Zoe Schnepp

From Paper to Structured Carbon Electrodes by Inkjet Printing

Electronics undoubtedly provide the foundation of information technology, uniting efforts from a wide range of scientific disciplines. Generations of materials scientists have strived to develop new processes to meet the demand for more advanced materials while providing enhanced processability and making microelectronics even more affordable. However, microelectronics processing is highly integrated, and the process chain is not readily accessible. Furthermore, there is a trend towards simpler approaches, both to reduce the price and environmental impact and to allow more flexible layout and smaller numbers of units (down to single, customdesigned units), thus accelerating development processes and leading to new applications. Functional printing techniques have been identified as the most promising approach for this type of electronics. To date, processes are often difficult to scale up and, most importantly, they almost exclusively use thermally unstable precursors (usually the support). This has hampered the integration of printing techniques with well-established high-temperature processing techniques, a key requirement for future electronics. Herein we describe a solution to these problems, without sacrificing simplicity, by using a paper support and catalytic ink as two “reactants” to generate functional carbon/ceramic arrays and three-dimensional structures. This simple “beyond the lab” process with off-the-shelf equipment is suitable for the largescale and high-temperature production of materials with applicationas as electrodes and catalysts. The printing of chemically active substances has spurred key advances in several fields including colloid science and biopharmacy, in the construction of microstructured functional materials by means of sol–gel chemistry, in the manufacture of functional coatings, and in ionogel-based flexible electronics. This approach has already been used to generate a wide variety of materials and properties. Although some work has been done in the field of carbon conductors, it relied on the dispersal and printing of preformed carbon structures rather than an in situ process. Furthermore none of these methods addressed the application to the existing industry-standard high-temperature processing used in microelectronics manufacture. In a first step, we filled the cartridges of a commercial inkjet printer (see Figure S1 in the Supporting Information) with a metal catalyst precursor and printed defined two-dimensional, lateral patterns on clean cellulose paper. The resolution here is controlled by the printing process and above all by the paper structure. In a possible second step, this paper can be shaped, processed, or simply folded to a desired threedimensional structure. Final thermal conversion of this structure then leads to the reaction of the catalytic ink with the paper, thus creating in this case conductive structures of iron carbide in graphitic carbon. The precision with which the spatial conformation of a 3D paper object can be retained was shown by folding a paper crane (see Figure 1). We used a sheet of filter paper, folded it into an origami crane, soaked it with the catalytic ink (see below), and then calcined it under inert atmosphere. Finally, the calcined crane was coated with copper to demonstrate the homogeneity of the final structure and the high degree of processability that is possible with this system. Similarly, the catalytic carbonization of thin tissue paper demonstrates the flexibility and durability of the final material for improved handling and broader applications (see Figure 1E and Figure S4 in the Supporting Information). All experiments were repeated in parallel with powdered microcrystalline cellulose instead of filter paper (using the same ink but simply soaking the cellulose powder) in order to establish whether this process can be scaled up to larger quantities and whether the actual fiber form of the cellulose is required, for example, as a structural template. This scaling was possible, and the cellulose powder proved to be a good model system. A catalytic ink of iron(III) nitrate (14 g) in water (15 mL) was transferred into an empty ink cartridge with a syringe. The cartridge was placed back into the printer and could be used directly. For the sake of simplicity and to exclude the possibility that additives in printer paper influence the product formation, we mounted a piece of pure, cellulose filter paper (laboratory grade) on a sheet of standard A4 printer paper (see Figure S2 in the Supporting Information). The printed area (Figure 2A) was cut out and placed between two slides of quartz glass to prevent wrinkling during subsequent carbonization. Conversion to Fe3C, graphitic carbon, and amorphous carbon was achieved by a single heating step at 10 K min 1 to 800 8C under N2 flow followed immediately by cooling to room temperature (Figure 2B). The experiments were also performed with a heating rate of 2 K min 1 with no difference in the produced products. The final product shrinks to approximately 60% of the initial dimensions on the centimeter or micrometer scale (see Figure S3 in the Supporting Information). The microscopic [*] S. Glatzel, Dr. C. Giordano Colloid Chemistry, Max Planck Institute of Colloids and Interfaces Am M hlenberg 1, 14476 Golm (Germany) E-mail: cristina.giordano@mpikg.mpg.de

Biopolymer-mediated synthesis of anisotropic piezoelectric nanorods

Alginate biopolymer was used to control the crystal growth of the lead-free piezoelectric material langasite. The piezo-response of these nanorods was demonstrated to be equivalent to that of ZnO. This is the first time that templated growth of langasite and its associate phases has been demonstrated.

Alginate-mediated routes to the selective synthesis of complex metal oxide nanostructures

The exceptional electronic, magnetic, optical and catalytic properties demonstrated by many ceramic materials when confined to the nanoscale are well established. However, the synthesis of multicomponent metal oxide nanowires and nanoparticles is notoriously problematic due to the difficulty of controlling homogeneity and achieving the correct stoichiometry. In this paper, we demonstrate a selective route to nanowires or nanoparticles of a quaternary metal oxide product using sodium or ammonium alginate respectively. By pre-organizing metal cations within an alginate gel the nucleation and growth of precursor crystalline phases can be constrained to the nanoscale. On further calcination the alginate decomposition products prevent sintering of these precursor nanoparticles prior to conversion to the final product. The cooperative effect of polymer microstructure and decomposition products allows an exceptional level of control over nucleation, growth and transport of the intermediate phases and subsequently on the particle size and morphology of the final product.

A flexible one-pot route to metal/metal oxide nanocomposites

We report a one-pot route to Au/CeO2 nanocomposites. A readily-available biopolymer, sodium alginate, is exploited for controlled formation and stabilisation of gold nanoparticles followed by in situ growth of a sponge-like network of CeO2 nanoparticles. The flexible nature of this method as a general route to mixed metal/metal oxide nanocomposites is also demonstrated.

Synthesis and applications of superacids. 1,1,2,2-Tetrafluoroethanesulfonic acid, supported on silica

In this paper we focus on the synthesis and use of superacids, in particular 1,1,2,2-tetrafluoroethanesulfonic acid(TFESA), and describe how these can be optimized for reactions of key industrial importance. One area of considerable interest is the field of superacid catalysis and, specifically, the development of safer and more cost-effective acid catalysts. We report a new simplified route for preparation of these acids, making these more readily available and opening up a large number of opportunities. Partially fluorinated superacids offer several advantages over the acids commonly used in catalysis (sulfuric, hydrofluoric acid and aluminium chloride): lower loadings, lower reaction temperatures (leading to increased selectivity), fewer by-products, shorter reaction times and higher throughput. TFESA and its longer chain analogs are much less volatile than triflic acid (CF3SO3H). We tested these superacids in several processes (aromatic alkylation, acylation of arenes, isomerization, oligomerization and the Fries rearrangement). These materials are excellent acid catalysts, comparable to triflic acid, and yet easier to handle. We have also prepared supported versions of these catalysts and introduced the ability to recycle.

One-step route to a hybrid TiO2/TixW1?xN nanocomposite by in?situ selective carbothermal nitridation

Abstract Metal oxide/nitride nanocomposites have many existing and potential applications, e.g. in energy conversion or ammonia synthesis. Here, a hybrid oxide/nitride nanocomposite (anatase/TixW1−xN) was synthesized by an ammonia-free sol–gel route. Synchrotron x-ray diffraction, complemented with electron microscopy and thermogravimetric analysis, was used to study the structure, composition and mechanism of formation of the nanocomposite. The nanocomposite contained nanoparticles (<5 nm diameter) of two highly intermixed phases. This was found to arise from controlled nucleation and growth of a single oxide intermediate from the gel precursor, followed by phase separation and in situ selective carbothermal nitridation. Depending on the preparation conditions, the composition varied from anatase/TixW1−xN at low W content to an isostructural mixture of Ti-rich and W-rich TixW1−xN at high W content. In situ selective carbothermal nitridation offers a facile route to the synthesis of nitride-oxide nanocomposites. This conceptually new approach is a significant advance from previous methods, which generally require ammonolysis of a pre-synthesized oxide.