Oxygen vacancy-modified MnCo₂O₄ nanoneedles grown on a nickel-titanium fiber support for boosting solid-phase microextraction of trace ultraviolet filters from water

Ultraviolet filters (UVFs) are widely used in personal care products to protect human skin from UV radiation in sunlight. The accumulation of these synthetic chemicals in environmental water may pose potential risks to ecosystems and human health. Therefore, sensitive and rapid determination of trace UVFs in environmental water samples is of significant concern. Solid-phase microextraction (SPME) is a simple and efficient solvent-free sample pre-treatment technique that combines sampling, extraction, pre-concentration, cleanup with sample injection in a single step. Due to its high enrichment factor, environmental friendliness and easy hyphenation with chromatography, SPME is preferential to the pre-concentration and detection of UVFs in environmental water.

Using the hydrothermal in-situ growth method, MnCo₂O₄ nanoneedles (MnCo₂O₄NNs) were fabricated on an activated nickel-titanium alloy (Ni-Ti) fiber support. After annealing, the obtained fiber was reduced in a NaBH₄ solution, resulting in successful construction of a reduced MnCo₂O₄NNs (r-MnCo₂O₄NNs) coating with abundant oxygen vacancies. Impressively, the Ni-Ti@r-MnCo₂O₄NNs fiber exhibited significantly enhanced adsorption capacity for UVFs compared to the original Ni-Ti@MnCo₂O₄NNs fiber. After optimizing the SPME conditions, the proposed SPME-HPLC-UV method demonstrated excellent analytical performance in the pre-concentration and determination of trace UVFs in water along with linear ranges of 0.05-200 μg/L and correlation coefficients (R²) greater than 0.9991. LODs (S/N = 3) and LOQs (S/N = 10) were in the ranges of 0.012-0.133 μg/L and 0.041-0.438 μg/L, respectively. The recovery of 95.4-105% was achieved. Additionally, the proposed method demonstrated good repeatability for a single fiber and good reproducibility for different fibers constructed under the same conditions.

The Ni-Ti@r-MnCo₂O₄NNs fiber exhibits boosted adsorption capability and improved adsorption selectivity in pre-concentrating UVFs. This fiber holds promise as an alternative to the commercial fibers in the adsorption and pre-concentration of UVFs in environmental water samples. More importantly, this strategy for introducing oxygen vacancies into the metal oxide nanostructures offers a new perspective for the construction of high-performance metal oxide coatings in practical SPME application.