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

Abstract

Membrane pore wetting is the main problem hindering long term stability of permeate flux quality in membrane distillation (MD) applications. A superhydrophobic membrane with micro and nanostructured surface features can offer a unique solution to resolve this issue. Thus, a modified electrospun membrane was fabricated using a combination of electrospinning and electrospraying. The membrane surface hydrophobicity was enhanced by constructing a beaded structure from spraying a mixture of non-fluorinated alumina (Al2O3) nanoparticles (NPs) mixed with low concentration of PVDF polymer on an electrospun base membrane made from PVDF. The results revealed that a rough surface with a hierarchical structure can be constructed, which could not only enhance the membrane hydrophobicity, but also further enhance the permeate efficiency by improving parameters such as flux and rejection. Additionally, the membrane hydrophobicity could be further tuned by controlling the bead spinning volume. Our study shows that the modified membrane with 7.8µm beads layer thickness has boosted the liquid entry pressure (LEP) by 61% from 15.5 psi and the water contact angle to 154 o. The performance of modified membranes with different spraying volume (1-5 ml) along with the neat electrospun and commercial membranes were examined in an air gap membrane distillation (AGMD) application for 5 hours using a 2.5 wt% of synthetic heavy metal solution as a wastewater model. Then, the optimized superhydrophobic membrane with 2 ml spinning volume (ES15-2) was further tested in comparison with the commercial membrane during long-term operations (30 h) using 3.5 wt% of mixed heavy metals. The flux was 18.67 LMH (L m −2 h −1) for modified membrane (ES15-2) compare with 12.62 LMH for commercial PVDF membrane during 30 h of long-term operation with feed and coolant temperature at 60 o C, 20 o C, respectively. The present superhydrophobic membrane fabricated by a combined electrospinning/electrospray method shows high potential for MD applications.

The Role of Electrospun Nanomaterials in the Future of Energy and Environment

“…Very good performance in an AGMD, reported to be achieved by modifying the hydrophobicity and the surface structure of the membranes. Attia et al synthesized composite nanofibers by embedding alumina nanoparticles in nanofibrous structures [ 220 ]. The hierarchical composite membrane consisted of electrospun nanofibers of PVDF as the support layer and a beaded layer on top was evaluated for treatment of contaminated water with AGMD.…”

Surface Engineering of Ceramic Nanomaterials for Separation of Oil/Water Mixtures

“…There are other examples where this combination of properties has been used to engineer materials for oil/water separation (Zhu et al, 2017 ; Ge et al, 2019 , 2020a ). A variety of nanomaterials have been used to create meshes (Jiang et al, 2017 ; Zhang et al, 2018a , 2019 ; Nanda et al, 2019 ; Wang et al, 2019 ; Gong et al, 2020 ), membranes (Attia et al, 2018 ; Huang et al, 2018 ; Ma et al, 2018 ; Qing et al, 2018 ; Zhao et al, 2018 ; Subramanian et al, 2019 ; Cheng et al, 2020 ), sponges (Huang et al, 2019b ; Li et al, 2019b ), and fabrics (Cheng et al, 2018 ; Chauhan et al, 2019 ; Lin et al, 2019 ; Zhou et al, 2019 ; Dan et al, 2020 ) with superhydrophobic and superoleophilic properties for oil/water separation (Ferrero et al, 2019 ; Zulfiqar et al, 2019 ; Latthe et al, 2020 ; Lin et al, 2020 ; Topuz et al, 2020 ; Zhang et al, 2020b ). Most of these materials separate oil either by filtration, absorption, or both.…”

One-Step Methods to Fabricate Durable Superhydrophobic Coatings for Flexible Electronic Sensors

“…With a high water contact angle (WCA, >150 • ), and a low sliding angle (SA, <10 • ), superhydrophobic surfaces, inspired by natural creatures, have attracted extensive attention in academia [1,2]. Many methods, such as electrospinning [3,4], sol-gel [5][6][7], etching [8][9][10], hydrothermal [11,12], self-assembly [13,14] and template methods [15,16], have been used to prepare superhydrophobic surfaces. With the development of superhydrophobic technology, a single superhydrophobic surface cannot meet our requirements.…”