2.4 Demulsification study
Firstly, 40 ml of oleic acid was added into 200 ml of ultrapure water contained 0.2 g of SDS, stirring by the homogenizer at a speed of 3800 rpm·min-1, to prepare the model emulsion. The model emulsion was used after diluting by ultrapure water in the next investigation. The concentration of model emulsion was expressed with a volume ratio (v·v-1) of oleic acid in water.
Initially, demulsification performance was investigated at different conditions of dosage, concentration, time, pH and salinity using the as-prepared material. The regenerability was studied following washing used material with ethanol and petroleum ether. Typically, 0.10 g of the as-prepared material was suspended in 19.6 ml ultrapure water, then 0.4 ml of the model emulsion was added into the as-prepared material suspension. After that, the suspension contained as-prepared material and model emulsion was silence following shock drastic. And the cycle of shock-silence did several times in 30 min. Subsequently, the suspension was filtrated. The filter liquor was extracted by petroleum ether. The absorbance of extracted liquor was measured at 268 nm by a UV-vis spectrophotometer (Shimadzu, UV-2600). The demulsification efficiency (DE) was calculated according to the Eq. 1 :
\(DE=(A_{0}-A_{1})/A_{0}\times 100\%\) (Eq. 1 )
Where, DE (%) was the demulsification efficiency for the model emulsion using the as-prepared material, A 0 andA 1 were absorbances of extract liquors before and after demulsification.
To exhibit the demulsification process, the demulsification phenomenon was recorded by an inverted microscope (AMG EVOSFL, Amercian). The interaction between as-prepared material and model emulsion was reveal by attenuated total reflection infrared spectroscopy (ATR-IR, Nicolet iS5,Thermo Fisher Scientific), X-ray photoelectron spectroscopy (XPS, ES CALAB 250Xi, Thermo Fisher Scientific) and Zeta potential (Marlven Nano-ZS, England). Additionally, the components of SDS solution after interacting with as-prepared material were measured by ion chromatogram (IC) and liquid chromatogram-mass spectroscopy (LC-MS).