Thin-film nanocomposite membrane doped with carboxylated covalent organic frameworks for efficient forward osmosis desalination
Graphical abstract
Introduction
Membrane technologies provide promising solutions to address the growing fresh water scarcity and contamination issues [1]. Forward osmosis (FO), as an emerging membrane technology, has received ever-increasing attention in water treatment [2]. Different from pressure-driven reverse osmosis (RO) process [3], FO utilizes the inherent osmosis pressure between feed solution (FS) and concentrated draw solution (DS) as driving force to achieve water transport across a semipermeable membrane. Attractive advantages of FO process, including negligible operation pressure, superior efficacy, low fouling propensity and small footprint, make it having extensive potential applications, such as municipal/agricultural wastewater reclamation for irrigation [4,5], landfill leachate treatment [6], emergency water bag for expedition [7], food and drug concentration [8].
Enlarged applications of membranes have come with a renewed focus on membrane materials research. One of current technical obstacles for FO development was the high-performance FO membranes. Thin-film composite (TFC) FO membranes comprised of an ultrathin active polyamide (PA) layer and a porous ultrafiltration (UF) substrate have been dominating the FO membrane market, due to their merits of relatively high water permeability and wide pH tolerance. However, permeability resistance arising from amorphous PA layer with non-uniform pore, limited porosity and poor inter-connectivity, severely hinders the desalination efficiency. Besides, internal concentration polarization (ICP) attributed to UF substrates drastically reduces the effective osmotic driving force and further deteriorates the separation efficiency [9]. To exert the potential application of FO process, advanced membrane materials and well-designed structures are crucial to develop. Some strategies have been applied to regulate the pore size and interconnected voids of PA layer by adding nanofillers with defined cavities [10], such as aquaporin [11], metal organic frameworks [12], graphene [13], nanotubes [14], and self-assembled small molecules [15], fabricating the thin-film nanocomposite (TFN) membranes with a high water permeability. However, the nanofiller aggregation derived from the weak affinity with PA matrix, as well as the incompatible nanofiller size with the thickness of the PA layer, might lead to the interfacial microvoids and thus deteriorate the selectivity [4,10]. Therefore, adopting a new porous organic-nanofiller with chemical similarity and affinity to PA matrix is important for an advanced FO membrane with both high water permeability and selectivity.
Covalent organic frameworks (COFs), as a burgeoning class of crystalline porous polymers via strong covalent bonds, have been attractive candidates for advanced water-treatment membranes owing to their high porosity and well-organized channel structures [16]. Based on their orderly arranged pore structures with diameter of 0.7–4.7 nm [[17], [18], [19]] and versatile tailored functionalities, COFs showed a great potential in gas separation [20]. Our group conducted a pioneering research on the water-stable COFs (TpPa-2) as an organic nanofiller to fabricate a novel efficient UF membrane [21], achieving synchronous improvements in water permeability and humic acid rejection. In order to match the thickness of PA layer, TpPa-2 was exfoliated into nanosheets and then incorporated into PA layer, performing over three times improvement on water permeability and an excellent H2O/NaCl selectivity, which shed light on the great potentials of COFs in water treatment [22]. Recently, COFs have been employed in the fields of dye sieving [23] and desalination application [[24], [25], [26], [27]]. However, relatively hydrophobic backbone of COFs hampered water affinity and transport through PA layer [19,27]. And the complicated and time/cost-consuming fabrication of COFs hindered the scale of COF-based TFN membranes.
Commonly, the hydrophilicity and charge property of PA layer are attributed to the carboxylic groups (-COOH) on the membrane surface, which derives from the hydrolysis of unreacted acyl chloride groups. If the COFs introduced into the PA layer is rich in -COOH groups, the membrane would exhibit a satisfactory hydrophilicity and an electrostatic repulsion effect to hydrated anion [19]. Such a speculation has been confirmed by a mixed matrix UF membrane containing carboxyl-functionalized COFs (COF-COOH), exhibiting a more hydrophilic and negatively charged surface [27]. While, the research on the TFC membranes containing COF-COOH for desalination is lacking. In this study, a novel TFC membrane incorporated with COF-COOH was fabricated on a macro-porous substrate via interfacial polymerization. COF-COOH was obtained from commercially available raw chemicals of trimesoyl chloride (TMC) and p-phenylenediamine (PPD) [28], probably rendering an excellent compatibility with PA layer due to their similar chemical structure [28,29]. In addition, compared to the NH2-functionalized COFs (COF-NH2) [25], COF-COOH also yields a lower susceptibility to chlorine attack [22]. Effects of COF-COOH on membrane morphology, surface charge, hydrophilicity, mechanical robustness and pore size distribution of PA layer were comprehensively investigated. Separation performance of the TFN membrane was tested under both osmotic-driven FO and pressure-driven RO processes, further exploring the potential of COFs in a highly efficient membrane for desalination and water purification.
Section snippets
Materials
Unless stated otherwise, all solutions and reagents were used without further purification. MPD (99%, Sigma-Aldrich), PPD (99%, Sigma-Aldrich), TMC (98%, Sigma-Aldrich), n-hexane (≥97%, Sinopharm chemical Reagent Co., Ltd), ethyl acetate (EA), absolute alcohol, acetone, ethylene glycol and polyethylene glycol (PEG, molecular weight of 200, 400, 600, Sinopharm Chemical Reagent Co., Ltd). Mixed cellulose ester (MCE) membrane with average pore size of 0.1 μm and average thickness of 135.2 μm was
Characterization of COF-COOH
The COF-COOH was obtained from the polymerization reaction of TMC and PPD as shown in Scheme 1a. From SEM image, COF-COOH showed a regular spherical-like morphology with a particle size distribution of 60–72 nm (Fig. 1a and b). Apparent Tyndall effect further affirmed its size in colloid scale (within 100 nm). It indicated the COF-COOH particle size was well-matched with the thickness of PA layer (100 - 300 nm), making it possible that COF-COOH could manipulate defect-free PA layer. The
Conclusions
From the perspective of membrane structure and chemistry, this work intended to explore the science and engineering of constructing TFN desalination membranes with high water permeability and selectivity by incorporating hydrophilic COF-COOH. The abundant -COOH groups in COF-COOH originated from the commercially available raw materials (TMC and PPD), rendering PA layer with improved hydrophilicity (WAC decline from 93.7° to 53.5°), more negatively surface charge (Zeta potential increase from
Author statement
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by NSFC (No. 21878279), Natural science fund of Shandong Province Project (No. ZR2018MB032), Fundamental Research funds for the Central Universities (No. 201841012). The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
References (49)
- et al.
Membrane-based seawater desalination: present and future prospects
Desalination
(2017) - et al.
Membrane scaling and flux decline during fertiliser-drawn forward osmosis desalination of brackish groundwater
Water Res.
(2014) - et al.
Combination and performance of forward osmosis and membrane distillation (FO-MD) for treatment of high salinity landfill leachate
Desalination
(2017) - et al.
Fabrication of a robust high-performance FO membrane by optimizing substrate structure and incorporating aquaporin into selective layer
J. Membr. Sci.
(2017) - et al.
Polyvinylpyrrolidone modified graphene oxide as a modifier for thin film composite forward osmosis membranes
J. Membr. Sci.
(2017) - et al.
A novel TFC-type FO membrane with inserted sublayer of carbon nanotube networks exhibiting the improved separation performance
Desalination
(2017) - et al.
Ordered covalent organic frameworks, COFs and PAFs. From preparation to application
Coord. Chem. Rev.
(2016) - et al.
Enhanced performance of mixed matrix membrane by incorporating a highly compatible covalent organic framework into poly(vinylamine) for hydrogen purifification
Int. J. Hydrogen Energy
(2016) - et al.
TpPa-2-incorporated mixed matrix membranes for effient water purification
J. Membr. Sci.
(2017) - et al.
Multifunctional thin-film nanocomposite membranes comprising covalent organic nanosheets with high crystallinity for efficient reverse osmosis desalination
J. Membr. Sci.
(2020)
Covalent organic framework modified polyamide nanofiltration membrane with enhanced performance for desalination
J. Membr. Sci.
Covalent organic frameworks (COFs) for environmental applications
Coord. Chem. Rev.
Carboxyl-functionalized covalent organic framework as a two-dimensional nanofiller for mixed-matrix ultrafiltration membranes
J. Membr. Sci.
A novel benzimidazole-functionalized 2-D COF material: synthesis and application as a selective solid-phase extractant for separation of uranium
J. Colloid Interface Sci.
Highly hydrophilic thin-film composition forward osmosis (FO) membranes functionalized with aniline sulfonate/bisulfonate for desalination
J. Membr. Sci.
Novel nanofiltration membrane with ultrathin zirconia film as selective layer
J. Membr. Sci.
The characterization of flat composite nanofiltration membranes and their applications in the separation of Cephalexin
J. Membr. Sci.
Feasibility of forward osmosis using ultra low pressure RO membrane and Glauber salt as draw solute for wastewater treatment
J Environ Chem Eng
Direct quantification of negatively charged functional groups on membrane surfaces
J. Membr. Sci.
Switchable oil/water separation with efficient and robust Janus nanofiber membranes
Carbon
Open porous hydrophilic supported thin-film composite forward osmosis membrane via co-casting for treatment of high-salinity wastewater
Desalination
A novel TFC forward osmosis (FO) membrane supported by polyimide (PI) microporous nanofiber membrane
Appl. Surf. Sci.
Relating performance of thin-film composite forward osmosis membranes to support layer formation and structure
J. Membr. Sci.
Thin film composite forward osmosis membranes based on polydopamine modified polysulfone substrates with enhancements in both water flux and salt rejection
Chem. Eng. Sci.
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