Mesoporous metal oxides by vapor infiltration and atomic layer deposition on ordered surfactant polymer films

Catalysis, chemical separations, and energy conversion devices often depend on well-defined mesoporous materials as supports or active component elements. Herein, we show that ordered assembled organic surfactant films can directly template porous inorganic solids with surface area exceeding 1000 m(2)/g by infusing the polymers with reactive inorganic vapors, followed by anneal. The specific surface area, pore size, chemical composition, and overall shape of the product material are tuned by choice of the polymer and precursor materials as well as the influsion and postinfusion treatment conditions. X-ray diffraction, infrared spectroscopy, and electron microscopy show that vapor infusion changes both the physical and chemical structure of the starting ordered polymer films, consistent with quantified trends in specific surface area and pore size distribution measured by nitrogen adsorption after film annealing. This method yields porous TiO(2) films, for example, that function as an anode layer in a dye-sensitized solar cell.     

Photoelectrochemical investigation of ultrathin film iron oxide solar cells prepared by atomic layer deposition

Atomic layer deposition was used to grow conformal thin films of hematite with controlled thickness on transparent conductive oxide substrates. The hematite films were incorporated as photoelectrodes in regenerative photoelectrochemical cells employing an aqueous [Fe(CN)(6)](3-/4-) electrolyte. Steady state current density versus applied potential measurements under monochromatic and simulated solar illumination were used to probe the photoelectrochemical properties of the hematite electrodes as a function of film thickness. Combining the photoelectrochemical results with careful optical measurements allowed us to determine an optimal thickness for a hematite electrode of ～20 nm. Mott-Schottky analysis of differential capacitance measurements indicated a depletion region of ～17 nm. Thus, only charge carriers generated in the depletion region were found to contribute to the photocurrent.     

Tailoring nanoporous materials by atomic layer deposition

Atomic layer deposition (ALD) is a cyclic process which relies on sequential self-terminating reactions between gas phase precursor molecules and a solid surface. The self-limiting nature of the chemical reactions ensures precise film thickness control and excellent step coverage, even on 3D structures with large aspect ratios. At present, ALD is mainly used in the microelectronics industry, e.g. for growing gate oxides. The excellent conformality that can be achieved with ALD also renders it a promising candidate for coating porous structures, e.g. for functionalization of large surface area substrates for catalysis, fuel cells, batteries, supercapacitors, filtration devices, sensors, membranes etc. This tutorial review focuses on the application of ALD for catalyst design. Examples are discussed where ALD of TiO(2) is used for tailoring the interior surface of nanoporous films with pore sizes of 4-6 nm, resulting in photocatalytic activity. In still narrower pores, the ability to deposit chemical elements can be exploited to generate catalytic sites. In zeolites, ALD of aluminium species enables the generation of acid catalytic activity.     

原子层沉积技术制备单原子催化剂

贵金属单原子催化剂因具有独特的催化性能和高的利用率而迅速引人关注.原子层沉积(ALD)逐渐成为大批量合成稳定单原子的有力工具.本文总结了采用ALD合成单原子的最新进展,以及未来的研究方向和趋势.     

Growth of p-type hematite by atomic layer deposition and its utilization for improved solar water splitting

Mg-doped hematite (α-Fe(2)O(3)) was synthesized by atomic layer deposition (ALD). The resulting material was identified as p-type with a hole concentration of ca. 1.7 × 10(15) cm(-3). When grown on n-type hematite, the p-type layer was found to create a built-in field that could be used to assist photoelectrochemical water splitting reactions. A nominal 200 mV turn-on voltage shift toward the cathodic direction was measured, which is comparable to what has been measured using water oxidation catalysts. This result suggests that it is possible to achieve desired energetics for solar water splitting directly on metal oxides through advanced material preparations. Similar approaches may be used to mitigate problems caused by energy mismatch between water redox potentials and the band edges of hematite and many other low-cost metal oxides, enabling practical solar water splitting as a means for solar energy storage.     

New baths for the deposition of manganese and cobalt oxides

New methods have been adopted for the anodic deposition of the different manganese and cobalt oxides. The deposition of the diferent oxides is usually carried out from their metal salt solutions in presence of a reducing agent. The oxides deposited are as follows: Mn₂O₃ from manganous sulphate in presence of boric, acid and formaldehyde at pH=5.5, Mn₃O₄ from manganous sulphate in presence of formic acid at pH=5.0 MnO from manganous sulphate-ammonium chloride solution in presence of telluric acid, Co₂O₃ from cobalt chloride in presence of telluric acid and sodium fluoride, Co₃O₄ from cobaltite in presence of formaldehyde and potassium chloride and finally CoO from cobalt chloride in presence of alcohol. The results of chemical analysis revealed that the purity of the oxides is 99.99% and their molecular formulae are MnO_1.5, MnO_1.33, MnO, CoO_1.5, CoO_1.33 and CoO respectively.     

ZnS薄膜原子层沉积机理的密度泛函理论研究

使用密度泛函方法研究了以二乙基锌(DEZn)和H2S作为前驱体在硅表面原子层沉积ZnS的初始反应机理.ZnS薄膜的原子层沉积包括2个连续的"半反应":即DEZn与H2S"半反应".研究显示:DEZn与H2S"半反应"都经历了一个C2H6消去过程.通过对比在单硫氢基及双硫氢基硅表面上的反应,发现邻位硫氢基的存在有利于前驱体分子的吸附并能够降低反应活化能,这意味着双硫氢基硅表面上的反应是能量上更有利的反应.另外,也发现DEZn"半反应"比H2S"半反应"更容易进行.     

原子层沉积方法在设计制备高效电催化剂中的应用（英文）

人类对不可再生化石能源的依赖导致了全球范围内的能源危机和环境污染.电化学能源转换技术由于具有清洁、高效、原料来源广泛及可再生等优点而受到广泛关注.电催化剂能加快反应动力学,提高目标产物选择性,在电化学能源转换技术中起着至关重要的作用.目前, Pt是多数重要的电化学反应(如电解水、氧还原以及一些小分子醇类和酸类的氧化反应)中使用最多和最有效的催化剂之一.然而Pt催化剂面临着价格昂贵、易中毒、易流失等问题,使其在大规模工业化应用中受到限制.为了提高Pt催化剂的利用率和稳定性,研究人员进行了大量工作.例如,制备尺寸小的Pt纳米颗粒,增加单位质量Pt表面积和Pt利用率;在Pt催化剂中加入Ru或Pd等其它金属,促进醇类和酸类氧化反应中间产物的氧化,减缓Pt中毒;选用抗腐蚀性能好的载体,增加Pt与载体间相互作用,从而抑制Pt颗粒在高电位、高湿度、高酸碱度电化学工作环境中的脱落和聚集.尽管如此,利用传统的方法仍然很难精确调控电催化剂的组成、尺寸和纳米结构,无法最大程度提高贵金属Pt的利用效率.原子层沉积(ALD)技术可在原子尺度控制物质生长,既能在多孔、复杂基体上沉积尺度均一的纳米薄膜或颗粒,也能精...     

Barrier properties of polymer/alumina nanocomposite membranes fabricated by atomic layer deposition

Novel polymer/ceramic nanocomposite membranes were fabricated, characterized and tested for their barrier performance. Atomic layer deposition (ALD) was used to deposit alumina films on primary, micron-sized (16 and 60 μm) high-density polyethylene (HDPE) particles at a rate of 0.5 nm/cycle at 77 °C. Well-dispersed polymer/ceramic nanocomposites were obtained by extruding alumina coated HDPE particles. The dispersion of alumina flakes can be controlled by varying the number of ALD coating cycles and substrate polymer particle size. The diffusion coefficient of fabricated nanocomposite membranes can be reduced to half with the inclusion of 7.29 vol.% alumina flakes. However, a corresponding increase in permeability was also observed due to the voids formed at or near the interface of the polymer and alumina flakes during the extrusion process, as evidenced by electron microscopy. The low surface wettability of the alumina outerlayers was believed to be one of the main reasons of void formation. Particle surface wettability was improved using 3-aminopropyltriethoxysilane (APS) to coat the particle ALD surface modified polymer particles prior to extrusion. The diffusion coefficient and permeability of the membrane using surfactant-modified particles decreased by 20%, relative to the non-modified case.     

Nanometer-thick conformal pore sealing of self-assembled mesoporous silica by plasma-assisted atomic layer deposition

On a porous substrate, regular atomic layer deposition (ALD) not only takes place on top of the substrate but also penetrates into the internal porosity. Here we report a plasma-assisted process in which the ALD precursors are chosen to be nonreactive unless triggered by plasma, so that ALD can be spatially defined by the supply of plasma irradiation. Since plasma cannot penetrate within the internal porosity, ALD has been successfully confined to the immediate surface. This not only gives a possible solution for sealing of porous low dielectric constant films with a conformal layer of nm-scale thickness but also enables us to progressively reduce the pore size of mesoporous materials in a sub-A/cycle fashion for membrane formation.     

Atomic layer deposition of metal oxides on pristine and functionalized graphene

We investigate atomic layer deposition (ALD) of metal oxide on pristine and functionalized graphene. On pristine graphene, ALD coating can only actively grow on edges and defect sites, where dangling bonds or surface groups react with ALD precursors. This affords a simple method to decorate and probe single defect sites in graphene planes. We used perylene tetracarboxylic acid (PTCA) to functionalize the graphene surface and selectively introduced densely packed surface groups on graphene. Uniform ultrathin ALD coating on PTCA graphene was achieved over a large area. The functionalization method could be used to integrate ultrathin high-kappa dielectrics in future graphene electronics.     

Active sites engineering of Pt/CNT oxygen reduction catalysts by atomic layer deposition

Understanding carbon-supported Pt-catalyzed oxygen reduction reaction(ORR)from the perspective of the active sites is of fundamental and practical importance.In this study,three differently sized carbon nanotube-supported Pt nanoparticles(Pt/CNT)are prepared by both atomic layer deposition(ALD)and impregnation methods.The performances of the catalysts toward the ORR in acidic media are comparatively studied to probe the effects of the sizes of the Pt nanoparticles together with their distributions,electronic properties,and local environments.The ALD-Pt/CNT catalysts show much higher ORR activity and selectivity than the impregnation-Pt/CNT catalysts.This outstanding ORR performance is ascribed to the well-controlled Pt particle sizes and distributions,desirable Pt^04f binding energy,and the Cl-free Pt surfaces based on the electrocatalytic measurements,catalyst characterizations,and model calculations.The insights reported here could guide the rational design and fine-tuning of carbon-supported Pt catalysts for the ORR.     

Enhanced UV photosensing properties of ZnO nanowires prepared by electrodeposition and atomic layer deposition

A new process enabling the synthesis of zinc oxide (ZnO) and Al-doped ZnO nanowires (NWs) for photosensing applications is reported. By combining atomic layer deposition (ALD) for the seed layer preparation and electrodeposition for the NW growth, high-quality ZnO nanomaterials were prepared and tested as ultraviolet (UV) sensors. The obtained NWs are grown as arrays perpendicular to the substrate surface and present diameters between 70 and 130 nm depending on the Al doping, as seen from scanning electron microscopy (SEM) studies. Their hexagonal microstructure has been determined using X-ray diffraction and Raman spectroscopy. An excellent performance in UV sensing has been observed for the ZnO NWs with low Al doping, and a maximal photoresponse current of 11.1 mA has been measured. In addition, initial studies on the stability have shown that the NW photoresponse currents are stable, even after ten UV on/off cycles.     

Mechanism of carbothermal reduction of iron, cobalt, nickel and copper oxides

A new scheme of thermal dissociation which is based on the dissociative evaporation of the reactant with simultaneous condensation of the low-volatile product has been invoked to interpret the kinetics of reduction of FeO, CoO, NiO and Cu₂O by carbon. A critical analysis of literature data and their comparison with theoretical calculations has shown that the main kinetic characteristics of carbothermal reduction, including the initial decomposition temperature and activation energy are in full agreement with the proposed mechanism of decomposition. Condensation of the low-volatile product (metal vapour) in the reaction zone and partial transport of condensation energy to the oxide account for the features which are typical of solid state reactions and manifest themselves in the appearance of periods of induction and acceleration in the course of the process. Carbon fulfils the role of buffer in this process. This is supported by an appearance of metals in the condensed phase and a higher than equilibrium partial pressure of oxygen in high-vacuum experiments with Knudsen cells.     

Influence of the pore structure of MCM-41 and SBA-15 silica fibers on atomic layer chemical vapor deposition of cobalt carbonyl

Mesoporous high surface area MCM-41 and SBA-15 type silica materials with fibrous morphology were synthesized and used as support materials for the ALCVD (atomic layer chemical vapor deposition) preparation of Co/MCM-41 and Co/SBA-15 catalysts. Co/MCM-41 and Co/SBA-15 catalysts were prepared by deposition of Co2(CO)8 from the gas phase onto the surfaces of preheated support materials in a fluidized bed reactor. For both silica materials, two different kinds of preparation methods, direct deposition and a pulse deposition method, were used. Pure silica supports as well as supported cobalt catalysts were characterized by various spectroscopic (IR) and analytical (X-ray diffraction, Brunauer-Emmett-Teller, elemental analysis) methods. MCM-41 and SBA-15 fibers showed considerable ability to adsorb Co2(CO)8 from the gas phase. For MCM-41 and SBA-15 silicas, cobalt loadings of 13.7 and 12.1 wt % were obtained using the direct deposition method. The cobalt loadings increased to 23.0 and 20.7 wt % for MCM-41 and SBA-15 silicas, respectively, when the pulse deposition method was used. The reduction behavior of silica-supported cobalt catalysts was found to depend on the catalyst preparation method and on the mesoporous structure of the support material. Almost identical reduction properties of SBA-15-supported catalysts prepared by different deposition methods are explained by the structural properties of the mesoporous support and, in particular, by the chemical structure of the inner surfaces and walls of the mesopores. Pulse O2/H2 chemisorption experiments showed catalytically promising redox properties and surface stability of the prepared MCM-41- and SBA-15-supported cobalt catalysts.     

Effect of hydrogen on atomic absorption of iron,cobalt and nickel

Addition of hydrogen to the argon purge gas used for the electrothermal atomic absorption spectrometry of iron, cobalt and nickel in a molybdenum tube provided narrower and more sensitive peaks than those obtained in pure argon. Reproducibility and background were also improved and atomizer lifetime was prolonged. Optimal gas flow rates are reported.     

Mechanisms of atomic layer deposition on substrates with ultrahigh aspect ratios

Atomic layer deposition (ALD) appears to be uniquely suited for coating substrates with ultrahigh aspect ratios (> or similar 10(3)), including nanoporous solids. Here, we study the ALD of Cu and Cu3N on the inner surfaces of low-density nanoporous silica aerogel monoliths. Results show that Cu depth profiles in nanoporous monoliths are limited not only by Knudsen diffusion of heavier precursor molecules into the pores, as currently believed, but also by other processes such as the interaction of precursor and reaction product molecules with pore walls. Similar behavior has also been observed for Fe, Ru, and Pt ALD on aerogels. On the basis of these results, we discuss design rules for ALD precursors specifically geared for coating nanoporous solids.