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[en] Highlights: • Novel nanocomposite thin films consisting of nanocrystalline chromium embedded in an amorphous chromium carbide matrix are reported for the first time. • The novel nanocomposite films show ultra low nanowear and a relatively high hardness of around 22 GPa. • The nanocomposite films show a strong correlation between the macro and nano-tribological properties. - Abstract: In this work, we report the first observation of novel nanocomposite thin films consisting of nanocrystalline chromium embedded in an amorphous chromium carbide matrix (nc-Cr/a-CrC) with relatively high hardness (∼22,3 GPa) and ultra low nanowear. The films were deposited onto silicon substrates using a magnetic filtered cathodic arc deposition system at various negative bias voltages, from 50 to 450 V. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) suggested the co-existence of chromium and chromium carbide phases, while high resolution transmission electron microscopy (HRTEM) confirmed the presence of the nc-Cr/a-CrC structure. The friction coefficient measured with the ball-on disk technique and the nanowear results showed a strong correlation between the macro and nano-tribological properties of the samples. These novel nanocomposite films show promising properties as solid lubricant and wear resistant coatings with relatively high hardness, low friction coefficient and ultra low nanowear.
[en] Highlights: • Humic acid-HA, NaHCO3, MgSO4, KCl and CaCl2 change the stability and oxidation state of silver nanoparticle-AgNPs surface. • Ag3+ is formed on AgNPs surface mainly in presence of NaHCO3, MgSO4 and HA. • Toxicological endpoints in zebrafish embryos exposed to Ag3+ were not significant for acute exposure. • HA coated on AgNPs surface reduces the concentration of Ag ions released and the toxicity in zebrafish embryos. • HA acts as a natural attenuator/remediator of polluted water with AgNPs. - Abstract: The use of silver nanoparticles (AgNPs) result in an inevitable contact with aquatic environments. Here we study the behavior of AgNPs and the developmental toxicity in zebrafish embryos exposed to these nanoparticles (0–10 mg/L) with and without the presence of HA (20 mg/L), using zebrafish facility water (ZFW) and zebrafish growing media (ZGM). The presence of cations and HA gave rise to a decrease in Ag ion release and ζ-potential, an increase in the hydrodynamic diameter and oxidation of the AgNP surface. The results show that the presence of HA and cations in the media, as well as the silver speciation, i.e., the unusual presence of Ag3+, decreases the toxicity of AgNPs (LC50AgNPs: 1.19 mg/L; LC50AgNPs+HA: 3.56 mg/L), as well as silver bioavailability and toxicity in zebrafish embryos. Developmental alterations and the LC50 (1.19 mg/L) of AgNPs in ZFW were more relevant (p ≤ 0.05) than for AgNPs in ZGM (LC50 > 10 mg/L). It was demonstrated that the bioaccumulation and toxicity of AgNPs depends on several factors including AgNPs concentration, nanoparticle aggregation, dissolved silver ions, speciation of silver ions, the amount of salt in the environment, the presence of humic substances and others, and different combinations of all of these factors.