Jun Zhou,Xiuying Qiao,Bernard P. Binks,Kang Sun,Mingwen Bai,Yunlong Li,Yi Liu
Superparamagnetic Fe3O4 nanoparticles prepared by a classical coprecipitation method were used as the stabilizer to prepare magnetic Pickering emulsions, and the effects of particle concentration, oil/water volume ratio, and oil polarity on the type, stability, composition, and morphology of these functional emulsions were investigated. The three-phase contact angle (θow) of the Fe3O4 nanoparticles at the oil−water interface was evaluated using the Washburn method, and the results showed that for nonpolar and weakly polar oils of dodecane and silicone, θow is close to 90°, whereas for strongly polar oils of butyl butyrate and 1-decanol, θow is far below 90°. Inherently hydrophilic Fe3O4 nanoparticles can be used to prepare stable dodecane−water and silicone−water emulsions, but they cannot stabilize butyl butyrate−water and decanol−water mixtures with macroscopic phase separation occurring, which is in good agreement with the contact angle data. Emulsions are of the oil-in-water type for both dodecane and silicone oil, and the average droplet size increases with an increase in the oil volume fraction. For stable emulsions, not all of the particles are adsorbed to drop interfaces; the fraction adsorbed decreases with an increase in the initial oil volume fraction. Changes in the particle concentration have no obvious influence on the stability of these emulsions, even though the droplet size decreases with concentration.
Xiaoji Cao,Mei Fang,Danqi Dong,Beibei Ye,Jiahui Xu,Xuemin Ye,Weimin Mo
A dispersive liquid–liquid extraction based on Pickering emulsion stabilized with ferroferric oxide grafted nitrogen-doped graphitized carbon black has been developed to simultaneously determine seven aldehydes in environmental water samples, in combination with pentafluorobenzyl hydroxylamine precolumn derivatization gas chromatography–tandem mass spectrometry. The nitrogen-doped graphitized carbon was prepared from dicyandiamide waste residue with a simple acid wash process. The effects of magnetic emulsifier amount, extraction time, solution pH, and oil/water volume ratio on the formation of magnetically responsive Pickering emulsion and the extraction efficiency of the proposed dispersive liquid–liquid extraction were also investigated. Under the optimized conditions, satisfactory linearities were obtained for all aldehydes with correlation coefficients larger than 0.9984. The limits of detection and quantitation of seven aldehydes were in the range of 17.3–30.1 ng/L and 54.3–103.4 ng/L, respectively, with intra- and interday relative standard deviations less than 8.6%. The mean recoveries at three spiked levels ranged from 70.0 to 101.4%. With the Pickering emulsion as a “minimized extractor”, the extraction was accomplished within 5 min. After extraction, the magnetic disperser could be recovered for reuse at least five times by an external magnetic field. The proposed method was demonstrated to be feasible, simple, and economic for the trace analysis of the aldehydes in environmental water samples.
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