Graphene (G) reactivity toward oxygen is very poor, which limits its use as electrode for the oxygen reduction reaction (ORR). Contrarily, boron-doped graphene was found to be an excellent catalyst for the ORR. Through a density functional study, comparing molecular and periodic approaches and different functionals (B3LYP vs PBE), we show how substitutional boron in the carbon sheet can boost the reactivity with oxygen leading to the formation of bulk borates covalently bound to graphene (BO3–G) in oxygen-rich conditions. These species are highly interesting intermediates for the OO breaking step in the reduction process of O2 to form H2O as they are energetically stable.

The "catalysis under cover" involves chemical processes which take place in the confined zone between a 2D material, such as graphene, h-BN, or MoS2, and the surface of an underlying support, such as a metal or a semiconducting oxide. The hybrid interface between graphene and anatase TiO2 is extremely important for photocatalytic and catalytic applications because of the excellent and complementary properties of the two materials. We investigate and discuss the reactivity of O2 and H2O on top and at the interface of this hybrid system by means of a wide set of dispersion-corrected hybrid density functional calculations. Both pure and boron- or nitrogen-doped graphene are interfaced with the most stable (101) anatase surface of TiO2 in order to improve the chemical activity of the C-layer. Especially in the case of boron, an enhanced reactivity toward O2 dissociation is observed as a result of both the contribution of the dopant and of the confinement effect in the bidimensional area between the two surfaces. Extremely stable dissociation products are observed where the boron atom bridges the two systems by forming very stable B-O covalent bonds. Interestingly, the B defect in graphene could also act as the transfer channel of oxygen atoms from the top side across the C atomic layer into the G/TiO2 interface. On the contrary, the same conditions are not found to favor water dissociation, proving that the "catalysis under cover" is not a general effect, but rather highly depends on the interfacing material properties, on the presence of defects and impurities and on the specific reaction involved.

Functionalizing nanoparticles (NPs) with biological molecules is a promising modern strategy in bionanotechnology to build up smart bioinorganic devices for medical applications. Bifunctional linkers provide an interesting and ductile bioconjugation approach especially because they behave not only as anchoring and tethering agents but also as spacers between the NP and the biomolecules, which helps in maintaining their 3D structural and functional properties. In this work, by means of a wide set of density functional theory (DFT) electronic structure calculations and density functional tight binding (DFTB) molecular dynamics simulations, we provide an all-round investigation of the functionalization of realistic curved TiO2 NPs (2–3 nm size with ∼800 atoms) with a catechol derivative, such as dopamine and DOPAC. We span from single-molecule adsorption to the full coverage regime. For the low coverage, we achieve a detailed description of the mechanisms of molecular adsorption, of the interfacial electronic charge-transfer effects, and of the processes following visible light irradiation (exciton formation, trapping, charge carrier diffusion, or recombination). We then consider a growing molecular layer on the NP and analyze the self-assembling mechanism and the effects on the electronic properties of the complex. Finally, for the maximum coverage (46 molecules per NP) we perform molecular dynamics runs at 300 K to compare the molecular configuration and electronic properties of the NP/linker complex interface before and after thermal treatment to better account for the competition between molecule/surface and molecule/molecule interactions. The use of curved NP surfaces combined with dopamine, with respect to a flat one and DOPAC, respectively, is found to be more effective for bioconjugation.

Understanding magnetism in defective graphene is paramount to improve and broaden its technological applications. A single vacancy in graphene is expected to lead to a magnetic moment with both a σ (1 μB) and a π (1 μB) component. Theoretical calculations based on standard LDA or GGA functional on periodic systems report a partial quenching of the π magnetization (0.5 μB) due to the crossing of two spin split bands at the Fermi level. In contrast, STS experiments (Phys. Rev. Lett.2016117166801) have recently proved the existence of two defect spin states that are separated in energy by 20–60 meV. In this work, we show that self-interaction corrected hybrid functional methods (B3LYP-D*) are capable of correctly reproducing this finite energy gap and, consequently, provide a π magnetization of 1 μB. The crucial role played by the exact exchange is highlighted by comparison with PBE-D2 results and by the magnetic moment dependence with the exact exchange portion in the functional used. The ground state ferromagnetic planar solution is compared to the antiferromagnetic and to the diamagnetic ones, which present an out-of-plane distortion. Periodic models are then compared to graphene nanoflakes of increasing size (up to C383H48). For large models, the triplet spin configuration (total magnetization 2 μB) is the most stable, independently of the functional used, which further corroborates the conclusions of this work and puts an end to the long-debated issue of the magnetic properties of an isolated C monovacancy in graphene.

Quantum mechanical study of TETT-functionalized TiO2 Nanoparticles loaded by doxorubicin with applications in drug delivery and photodynamic therapy.