Recent advances in nanomaterial-modified polyamide thin-film composite membranes for forward osmosis processes

Abstract

Polyamide thin-film composite (PA TFC) membranes have attained much attention for forward osmosis (FO) applications in separation processes, water and wastewater treatment due to their superior intrinsic properties, such as high salt rejection and water permeability compared to the first generation of cellulose-based FO membranes. Nonetheless, several problems like fouling and trade-off between membrane selectivity and water permeability are hindering the progress of conventional PA TFC FO membranes for real applications. To overcome these issues, nanomaterials or chemical additives have been integrated into the TFC membranes. Nanomaterial-modified membranes have demonstrated significant improvement in their anti-fouling properties and FO performance. In addition, PA TFC membranes can be designed for specific applications like heavy metal removal and osmotic membrane bioreactor by using nanomaterials to modify their physicochemical properties (porosity, surface charge, hydrophilicity, membrane structure and mechanical strength). This review provides a comprehensive summary of the progress of nanocomposite PA TFC membrane since its first development for FO in the year 2012. The nanomaterialincorporated TFC membranes are classified into four categories based on the location of nanomaterial in/on the membranes: embedded inside the PA active layer, incorporated within the substrate, coated on the PA layer surface, or deposited as an interlayer between the substrate and the PA active layer. The key challenges still being confronted and the future research directions for nanocomposite PA TFC FO are also discussed.

Effect of the Zwitterion, p(MAO-DMPA), on the Internal Structure, Fouling Characteristics, and Dye Rejection Mechanism of PVDF Membranes

“…The cake layer only formed on the surface and did not go deep into the membrane due to the smaller pore sizes observed in Figure 5 but was able to penetrate the larger pores wherein it was difficult to dislodge. Thus, membranes with intermediate zwitterion content that had reduced surface roughness (Figure 8) seem to be far better than those with the least or the most zwitterion content with relatively higher surface roughness [82]. The influence of surface roughness is reported to be important with hydrophobic surface characteristics, which is similar to the current observations for MZ4 compared to others [83,84].…”

Thin Film Composite Forward Osmosis Membrane with Single-Walled Carbon Nanotubes Interlayer for Alleviating Internal Concentration Polarization

“…The lowest S value of only 88 µm was appeared on TFC5 membrane, which represented the weakest ICP effect supporting the highest water flux. Notably, the S value of prepared TFC membrane was lower than those reported in most literature [21,[50][51][52], demonstrating that the SWCNTs interlayer was of great significance to prepare high-flux Membrane structure parameter (S) is a direct characterization of ICP effect, which has units of length and can be thought as the distance that a solute particle must travel from the bulk draw solution to the membrane active layer [36]. In Figure 7c, all the TFC membranes with the SWCNTs interlayer presented the lower S value compared to the TFC 0 membrane, attributing that the interconnected SWCNTs with ultrahigh length-to-diameter ratio endowed the low tortuosity.…”

“…The lowest S value of only 88 µm was appeared on TFC 5 membrane, which represented the weakest ICP effect supporting the highest water flux. Notably, the S value of prepared TFC membrane was lower than those reported in most literature [21,[50][51][52], demonstrating that the SWCNTs interlayer was of great significance to prepare high-flux FO membrane. The variation trend of the time-dependent normalized water flux can also show the effect of ICP on separation performance of FO membrane [49].…”

“…However, it is still difficult to form a dense, uniform, and defect-free PA layer on the MF substrates due to a rapid and violent MPD eruption to form large initial PA oligomers and PA layer inside the substrate large pore [20]. Inspired by nanomaterials and nanotechnologies developed, carbon nanotubes (CNTs) with a hollow nano-tubular structure, an excellent chemical stability and polymer-like flexibility [21] were incorporated in the PA layer or support layer to promote the water permeability and selectivity [22,23]. However, this approach was hindered by CNTs agglomeration and CNTs/polymer incompatibility.…”

Recent Progresses of Forward Osmosis Membranes Formulation and Design for Wastewater Treatment

“…Furthermore, a wide selection of nanomaterials ranging from inorganic to biomimetic materials can also be favorably used to prepare the nanocomposite FO membrane [81]. Figure 3 depicts the typical preparation and structures of TFC PA FO membranes [82]. The simplest and the most commonly reported preparation is accomplished through physical blending of the nanomaterials with the polymer dope prior to the phase inversion process.…”