中空笼状多孔结构镍钴层状氢氧化物的制备及其电化学性能

超级电容器以功率密度高、寿命长、环境友好等优点在各种能量存储设备中受到广泛关注.所以,提高电极材料的储能性能对超级电容器的开发与应用具有重要的意义.具有特定纳米结构的功能材料作为超级电容器电极材料时具有优异的电化学性能,原因在于其能提供丰富的电化学活性位点、高的比表面积和增加电解质与材料的接触面积.因此,本文以ZIF-67纳米晶为模板,利用硝酸盐刻蚀的方法制备中空笼状镍钴层状氢氧化物(NiCo-LDH),并研究其作为超级电容器电极材料的储能性能.借助X射线衍射、扫描电镜、透射电镜、低温氮气吸附/脱附和电化学测试等手段分析所得NiCo-LDH的结构、形貌和电化学性能.结果表明:NiCo-LDH由纳米片组装形成中空笼状结构,拥有丰富的介孔和大孔孔道以及较高的比表面积,从而有助于增加电活性位点,促使电解液与电极材料的充分接触,进而显著提高材料的储能性能.当刻蚀用镍、钴盐质量比为1:1时,样品Ni₁Co₁-LDH的比电容可达801 F·g^-1(电流密度为0.5 A·g^-1),且在大电流密度下(10 A·g<...     

超高比表面积氮掺杂碳气凝胶的制备及其电化学性能

以间苯二酚和甲醛为反应前驱体, 三聚氰胺为氮源, 通过溶胶-凝胶法制备出氮掺杂碳气凝胶(N-CA), 并对其进行CO2活化后得到活化氮掺杂碳气凝胶(N-ACA), 分别通过扫描电子显微镜、氮吸附、X-光电子能谱和元素分析研究样品的表面形态、孔结构以及含氮官能团的存在形态, 并利用恒流充放电(GV)、循环伏安(CV)、电化学阻抗谱等检测技术评价了其在6 molL-1 KOH电解液中的电化学性能。 实验结果表明: 丰富的孔隙结构和含氮官能团的存在形态是影响碳基电容器性能的决定性因素。 经CO2活化后的N-CA富含较多的的微孔和介孔, 比表面积高达4082 m2g-1, 供电子能力较强的吡咯氮含量有所增加, 在1 mA电流密度下测试的比电容值高达211.9 Fg-1, 经1200次充放电后比电容值保持在98%以上。     

固体核磁共振谱学研究层状双氢氧化物

层状双氢氧化物(LDHs)作为一类非常重要的无机超分子材料,已经被广泛应用于催化、离子交换、生命科学等众多领域．固体核磁共振谱学是研究层状双氢氧化
物局域结构和动态特征的一种强有力手段,提供了非常丰富的信息．特别是最近,借助固体核磁共振在探索层状双氢氧化物的结构方面取得了非常重要的进展（如：阳离子的有序性信息）．该文主要介绍了最近40 年来固体核磁共振研究层状双氢氧化物方面的重要进展．     

层状二氧化锰材料的制备及其电容特性

基于高锰酸钾和5-氨基四唑之间的氧化还原反应,采用常压加热法制备了二氧化锰材料.应用X-射线衍射、扫描电镜和透射电镜技术对所得材料的结构和形貌进行表征,结果表明,所得材料具有层状结构,为纳米片组成的颗粒.电化学测试显示,制备材料表现出优良的电容特性.当电流密度为0.50A/g时,比电容为196F/g.不同扫速下的循环寿命测试结果证明制备材料具有优异的循环稳定性.     

二氧化钛阵列的制备及其光学性能

以水热法制备了由纳米棒组成的二氧化钛阵列。通过控制反应时间,对组成阵列的二氧化钛纳米棒的尺寸进行调节。利用扫描电镜和X射线衍射光谱分析了样品的形貌和晶体结构,发现将反应时间由4 h延长至8 h,二氧化钛纳米棒的直径由100 nm增大到200 nm。利用紫外-可见吸收光谱测量了样品的光吸收特性,发现了尺寸效应引起的吸收边和带隙变化,反应时间由4 h延长至8 h,样品带隙由3.09 eV变化至2.97 eV。利用荧光光谱研究样品的光致发光性能,发现了样品的近带边发光(382 nm左右)、自陷激子发光(420 nm左右)、束缚激子发光(456 nm左右)和缺陷能级发光(492 nm左右)。     

水热法制备TiO2薄膜的研究

采用水热法在玻璃基片上制备了TiO2薄膜.利用x射线衍射(XRD)、x射线光电子能谱(XPS)、扫描电子显微镜(SEM)等分析测试手段对所制备的TiO2薄膜的相结构、表面化学组成及形貌等进行了分析和表征,研究了不同水热条件对所制备TiO2薄膜的光吸收特性的影响.结果表明,所制备的薄膜为锐钛矿型TiO2,均匀、致密、无可视缺陷,具有优异的可见光透过性和紫外吸收特性 关键词： 水热法 TiO2薄膜 比消光度     

海胆状ZnO纳米线阵列的制备及其光学性能

采用一种低成本的有效方法制备出了有序排列的海胆状ZnO纳米线阵列。首先利用自组装的方法得到了单层的聚苯乙烯(PS)小球,以其为模板用水热法在小球表面生长ZnO纳米线,得到了由PS小球和ZnO纳米线构成的海胆状结构。纳米线的直径均一,长度可通过水热反应时间进行控制。利用这种方法制备的一维ZnO纳米结构在传感器、太阳能电池及光催化领域有潜在的应用价值。     

花状的氧化锌纳米结构的制备及其光学性能

以氢氧化钠和六水合硝酸锌为反应物,在未使用任何表面活性剂的简单反应体系中制得了玫瑰花状ZnO纳米结构,采用X射线衍射(XRD)、扫描电子显微镜(SEM)和室温荧光光谱对产物的晶体结构、形貌和发光性质进行了表征和分析.测试结果表明,所得产物为六方纤锌矿结构ZnO纳米材料,产物结晶完整,尺寸较均匀.这种简单水热法制备的ZnO纳米材料仅在384nm处具有一个较强的紫外发光峰,而在黄绿区几乎没有发光峰,进一步证明了所得样品结晶良好,没有缺陷和空位.以上结果表明所制备的氧化锌纳米材料具有优异的紫外光发射能力.     

MnO_2/石墨烯复合电极材料的制备与储能性能

以葡萄糖为还原剂,天然石墨片为原料,采用Hummer法制备了石墨烯粉末(Graphene);并以该产物、KMnO4和HCl为原料,采用水热法制备了MnO2/Graphene复合材料。用扫描电子显微镜和X射线衍射对所制备的复合材料进行了表征,结果表明,水热法制备的MnO2材料为纯的α-MnO2相,且石墨烯粉末的加入并没有影响MnO2的晶体结构。在1mol/L Na2SO4电解液中进行了循环伏安和计时电位扫描测试,电极材料电化学性能稳定,具有较好的可逆性,在1.27mA/cm2电流密度下进行充放电测试时,电极比电容为147.9F/g;再循环1000次后,电极仍能保持稳定的电容,是一种理想的电化学电极材料。     

ZnS:Mn纳米晶的制备及其发光性能研究

以C19H42BrN为表面活性剂,采用水热法合成了ZnS:Mn纳米晶,分别利用XRD、TEM、荧光光谱仪对其物相、形貌及光学性能进行了研究。结果表明:ZnS:Mn纳米晶为闪锌矿ZnS结构,颗粒近似球形,平均粒径为4～8 nm。荧光光谱显示,ZnS:Mn纳米晶的荧光发射峰强度随着Mn2+掺杂浓度和表面活性剂含量的增加而逐渐增强。     

Structural characterisation of aluminium layered double hydroxides by Al solid-state NMR

²⁷Al solid-state NMR has been applied to study the local structure of pristine and chemically modified aluminium layered double hydroxides (LDH). The pristine LDH only shows six-fold coordinated, octahedral, aluminium, while the calcined and subsequently surfactant treated LDH sample shows a significant fraction of four-fold coordinated tetrahedral aluminium. The co-existence of two types of octahedral sites with different quadrupolar parameters is clearly observed in both samples. Quadrupolar coupling constants and isotropic chemical shifts have been measured from the ²⁷Al triple-quantum MAS NMR allowing to fit the ²⁷Al MAS spectra and quantify the different species in the samples. The quantitative analysis reveals that 30% of the aluminium is in four-fold coordination in the surfactant-modified LDH. We show that this chemical modification retains the two types of AlO₆ sites with a decreased intensity of the site showing the lowest quadrupolar coupling constant.     

Ultrasonic-assisted reduction for facile synthesis of ultrafine supported Pd nanocatalysts by hydroxyl groups on the surfaces of layered double hydroxides and their catalytic properties

Layered double hydroxide (LDH)-supported Pd nanocatalysts (Pd/LDH-OH) were prepared by ultrasonic-assisted reduction at 30 °C using an ultrasonic bath at a frequency of 25 kHz and an input power of 400 W for 30 min without the addition of any stabilizing reagent or chemical reductant, using LDH with a layered structure and interparticle mesoporosity as the reductant and carrier. This kind of pore structure allows ultrasound waves to spread inside the pore and make ultrasound directly act on the surface hydroxyl groups of LDH, producing highly reductive free radicals (H). The reductive free radicals rapidly reduced Pd²⁺ to Pd⁰, forming ultrafine Pd nanoparticles (PdNPs) with a particle size distribution of 1.85 nm–3.45 nm and an average particle size of 2.52 nm. The surface hydroxyl groups were converted to exposed oxygen groups after dissociation of hydrogen radicals, which is beneficial for anchoring and dispersing the resultant PdNPs. The resultant PdNPs were uniformly dispersed on the surface of the LDH carrier. The yield of the Suzuki coupling reaction between 4-bromotoluene and phenylboronic acid catalyzed by Pd/LDH-OH at 60 °C was 95.49% for 5 min and the TOF was 190.98 min⁻¹. After repeated for 5 times, the yield was maintained at 84.59%. The prepared Pd/LDH-OH nanocatalyst and the catalytic system are useful for Suzuki-Miyaura coupling reactions of N- and S-heterocyclic substrates. This provides an efficient and green approach for the preparation of supported nanopalladium catalysts.     

The iron oxidation state in Mg-Al-Fe mixed oxides derived from layered double hydroxides: An XPS study

Mixed oxides with large surface area and high thermal stability can be obtained by thermal treatment of the layered double hydroxides (LDH). Mg-Al-Fe mixed oxide samples with varying Mg/Al ratio and 5 mol.% of Fe were prepared in this way and the iron oxidation state (Fe_ox) in these compounds was studied by X-ray photoelectron spectroscopy (XPS), using a calibration based on the relation of Fe_ox to the splitting between the O 1s and Fe 2p_3/2 centroids. The XPS results confirm Fe³⁺ as a dominant oxidation state in the studied mixed oxides. A vacuum-induced reduction of iron in the Fe₂O₃ and Mg-Al-Fe oxide samples has been observed and an influence of the Mg:Al ratio on this effect in mixed oxides has been detected. The role of the local variations of the electron density distribution in the close neighbourhood of the surface oxygen atoms in the mixed oxides in the reduction processes is discussed.     

Synthesis,characterization and electrochemical study of layered double hydroxides intercalated with 2-thiophenecarboxylate anions

The synthesis, characterization, and electrochemical study of the Zn(II)–Al(III) and Zn(II)–Cr(III) Layered Double Hydroxides (LDHs) containing 2-thiopenecarboxylate as the interlayer anions are described. The LDHs were prepared by the constant pH coprecipitation technique followed by hydrothermal treatment for 72 h. The materials were analyzed by PXRD, FT-IR, ¹³C CP-MAS, EDX, TEM, and CV. The presence of the organic heterocyclic anions was confirmed by FT-IR and the related solid-state ¹³C NMR data strongly suggested that these were dimerised during coprecipitation. Accordingly, the basal spacing found by the X-ray technique was ∼15.3 Å, a distance coincident with the formation of bilayers of the intercalated anions. The structural organization of all the new materials was greatly enhanced by hydrothermal treatment, as shown by PXRD. The improved organization of the bilayered structures had a strong influence in the electrochemical behaviour of clay-modified electrodes produced with these materials, such as the diminished resistance to the ionic flow through the LDHs films.     

Nanomaterials based upon silylated layered double hydroxides

A class of nanomaterials based upon the surface modification of layered double hydroxides (LDHs) have been synthesized by grafting silanes onto the surfaces of the LDH. By in situ coprecipitation, the surfaces of a LDH have been modified through grafting of 3-aminopropyltriethoxysilane (APTS) using the anionic surfactant Na-dodecylsulfonate (SDS). The synthesized nanomaterials were characterized by X-ray diffraction (XRD), attenuated total reflection Fourier-transform infrared spectroscopy (ATR FTIR), thermogravimetry (TG) and transmission electron microscopy (TEM). The grafted LDH (LDH-G) displays distinct XRD patterns proving the obtained materials are a new and different phase. The FTIR spectra of the silylated hydrotalcite show bands attributed to Si-O-M (M = Mg and Al) vibration at 996 cm⁻¹, suggesting that APTS has successfully been grafted onto the LDH layers. The TG curves prove the grafted sample has less M-OH concentration and less interlayer water molecules, as indicated by the M-OH consumption during the condensation reaction between Si-OH and M-OH on the LDH surface. The grafted sample displays a ribbon-like thin sheet in the TEM images, with the lateral thickness estimated as 2.5 nm.     

Mg-Al layered double hydroxides (LDHs) and their derived mixed oxides grown by laser techniques

Layered double hydroxides (LDHs) have been widely studied due to their applications as multifunctional materials, catalysts, host materials, anionic exchangers, adsorbents for environmental contaminants and for the immobilization of biological materials. As thin films, LDHs are good candidates for novel applications as sensors, corrosion resistant coatings or components in electro optical devices. For these applications, lamellar orientation-controlled film has to be fabricated.In this work, the successful deposition of LDH and their derived mixed oxides thin films by laser techniques is reported. Pulsed laser deposition (PLD) and matrix assisted pulsed laser evaporation (MAPLE) were the methods used for thin films deposition. The ability of Mg-Al LDHs as a carrier for metallic particles (Ag) has been considered. Frozen targets containing 10% powder in water were used for MAPLE, while for PLD the targets consisted in dry-pressed pellets.The structure and the surface morphology of the deposited films were examined by X-ray Diffraction, Atomic Force Microscopy, Scanning Electron Microscopy and Secondary Ion Mass Spectrometry.     

Adsorption and photodegradation properties of anionic dyes by layered double hydroxides

The adsorption and photodegradation behavior of methyl orange (MO) and fast green (FG) over ZnAl- and MgAl-based layered double hydroxide (LDH) adsorbents have been examined. ZnAl-LDHs were prepared with Zn/Al ratios of 2 to 4 by co-precipitation at pH 8. The ZnAl-LDHs and a commercial MgAl-LDH with a Mg/Al ratio of 3 were evaluated for their ability to adsorb MO and FG and for the photodegradation behavior of these dyes under UV irradiation. Structure analysis of the LDH-dyes-adsorbed complexes revealed that the adsorption produced two types of structures, an intercalation complex for MO and a surface-adsorbed complex for FG. The maximum adsorption of MO on the LDHs was significantly higher (more than tenfold) than FG. Results indicated the adsorption isotherms for the retention of both dyes by ZnAl- and MgAl-LDHs could be fitted to a Freundlich equation, showing a higher affinity for dyes on MgAl-LDH compared to those on ZnAl-LDH. The catalytic degradation ability of dye-LDH complex solid films on a quartz plate was superior to pure dye films under UV irradiation. The FG non-intercalated LDH complexes showed much faster photodegradation under UV irradiation than the MO-intercalated LDH complexes, which pointed to the important role of the LDH materials containing sensitized dyes in enhancing the generation of labile hydroxyl ions from the hydrophilic LDH surface.     

Ultrasound-assisted synthesis of NiFe- layered double hydroxides as efficient electrode materials in supercapacitors

Under ultrasound irradiation, NiFe-layered double hydroxide (NiFe-LDH) nanostructures with three molar ratios and three dissimilar reaction times were prepared. The powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and Fourier transform infrared spectroscopy (FT-IR) were employed to characterize the synthesized nanomaterials. Using a sonochemichal route, various morphologies of the NiFe-LDH nanostructures without any impurity and variations in the structure were produced. During the optimization process, it was found that sonication time and reagent concentration in a fixed irradiation frequency can affect the size and the morphology of the produced nanostructures. Under ultrasound irradiation, non-aggregated particles with uniform, spherical morphology were obtained with molar ratios of 4:1 (Ni:Fe) with 45 W at 180 min. The NiFe-LDH samples were observed to be supercapacitor under a 6 M KOH solution. When morphologically-controlled NiFe-LDH samples were used, the pseudo-capacitive behavior of the nanostructures was tuned. After 3 h of ultrasonic irradiation, the optimized sample (NiFe-LDH spherical nanostructures with 4:1 M ratio) had a high value of specific capacitance (168F g⁻¹).