Morphological and Chemical/Physical Characterization of Fe-Doped Synthetic Chrysotile Nanotubes

Abstract

In the field of thin‐layer‐structured inorganic nanotubes, morphological, structural, and chemical/physical modifications induced in synthetic stoichiometric chrysotile nanotubes have been evaluated as a function of the extent of Fe doping. Fe‐doped synthetic chrysotile nanocrystals have been obtained in the range from 0.29 wt.‐% up to 1.37 wt.‐% Fe. A partial Fe replacement for Si and Mg has been observed through the modification of Fourier‐transform infrared (FTIR) absorption bands. FTIR spectroscopic, X‐ray diffraction, and thermogravimetric analyses provide evidence for Fe inclusion into the chrysotile crystal structure, in both octahedral and tetrahedral sites, which induces a flattening of the curved brucite‐like layers in the stoichiometric chrysotile. Further characterization by morphological analysis (scanning electron microscopy, transmission electron microscopy, and atomic force microscopy) has revealed the effect of Fe doping on the aggregation of chrysotile nanotubes. The results appear interesting in light of the proposed possibilities of synthetic chrysotile fibers to represent an alternative to carbon nanotubes for innovative technological applications.

The Iron‐Related Molecular Toxicity Mechanism of Synthetic Asbestos Nanofibres: A Model Study for High‐Aspect‐Ratio Nanoparticles

“…This study has been developed along the following lines: 1) a stoichiometric, geoinspired, iron-free chrysotile nanofibre was synthesised by means of a hydrothermal procedure; [15] 2) the iron-free chrysotile sample [15] was compared to a natural chrysotile (UICC standard sample). Unlike the natural specimen, no cytotoxic, no oxidative stress and no DNA damage in several in vitro tests was reported upon contact with the synthetic iron-free nanofibre; [16] 3) an iron-doped synthetic chrysotile was consequently synthesised with the same synthesis procedure; 4) the iron-doped synthetic chrysotile was shown to be active in ROS production, to induce oxidative stress in vitro and to be as toxic as natural UICC chrysotile, thereby providing for the first time, without confounding factors, a direct cause-and-effect correlation between cellular toxicity and occurrence of iron in asbestos; [17] 5) a set of five Fe-doped synthetic chrysotile fibres was synthesised, and the fibres had features consistent with both natural and iron-free synthetic fibres; [18] Finally, as we report here, the set of fibres has been exploited to clarify the following issues: i) whether extremely low iron loadings (down to 0.67 wt %) are sufficient to trigger free-radical release, thus imparting toxic properties to synthetic nanofibres; ii) the effect of variation in iron-loading on radical release; and iii) last but not least, the correlation between position of iron active sites in the crystal lattice and their potential to generate free radicals. By adopting the well-known spin-trapping technique, which is associated with electron paramagnetic resonance spectroscopy (EPR), we have measured the amount and type of fibre-derived free-radical species by contacting chrysotile nanofibres with hydrogen peroxide and formate ion.…”

Synthesis of Fe‐doped chrysotile and characterization of the resulting chrysotile fibers

“…The presence of these substitutive impurities in chrysotile, even to a limited extent, affects its morphology and chemical/physical properties [3,[9][10][11] and it also could play an important role in pathological effects. Infact several authors attribute the chrysotile noxiousness to its morphology and chemical composition [12,13].…”

Adsorption of bovine serum albumin onto synthetic Fe-doped geomimetic chrysotile

“…In fact, octahedral coordinated Fe has been observed in all the substitution range in Fe-doped chrysotile synthesized in absence of metallic Fe. On the contrary, tetrahedral coordinated Fe inducing a flattening of the chrysotile structure appears prevalent in respect of octahedral coordinated Fe in highly Fe-doped chrysotile synthesized when metallic Fe is available in the synthetic environment [19,[21][22][23]. The position of the sites responsible for catalytic and redox activity of Fe of asbestos is currently unknown, even if the fibre surface appears mainly to control the Fe reactivity.…”

“…With regard to chrysotile fibres doped with iron, they have been synthesized as single-tube nanocrystals with a central hole diameter of 7 nm and wall thickness of about the same size [19]. Chrysotile nanotubes show structural modifications as a function of the Fe doping extent affecting their morphological aggregation.…”