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To enhance the water flux and salt rejection of reverse osmosis membranes, thin film nanocomposite reverse osmosis membranes were prepared by incorporating functionalised single-walled carbon nanotubes (SWNTs). The functionalised SWNTs were obtained by chemical process such as mixed acid oxidation and substitution reaction. The SWNTs were characterised by HRTEM, FTIR, TGA, Raman spectra, UV-Vis and XPS, etc. The surface morphology and structure of membrane were characterised by SEM and contact angle measurement, respectively. The results showed that carboxyl, acyl, amide and amine were successfully grafted on the tip and inner wall of the single-walled carbon nanotubes. The dispersity of the functionalised SWNTs in water was tested, indicating a good hydrophilic property. The polyamide/modified CNT nanocomposite reverse osmosis membrane was prepared. Compared with the bare polyamide membrane, the SWNT-polyamide thin film nanocomposite membranes showed higher property in hydrophilic surface and its water flux, as along with salt rejection, improved dramatically. The experimental results revealed that the modified SWNTs (especially those containing hydrophilic groups such as carboxyl groups and amino groups) well dispersed in the polyamide thin film layer, and hence improved the water permeation, and the salt rejection. [ABSTRACT FROM AUTHOR]

Abstract: An ultrafiltration–nanofiltration (UF–NF) integrated membrane system (IMS) was operated for 500h to examine the performance of the NF membrane in seawater desalination pretreatment. The rejection of divalent ions, TDS, TOC and UV254 by the NF membrane as well as the permeation flux decreased gradually with operating time before each chemical cleaning procedure, while the calculated Stiff and Davis Stability Index (S&DSI) increased gradually from negative up to positive. The result indicates that there exists inorganic fouling during the long run. However, the IMS produced excellent effluent with 93.6% removal of total organic carbon (TOC) for long-term operation. The TOC concentration of the NF permeation samples was in the range of 0.06–0.35mg/L. The chemical cleaning results indicated that inorganic fouling should be preferentially paid attention to, and a combination of citric acid cleaning and NaOH cleaning may achieve an optimal cleaning efficiency. The long-term operation reveals that the membrane is more prone to fouling gradually after chemical cleaning. [Copyright &y& Elsevier]

For nanofiltration (NF) membranes, constructing the interlayer between the substrate and polyamide (PA) layer could balance the trade-off effect between the selectivity and permeability. However, the influencing mechanism of the interlayer to the PA layer is mostly indirect, and how to regulate the physicochemical properties of the PA layer to improve the membrane property remains to be investigated. In this study, porous Zn-TCPP nanosheets with active reaction sites were used to construct interlayer and directly participated in interfacial polymerization (IP) reaction through the edge COOH of nanosheets reacting with piperazine (PIP) to further regulate PA layer physicochemical properties. Controlling the amount of nanosheets involved in the reaction, NF membranes with striated Turing structures, higher negatively charged surface and larger effective filtration area were obtained. The NF membrane permeability with Zn-TCPP interlayer was significantly improved by 123 % while the Cl−/ SO 4 2 − selectivity was greatly enhanced to 72.69, meanwhile it showed excellent performance stability. This study presents a new perspective that the interlayer can modulate the NF membrane physicochemical properties to improve its performance by directly participating in the IP reaction. [Display omitted] • Porous Zn-TCPP interlayer directly participates in the IP reaction via peripheral carboxyl groups. • Zn-TCPP interlayer reduces the pore size of substrate and inhibits the downward growth of polyamide. • Surface morphology of NF membranes is changed, and hydrophilicity and electronegativity are enhanced. • Zn-TCPP interlayer improves the selectivity of NF membrane for mono-/di-anions. [ABSTRACT FROM AUTHOR]

Embedding nanomaterials in thin film composite membranes to overcome the dynamic balance between salt rejection and permeability has become a research hotspot. Apparently, the filling positions of nanomaterials in membranes have a significant influence on membrane properties. In this work, GO@CS core-shell nanomaterials was firstly successfully synthesized, with good hydrophilicity and fast water transmission channels. Then the influences of addition amounts and loading positions of GO@CS on membrane performance were explored. Results demonstrated that embedding GO@CS with 0.01 wt% in the polyamide layer could give full play to the advantages of core-shell nanomaterials and improve the water flux and salt rejection (water flux increased by 115%, salt rejection increased to 99.10%), as well as the performance stability. Compared with TFN membrane with GO@CS embedded between the polyamide layer and supporting layer, the TFN membrane with GO@CS embedded in the polyamide layer could make full use of advantages provided by GO@CS that fast water transmission channels and the interlayer spacing assisting in salt rejection. This work provided guidances for the effect of nanomaterials with hierarchical pores embedding position on membrane performance. Image 1 • GO@CS core-shell nanomaterials were synthesized. • TFN membranes with different loading positions of GO@CS were prepared. • TFN-M membranes showed higher water flux and NaCl rejection. [ABSTRACT FROM AUTHOR]

Abstract This paper reports a novel class of thin film composite (TFC) membranes for forward osmosis (FO) desalination. The TFC membranes were fabricated via interfacial polymerization (IP) of aqueous mixture of polyethyleneimine (PEI) and graphene quantum dots (GQDs) with organic solution of trimesoyl chloride (TMC) on modified polyacrylonitrile (PAN) ultrafiltration substrates. The chemical structures and morphologies of the synthesized GQDs and the GQDs-incorporated membranes were studied by various characterization techniques. The synthesized GQDs exhibited a narrow size distribution of 1.0–4.0 nm with an average size of 2.19 nm, and the thickness were one to three graphene layers. The results showed that GQDs nanoparticles were covalently bonded to the polyamide chains. The optimized TFC membrane with 0.050 wt% GQDs loading exhibited quite hydrophilic and neutrally charged membrane surface, along with an enhanced water flux of 12.9 L m−2 h−1 and a comparable reverse salt flux of 1.41 g m−2 h−1 when DI water and 0.5 M MgCl 2 were used as the feed solution and the draw solution, respectively. Also, the optimized GQDs-incorporated TFC membrane presented an especially good anti-fouling performance. Thus, incorporating the novel graphene nanomaterial into polymer membranes may present its great potential application in desalination, purification and wastewater treatment. Graphical abstract Unlabelled Image Highlights • TFC FO membranes fabricated via interfacial polymerization with GQDs incorporated. • GQDs nanoparticles are covalently bonded to the polyamide chains to avoid leaching. • Water flux increases 22%, reverse salt flux decreases 32% at optimal GQDs loading. • Optimal GQDs loading mitigates the inner concentration polarization extent by 21%. • The optimal TFC FO membrane exhibits remarkable anti-fouling capacity. [ABSTRACT FROM AUTHOR]

Thin film nanocomposite (TFN) organic solvent nanofiltration (OSN) membrane with improved separation performance was fabricated via interfacial polymerization reaction between amine-functionalized graphene quantum dots (af-GQDs) doped aqueous monomer solution of m -phenylenediamine (MPD) and n -hexane solution containing trimesoyl chloride (TMC) monomer. We emphasize the employment of extra-low content for both af-GQDs and MPD, so that we could maximize the function of these nanomaterials and eliminate their aggregation at the same time. The af-GQDs nanomaterials could regulate the interfacial polymerization process and could be strongly anchored in the polyamide film via covalent bonding, hence could prevent their loss while providing more channels for faster solvent penetration. As a result, the optimized OSN membrane, TFN-50, shows a super-smooth surface, with a surface roughness as low as 4.3 ± 0.2 nm, and excellent pure solvent permeances which reach 135.8, 112.7, and 69.8 L m−2 h−1 MPa−1 for methanol, DMF and ethanol, respectively, as well as a very high Rhodamine B (RDB, 479 Da) rejection of up to 99.2%, and an ethanol permeance of 61.4 L m−2 h−1 MPa−1. Furthermore, the TFN-50 OSN membrane still shows excellent filtration performance after being submerged in DMF for 336 h or continuous crossflow filtration with Rose bengal (RB, 1017 Da)/DMF solution for 136 h, demonstrating its excellent solvent resistance. [Display omitted] • TFN OSN membrane incorporated with af-GQDs nanomaterials is prepared via interfacial polymerization method. • Ultra-low content for af-GQDs and MPD is used in the aqueous phase during the interfacial polymerization process. • Af-GQDs effectively manipulate the interfacial polymerization process and help to form a selectivity layer with ultra-smooth surface. • Higher solvent permeance and excellent dye rejection performance are achieved with the aid of af-GQDs. • The af-GQDs doped OSN membrane has excellent durability performance in harsh strong polar solvents. [ABSTRACT FROM AUTHOR]

The separation performance of current organic solvent nanofiltration (OSN) membranes are still not satisfied. In this work, an ultra-thin TpHz covalent organic frameworks (COFs) interlayer was in situ constructed in advance on polyimide substrate, then an ultra-thin polyamide separation layer incorporated with amino-functionalized graphene quantum dots (af-GQDs) was constructed via interfacial polymerization (IP). A high performance interlayered thin-film nanocomposite (iTFN) OSN membrane with integrally covalent bonding structure, ultra-thin and ultra-smooth surface was obtained after post crosslinking and activation. The effect of ultra-low concentrations for the polyamide reaction monomers, the COFs monomer Tp and the doped af-GQDs nanoparticle reveals that they could help to form a very thin (7–8 nm in thickness) and defect-free skin layer with very smooth surface (about 2.7 nm in roughness). The iTFN OSN membrane shows excellent solvent permeance and solute selectivity, with an ethanol permeance reaching 97.6 L m−2 h−1 MPa−1 and an RDB rejection higher than 99%. After a 180 h long-term filtration with 100 mg L−1 RB/DMF solution, it remained an RB rejection of higher than 99%, demonstrating its superior resistance to strong polar solvent. Our work paves a unique way for the fabrication of novel OSN membrane with both in situ constructed nanomaterials interlayer and nanomaterials incorporated in skin layer. [Display omitted] • Integrally covalent iTFN OSN membrane has COFs interlayer and af-GQDs incorporated. • Ultra-thin TpHz COFs layer constructed in situ with ultra-low content of Tp and Hz. • Ultra-thin polyamide skin formed using ultra-low content for MPD, TMC and af-GQDs. • Ethanol permeance reaches 97.6 L m−2 h−1 MPa−1 with RDB rejection of above 99%. • The integrally covalent iTFN OSN membrane achieves superior solvent resistance. [ABSTRACT FROM AUTHOR]

Aiming at enhancing the permeability of reverse osmosis (RO) membranes, polyaniline-co-polypyrrole hollow mesoporous nanospheres (PPHMNs) were synthesized with aniline and pyrrole monomers via a simple and rapid one-step method, and then added to the aqueous phase of interfacial polymerization to fabricate thin-film nanocomposite (TFN) membranes. Hollow cores of the PPHMNs embedded in polyamide layers could reduce the interior transfer resistance of the membrane and shorten the transmission pathway of water molecules. Mesoporous shell of PPHMNs provided more channels for rapid transmission of water molecules. Moreover, amino groups in PPHMNs originated from the monomer of aniline could not only be bonded to polyamide (PA) layer by reacting with acyl chloride groups to prevent the leakage but also improve hydrophilicity of the membrane. Water flux of TFN membrane doped with PPHMNs (TFN-Ps) of 0.005 wt% addition concentration was 34.1 L·m−2·h−1 which is 76.7% higher than that of thin-film composite (TFC) membrane, and the NaCl rejection all kept over 99.0%. The TFN-Ps also showed excellent long-term stability, chlorine resistance and anti-fouling performance. This work opens an avenue for application of mesoporous hollow nanospheres with amino groups synthesized by simple and time-saving methods in developing TFN membranes with improved water flux. [Display omitted] • Mesoporous hollow nanosphere with amino groups was synthesized via a one-step method. • Nanospheres have uniform sizes of 130 nm and spherical shell ranges from 21 to 35 nm. • Water flux of RO membranes raised from 19.3 to 34.1 LMH with NaCl rejection over 99%. • TFN membrane showed long-term stability, chlorine-resistant and antifouling property. [ABSTRACT FROM AUTHOR]

We successfully fabricated a kind of novel sandwich-like thin-film nanocomposite (TFN) polyamide (PA) membranes via interfacial polymerization (IP) method on polyimide (PI) support surface which was modified by a layer of nanosized amine-modified zeolitic imidazolate framework - 8 (mZIF-8) nanoparticles for organic solvent nanofiltration (OSN). Uniform distribution of the nanoparticles was obtained via directly immersing the PI support membrane in aqueous mZIF-8 suspension prior to the IP. A post-IP cross-linking procedure was conducted to enhance further the solvent resistance of the fabricated TFN OSN membranes. Ultra-smooth (average surface roughness of 13.7 nm) and ultra-thin (average thickness of about 33 nm) skin layer was achieved, together with high Rhodamine B (RDB, 479 Da) rejection (99.1%) and reasonable ethanol permeance (~28 L m−2 h−1 MPa−1), as well as nearly unchanged RDB rejection after being submerged in DMF at high temperature (80 °C) for 120 h, indicating their very good resistance in very harsh strong polar solvent circumstance and the promising aspect of their industrial application. • The OSN membrane was fabricated with covalent bonding between layers. • The mZIF-8 interlayer helped to form an ultra-smooth and ultra-thin skin layer. • OSN membrane permeance was effectively increased without sacrificing rejection. • The OSN membrane kept super stability in DMF at 80 °C for 120 h. [ABSTRACT FROM AUTHOR]