micelle enhances the scavenging compared to water solution (k in H₂O, 8.3 × 10⁹; CTAB, 7 × 10⁸; and SDS, 2.05 × 10¹⁰ M⁻¹ s⁻¹). For the comproportionation reaction between Fe(bipy)₂(CN)₂⁺ and Fe(bipy)₂(CN)₂⁻ both micelles reduce the rate (k in H₂O, 3.3 × 10¹⁰; CTAB, 2.3 × 10¹⁰; and SDS, 1.05 × 10¹⁰ M⁻¹s⁻¹), but while the reaction of Fe(bipy)₂(CN)₂⁺ with MV⁺ is increased in CTAB compared to water, it is slowed in SDS (k in H₂O, 2.4 × 10¹⁰; CTAB, 8.9 × 10¹⁰; and SDS, 1.8 × 10¹⁰ M⁻¹s⁻¹). All effects observed in these microheterogeneous systems can be uniformly interpreted in terms of Coulombic interactions between the actual reactants and the charged surface of the micelles.     

Distance dependence analysis of the electron transfer reactivity for the metastable FeOH2/FeOH2 system: an ab initio investigation

A novel theoretical scheme and ab initio application in discussing the electron transfer (ET) reactivity are presented in this paper, and are also calibrated in terms of the mono-hydrated iron ion system, Fe²⁺–OH₂/Fe³⁺–OH₂. The detailed geometry optimizations have been made at UMP2(full)/6-311+G^* level, and the activation geometrical configuration and the energy have been obtained at this level of theory using the activation model and the ab initio potential energy surface fitted from MP2(full)/6-311+G^* single point energies. The corresponding energy quantities (such as the activation energy, and dissociation energy) have also been obtained at different levels of theory (HF, MP2, MP3, MP4, QCISD and PUHF, PMP2 and PMP3 with the spin-projection) and a same basis set (6-311+G^*). The electron correlation calculations include the all electron correlation and the valence electron correlation. The electronic transmission coefficient is calculated using the ab initio potential energy surface slopes and the coupling matrix element determined from the two-state model and the Slater-type d-electron wave functions. The pair distribution function is calculated using two different schemes. Taking the pair distribution function and the local ET rate into account, a statistically averaged overall observed ET rate scheme and a spherically averaged local ET rate scheme are proposed. The relevant kinetic parameters are obtained in terms of these new schemes at different ab initio calculational levels. The contact distance dependence of these parameters and the applicability of the presented models and ab initio calculational method are also discussed.     

凹凸棒黏土负载纳米TiO2-Fe3O4吸附剂的制备及Cr(Ⅵ)的脱除

采用溶胶-凝胶法、一锅反应法制备了负载纳米TiO₂和Fe₃O₄的凹凸棒黏土(TiO₂-Fe₃O₄-ATP)吸附剂,并进行了模拟废水中Cr(Ⅵ)的吸附及脱附性能的研究。 通过扫描电子显微镜(SEM)、X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)和EDS等分析方法对ATP负载纳米TiO₂-Fe₃O₄前后结构进行了表征,考察了物料配比及吸附时间、pH值、温度、投加量和初始质量浓度对Cr(Ⅵ)吸附率的影响。 结果表明,吸附剂在Ti元素含量与负载总量的摩尔比为3：4时吸附效果最佳。 当吸附剂质量为0.6 g,Cr(Ⅵ)离子初始质量浓度小于0.8 mg/L时,pH=6,温度20 ℃,吸附剂对Cr(Ⅵ)的吸附率为79.8%。 TiO₂-Fe₃O₄-ATP吸附剂对Cr(Ⅵ)离子吸附满足Freundlich模型。 在20~40 ℃ 条件下,吸附过程ΔG<0、ΔS=-43.55 J/(mol·K)、ΔH=-14.36 kJ/mol,表明该吸附是个自发、熵减、放热的过程。 吸附过程符合准二级动力学模型,吸附速率控制步骤以表面化学反应为主。 TiO₂-Fe₃O₄-ATP吸附剂在循环使用4次后,吸附率仍能达到65%以上。     

Nd3+-doped Li3V2(PO4)3 cathode material with high rate capability for Li-ion batteries

A series of Nd3+-doped Li3NdxV2àx(PO4)3(x = 0.00, 0.02, 0.05, 0.08 or 0.1) composites are synthesized by the rheological phase reaction method. The XRD results indicate that Nd3+ions have been successfully merged into a lattice structure. Doped samples show good electrochemical performance in high discharge rate and long cycle. In the potential range of 3.0–4.3 V, Li3Nd0.08V1.92(PO4)3exhibits an initial discharge capacity of 115.8 m Ah/g at 0.2 C and retain 80.86% of capacity retention at 2 C in the 51 st cycle.In addition, Li3Nd0.05V1.95(PO4)3holds at 100.4 m Ah/g after 80 cycles at 0.2 C with a capacity retention of92.4%. Finally, the CV test proves that the potential polarization of Li3Nd0.08V1.92(PO4)3decreased compared with the un-doped one.     

可见光下Fe3+掺杂对K2La2Ti3O10分解水制氢性能的影响

采用溶胶-凝胶法制备了Fe3+掺杂的Fe-K2La2Ti3O10光催化剂, 并通过X射线衍射(XRD)、紫外-可见漫反射(DRS)、X射线光电子能谱(XPS)等技术对其进行了表征和分析, 考察了不同掺杂量对K2La2Ti3O10的性质及光催化分解水制氢活性的影响. 结果表明, Fe-K2La2Ti3O10在400-650 nm范围内显示强吸收, 光谱响应扩展到可见光区(λ>400 nm), 掺杂Fe3+后, K2La2Ti3O10的可见光区的光催化制氢活性显著提高, 掺杂量为nFe/nTi=0.04时活性最佳, 当催化剂用量为0.1 g, 反应液为CH3OH(30 mL)+H2O(90 mL)时, 产氢量达到1.92 μmol·h-1, 为未掺杂时的4倍.     

Improvement of stability of a Fe/Mg/Al2O3 catalyst for the decomposition of methane in the presence of O2/CO2

The stability of an Fe/Al₂O₃ catalyst in the methane decomposition in the presence of O₂/CO₂ was found to be improved by the addition of Mg into the catalyst (Mg/Fe=1/1 wt ratio), probably due to suppression of carbon deposition even under CH₄/ O₂/CO₂ (80/10/5 vol. ratio) conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ti3+自掺杂的TiO2(A)/TiO2(R)/In2O3纳米异质结的制备与可见光催化性能

以TiCl₃和InCl₃为Ti源和In源,在不使用还原剂的条件下,首先通过液相沉淀反应制备前驱体沉淀,然后采用后续水热处理制备Ti³⁺自掺杂的TiO₂(A)/TiO₂(R)/In₂O₃纳米异质结,考察了水热处理温度对材料结构和性能的影响。利用X射线衍射、透射电子显微镜、X射线光电子能谱和紫外-可见漫反射光谱对样品进行表征。分别以罗丹明B和苯酚溶液为模拟废水评价了样品的可见光催化降解性能。结果表明,与纯的TiO₂、In₂O₃以及Ti³⁺自掺杂的TiO₂相比,Ti³⁺自掺杂的TiO₂(A)/TiO₂(R)/In₂O₃纳米异质结在可见光区有明显的吸收,并具有良好的可见光催化降解性能,200℃下水热处理24 h所得样品光催化降解罗丹明B的反应速率常数(0.0444 min^-1)分别是纯TiO₂和In₂O₃的17.76倍和8.71倍。瞬态光电流时间响应结果表明样品的光催化性能主要来源于TiO₂(A)/TiO₂(R)/In₂O₃纳米异质结导致的提高的光生电子和空穴分离效率。     

Photocatalytic efficiency of TiO2/poly[acrylamide-co-(acrylic acid)] composite for textile dye degradation

A novel photocatalytically degradable TiO₂/poly[acrylamide-co-(acrylic acid)] composite hydrogel (TiO₂/poly[AAm-co-AAc]) was synthesized by polymerization in an aqueous solution with N,N’-methylenebisacrylamide as the crosslinker and ammonium persulphate and TEMED as the initiator pair. The combined and separate effects of photodegradation and adsorption processes for dye removal were evaluated using methylene blue (MB) as the model dye for a photodegradation target, and compared with those of the neat poly[AAm-co-AAc], and a commercially available TiO₂ photocatalyst (Degussa P-25). Without photodegradation (i.e. in the dark), the TiO₂/poly[AAm-co-AAc] composite adsorbed up to 85% of the MB from a 5 mg L⁻¹ MB solution in 15 min compared to only 10% for the pristine TiO₂. The reproducibility in photodegradation of the reused poly[AAm-co-AAc] composite was also investigated, where poly[AAm-co-AAc] was found to be photocatalytically degraded under UV irradiation. Therefore, the TiO₂/poly[AAm-co-AAc] composite hydrogel is a good dye adsorber with self-photodegradability and it also can easily be separated from the reaction by simple filtration. With these properties, the TiO₂/poly[AAm-co-AAc] hydrogel can be called a green polymer for use in the photodegradation-adsorption process for the abatement of various pollutants.     

负载Fe2O3的Zr基钙钛矿催化剂对逆水煤气反应的影响

采用固相反应法制备了钙钛矿结构的BaZr_0.9Y_0.1O₃,并用BaZr_0.9Y_0.1O₃作为载体负载Fe₂O₃,通过X射线衍射分析（XRD）、扫描电子显微镜（SEM）观察负载型催化剂的晶相结构和微观形貌,同时考察了制备的催化剂的逆水煤气反应催化活性。结果表明,BaZr_0.9Y_0.1O₃粉体1200℃煅烧5h时,负载型催化剂具有较好的催化活性;BaZr_0.9Y_0.1O₃对逆水煤气反应有一定的催化作用,负载少量的Fe₂O₃催化剂可以明显促进CO₂还原,在空速为1.13h^-1,温度为650℃时,CO收率可以达到31%;催化剂经过长时间运行催化效果良好,制备的催化剂活性较稳定。     

Role of oxygen in the degradation of atrazine by UV/Fe(III) process

In this study, the role of oxygen in the regeneration of Fe(III) during the degradation of atrazine in UV/Fe(III) process was studied. The degradations of atrazine in UV/Fe(III) and UV-photolysis processes in the presence and absence of oxygen were compared. The results showed that the degradations of atrazine in these processes followed the pseudo-first-order kinetics well. The process exhibiting the highest rate constant (k) was UV/Fe(III)/air process, because k-value for UV/Fe(III)/air process was about 1.47, 2.23 and 2.56 times of those for UV/Fe(III)/N₂, UV/air and UV/N₂ processes, respectively. The degradation of atrazine was enhanced by oxygen in UV/Fe(III) process and the enhancement was more remarkable at higher initial concentrations of Fe(III). The investigation into the changes of Fe(III) concentrations demonstrated that the presence of oxygen led to the regeneration of Fe(III), which resulted in the enhancement of atrazine degradation. With air bubbling, the ferric ions were 25% more than those with N₂ bubbling. The experimental data showed the regeneration of Fe(III) required the excited organic molecules and oxygen and on the basis of these results, the regeneration mechanism of Fe(III) was proposed. It was also found that due to the oxidation of Fe(II), the degradation of atrazine in UV/Fe(II)/air process was effective at a low Fe(II) concentration of 7 mg/L, similar to that in UV/Fe(III)/air process. This study makes clear the role of oxygen in the regeneration of Fe(III), and thus it provides a guide to reduce the input of Fe(III) and is helpful to the application of UV/Fe(III) process in practice.     

Cr2(WO4)3和Cr2(MoO4)3的负热膨胀特性研究

用液相反应-前驱物烧结法制备了Cr₂(WO₄)₃和Cr₂(MoO₄)₃粉体。298～1 073 K的原位粉末X射线衍射数据表明Cr₂(WO₄)₃和Cr₂(MoO₄)₃的晶胞体积随温度的升高而增大, 本征线热膨胀系数分别为(1.274±0.003)×10^-6 K^-1和(1.612±0.003)×10^-6 K^-1。用热膨胀仪研究了Cr₂(WO₄)₃和Cr₂(MoO₄)₃在静态空气中298～1 073 K范围内热膨胀行为，即开始表现为正热膨胀，随后在相转变点达到最大值，最后表现为负热膨胀，其负热膨胀系数分别为(-7.033±0.014)×10^-6 K^-1和(-9.282±0.019)×10^-6 K^-1。