Steffen Oswald

Fast and Selective Sugar Conversion to Alkyl Lactate and Lactic Acid with Bifunctional Carbon–Silica Catalysts

A novel catalyst design for the conversion of mono- and disaccharides to lactic acid and its alkyl esters was developed. The design uses a mesoporous silica, here represented by MCM-41, which is filled with a polyaromatic to graphite-like carbon network. The particular structure of the carbon-silica composite allows the accommodation of a broad variety of catalytically active functions, useful to attain cascade reactions, in a readily tunable pore texture. The significance of a joint action of Lewis and weak Brønsted acid sites was studied here to realize fast and selective sugar conversion. Lewis acidity is provided by grafting the silica component with Sn(IV), while weak Brønsted acidity originates from oxygen-containing functional groups in the carbon part. The weak Brønsted acid content was varied by changing the amount of carbon loading, the pyrolysis temperature, and the post-treatment procedure. As both catalytic functions can be tuned independently, their individual role and optimal balance can be searched for. It was thus demonstrated for the first time that the presence of weak Brønsted acid sites is crucial in accelerating the rate-determining (dehydration) reaction, that is, the first step in the reaction network from triose to lactate. Composite catalysts with well-balanced Lewis/Brønsted acidity are able to convert the trioses, glyceraldehyde and dihydroxyacetone, quantitatively into ethyl lactate in ethanol with an order of magnitude higher reaction rate when compared to the Sn grafted MCM-41 reference catalyst. Interestingly, the ability to tailor the pore architecture further allows the synthesis of a variety of amphiphilic alkyl lactates from trioses and long chain alcohols in moderate to high yields. Finally, direct lactate formation from hexoses, glucose and fructose, and disaccharides composed thereof, sucrose, was also attempted. For instance, conversion of sucrose with the bifunctional composite catalyst yields 45% methyl lactate in methanol at slightly elevated reaction temperature. The hybrid catalyst proved to be recyclable in various successive runs when used in alcohol solvent.

Carbon nanotubes filled with a chemotherapeutic agent: a nanocarrier mediates inhibition of tumor cell growth

AIM In this paper, carbon nanotubes (CNTs) are presented as feasible carriers for carboplatin, a therapeutic agent for cancer treatment. The drug was introduced into CNTs to demonstrate that they are suited as nanocontainers and nanocarriers and can release the drug to initialize its medical virtue. METHOD The filling was accomplished by a wet-chemical approach after the CNTs were opened. The effect on cell proliferation and cytotoxicity of the carboplatin-filled CNT was investigated by using a viability assays. RESULTS Using different analysis methods such as electron energy loss spectroscopy and x-ray photoelectron spectroscopy the structure of carboplatin incorporated into the CNTs was found to be retained. In vitro studies showed that carboplatin-filled CNTs inhibited growth of bladder cancer cells whereas unfilled, opened CNTs barely affected cancer cell growth. CONCLUSION A reversible filling-emptying process could be performed successfully within this work. This highlights the potential of CNTs for applications in the field of drug delivery.

On chip, all solid-state and flexible micro-supercapacitors with high performance based on MnOx/Au multilayers

In this work, we introduce a new concept to fabricate on chip, all solid-state and flexible micro-supercapacitors based on MnOx/Au multilayers, which are compatible with current microelectronics. The micro-supercapacitor exhibits a maximum energy density of 1.75 mW h cm−3 and a maximum power density of 3.44 W cm−3, which are both much higher than the values obtained for other solid-state supercapacitors. At a scan rate of 1 V s−1, a volumetric capacitance of 32.8 F cm−3 is obtained for MnOx/Au multilayer electrodes, which is much higher than the bare MnOx electrode. Electrochemical impedance spectroscopy (EIS) and evolution complex capacitance confirm that the electrical conductivity of MnOx is improved due to the incorporation of gold, and a low relaxation time constant around 5 ms is observed. The MnOx/Au multilayer micro-supercapacitor also shows good long-term cycling stability, with a capacitance retention rate of 74.1% after a large cycling number of 15000 times. Compared with other supercapacitors, which are not portable and are relatively bulky, the device demonstrated here allows fast and reliable applications in a portable and smart fashion. Furthermore, the nature of the process allows the micro-supercapacitor to be integrated with other micro-devices, to meet the need for micro-scale energy storage.

Naturally Rolled‐Up C/Si/C Trilayer Nanomembranes as Stable Anodes for Lithium‐Ion Batteries with Remarkable Cycling Performance

Lithium-ion batteries (LIBs) have attracted considerable interest because of their wide range of environmentally friendly applications, such as portable electronics, electric vehicles (EVs), and hybrid electric vehicles (HEVs). For the next generation of LIBs with high energy and high power density, improvements on currently used electrode materials are urgently needed. Among various anode materials, Si has been extensively studied owing to its highest theoretical capacity (4200 mAhg ), abundance in nature, low cost, and nontoxicity. However, Si-based anodes are notoriously plagued by poor capacity retention resulting from large volume changes during alloy/de-alloy processes (400%). The intrinsic strain generated during such expansion and contraction easily leads to electrode pulverization and capacity fading. Thus, it is a big challenge to achieve both excellent cyclability and enhanced capacity of Si-based anode materials. Significant efforts have been devoted to circumvent this issue caused by the volume change of silicon. Recently, a number of Si nanostructures, including nanoparticles, nanowires/nanorods, nanotubes, and porous nanostructures 22] as well as their composites, have been fabricated to achieve improved cycling performance. Among them, tubular structures, with extra interior space for electron and ion transport, as well as for accommodating volume changes, are one of the most attractive and promising configurations for LIBs. However, such anode materials are still far from commercialization, and new strategies for the synthesis of novel structures with superior cycling performance and stability are still much sought-after. Herein, we report a new tubular configuration made from naturally rolled-up C/Si/C trilayer nanomembranes, which exhibits a highly reversible capacity of approximately 2000 mAh g 1 at 50 mA g , and approximately 100 % capacity retention at 500 mA g 1 after 300 cycles. The sandwich-structured C/Si/C composites, with moderate kinetic properties toward Li ion and electron transport, are of the highest quality. The excellent cycling performance is related to the thin-film effect combined with carbon coating, which play a structural buffering role in minimizing the mechanical stress induced by the volume change of Si. The energy reduction in C/Si/C trilayer nanomembranes after rolling up into multi-winding microtubes results in a significantly reduced intrinsic strain, which can improve capacity and cycling performance. This synthetic process could be compatible with existing industrial sputtering deposition processes as well as roll-to-roll thin-film fabrication technology. The strategy for the self-release of C/Si/C trilayer nanomembranes using rolled-up nanotechnology to form multilayer C/Si/C microtubes is shown in Scheme 1. First, a sacrificial layer (red color, photoresist ARP 3510) was deposited on top of the Si substrates by spin-coating, then trilayer C/Si/C (10/40/10 nm, respectively) nanomembranes were sequentially deposited by radio frequency sputtering, during which the intrinsic strain caused by thermal expansion effects was generated. When the sacrificial layer was selectively under-

Metal Sulfide in a C82 Fullerene Cage: A New Form of Endohedral Clusterfullerenes

The row of endohedral fullerenes is extended by a new type of sulfur-containing clusterfullerenes: the metal sulfide (M(2)S) has been stabilized within a fullerene cage for the first time. The new sulfur-containing clusterfullerenes M(2)S@C(82)-C(3v)(8) have been isolated for a variety of metals (M = Sc, Y, Dy, and Lu). The UV-vis-NIR, electrochemical, and FTIR spectroscopic characterization and extended DFT calculations point to a close similarity of the M(2)S@C(82) cage isomeric and electronic structure to that of the carbide clusterfullerenes M(2)C(2)@C(2n). The bonding in M(2)S@C(82) is studied in detail by molecular orbital analysis as well as with the use of quantum theory of atom-in-molecules (QTAIM) and electron localization function (ELF) approaches. The metal sulfide cluster formally transfers four electrons to the carbon cage, and metal-sulfur and metal-carbon cage bonds with a high degree of covalency are formed. Molecular dynamics simulations show that Sc(2)S cluster exhibits an almost free rotation around the C(3) axis of the carbon cage, resulting thus in a single line (45)Sc NMR spectrum.

Direct catalytic conversion of cellulose to liquid straight-chain alkanes

High yields of liquid straight-chain alkanes were obtained directly from cellulosic feedstock in a one-pot biphasic catalytic system. The catalytic reaction proceeds at elevated temperatures under hydrogen pressure in the presence of tungstosilicic acid, dissolved in the aqueous phase, and modified Ru/C, suspended in the organic phase. Tungstosilicic acid is primarily responsible for cellulose hydrolysis and dehydration steps, while the modified Ru/C selectively hydrogenates intermediates en route to the liquid alkanes. Under optimal conditions, microcrystalline cellulose is converted to 82% n-decane-soluble products, mainly n-hexane, within a few hours, with a minimum formation of gaseous and char products. The dominant route to the liquid alkanes proceeds via 5-hydroxymethylfurfural (HMF), whereas the more common pathway via sorbitol appears to be less efficient. High liquid alkane yields were possible through (i) selective conversion of cellulose to glucose and further to HMF by gradually heating the reactor, (ii) a proper hydrothermal modification of commercial Ru/C to tune its chemoselectivity to furan hydrogenation rather than glucose hydrogenation, and (iii) the use of a biphasic reaction system with optimal partitioning of the intermediates and catalytic reactions. The catalytic system is capable of converting subsequent batches of fresh cellulose, enabling accumulation of the liquid alkanes in the organic phase during subsequent runs. Its robustness is illustrated in the conversion of the raw (soft)wood sawdust.

Sandwich-Stacked SnO2/Cu Hybrid Nanosheets as Multichannel Anodes for Lithium Ion Batteries

We have introduced a facile strategy to fabricate sandwich-stacked SnO2/Cu hybrid nanosheets as multichannel anodes for lithium-ion batteries applying rolled-up nanotechnology with the use of carbon black as intersheet spacer. By employing a direct self-rolling and compressing approach, a much higher effective volume efficiency is achieved as compared to rolled-up hollow tubes. Benefiting from the nanogaps formed between each neighboring sheet, electron transport and ion diffusion are facilitated and SnO2/Cu nanosheet overlapping is prevented. As a result, the sandwich-stacked SnO2/Cu hybrid nanosheets exhibit a high reversible capacity of 764 mAh g(-1) at 100 mA g(-1) and a stable cycling performance of ~75% capacity retention at 200 mA g(-1) after 150 cycles, as well as a superior rate capability of ~470 mAh g(-1) at 1 A g(-1). This synthesis approach presents a promising route to design multichannel anodes for high performance Li-ion batteries.

Hierarchically Designed SiOx/SiOy Bilayer Nanomembranes as Stable Anodes for Lithium Ion Batteries

Hierarchically designed SiOx /SiOy rolled-up bilayer nanomembranes are used as anodes for lithium-ion batteries. The functionalities of the SiO(x,y) layers can be engineered by simply controlling the oxygen content, resulting in anodes that exhibit a reversible capacity of about 1300 mA h g(-1) with an excellent stability of over 100 cycles, as well as a good rate capability.

Copper Oxide Films Grown by Atomic Layer Deposition from Bis(tri-n-butylphosphane)copper(I)acetylacetonate on Ta, TaN, Ru, and SiO2

The thermal atomic layer deposition (ALD) of copper oxide films from the nonfluorinated yet liquid precursor bis(tri-n-butylphosphane)copper(I)acetylacetonate, [( n Bu 3 P) 2 Cu(acac)], and wet O 2 on Ta, TaN, Ru, and SiO 2 substrates at temperatures of < 160°C is reported. Typical temperature-independent growth was observed at least up to 125°C with a growth-per-cycle of ∼0. A for the metallic substrates and an ALD window extending down to 100°C for Ru. On SiO 2 and TaN, the ALD window was observed between 110 and 125°C, with saturated growth shown on TaN still at 135°C. Precursor self-decomposition in a chemical vapor deposition mode led to bimodal growth on Ta, resulting in the parallel formation of continuous films and isolated clusters. This effect was not observed on TaN up to ∼130°C and neither on Ru or SiO 2 for any processing temperature. The degree of nitridation of the tantalum nitride underlayers considerably influenced the film growth. With excellent adhesion of the ALD films on all substrates studied, the results are a promising basis for Cu seed layer ALD applicable to electrochemical Cu metallization in interconnects of ultralarge-scale integrated circuits.

Highly textured La2Zr2O7 buffer layers for YBCO-coated conductors prepared by chemical solution deposition

Recent results of La2Zr2O7 (LZO) buffer layer development for YBa2Cu3O7−x (YBCO-) coated conductors are presented. The major achievement is the development of a new precursor solution starting from 2,4-pentanedionates of lanthanum and zirconium leading to the formation of highly textured LZO buffer layers at low annealing temperatures. The preparation of the precursor solution using only a carboxylic acid as the solvent is simple and can be carried out at room temperature under atmospheric conditions. Reproducible highly textured buffer layers were obtained at annealing temperatures as low as 900 °C. The simplicity of the precursor solution preparation and the low annealing temperature (similar to the processing temperature of the YBCO layer) for preparation of an LZO buffer layer are the main advantages of this new process for cost-effective buffer layer deposition on Ni-RABiTS (rolling-assisted biaxially textured substrates).