Frantisek Karlicky | University of Ostrava (original) (raw)

Papers by Frantisek Karlicky

Nanoscale Advances

We investigated basic models of Ti-based MXene quantum dots and described their structural stabil... more We investigated basic models of Ti-based MXene quantum dots and described their structural stability, and electronic and magnetic properties depending on different lateral dimensions and edge functionalization.

Journal of Materials Chemistry C

We use time-dependent density functional theory together with the HSE06 hybrid functional to inve... more We use time-dependent density functional theory together with the HSE06 hybrid functional to investigate the optical and excitonic properties of two-dimensional transition metal carbides, MXenes. We determine reliable optical gaps,...

Bulletin of the American Physical Society, 2019

Physical Chemistry Chemical Physics

The electronic and magnetic properties of fluorographene (CF) in presence of F-vacancies defects ... more The electronic and magnetic properties of fluorographene (CF) in presence of F-vacancies defects and/or chemical groups (-OH, -CN, and -NH2) were computationally investigated within the framework of the Density Functional...

Phys. Chem. Chem. Phys. 22, 23258, 2020

Surface modification of zero-valent iron (nZVI) nanoparticles, which are frequently used in the r... more Surface modification of zero-valent iron (nZVI) nanoparticles, which are frequently used in the removal of chlorinated hydrocarbons from contaminated groundwater, can increase their surface stability without significant loss of reactivity. Sulfidation is a process during which thin iron sulfide phases are formed on nZVI particles. In this work, the adsorption capability of two iron sulfide minerals (mackinawite and pyrite) and ZVI with respect to two small polar molecules (H 2 O and H 2 S) and trichloroethylene (TCE) was modeled by using the quantum mechanics (QM) approach. High-level QM methods used on cluster models helped in benchmarking and validation of density functional theory methods used on periodic slab models of the (001) surfaces of iron sulfides and the (111) surface of ZVI. This careful computational treatment was necessary for achieving reliable results because modeled iron containing compounds represent computationally demanding systems. The results showed that adsorption was strongly affected by surface topology, accessibility of surface sites, and the shape of adsorbed molecular species. The mackinawite surface is practically hydrophobic having weak interactions with polar molecules (about À5/À6 kcal mol À1), in contrast to the surfaces of pyrite and ZVI (adsorption energies are about three times larger). On the other hand, the adsorption of weakly polar planar TCE molecule is relatively strong and similar for all three surfaces (in the range of À11 to À17 kcal mol À1). Moreover, it was shown that the dominant component of the adsorption energy of TCE had originated from dispersion interactions, which were less important for small polar molecules.

J. Chem. Theory Comput. 16, 5876, 2020

The optical properties of two-dimensional (2D) materials are accurately described by many-body me... more The optical properties of two-dimensional (2D) materials are accurately described by many-body methods including specifically pronounced electron−electron and electron−hole effects. Such methods are, however, computationally demanding and applicable on small computational cells only. We provide approximate optical gaps for 2D materials from time-dependent (TD) density functional theory based on a set of specific screened hybrid functionals and show that this approach effectively accounts for all important physical effects including excitons. Optical gap values obtained from the TD-HSE06 approach for a broad gap range 1−6 eV of eight 2D materials are in agreement with both experimental optical gaps and accurate GW+BSE calculations. Further, we show that such an approach is eligible and practicable for van der Waals heterostructures containing incommensurate cells of different monolayers and enables detailed analysis of intra-and interlayer excitonic wave functions. TD-HSE06 is therefore a suitable method for a reliable description of the optical properties of extended periodic 2D systems.

Small 15, 1902771, 2019

In spite of having several advantages such as low cost, high chemical stability, and environmenta... more In spite of having several advantages such as low cost, high chemical stability, and environmentally safe and benign synthetic as well as operational procedures, the full potential of carbon dots (CDs) is yet to be explored as photosensitizers due to the challenges associated with the fabrication of well-arrayed CDs with many other photocatalytic heterostructures. In the present study, a unique combination of metal–organic framework (MOF)-decorated zinc oxide (ZnO) 1D nanostructures as host and CDs as guest species are explored on account of their potential application in photoelectrochemical (PEC) water splitting performance. The synthetic strategy to incorporate well-defined nitrogen-doped carbon dots (N-CDs) arrays onto a zeolitic imidazolate framework-8 (ZIF-8) anchored on ZnO 1D nanostructures allows a facile unification of different components which subsequently plays a decisive role in improving the material’s PEC water splitting performance. Simple extension of such strategies is expected to offer significant advantages for the preparation of CD-based heterostructures for photo(electro)catalytics and other related applications.

Phys. Chem. Chem. Phys. 21, 3999, 2019

Many-body perturbational GW approximation in conjunction with the Bethe-Salpeter equation (BSE) h... more Many-body perturbational GW approximation in conjunction with the Bethe-Salpeter equation (BSE) has been employed to calculate accurate electronic and optical band gaps of bulk hexagonal boron nitride (h-BN) in the two most important stacking configurations, AA' and AB. The carefully converged results revealed h-BN as an indirect material (indirect gap 6.1 eV) with a huge excitonic effect (0.8 eV) in perfect agreement with recent experiments [Nat. Photonics, 2016, 10, 262; Appl. Phys. Lett., 2016, 109, 122101]. The K-H region of the first Brillouin zone has been shown as the most important for lowest optical excitations in h-BN. Surprisingly, simple scissor corrected DFT has described h-BN band structure at the GW level and subsequent time-dependent DFT with a suitable exchange correlation kernel has provided absorption spectra similar to the full GW+BSE spectra.

Phys.Chem.Chem.Phys. 20, 30247, 2018

The kinetics and mechanism of ferrate(IV), (V) and (VI) transformations in water and in polar org... more The kinetics and mechanism of ferrate(IV), (V) and (VI) transformations in water and in polar organic solvents (namely ethanol and tetrahydrofuran) have been investigated by the method of 57 Fe Mössbauer spectroscopy of frozen solutions. Ethanol with a very limited amount of water under an inert atmosphere, significantly slows down the transformation reactions of ferrates(IV and V) and provides direct proof of the existence of intermediate states. Simultaneously, ethanol is oxidized to caboxylates in the close vicinity of the surface of ferrate crystallites as proven by X-ray photoelectron spectroscopy. On the contrary, any transformation of ferrate(VI) in pure ethanol (with a very limited amount of water) was not observed. Mössbauer spectroscopy of frozen solutions enabled us to experimentally identify and quantify intermediates of ferrate(IV) and ferrate(V) transformations for the first time. Sodium ferrate(IV) in its tetrahedral form, Na 4 FeO 4 , undergoes a two-step charge disproportionation to Fe(III) and Fe(VI) via a Fe(V) intermediate without any evolution of oxygen in polar protic and aprotic solvents, specifically 2Fe(IV)-Fe(III) + Fe(V), and Fe(IV) + Fe(V)-Fe(III) + Fe(VI), i.e. in sum 3Fe(IV)-2Fe(III) + Fe(VI). Ferrate(V) (K 3 FeO 4) transforms to Fe(III) and Fe(VI) without any indication of the Fe(IV) intermediate within the detection limit of the method. In addition to a charge disproportionation reaction proceeding in polar liquids, 3Fe(V)-Fe(III) + 2Fe(VI), a competitive reduction of Fe(V) directly to Fe(III) accompanied by oxygen evolution takes place in water. Oxygen evolution was also measured for ferrate(IV and VI) transformations in water, but to a higher and a smaller extent compared to ferrate(V), respectively. The thermodynamics of the suggested ferrate(IV) and ferrate(V) transformation pathways was examined by DFT calculations.

Carbon 135, 134, 2018

We present structural, vibrational, electronic and optical properties of recently prepared fully ... more We present structural, vibrational, electronic and optical properties of recently prepared fully fluorinated and hydrogenated graphene, called fluorographane. We consider 1:1 ratio of F and H adatoms and we carefully investigate possible structural conformers in C2FH stoichiometric material. The reported results show that all conformers are dynamically stable and homogeneous structures with F and H atoms on both sides of carbon honeycomb structure are more stable than the Janus structures with F atoms on one side and all H atoms on the other. While the main structural and vibrational features are roughly similar for various conformers, electronic and optical properties are very sensitive to local structure (namely specific combinations of F and H adatoms on the graphene surface) and differ significantly. Our highly accurate results based on many-body methods (GW and BSE) indicate that homogeneous fluorographane has unusually wide indirect electronic band gap of ~10 eV (larger than both pure graphane CH and pure fluorographene CF) and embodies a huge excitonic effect (~3 eV). Fluorographane C2FH is therefore a material with the widest electronic gap and a largest binding energy of exciton in the class of currently known 2D materials.

Chem. Phys. Lett. 700, 96, 2018

Photoabsorption cross-sections have been calculated for He þ N clusters of selected sizes (N = 3,... more Photoabsorption cross-sections have been calculated for He þ N clusters of selected sizes (N = 3, 4, 10) over a broad range of photon energies (E phot = 2 - 14 eV) and compared with available experimental data. Semiempirical electronic Hamiltonians derived from the diatomics-in-molecules approach have been used for electronic structure calculations and a quantum, path-integral Monte Carlo method has been employed to model the delocalization of helium nuclei. While a quantitative agreement has been achieved between the theory and experiment for He3+ and He4+ , only qualitative correspondence is seen for He10+.

Small 14, 1703860, 2018

Here, a Sb-doped SnO2 (ATO) nanorod underneath an α-Fe2O3 nanorod sheathed with TiO 2 for photoel... more Here, a Sb-doped SnO2 (ATO) nanorod underneath an α-Fe2O3 nanorod sheathed with TiO 2 for photoelectrochemical (PEC) water splitting is reported. The experimental results, corroborated with theoretical analysis, demonstrate that the ATO nanorod underlayer effect on the α-Fe2O3 nanorod sheathed with TiO2 enhances the PEC water splitting performance. The growth of the well-defined ATO nanorods is reported as a conductive underlayer to improve α-Fe2O3 PEC water oxidation performance. The α-Fe2O3 nanorods grown on the ATO nanorods exhibit improved performance for PEC water oxidation compared to α-Fe2O3 grown on flat fluorine-doped tin oxide glass. Furthermore , a simple and facile TiCl4 chemical treatment further introduces TiO2 passivation layer formation on the α-Fe2O3 to reduce surface recombination. As a result, these unique nanostructures show dramatically improved photo-current density (139% higher than that of the pure hematite nanorods).

J. Chem. Theory Comput. 13, 1328, 2017

Understanding strength and nature of noncovalent binding to surfaces imposes significant challeng... more Understanding strength and nature of noncovalent binding to surfaces imposes significant challenge both for computations and experiments. We explored the adsorption of five small nonpolar organic molecules (acetone, acetonitrile, dichloro-methane, ethanol, ethyl acetate) to fluorographene and fluorographite using inverse gas chromatography and theoretical calculations, providing new insights into the strength and nature of adsorption of small organic molecules on these surfaces. The measured adsorption enthalpies on fluorographite range from −7 to −13 kcal/mol and are by 1−2 kcal/mol lower than those measured on graphene/graphite, which indicates higher affinity of organic adsorbates to fluorographene than to graphene. The dispersion-corrected functionals performed well, and the nonlocal vdW DFT functionals (particularly optB86b-vdW) achieved the best agreement with the experimental data. Computations show that the adsorption enthalpies are controlled by the interaction energy, which is dominated by London dispersion forces (∼70%). The calculations also show that bonding to structural features, like edges and steps, as well as defects does not significantly increase the adsorption enthalpies, which explains a low sensitivity of measured adsorption enthalpies to coverage. The adopted Langmuir model for fitting experimental data enabled determination of adsorption entropies. The adsorption on the fluorographene/ fluorographite surface resulted in an entropy loss equal to approximately 40% of the gas phase entropy.

Nature Communications 8, 14525, 2017

Materials based on metallic elements that have d orbitals and exhibit room temperature magnetism ... more Materials based on metallic elements that have d orbitals and exhibit room temperature magnetism have been known for centuries and applied in a huge range of technologies. Development of room temperature carbon magnets containing exclusively sp orbitals is viewed as great challenge in chemistry, physics, spintronics and materials science. Here we describe a series of room temperature organic magnets prepared by a simple and controllable route based on the substitution of fluorine atoms in fluorographene with hydroxyl groups. Depending on the chemical composition (an F/OH ratio) and sp 3 coverage, these new graphene derivatives show room temperature antiferromagnetic ordering, which has never been observed for any sp-based materials. Such 2D magnets undergo a transition to a ferromagnetic state at low temperatures, showing an extraordinarily high magnetic moment. The developed theoretical model addresses the origin of the room temperature magnetism in terms of sp 2-conjugated diradical motifs embedded in an sp 3 matrix and superexchange interactions via-OH functionalization.

J. Vac. Sci. Technol. B 34, 061208, 2016, Oct 18, 2016

Electronic field emission current (dark current) from surfaces under vacuum at high field strengt... more Electronic field emission current (dark current) from surfaces under vacuum at high field strengths can be reduced by the injection of gas into the ambient volume. A possible reversible mechanism responsible for this gas effect is proposed. The mechanism involves the formation of nanoscale emitter structures by polymerization of hydrocarbon contamination with low-flux ion bombardment at low pressure, and the destruction of these structures by high flux ion bombardment at sufficiently high pressure. Experimental evidence, in particular, x-ray photoelectron spectroscopy analysis of the electrode, is provided in support of this mechanism. Density functional theory calculations are presented to show that the morphology of the carbon layer, not its chemical composition, is the important parameter influencing dark current levels.

Nanoscale, 2017,9, 134-142, Nov 2, 2017

We report the fabrication of 3D hierarchical hetero-nanostructures composed of thin α-Fe 2 O 3 na... more We report the fabrication of 3D hierarchical hetero-nanostructures composed of thin α-Fe 2 O 3 nanoflakes branched on TiO 2 nanotubes. The novel α-Fe 2 O 3 /TiO 2 hierarchical nanostructures, synthesized on FTO through a multi-step hydrothermal process, exhibit enhanced performances in photo-electrochemical water splitting and in the photocatalytic degradation of an organic dye, with respect to pure TiO 2 nano-tubes. An enhanced separation of photogenerated charge carriers is here proposed as the main factor for the observed photo-activities: electrons photogenerated in TiO 2 are efficiently collected at FTO, while holes are transferred to the α-Fe 2 O 3 nanobranches that serve as charge mediators to the electrolyte. The morphology of α-Fe 2 O 3 that varies from ultrathin nanoflakes to nanorod/nanofiber structures depending on the Fe precursor concentration was shown to have a significant impact on the photo-induced activity of the α-Fe 2 O 3 /TiO 2 composites. In particular, it is shown that for an optimized photo-electrochemical structure, a combination of critical factors should be achieved such as (i) TiO 2 light absorption and photo-activation vs. α-Fe 2 O 3-induced shadowing effect and (ii) the availability of free TiO 2 surface vs. α-Fe 2 O 3-coated surface. Finally, theoretical analysis, based on DFT calculations, confirmed the optical properties experimentally determined for the α-Fe 2 O 3 /TiO 2 hierarchical nanostructures. We anticipate that this new multi-step hydrothermal process can be a blueprint for the design and development of other hierarchical heterogeneous metal oxide electrodes suitable for photo-electrochemical applications.

Nanoscale 8, 12134, Jan 14, 2016

Graphene derivatives are promising materials for the electrochemical sensing of diverse biomolecu... more Graphene derivatives are promising materials for the electrochemical sensing of diverse biomolecules and development of new biosensors owing to their improved electron transfer kinetics compared to pristine graphene. Here, we report complex electrochemical behavior and electrocatalytic performance of variously fluorinated graphene derivatives prepared by reaction of graphene with a nitrogen-fluorine mixture at 2 bars pressure. The fluorine content was simply controlled by varying the reaction time and temperature. The studies revealed that electron transfer kinetics and electrocatalytic activity of CFx strongly depend on the degree of fluorination. The versatility of fluorinated graphene as a biosensor platform was demonstrated by cyclic voltammetry for different biomolecules essential in physiological processes, i.e. NADH, ascorbic acid and dopamine. Importantly, the highest electrochemical performance, even higher than pristine graphene, was obtained for fluorinated graphene with the lowest fluorine content (CF0.084) due to its high conductivity and enhanced adsorption properties combining π–π stacking interaction with graphene regions with hydrogen-bonding interaction with fluorine atoms.

Phys. Chem. Chem. Phys., 2016,18, 6351, Jun 22, 2016

Graphene has attracted great interest because of its remarkable properties and numerous potential... more Graphene has attracted great interest because of its remarkable properties and numerous potential applications. A comprehensive understanding of its structural and dynamic properties and those of its derivatives will be required to enable the design and optimization of sophisticated new nanodevices. While it is challenging to perform experimental studies on nanoscale systems at the atomistic level, this is the ‘native’ scale of computational chemistry. Consequently, computational methods are increasingly being used to complement experimental research in many areas of chemistry and nanotechnology. However, it is difficult for non-experts to get to grips with the plethora of computational tools that are available and their areas of application. This perspective briefly describes the available theoretical methods and models for simulating graphene functionalization based on quantum and classical mechanics. The benefits and drawbacks of the individual methods are discussed, and we provide numerous examples showing how computational methods have provided new insights into the physical and chemical features of complex systems including graphene and graphene derivatives. We believe that this overview will help non-expert readers to understand this field and its great potential.

J. Phys. Chem. C 119 (35), 20535, Aug 17, 2015

We present a combined experimental and theoretical study aimed at understanding the behavior of p... more We present a combined experimental and theoretical study aimed at understanding the behavior of polar probe ethanol on graphene and graphite hydrophobic surfaces. We measured isosteric adsorption enthalpies and entropies by inverse gas chromatography for coverages ranging from 0.1 to 20%. The adsorption enthalpies were found to vary with surface coverage and differed considerably between the materials at low coverage. However, they approached the same adsorption enthalpy value of −12.0 ± 0.4 kcal/mol for T centered at 303–393 K and coverages above 5%. We explained the observed behavior using molecular dynamics simulations by employing empirical force-field and density functional theory calculations on two graphene models: circumcoronene and infinite graphene. The simulations showed that various hydrogen-bonded ethanol clusters formed spontaneously from isolated ethanol molecules on graphene and provided a distribution of cluster sizes. Nonlocal density functional theory was used to calculate adsorption enthalpies for various sizes of ethanol clusters. A theoretical adsorption enthalpy of −11.6 kcal/mol at 340 K was obtained from the weighted average of the cluster size distribution, while the adsorption enthalpy of single ethanol molecule to graphene was −6.3 kcal/mol at 323 K.

Journal of Physical Chemistry C, 2007