TY  - GEN
A1  - Ehlert, Christopher
A1  - Unger, Wolfgang E. S.
A1  - Saalfrank, Peter
T1  - C K-edge NEXAFS spectra of graphene with physical and chemical defects
BT  - a study based on density functional theory
N2  - Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 173 
KW  - absorbtion fine-structure
KW  - graphite
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-74429
SP  - 14083
EP  - 14095
ER  - 
TY  - GEN
A1  - Wirth, Jonas
A1  - Neumann, Rainer
A1  - Antonietti, Markus
A1  - Saalfrank, Peter
T1  - Adsorption and photocatalytic splitting of water on graphitic carbon nitride
BT  - a combined first principles and semiempirical study
N2  - Graphitic carbon nitride, g-C₃N₄, is a promising organic photo-catalyst for a variety of redox reactions. In order to improve its efficiency in a systematic manner, however, a fundamental understanding of the microscopic interaction between catalyst, reactants and products is crucial. Here we present a systematic study of water adsorption on g-C₃N₄ by means of density functional theory and the density functional based tight-binding method as a prerequisite for understanding photocatalytic water splitting. We then analyze this prototypical redox reaction on the basis of a thermodynamic model providing an estimate of the overpotential for both water oxidation and H⁺ reduction. While the latter is found to occur readily upon irradiation with visible light, we derive a prohibitive overpotential of 1.56 eV for the water oxidation half reaction, comparing well with the experimental finding that in contrast to H₂ production O₂ evolution is only possible in the presence of oxidation cocatalysts.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 172 
KW  - augmented-wave method
KW  - hydrogen
KW  - initio molecular-dynamics
KW  - oxidation
KW  - photooxidation
KW  - reduction
KW  - simulations
KW  - tight-binding
KW  - transition
KW  - visible-light
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-74391
SP  - 15917
EP  - 15926
ER  -