煤质碳化硅纳米颗粒的合成与表征

以廉价的煤和Na2SiO3.9H2O为原料,辅以Fe(NO3)3.9H2O为助剂,在1300℃氩气气氛下通过碳热还原反应制备出碳化硅纳米颗粒。采用X射线分析衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、荧光光谱仪(PL)和低温氮吸附-脱附对所制备的碳化硅样品进行了表征。结果表明,制得的β-SiC纳米颗粒尺寸介于20～60nm,当n(Fe)/n(Si)=0.01时,碳化硅颗粒比表面积最高,为32m2/g。     

以钛精粉为载体由CO歧化反应制备纳米碳管

以攀枝花钛精粉为载体,使用大载荷热重分析仪,在H2和CO混合气中,研究了纳米碳管的制备工艺.利用热重分析(TG)、气相色谱分析(GC)、扫描电镜(SEM)、比表面积(BET)、透射电镜(TEM)和X射线衍射(XRD)对工艺过程中产物相组成及其微观形貌进行了表征.结果表明:攀枝花钛精粉在H2-CO气氛中,由于气基还原和析碳作用,其热重曲线首先随时间的延长而逐渐降低,达最低点后逐渐升高;生成纳米碳管的最佳工艺参数是钛精粉首先经过还原制备还原产物,其相主要由Fe和M3O5固溶体组成;随后在体积浓度80%的一氧化碳气氛中逐渐降温,温度达550℃时恒温2 h;制备的纳米碳管量约是原矿粉质量的3.5倍,直径小于100 nm、比表面积约151 m2/g;纳米碳管的产生是以铁为析碳基体,且还原产物中其他矿相有效阻止了铁颗粒的团聚,其生长是吸附-反应-产物扩散的过程.     

钯纳米颗粒的形貌控制合成

为优化钯纳米颗粒的化学还原法制备工艺,本文以氯钯酸(H₂PdCl₄)为前驱体,抗坏血酸(C₆H₈O₆)为还原剂,聚丙烯酸钠(PAAS)为表面活性剂制备钯纳米颗粒。采用正交实验探究不同工艺参数对钯纳米颗粒粒径和形貌的影响。通过 X射线粉末衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)及电化学工作站对制备产物的结构、物相、形貌、电催化性能进行了表征。结果表明:在相同的工艺体系下,通过温度的改变,40 ℃条件下可以得到粒径大小为64.5 nm,球形度较好,分散性高的钯纳米颗粒;90 ℃条件下可以得到粒径大小为45.9 nm的立方体钯纳米颗粒。所制备的球形和立方体钯纳米颗粒对甲酸的电氧化催化活性分别为商业钯黑的1.57倍和1.49倍,在催化剂制备领域有广泛的应用前景。     

多元醇法合成高比表面积纳米碳颗粒

提出了一种多元醇法敞开体系下制备具有高比表面积的非晶态纳米碳颗粒的方法.以三甘醇作为高沸点溶剂溶解溴化铵,将溶解有二茂铁的无水乙醇在200℃有氧气氛下滴入三甘醇中,利用溴化铵与二茂铁在溶剂中反应制备尺寸均匀的纳米碳颗粒.通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和氮气吸附-脱附等温线对纳米碳颗粒的微观结构进行了表征.结果表明碳颗粒近似为等轴状,尺寸分布在30～70nm之间,是完全的非晶态结构,比表面积为578.68m2/g,孔容为0.39cm3/g.反应物在三甘醇中的均匀溶解、反应是生成尺寸均一的纳米碳颗粒的主要因素.     

纳米TiO2微球的制备及其光催化性能研究

以四氯化钛为钛源,采用无模板溶剂热法合成了纳米TiO_2微球,采用X射线衍射仪(XRD)、场发射扫描电子显微镜(FESEM)、紫外-可见分光光度计(UV-Vis)、N_2吸附-脱附等分析方法对样品进行表征,考察水热反应时间对纳米TiO_2微球的形成及光催化降解气相苯的影响。结果表明:纳米TiO_2微球是由锐钛矿相纳米颗粒自组装形成的分级微/纳结构,光吸收出现"蓝移",比表面积高达239.2m~2/g;纳米TiO_2微球的结构参数对其最终的光催化性能影响较大,在水热温度180℃、水热反应时间24h条件下制备的纳米微球表现出最高的光催化活性,其矿化率高于商用P25TiO_2近2倍;纳米TiO_2微球优异的光催化性能得益于其优良的结晶度、相对大的比表面积和丰富的介孔结构。     

金/钯哑铃状纳米晶的制备及其催化对硝基苯酚还原研究

采用晶种-溶液生长法制备了单分散性良好、长径比均一的Au纳米棒, 利用H₂PdCl₄作为前驱体, CTAC作为软模版, 抗坏血酸作为还原剂对Au纳米棒进行改性合成了金/钯哑铃状结构纳米晶(Au/Pd NDs)。采用透射电子显微镜(TEM)、X射线能谱仪(EDS)和紫外-可见分光光度计(UV-Vis-NIR)对样品的结构和形貌进行表征, 探讨了铃铛状结构形成的机理, 并研究了其对硼氢化钠还原对硝基苯酚反应的催化性能。结果表明: 大量的多晶钯颗粒定向选择生长在金纳米棒(AuNRs)两端, 形成哑铃状结构; 通过调控还原剂与前驱体的比例, 铃铛尺寸连续可调。当钯的分散性好且总的催化活性位点多时, 金/钯哑铃状结构纳米晶催化对硝基苯酚还原的效率高。钯颗粒尺寸为20.7 nm的Au/Pd NDs(0.04 mg/mL)催化对硝基苯酚还原的反应速率常数可达0.44 min^-1, 证明其是一种非常有效的催化剂。     

高比表面椰壳活性炭和纳米级Pd/C催化剂的制备与表征

以海南椰壳为原料,粉碎、过筛后,采用二步活化法制备活性炭.先500℃下碳化,然后以KOH为活化剂,炭碱质量比1∶2、1∶3、1∶4,炉温分别为700℃、800℃和900℃在氮气保护下活化.在炭碱比1∶4,活化温度800℃时,得到的活性炭比表面积高达3275m2/g.将得到的比表面积在1100～3200m2/g活性炭通过PdCl2超声浸渍法,水合肼还原制备纳米级钯炭催化剂,经SA、XRD、TEM等分析,得出比表面积越大,纳米钯粒子在活性炭上的分布越均匀,粒子颗粒越小.     

碳包覆NiO纳米颗粒的制备与性能

采用直流电弧放电等离子体技术成功制备了碳包覆NiO(NiO@C)纳米颗粒,并对样品的形貌、晶体结构、粒度、比表面积和孔结构采用高分辨透射电子显微镜、X射线衍射、X射线能量色散分析谱仪、拉曼散射光谱和N_2吸-脱附等测试手段进行了分析。实验结果表明:直流电弧等离子体技术制备的NiO@C纳米颗粒具有典型的核壳结构,内核为面心立方结构的NiO纳米颗粒,外壳为碳层。颗粒形貌主要为立方体结构,粒度均匀,分散性良好,粒径分布在30~70nm范围,平均粒径为50nm,外壳碳层的厚度为5nm。NiO@C纳米颗粒BET比表面积为28m~2/g,等效直径为46nm,与TEM和XRD测得的结果基本一致。Raman光谱说明样品中碳包覆层的石墨化程度较低,发生了红移现象。     

碳包覆氧化亚钴纳米颗粒的制备与性能研究

采用直流电弧放电等离子体技术成功制备了碳包覆氧化亚钴纳米颗粒,并对样品的形貌、晶体结构、粒度、比表面积和孔结构采用高分辨透射电子显微镜(HRTEM)、X射线衍射(XRD)、X射线能量色散光谱(XEDS)、拉曼散射光谱(Raman)和N_2吸-脱附等测试手段进行了分析。HRTEM表明该方法制备的碳包覆氧化亚钴纳米颗粒具有典型的核壳结构,颗粒形貌主要为球形或椭球结构,粒度均匀,分散性良好,粒径分布在20~60nm,平均粒径为40nm,外壳碳层的厚度为5nm。XRD证明样品的内核为面心立方结构的氧化亚钴纳米颗粒,外壳为碳层。XEDS图谱表明样品中主要存在Co、O和C元素的特征峰。Raman光谱说明样品中碳外包覆层的石墨化程度较低,发生了红移现象。样品的N_2吸附-脱附等温曲线属Ⅳ型,BET比表面积为33m~2/g,BJH脱附累积总孔孔容和脱附平均孔径分别为0.078cm~3/g和11nm。当量粒径为43nm,与TEM和XRD测得的结果基本一致。     

纤维素纳米纤丝复合气凝胶的制备与性能研究

以高长径比的纤维素纳米纤丝(CNF)与片层结构的氧化石墨(GO)为原料，采用乙二胺还原和液氮梯度冷冻干燥制备纤维素纳米纤丝/石墨烯(CNF/rGO)复合气凝胶，并通过红外光谱、X射线衍射、X射线光电子能谱、扫描电镜、比表面积(BET)、电化学测试仪等对其进行性能表征。结果表明，所制备的CNF/rGO复合气凝胶具有完整的三维网络结构，当CNF和GO质量比为10∶1时，复合气凝胶的平均孔径为13nm,比表面积为110.2m²/g,在电流密度为1A/g下获得的质量比电容约为156F/g。     

Dechlorination of chlorinated methanes by Pd/Fe bimetallic nanoparticles

This paper examined the potential of using Pd/Fe bimetallic nanoparticles to dechlorinate chlorinated methanes including dichloromethane (DCM), chloroform (CF) and carbon tetrachloride (CT). Pd/Fe bimetallic nanoparticles were prepared by chemical precipitation method in liquid phase and characterized in terms of specific surface area (BET), size (TEM), morphology (SEM), and structural feature (XRD). With diameters on the order of 30-50 nm, the Pd/Fe bimetallic nanoparticles presented obvious activity, and were suited to efficient catalytic dechlorination of chlorinated methanes. The effects of some important reaction parameters, such as Pd loading (weight ratio of Pd to Fe), Pd/Fe addition (Pd/Fe bimetallic nanoparticles to solution ratio) and initial pH value, on dechlorination efficiency were sequentially studied. It was found that the maximum dechlorination efficiency was obtained for 0.2 wt% Pd loading. The dechlorination efficiency was observed to increase with increasing Pd/Fe addition. The optimal pH value for dechlorination reaction of chlorinated methanes was about 7. Kinetics of chlorinated methane dechlorination in the catalytic reductive system of Pd/Fe bimetallic particles were investigated. The dechlorination reaction complied with pseudo-first-order kinetics.     

掺杂Fe元素对Pd/C催化剂性能的影响

用Fe作为掺杂元素, 以活性炭为载体, 通过浸渍还原方法制备了Pd:Fe原子比分别为1:1、2:1、1:2的Pd-Fe/C催化剂.采用TEM和XRD技术对合金催化剂的物理性质进行了测试. 结果表明, 获得的Pd-Fe/C催化剂合金粒子在载体上分布均匀, 粒径<5nm,Fe的掺杂量对Pd/C催化剂晶体结构有很大影响, 通过电化学性能测试比较, 分析了三个不同比例的Pd-Fe/C催化剂和Pd/C催化剂对氢和甲酸的电催化氧化性能. 结果得出:在相同的峰值电位下, 几种催化剂的电流密度大小顺序为: Pd-Fe/C(1:1)>Pd-Fe/C(2:1)>Pd/C>Pd-Fe/C(1:2). 结果表明, 适量掺杂Fe提高了Pd/C催化剂的催化性能, 且Pd:Fe原子比为1:1时催化性能最好.     

Catalytic dechlorination of polychlorinated biphenyls in soil by palladium-iron bimetallic catalyst

Pd/Fe bimetallic particles were synthesized by chemical deposition and used to dechlorinate 2,2',4,5,5'-pentachlorobiphenyl in soil. Batch experiments demonstrated that the Pd/Fe bimetallic particles could effectively dechlorinate 2,2',4,5,5'-pentachlorobiphenyl. Dechlorination was affected by several factors such as reaction time, Pd loading, the amount of Pd/Fe used, initial soil pH, and 2,2',4,5,5'-pentachlorobiphenyl concentration. The results showed that higher Pd loading, higher dosage of Pd/Fe, lower initial concentration of 2,2',4,5,5'-pentachlorobiphenyl and slightly acid condition were beneficial to the catalytic dechlorination of 2,2',4,5,5'-pentachlorobiphenyl. The degradation of 2,2',4,5,5'-pentachlorobiphenyl, catalyzed by Pd/Fe followed pseudo-first-order kinetics.     

Microstructural evolution of oxide-dispersion-strengthened Fe–Cr model steels during mechanical milling and subsequent hot pressing

Oxide-dispersion-strengthened (ODS) ferritic steels of Fe–9Cr–0.3Y₂O₃ and Fe–9Cr–0.2Ti–0.3Y₂O₃ (in mass) incorporating nanoscale oxide particles, were produced by mechanical milling (MM) followed by hot pressing (HP). Microstructural evolution of these two types of ODS steels were structurally characterized at each step of the elaboration processes by means of scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), and optical microscope. The observations of structure of the mixed powders and the nanoscale oxide particles in both ODS steels after MM indicate that the initial powders, coupled with the original yttria powders, get fractured by severe plastic deformation and ultrafine bcc grains (~20 nm) of the matrix and Y₂O₃ nanocrystals with irregular edges are formed during MM. The addition of titanium (Ti) promotes the refinement of bcc grains, Y₂O₃ nanocrystals and the formation of amorphous phase of Y₂O₃ during MM. TEM observations of these two Oxide-dispersion-strengthened (ODS) steels exhibit a very fine structure of micrometer-scale grains in which large number of nanoscale oxide particles are distributed after HP process. The observation of some unreinforced domains without the nanoscale oxide particles indicates that there still exist inhomogeneous areas, although the size of those oxide particles reaches nanoscale. Threshold stress of the HPped Fe–9Cr–0.2Ti–0.3Y₂O₃ steel with the relatively homogeneous dispersion was carefully evaluated on the basis of higher magnified images of the nanoscale oxide particles. Different values of threshold stress were obtained due to the various dispersions of the nanoscale oxide particles within different areas. That may be the reason why the threshold stress cannot be clearly obtained by the results of creep tests.     

Microbial synthesis of core/shell gold/palladium nanoparticles for applications in green chemistry

We report a novel biochemical method based on the sacrificial hydrogen strategy to synthesize bimetallic gold (Au)–palladium (Pd) nanoparticles (NPs) with a core/shell configuration. The ability of Escherichia coli cells supplied with H₂ as electron donor to rapidly precipitate Pd(II) ions from solution is used to promote the reduction of soluble Au(III). Pre-coating cells with Pd(0) (bioPd) dramatically accelerated Au(III) reduction, with the Au(III) reduction rate being dependent upon the initial Pd loading by mass on the cells. Following Au(III) addition, the bioPd–Au(III) mixture rapidly turned purple, indicating the formation of colloidal gold. Mapping of bio-NPs by energy dispersive X-ray microanalysis suggested Au-dense core regions and peripheral Pd but only Au was detected by X-ray diffraction (XRD) analysis. However, surface analysis of cleaned NPs by cyclic voltammetry revealed large Pd surface sites, suggesting, since XRD shows no crystalline Pd component, that layers of Pd atoms surround Au NPs. Characterization of the bimetallic particles using X-ray absorption spectroscopy confirmed the existence of Au-rich core and Pd-rich shell type bimetallic biogenic NPs. These showed comparable catalytic activity to chemical counterparts with respect to the oxidation of benzyl alcohol, in air, and at a low temperature (90°C).     

Structure determination of chitosan-stabilized Pt and Pd based bimetallic nanoparticles by X-ray photoelectron spectroscopy and transmission electron microscopy

Chitosan (CTS)-stabilized bimetallic nanoparticles were prepared at room temperature (rt.) in aqueous solution. Palladium (Pd) and platinum (Pt) were selected as the first metals while iron (Fe) and nickel (Ni) functioned as the second metals. In order to obtain the noble metal core-transition metal shell structures, bimetallic nanoparticles were prepared in a two-step process: the preparation of mono noble metallic (Pd or Pt) nanoparticles and the deposition of transition metals (Fe or Ni) on the surface of the monometallic nanoparticles. The structures of the nanoparticles were studied using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The XPS results show that Pd and Pt exist mainly in zero valences. The presence of Fe and Ni in the bimetallic nanoparticles affects the binding energy of Pd and Pt. Moreover, the studies of O 1s spectra indicate the presence of Fe or Ni shells. The analyses of TEM micrographs give the particle size and size distributions while the high-resolution TEM (HRTEM) micrographs show the existence of noble metal core lattices. The results confirm the formation of noble metal core-transition metal shell structures.     

Structural,electrical, and rheological properties of palladium/silver bimetallic nanoparticles prepared by conventional and ultrasonic-assisted reduction methods

Polyvinylpyrrolidone stabilized Pd/Ag bimetallic nanoparticles (NPs) with average particle sizes of 9 and 6 nm were synthesized by simultaneous reduction in the presence and absence of ultrasound waves, respectively. The prepared NPs were characterized by six methods including X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution-TEM (HRTEM), UV–vis spectroscopy, scanning tunneling microscopy (STM), and energy dispersive X-ray (EDX) analysis. The rheological properties of Pd/Ag NPs in ethylene glycol as a base fluid with various mass fractions of NPs from 2% to 5% at different temperatures were studied experimentally and theoretically. The experimental results showed that viscosity of Pd/Ag NPs in ethylene glycol increases with increasing particle mass fraction and decreases with increasing temperature. A maximum of 31.58% increase in viscosity of ethylene glycol at 20 °C was observed when 5% Pd/Ag NPs was added. Measurement of the electrical conductivity of nanofluids of Pd/Ag bimetallic NPs in distilled water at different mass fractions and temperatures was performed. A 3841% increase in electrical conductivity of distilled water at 25 °C was observed when 1% Pd/Ag NPs was added. Both the rheological and electrical properties of Pd/Ag bimetallic NPs were measured in ethylene glycol and distilled water, respectively for the first time.     

Thermal diffusivity of nanofluids containing Au/Pd bimetallic nanoparticles of different compositions

Colloidal suspensions of bimetallic Au/Pd nanoparticles were prepared by simultaneous reduction of the metal ions from their corresponding chloride salts with polymer (PVP) stabilizer. Thermal properties of water containing bimetallic nanoparticles with different nominal compositions (Au/Pd = 12/1, 5/1, 1/1, 1/5) were measured using the mode mismatched dual-beam thermal lens technique to determine the effect of particle composition on the thermal diffusivity of the nanofluids. The characteristic time constant of the transient thermal lens was estimated by fitting the experimental data to the theoretical expression for transient thermal lens. The thermal diffusivity of the nanofluids (water, containing Au/Pd bimetallic nanoparticles) is seen to be strongly dependent on the composition of the particles. The maximum diffusivity was achieved for the nanoparticles with highest Au/Pd molar ratio. A possible mechanism for such high thermal diffusivity of the nanofluids with bimetallic particles is given. UV-Vis spectroscopy, TEM and high-resolution electron microscopy (HREM) techniques were used to characterize the Au/Pd bimetallic nanoparticles.     

Radiation induced synthesis of Au-Pd nanoparticles of random alloy structure supported on carbon particles using the high energy electron beam

Au-Pd bimetallic nanoparticles supported on carbon particles were synthesized by reduction of precursor ions in an aqueous solution irradiated with a high energy electron beam. The composition of the samples was analyzed by the inductively coupled plasma atomic emission spectrometry (ICP-AES), and the morphology of the samples was observed by the transmission electron microscope (TEM). TEM micrographs indicated that Au-Pd particles of ca. 5-nm were well dispersed on the surface of carbon particles of ca. 30-nm without any serious agglomeration. Addition of citric acid to the initial solution and high pH were found to be effective for formation of random alloy structure in the resultant bimetallic nanoparticles. The change in the bimetallic structure from core-shell to random alloy was identified by techniques of the X-ray diffraction (XRD) and the extended X-ray absorption fine structure (EXAFS).     

Bimetallic iron and cobalt incorporated MFI/MCM-41 composite and its catalytic properties

The MFI/MCM-41 composite material with bimetallic Fe and Co incorporation was prepared using templating method via a two-step hydrothermal crystallization procedure. The obtained products were characterized by a series of techniques including powder X-ray diffraction, N₂ sorption, transmission electron microscopy, scanning electron microscope, H₂ temperature programmed reduction, thermal analyses, and X-ray absorption fine structure spectroscopy of the Fe and Co K-edge. The catalytic properties of the products were investigated by residual oil hydrocracking reactions. Characterization results showed that the FeCo-MFI/MCM-41 composite simultaneously possessed two kinds of stable meso- and micro-porous structures. Iron and cobalt ions were incorporated into the silicon framework, which was confirmed by H₂ temperature programmed reduction and X-ray absorption fine structure spectroscopy. This composite presented excellent activities in hydrocracking of residual oil, which was superior to the pure materials of silicate-1/MCM-41.