Correlation between barrier layer Tg and a thin-film composite polyamide membrane's performance: Effect of chlorine treatment

Covalent organic frameworks as promising adsorbent paradigm for environmental pollutants from aqueous matrices: Perspective and challenges

Covalent organic frameworks (COFs) are an emerging class of new porous crystalline polymers materials having robust framework, outstanding structural regularity, highly ordered aperture size, inherent porosity, and chemical stability with designer properties, making them an ideal material for adsorbing a variety of contaminants from water bodies. Presented study focusses on the current advances and progress of pristine COFs as well as COFs based composites as an emerging substitute for the adsorption and removal of a variety of pollutants including water desalination technique, heavy metals, pharmaceuticals, dyes and organic pollutants. The absorption capabilities of COFs-derived architecture are evaluated and equated with those of other commonly used adsorbents. The interaction between sorption ability and structural property as well as some regularly utilized ways to improve the adsorption performance of COFs-based materials are also reviewed. Finally, perspective and a summary about the challenges and opportunities of COFs and COFs-derived materials are discussed to deliver some exciting data for fabricating and designing of COFs and COFs-derived materials for remediation of environmental pollutants.

Fabrication and prospective applications of graphene oxide-modified nanocomposites for wastewater remediation

Water bodies have become polluted with heavy metals and hazardous contaminants as a result of fast development. Many strategies have been devised by researchers in order to remove hazardous contaminants from the aquatic environment. Utilizing graphene oxide-based composite materials as efficient adsorbents for waste water treatment, desalination, separation, and purification is gaining attraction nowadays. Some of their defining properties are high mechanical strength, hydrophilicity, remarkable flexibility, ease of synthesis, atomic thickness, and compatibility with other materials. In water treatment, high separation performance and stable graphene-based laminar structures have been the main goals. Magnetic separation is among the methods which received a lot of attention from researchers since it has been shown to be quite effective at removing harmful pollutants from aqueous solution. Graphene oxide-modified nanocomposites have provided optimal performance in water purification. This review article focusses on the fabrication of GO, rGO and MGO nanocomposites as well as the primary characterization tools needed to assess the physiochemical and structural properties of graphene-based nanocomposites. It also discusses the approaches for exploiting graphene oxide (GO), reduced graphene (rGO), and magnetic graphene oxide (MGO) to eliminate contaminants for long-term purification of water. The potential research hurdles for using fabricated MGOs as an adsorbent to remediate water contaminants like hazardous metals, radioactive metal ions, pigments, dyes, and agricultural pollutants are also highlighted.

Synthesis and chacterization of graphene-based materials (GO, rGO, and MGO) by FT-IR, XRD, UV-VIS, SEM, and Raman spectroscopy, and their potential applications for wastewater treatment.

Reverse osmosis membrane fabrication and modification technologies and future trends: A review

Reverse osmosis (RO) is the most widely used technology in water treatment and desalination technologies for potable water production. Since its invention, RO has undergone significant developments in terms of material science, process, system optimization, methods of membrane synthesis, and modifications. Among various materials used for the synthesis of an RO membrane, the polyamide thin-film composite (PA-TFC) is by far the most common, owing to its excellent water permeability high salt rejection, and stability. However, a tradeoff between membrane permeability and salt rejection and membrane fouling has been a major hindrance for the effective application of this membrane. Thus, a broad investigation has been carried out to address these problems, and among which co-solvent interfacial polymerization (CAIP) and the surface modification of substrates and active layers of RO membrane have been the most effective approaches for controlling and improving the surface properties of the PA-TFC membrane. In this review paper, the problems associated with the RO membrane processes and strategies has been discussed and addressed in detail. Furthermore, as the focus of this review, the major advancements in the strategies used for enhancement of RO membrane performance through CAIP, and surface modifications were scrutinized and summarized.

Controlled Growth of Polyamide Films atop Homogenous and Heterogeneous Hydrogels using Gel-Liquid Interfacial Polymerization

Controlled growth of crosslinked polyamide (PA) thin films is demonstrated at the interface of a monomer-soaked hydrogel and an organic solution of the complementary monomer. Termed gel-liquid interfacial polymerization (GLIP), the resulting PA films are measured to be chemically and mechanically analogous to the active layer in thin film composite membranes. PA thin films are prepared using the GLIP process on both a morphologically homogeneous hydrogel prepared from poly(2-hydroxyethylmethacrylate) (PHEMA) and a phase-separated, heterogeneous hydrogel prepared from poly(acrylamide) (PAAm). Two monomer systems are examined: trimesoyl chloride (TMC) reacting with m-phenylene diamine (MPD) and TMC reacting with piperazine (PIP). Unlike the self-limiting growth behavior in TFC membrane fabrication, diffusion-limited, continuous growth of the PA films is observed, where both the thickness and roughness of the PA layers increase with reaction time. A key morphological difference is found between the two monomer systems using the GLIP process: TMC/MPD produces a ridge-and-valley surface morphology whereas TMC/PIP produces nodule/granular structures. The GLIP process represents a unique opportunity to not only explore the pore characteristics (size, spacing, and continuity) on the resulting structure and morphology of interfacially polymerized thin films, but also a method to modify the surface of (or encapsulate) hydrogels.

A novel high-flux, thin-film composite reverse osmosis membrane modified by chitosan for advanced water treatment

This work demonstrates a novel method for improving the performance of thin-film composite RO membrane by making a polyamide–chitosan composite.

Effect of chlorination condition and permeability of chlorine species on the chlorination of a polyamide membrane

Most studies on membrane chlorination have been investigated in an unpressurized chlorination mode, even if the polyamide membrane was continuously exposed to chlorine under high operating pressure in real water/wastewater treatment plants. In this study, performance changes due to polyamide membrane chlorination were investigated in both pressurized and unpressurized chlorination modes. Chlorination in an unpressurized mode showed a flux increase at high pH and a flux decline at low pH due to the compaction and swelling of the polyamide chains, respectively. On the other hand, chlorination performed in a pressurized mode decreased the water flux in both acidic and alkaline conditions, showing that compaction is overwhelming compared to swelling. The permeability of HOCl, a dominant species at low pH, through the polyamide membrane was pH independent and almost similar to the system recovery, but the permeability of OCl(-), which is dominant at high pH, was maxima at a neutral pH. The different performance behaviors of membranes chlorinated at various pH conditions in the presence or absence of applied pressure could be explained by the permeability of chlorine species and compaction/swelling of polymer chains after chlorination. The effect of membrane chlorination on the chemical property changes at the two different modes was confirmed using attenuated total reflection Fourier transform infrared analysis, and a conceptual model of performance change was proposed to explain the performance discrepancy between the two chlorination modes.