The role of the surfactant sodium dodecyl sulfate to dynamically reduce mass transfer resistance of SPEEK coated membrane for oil-in-water emulsion treatment

Poly(arylene ether)s-Based Polymeric Membranes Applied for Water Purification in Harsh Environment Conditions: A Mini-Review

Confronting the pressing challenge of freshwater scarcity, polymeric membrane-based water treatment technology has emerged as an essential and effective approach. Poly(arylene ether)s (PAEs) polymers, a class of high-performance engineering thermoplastics, have garnered attention in recent decades as promising membrane materials for advanced water treatment approaches. The PAE-Based membranes are employed to resist the shortages of most common polymeric membranes, such as chemical instability, structural damage, membrane fouling, and shortened lifespan when deployed in harsh environments, owing to their excellent comprehensive performance. This article presents the advancements in the research of several typical PAEs, including poly(ether ether ketone) (PEEK), polyethersulfone (PES), and poly(arylene ether nitrile) (PEN). Techniques for membrane formation, modification strategies, and applications in water treatment have been reviewed. The applications encompass processes for oil/water separation, desalination, and wastewater treatment, which involve the removal of heavy metal ions, dyes, oils, and other organic pollutants. The commendable performance of these membranes has been summarized in terms of corrosion resistance, high-temperature resistance, anti-fouling properties, and durability in challenging environments. In addition, several recommendations for further research aimed at developing efficient and robust PAE-based membranes are proposed.

Transport of Heptane Molecules across Water-Vapor Interfaces Laden with Surfactants

Molecular transport across liquid-vapor interfaces covered by surfactant monolayers plays a key role in applications such as fire suppression by foams. The molecular understanding of such transport, however, remains incomplete. This work uses molecular dynamics simulations to investigate the heptane transport across water-vapor interfaces populated with sodium dodecyl sulfate (SDS) surfactants. Heptane molecules' potential of mean force (PMF) and local diffusivity profiles across SDS monolayers with different SDS densities are calculated to obtain heptane's transport resistance. We show that a heptane molecule experiences a finite resistance as it crosses water-vapor interfaces covered by SDS. Such interfacial transport resistance is contributed significantly by heptane molecules' high PMF in the SDS headgroup region and their slow diffusion there. This resistance increases linearly as the SDS density rises from zero but jumps as the density approaches saturation when its value is equivalent to that afforded by a 5 nm thick layer of bulk water. These results are understood by analyzing the micro-environment experienced by a heptane molecule crossing SDS monolayers and the local perturbation it brings to the monolayers. The implications of these findings for the design of surfactants to suppress heptane transport through water-vapor interfaces are discussed.

Switchable wettability of grain-stacked filter layers from polyurethane plastic waste for oil/water separation

HYPOTHESIS

Polyurethane plastic waste (PUPW), a port-abundant solid waste, is difficult to degrade naturally and poses a severe threat to the environment. Hence, the effective recycling of PUPW remains a challenge.

EXPERIMENTS

Herein, a strategy of converting PUPW into stacked oil/water filtration layer grain through a layer-by-layer (LBL) assembly process is investigated. Notably, such PU-based, grain-stacked, and switchable wettability of the oil/water filter layer is first reported.

FINDINGS

The grain-stacked filter layers are flexible for separating immiscible oil/water mixtures, water-in-oil emulsions (WOE), and oil-in-water emulsions (OWE) under gravity over 10 cycle-usages. They can withstand strong acid/alkali solutions (pH = 1-14) and salt solutions over 12 h. Besides, 100-times scale-up experiments have indicated that the obtained filter layers exhibit an upper to 98.2 % separation efficiency for 10 L real industrial oil/water emulsion in the 24 h continuous operation. The demulsification mechanism for emulsions is that the electrostatic interaction along with adsorption between emulsion droplets and grains leads to the uneven distribution of surfactants on the interface film of the emulsion droplets, increasing the probability of tiny droplets colliding and coalescing into large droplets to achieve oil/water separation. This work proposes an effective and economical method of abundant plastic waste for industrial-scale oil-water separation rather than just on the laboratory-scale.

A cationic fluorescent probe for highly selective detection of sodium dodecyl sulfate (SDS) by electrostatic and hydrophobic self-assembly

Sodium dodecyl sulfate (SDS) has a wide range of applications in the chemical industry due to its excellent characteristics including good emulsification, foaming, water solubility and stability, easy synthesis and low price. However, it is a kind of anionic surfactant which is slightly toxic to the human body, and use of a large amount will cause potential pollution of the environment. Therefore, the development of a simple method to realize the monitoring of SDS in the environment is of great significance. Herein, a cationic fluorescent probe was prepared by the condensation reaction between 4-di-p-tolylamino-benzaldehyde and 3-ethylbenzothiazolium iodide. It can be used for the quantitative determination of SDS in the range of 5-50 μM showing red fluorescence and high selectivity by forming banded assemblies. This work provides an effective tool based on a new strategy for the detection of SDS.

Electrospun stereocomplex polylactide porous fibers toward highly efficient oil/water separation

The urgent needs for water protection are not only developing the highly efficient wastewater treatment technologies but also designing the eco-friendly materials. In this work, the eco-friendly composite fibers composed of poly(L-lactide) (PLLA), poly(D-lactide) (PDLA) and maghemite nanoparticles γ-Fe₂O₃ nanoparticles were fabricated through electrospinning technology. Through regulating the processing parameters and introducing additional annealing treatment, nanoscale porous structure and the stereocomplex crystallites (SCs) are simultaneously constructed in the composite electrospun fibers. Physicochemical performances measurements exhibited that the fiber membranes had excellent lipophilicity, good mechanical performances, and high hydrolysis resistance, and all of which endowed the fiber membranes with high oil adsorption capacities, and the maximum oil adsorption capacities achieved 148.9 g/g at 23 °C and 114.8 g/g at 60 °C. Further results showed that the fiber membranes had good oil/water separation ability. The gravity-driven oil flux was 6824.4 L/m²h², and the water rejection ratio was nearly 100% during separating oil/water mixture. Specifically, the fiber membranes showed good stability during the cycling measurements. It is evidently confirmed that the composite PLLA-based fiber membranes with porous structure and SCs can be used in wastewater treatment, especially in some rigorous circumstances.

Synthesis of the cationic fluorescent probes for the detection of anionic surfactants by electrostatic self-assembly

Anionic surfactants were widespread used in car cleaning agents, household detergents, agricultural and industrial processes, and considered as a major source of environmental pollutant. Therefore, it is necessary to develop a fast, simple, highly selective and sensitive probe for the detection of anionic surfactants. Here, we synthesized two aggregation induced emission (AIE)-active molecules 4,4',4″,4‴-(ethene-1,1,2,2-tetrayltetrakis(benzene-4,1-diyl))tetrakis (1-(4-bromobenzyl)pyridin-1-ium) bromide (TPE-Br) and 4,4',4″,4‴-(ethene-1,1,2,2-trayltetrakis(benzene-4,1-diyl))tetrakis(1-methylpyridin-1-ium)iodide (TPE-I), which were then applied as fluorescence probes for detecting sodium dodecyl sulfate (SDS) with high selectivity and sensitivity. In the presence of SDS, a multi-fold fluorescence emission intensity enhancement was observed in both two probes (TPE-Br and TPE-I) due to the electrostatic self-assembly of AIE molecular. The limits of detection are 71.5 and 120 nM for TPE-Br and TPE-I, respectively. This study may provide a new strategy for environmental monitoring by AIE-based fluorescent probe.

Aggregation-induced-emission (AIE) directed assembly of a novel responsive nanoprobe for dual targets sensing

The employment of aggregation induced emission (AIE) species for detecting analytes has become ubiquitous in many applications ranging from environmental monitoring to novel chemical sensing processes. Herein, a new organic building block (4,4',4″,4″'-(ethene-1,1,2,2-trayltetrakis (benzene-4,1-diyl))tetrakis(1-methylpyridin-1-ium) boric acid (TPE-B)) has been synthesized and such chromophore exhibits very weak emission in aqueous solution. The molecule-surfactant interaction can lead to distinguished yellow emissions and the incorporation of sodium dodecyl sulfonate (SDS) will generate morphological changes from irregular organic clusters to aggregated nanoparticles with the size of 45 nm. A six-fold intensity enhancement has been observed and the electrostatic forces are believed to act as the primary role for the selective response to SDS. Based on the in situ established TPE-B-SDS framework, a switched-off effect has been observed in the presence of ClO^- and this signal change will allow us to accurately determine the concentration of such reactive oxygen species (ClO^-). The limits of detection for SDS and ClO^- are calculated to be 54.2 nM and 14.2 nM, respectively. These excellent optical properties have been extended into practical range and the results for the detection of SDS and ClO^- in tap water samples are satisfactory. It is anticipated that the responsive probe will provide deeper insights into multi-targets sensing in extensive systems.