Abstract: The structural complexity of the antiferromagnetic oxide selenide CaFeSeO is described. The compound contains puckered FeSeO layers composed of FeSe2O2 tetrahedra sharing all their vertexes. Two polymorphs coexist that can be derived from an archetype BaZnSO structure by cooperative tilting of the FeSe2O2 tetrahedra. The polymorphs differ in the relative arrangement of the puckered layers of vertex-linked FeSe2O2 tetrahedra. In a noncentrosymmetric Cmc21 polymorph (a = 3.89684(2) A, b = 13.22054(8) A, c = 5.93625(2) A) the layers are related by the C-centering translation, while in a centrosymmetric Pmcn polymorph, with a similar cell metric (a = 3.89557(6) A, b = 13.2237(6) A, c = 5.9363(3) A), the layers are related by inversion. The compound shows long-range antiferromagnetic order below a Neel temperature of 159(1) K with both polymorphs showing antiferromagnetic coupling via Fe-O-Fe linkages and ferromagnetic coupling via Fe-Se-Fe linkages within the FeSeO layers. The magnetic susceptibility also shows evidence for weak ferromagnetism which is modeled in the refinements of the magnetic structure as arising from an uncompensated spin canting in the noncentrosymmetric polymorph. There is also a spin glass component to the magnetism which likely arises from the disordered regions of the structure evident in the transmission electron microscopy.

Abstract: Direct experimental measurement of thermal expansion coefficient without substrate effects is a challenging task for two-dimensional (2D) materials, and its accurate estimation with large-scale ab initio molecular dynamics is computationally very expensive. Machine learning-based interatomic potentials trained with ab initio data have been successfully used in molecular dynamics simulations to decrease the computational cost without compromising the accuracy. In this study, we investigated using Gaussian approximation potentials to reproduce the density functional theory-level accuracy for graphene within both lattice dynamical and molecular dynamical methods, and to extend their applicability to larger length and time scales. Two such potentials are considered, GAP17 and GAP20. GAP17, which was trained with pristine graphene structures, is found to give closer results to density functional theory calculations at different scales. Further vibrational and structural analyses verify that the same conclusions can be deduced with density functional theory level in terms of the reasoning of the thermal expansion behavior, and the negative thermal expansion behavior is associated with long-range out-of-plane phonon vibrations. Thus, it is argued that the enabled larger system sizes by machine learning potentials may even enhance the accuracy compared to small-size-limited ab initio molecular dynamics.

Abstract: A biomimetic sensor for cefquinome (CFQ) was designed at multi-walled carbon nanotubes modified graphite screen-printed electrodes (MWCNTs-G-SPEs) as a proof-of-concept for the creation of a sensors array for beta-lactam antibiotics detection in milk. The sensitive and selective detection of antibiotic residues in food and environment is a fundamental step in the elaboration of prevention strategies to fight the insurgence of antimicrobial resistance (AMR) as recommended by authorities around the world (EU, WHO, FDA). The detection strategy is based on the characteristic electrochemical fingerprint of the target antibiotic cefquinome. A conducive electropolymerized molecularly imprinted polymer (MIP) coupled with MWCNTs was found to be the optimal electrode modifier, able to provide an increased selectivity and sensitivity for CFQ detection. The design of CFQ-MIP was facilitated by the rational selection of the monomer, 4-aminobenzoic acid (4-ABA). The electropolymerization process of 4-ABA have not been fully elucidated yet; for this reason a thorough study and optimization of electropolymerization conditions was performed to obtain a conducive and stable poly(4-ABA) film. The modified electrodes were characterized by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and cyclic voltammetry (CV). CFQ-MIP were synthesized at MWCNT-G-SPEs by electropolyrnerization in pH approximate to 1 (0.1 M sulphuric acid) with a monomer:template ratio of 5:1. Two different analytical protocols were tested (single and double step detection) to minimize unspecific adsorptions and improve the sensitivity. Under optimal conditions, the lowest CFQ concentration detectable by square wave voltammetry (SWV) at the modified sensor was 50 nM in 0.1 M phosphate buffer pH 2.

Abstract: In this study, the multi-layer self-assembled molecular network formation of an alkylated tetrathiafulvalene compound is studied at the liquid-solid interface between 1-phenyloctane and graphite. A combined theoretical/experimental approach associating force-field and quantum-chemical calculations with scanning tunnelling microscopy is used to determine the two-dimensional self-assembly beyond the monolayer, but also to further the understanding of the molecular adsorption conformation and its impact on the molecular packing within the assemblies at the monolayer and bilayer level.

Abstract: To gain full control over the growth of carbon nanotubes (CNTs) using plasma-enhanced chemical vapor deposition (PECVD), a thorough understanding of the underlying plasma-catalyst mechanisms is required. Oxygen-containing species are often used as or added to the growth precursor gas, but these species also yield various radicals and ions, which may simultaneously etch the CNT during the growth. At present, the effect of these reactive species on the growth onset has not yet been thoroughly investigated. We here report on the etching mechanism of incipient CNT structures from OH and O radicals as derived from combined (reactive) molecular dynamics (MD) and force-bias Monte Carlo (tfMC) simulations. Our results indicate that the oxygen-containing radicals initiate a dissociation process. In particular, we show how the oxygen species weaken the interaction between the CNT and the nanocluster. As a result of this weakened interaction, the CNT closes off and dissociates from the cluster in the form of a fullerene. Beyond the specific systems studied in this work, these results are generically important in the context of PECVD-based growth of CNTs using oxygen-containing precursors.

Abstract: A simple and low-cost method to create metal−metal hybrid nanostructures possessing fairly regularly spaced hot-spots of surface plasmon resonances is proposed. The nanohybrid structure was prepared via self-assembly during a simple drop-casting procedure, using chemically synthesized silver nanowires and silver nanoparticles prepared in a single batch of a polyol process. Wide field illumination of these nanohybrids produced hot-spots with spacings of around 500 nm to 1 ìm. The intensity of the emission/scattering from the hot-spots fluctuates over time. The proposed structure can be useful for the development of molecular-sensors or as a substrate for surface enhanced Raman/fluorescence spectroscopy.

Abstract: Multi-wall carbon nanotubes have been produced by the catalytic decomposition of acetylene. Go-Mo, Co-V and Co-Fe mixtures supported either on zeolite or corundum alumina were used as catalysts. When Fe or V is added to Co, the carbon deposit increases. The nanotubes were characterized by both low and high resolution TEM. From histograms representing the outer diameter distributions, it is clear that the outer diameter of the nanotubes can be controlled by choosing the appropriate catalyst. (C) 2000 Elsevier Science B.V. All rights reserved.

Abstract: High-quality single-walled carbon nanotubes (SWNTs) are synthesized in gram amount on Fe-Mo/MgO catalysts by catalytic decomposition of CH4 in H-2 or N-2. Raman data reveal that the as-prepared SATNTs have a diameter of about 0.74-1.29 nm. It is found that the diameter of the as-prepared SWNTs can be controlled mainly by adjusting the molar ratio of Fe-Mo versus the MgO support. Several other factors that potentially influence the growth of SWNTs have been studied in detail. The experimental results show that the nature of the catalyst determines the diameter of the as-prepared SWNTs. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: With the aim of an improved understanding of the metal-complexation properties of alicyclic β-amino acid stereoisomers, and their peptides, the complex equilibria and modes of coordination with copper(II) of l-phenylalanine (F) derivatives of cis/trans-2-aminocyclohexanecarboxylic acid (c/tACHC), i.e. the dipeptides F-c/tACHC and c/tACHC-F, were investigated by a combination of CW and pulsed EPR methods. For the interpretation of the experimental data, DFT quantum-chemical calculations were carried out. Simulation of a pH-dependent series of room-temperature CW-EPR spectra revealed the presence of EPR-active complexes ([Cu(aqua)]2+, [CuL]+, [CuLH1], [CuLH2]−, and [CuL2H1]−), and an EPR-inactive species ([Cu2L2H3]−) in aqueous solutions for all studied cases. [CuLH]2+ was included in the equilibrium model for the c/tACHC-Fcopper(II) systems, and [CuL2], together with two coordination isomers of [CuL2H1]−, were also identified in the F-tACHCcopper(II) system. Comparison of the complexation properties of the diastereomeric ligand pair F-(1S,2R)-ACHC and F-(1R,2S)-ACHC did not reveal significant differences. Considerably lower formation constants were obtained for the trans than for the cis isomers for both the F-c/tACHC and the c/tACHC-F pairs in the case of [CuLH1] involving tridentate coordination by the amino, the deprotonated peptide, and the carboxylate groups. A detailed structural analysis by pulsed EPR methods and DFT calculations indicated that there was no significant destabilization for the complexes of the trans isomers. The lower stability of their complexes was explained by the limitation that only the conformer with donor groups in equatorialequatorial ring positions can bind to copper(II), whereas both equatorial-axial conformers of the cis isomers are capable of binding. From a consideration of the proton couplings obtained with X-band 1H HYSCORE, 2H exchange experiments, and DFT, the thermodynamically most stable cyclohexane ring conformer was assigned for all four [CuLH1] complexes. For the F-cACHC case, the conformer did not match the most stable conformer of the free ligand.

Abstract: In the commercialisation of photocatalytic air purifiers, the performance as well as the cost of the catalytic material plays an important role. Where most comparative studies only regard the photocatalytic activity as a decisive parameter, in this study both activity and cost are taken into account. Using a cost-effectiveness analysis, six different commercially available TiO2-based catalysts are evaluated in terms of their activities in photocatalytic degradation of acetaldehyde as a model reaction for indoor air purification.

Abstract: Assemblies of closely separated gold nanoparticles exhibit a strong collective plasmonic response due to coupling of the plasmon modes of the individual nanostructures. In the context of self-assembly of nanoparticles, close-packed two-dimensional (2D) clusters of spherical nanoparticles present an important composite system that promises numerous applications. The present study probes the collective plasmonic characteristics and resulting photothermal behavior of close-packed 2D Au nanoparticle clusters to delineate the effects of the cluster size, interparticle distance, and particle size. Smaller nanoparticles (20 and 40 nm in diameter) that exhibit low individual scattering and high absorption were considered for their relevance to photothermal applications. In contrast to typical literature studies, the present study compares the optical response of clusters of different sizes ranging from a single nanoparticle up to large assemblies of 61 nanoparticles. Increasing the cluster size induces significant changes to the spectral position and optophysical characteristics. Based on the model outcome, an optimal cluster size for maximum absorption per nanoparticle is also determined for enhanced photothermal effects. The effect of the particle size and interparticle distance is investigated to elucidate the nature of interaction in terms of near-field and far-field coupling. The photothermal effect resulting from absorption is compared for different cluster sizes and interparticle distances considering a homogeneous water medium. A strong dependence of the steady-state temperature of the nanoparticles on the cluster size, particle position in the cluster, incident light polarization, and interparticle distance provides new physical insight into the local temperature control of plasmonic nanostructures.

Abstract: Surface charging is an often overlooked factor in many plasma-surface interactions and in particular in plasma catalysis. In this study, we investigate the effect of excess electrons induced by a plasma on the adsorption properties of CO2 on titania-supported Cu-5 and Ni-5 clusters using spin-polarized and dispersion-corrected density functional theory calculations. The effect of excess electrons on the adsorption of Ni and Cu pentamers as well as on CO2 adsorption on a pristine anatase TiO2(101) slab is studied. Our results indicate that adding plasma-induced excess electrons to the system leads to further stabilization of the bent CO2 structure. Also, dissociation of CO2 on charged clusters is energetically more favorable than on neutral clusters. We hypothesize that surface charge is a plausible cause for the synergistic effects sometimes observed in plasma catalysis.

Abstract: In this paper we study dry reforming of methane (DRM) in a gliding arc plasmatron (GAP) in the presence of N₂and O₂. N₂is added to create a stable plasma at equal fractions of CO₂and CH₄, and because emissions from industrial plants typically contain N₂, while O₂is added to enhance the process. We test different gas mixing ratios to evaluate the conversion and energy cost. We obtain conversions between 31 and 52% for CO₂and between 55 and 99% for CH₄, with total energy costs between 3.4 and 5.0 eV per molecule, depending on the gas mixture. This is very competitive when benchmarked with the literature. In addition, we present a chemical kinetics model to obtain deeper insight in the underlying plasma chemistry. This allows determination of the major reaction pathways to convert CO₂and CH₄, in the presence of O₂and N₂, into CO and H₂. We show that N₂assists in the CO₂conversion, but part of the applied energy is also wasted in N₂excitation. Adding O₂enhances the CH₄conversion, and lowers the energy cost, while the CO₂conversion remains constant, and only slightly drops at the highest O₂fractions studied, when CH₄is fully oxidized into CO₂.