Controllable in situ growth of novel octahedral TiO2 nanoparticles on nickel/titanium alloy fiber substrate for selective solid-phase microextraction of ultraviolet filters in water samples

Abstract

The nature and fabrication of fiber coatings with good adsorption capacity and selectivity play a decisive role in solid-phase microextraction (SPME). In this work, a novel SPME fiber was fabricated through hydrothermal in situ growth of octahedral TiO₂ nanoparticles (TiO₂NPs) on a superelastic nickel/titanium alloy (NiTi) wire substrate in acid solution. The resulting fiber coatings were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. Acid types, acid concentration as well as hydrothermal temperature and time were found to be effective route to manipulate the morphologies and composition of TiO₂-based nanoflakes grown on the NiTi fiber substrates. At the concentration of 0.4 mol L^-1 HCl as well as hydrothermal temperature of 150 °C and hydrothermal time of 12 h, TiO₂NPs were in situ grown on the NiTi wire substrates. The obtained NiTi wire with the TiO₂NPs coating (NiTi@TiO₂NPs fiber) was employed to investigate the adsorption of some representative aromatic analytes in water samples coupling with high-performance liquid chromatography with UV detection (HPLC/UV). The results clearly demonstrate that the fiber exhibits good extraction selectivity for ultraviolet filters (UVFs). In view of good extraction selectivity for the selected UVFs, the key experimental parameters were optimized. Under the optimum conditions, the calibration curves were linear in the ranges of 0.05-100 μg L^-1 with the correlation coefficients greater than 0.998. Limits of detection (LODs) were 0.007 to 0.064 μg L^-1. Furthermore, the intra-day and inter-day repeatability of the proposed method with the single fiber varied from 4.3% to 6.1% and from 4.5% to 6.8%, respectively. The fiber-to-fiber reproducibility ranged from 5.8% to 8.2%. The developed SPME-HPLC/UV method was applied to selective preconcentration and sensitive determination of target UVFs from real water samples. Moreover, the fabricated fiber showed precisely controllable growth and 150 extraction and desorption cycles.

Fig. 1. Surface SEM images and EDX spectra of the oxide coatings grown on the pretreated NiTi wire by hydrothermal reaction in HCl solution (a and b), HNO₃ solution (c and d) and glacial acetic acid (e and f) at 150 °C for 12 h.

Fig. 2. Typical chromatograms of SPME-HPLC with the NiTi@TiO₂NPs fiber obtained in HNO₃ solution (a), the NiTi@TiO₂NPs fibers obtained in HCl solution within 6 h (b) and 12 h (c) for CPs, PAEs, UVFs and PAHs.

Fig. 3. The extraction capability of the PA fiber and the NiTi@TiO₂NPs fiber for UVFs.

Fig. 4. Dependence of extraction efficiency on ionic strength (a), stirring rate (b), extraction temperature (c), pH (d) as well as extraction time (e) and desorption time (f).