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Povzetek: Water interaction with mineral surfaces is a complex living system decisive for any photocatalytic process. Resolving atomistic structure of mineral–water interfaces is thus crucial for understanding these processes. Fibrous rutile TiO2, grown hydrothermally on twinned rutile seeds under acidic conditions, was studied in terms of interface translation, atomic structure and surface chemistry in the presence of water, by means of advanced microscopy and spectroscopy methods combined with structure modeling and density functional theory calculations. We show that fibers while staying in stable separation during their growth, adopt special crystallographic registry that is controlled by repulsion forces between fully hydroxylated and protonated (110) surfaces. During relaxation, a turbulent proton transfer and cracking of O–H bonds is observed, generating a strong acidic character via proton jump from bridge –OHb to terminal –OHt groups, and spontaneous dissociation of interfacial water via a transient protonation of the –OHt groups. It is shown, that this specific interface structure can be implemented to induce acidic response in initially neutral medium, when re–immersed. To our knowledge this is the first demonstration of a 2D, quantum confined mineral–water interface, capable of memorizing its past and conveying its structurally encoded properties into a new environment.
Ključne besede: mineral-water interfaces, atomistic structure, photocatalysis
Objavljeno v DiRROS: 20.04.2026; Ogledov: 129; Prenosov: 118
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Objavljeno v DiRROS: 30.03.2026; Ogledov: 201; Prenosov: 135
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Objavljeno v DiRROS: 30.03.2026; Ogledov: 159; Prenosov: 129
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Povzetek: Loparite is a natural perovskite (ABO3) with a complex composition, essentially a solid solution between loparite(-Ce) (Na0.5Ce0.5TiO3), lueshite (NaNbO3), and perovskite (CaTiO3), with small amounts of many other elements. The majority of reported loparite crystals are spinel-type interpenetration twins with compositional zoning. Associated with the high variability of compositions, different crystal structures of loparite were described, and the origin of twinning has not been addressed so far. In this work, we studied a loparite twin composed of two symmetrically intergrown cuboctahedra. Microprobe analyses revealed that the cubic and octahedral growth sectors have slightly different compositions. According to atomic-scale analyses, the cubic sectors with a lower Na:LREE ratio have a disordered orthorhombic structure, while the octahedral sectors with a higher Na:LREE ratio show partial ordering of Na and light rare-earth elements along A-type lattice planes in the [001] direction. The degree of ordering was evaluated by quantitative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Atomic-scale analyses of (111) and {112} twin boundary (TB) contacts have shown that all TBs contain a 1–2 nm thin layer of an Si-rich amorphous phase. Our observations suggest that the loparite twin was established in the nucleation stage of crystallisation, followed by independent crystallisation of both twin domains from the melt. The initial crystal form was cubic; octahedral sectors evolved when the crystal size was still in the nanometre range, as a result of slow crystal growth. Differences in structural ordering between adjacent growth sectors developed during slow cooling due to the compositional variations. Our results imply that compositionally zoned crystals might show different structural ordering within single domains, which should be considered when interpreting bulk diffraction data of compositionally zoned perovskites.
Ključne besede: loparite, loparite twin, growth sectors, morphology
Objavljeno v DiRROS: 02.03.2026; Ogledov: 281; Prenosov: 210
Celotno besedilo (12,71 MB)
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Povzetek: Light-powered strategies for the semi-hydrogenation of acetylene to ethylene are rapidly emerging as sustainable alternatives to the traditional thermochemical processes. The development of a robust, selective, as well as recyclable, non-noble catalyst that can be powered by visible light and uses water as proton source to accomplish this important reaction remains a key challenge. Here the first demonstration of a cobalt single-atom catalyst supported on carbon-nitride (Co−CN) as an all-in-one photocatalyst for the semi-hydrogenation of acetylene to ethylene is reported using water as the proton source, offering advantages over current hydrogenation technologies. Carbon nitride hosts the individual catalytic active sites of cobalt thus combining photosensitizer and cocatalyst in one unit, in line with first-principles modelling. Under visible light irradiation, Co−CN reduces acetylene to ethylene with stable activity for over 40 days of continuous operation, ≥99.9% selectivity, and provides means for coupling organic upgrading to produce valuable oxidation products. The heterogeneous Co−CN can be easily recovered and reused repeatedly without loss of catalytic activity and structural integrity. Thereby, the integrated and recyclable platform overcomes the need of coupling a separate photosensitizer to a catalyst, and using noble metal catalysts with an external H2 gas feed.
Objavljeno v DiRROS: 04.02.2026; Ogledov: 550; Prenosov: 211
Celotno besedilo (2,12 MB)
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