Reduced graphene oxide coated nickel foam for stir bar sorptive extraction of benzotriazole ultraviolet absorbents from environmental water.

The use of porous carrier and coating sorbents in stir bar sorptive extraction (SBSE) contributes to the improvement of extraction efficiency and dynamics. Herein, porous nickel foam (NF) with large surface area and magnetic property was used as the carrier of stir bar. NF was added into the mixture of graphene oxide (GO) and reducing agent, and reduced graphene oxide (RGO) coating was obtained on the surface of NF substrate by in situ hydrothermal reduction. The characterization results of Fourier transform infrared spectroscopy, X-ray power-diffraction and scanning electron microscope showed that GO was partially reduced into RGO, and the RGO coating was uniformly loaded on the NF surface. The obtained RGO-NF composite was used as the stir bar coating for the analysis of six benzotriazole (BZTs) UV absorbents. The extraction efficiency was between 48 and 64% for six BZTs. RGO-NF stir bar exhibited faster adsorption/desorption kinetics than commercial polydimethylsiloxane coated stir bar (50 min vs 120/360 min) due to its porous structure and large specific surface area. On this basis, a method of RGO-NF coated stir bar sorptive extraction combined with high performance liquid chromatography (HPLC)-DAD was established for the determination of six BZTs. Under the optimized conditions, the limits of detection were 0.33-0.50 μg/L for six target BZTs, and the linear range was 1-100 μg/L. The proposed method merits good ability to resist matrix and was used to analyze six BZTs in environmental water samples. The recoveries of target BZTs were obtained within 83.0-112% in the spiked East Lake water and 97.0-111% in the spiked Yangtze River water, respectively.