Preparation of Magnetically Recyclable Fluorinated Graphene and Its Demulsification Performance for Emulsified Oily Wastewater†

doi:10.7503/cjcu20180559

Abstract

Abstract:

Fluorinated graphene(FG) was firstly reduced by hydrazine hydrate to form the hydrophilic FG(HFG), and then magnetic Fe₃O₄ nanoparticles were further grafted onto the surface of HFG to synthesize HFG-Fe₃O₄ composite. The morphology, structure and chemical property of the samples were characterized by TEM, SEM, FTIR, XRD and XPS. In addition, the demulsification performance of HFG-Fe₃O₄ for oily wastewater was investigated and some affecting factors were discussed in detail. Moreover, the demulsification mechanism of HFG-Fe₃O₄ was proposed as well. The results show that the HFG-Fe₃O₄ is one kind of two-dimensional sheet-like material with Fe₃O₄ nanoparticles being uniformly distributed on its surface. The HFG-Fe₃O₄ has good demulsification performance on acidic and neutral oily wastewater, and its optimum dosage is 600 mg/L. Under the acidic and neutral conditions, the electrostatic attraction between HFG-Fe₃O₄ and the oily wastewater, as well as the π-π interaction between HFG-Fe₃O₄ and asphaltenes are the main forces promoting the oil separation from oily wastewater. However, the electrostatic repulsion between HFG-Fe₃O₄ and oily wastewater increases drastically under the alkaline condition, and ultimately results in the reduction of demulsification efficiency. What’s more, HFG-Fe₃O₄ still has excellent demulsification performance after 4 cycles, suggesting it has superior recyclability.

Key words: Fluorinated graphene, Emulsified oily wastewater, Oil-water separation, Recyclability, Demulsification mechanism

CLC Number:

O647.32

TrendMD:

XU Haiyan,REN Sili,JIA Weihong,WANG Jinqing. Preparation of Magnetically Recyclable Fluorinated Graphene and Its Demulsification Performance for Emulsified Oily Wastewater^†[J]. Chem. J. Chinese Universities, 2019, 40(3): 508.

Figures/Tables 13

Scheme 1 Preparation process of HFG-Fe3O4

Fig.1 TEM images of Fe3O4 nanoparticles(A), HFG(B), HFG-Fe3O4(C) and EDS of HFG-Fe3O4(D)

Fig.2 SEM images of Fe3O4 nanoparticles(A), HFG(B), HFG-Fe3O4(C), the element mapping regions of HFG-Fe3O4(D) and the corresponding element mapping images of HFG-Fe3O4(E—I)(E) C; (F) O; (G) F; (H) N; (I) Fe.

Fig.3 FTIR spectra of the samples

Fig.4 XRD patterns of the samples

Fig.5 XPS spectra of the samples

Table 1 Surface species of FG, HFG and HFG-Fe3O4 samples determined by XPS analysis

Sample	Atomic ratio(%)
Sample	C	O		F		N		Fe
FG	54.62		1.74		43.64
HFG	86.95		3.31		4.47		5.27
HFG-Fe₃O₄	63.93		26.47		0.36		0.71		8.53

Fig.6 TGA curves of Fe3O4(a), HFG(b) and HFG-Fe3O4(c) samples(A) and magnetic hysteresis loops of Fe3O4(a) and HFG-Fe3O4(b) at room temperature(B)The insets in (B) show the magnetic separation-redispersion results of HFG-Fe3O4(a and b).

Fig.7 Zeta potentials of HFG,HFG-Fe3O4 and emulsified oily wastewater at various pH levels

Fig.8 Effects of HFG-Fe3O4 dosage and pH value of oily wastewater on demulsification performance of HFG-Fe3O4(A) pH=2.0, c(HFG-Fe3O4)/(mg·L-1) from a to i: 0, 50, 100, 200, 300, 400, 500, 600,700. (B) pH=2.0; (C) pH=4.0; (D) pH=6.0.

Fig.9 Reusability of HFG-Fe3O4 at pH=2.0

Fig.10 POM images of the emulsified oily wastewater(A), the newly formed floccule(B), the newly formed oil phase(C), the oil phase after magnetic separation and settlement(D), the newly separated water phase(E), and the separated water phase after being treated by a magnet(F)

Scheme 2 Demulsification mechanism of HFG-Fe3O4

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