sol-gel法制备CeO2-TiO2/凹凸棒石复合材料的催化性能

以凹凸棒石(ATP)为载体,Ce(NO₃)₃·6H₂O和Ti(OBu)₄为原料,冰醋酸为抑制剂,采用溶胶-凝胶法制备CeO₂-TiO₂/ATP纳米复合材料。利用TG-DSC、TEM、XRD和N₂吸附/脱附仪对复合材料进行表征,考察铈钛摩尔比对所制备样品催化降解罗丹明B溶液性能的影响。结果表明,当Ce/Ti≥5/5时,具有立方萤石结构的氧化物颗粒以固溶体形式均匀分布在ATP表面,颗粒尺寸约5~10 nm;随Ti⁴⁺的进一步增加,样品中的CeO₂结晶不完全;当Ce/Ti<3/7时,样品中出现锐钛矿型TiO₂的分离相。适量的Ti⁴⁺掺杂能促进CeO₂产生较多的结构缺陷,有利于增加晶格氧空位的浓度,提高样品的催化活性。对罗丹明B的催化降解实验表明,当Ce/Ti=5/5时,样品的催化性能较好,对罗丹明B溶液的化学需氧量(COD)去除率可达96%以上。     

Constructing porous ZnO/SnO2 nanocomposites for the detection of methane at low operating temperature

Journal of Porous Materials - Aimed at detecting methane (CH4) gas at low operating temperature, porous ZnO/SnO2 nanocomposites were constructed through a simple two-step method. Pure SnO2 with a...     

Catalyst deactivation and regeneration in low temperature ethanol steam reforming with Rh/CeO2–ZrO2 catalysts

Rh/CeO₂–ZrO₂ catalysts with various CeO₂/ZrO₂ ratios have been applied to H₂ production from ethanol steam reforming at low temperatures. The catalysts all deactivated with time on stream (TOS) at 350 °C. The addition of 0.5% K has a beneficial effect on catalyst stability, while 5% K has a negative effect on catalytic activity. The catalyst could be regenerated considerably even at ambient temperature and could recover its initial activity after regeneration above 200 °C with 1% O₂. The results are most consistent with catalyst deactivation due to carbonaceous deposition on the catalyst.     

Elaboration and dielectric property of modified PZT/epoxy nanocomposites

Composites of lead zirconate titanate (PZT) 50 nm nanoparticles and epoxy resins have been produced with various PZT contents from 0 to 20 wt%. The morphology and thermal properties of prepared composites were characterized using scanning electron microscopy and differential scanning calorimetry. The PZT nanoparticles were found to be well dispersed in the epoxy resin matrix. The glass transition temperature (T_g) value of the nanocomposites increases from 164 to 178°C with increasing the PZT weight fraction. The dielectric composites properties dependences were studied via a wide range of frequency from 10 Hz to 100 kHz. The dielectric constant of PZT/epoxy composite was increased from 5.56 to 6.29 (at f = 1 kHz, T = 30°C), respectively to the incorporated PZT amount, and these values are higher than that the dielectric constant of pure cured epoxy resin, ε = 4.86. POLYM. COMPOS., 37:455–461, 2016. © 2014 Society of Plastics Engineers     

2D/2D SnO2 nanosheets/Ti3C2Tx MXene nanocomposites for detection of triethylamine at low temperature

Highly active two-dimensional (2D) nanocomposites have been widely concerned in the field of gas sensors because of their unique advantages and synergistic effects. 2D/2D SnO₂ nanosheets/Ti₃C₂T_x MXene nanocomposites were synthesized by using layered Ti₃C₂T_x MXene and uniform SnO₂ nanosheets by hydrothermal method. Characterization results show that the SnO₂ nanosheets are well dispersed and vertically anchored on the layered Ti₃C₂T_x MXene surface, forming heterogeneous interfaces. Based on the gas-adsorption capabilities and synergistic effects of electronic properties, SnO₂ nanosheets/Ti₃C₂T_x MXene nanocomposites show high triethylamine (TEA) gas-sensing performance at low temperature (140 °C). The sensor responses of the nanocomposites and pure SnO₂ nanosheets to 50 ppm of TEA are 33.9 and 3.4, respectively. An enhancement mechanism for SnO₂ nanosheets/Ti₃C₂T_x MXene nanocomposites is proposed for highly sensitive and selective detection of TEA at low temperature. The combination strategy of two-dimensional metal oxide semiconductor and multilayer MXene provides a new way for the development of cryogenic gas sensors in the future.     

Sintering and grain growth of CoO-doped CeO2 ceramics

Co-doped CeO₂ powders with atomic ratios equal to 0.25, 1 and 3% were synthesized by the conventional mixed-oxide method. No binary compounds were detected in the CeO₂–CoO system, and the Co element exists as the state of Co²⁺ in the samples sintered above 1000°C. A small amount of Co doping reduces sintering temperatures and promotes grain boundary mobility dramatically. Over 99.0% of relative density (R.D.) can be obtained for 0.25% Co-doped sample sintered at 1300°C for 2 h, compared with ∼ 96% of relative density for pure CeO₂ sintered at 1525°C for 2 h. The results from grain growth kinetics study indicate that grain growth exponent, n, and activation energy, Q, are 3 and 697 ± 37 kJ/mol for pure CeO₂, 4 and 572 ± 57 kJ/mol for 0.25% Co-doped CeO₂, respectively.     

Effect of additives on the WGS activity of combustion synthesized CuO/CeO2 catalysts

This paper presents a study on the role of additives (samaria, lanthana, zirconia, and zinc oxide) to ceria as a support of copper catalysts for low-temperature WGSR. A single-step urea-combustion procedure was used for preparation of highly active catalysts. The results revealed the beneficial role of Sm₂O₃ and ZnO doping in increasing BET surface area and total pore volume of the catalysts and decreasing the degree of crystallinity of ceria. TPR profiles evidenced enhanced reducibility of modified catalysts. The WGS activity of these catalysts correlates well with BET, XRD, and TPR data. By comparing the catalysts with a commercial CuO–ZnO–Al₂O₃ sample we point out the feasibility of using CuO/doped-ceria catalysts for low-temperature WGSR.     

Interaction of SO2 with CeO2 and Cu/CeO2 catalysts: photoemission, XANES and TPD studies

CeO₂ and Cu/CeO₂ are effective catalysts/sorbents for the removal or destruction of SO₂. Synchrotron‐based high‐resolution photoemission, X‐ray absorption near‐edge spectroscopy (XANES), and temperature‐programmed desorption (TPD) have been employed to study the reaction of SO₂ with pure and reduced CeO₂ powders, ceria films (CeO₂, CeO_2−x, Ce₂O_3+x) and model Cu/CeO₂ catalysts. The results of XANES and photoemission provide evidence that SO₄ was formed upon the adsorption of SO₂ on pure powders or films of CeO₂ at 300 K. The sulfate decomposed in the 390–670 K temperature range with mainly SO₂ and some SO₃ evolving into gas phase. At 670 K, there was still a significant amount of SO₄ present on the CeO₂ substrates. The introduction of O vacancies in the CeO₂ powders or films favored the formation of SO₃ instead of SO₄. Ceria was able to fully dissociate SO₂ to atomic S only if Ce atoms with a low oxidation state were available in the system. When Cu atoms were added to CeO₂ new active sites for the destruction of SO₂ were created improving the catalytic activity of the system. The surface chemistry of SO₂ on the Cu‐promoted CeO₂ was much richer than on pure CeO₂. The behavior of ceria in several catalytic processes (oxidation of SO₂ by O₂, reduction of SO₂ by CO, automobile exhaust converters) is discussed in light of these results. This revised version was published online in July 2006 with corrections to the Cover Date.     

Facile synthesis of reduced graphene oxide/CeO2 nanocomposites and their application in supercapacitors

The combination of the attractive properties of graphene with excellent characteristics of other functional nanomaterials has become a popular pathway for achieving applications in multiple fields. Herein, reduced graphene oxide (RGO)/CeO₂ nanocomposites with enhanced capacitive performance were designed and synthesized by a facile two-step approach with a self-assembly method followed by thermal treatment. The structure, morphology and composition of the resulting RGO/CeO₂ nanocomposites were systematically investigated. The presence of RGO can prevent the aggregation and control the structures of the CeO₂ nanocrystals in the annealing process. The nanocomposites as electrode materials for supercapacitor exhibited an enhanced capacitive performance due to the synergic effect between RGO nanosheets and CeO₂ nanocrystals. The excellent capacitive performance of the RGO/CeO₂ nanocomposites offer great promise for supercapacitor applications.     

Optical and ferromagnetic properties of hydrothermally synthesized CeO2/CuO nanocomposites

Nanostructured CeO₂/CuO composites are synthesized using a facile hydrothermal reaction. Results signify that Cu ions prefer to enter into CeO₂ lattice forming solid solution at low concentration, and would be transformed into CuO phase at moderate concentration. Moreover, the addition of CuO species into CeO₂ promotes the reduction of Ce⁴⁺ and the creation of oxygen vacancy (V_O) defects. Raman analyses confirm V_O concentration initially increases and then decreases with the increasing CuO phase and the sample Ce1Cu2 exhibits the highest defect concentration. The room temperature ferromagnetic behavior is observed firstly in CeO₂/CuO nonmagnetic system and the maximal saturation magnetization appears in Ce1Cu2. The emergent ferromagnetism appears to be relevant to the extensive V_O defects, which can be interpreted by the indirect double-exchange model. The synthetic interaction between CeO₂ and CuO results in the redshift of the bandgap in prepared CeO₂/CuO nanocomposites.     

BIIR/OMMT纳米复合材料的阻透性能和耐寒性能

采用机械混炼法制备了溴化丁基橡胶/有机蒙脱土(BIIR/OMMT)纳米复合材料,采用SEM和XRD对其亚微观结构进行了表征,并对其耐寒性能和阻透性能进行了研究。实验结果表明:OMMT片层以剥离状态分散于BIIR基体中;添加OMMT之后,BIIR的交联密度明显提高;OMMT能够略微降低BIIR的耐寒性能;OMMT片层具有优异的阻透效应,能够明显提高BIIR的热稳定性能和耐油性能。     

Synthesis of PZT fine particles using Ti precursor at a low hydrothermal temperature of 110 °C

Lead zirconate titanate (PZT) fine particles (80 nm to 0.8 μm) were prepared by hydrothermal method using a Ti³⁺ precursor, TiCl₃. In contrast with conventional hydrothermal methods using Ti⁴⁺-reagents, pure PZT particles without lead titanate (PTO) impurities were synthesized using the Ti³⁺-reagent at a low temperature of 110 °C which is lower than the previously reported temperatures of 160 and 130 °C, using Ti⁴⁺-reagents of TiO₂ and TiCl₄, respectively. Additionally, the crystallization time using the Ti³⁺-reagent is shorter than those using Ti⁴⁺-reagents at the same temperature of 140 °C. The high reaction rate of the Ti³⁺-reagent containing gels prepared here is probably due to the presence of much more defects in their PTO intermediates. The present hydrothermal method using Ti³⁺ precursor could lead to energy savings because of low temperature synthesis and the present method is potentially useful for non-pressurized equipment in manufacturing plants for synthesizing PZT particles.     

Mechanical properties of low temperature synthesized dense and fine-grained Cr2AlC ceramics

Mechanically activated hot-pressing technology was used to synthesize a fine-crystalline Cr₂AlC ceramic at relatively low temperatures. A mixture of Cr, Al and C powders with a molar ratio of 2:1.2:1 was mechanically alloyed for 3 h, and then subjected to hot pressing at 30 MPa and different temperatures for 1 h in Ar atmosphere. The results show that a dense Cr₂AlC ceramic with a grain size of about 2 μm can be synthesized at a relatively low temperature of 1100 °C. The synthesized fine-grained Cr₂AlC has a high density of 99%, which is higher than the 95% density for the coarse-grained Cr₂AlC (grain size of about 35 μm) as synthesized by hot pressing unmilled Cr, Al and C. The flexural strength, fracture toughness and Vickers hardness of the fine-grained Cr₂AlC were determined and compared with the values for the coarse-grained Cr₂AlC.     

低温微细油井水泥的研制

采用低温早强特种油井水泥熟料作为主要原材料而研制的低温微细油井水泥,适用于井底温度３０～６０℃的油气井修井工程。克服了硅酸盐水泥在低温下早期强度发挥慢的缺点,具有早强、高强的特点。通过对该水泥在相应的温度压力下,不同水灰比的水泥浆的稠化性、流变性、游离液含量和水泥石的抗压强度及长期耐久性的试验,并与国内外同类产品进行性能对比,表明该水泥是目前性能较为优秀的堵水材料。采用ＸＲＤ、ＳＥＭ和ＴＧ等检测方法对该水泥在不同温度压力下的水化产物和其结晶形貌进行了分析。     

High optical quality Y2O3 transparent ceramics with fine grain size fabricated by low temperature air pre-sintering and post-HIP treatment

High optical quality Y₂O₃ transparent ceramics with fine grain size were successfully fabricated by air pre-sintering at various temperature ranging from 1500 to 1600 °C combined with a post-hot-isostatic pressing (HIP) treatment using co-precipitated powders as the starting material. The fully dense Y₂O₃ transparent ceramic with highest transparency was obtained by pre-sintered at 1550 °C for 4 h in air and post-HIPed at 1600 °C for 3 h (the pressure of HIP 200 MPa), and it had fine microstructure and the average grain size was 0.96 μm. In addition, the in-line transmittance of the ceramic reached 81.7% at 1064 nm (1 mm thickness). By this approach, the transparent Y₂O₃ ceramics with fine grain size (<1.6 μm) were elaborated without any sintering aid.     

Complex impedance spectra of polymer-derived SiC annealed at ultrahigh temperature

This study reports the complex impedance and alternative current conductivity of polymer-derived ceramic SiC (PDC-SiC) annealed at ultrahigh temperatures. The PDC-SiC shows an inductive response when annealed at temperatures of 1700°C-1900°C due to the percolation of turbostratic carbon. The material returns to a capacitive response at an annealing temperature of 2000°C due to the dissolution of carbon into the SiC lattice. The electrical resistance of the carbon phase decreases with the increase in annealing temperature. These results provide new insights into the effects of processing temperature on microstructure evolution and electrical and dielectric property development of the PDC-SiC ceramic system.     

Excellent electrostrictive properties of low temperature sintered PZT ceramics with high concentration LiBiO2 sintering aid

The effect of LiBiO₂ (LBO) additive on the sintering of Pb_0.97La_0.03(Zr_0.53Ti_0.47)_0.9925O₃ (PLZT) ceramics was carefully investigated. 6.0 wt% LBO added PLZT powders could be fully densified to 98% relative density at a temperature as low as 950 °C. It is worthy to notice that there are distinct enhancements in piezoelectric and electrostrictive properties by increasing the soaking time from 2 h to 7 h, which could mainly originate from the improvement of crystallinity and grain size of PLZT ceramics. By controlling the soaking time and concentration of LBO addition, PLZT ceramics sintered at 950 °C could exhibit high curie temperature of 240 °C and very high S₁₁ of 0.22% under 3.0 kV/mm, which is even better than that of traditionally sintered PZT-5, PMN–PZT, and this is very promising for actuators designed in multilayer structure in high temperature environment.     

Morphologies and applied properties of PSI/PA composite particles synthesized at low temperature

Latex with a poly(dimethyl‐siloxane) core and a poly(methylmethacrylate‐ butylacrylate‐ 2‐hydroxypropyl acrylate) shell have been prepared at low temperature with potassium‐persulphate (KPS), sodium formaldehyde sulfoxylate (SFS) and 2,2′‐azobis [2‐(2‐imidazolin‐ 2‐yl)propane] dihydrochloride (VA‐044) as composite initiators by staged emulsion polymerization. Reactive surfactants were used to significantly improve the applied properties such as water adsorption ratio and thermo‐properties. Transmission electron microscopy (TEM) results indicated that increasing the amount of 2‐hydroxypropyl acrylate (HPA) and butylacrylate (BA) was favorable to form the core/shell particles. Particle size distribution results showed with increasing the dosages of surfactants, initiators, and seed‐latex, particle size decreased. Differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) results indicated the high temperature‐reserved of copolymer was improved in the presence of polysiloxane. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Polymer/silicate nanocomposites synthesized with potassium persulfate at room temperature: polymerization mechanism, characterization, and mechanical properties of the nanocomposites

Polymer/silicate nanocomposites were synthesized using potassium persulfate (KPS) in the presence of silicate and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) without exterior redox co-catalysts at a room temperature. A mechanism for the room temperature polymerization in the presence of silicate was suggested: AMPS attached on the surface of silicate layers would oxidize Fe⁺² in silicate lattice to become Fe⁺³ and the Fe⁺³ would decompose KPS to form radicals like redox co-catalysts. Poly (acrylonitrile) (PAN)/silicate nanocomposite showed an exfoliated structure, but poly (methyl methacrylate) (PMMA)/silicate nanocomposite showed an intercalated structure. Polymers recovered from the nanocomposites synthesized at a room temperature had high isotactic configurations compared to bulk polymers. The dipole–dipole interaction between monomers and silicate surface might make the lamella of monomers to form on the silicate layer surface and produced polymers with more isotactic configurations. PAN/silicate nanocomposite showed two glass transition temperatures at 113 and 151 °C. The lower temperature might be related to the molecules with low molecular weight. PMMA/silicate nanocomposite had a storage modulus of 4.47×10⁹ Pa at 40 °C.     

Effect of Li2O content and sintering temperature on the grain growth and electrical properties of Gd-doped CeO2 ceramics

The sintering behavior and electrical properties of Gd-doped CeO₂ (GDC), with and without Li₂O as a sintering additive, were examined. With increasing Li₂O content, the grain growth of GDC was enhanced because of an increase in the duration for which a Li-rich liquid phase existed during sintering. The migration of Li ions led to an increase in the electrical conductivity of the Li-doped GDC. When the Li-doped GDC was sintered at a high temperature of 1400 °C, the Li evaporated, resulting in a decrease in the electrical conductivity.