Preparation of hydrophilic poly(vinylidene fluoride) membrane for oil/water emulsion separation and heavy metal ions adsorption

doi:10.11949/0438-1157.20201315

Abstract

Abstract:

Polyvinylidene fluoride (PVDF) membrane is widely used in the field of wastewater treatment due to its excellent chemical and mechanical stability. However, the hydrophobicity of the PVDF membrane makes it easy to be contaminated by oil droplets during the treatment of oily wastewater, which causes the pores of the membrane to be blocked and the decrease in permeation flux. In this study, we developed an approach for preparing a hydrophilic PVDF membrane. Specially, the co-deposition of tannic acid (TA) and polyethyleneimine (PEI) on the PVDF membrane was conducted for the formation of TA/PEI adhesive layer, which was covalently grafted with cysteine via glutaraldehyde to fabricate a modified PVDF membrane (PVDF@TA/PEI-Cys). The PVDF@TA/PEI-Cys membrane has good hydrophilicity and underwater superoleophobicity. The water contact angle and underwater oil contact angle were 22.2° and 150.2°, respectively. The pure water flux of the PVDF@TA/PEI-Cys membrane reached 6328 L/(m²·h) under 0.09 MPa and the separation efficiency of the oil-in-water emulsions was as high as 99.9%. In addition, the modified PVDF membrane can also be used for the adsorption of mercury ions with the maximum adsorption capacity of 24.7 mg/g.

Key words: membrane separation, heavy metal ions, adsorption, emulsion, hydrophilicity

摘要：

聚偏氟乙烯（PVDF）膜因其优异的化学和力学稳定性而被广泛应用于水处理领域，但PVDF膜本身的疏水性，容易使其在处理含油废水的过程中被油滴污染，造成膜孔堵塞。以PVDF微滤膜为基底，通过单宁酸（TA）和聚乙烯亚胺（PEI）共沉积形成了TA/PEI黏附层，经戊二醛共价交联和接枝半胱氨酸（Cys），制备了一种PVDF改性膜（PVDF@TA/PEI-Cys）。改性后的PVDF膜具有良好的亲水性和水下超疏油性，水接触角和水下油接触角分别为22.2°和150.2°。在0.09 MPa下，PVDF@TA/PEI-Cys膜的纯水通量达6328 L/（m²·h），水包油型乳液分离效率高达99.9%。此外，该改性膜还可同时吸附水中的汞离子，最大吸附量为24.7 mg/g。

关键词: 膜分离, 重金属, 吸附, 乳液, 亲水性

CLC Number:

TQ 028.8

WU Zhongjie, LIU Zeyan, XIE Lianke, CUI Mei, HUANG Renliang. Preparation of hydrophilic poly(vinylidene fluoride) membrane for oil/water emulsion separation and heavy metal ions adsorption[J]. CIESC Journal, 2021, 72(S1): 421-429.

吴中杰, 刘则艳, 谢连科, 崔美, 黄仁亮. 聚偏氟乙烯膜亲水改性及其乳液分离与重金属吸附应用[J]. 化工学报, 2021, 72(S1): 421-429.

Figures/Tables 13

Fig.1 Surface morphology of different PVDF membranes

Fig.2 XPS spectra of different PVDF membranes (a) and high-resolution S 2p spectrum of PVDF@TA/PEI-Cys membrane (b)

Fig.3 Water contact angles of different PVDF membranes and their changes with different time

Fig.4 Pure water flux of different PVDF membranes

Fig.5 Underwater oil contact angles of different PVDF membrane

Fig.6 Emulsion flux and oil rejection ratio of SDS stabilized oil-in-water emulsions (a)； Different surfactant stabilized diesel oil-in-water emulsions (b); Photographs and optical microscope images of SDS stabilized diesel oil-in-water emulsion and filtrate (c)

Fig.7 Flux recovery rate of different oil-in-water emulsions

Fig.8 Emulsion flux recovery in separation of SDS stabilized diesel oil-in-water emulsion

Fig.9 Changes in Hg2+ concentrations with adsorption time (a); Pseudo-second-order kinetic fitting curve of Hg2+ concentrations with adsorption time (b)

Table 1 Parameters of pseudo-second-order kinetic model for Hg2+ adsorption

Ion	q_e(exp)/(mg/g)	Pseudo-second-order kinetic
Ion	q_e(exp)/(mg/g)	q_e/(mg/g)	K₂/(g/(mg·min))	R²
Hg²⁺	15.9	15.82	0.004	0.9994

Fig.10 Adsorption capacity of PVDF@TA/PEI-Cys membrane at different initial concentrations of Hg2+(a)； Fitting curve of Langmuir isotherm adsorption model (b)

Table 2 Parameters of Langmuir model for Hg2+ adsorption

Ion	q_e(exp)/(mg/g)	Langmuir model
Ion	q_e(exp)/(mg/g)	q_m/(mg/g)	K_L/(L/mg)	R²
Hg²⁺	24.7	25.96	120.9	0.9913

Table 3 Comparison of maximum adsorption capacity of different membrane materials for heavy metal ions

Membrane	Ion	Capacity/(mg/g)	Ref.
PVDF@TA/PEI-Cys	Hg²⁺	24.7	this work
Zr(Ⅳ)-PVDF	As⁵⁺	21.5	[17]
PES/FMBO	As³⁺	73.5	[18]
PVDF-PAA-MEA	Hg²⁺	55.0	[19]
PC/HMO	Cu²⁺	29.6	[20]
PSf/GO	Cu²⁺	68.3	[21]
PSf/HFO	Pb²⁺	13.2	[22]
PSf/NFO	Cd²⁺	23.8	[23]
PVA-PVDF	Pb²⁺	121.2	[24]

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