Efficacy of different generations and concentrations of PAMAM–NH2 on the performance and structure of TFC membranes

TETA-anchored graphene oxide enhanced polyamide thin film nanofiltration membrane for water purification; performance and antifouling properties

This work investigates the performance and structure of polyamide thin film nanocomposite (PA-TFN) membrane incorporated with triethylenetetramine-modified graphene oxide (GO-TETA). The embedment of GO-TETA nanosheets within the structure of PA-TFN membrane was evaluated at different concentrations (0.005, 0.01, 0.03 wt%; in aqueous piperazine (PIP)) through interfacial polymerization (IP). The physicochemical properties of the prepared membrane were investigated by SEM, AFM, water contact angle, and zeta potential as well as ATR-IR spectroscopy. The presence of longer chains of amino groups (in comparison with the directly linked amino ones) among the stacked GO nanosheets was assumed to increase interlayer spacing, resulting in remarkable changes in water permeance and separation behavior of modified polyamide (PA) membrane. It is seen that GO-TETA nanosheets were uniformly distributed in the matrix of PA layer. With increasing the concentration of GO-TETA, the flux of TFN membranes under 6 bar was increased from 49.8 l/m² h (no additive) to 73.2 l/m² h (TFN comprising 0.03 wt% GO-TETA. In addition, more loading GO-TETA resulted in a significant decrease in the average thickness of the polyamide layer from ~380 to ~150 nm. Furthermore, addition of GO-TETA improved the hydrophilicity of nanocomposite membranes, resulting in superb water flux recovery (antifouling indicator) as high as 95% after filtration of bovine serum albumin solution. Also, the retention capability of the TFN membranes towards some textile dyes increased as high as 99.6%.

The Recent Progress in Modification of Polymeric Membranes Using Organic Macromolecules for Water Treatment

For decades, the water deficit has been a severe global issue. A reliable supply of water is needed to ensure sustainable economic development in population growth, industrialization and urbanization. To solve this major challenge, membrane-based water treatment technology has attracted a great deal of attention to produce clean drinking water from groundwater, seawater and brackish water. The emergence of nanotechnology in membrane science has opened new frontiers in the development of advanced polymeric membranes to enhance filtration performance. Nevertheless, some obstacles such as fouling and trade-off of membrane selectivity and permeability of water have hindered the development of traditional polymeric membranes for real applications. To overcome these issues, the modification of membranes has been pursued. The use of macromolecules for membrane modification has attracted wide interests in recent years owing to their interesting chemical and structural properties. Membranes modified with macromolecules have exhibited improved anti-fouling properties due to the alteration of their physiochemical properties in terms of the membrane morphology, porosity, surface charge, wettability, and durability. This review provides a comprehensive review of the progress made in the development of macromolecule modified polymeric membranes. The role of macromolecules in polymeric membranes and the advancement of these membrane materials for water solution are presented. The challenges and future directions for this subject are highlighted.

Polyamidoamine dendrimer grafted forward osmosis membrane with superior ammonia selectivity and robust antifouling capacity for domestic wastewater concentration

Developing a forward osmosis (FO) membrane with superior ammonia selectivity and robust antifouling performance is important for treating domestic wastewater (DW) but challenging due to the similar polarities and hydraulic radii of NH₄⁺ and water molecules. Herein, we investigated the feasibility of using polyamidoamine (PAMAM) dendrimer to simultaneously enhance the ammonia rejection rate and antifouling capacity of the thin-film composite (TFC) FO membrane. PAMAM dendrimer with abundant, easily-protonated, terminal amine groups was grafted on TFC-FO membrane surface via covalent bonds, which inspired the TFC-FO membrane surface with appreciable Zeta potential (isoelectric point: pH = 5.5) and outstanding hydrophilicity (water contact angle: 39.83 ± 0.57°). Benefiting from the electrostatic repulsion between the protonated amine layer and NH₄⁺-N as well as the concentration-induced diffusion resistance, the introduction of PAMAM dendrimer endowed the grafted membrane with a superior NH₄⁺-N rejection rate of 98.23% and a significantly reduced the reverse solute flux when using NH₄Cl solutions as feed solution. Meanwhile, the perfect balance between the electrostatic repulsion to positively-charged micromoleculer ions (metal ions and NH₄⁺-N) and the electrostatic attraction to negatively-charged macromolecular organic foulants together with the hydrophilic nature of amine groups facilitated the enhancement of the grafted membranes in antifouling capacity and hence the NH₄⁺-N selectivity (rejection rate of 91.81%) during the concentration of raw DW. The overall approach of this work opens up a frontier for preparation of ammonia-selective and antifouling TFC-FO membrane.

Three-channel capillary NF membrane with PAMAM-MWCNT-embedded inner polyamide skin layer for heavy metals removal

Nanofiltration (NF) membranes with simultaneous high rejection of divalent cations and anions and high water permeation were designed and fabricated via interfacial polymerization (IP) on three-channel capillary ultrafiltration (UF) membranes. MWCNTs-COOH were modified with poly(amidoamine) (PAMAM) and the as-synthesized MWCNTs-PAMAM were embedded into the inner polyamide skin-layer of the NF membranes by incorporating them into a piperazine (PIP) aqueous solution, followed by IP with trimesoyl chloride (TMC). The rigid MWCNTs and the dendrimer PAMAM molecules endow the as-fabricated NF membranes with high porosity and good hydrophilicity. Additionally, the -NH2 groups of PAMAM introduce some positive sites into the polyamide layer. The as-prepared NF membranes with incorporated MWCNTs-PAMAM exhibit a pure water flux of 48.7 L m-2 h-1 and 92.6% and 88.5% rejection for Na2SO4 and MgCl2, respectively, at 4 bar. Moreover, the NF membranes display high rejection for sulfates and metal cations, including heavy metal ions. The practicability of the membranes for mine-wastewater treatment was tested, and the membranes showed above 80% rejection of heavy metals and solution flux of about 30 L m-2 h-1. In addition, their separation performance and stability were satisfactory during the long-term run. The high rejection of the membranes for metal cations is ascribed to the positive sites offered by MWCNTs-PAMAM and the narrow membrane pores since both electrostatic repulsion and size exclusion play a role during membrane filtration. The good separation performance of the membranes for multivalent anions and heavy metal cations illustrates their potential for applications in heavy metal wastewater treatment.

Interfacial Microstructure and Enhanced Mechanical Properties of Carbon Fiber Composites Caused by Growing Generation 1-4 Dendritic Poly(amidoamine) on a Fiber Surface

In an attempt to improve the mechanical properties of carbon fiber composites, propagation of poly(amidoamine) (PAMAM) dendrimers by in situ polymerization on a carbon fiber surface was performed. During polymerization processes, PAMAM was grafted on carbon fiber by repeated Michael addition and amidation reactions. The changes in surface microstructure and the chemical composition of carbon fibers before and after modification were investigated by atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. All the results indicated that PAMAM was successfully grown on the carbon fiber surface. Such propagation could significantly increase the surface roughness and introduce sufficient polar groups onto the carbon fiber surface, enhancing the surface wettability of carbon fiber. The fractured surface of carbon fiber-reinforced composites showed a great enhancement of interfacial adhesion. Compared with those of desized fiber composites, the interlaminar shear strength and interfacial shear strength of PAMAM/fiber-reinforced composites showed increases of 55.49 and 110.94%, respectively.

Novel polyamide thin-film composite nanofiltration membrane modified with poly(amidoamine) and SiO2 gel

Recently, poly(amidoamine) (PAMAM) has emerged as a novel material due to its high density of functional groups, hyper-branched structure and hydrophilic nature.

A water-soluble hyperbranched copolymer based on a dendritic structure for low-to-moderate permeability reservoirs

An excellent matching relationship in size exists between HPDA and the pore throat with a permeability reservoir of under 500–100 mD.