Fabrication and microwave absorption properties of magnetite nanoparticle–carbon nanotube–hollow carbon fiber composites

Absorbents with “tree-like” structures, which were composed of hollow porous carbon fibers (HPCFs) acting as “trunk” structures, carbon nanotubes (CNTs) as “branch” structures and magnetite (Fe₃O₄) nanoparticles playing the role of “fruit” structures were prepared by chemical vapor deposition technique and chemical reaction. Microwave reflection loss, permittivity and permeability of Fe₃O₄–CNTs–HPCFs composites were investigated in the frequency range of 2–18 GHz. It was proven that prepared absorbents possessed the excellent electromagnetic wave absorbing performances. The bandwidth with a reflection loss less than −15 dB covers a wide frequency range from 10.2 to 18 GHz with the thickness of 1.5–3.0 mm, and the minimum reflection loss is −50.9 dB at 14.03 GHz with a 2.5 mm thick sample layer. Microwave absorbing mechanism of the Fe₃O₄–CNTs–HPCFs composites is concluded as dielectric polarization and the synergetic interactions exist between Fe₃O₄ and CNTs–HPCFs.     

Yolk–shell structured iron carbide/N-doped carbon composite as highly efficient and stable oxygen reduction reaction electrocatalyst

We report a simple route to synthesize iron carbide/carbon yolk–shell composite via a facile two-step process including polymerization of pyrrole using Fe₃O₄ as a sacrificial template to form a Fe₃O₄/polypyrrole composite, followed by annealing at high temperature in N₂ atmosphere. The yolk–shell composite, with iron carbide (Fe_2.5C) embedded in nitrogen-doped carbon layers, shows impressively high catalytic activity and stability for oxygen reduction reaction in alkaline solution. Both the pyridinic-N and graphic-N in the shell of Fe₃O₄–PPy-700, together with the Fe_2.5C confined in carbon layers are believed to be the active sites for the ORR.     

Preparation of M/Ce1–xTixO2 (M=Pt,Rh, Ru) from sol-gel method and their catalytic oxidation activity for diesel soot

A series of Ce_1–xTi_xO₂ mixed oxide catalysts were synthesized by sol-gel method and then loading of noble metal (M = Pt, Rh, Ru) was used for soot oxidation. Ti-doped Ce_1–xTi_xO₂ catalysts (x is the molar ratio of Ti/(Ti + Ce) and ranges from 0.1 to 0.5) exhibit much better oxidation performance than CeO₂ catalyst, and the Ce_0.9Ti_0.1O₂ catalyst calcined at 500 °C has the best catalysis activity. Each noble metal (1 wt%) was supported on Ce_0.9Ti_0.1O₂ (M/C9T1) and the properties of the catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, Brunauer–Emmett–Teller (BET) method, and H₂-temperature programmed reduction (H₂-TPR) results. Results show that the introduction of Ti into CeO₂ forming Ti-O-Ce structure enhances the catalytic activity and increases the number of oxygen vacancies at the catalyst surface. The noble metal is highly dispersed over Ce_0.9Ti_0.1O₂, and M/C9T1 catalysts present enhanced activity in comparison to Ce_0.9Ti_0.1O₂. It is found that noble metals can greatly increase the activity of the catalyst and the corresponding oxidation rate of soot can enhance the electron transfer capacity and oxygen adsorption capacity of the catalyst. A small amount of Ti doping in CeO₂ can significantly improve the activity of the catalyst, while a large amount of Ti reduces the performance of the catalyst because a large amount of Ti is enriched on the surface of the catalyst, which hinders the contact and reaction between the catalyst and the soot.     

C_2-轴对称联苯类手性双膦配体的研究进展(一)

手性膦配体的合成及其在手性诱导催化反应中的应用一直是不对称合成与催化研究中非常重要的研究领域之一。近10年来,大量的C2-轴对称手性双膦配体被合成出来并成功地应用于不对称催化研究,本文从C2-轴对称联苯类手性双膦配体的介绍、合成方法,C2-轴对称联苯类手性双膦配体在不对称催化氢化,以及其在其他不对称诱导反应中的应用4个方面综述了相关研究进展,并对今后配体的合成及应用前景进行了展望。     

Impact of gypsum supersaturated solution on surface properties of silica and sphalerite minerals

In some sulphide mineral flotation operations, the process water contains high concentrations of calcium and sulphate ions that exceed the solubility limit of gypsum. It has been speculated that the gypsum supersaturated process water would lead to precipitation of gypsum which could coat on mineral surfaces by either nucleation or coagulation, resulting in reduced flotation recovery and selectivity. In this study, a laboratory prepared gypsum supersaturated solution is used to represent the gypsum supersaturated process water, the effect of gypsum supersaturated solution on the surface properties of silica and sphalerite minerals was investigated using zeta potential distribution measurements, scanning electron microscope (SEM), X-ray photon spectroscopy (XPS), Auger electron spectroscopy (AES), and quartz crystal microbalance with dissipation (QCM-D). Our results show that silica and sphalerite minerals carry identical surface charge (−10 mV of zeta potential) in the gypsum supersaturated solution at pH 10 although they are charged differently in simple electrolyte solution at the same pH. Needle shape gypsum precipitates are found in both silica and sphalerite minerals systems conditioned with gypsum supersaturated solution. The gypsum precipitates do not grow on the minerals surfaces but form in the bulk gypsum supersaturated solution. The heterocoagulation between the examined minerals and gypsum particles is insignificant in the gypsum supersaturated solution. It is the high calcium concentration in the gypsum supersaturated solution that has significant effect on the surface properties of silica and sphalerite minerals. The zeta potentials of silica and sphalerite in a 800 ppm calcium solution (similar to the calcium concentration in the gypsum supersaturated solution) are similar to those measured in the gypsum supersaturated solutions. Both silica and sphalerite minerals surfaces are indiscriminately coated with calcium. The surface coating of calcium results in the identical surfaces between silica and sphalerite minerals, and ultimately causes problems for the flotation separation of silica and sphalerite.     

磷石膏基矿井充填材料制备及其性能研究

为实现磷石膏的资源化利用,制备了以原状磷石膏为主要原料、赤泥为碱性激发剂的矿井充填材料,并分析了高效减水剂掺量、水泥掺量、赤泥掺量对其性能的影响。实验结果表明,水灰质量比为0.2,聚羧酸盐减水剂掺量为0.5%（质量分数）时,浆料的初始流动度约为230 mm,满足充填材料性能要求;水泥掺量从0增加到10%时,28 d抗压强度从2.03 MPa提升至10.75 MPa,初始流动度从180 mm增加到235 mm,强度保持率从0.39提升至1,表明水泥掺量直接影响充填材料的强度、流动性及耐水性能;赤泥掺量从0增加到5%时,28 d抗压强度提升了50%,强度保持率从0.82提升至1,激发作用明显,对材料的流动性有相反的影响。     

F-在方解石表面的吸附及其对方解石表面性质的影响

氟元素主要存在于磷矿和萤石等矿物中,这些矿物中都伴生有方解石脉石矿物,在浮选分离的弱酸条件下,矿物表面的F^-会部分溶出并吸附到矿物表面,从而影响矿物表面性质。本文研究了F^-在方解石表面的吸附及其对方解石表面性质的影响机理。结果表明,在矿浆pH 值为5.5时,F^-以化学吸附的方式吸附在方解石表面,随着吸附时间的增加吸附量逐渐增加,90 min时方解石对F^-的吸附达到平衡。在油酸钠(NaOL)为捕收剂时,F^-的存在会降低方解石表面的疏水性。通过Zeta电位测试、溶液化学计算和X射线光电子能谱仪(XPS)分析表明,F^-会和方解石表面的Ca²⁺反应生成CaF₂沉淀,占据方解石表面的Ca位点,降低NaOL在方解石表面的吸附量。     

双电层电容器用中微双孔活性炭的研究进展

文章介绍了中微双孔活性炭的制备方法,综述了用作双电层电容器的最新应用研究,为中微双孔活性炭在双电层电容器中的应用提供参考。     

2-(吡啶-4-基)乙腈的合成

文章介绍了标题化合物的合成方法。以4-氯吡啶盐酸盐和氰乙酸乙酯作为起始原料,经两步反应,合成了目标化合物,并经MS和1HNMR对其结构进行了表征。本合成反应原料易得、条件温和、操作简便,适合工业化生产。反应总收率为84.5%。     

土壤汞污染生物修复法的研究现状及发展前景

近年来,利用生物修复法来治理受汞污染的土壤得到了迅速发展,并取得了很多的成果。文章对土壤汞污染生物修复技术的国内外研究现状进行综述,进而展望其发展前景,以对今后土壤修复进行指导。