Composites with Immobilized Bioactive Spirulina on an Inorganic Substrate (Yellow Clay, Hydroxyapatite, SiO2, TiO2, ZnO)

In order to improve the structural properties of clays and composites of powdered spirulina, clay, nanosilica, hydroxyapatite, TiO2 and ZnO were used as an additive for mechanical processing. As a result, composites with natural nanostructured materials (NNM) are prepared with improved structural properties and bioactivity. The mixtures based on NNM with crystalline kaolinite, clays and admixtures were processed in a knife mill. The materials were characterized using FTIR spectroscopy, nitrogen adsorption and desorption, SEM release of bioactive components (anthocyanin 0,004-0,07 mg/g; chlorophyll 20-29 mg/g), composite toxicity level (below 25%), particle size measurement and surface charge density, zeta potential. Adsorption enthalpies during the formation of an intermolecular complex during the interactions of an anthocyanin molecule with the appropriate component of the composite were also calculated. There are regularities in the characteristics depending on the type of NNM, particle morphology and textural features of solids. The morphological and structural properties of the components changed slighty in the blends because the processing was conducted under relatively low mechanical stress. The morphological, textural and structural characteristics of the composites as well as the transformation to a nanostructured state, assume great bioactive activity of the composites, interesting for practical applications in medicine and cosmetics.

Dendrite-Free Zinc Anodes Enabled by Exploring Polar-Face-Rich 2D ZnO Interfacial Layers for Rechargeable Zn-Ion Batteries

Zinc metal is a promising candidate for anodes in zinc-ion batteries (ZIBs), but its widespread implementation is hindered by dendrite growth in aqueous electrolytes. Dendrites lead to undesirable side reactions, such as hydrogen evolution, passivation, and corrosion, causing reduced capacity during prolonged cycling. In this study, an approach is explored to address this challenge by directly growing 1D zinc oxide (ZnO) nanorods (NRs) and 2D ZnO nanoflakes (NFs) on Zn anodes, forming artificial layers to enhance ZIB performance. The incorporation of ZnO on the anode offers both chemical and thermal stability and leverages its n-type semiconductor nature to facilitate the formation of ohmic contacts. This results in efficient electron transport during Zn ion plating and stripping processes. Consequently, the ZnO NFs-coated Zn anodes demonstrate significantly improved charge storage performance, achieving 348 mAh g-1, as compared to ZnO NRs (250 mAh g-1) and pristine Zn (160 mAh g-1) anodes when evaluated in full cells with V2O5 cathodes. One significant advantage of ZnO NFs lies in their highly polar surfaces, promoting strong interactions with water molecules and rendering them exceptionally hydrophilic. This characteristic enhances the ability of ZnO NFs to desolvate Zn2+ ions, leading to improved charge storage performance.

Theory-guided unraveling of the mechanism underlying Cu1.0/Mn1.0-ZnO with dual reaction centers for enhanced peroxymonosulfate activation

Developing efficient catalytic systems for water contamination removal is a topic of great interest. However, the use of heterogeneous catalysts faces challenges due to insufficient active sites and electron cycling. In this study, results from first-principles calculations demonstrate that dual reaction centers (DRCs) are produced around the Cu and Mn sites in Cu1.0/Mn1.0-ZnO due to the electronegativity difference. Experimental results reveal the material with DRCs greatly enhances electron transfer efficiency and significantly impacts the oxidation and reduction of peroxymonosulfate (PMS). In addition, the self-consistent potential correction (SCPC) method was introduced to correct the energy and charge of charged periodic systems simulating a catalytic process, resulting in more precise catalytic results. Specifically, the material exhibits a preference for adsorbing negatively charged PMS anions at electron-deficient Mn sites, facilitating PMS oxidation for the generation of 1O2, and PMS reduction around the electron-rich Cu for the formation of •OH and SO4•-. The major reactive oxygen species is 1O2, showcasing effective performance in various degradation systems. Overall, our work provides novel insights into the persulfate-based heterogeneous catalytic oxidation process, paving the way for the development of high-performance catalytic systems for water purification.

Exchange Functionals and Basis Sets for Density Functional Theory Studies of Water Splitting on Selected ZnO Nanocluster Catalysts

In this communication, we use density functional theory (DFT) to study the structural (geometry) and electronic properties (vertical detachment energy and electron affinity) of ZnO monomers and dimers that can be used to form ZnO clusters of different sizes, with a view to adapting one or more of them as catalysts or photocatalysts, standing alone or on suitable substrates like graphene, to split water. We also investigate different pairs of exchange functionals and basis sets to optimize their choice in our DFT calculations and to compare the singlet-triplet energy gaps of small ZnO clusters of different sizes to select an optimal cluster size for water splitting. We find that the B3LYP/DGDZVP2 exchange functional/basis set is a reliable combination for use with DFT to calculate the geometry and electronic properties of small ZnO nanoclusters from among several other combinations of exchange functionals and basis sets. Comparisons of the singlet-triplet energy gaps show that the trimer (ZnO)₃ has an energy gap of 58.66 k cal/mol. which is approximately equal to the energy of a visible photon at a wavelength of 500 nm, and a HOMO-LUMO gap of 4.4 eV, making it a suitable choice of photocatalyst for the oxidation of water from among six (ZnO) _n nanoclusters of monomers, with n ranging from 1 to 6. We used this exchange functional/basis set to study the structural and energetic details of hydration and hydrolysis of water absorbed on the (ZnO)₃ nanocatalyst and calculated the corresponding potential energy profiles to identify three sets of singlet-triplet pathways for water splitting. Detailed study of a pathway showed that oxygen is produced after hydrogen, and the rate-determining step is the formation of hydrogen.

Unveiling the Atomic Structure and Growth Dynamics of One-Dimensional Water on ZnO(10-10)

The adsorption and organization state of water on the metal oxide surface is of critical importance for wide fields where interface chemistry dominates. On the technically important ZnO(10-10) surface, we found water assembles into an one-dimensional (1D) chain structure at submonolayer coverage instead of the well-known half-dissociated two-dimensional (2D) island. With a combination of high resolution scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we clearly distinguished the single and double water chains, which are composed of dissociated monomers and half-dissociated dimers, respectively. Moreover, we unambiguously determined that single water molecules dissociate spontaneously before agglomerating into ordered phase, which is contrary to the proposition of previous studies. These results have deepened our understandings of the adsorbed water species on the ZnO surface, which may bring new insights into the mechanisms of water-stimulated surface reactions.

Aging-Dependent Changes in Mechanical Properties of the New Generation of Bulk-Fill Composites

This study evaluated the behavior of a new generation of bulk-fill resin composites after prolonged exposure to an aqueous environment and accelerated aging in ethanol. Six bulk-fill materials were tested (Tetric PowerFill, Filtek One Bulk Fill Restorative, Tetric EvoCeram Bulk Fill, Fill-Up!, Tetric PowerFlow, SDR Plus Bulk Fill Flowable) and compared to two conventional reference materials (Tetric EvoCeram and Tetric EvoFlow). Flexural strength, modulus, and Weibull parameters were examined at three time points: 1 day, 30 days, and 30 days followed by ethanol immersion. Degree of conversion after 30 days, water sorption, and solubility up to 90 days were also investigated. Filtek One Bulk Fill had the highest flexural strength and modulus among the tested materials, followed by Tetric PowerFill and SDR plus. Flexural strength and modulus of high-viscosity bulk-fill materials showed higher stability after accelerated aging in ethanol compared to their low-viscosity counterparts and reference materials. After 30 days, the degree of conversion was above 80% for all tested materials. Dual-cure material Fill-Up! was the best-cured material. The water sorption was highest for Fill-Up!, Filtek One Bulk Fill Restorative, and Tetric EvoFlow, while solubility was highest for Tetric EvoCeram. After aging in water and ethanol, new generation high-viscosity bulk-fill materials showed better mechanical properties than low-viscosity bulk-fill and conventional composites under extended light curing conditions.

Single Molecular Reaction of Water on a ZnO Surface

The dissociation of a single water molecule on a ZnO(101̅0) surface has been investigated at the atomic level by low temperature STM manipulation combined with DFT calculations. The positive pulses applied from the tip inject electrons into the system and break the bonding between water and the ZnO surface, thus leading to the hopping of water molecules. Negative pulses inject holes wherein the lower energy ones split the free O-H bond pointing out of the surface whereas the higher energy ones split the second O-H bond that is directed to the surface through hydrogen bonding. Moreover, the yielded proton and hydroxyl species present distinctly charged status through different reaction pathways, manifesting their unique impacts on tailoring the surface properties of the metal oxide.

Comparative Study of Cold Sintering Process and Autoclave Thermo-Vapor Treatment on a ZnO Sample

Analysis of scanning electron microscopy images was used to study the changes in the crystal size distribution of ZnO, which occurred during its processing in an aqueous medium at 220–255 °C and an equilibrium vapor pressure in an autoclave. The results were compared with those of ZnO placed in a die for treatment under similar conditions supplemented with mechanical pressure application in the cold sintering process. In both cases, ZnO was treated in the presence of an activating additive: either zinc acetate or ammonium chloride. During autoclaving, a powder consisting of fine ZnO monocrystals was obtained, while the cold sintering process led to ceramics formation. Under vapor pressure and mechanical pressure, the aqueous medium affected ZnO transformation by the same mechanism of solid-phase mobility activation due to the additives’ influence. The higher the content of additives in the medium, and the higher the mechanical pressure, the more pronounced activating effect was observed. Mass transfer during the cold sintering process occurred mainly by the coalescence of crystals, while without mechanical pressure, the predominance of surface spreading was revealed. In the initial ZnO powder, the average crystal size was 0.193 μm. It grew up to 0.316–0.386 μm in a fine-crystalline powder formed in the autoclave and to an average grain size of 0.244–0.799 μm in the ceramics, which relative density reached 0.82–0.96. A scheme explaining the influence of an aqueous medium on the solid-phase mobility of ZnO structure was proposed. It was found that the addition of 7.6 mol% ammonium chloride to the reaction medium causes the processes of compaction and grain growth similar to those observed in ZnO Cold Sintering Process with the addition of 0.925 mol% zinc acetate.

Water-Mediated Ionic Migration in Memristive Nanowires with a Tunable Resistive Switching Mechanism

Memristive devices based on electrochemical resistive switching effects have been proposed as promising candidates for in-memory computing and for the realization of artificial neural networks. Despite great efforts toward understanding the nanoionic processes underlying resistive switching phenomena, comprehension of the effect of competing redox processes on device functionalities from the materials perspective still represents a challenge. In this work, we experimentally and theoretically investigate the concurring reactions of silver and moisture and their impact on the electronic properties of a single-crystalline ZnO nanowire (NW). A decrease in electronic conductivity due to surface adsorption of moisture is observed, whereas, at the same time, water molecules reduce the energy barrier for Ag+ ion migration on the NW surface, facilitating the conductive filament formation. By controlling the relative humidity, the ratio of intrinsic electronic conductivity and surface ionic conductivity can be tuned to modulate the device performance. The results achieved on a single-crystalline memristive model system shed new light on the dual nature of the mechanism of how moisture affects resistive switching behavior in memristive devices.

Interaction of H2O with the Platinum Pt (001), (011), and (111) Surfaces: A Density Functional Theory Study with Long-Range Dispersion Corrections

Platinum is a noble metal that is widely used for the electrocatalytic production of hydrogen, but the surface reactivity of platinum toward water is not yet fully understood, even though the effect of water adsorption on the surface free energy of Pt is important in the interpretation of the morphology and catalytic properties of this metal. In this study, we have carried out density functional theory calculations with long-range dispersion corrections [DFT-D3-(BJ)] to investigate the interaction of H₂O with the Pt (001), (011), and (111) surfaces. During the adsorption of a single H₂O molecule on various Pt surfaces, it was found that the lowest adsorption energy (E _ads) was obtained for the dissociative adsorption of H₂O on the (001) surface, followed by the (011) and (111) surfaces. When the surface coverage was increased up to a monolayer, we noted an increase in E _ads/H₂O with increasing coverage for the (001) surface, while for the (011) and (111) surfaces, E _ads/H₂O decreased. Considering experimental conditions, we observed that the highest coverage was obtained on the (011) surface, followed by the (111) and (001) surfaces. However, with an increase in temperature, the surface coverage decreased on all the surfaces. Total desorption occurred at temperatures higher than 400 K for the (011) and (111) surfaces, but above 850 K for the (001) surface. From the morphology analysis of the Pt nanoparticle, we noted that, when the temperature increased, only the electrocatalytically active (111) surface remained.

Infrared photodissociation spectroscopic studies of ScO(H2O)n=1–3Ar+ cluster cations: solvation induced reaction of ScO+ and water

We investigate the gaseous ScO(H₂O)_1–3Ar⁺ cations prepared by laser vaporization coupled with supersonic molecular beam using infrared photodissociation spectroscopy in the O–H stretching region.

One-dimensional vs. two-dimensional proton transport processes at solid-liquid zinc-oxide-water interfaces

Neural network molecular dynamics simulations unravel the long-range proton transport properties of ZnO–water interfaces.

Long-range charge transport is important for many applications like batteries, fuel cells, sensors, and catalysis. Obtaining microscopic insights into the atomistic mechanism is challenging, in particular if the underlying processes involve protons as the charge carriers. Here, large-scale reactive molecular dynamics simulations employing an efficient density-functional-theory-based neural network potential are used to unravel long-range proton transport mechanisms at solid–liquid interfaces, using the zinc oxide–water interface as a prototypical case. We find that the two most frequently occurring ZnO surface facets, (101[combining macron]0) and (112[combining macron]0), that typically dominate the morphologies of zinc oxide nanowires and nanoparticles, show markedly different proton conduction behaviors along the surface with respect to the number of possible proton transfer mechanisms, the role of the solvent for long-range proton migration, as well as the proton transport dimensionality. Understanding such surface-facet-specific mechanisms is crucial for an informed bottom-up approach for the functionalization and application of advanced oxide materials.

Water agglomerates on Fe3O4(001)

Determining the structure of water adsorbed on solid surfaces is a notoriously difficult task and pushes the limits of experimental and theoretical techniques. Here, we follow the evolution of water agglomerates on Fe3O4(001); a complex mineral surface relevant in both modern technology and the natural environment. Strong OH-H2O bonds drive the formation of partially dissociated water dimers at low coverage, but a surface reconstruction restricts the density of such species to one per unit cell. The dimers act as an anchor for further water molecules as the coverage increases, leading first to partially dissociated water trimers, and then to a ring-like, hydrogen-bonded network that covers the entire surface. Unraveling this complexity requires the concerted application of several state-of-the-art methods. Quantitative temperature-programmed desorption (TPD) reveals the coverage of stable structures, monochromatic X-ray photoelectron spectroscopy (XPS) shows the extent of partial dissociation, and noncontact atomic force microscopy (AFM) using a CO-functionalized tip provides a direct view of the agglomerate structure. Together, these data provide a stringent test of the minimum-energy configurations determined via a van der Waals density functional theory (DFT)-based genetic search.

Water adsorbate phases on ZnO and impact of vapor pressure on the equilibrium shape of nanoparticles

ZnO nanoparticles are used as catalysts and have potential applications in gas-sensing and solar energy conversion. A fundamental understanding of the exposed crystal facets, their surface chemistry, and stability as a function of environmental conditions is essential for rational design and improvement of synthesis and properties. We study the stability of water adsorbate phases on the non-polar low-index (101¯0) and (112¯0) surfaces from low coverage to multilayers using ab initio thermodynamics. We show that phonon contributions and the entropies due to a 2D lattice gas at low coverage and multiple adsorbate configurations at higher coverage have an important impact on the stability range of water adsorbate phases in the (T,p) phase diagram. Based on this insight, we compute and analyze the possible growth mode of water films for pressures ranging from UHV via ambient conditions to high pressures and the impact of water adsorption on the equilibrium shape of nanoparticles in a humid environment. A 2D variant of the Wulff construction shows that the (101¯0) and (112¯0) surfaces coexist on 12-faceted prismatic ZnO nanoparticles in dry conditions, while in humid environment, the (101¯0) surface is selectively stabilized by water adsorption resulting in hexagonal prisms.

Recycling of zincite (ZnO) via uptake of hydrogen halides

We investigate chemical interplay between HCl/HBr and zincite surfaces as a representative model for structures of zinc oxides in EAFD.

ZnO powders as multi-facet single crystals

Oxides are most commonly found in divided forms with properties difficult to control since their crystallographic orientations usually escape analysis. To overcome this an appropriate model system can be provided by ZnO smoke which, obtained by combustion of Zn in air, exhibits nanoparticles with well-defined surface facets. The present work focuses on the interaction of water with ZnO smokes by combining density functional theory based simulations and infrared spectroscopy measurements with applied pressures from 10^-7 to 1 mbar. We demonstrate that the use of ultra-high vacuum allows the analysis of the very first stages of the adsorption, and report on water structures on ZnO(112[combining macron]0) for the first time. We further show that ZnO powders behave as multi-facet single crystals involving (101[combining macron]0), (112[combining macron]0), (0001), and (0001[combining macron]) surfaces with the polar orientations corresponding to 25% of the total surface area. A great deal of cross-agreements between experimental results and simulation provides a simple approach for the examination of hydroxylated/hydrated ZnO smokes and can be widely applied on other ZnO-related powders.