Markus Antonietti

A metal-free polymeric photocatalyst for hydrogen production from water under visible light

The production of hydrogen from water using a catalyst and solar energy is an ideal future energy source, independent of fossil reserves. For an economical use of water and solar energy, catalysts that are sufficiently efficient, stable, inexpensive and capable of harvesting light are required. Here, we show that an abundant material, polymeric carbon nitride, can produce hydrogen from water under visible-light irradiation in the presence of a sacrificial donor. Contrary to other conducting polymer semiconductors, carbon nitride is chemically and thermally stable and does not rely on complicated device manufacturing. The results represent an important first step towards photosynthesis in general where artificial conjugated polymer semiconductors can be used as energy transducers.

Polymer Semiconductors for Artificial Photosynthesis: Hydrogen Evolution by Mesoporous Graphitic Carbon Nitride with Visible Light

We investigated semiconductor characteristics for polymeric carbon nitride as a metal-free photocatalyst working with visible light and have shown that the efficiency of hydrogen production by photochemical water reduction can be improved by approximately 1 order of magnitude by introducing the right type of mesoporosity into polymeric C(3)N(4). We anticipate a wide rang of potential application of C(3)N(4) as energy transducers for artificial photosynthesis in general, especially with a 3D continuous nanoarchitecture. Moreover, the results of finding photoactivity for carbon nitride nanoparticles can enrich the discussion on prebiotic chemistry of the Earth, as HCN polymer clusters are unequivocal in the solar system.

Amphiphilic Block Copolymers in Structure‐Controlled Nanomaterial Hybrids

Amphiphilic block copolymers (ABCs) represent a new class of functional polymers that are unique building blocks serving a number of applications mainly related to the energetic and structural control of materials interfaces. The chemical structure of ABCs can be programmed such that interfaces between materials with very different chemical nature, polarity, and cohesion energy can be controlled to a much broader extent than currently possible with low molecular weight surfactants. This is the physical basis for the construction of thermodynamically stable materials hybrids with nanoscale structure and order that consist of a polymer on one side and metal or ceramic nanoparticles or nanophases on the other. These hybrids are particularly interesting since they inherit some of the properties of both the polymer and the inorganic materials, such as mechanical performance and magnetic and optical characteristics.

Superior Storage Performance of a Si@SiOx/C Nanocomposite as Anode Material for Lithium-Ion Batteries

Rechargeable lithium-ion batteries are essential to portable electronic devices. Owing to the rapid development of such equipment there is an increasing demand for lithium-ion batteries with high energy density and long cycle life. For high energy density, the electrode materials in the lithium-ion batteries must possess high specific storage capacity and coulombic efficiency. Graphite and LiCoO2 are normally used and have high coulombic efficiencies (typically >90%) but rather low capacities (372 and 145 mAhg, respectively).[1–5] Various anode materials with improved storage capacity and thermal stability have been proposed for lithium-ion batteries in the last decade. Among these, silicon has attracted great interest as a candidate to replace commercial graphite materials owing to its numerous appealing features: it has the highest theoretical capacity (Li4.4Sio4200 mAhg) of all known materials, and is abundant, inexpensive, and safer than graphite (it shows a slightly higher voltage plateau than that of graphite as shown in Figure S1, and lithiated silicon is more stable in typical electrolytes than lithiated graphite[6]).

Synthesis of a Carbon Nitride Structure for Visible‐Light Catalysis by Copolymerization

and nonmetallic elements (N, C, B) creates localized/ delocalized states in the band gap and thus extends its optical absorption to the visible region, but doping usually comes with accelerated charge recombination and lower stability of the doped materials. Meanwhile, various other inorganic, non-TiO2-based, visible-light catalysts have been developed (e.g., metal oxides, nitrides, sulfides, phosphides, and their mixed solid solutions), whereby Ga, Ge, In, Ta, Nb, and W are the main metal constituents. However, sustained utilization of solar energy calls for the development of more abundant and stable catalysts working with visible light, and this has remained challenging so far. Recently, a polymeric semiconductor on the basis of a defecteous graphitic carbon nitride (g-C3N4), was introduced as a metal-free photocatalyst which fulfills the basic requirements for a water-splitting catalyst, including being abundant, stable, and responsive to visible light. In the following, we use the notation “g-C3N4” to describe this class of materials rather than the idealized structure. The most active system is in fact presumably an N-bridged “poly(tri-s-triazine)”, already described by Liebig as “melon”. A semiconductor structure with band edges straddling the water redox potential was revealed for melon by DFT calculations, albeit electrochemical analysis is still awaited. g-C3N4 is considered to be the most stable phase of covalent carbon nitride, and facile synthesis of the melon substructure from simple liquid precursors and monomers allows easy engineering of carbon nitride materials to achieve the desired nanostructures via soft-chemical processing routes and methods. For instance, a high surface area (67–400 mg ) can be imparted on g-C3N4 materials by polymerization of cyanamide on a silica template, which results in photocatalytically more active g-C3N4 nanostructures. [8] Metal-doped gC3N4 can also be conveniently obtained by polymerization of dicyandiamine in the presence of metal salts, and thus multifunctionalization of such materials for a variety of applications can be achieved. Most importantly, the electronic and optical properties of carbon nitride, regarded as a polymer semiconductor, are in principle adjustable by organic protocols. Such organic protocols have been widely used to control the performance of traditional p-conjugated polymers, for example, to improve solar-cell efficiencies by constructing copolymerized donor–acceptor structures, or to modify electronic properties by co-blending with p/n-type organic dopants. Our aim was to use such organic modifications to extend the insufficient light absorption of g-C3N4 (a result of its large band gap of 2.7 eV, which corresponds to wavelengths shorter than 460 nm) towards the maximum of the solar spectrum. Here we demonstrate that the optical absorption of carbon nitride semiconductor materials is extendable into the visible region up to about 750 nm by simple copolymerization with organic monomers like barbituric acid (BA). The electronic and photoelectric properties of the modified carbon nitrides were then investigated to elucidate their enhanced activity for hydrogen production from water containing an appropriate sacrificial reagent with visible light. In principle, BA can be directly incorporated into the classical carbon nitride condensation scheme (Scheme 1). New carbon nitride structures were therefore synthesized by dissolving dicyandiamide with different amounts of BA in water, followed by thermally induced copolymerization at 823 K. For simplicity, the resulting samples are denoted CNBx, where x (0.05, 0.1, 0.2, 0.5, 1, 2) refers to the weighedin amount of BA. The structure, texture, and electrochemical properties of these materials were characterized, and their photochemical performance analyzed. Their XRD patterns (Figure S1, Supporting Information) are dominated by the characteristic (002) peak at 27.48 of a graphitic, layered structure with an interlayer distance of d = [*] J. Zhang, X. Chen , Prof. X. Fu, Prof. X. Wang State Key Laboratory Breeding Base of Photocatalysis Fuzhou University, Fuzhou 350002 (China) E-mail: xcwang@fzu.edu.cn

Nitrogen‐Containing Hydrothermal Carbons with Superior Performance in Supercapacitors

[ ∗] L. Zhao , Prof. M. Antonietti , Dr. M.-M. Titirici Colloid Chemistry Department Max-Planck Institute for Colloids and Interfaces Am Muehlenberg 1, 14424 Potsdam (Germany) E-mail: Magdalena.Titirici@mpikg.mpg.de Prof. L.-Z. an , F M.-Q. Zhou , H. Guan , Qiao S. . YSchool of Materials Science and Engineering University of Science and Technology Beijing 100083 Beijing (China) E-mail: fanlizhen@ustb.edu.cn L. Zhao Institute of Coal Chemistry Chinese Academy of Sciences 27th Taoyuan South Road, 030001 Taiyuan (China)

Efficient Metal-Free Oxygen Reduction in Alkaline Medium on High-Surface-Area Mesoporous Nitrogen-Doped Carbons Made from Ionic Liquids and Nucleobases

Mesoporous nitrogen-doped carbon materials with high surface areas up to 1500 m(2) g(-1) were conveniently made by the carbonization of nucleobases dissolved in an all-organic ionic liquid (1-ethyl-3-methylimidazolium dicyanamide). Using hard templating with silica nanoparticles, this process yields high-surface-area nitrogen-doped carbon materials with nitrogen contents as high as 12 wt %, narrow mesopore size distribution of ca. 12 nm diameter, and local graphitic carbon structure. It is demonstrated that the resulting nitrogen-doped carbons show very high catalytic activity, even in the metal-free case in the oxygen reduction reaction (ORR) for fuel cells. Specifically, the as-prepared materials exhibit a low onset voltage for ORR in alkaline medium and a high methanol tolerance, compared with those of commercial 20 wt % Pt/C catalyst. We regard this as a first step toward an all-sustainable fuel cell, avoiding noble metals.

Polyreactions in miniemulsions

Miniemulsions are specially formulated heterophase systems where stable nanodroplets of one phase are dispersed in a second, continuous phase. It is delineated that miniemulsions rely on the appropriate combination of saturated high shear treatment, surfactants, and the presence of an osmotic pressure agent insoluble in the continuous phase. The droplet diameter is adjusted by the type and amount of surfactant, the volume fraction of disperse phase, and the general dispersion problem and lies between 30 and 500 nm. Since each of those droplets can be regarded as an individual batch reactor, a whole variety of polymerization reactions can be performed starting from miniemulsions, clearly extending the profile of classical emulsion polymerization. This article gives an overview about the mechanisms of formation of and polymerization in miniemulsions and reviews the current standing of the field for both the synthesis of new polymers and disperses hybrid systems from heterophase situations.

Fe-g-C3N4-Catalyzed Oxidation of Benzene to Phenol Using Hydrogen Peroxide and Visible Light

A bioinspired iron-based catalyst with semiconductor photocatalytic functions in combination with a high surface area holds promise for synthetic chemistry via combining photocatalysis with organosynthesis. Here exemplified for phenol synthesis, Fe-g-C(3)N(4)/SBA-15 is able to oxidize benzene to phenol with H(2)O(2) even without the aid of strong acids or alkaline promoters. By taking advantage of both catalysis and photocatalysis functions of g-C(3)N(4) nanoparticles, the yield of the phenol can be markedly promoted.

Ionothermal Synthesis of Crystalline, Condensed, Graphitic Carbon Nitride

Herein we report the synthesis of a crystalline graphitic carbon nitride, or g-C(3)N(4), obtained from the temperature-induced condensation of dicyandiamide (NH(2)C(=NH)NHCN) by using a salt melt of lithium chloride and potassium chloride as the solvent. The proposed crystal structure of this g-C(3)N(4) species is based on sheets of hexagonally arranged s-heptazine (C(6)N(7)) units that are held together by covalent bonds between C and N atoms which are stacked in a graphitic, staggered fashion, as corroborated by powder X-ray diffractometry and high-resolution transmission electron microscopy.