Novel hierarchical yolk-shell α-Ni(OH)2/Mn2O3 microspheres as high specific capacitance electrode materials for supercapacitors

For high performance supercapacitors, novel hierarchical yolk-shell a-Ni(OH)₂/Mn₂O₃ microspheres were controllably synthesized using a facile two-step method based on the solvothermal treatment. The unique a-Ni(OH)₂ based yolk-shell microstructures decorated with numerous interconnected nanosheets and the hetero-composition features can synergistically enhance reactive site exposure and electron conduction within the microspheres, facilitate charge transfer between electrolyte and electrode materials, and release structural stress during OH⁻ chemisorption/desorption. Moreover, the Mn₂O₃ sediments distributed over the a-Ni(OH)₂ microspheres can serve as an effective protective layer for electrochemical reactions. Consequently, when tested in 1 mol·L⁻¹ KOH aqueous electrolyte for supercapacitors, the yolk-shell a-Ni(OH)₂/Mn₂O₃ microspheres exhibited a considerably high specific capacitance of 2228.6 F·g⁻¹ at 1 A·g⁻¹ and an impressive capacitance retention of 77.7% after 3000 cycles at 10 A·g⁻¹. The proposed a-Ni(OH)₂/Mn₂O₃ microspheres with hetero-composition and unique hierarchical yolk-shell microstructures are highly promising to be used as electrode materials in supercapacitors and other energy storage devices.     

Ag-Zn_3(VO_4)_2光催化剂催化降解甲基橙溶液

采用水热法结合高温热处理制备Ag-Zn_3(VO_4)_2光催化剂,研究催化剂在可见光下降解甲基橙溶液的性能,并考察催化剂用量、甲基橙溶液初始浓度、pH值、盐效应和H_2O_2用量对光催化性能的影响,评价Ag-Zn_3(VO_4)_2光催化剂的重复使用性能。结果表明,在催化剂用量2.0 g·L~(-1)、甲基橙溶液初始浓度20 mg·L~(-1)和溶液pH=6.2条件下光照反应5 h,甲基橙溶液脱色率可达99.18%,Na_2SO_4对光催化降解甲基橙起抑制作用,且随着溶液中盐浓度增加,抑制作用更明显。H_2O_2在一定浓度范围可促进光催化降解甲基橙,100 mL甲基橙溶液中30%H_2O_2加入量为1.0 mL时,甲基橙溶液脱色率可提高21.68个百分点。催化剂重复使用5次后,光照5 h的甲基橙溶液脱色率仍可达到75.99%。     

加热时间对Co_3O_4颗粒光催化性能的影响

以Co(NO_3)_2·6H_2O和CO(NH_2)_2为原料,十六烷基三甲基溴化铵为活性剂,采用水热-热分解法在不同加热时间(2 h、3 h、4 h、5 h)条件下制备纯相尖晶石结构的Co_3O_4颗粒。利用X射线衍射和电子扫描电镜研究Co_3O_4颗粒的结构和形貌,并以甲基橙为模拟废水,研究加热时间对Co_3O_4颗粒光催化性能的影响。结果表明,加热时间对Co_3O_4颗粒形貌影响很大,并直接影响其光催化性能。加热时间5 h制备的Co_3O_4结构疏松多孔,光催化性能最好,光照20 min,甲基橙降解率达95%。     

Lean reduction of NO by C3H6 over Ag/alumina derived from Al2O3, AlOOH and Al(OH)3

The effectiveness of Ag/Al₂O₃ catalyst depends greatly on the alumina source used for preparation. A series of alumina-supported catalysts derived from AlOOH, Al₂O₃, and Al(OH)₃ was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible (UV–vis) spectroscopy, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, O₂, NO + O₂-temperature programmed desorption (TPD), H₂-temperature programmed reduction (TPR), thermal gravimetric analysis (TGA) and activity test, with a focus on the correlation between their redox properties and catalytic behavior towards C₃H₆-selective catalytic reduction (SCR) of NO reaction. The best SCR activity along with a moderated C₃H₆ conversion was achieved over Ag/Al₂O₃ (I) employing AlOOH source. The high density of Ag–O–Al species in Ag/Al₂O₃ (I) is deemed to be crucial for NO selective reduction into N₂. By contrast, a high C₃H₆ conversion simultaneously with a moderate N₂ yield was observed over Ag/Al₂O₃ (II) prepared from a γ-Al₂O₃ source. The larger particles of Ag_mO (m > 2) crystallites were believed to facilitate the propene oxidation therefore leading to a scarcity of reductant for SCR of NO. An amorphous Ag/Al₂O₃ (III) was obtained via employing a Al(OH)₃ source and 500 °C calcination exhibiting a poor SCR performance similar to that for Ag-free Al₂O₃ (I). A subsequent calcination of Ag/Al₂O₃ (III) at 800 °C led to the generation of Ag/Al₂O₃ (IV) catalyst yielding a significant enhancement in both N₂ yield and C₃H₆ conversion, which was attributed to the appearance of γ-phase structure and an increase in surface area. Further thermo treatment at 950 °C for the preparation of Ag/Al₂O₃ (V) accelerated the sintering of Ag clusters resulting in a severe unselective combustion, which competes with SCR of NO reaction. In view of the transient studies, the redox properties of the prepared catalysts were investigated showing an oxidation capability of Ag/Al₂O₃ (II and V) > Ag/Al₂O₃ (IV) > Ag/Al₂O₃ (I) > Ag/Al₂O₃ (III) and Al₂O₃ (I). The formation of nitrate species is an important step for the deNO_x process, which can be promoted by increasing O₂ feed concentration as evidenced by NO + O₂-TPD study for Ag/Al₂O₃ (I), achieving a better catalytic performance.     

Hydrothermal transformation of the calcium aluminum oxide hydrates CaAl2O4·10H2O and Ca2Al2O5·8H2O to Ca3Al2(OH)12 investigated by in situ synchrotron X-ray powder diffraction

The hydrothermal transformation of calcium aluminate hydrates were investigated by in situ synchrotron X-ray powder diffraction in the temperature range 25 to 170 °C. This technique allowed the study of the detailed reaction mechanism and identification of intermediate phases. The material CaAl₂O₄·10H₂O converted to Ca₃Al₂(OH)₁₂ and amorphous aluminum hydroxide. Ca₂Al₂O₅·8H₂O transformed via the intermediate phase Ca₄Al₂O₇·13H₂O to Ca₃Al₂(OH)₁₂ and gibbsite, Al(OH)₃. The phase Ca₄Al₂O₇·19H₂O reacted via the same intermediate phase to Ca₃Al₂(OH)₁₂ and mainly amorphous aluminum hydroxide. The powder pattern of the intermediate phase is reported.     

Sintering behavior and mechanical properties of nano-sized Cr3C2/Al2O3 composites prepared by MOCVI process

A process using metal-organic chemical vapor infiltration (MOCVI) conducted in fluidized bed was employed for the preparation of nano-sized ceramic composites. The Cr-species was infiltrated into Al₂O₃ granules by the pyrolysis of chromium carbonyl (Cr(CO)₆) at 300–450 °C. The granulated powder was pressureless sintered or hot-pressed to achieve high density. The results showed that the dominant factors influencing the Cr-carbide phases formation, either Cr₃C₂ or Cr₇C₃, in the composite powders during the sintering process were the temperature and oxygen partial pressure in the furnace. The coated Cr-phase either in agglomerated or dispersive condition was controlled by the use of colloidal dispersion. The microstructures showed that fine (20 –600 nm) Cr_xC_y grains (≤8 vol.%) located at Al₂O₃ grain boundaries hardly retarded the densification of Al₂O₃ matrix in sintering process. The tests on hardness, strength and toughness appeared that the composites with the inclusions (Cr₃C₂) had gained the advantages over those by the rule of mixture. Even 8 vol.% ultrafine inclusions have greatly improved the mechanical properties. The strengthening and toughening mechanisms of the composites were due to grain-size reduction, homogenous dispersion of hard inclusions, and crack deflection.     

Synthesis and H2 uptake of Cu2(OH)3Cl, Cu(OH)2 and CuO nanocrystal aggregate

Monodispersed Cu₂(OH)₃Cl nanoplatelets, Cu(OH)₂ nanowires, CuO nanoparticles and nanoribbons with a spherical morphology were synthesized using hydrothermal and heat-treatment reactions, and their H₂ storage characteristics were examined. The Cu₂(OH)₃Cl nanoplatelets particles formed immediately after mixing the reactant, which subsequently formed larger uniform spherical particles in the submicron range. This procedure highlights a practical strategy for producing spherical Cu(OH)₂ and CuO materials consisting of monodispersed nanocrystals. The spherical aggregates of Cu₂(OH)₃Cl nanoplatelets heat-treated at 473 K could reversibly store up to 2.35 wt.% H₂ at 38 bar and 293 K.     

Electrochemical performance of nanocrystalline Li3V2(PO4)3/carbon composite material synthesized by a novel sol–gel method

A novel sol–gel method based on V₂O₅·nH₂O hydro-gel was developed to synthesize nanocrystalline Li₃V₂(PO₄)₃/carbon composite material. In this route, V₂O₅·nH₂O hydro-gel, NH₄H₂PO₄, Li₂CO₃ and high-surface-area carbon were used as starting materials to prepare precursor, and the Li₃V₂(PO₄)₃/carbon was obtained by sintering precursor at 750 °C for 4 h in flowing argon. The sol–gel synthesis ensures homogeneity of the precursors and improved reactivity. The sample was characterized by XRD, SEM and TEM. X-ray diffraction results show Li₃V₂(PO₄)₃ sample is monoclinic structure with the space group of P2₁/n. The TEM image indicates that the Li₃V₂(PO₄)₃ particles modified by conductive carbon are about 70 nm in diameter. The Li₃V₂(PO₄)₃/carbon system showed that the discharge capacities in the first and 50th cycle are about 155.3 and 143.6 mAh/g, respectively, in the range of 3.0–4.8 V. The sol–gel method is fit for the preparation of Li₃V₂(PO₄)₃/carbon composite material which may offer some favorable properties for commercial application.     

AgBr/Zn3(OH)2V2O7·2H2O可见光催化降解亚甲基蓝溶液

采用水热和沉淀两步合成法制备AgBr/Zn₃(OH)₂V₂O₇·2H₂O催化剂,研究其在可见光下降解亚甲基蓝溶液的性能,并考察催化剂用量、亚甲基蓝溶液初始浓度、pH值以及盐浓度对光催化性能的影响,评价AgBr/Zn₃(OH)₂V₂O₇·2H₂O催化剂的重复使用性能。结果表明,在前驱液pH为10、120 ℃水热10 h、Ag与Br物质的量比为0.20条件下制备的复合催化剂在可见光下反应120 min后,1.0 g·L^-1的催化剂对10 mg·L^-1的亚甲基蓝溶液脱色率达到85.2%。NaCl对亚甲基蓝的降解起抑制作用,Na₂SO₄对亚甲基蓝的降解起促进作用。催化剂重复使用4次后,光照120 min后的亚甲基蓝溶液脱色率可达66.4%。催化剂对不同初始浓度亚甲基蓝溶液的光催化降解符合一级动力学模型。     

Exchange and oxidation of CO on O-predosed Rh---Al2O3 and Rh---CeO2 catalysts

Exchange and oxidation of C¹⁶O were investigated at 450°C on ¹⁸O-predosed Rh and Pt catalysts supported on A1₂O₃, CeO₂ and CeO₂-Al₂O₃. In all cases, a rapid exchange of C¹⁶O with the surface can be observed. CO oxidation leads to C¹⁶O₂, C¹⁶O¹⁸O and C¹⁸O₂. Significant formation of C¹⁶O₂ is due to the relatively high ¹⁶O coverage in reaction resulting from the C¹⁶O exchange and from an exchange between O surface species and ¹⁶O internal atoms. Hydrogen is also formed via a water-gas shift reaction (CO + surface OH) in higher proportion on CeO₂-containing catalysts than on A1₂O₃. Chlorine inhibits all the reactions (exchange, oxidation and WGS) and particularly the internal exchange.     

Ni(OH)2修饰对a-Fe2O3薄膜光电化学性能的增强效应

利用一种简便的电沉积方法制备氧化铁薄膜,并在过程中引入Ni(OH)₂进行修饰,对具体电沉积实验参数进行优化,从而建立最佳制备条件。利用场发射扫描电子显微镜、X射线粉末衍射对Fe₂O₃/Ni(OH)₂光电极膜的结构进行表征。利用循环伏安和计时电流测量析氧过电位和光电流密度。结果表明,Ni(OH)₂修饰的α-Fe₂O₃薄膜可提高光生电子与空穴的分离效率,从而显著提高光电催化活性。     

In-situ growth of needlelike LaAl11O18 for reinforcement of alumina composites

In situ growth of needlelike LaAl₁₁O₁₈ grains reinforcing Al₂O₃ composites can be fabricated by a coprecipitation method using La(NO₃)₃√6H₂O and Al(NO₃)₃√9H₂O as starting materials. The new two-step process involved firstly preparing needlelike LaAl₁₁O₁₈ grains distributed homogeneously in Al₂O₃ powder and then pressureless sintering the composite powders. The Al₂O₃/25 vol.%LaAl₁₁O₁₈ samples pressureless sintered at 1550°C for 4 h achieve relative density up to 96.5% and exhibit a bending strength of 420±30 MPa and a fracture toughness of 4.3±0.4 MPa m^1/2.     

Iminium cations as intermediates in the hydrodenitrogenation of alkylamines over sulfided NiMo/γ-Al2O3

The mechanism of the hydrodenitrogenation of the mixed dialkyl- and trialkylamines C₁NHC₆ and C₁N(C₆)₂ was studied over sulfided NiMo/γ-Al₂O₃ at 280 °C and 3 MPa. C₁NHC₆ reacted by disproportionation to C₁N(C₆)₂ as well as C₆N(C₁)₂ and by substitution by H₂S to methylamine and hexanethiol as well as hexylamine and methanethiol. C₁N(C₆)₂ reacted by substitution with H₂S to C₁NHC₆ and C₆NHC₆ and methane- and hexanethiol. The probability of breaking the C₁N bond was only slightly smaller than of breaking the C₆N bond in C₁N(C₆)₂. In the reaction of an equimolar mixture of C₅NHC₅ and C₁N(C₆)₂ both C₁N(C₅)₂ and C₆N(C₅)₂ were formed. The transfer of the methyl group in these reactions cannot be explained by imine and enamine intermediates, only iminium cation intermediates can explain all the products in the hydrodenitrogenation of monoalkyl-, dialkyl- and trialkylamines.     

Photocatalytic degradation of aqueous organocholorine pesticide on the layered double hydroxide pillared by Paratungstate A ion, Mg12Al6(OH)36(W7O24)·4H2O

Layered double hydroxide pillared by Paratungstate A ion, Mg₁₂Al₆(OH)₃₆(W₇O₂₄)·4H₂O, was prepared via anion exchange reaction of the synthetic precursor, Mg₄Al₂(OH)₁₂TA·xH₂O (TA²⁻=terephthalate), and [W₇O₂₄]⁶⁻ ion. Some physico-chemical properties were measured and the preparation conditions were studied. Trace aqueous organocholorine pesticide, hexachlorocyclohexane (HCH), was totally degraded and mineralized into CO₂ and HCl by irradiating a Mg₁₂Al₆(OH)₃₆(W₇O₂₄)·4H₂O suspension in the near UV area. Disappearance of trace HCH follows Langmuir–Hinshelwood first-order kinetics. The model and mechanism for the photocatalytic degradation of HCH on the Mg₁₂Al₆(OH)₃₆(W₇O₂₄)·4H₂O were proposed, indicating that the interlayer space is the reaction field, and that photogeneration of OH√ radicals are responsible for the degradation pathway.     

Oxidation behavior of hot-pressed Si3N4 with Re2O3 (Re=Y, Yb, Er, La)

Four different β-Si₃N₄ ceramics with silicon oxynitrides [Y₁₀(SiO₄)₆N₂, Yb₄Si₂N₂O₇, Er₂Si₃N₄O₃, and La₁₀(SiO₄)₆N₂, respectively] as secondary phases have been fabricated by hot-pressing the Si₃N₄–Re₄Si₂N₂O₇ (Re=Y, Yb, Er, and La) compositions at 1820°C for 2 h under a pressure of 25 MPa. The oxidation behavior of the hot-pressed ceramics was characterized and compared with that of the ceramics fabricated from Si₃N₄–Re₂Si₂O₇ compositions. All Si₃N₄ ceramics investigated herein showed a parabolic weight gain with oxidation time at 1400°C and the oxidation products of the ceramics were SiO₂ and Re₂Si₂O₇. The Si₃N₄–Re₄Si₂N₂O₇ compositions showed inferior oxidation resistance to those from Si₃N₄–Re₂Si₂O₇ compositions, owing to the incompatibility of the secondary phases of those ceramics with SiO₂, the oxidation product of Si₃N₄. Si₃N₄ ceramics from a Si₃N₄–Er₄Si ₂N₂O₇ composition showed the best oxidation resistance of 0·198 mg cm⁻² after oxidation at 1400°C for 192 h in air among the compositions investigated herein.     

Mechanical properties of Al2O3/ZrO2 composites

In the present study, both t-phase zirconia and m-phase zirconia particles are incorporated into an alumina matrix. Dense Al₂O₃/(t-ZrO₂+m-ZrO₂) composites were prepared by sintering pressurelessly at 1600 °C. The microstructure of the composites are characterized, the elastic modulus, strength and toughness determined. Because the ZrO₂ inclusions are close to each other in the Al₂O₃ matrix, the yttrium ion originally in t-ZrO₂ particles can diffuse to nearby m-ZrO₂ particles during sintering, and the m-phase zirconia is thus stabilized after sintering. The strength of the Al₂O₃/(t-ZrO₂+m-ZrO₂) composites after surface grinding can reach values as high as 940 MPa, which is roughly three times that of Al₂O₃ alone. The strengthening effect is contributed by microstructural refinement together with the surface compressive stresses induced by grinding. The toughness of alumina is also enhanced by adding both t-phase and m-phase zirconia, which can reach values as high as two times that of Al₂O₃ alone. The toughening effect is attributed mainly to the zirconia t–m phase transformation.     

Development of Fe2O3-CeO2-TiO2/γ-Al2O3 as catalyst for catalytic wet air oxidation of methyl orange azo dye under room condition

In order to develop a catalyst with high activity and stability for catalytic wet air oxidation (CWAO) process at room temperature and atmospheric pressure, we prepared Fe₂O₃-CeO₂-TiO₂/γ-Al₂O₃ by consecutive impregnation, and determined its properties using BET, SEM, XRF, XPS and chemical analysis techniques. The degradation of an azo dye, methyl orange, in CWAO process with Fe₂O₃-CeO₂-TiO₂/γ-Al₂O₃ used as catalyst at room temperature and atmospheric pressure was also investigated, and the results show that the catalyst has an excellent catalytic activity in treating synthetic wastewater containing 500 mg/L methyl orange, and 98.09% of color and 96.08% of total organic carbon (TOC) can be removed in 2.5 h. The degradation pathway of methyl orange was analyzed by UV–vis and FT-IR spectra. The result of leaching tests shows the catalyst has an excellent stability with negligible leaching ions, and the leaching of Ce is effectively controlled by adding Ti, because Ce and Ti in the catalyst take the form of compound oxides, and the deactivation of the catalyst in successive runs is caused by the adsorption of intermediates on the surface and coverage of the active sites. The catalytic activity of the deactivated catalyst can be generally restored by rinsing it in hydrochloric acid followed by calcination.     

K2CO3/γ-A12O3催化剂在棉籽油制备生物柴油中的应用

利用等体积浸渍法制备K₂CO₃/γ-A1₂O₃负载型固体碱催化剂,应用于棉籽油和甲醇酯交换反应制备生物柴油。对催化剂使用前的保存条件、水分、重复使用性能、游离脂肪酸影响以及失活和再生进行了分析。结果表明,固体催化剂K₂CO₃/γ-Al₂O₃具有较好的抗水性,酸度对催化剂影响明显,重复使用4次未经活化的催化剂,催化活性明显降低,催化剂应密封保存。K₂CO₃/γ-A1₂O₃负载型固体碱催化剂经济实惠且催化效果良好。     

Processing of hot pressed Al2O3–Cr2O3/Cr-carbide nanocomposite prepared by MOCVD in fluidized bed

Nanosized particles dispersed uniformly on Al₂O₃ particles were prepared from the decomposition of precursor Cr(CO)₆ by metal organic chemical vapor deposition (MOCVD) in a fluidized chamber. These nanosized particles consisted of Cr₂O₃, CrC_1−x, and C. A solid solution of Al₂O₃–Cr₂O₃ and an Al₂O₃–Cr₂O₃/Cr₃C₂ nanocomposite were formed when these fluidized powders were pre-sintered at 1000 and 1150 °C before hot-pressing at 1400 °C, respectively. In addition, an Al₂O₃–Cr₂O₃/Cr-carbide (Cr₃C₂ and Cr₇C₃) nanocomposite was formed when the particles were directly hot pressed at 1400 °C. The interface between Cr₃C₂ and Al₂O₃ is non-coherent, while the interface between Cr₇C₃ and Al₂O₃ is semi-coherent.     

Porous structures constructed from [SiMo12O40] and [SiW12O40] Keggin units

Three compounds, K₂(H₂O)₄H₂SiMo₁₂O₄₀ · 7H₂O (1), K₂Na₂(H₂O)₄SiW₁₂O₄₀ · 4H₂O (2), and Na₄(H₂O)₈SiMo₁₂O₄₀ · 6H₂O (3) have been synthesized and structurally characterized by single-crystal X-ray analysis, IR, and thermogravimetry. Compounds 1 and 2 both show the high symmetry trigonal space group P3₂21 and a novel 3D network structure. The Keggin anions [SiM₁₂O₄₀]⁴⁻(M = Mo, W) are linked by potassium or sodium cations to generate hexagon-shaped channels along the c-axis, in which water molecules are accommodated. Compound 3 is tetragonal, space group P4/mnc constructed from [SiMo₁₂O₄₀]⁴⁻ anions and Na ions.