Superhydrophobic electrospun membrane for heavy metals removal by air gap membrane distillation (AGMD)

Abstract

This paper presents a novel approach to fabricate superhydrophobic membranes by using environmentally friendly and cost effective superhydrophobic nanoparticles to enhance nanofibrous membrane performance in term of flux and rejection of heavy metals in Membrane distillation applications. Polyvinylidene fluoride (PVDF) membranes were fabricated using an electrospinning technique, in which electrospinning parameters such as polymer concentration, voltage, solvent ratio, and cationic surfactant were studied to optimize the membrane fibre diameters and produce beadless nanofibrous membranes. The nanofibrous membranes were characterized in terms of pore size, porosity, liquid entry pressure, contact angle, permeate flux and rejection percentage, and were compared to a commercial membrane. Air gap membrane distillation (AGMD) was used to demonstrate the improved ability of superhydrophobic PVDF membranes for removing heavy metals (such as lead) in comparison with pristine and commercial membranes. The results showed that pristine beadless membrane mat can be fabricated by using 15 wt% polymer concentration, 0.05 wt% cationic surfactant with 6:4 DMF to acetone ratio and 14 KV with lead rejection rate of 72.77 %, liquid entry pressure (17 psi) and water contact angle of 132º. In comparison, the composite 11 wt% PVDF membranes with 20 wt% of functionalized alumina (Al2O3) showed 150º WCA and 27 psi as liquid entry pressure which led to 99.36 % of heavy metal rejection and 5.9% increase in permeate flux.

Robust superhydrophobic electrospun membrane fabricated by combination of electrospinning and electrospraying techniques for air gap membrane distillation

“…Next, both modified solutions (with and without NPs) followed the same procedure of electrospinning dope solution using incubated shaker and vacuum oven. Superhydrophobic Al2O3 NPs were prepared by using a non-fluorinated functional group (isostearyl acids) to functionalize nascent nanoparticles, as we previously described [25,26]. Furthermore, the dope solution viscosity was measured by taking the average value of the viscosity reading of the torque range (10-90 %) using a Rheometer (DV3 TLV, Brookfield Engineering Laboratories, USA) at 25 o C with spindle SC4-18.…”

“…Generally, two techniques can be utilized to fabricate superhydrophobic membrane, either by increasing the membrane surface roughness of a low surface energy material or by lowering the surface energy of rough surface membrane [10,11]. Many researchers have successfully increased electrospun membrane hydrophobicity by embedding the nanoparticles within the polymer dope solution to increase fibre roughness and lower the surface energy such as: PVDF-PTFE-CNT [12], PVDF-SiO2 [13], PVDF-PTFE-TiO2 [14], PVDF-PTFE-GO [15], PVDF-Al2O3 [16], PVDF-Clay [17], PSF-Cera flava [18]. Among them, Al2O3 NPs possess excellent thermochemical properties, low toxicity and are cost-effective materials with easy chemical surface functionalization by covalent bonds due to abundant OH groups on the NPs surface [19].…”

Modelling of air gap membrane distillation and its application in heavy metals removal

“…The membrane had a thickness around 100 µm and was fabricated using a homemade electrospinning machine as illustrated in Figure 3. The polymer solution was prepared by dissolving the polymer pellets in solvent mixture ratio 6:4 Dimethylformamide: Acetone, 0.05 wt%, cationic surfactant hexadecyl trimethyl ammonium bromide as well as 20 wt% of 13 nm alumina nanoparticles (Al2O3 NP) to polymer weight as previously reported by Attia et al [8] which were all purchased from Sigma Aldrich. Superhydrophobic Al2O3 NP was functionalized with isostearyl acids (Nissan Chemical Industries) according to the method reported by Shirin et al [16].…”

“…In terms of AGMD, desalination is considered to be one of the major applications for producing high quality water, particularly from sea water [2,3]. However, AGMD can be used for other applications, such as treatment of oil-produced water [4], removal of dyes from textile wastewater [5] and other environmental waste water issues such as tackling of heavy metal contamination [6][7][8].…”

“…Recently, a research group lead by Alexander [16] has suggested using alumina NP functionalized with environmentally friendly hydrocarbon branches instead of using silane and fluorinated groups to produce superhydrophobic surfaces. Based on this fact, Attia et al [8] reported fabrication of a superhydrophobic electrospun membrane using PVDF mixed with alumina NPs functionalized with isostearyl acids ( hydrocarbon branch) with a WCA 150 o .…”