Wojciech Zięba

The results of in vitro studies of single-walled carbon nanohorn (SWCNH) oxidized materials’ cytotoxicity obtained by the cell membrane integrity (Neutral Red Uptake (NRU)) and metabolic activity (by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)) on A549 and human dermal fibroblasts (HDF) cell lines are presented. We also present hemocompatibility studies on human and porcine blood, and an erythrocyte concentrate to prove that the obtained samples will not interfere with blood components. Characterization of the materials is supplemented by ζ-potential measurements, Transmission Electron Microscope (TEM) imaging, and thermogravimetric studies (TG). The presented results show the correlation between the specific surface area of materials and the platelet aggregation, when the I_D/I_G ratio determined from Raman spectra correlates with hemoglobin release from the erythrocytes (in whole blood testing). A plausible mechanism explaining the observed correlations is given. The cytotoxicity and hemocompatibility studies prove that the studied materials are acceptable for use in biomedical applications, especially a sample SWCNH-ox-1.5 with the best application potential.

We investigated the electrochemical performance of single-walled carbon nanohorns (SWCNHs) for use as supercapacitor electrodes. For the first time, we used acid-treatment for oxidation of SWCNHs and hole creation in their structure. A detailed study was performed on the correlation between the oxidation of SWCNHs via acid treatment and variable acid treatment times, the structural properties of the oxidized carbon nanostructures, and the specific capacitance of the SWCNH electrodes. We showed that simple functionalization of carbon nanostructures under controlled conditions leads to an almost 3-fold increase in their specific capacitance (from 65 to 180 F g⁻¹ in 0.1 M H₂SO₄). This phenomenon indicates higher accessibility of the surface area of the electrodes by electrolyte ions as a result of gradual opening of the SWCNH internal channels.

Spherical carbon nanomaterial coatings on the purified carbon fibres were obtained and characterized. The use of exactly the same conditions of electrophoretic deposition process made it possible to compare the impact of the initial carbon nanomaterial properties on the behaviour of various prepared surfaces. Obtained samples were characterized by scanning electron microscopy, atomic force microscopy, flat surface ζ‐potential and water contact angle measurements. Additionally, cytotoxic tests were carried out to compare biocompatibility of coated carbon fibres. Presented results show the impact of the initial materials properties on the characteristics of the deposited coatings.

It is well known that carbon nanotube (CNT) oxidation (usually with concentrated HNO₃) is a major step before the electrophoretic deposition (EPD). However, the recent discovery of the “onion effect” proves that multiwalled carbon nanotubes are not only oxidized, but a simultaneous unsheathing process occurs. We present the first report concerning the influence of unsheathing on the properties of the thus-formed CNT surface layer. In our study we examine how the process of gradual oxidation/unsheathing of a series of multiwalled carbon nanotubes (MWCNTs) influences the morphology of the surface formed via EPD. Taking a series of well-characterized and gradually oxidized/unsheathing Nanocyl™ MWCNTs and performing EPD on a carbon fiber surface, we analyzed the morphology and wettability of the CNT surfaces. Our results show that the water contact angle could be gradually changed in a wide range (125–163°) and the major property determining its value was the diameter of aggregates formed before the deposition process in the solvent. Based on the obtained results we determined the parameters having a crucial influence on the morphology of created layers. Our results shed new light on the deposition mechanism and enable the preparation of surfaces with steerable roughness and wettability.

We have studied the oxidation of multi-wall carbon nanotubes (MWCNTs) by boiling them in a nitrating mixture composed of conc. HNO₃/H₂SO₄ (v/v = 1/3). By analysis of the morphology and surface physicochemistry of the oxidation products as a function of MWCNT treatment time, we have revealed two interrelated phenomena. Firstly, the most outer walls were becoming more functionalized with carboxylic groups to the point of quasi-saturation where, secondly, oxidized MWCNTs could be desheathed uncovering the yet non-functionalized wall. These phenomena were manifested by the periodic-like nature of functionalization and de-functionalization. In the products of MWCNT oxidation – the number of graphitized MWCNT walls was determined by HR-TEM while quantification of oxygen functionalities was performed via Boehm titration. The above techniques coupled with the analysis of zeta potential and Raman spectroscopy allowed us to propose a pseudo-1^st order kinetic model for MWCNT oxidation translatable to other sp²-C allotropes. The findings mean that prolonged oxidation does not necessarily yield nanotubes of higher levels of functionalization. The final outcome is of great relevance in all fields of MWCNT applications from medicine to sensors to nanomaterials engineering.