Just Soaping Them: The Simplest Method for Converting Metal Organic Frameworks into Superhydrophobic Materials

The incorporation of superhydrophobic properties into metal organic framework (MOF) materials is highly desirable to enhance their hydrolytic stability, gas capture selectivity in the presence of humidity and efficiency in oil-water separations, among others. The existing strategies for inducing superhydrophobicity into MOFs have several weaknesses, such as increased cost, utilization of toxic reagents and solvents, applicability for limited MOFs, etc. Here, we report the simplest, most eco-friendly, and cost-effective process to impart superhydrophobicity to MOFs, involving a rapid (90 min) treatment of MOF materials with solutions of sodium oleate, a main component of soap. The method can be applied to both hydrolytically stable and unstable MOFs, with the porosity of modified MOFs approaching, in most cases, that of the pristine materials. Interestingly, this approach was used to isolate superhydrophobic magnetic MOF composites, and one of these materials formed stable liquid marbles, whose motion could be easily guided using an external magnetic field. We also successfully fabricated superhydrophobic MOF-coated cotton fabric and fiber composites. These composites exhibited exceptional oil sorption properties achieving rapid removal of floating crude oil from water, as well as efficient purification of oil-in-water emulsions. They are also regenerable and reusable for multiple sorption processes. Overall, the results described here pave the way for an unprecedented expansion of the family of MOF-based superhydrophobic materials, as virtually any MOF could be converted into a superhydrophobic compound by applying the new synthetic approach.

Flame Spray Pyrolysis Synthesis of Vo-Rich Nano-SrTiO3-x

Engineering of oxygen vacancies (Vo) in nanomaterials allows diligent control of their physicochemical properties. SrTiO3 possesses the typical ABO3 structure and has attracted considerable attention among the titanates due to its chemical stability and its high conduction band energy. This has resulted in its extensive use in photocatalytic energy-related processes, among others. Herein, we introduce the use of Flame Spray Pyrolysis (FSP); an industrial and scalable process to produce Vo-rich SrTiO3 perovskites. We present two types of Anoxic Flame Spray Pyrolysis (A-FSP) technologies using CH4 gas as a reducing source: Radial A-FSP (RA-FSP); and Axial A-FSP (AA-FSP). These are used for the control engineering of oxygen vacancies in the SrTiO3-x nanolattice. Based on X-ray photoelectron spectroscopy, Raman and thermogravimetry-differential thermal analysis, we discuss the role and the amount of the Vos in the so-produced nano-SrTiO3-x, correlating the properties of the nanolattice and energy-band structure of the SrTiO3-x. The present work further corroborates the versatility of FSP as a synthetic process and the potential future application of this process to engineer photocatalysts with oxygen vacancies in quantities that can be measured in kilograms.

Correlation of magnetic resonance (EPR, ssNMR) parameters and crystal-microstrain in marbles as a tool to probe their provenance

Marbles constitute a significant family of materials, for antiquities, as well as modern constructions. Herein, we have studied Greek marbles, using electron paramagnetic resonance (EPR) and solid-state nuclear magnetic resonance (ssNMR) spectroscopies, focusing on their structural microenvironment. Spin-Hamiltonian parameters derived from EPR spectra of naturally occurring 55Mn2+ (S = 5/2, I = 5/2) atoms in marbles, were studied as structural-probes. EPR data at 300 K provide a library of 55Mn2+ zero-field-splitting parameters (E, D). The effect of temperature (300 up to 700 K) on 55Mn2+-ZFS (E, D) and the strain of the D-tensor (Dstrain) was studied by high-temperature EPR spectroscopy. The EPR data, combined with 13C-ssNMR, provide detailed physicochemical information of the calcite and dolomite crystal phases in the marbles. In parallel, we have analyzed the lattice-microstrain (ε0) of the marbles' crystallites using high-resolution XRD data. Analysis of the correlation between the D-values of Mn2+ centers and (ε0)-XRD, reveals trends that reflect the provenance of the marbles. In this context, we discuss the correlation between the D-values of Mn2+ centers and (ε0)-microstrain as a novel tool to elucidate the provenance of marbles.

Spin-Injection in Graphene: An EPR and Raman Study

In this article, the enrichment of graphene and graphene oxide with free radicals through their functionalization with tyrosine is studied. In contrast with what is commonly observed in the functionalization of graphene with organic species the addition of tyrosine radicals on to the graphene substrate led to a remarkable increase of the aromatic character as indicated by the spectroscopic data. Similar behaviour was observed for the functionalization of graphene oxide. In addition, a brief analysis of the tyrosine functionalized graphene with EPR spectroscopy showed a remarkable enhancement of the spin density that could be useful in spintronics.

Non-graphitized carbon/Cu2O/Cu0 nanohybrids with improved stability and enhanced photocatalytic H2 production

Cu2O is a highly potent photocatalyst, however photocorrosion stands as a key obstacle for its stability in photocatalytic technologies. Herein, we show that nanohybrids of Cu2O/Cu0 nanoparticles interfaced with non-graphitized carbon (nGC) constitute a novel synthesis route towards stable Cu-photocatalysts with minimized photocorrosion. Using a Flame Spray Pyrolysis (FSP) process that allows synthesis of anoxic-Cu phases, we have developed in one-step a library of Cu2O/Cu0 nanocatalysts interfaced with nGC, optimized for enhanced photocatalytic H2 production from H2O. Co-optimization of the nGC and the Cu2O/Cu0 ratio is shown to be a key strategy for high H2 production, > 4700 μmoles g-1 h-1 plus enhanced stability against photocorrosion, and onset potential of 0.234 V vs. RHE. After 4 repetitive reuses the catalyst is shown to lose less than 5% of its photocatalytic efficiency, while photocorrosion was < 6%. In contrast, interfacing of Cu2O/Cu0 with graphitized-C is not as efficient. Raman, FT-IR and TGA data are analyzed to explain the undelaying structural functional mechanisms where the tight interfacing of nGC with the Cu2O/Cu0 nanophases is the preferred configuration. The present findings can be useful for wider technological goals that demand low-cost engineering, high stability Cu-nanodevices, prepared with industrially scalable process.

Quantitative In Situ Monitoring of Cu-Atom Release by Cu2O Nanocatalysts under Photocatalytic CO2 Reduction Conditions: New Insights into the Photocorrosion Mechanism

Cu₂O is among the most promising photocatalysts for CO₂ reduction, however its photocorrosion remains a standalone challenge. Herein, we present an in situ study of the release of Cu ions from Cu₂O nanocatalysts under photocatalytic conditions in the presence of HCO₃ as a catalytic substrate in H₂O. The Cu-oxide nanomaterials were produced by Flame Spray Pyrolysis (FSP) technology. Using Electron Paramagnetic Resonance (EPR) spectroscopy in tandem with analytical Anodic Stripping Voltammetry (ASV), we monitored in situ the Cu²⁺ atom release from the Cu₂O nanoparticles in comparison with CuO nanoparticles under photocatalytic conditions. Our quantitative, kinetic data show that light has detrimental effect on the photocorrosion of Cu₂O and ensuing Cu²⁺ ion release in the H₂O solution, up to 15.7% of its mass. EPR reveals that HCO₃ acts as a ligand of the Cu²⁺ ions, promoting the liberation of {HCO₃-Cu} complexes in solution from Cu₂O, up to 27% of its mass. HCO₃ alone exerted a marginal effect. XRD data show that under prolonged irradiation, part of Cu²⁺ ions can reprecipitate on the Cu₂O surface, creating a passivating CuO layer that stabilizes the Cu₂O from further photocorrosion. Including isopropanol as a hole scavenger has a drastic effect on the photocorrosion of Cu₂O nanoparticles and suppresses the release of Cu²⁺ ions to the solution. Methodwise, the present data exemplify that EPR and ASV can be useful tools to help quantitatively understand the solid-solution interface photocorrosion phenomena for Cu₂O.

MOF-Derived Defective Co3O4 Nanosheets in Carbon Nitride Nanocomposites for CO2 Photoreduction and H2 Production

In photocatalysis, especially in CO₂ reduction and H₂ production, the development of multicomponent nanomaterials provides great opportunities to tune many critical parameters toward increased activity. This work reports the development of tunable organic/inorganic heterojunctions comprised of cobalt oxides (Co₃O₄) of varying morphology and modified carbon nitride (CN), targeting on optimizing their response under UV-visible irradiation. MOF structures were used as precursors for the synthesis of Co₃O₄. A facile solvothermal approach allowed the development of ultrathin two-dimensional (2D) Co₃O₄ nanosheets (Co₃O₄-NS). The optimized CN and Co₃O₄ structures were coupled forming heterojunctions, and the content of each part was optimized. Activity was significantly improved in the nanocomposites bearing Co₃O₄-NS compared with the corresponding bulk Co₃O₄/CN composites. Transient absorption spectroscopy revealed a 100-fold increase in charge carrier lifetime on Co₃O₄-NS sites in the composite compared with the bare Co₃O₄-NS. The improved photocatalytic activity in H₂ production and CO₂ reduction is linked with (a) the larger interface imposed from the matching 2D structure of Co₃O₄-NS and the planar surface of CN, (b) improvements in charge carrier lifetime, and (c) the enhanced CO₂ adsorption. The study highlights the importance of MOF structures used as precursors in forming advanced materials and the stepwise functionalization of the individual parts in nanocomposites for the development of materials with superior activity.

Nanoantioxidant Materials: Nanoengineering Inspired by Nature

Oxidants are very active compounds that can cause damage to biological systems under specific environmental conditions. One effective way to counterbalance these adverse effects is the use of anti-oxidants. At low concentrations, an antioxidant is defined as a compound that can delay, control, or prevent an oxidative process. Antioxidants exist in plants, soil, and minerals; therefore, nature is a rich source of natural antioxidants, such as tocopherols and polyphenols. In nature, antioxidants perform in tandem with their bio-environment, which may tune their activity and protect them from degradation. In vitro use of antioxidants, i.e., out of their biomatrix, may encounter several drawbacks, such as auto-oxidation and polymerization. Artificial nanoantioxidants can be developed via surface modification of a nanoparticle with an antioxidant that can be either natural or synthetic, directly mimicking a natural antioxidant system. In this direction, state-of-the-art nanotechnology has been extensively incorporated to overcome inherent drawbacks encountered in vitro use of antioxidants, i.e., out of their biomatrix, and facilitate the production and use of antioxidants on a larger scale. Biomimetic nanoengineering has been adopted to optimize bio-medical antioxidant systems to improve stability, control release, enhance targeted administration, and overcome toxicity and biocompatibility issues. Focusing on biotechnological sciences, this review highlights the importance of nanoengineering in developing effective antioxidant structures and comparing the effectiveness of different nanoengineering methods. Additionally, this study gathers and clarifies the different antioxidant mechanisms reported in the literature and provides a clear picture of the existing evaluation methods, which can provide vital insights into bio-medical applications.

In Tandem Control of La-Doping and CuO-Heterojunction on SrTiO3 Perovskite by Double-Nozzle Flame Spray Pyrolysis: Selective H2 vs. CH4 Photocatalytic Production from H2O/CH3OH

ABO₃ perovskites offer versatile photoactive nano-templates that can be optimized towards specific technologies, either by means of doping or via heterojunction engineering. SrTiO₃ is a well-studied perovskite photocatalyst, with a highly reducing conduction-band edge. Herein we present a Double-Nozzle Flame Spray Pyrolysis (DN-FSP) technology for the synthesis of high crystallinity SrTiO₃ nanoparticles with controlled La-doping in tandem with SrTiO₃/CuO-heterojunction formation. So-produced La:SrTiO₃/CuO nanocatalysts were optimized for photocatalysis of H₂O/CH₃OH mixtures by varying the La-doping level in the range from 0.25 to 0.9%. We find that, in absence of CuO, the 0.9La:SrTiO₃ material achieved maximal efficient photocatalytic H₂ production, i.e., 12 mmol g^-1 h^-1. Introduction of CuO on La:SrTiO₃ enhanced selective production of methane CH₄. The optimized 0.25La:SrTiO₃/0.5%CuO catalyst achieved photocatalytic CH₄ production of 1.5 mmol g^-1 h^-1. Based on XRD, XRF, XPS, BET, and UV-Vis/DRS data, we discuss the photophysical basis of these trends and attribute them to the effect of La atoms in the SrTiO₃ lattice regarding the H₂-production, plus the effect of interfacial CuO on the promotion of CH₄ production. Technology-wise this work is among the first to exemplify the potential of DN-FSP for scalable production of complex nanomaterials such as La:SrTiO₃/CuO with a diligent control of doping and heterojunction in a single-step synthesis.

Antioxidant Hydrogen-Atom-Transfer to DPPH Radicals by Hybrids of {Hyaluronic-Acid Components}@SiO2

Hydrogen-atom-transfer (HAT) is among the key mechanisms of antioxidant and antiradical activity in natural systems. Hyaluronic acid (HyA) is currently used extensively in health and cosmetics applications. Herein it is shown that {HyA@SiO₂} hybrids based on hyaluronic acid (HyA) components grafted on SiO₂ nanoparticles enable significant HAT activity versus DPPH radicals, while the homogeneous HyA counterparts are practically inactive. The {HyA@SiO₂} hybrids consist of the two building blocks of HyA [d-glucuronic acid (GLA) and N-acetyl-d-glucosamine (GLAM)] covalently grafted on SiO₂ nanoparticles. Based on the kinetic-thermodynamic Arrhenius study, we show that the {SiO₂@GLA} hybrids operate spontaneously via hydrogen-atom-transfer (HAT) with a low activation energy barrier, i.e., by ΔΕ_α ∼ 20 kJ/mol vs the nongrafted counterparts. Moreover, a doubly grafted {GLA@SiO₂@GLAM} nanohybrid, i.e. that contains both components of HyA, shows the most significant antioxidant activity. FTIR and Raman analysis reveal that local H-bonding between the SiO₂ matrix, GLA, and GLAM in {GLA@SiO₂@GLAM} decreases the activation barrier of the HAT mechanism. Thus, {GLA@SiO₂@GLAM} nanohybrids exemplify a novel family of materials that are not the mere sum of their components. The present case is the first example of non-phenolic molecules being able to perform antiradical HAT, opening new perspectives not foreseen until today.

Control of Tyrosyl Radical Stabilization by {SiO2@Oligopeptide} Hybrid Biomimetic Materials

Tyrosine radicals are notoriously short-lived/unstable in solution, while they present an impressive degree of stability and versatility in bioenzymes. Herein, we have developed a library of hybrid biomimetic materials (HBMs), which consists of tyrosine-containing oligopeptides covalently grafted on SiO₂ nanoparticles, and studied the formation, lifetime, and redox properties of tyrosyl radicals. Using electron paramagnetic resonance spectroscopy, we have studied the radical-spin distribution as a probe of the local microenvironment of the tyrosyl radicals in the HBMs. We find that the lifetime of the tyrosyl radical can be enhanced by up to 6 times, by adjusting three factors, namely, a proximal histidine, the length of the oligopeptide, and the interface with the SiO₂ nanomatrix. This is shown to be correlated to a significant lowering of E_1/2 from +736 mV, in free tyrosine, to +548 mV in the {12-peptide}@SiO₂ material. Moreover, we show that grafting on SiO₂ lowers the E_1/2 of tyrosine radicals by ∼50 mV in all oligopeptides. Analysis of the spin-distribution by EPR reveals that the positioning of a histidine at a H-bonding distance from the tyrosine further favors tyrosine radical stabilization.

Detection and Sorption of Heavy Metal Ions in Aqueous Media by a Fluorescent Zr(IV) Metal-Organic Framework Functionalized with 2-Picolylamine Receptor Groups

Increasing global environmental pollution due to heavy metal ions raises the importance of research on new multifunctional materials for simultaneous detection and removal of these contaminants from water resources. In this study, we report a microporous 8-connected Zr⁴⁺ metal-organic framework (MOF) based on a terephthalate ligand decorated with a chelating 2-picolylamine side group (dMOR-2), which shows highly efficient fluorescence sensing and sorption of heavy metal cations. We demonstrate by detailed fluorescence studies the ability of a water-dispersible composite of dMOR-2 with polyvinylpyrrolidone for real-time detection of Cu²⁺, Pb²⁺, and Hg²⁺ in aqueous media. The limits of detection were found to be below 2 ppb for these species, while the system's performance is not affected by the presence of other potentially competitive ions. In addition, sorption studies showed that a composite of dMOR-2 with calcium alginate (dMOR-2@CaA) is an excellent sorbent for Pb²⁺ and Cu²⁺ ions with capacities of 376 ± 15 and 117 ± 4 mg per gram of dMOR-2@CaA, respectively, while displaying the capability for simultaneous removal of various heavy metal ions in low initial concentrations and in the presence of large excesses of other cationic species. Structural and spectroscopic studies with model ligands analogous to our material's receptor unit showed chelation to the 2-picolylamine moiety to be the main binding mode of metal ions to dMOR-2. Overall, dMOR-2 is shown to represent a rare example of a MOF, which combines sensitive fluorescence detection and high sorption capacity for heavy metal ions.

Coordination properties of Cu(II) ions towards a phosphorylated fragment from the R1 domain of the tau protein. The effect of Ser phosphorylation on Cu(II) binding affinity

Tau hyperphosphorylation plays a key role in Alzheimer’s disease, mediating tau protein aggregation and deposition as neurofibrillary tangles in the intracellular space of the neurons. The potential implication of the...

ZnO, Ag and ZnO-Ag nanoparticles exhibit differential modes of toxic and oxidative action in hemocytes of mussel Mytilus galloprovincialis

The present study investigates the cytotoxic and oxidative effects of custom-made nanoparticles (NPs) on hemocytes of Mytilus galloprovincialis, utilizing hemolymph serum (HS) as exposure medium. Specifically, hemocyte lysosomal membrane destabilization (in terms of neutral red retention time assay/NRRT), superoxide anion (O₂^-), nitric oxide (NO, in terms of nitrites) and lipid peroxidation content (in terms of malondialdehyde/MDA equivalents) were determined in cells treated for 1 h with different concentrations (0.1-50 μg mL^-1) of ZnO NPs, Ag NPs and ZnO-Ag NPs, as well as AgNO₃ and/or ZnCl₂ (bulk ions, respectively). According to the results, Ag NPs were more cytotoxic than ZnO-Ag NPs and/or ZnO NPs, while NRRT values observed in AgNO₃ treated cells were lower than those of ZnCl₂. Furthermore, high levels of both O₂^- and MDA were detected in cells treated with Ag NPs, ZnO-Ag NPs, and AgNO₃ at concentrations lower than 5 μg mL^-1, while high NO generation was observed only in cells treated with 5-25 μg mL^-1 of ZnO NPs or ZnCl₂. Despite the absence of data, regarding the formation of NP-serum protein corona complexes that could mediate NP surface energy and uptake efficiency, the current study firstly revealed that ZnO NPs, probably via their surface charge, particle agglomeration, and NP Zn⁺ release could promote an immune-related generation of O₂^- and NO via the respiratory burst stimulation, a process that is questioned in the case of Ag NPs and/or ZnO-Ag NPs. Moreover, ZnO-Ag NP interaction with biological membranes and their oxidative mode of action seemed to be regulated by the release and the antagonistic/synergistic response of its ionic counterparts (ZnO⁺ and Ag⁺), but further studies are needed to elucidate the oxidative mode of action of NP metal ions in complex NP mixtures.

Flame Spray Pyrolysis Co3O4/CoO as Highly-Efficient Nanocatalyst for Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is the rate-limiting reaction in the cathode side of fuel cells. In the quest for alternatives to Pt-electrodes as cathodes in ORR, appropriate transition metal oxide-based electrocatalysts are needed. In the present work, we have synthesized Co3O4 and CoO/Co3O4 nanostructures using flame spray pyrolysis (FSP), as electrocatalysts for ORR in acidic and alkaline media. A detailed study of the effect of (Co-oxide)/Pt ratio on ORR efficiency shows that the present FSP-made Co-oxides are able to perform ORR at very low-Pt loading, 0.4% of total metal content. In acid medium, an electrode with (5.2% Pt + 4.8% Co3O4), achieved the highest ORR performance (Jmax = 8.31 mA/cm2, E1/2 = 0.66 V). In alkaline medium, superior performance and stability have been achieved by an electrode with (0.4%Pt + 9.6% (CoO/Co3O4)) with ORR activity (Jmax = 3.5 mA/cm2, E1/2 = 0.08 V). Using XRD, XPS, Raman and TEM data, we discuss the structural and electronic aspects of the FSP-made Co-oxide catalysts in relation to the ORR performance. Cyclic voltammetry data indicate that the ORR process involves active sites associated with Co3+ cations at the cobalt oxide surface. Technology-wise, the present work demonstrates that the developed FSP-protocols, constitutes a novel scalable process for production of co-oxides appropriate for oxygen reduction reaction electrodes.

Lattice Defects Engineering in W-, Zr-doped BiVO4 by Flame Spray Pyrolysis: Enhancing Photocatalytic O2 Evolution

A flame spray pyrolysis (FSP) method has been developed, for controlled doping of BiVO4 nanoparticles with W and Zr in tandem with the oxygen vacancies (Vo) of the BiVO4 lattice. Based on XPS and Raman data, we show that the nanolattice of W-BiVO4 and Zr-BiO4 can be controlled to achieve optimal O2 evolution from H2O photocatalysis. A synergistic effect is found between the W- and Zr-doping level in correlation with the Vo-concentration. FSP- made W-BiVO4 show optimal photocatalytic O2-production from H2O, up to 1020 μmol/(g × h) for 5%W-BiVO4, while the best performing Zr-doped achieved 970 μmol/(g × h) for 5%Zr-BiVO4. Higher W-or Zr-doping resulted in deterioration in photocatalytic O2-production from H2O. Thus, engineering of FSP-made BiVO4 nanoparticles by precise control of the lattice and doping-level, allows significant enhancement of the photocatalytic O2-evolution efficiency. Technology-wise, the present work demonstrates that flame spray pyrolysis as an inherently scalable technology, allows precise control of the BiVO4 nanolattice, to achieve significant improvement of its photocatalytic efficiency.

Bioinspired tailoring of fluorogenic thiol responsive antioxidant precursors to protect cells against H2O2-induced DNA damage

Natural antioxidants, like phenolic acids, possess a unique chemical space that can protect cellular components from oxidative stress. However, their polar carboxylic acid chemotype reduces full intracellular antioxidant potential due to limited diffusion through biological membranes. Here, we have designed and developed a new generation of hydrophobic turn-on fluorescent antioxidant precursors that upon penetration of the cell membrane, reveal a more polar and more potent antioxidant core and simultaneously become fluorescent allowing their intracellular tracking. Their activation is stimulated by polarity alteration by sensing intracellular signals and specifically biothiols. In our design, the carboxylic group of phenolic acids that originally restricts cell entrance is derivatized and conjugated through Copper (I)-catalyzed azide-alkyne cycloaddition (CuAAC) to a coumarin derivative that its fluorescence properties are quenched with a biothiol activatable element. This more hydrophobic precursor readily penetrates cell membrane and once inside the cell the antioxidant core is revealed upon sensing glutathione, its fluorescence is restored in a turn-on manner and the generation of a more polar character traps the molecule inside the cell. This turn-on fluorescent antioxidant precursor that can be applied to phenolic acids, was developed for rosmarinic acid and the conjugate was named as RCG. The selectivity and responsiveness of RCG towards the most abundant biothiols was monitored through a variety of biophysical techniques including UV-Vis, fluorescence and NMR spectroscopy. The electrochemical behavior and free radical scavenging capacity of the precursor RCG and the active compound (RC) was evaluated and compared with the parent compound (rosmarinic acid) through cyclic voltammetry and EPR spectroscopy, respectively. The stability of the newly synthesized bioactive conjugate RC was found significantly higher than the parent rosmarinic acid when exposed to oxygen. Cell uptake experiments were conducted and revealed the internalization of RCG. The degree of intracellular DNA protection offered by RCG and its active drug (RC) on exposure to H₂O₂ was also evaluated in Jurkat cells.

Assessing the cyto-genotoxic potential of model zinc oxide nanoparticles in the presence of humic-acid-like-polycondensate (HALP) and the leonardite HA (LHA)

The present study investigates the potential cyto-genotoxic effects of model zinc oxide nanoparticles (ZnO NPs) on human lymphocytes, with and/or without humic acids (HAs). Two types of HAs were studied, a natural well-characterized leonardite HA (LHA) and its synthetic-model, a humic-acid-like-polycondensate (HALP). The Cytokinesis Block Micronucleus (CBMN) assay was applied in cell cultures treated with different concentrations of ZnO NPs (0.5, 5, 10, 20 μg mL^-1) and under different concentrations of either HALP or LHA (ZnO NPs-HALP and ZnO NPs-LHA, at concentrations of 0.5-0.8, 5-8, 10-16, 20-32 and 0.5-2, 5-20, 10-40, 20-80 μg mL^-1, respectively). According to the results, ZnO NPs lacked genotoxicity but demonstrated cytotoxic potential. Binary mixtures of ZnO NPs-HAs (ZnO NPs-HALP or ZnO NPs-LHA) showed negligible alterations of micronuclei (MN) formation in challenged cells, with cytotoxic effects revealed only in case of cells treated with ZnO NPs-LHA at the concentration 5-20 μg mL^-1. Furthermore, no genotoxic phenomena were exerted neither by the ZnO NPs nor from their mixtures with HAs. These findings indicate [i] the cytotoxic activity of used ZnO NPs on human lymphocytes, and [ii] reveal the protective role of HAs against ZnO NPs mediated cytotoxicity.