Miroslav Kolos

The emergence of two-dimensional van der Waals (vdW) heterostructures has revolutionized exciton-based research due to their tunable electronic and optical properties. Here, we present a systematic many-body study of a BP/CrSe₂ vdW heterostructure composed of experimentally realized boron phosphide (BP) and chromium diselenide (CrSe₂) monolayers. We find a robust type-II band alignment across all stacking configurations; however, interlayer excitons emerge selectively depending on the stacking order. The vdW heterostructure exhibits strong exciton binding energy (0.34-0.44 eV, depending on stacking) and nanosecond-scale room-temperature radiative lifetimes, indicating long-lived excitonic states. Additionally, its optical absorption extends from the visible to the near-infrared regime, underscoring its potential for optoelectronic and excitonic applications. Our findings highlight the critical role of stacking-dependent interlayer coupling in controlling the excitonic properties of vdW heterostructures, paving the way for tailored design strategies in next-generation light-harvesting and quantum technologies.

Chlorinated hydrocarbons, widely used in industrial applications, pose significant environmental and health risks due to their persistence and toxicity. Conventional remediation methods often face efficiency limitations, necessitating the exploration of innovative materials for effective pollutant degradation. MXenes, a novel class of two-dimensional materials, have emerged as promising candidates for environmental remediation due to their exceptional chemical reactivity and tunable surface properties. This study employs density functional theory to investigate trichloroethylene’s (TCE) adsorption and dechlorination mechanisms on variously terminated MXenes. Our results reveal that Ti₂C(OH)₂ and V₂C(OH)₂ facilitate spontaneous TCE dechlorination. With realistic termination ratios, the reaction barriers of TCE dechlorations are below 1 eV. Remarkably, only with just 17% of –O terminations substituted by –OH, non-defected Ti₂CO₂ demonstrates robust dechlorination, forming dichloroethylene and hydrochloric acid (HCl). Additionally, single terminal vacancy MXenes exhibit highly favorable reaction pathways with barriers as low as 0.1 eV. Beyond TCE, chlorinated hydrocarbons lindane and dichlorodiphenyltrichloroethane (DDT) spontaneously dechlorinate on pristine Ti₂C(OH)₂, underscoring the broad applicability of MXenes in chlorinated hydrocarbon remediation. This work highlights MXenes as scalable, efficient, and versatile materials for addressing persistent organic pollutants, providing critical insights into their mechanisms and potential for practical implementation in environmental cleanup strategies.

Semiconducting MXenes are an intriguing two-dimensional (2D) material class with promising electronic and optoelectronic properties. Here, we focused on recently prepared Hf-based MXenes, namely, Hf3C2O2 and Hf2CO2. Using the first-principles calculation and excited state corrections, we proved their dynamical stability, reconciled their semiconducting behavior, and obtained fundamental gaps by using the many-body GW method (indirect 1.1 and 2.2 eV; direct 1.4 and 3.5 eV). Using the Bethe–Salpeter equation, we subsequently provided optical gaps (0.9 and 2.7 eV, respectively), exciton binding energies, absorption spectra, and other properties of excitons in both Hf-based MXenes. The indirect character of both 2D materials further allowed for a significant decrease of excitation energies by considering indirect excitons with exciton momentum along the Γ-M path in the Brillouin zone. The first bright excitons are strongly delocalized in real space while contributed by only a limited number of electron–hole pairs around the M point in the k-space from the valence and conduction band. A diverse range of excitonic states in Hf3C2O2 MXene lead to a 4% and 13% absorptance for the first and second peaks in the infrared region of absorption spectra, respectively. In contrast, a prominent 28% absorptance peak in the visible region appears in Hf2CO2 MXene. Results from radiative lifetime calculations indicate the promising potential of these materials in optoelectric devices requiring sustained and efficient exciton behavior.

We tested the precision of accurate many-body GW and BSE methods on seven hexagonal 2D III–V binary semiconductors (BN, BP, BAs, AlN, GaN, GaP, and GaAs), and we provided benchmark electronic and optical properties.

Nitriding has been used for decades to improve the corrosion resistance of iron and steel materials. Moreover, iron nitrides (Fe_xN) have been shown to give an outstanding catalytic performance in a wide range of applications. We demonstrate that nitriding also substantially enhances the reactivity of zerovalent iron nanoparticles (nZVI) used for groundwater remediation, alongside reducing particle corrosion. Two different types of Fe_xN nanoparticles were synthesized by passing gaseous NH₃/N₂ mixtures over pristine nZVI at elevated temperatures. The resulting particles were composed mostly of face-centered cubic (γ′-Fe₄N) and hexagonal close-packed (ε-Fe_2–3N) arrangements. Nitriding was found to increase the particles’ water contact angle and surface availability of iron in reduced forms. The two types of Fe_xN nanoparticles showed a 20- and 5-fold increase in the trichloroethylene (TCE) dechlorination rate, compared to pristine nZVI, and about a 3-fold reduction in the hydrogen evolution rate. This was related to a low energy barrier of 27.0 kJ mol^–1 for the first dechlorination step of TCE on the γ′-Fe₄N(001) surface, as revealed by density functional theory calculations with an implicit solvation model. TCE dechlorination experiments with aged particles showed that the γ′-Fe₄N nanoparticles retained high reactivity even after three months of aging. This combined theoretical-experimental study shows that Fe_xN nanoparticles represent a new and potentially important tool for TCE dechlorination.

The adsorption properties of two iron sulfide minerals (mackinawite and pyrite) and zero-valent iron with respect to two small polar molecules (H₂O and H₂S) and trichloroethylene (TCE) were modeled.