Morphology, composition and selectivity of nickel/titanium oxide nanoflakes grown on a superelastic nickel/titanium alloy fiber substrate for highly efficient solid-phase microextraction of aromatic compounds

Abstract

Direct in situ hydrothermal growth of nickel/titanium oxide nanoflakes (NiO/TiO₂NFs) was carried out on superelastic nickel/titanium alloy (NiTi) wires for solid-phase microextraction. The resulting fiber coatings were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. Control of the NaOH concentration was found to be an effective route to manipulate the morphology and composition of NiO-based nanoflakes grown on the NiTi fiber substrates via a hydrothermal reaction. At higher concentrations of NaOH, pristine NiO nanoflakes (NiONFs) were in situ grown on the NiTi fiber substrates for the first time. Their extraction performance was evaluated using typical aromatic compounds by high-performance liquid chromatography with UV detection. The results clearly demonstrate that the extraction selectivity is subject to the surface elemental composition of the nanoflake coatings and the extraction capability greatly depends on their surface morphology. In view of the good extraction selectivity of the NiONF coating for the selected polycyclic aromatic hydrocarbons (PAHs), the key experimental parameters were optimized. Under the optimum conditions, the calibration curves were linear in the range of 0.05–100 μg L⁻¹ with correlation coefficients greater than 0.999. Limits of detection were 0.009–0.036 μg L⁻¹. Furthermore, the intra-day and inter-day repeatability of the proposed method with the single fiber varied from 3.7% to 5.3% and from 5.4% to 5.8%, respectively. The fiber-to-fiber reproducibility ranged from 5.8% to 8.6%. The proposed method was suitable for selective enrichment and determination of target PAHs from real water samples. Moreover, the fabricated fibers showed precisely controllable growth of NiONFs and a long-term recyclability of 150 cycles.