Centrum pre nanodiagnostiku materiálov

GERULOVÁ, Kristína – KUCMANOVÁ, Alexandra – SANNY, Zuzana – GARAIOVÁ, Zuzana – SEILER, Eugen – ČAPLOVIČOVÁ, Mária – ČAPLOVIČ, Ľubomír – PALCUT, Marián

In Nanomaterials. Vol. 12, iss. 11 (2022)

https://doi.org/10.3390/nano12111786

Abstract

Magnetic separation of microalgae using magnetite is a promising harvesting method as it is fast, reliable, low cost, energy-efficient, and environmentally friendly. In the present work, magnetic harvesting of three green algae (Chlorella vulgaris, Chlorella ellipsoidea, and Auxenochlorella protothecoides) and one cyanobacteria (Microcystis aeruginosa) has been studied. The biomass was flushed with clean air using a 0.22 μm filter and fed CO₂ for accelerated growth and faster reach of the exponential growth phase. The microalgae were harvested with magnetite nanoparticles. The nanoparticles were prepared by controlled co-precipitation of Fe²⁺ and Fe³⁺ cations in ammonia at room temperature. Subsequently, the prepared Fe₃O₄ nanoparticles were coated with polyethyleneimine (PEI). The prepared materials were characterized by high-resolution transmission electron microscopy, X-ray diffraction, magnetometry, and zeta potential measurements. The prepared nanomaterials were used for magnetic harvesting of microalgae. The highest harvesting efficiencies were found for PEI-coated Fe₃O₄. The efficiency was pH-dependent. Higher harvesting efficiencies, up to 99%, were obtained in acidic solutions. The results show that magnetic harvesting can be significantly enhanced by PEI coating, as it increases the positive electrical charge of the nanoparticles. Most importantly, the flocculants can be prepared at room temperature, thereby reducing the production costs.

ZÁCHENSKÁ, Jana – JORÍK, Vladimír – VANČO, Ľubomír – MIČUŠÍK, Matej – ZEMANOVÁ, Matilda

In Electrocatalysis. Vol. 13, iss. 4 (2022)

https://doi.org/10.1007/s12678-022-00734-6

Abstract

Ni–Fe cathode catalyst for zero-gap alkaline water electrolysis was studied. Ni–Fe coatings on nickel foam were prepared by direct current (DC) and pulse current (PC) electrodeposition. The influence of different plating conditions and composition of the electrolyte on the morphology of the samples was studied. It was found that under DC electrodeposition, iron is dominant in the coating. Under PC plating conditions, Ni is the dominant element in Ni–Fe coatings. Ni–Fe coatings prepared under DC electrodeposition provide an effective catalyst in zero-gap electrolysis. Increasing Fe content in the coatings improves the catalytic activity of Ni–Fe catalyst. The study of convenient parameters of PC electrodeposition seems to be complex to reach a highly active surface area.

BAKARDJIEVA, Snejana – MAREŠ, Jakub – KOCI, Eva – TOLASZ, Jakub – FAJGAR, Radek – RYUKHTIN, Vasyl – KLEMENTOVÁ, Mariana – MICHNA, Štefan – BIBOVÁ, Hana – HOLMESTAD, Randi – TITORENKOVA, Rositsa – ČAPLOVIČOVÁ, Mária.

In Nanomaterials. Vol. 12, iss. 5 (2022)

https://doi.org/10.3390/nano12050750

Abstract

Ag-decorated TiO₂ nanostructured materials are promising photocatalysts. We used non-standard cryo-lyophilization and ArF laser ablation methods to produce TiO₂ nanosheets and TiO₂ nanostructured thin films decorated with Ag nanoparticles. Both methods have a common advantage in that they provide a single multiply twinned Ag⁽⁰⁾ characterized by {111} twin boundaries. Advanced microscopy techniques and electron diffraction patterns revealed the formation of multiply twinned Ag⁽⁰⁾ structures at elevated temperatures (500 °C and 800 °C). The photocatalytic activity was demonstrated by the efficient degradation of 4-chlorophenol and Total Organic Carbon removal using Ag-TiO₂ nanosheets, because the multiply twinned Ag⁽⁰⁾ served as an immobilized photocatalytically active center. Ag-TiO₂ nanostructured thin films decorated with multiply twinned Ag⁽⁰⁾ achieved improved photoelectrochemical water splitting due to the additional induction of a plasmonic effect. The photocatalytic properties of TiO₂ nanosheets and TiO₂ nanostructured thin films were correlated with the presence of defect-twinned structures formed from Ag⁽⁰⁾ nanoparticles with a narrow size distribution, tuned to between 10 and 20 nm. This work opens up new possibilities for understanding the defects generated in Ag-TiO₂ nanostructured materials and paves the way for connecting their morphology with their photocatalytic activity.