Міжнародна наукова конференція "Архівознавство як наука"

Проаналізовано внесок істориків і архівістів України в розвиток архівної науки. Вказуються основні розділи архівознавства як науки, що вимагають подальших досліджень.Проанализирован вклад историков и архивистов Украины в развитие архивной науки. Указываются основные разделы архивоведения как науки, которые требуют дальнейших исследований.A contribution of Ukrainian historians and archivists to the archival science development is covered. The basic sections of the archival science which need the further study are indicated

Pinpointing the active species of the Cu(DAT) catalyzed oxygen reduction reaction

\u3cp\u3eDinuclear Cu\u3csup\u3eII\u3c/sup\u3e complexes bearing two 3,5-diamino-1,2,4-triazole (DAT) ligands have gained considerable attention as a potential model system for laccase due to their low overpotential for the oxygen reduction reaction (ORR). In this study, the active species for the ORR was investigated. The water soluble dinuclear copper complex (Cu(DAT)) was obtained by mixing a 1 : 1 ratio of Cu(OTf)\u3csub\u3e2\u3c/sub\u3e and DAT in water. The electron paramagnetic resonance (EPR) spectrum of Cu(DAT) showed a broad axial signal with a g factor of 2.16 as well as a low intensity M\u3csub\u3es\u3c/sub\u3e = ±2 absorption characteristic of the Cu\u3csub\u3e2\u3c/sub\u3e(μ-DAT)\u3csub\u3e2\u3c/sub\u3e moiety. Monitoring the typical 380 nm peak with UV-Vis spectroscopy revealed that the Cu\u3csub\u3e2\u3c/sub\u3e(μ-DAT)\u3csub\u3e2\u3c/sub\u3e core is extremely sensitive to changes in pH, copper to ligand ratios and the presence of anions. Electrochemical quartz crystal microbalance experiments displayed a large decrease in frequency below 0.5 V versus the reversible hydrogen electrode (RHE) in a Cu(DAT) solution implying the formation of deposition. Rotating ring disk electrode experiments showed that this deposition is an active ORR catalyst which reduces O\u3csub\u3e2\u3c/sub\u3e all the way to water at pH 5. The activity increased significantly in the course of time. X-ray photoelectron spectroscopy was utilized to analyze the composition of the deposition. Significant shifts in the Cu 2p\u3csub\u3e3/2\u3c/sub\u3e and N 1s spectra were observed with respect to Cu(DAT). After ORR catalysis at pH 5, mostly Cu\u3csup\u3eI\u3c/sup\u3e and/or Cu\u3csup\u3e0\u3c/sup\u3e species are present and the deposition corresponds to previously reported electrodepositions of copper. This leads us to conclude that the active species is of a heterogeneous nature and lacks any structural similarity with laccase.\u3c/p\u3

Role of dissociatively adsorbed water on the formation of shallow trapped electrons in TiO2 photocatalysts

The mismatch between short lifetimes of free charge carriers and slow kinetics of surface redox reactions substantially limits the efficiency of most photocatalytic systems. Hence, the knowledge of trapping and recombination of photogenerated electrons and holes at different time scales is key for a rational optimization of photocatalytic materials. In this study, we used subsecond time-resolved diffuse-reflectance FTIR spectroscopy to investigate how energy and intensity of the incident irradiation affect the dynamics of photogenerated charge carriers in TiO2 P25 photocatalysts subjected to different pretreatments and how shallow trapped electrons (STE) are formed under these conditions. Intensity-dependent measurements demonstrated that electrons and holes generated by 325 and 409 nm irradiation undergo bimolecular and trap-assisted recombination, respectively. Analysis of characteristic times of photogenerated electron absorption rise and decay indicated that the apparent charge carrier dynamics at the time scale of seconds to minutes relate to chemical trapping of photogenerated electrons and holes. The presence of dissociatively adsorbed water on the oxide surface was required for efficient STE formation. This suggests that STE form at the seconds–minutes time scale upon surface-mediated self-trapping of electrons

Porous nitrogen-doped carbon/carbon nanocomposite electrodes enable sodium ion capacitors with high capacity and rate capability

\u3cp\u3eThe realization of electrochemical energy storage devices combining high energy and power density places high demands on the electrode materials. It remains difficult to provide high metal storage capacity and rate capability at the same time in one and the same material. By decoupling metal storage and electron transport in different phases of a nanostructured electrode composed of nitrogen-rich carbon nanoparticles which are embedded into a conductive mesoporous carbon matrix, this dilemma can be minimized. The composite material has a remarkable performance for sodium storage with a reversible capacity of 343 mAh g\u3csup\u3e−1\u3c/sup\u3e at 0.1 A g\u3csup\u3e−1\u3c/sup\u3e and capacity retention of 124 mAh g\u3csup\u3e−1\u3c/sup\u3e at 20 A g\u3csup\u3e−1\u3c/sup\u3e. This work shows that a properly designed nanocomposite material can fulfill both requirements and sheds new light on resolving the seemingly conflicting energy/power density demands in current electrochemical energy storage devices.\u3c/p\u3

Evaluating the stability of Co\u3csub\u3e2\u3c/sub\u3eP electrocatalysts in the hydrogen evolution reaction for both acidic and alkaline electrolytes

\u3cp\u3eThe evaluation of the stability of emerging earth-abundant metal phosphide electrocatalysts by solely electrochemical current-potential sweeps is often not conclusive. In this study, we investigated Co\u3csub\u3e2\u3c/sub\u3eP to evaluate its stability under both acidic (0.5 M H\u3csub\u3e2\u3c/sub\u3eSO\u3csub\u3e4\u3c/sub\u3e) and alkaline (1.0 M KOH) hydrogen evolution (HER) conditions. We found that the electrochemical surface area (ECSA) of Co\u3csub\u3e2\u3c/sub\u3eP only slightly increased in acidic conditions but almost doubled after electrolysis in alkaline electrolyte. The surface composition of the electrode remained almost unchanged in acid but was significantly altered in alkaline during current-potential sweeps. Analysis of the electrolytes after the stability test shows almost stoichiometric composition of Co and P in acid, but a preferential dissolution of P over Co could be observed in alkaline electrolyte. Applying comprehensive postcatalysis analysis of both the electrode and electrolyte, we conclude that Co\u3csub\u3e2\u3c/sub\u3eP, prepared by thermal phosphidization, dissolves stoichiometrically in acid and degrades to hydroxides under alkaline stability testing.\u3c/p\u3

Interfacial charge transfer in Pt-loaded TiO2 P25 photocatalysts studied by in-situ diffuse reflectance FTIR spectroscopy of adsorbed CO

\u3cp\u3eThe efficiency of photocatalytic systems is strongly depending on the charge carrier transfer from the excited semiconductor to co-catalyst particles attached on its surface. In this study, we investigated the influence of photo-induced charge transfer in photoplatinized TiO \u3csub\u3e2\u3c/sub\u3e P25 photocatalysts by diffuse reflectance FTIR spectroscopy of CO molecules adsorbed on the Pt co-catalyst under well-defined gas phase conditions. In contrast to aqueous conditions, where shifts of the CO stretching vibration of up to 50 cm \u3csup\u3e−1\u3c/sup\u3e have been reported, the observed shifts under gas phase conditions are very small (<1 cm \u3csup\u3e−1\u3c/sup\u3e). This demonstrates that the difference in dielectric properties between aqueous electrolytes and vacuum are critical for the development of prominent shifts of adsorbed CO bands upon trapping of photogenerated charge carriers on co-catalyst particles. The experimental findings are discussed in terms of an electrostatic Stark effect, charge screening, co-adsorption, coverage-dependent shifts of the vibrational bands of adsorbed CO and photocatalytic surface reactions. \u3c/p\u3

Mixed Cd-Zn sulfides / Pt-TiO2 composites : bottlenecks limiting efficiency of photocatalytic water reduction

Visible-light driven photocatalytic water reduction on composite materials consisting of platinized titania (Pt-TiO2) and transition metal sulfides (CdS or Cd0.5Zn0.5S) was investigated in detail. Sulfides were prepared by hydrothermal synthesis and room-temperature precipitation. The parameters limiting performance of these composite systems were elucidated. All composites with Pt-TiO2 demonstrated similar hydrogen evolution rates independent from their textural properties, bandgaps, electron transfer between components and intrinsic activities of the sulfides. Moreover, all platinized sulfides, except for the precipitated CdS, were more active than the corresponding composites with Pt-TiO2. This behavior – counterintuitive to the improved charge carrier separation found in the materials with heterojunctions – was rationalized by the low mobility of the conduction band electrons in TiO2. The slow electron transport severely limits efficiency of the investigated composite materials in the photocatalytic water reduction. This effect is especially apparent for highly active sulfides but less so for materials with inherently low activity. The low driving force of bare CdS toward water reduction results in an apparent synergy with Pt-TiO2 and makes the corresponding composites sensitive to Pt poisoning as the hydrogen evolution reaction predominantly takes place on Pt-TiO2. On the other hand, mixed sulfides, being more active water reduction photocatalysts, compete with Pt particles in this process making corresponding composites less sensitive to the state of Pt. The findings are discussed in terms of the intrinsic photocatalytic activity of sulfides, electron transfer from sulfides to titania, electrochemical potentials of conduction band electrons, poisoning of Pt nanoparticles, and charge carrier mobility

Imaging the effect of a hydrothermal treatment on the pore accessibility and acidity of large ZSM-5 zeolite crystals by selective staining

Confocal fluorescence microscopy has been used in combination with bulky non-reactive dyes (i.e. proflavine, stilbene and nile blue A) and two staining reactions (i.e. fluorescein synthesis and 4-fluorostyrene oligomerisation) to study the effect of steaming on pore accessibility and acidity of large ZSM-5 zeolite crystals. This approach enabled the 3-D visualization of cracks and mesopores connected to the outer zeolite surface as well as mesoporous cavities within steamed ZSM-5 zeolite crystals. It has been found that besides the generation of mesoporosity steaming makes the boundaries between the different crystal sub-units accessible for bulky molecules. Additionally, the fluorescein staining reaction reveals prominent formation of structural defects that are connected to the surface of the crystal via the microporous ZSM-5 system and which contain either Brønsted or Lewis acid sites. On the other hand, the 4-fluorostyrene staining reaction shows how mild steaming conditions increase the accessibility towards the Brønsted acid sites, while under severe steaming conditions the Brønsted acidity contained in the internal crystal sub-units is more accessible, although it is preferentially removed close to the surface of the lateral sub-units of ZSM-5 zeolite crystals