Stabilisation of low softening point petroleum pitch fibres by HNO3

This paper deals with the stabilisation of low softening point pitch fibres obtained from petroleum pitches using HNO3 as oxidising agent. This method presents some advantages compared with conventional methods: pitches with low softening point (SP) can be used to prepare carbon fibres (CF), the stabilisation time has been reduced, the CF yields are similar to those obtained after general methods of stabilisation, and the initial treatments to increase SP when low SP pitches are used to prepare CF, are avoided. The parent pitches were characterised by different techniques such as diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), elemental analysis and solvent extraction with toluene and quinoline. The interaction between HNO3 and the pitch fibres, as well as the changes occurring during the heat treatment, have been followed by DRIFTS.

Quaternary ammonium-functionalized silica sorbents for the solid-phase extraction of aromatic amines under normal phase conditions

Quaternary ammonium-functionalized silica materials were synthesized and applied for solid-phase extraction (SPE) of aromatic amines, which are classified as priority pollutants by US Environmental Protection Agency. Hexamethylenetetramine used for silica surface modification for the first time was employed as SPE sorbent under normal phase conditions. Hexaminium-functionalized silica demonstrated excellent extraction efficiencies for o-toluidine, 4-ethylaniline and quinoline (recoveries 101–107%), while for N,N-dimethylaniline and N-isopropylaniline recoveries were from low to moderate (14–46%). In addition, the suitability of 1-alkyl-3-(propyl-3-sulfonate) imidazolium-functionalized silica as SPE sorbent was tested under normal phase conditions. The recoveries achieved for the five aromatic amines ranged from 89 to 99%. The stability of the sorbent was evaluated during and after 150 extractions. Coefficients of variation between 4.5 and 10.2% proved a high stability of the synthesized sorbent. Elution was carried out using acetonitrile in the case of hexaminium-functionalized silica and water for 1-alkyl-3-(propyl-3-sulfonate) imidazolium-functionalized silica sorbent. After the extraction the analytes were separated and detected by liquid chromatography ultraviolet detection (LC-UV). The retention mechanism of the materials was primarily based on polar hydrogen bonding and π–π interactions. Comparison made with activated silica proved the quaternary ammonium-functionalized materials to offer different selectivity and better extraction efficiencies for aromatic amines. Finally, 1-alkyl-3-(propyl-3-sulfonate) imidazolium-functionalized silica sorbent was successfully tested for the extraction of wastewater and soil samples.