Mechanically durable biomimetic fibrous membrane with superhydrophobicity and superoleophilicity for aqueous oil separation

A Hydrogel-coated Wood Membrane with Intelligent Oil Pollution Detection for Emulsion Separation

Considering the potential threats posed by oily wastewater to the ecosystem, it is urgently in demand to develop efficient, eco-friendly, and intelligent oil/water separation materials to enhance the safety of the water environment. Herein, an intelligent hydrogel-coated wood (PPT/PPy@DW) membrane with self-healing, self-cleaning, and oil pollution detection performances is fabricated for the controllable separation of oil-in-water (O/W) emulsions and water-in-oil (W/O) emulsions. The PPT/PPy@DW is prepared by loading polypyrrole (PPy) particles on the delignified wood (DW) membranes, further modifying the hydrogel layer as an oil-repellent barrier. The layered porous structure and selective wettability endow PPT/PPy@DW with great separation performance for various O/W emulsions (≥98.69% for separation efficiency and ≈1000 L m-2 h-1 bar-1 for permeance). Notably, the oil pollution degree of PPT/PPy@DW can be monitored in real-time based on the changed voltage generated during O/W emulsion separation, and the oil-polluted PPT/PPy@DW can be self-cleaned by soaking in water to recover its separation performance. The high affinity of PPT/PPy@DW for water makes it effective in trapping water from the mixed surfactant-stabilized W/O emulsions. The prepared eco-friendly and low-cost multifunctional hydrogel wood membrane shows promising potential in on-demand oil/water separation and provides new ideas for the functional improvement of new biomass oil/water separation membrane materials.

Bubble Turbulent Gas-Permeable Membrane for Ammonia Recovery from Swine Wastewater: Mass Transfer Enhancement and Antifouling Mechanisms

Recovering ammonium from swine wastewater employing a gas-permeable membrane (GM) has potential but suffers from the limitations of unattractive mass transfer and poor-tolerance antifouling properties. Turbulence is an effective approach to enhancing the release of volatile ammonia from wastewater while relying on interfacial disturbance to interfere with contaminant adhesion. Herein, we design an innovative gas-permeable membrane coupled with bubble turbulence (BT-GM) that enhances mass transfer while mitigating membrane fouling. Bubbles act as turbulence carriers to accelerate the release and migration of ammonia from the liquid phase, increasing the ammonia concentration gradient at the membrane-liquid interface. In comparison, the ammonium mass transfer rate of the BT-GM process applied to real swine wastewater is 38% higher than that of conventional GM (12 h). Through a computational fluid dynamics simulation, the turbulence kinetic energy of BT-GM system is 3 orders of magnitude higher than that of GM, and the effective mass transfer area is nearly 3 times that of GM. Seven batches of tests confirmed that the BT-GM system exhibits remarkable antifouling ability, broadens its adaptability to complex water quality, and practically promotes the development of sustainable resource recycling.

Quasi-critical condition to balance the scaling and membrane lifespan tradeoff in hypersaline water concentration

Mineral scaling is an inconvenient obstacle for membrane distillation in hypersaline wastewater concentration applications, compromising membrane lifespan to maintain high water recovery. Although various measures are devoted to alleviating mineral scaling, the uncertainty and complexity of scale characteristics make it difficult to accurately identify and effectively prevent. Herein, we systematically elucidate a practically applicable principle to balance the trade-off between mineral scaling and membrane lifespan. Through experimental demonstration and mechanism analysis, we find a consistent concentration phenomenon of hypersaline concentration in different situations. Based on the characteristics of the binding force between the primary scale crystal and the membrane, the quasi-critical concentration condition is sought to prevent the accumulation and intrusion of mineral scale. The quasi-critical condition achieves the maximum water flux on the premise of guaranteeing the membrane tolerance, and the membrane performance can be restored by undamaged physical cleaning. This report opens up an informative horizon for circumventing the inexplicable scaling explorations and develops a universal evaluation strategy to provide technical support for membrane desalination.

Acid and alkali-resistant fabric-based triboelectric nanogenerator for self-powered intelligent monitoring of protective clothing in highly corrosive environments

The corrosion of materials severely limits the application scenarios of triboelectric nanogenerators (TENGs), especially in laboratories, chemical plants and other fields where leakage of chemically corrosive solutions is common. Here, we demonstrate a chemical-resistant triboelectric nanogenerator (CR-TENG) based on polysulfonamide (PSA) and polytetrafluoroethylene (PTFE) non-woven fabrics. The CR-TENG can stably harvest biological motion energy and perform intelligent safety protection monitoring in a strong corrosive environment. After treatment with strong acid and alkali solution for 7 days, the fabric morphology, diameter, tensile properties and output of CR-TENG are not affected, showing high reliability. CR-TENG integrated into protective equipment can detect the working status of protective equipment in real time, monitor whether it is damaged, and provide protection for wearers working in high-risk situations. In addition, the nonwoven-based CR-TENG has better wearing comfort and is promising for self-powered sensing in harsh environments.

Mechanically Robust and Flame-Retardant Superhydrophobic Textiles with Anti-Biofouling Performance

The attachment of bio-fluids to surfaces promotes the transmission of diseases. Superhydrophobic textiles may offer significant advantages for reducing the adhesion of bio-fluids. However, they have not yet found widespread use because dried remnants adhere strongly and have poor mechanical or chemical robustness. In addition, with the massive use of polymer textiles, features such as fire and heat resistance can reduce the injuries and losses suffered by people in a fire accident. We developed a superhydrophobic textile covered with a hybrid coating of titanium dioxide and polydimethylsiloxane (TiO₂/PDMS). Such a textile exhibits low adhesion to not only bio-fluids but also dry blood. Compared to a hydrophilic textile, the peeling force of the coated textile on dried blood is 20 times lower. The textile's superhydrophobicity survives severe treatment by sandpaper (400 mesh) at high pressure (8 kPa) even if some of its microstructures break. Furthermore, the textile shows excellent heat resistance (350 °C) and flame-retardant properties as compared to those of the untreated textile. These benefits can greatly inhibit the flame spread and reduce severe burns caused by polymer textiles adhering to the skin when melted at high temperatures.

Discrepant effects of monovalent cations on membrane fouling induced by colloidal polymer: Evaluation and mechanism investigation

Understanding how ionic conditions affect membrane fouling induced by anionic polyacrylamide (APAM) is important for achieving long-term and stable operation of a polymer flooding produced wastewater (PFPW) membrane separation process. However, there is lack of studies on the effects of monovalent cations (Na⁺ and K⁺) on APAM-based membrane fouling. In this work, the effects of Na⁺ and K⁺ on filtration efficiency, flux decline behavior, fouling resistance, and cleaning efficiency were studied through a series of microfiltration tests. Moreover, the influencing mechanism of membrane fouling was further comprehensively revealed from the aspects of the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the hydration force, and the microstructure characterizations. The XDLVO theory agreed well with membrane fouling behavior at various ionic strengths. The increase in ionic strength (0-10,000 mg/L) of Na⁺ and K⁺ exacerbated the reduction of relative flux (J/J₀) and the accumulation of fouling resistance, as well as made the porous APAM-induced fouling layer denser and more compact, boosting removal efficiency. Furthermore, K⁺ had a stronger aggravating effect on membrane fouling than Na⁺. Specifically, the final value of J/J₀ for APAM+K⁺ (0.08) was lower than that for APAM + Na⁺ (0.12), and the fouling resistance for APAM+K⁺ (12.25 × 10¹¹ m^-1) was higher than that for APAM + Na⁺ (12.01 × 10¹¹ m^-1) at an ionic strength of 10,000 mg/L, which was owing to the larger hydration force caused by Na⁺ with a smaller ionic radius. This research offers practical guidance for the PFPW membrane filtering process.

Photoaging of Baby Bottle-Derived Polyethersulfone and Polyphenylsulfone Microplastics and the Resulting Bisphenol S Release

This study evaluated the release of bisphenol S (BPS) from polyethersulfone (PES) and polyphenylsulfone microplastics (MPs) derived from baby bottles under UV irradiation. Released BPS fluctuates over time because it undergoes photolysis under UV₂₅₄ irradiation. Under UV₃₆₅ irradiation, the highest released concentration at 50 °C was 1.7 and 3.2 times that at 35 and 25 °C, respectively, as the activation energy of the photochemical reactions responsible for MP decay was reduced at high temperatures. Low concentrations of humic acid (HA, ≤10 mg·L^-1) promote BPS release because HA acts as a photosensitizer. A high concentration of HA (10∼50 mg·L^-1) decreases the BPS release because HA shields MPs from light and scavenges reactive radicals that are produced via photochemical reactions. For example, under UV irradiation, hydroxyl radicals (•OH) attack results in the breakage of ether bonds and the formation of phenyl radicals (Ph•) and phenoxy radicals (Ph-O•).The•OH addition and hydrogen extractions further produce BPS from the decayed MPs. A leaching kinetics model was developed and calibrated by the experimental data. The calibrated model predicts the equilibrium level of BPS release from MPs that varies with the surface coverage density of BPS and leaching rate constants. This study provides groundwork that deepens our understanding of environmental aging and the chemical release of MPs.

Comparative analysis of membrane fouling mechanisms induced by colloidal polymer: Effects of sodium and calcium ions

Polymer (anionic polyacrylamide, APAM) flooding produced wastewater has a relatively high degree of mineralization and abundant ionic species. A comprehensive and systematic investigation of the influence of ion identity on APAM-induced membrane fouling is extremely necessary but has not been conducted to date. A comparative investigation was performed herein to reveal the underlying mechanisms of the influence of Na⁺ and Ca²⁺ (1000 mg/L) on APAM-induced membrane fouling in the adsorption and microfiltration (MF) processes. Na⁺ and Ca²⁺ exhibited contrasting influences on the filtration efficiency, cleaning efficiency, and fouling resistance. Compared to Na⁺, Ca²⁺ promoted reversible fouling and the formation of a loose cake layer; moreover, a higher removal rate and flux recovery were achieved. Additionally, simulations based on adsorption kinetic and membrane fouling models, and a series of microscopic analyses were performed to validate the contradictory influences. During the APAM-based MF process, the membrane fouling was effectively mitigated at the applied ionic strength because of the stronger hydration repulsive force generated by hydrated Ca²⁺ compared to that by Na⁺. This study provides vital guidance for membrane fouling control in the microfiltration of polymer flooding produced wastewater.

All-Polymer and Self-Roughened Superhydrophobic PVDF Fibrous Membranes for Stably Concentrating Seawater by Membrane Distillation

Novel specially wettable membranes have been attracting significant attention for durable membrane distillation (MD). However, constructing a superhydrophobic interface often has to undergo complex modification procedures including roughness construction and hydrophobic modification. Herein, all-polymer and self-roughened superhydrophobic poly(vinylidene fluoride) fibrous membranes (PVDF FMs) with robustly stable pores were successfully constructed via electrospinning of fluorinated polyhedral oligomeric silsesquioxanes/PVDF (F-POSS/PVDF) emulsion solution in combination with hot-pressing. The comparative experiment reveals that proper hot-pressing, including adequate temperature and pressure, can help improve membrane pore stability by welding the intersecting fibers and increase the membrane surface hydrophobicity by transferring the inner fluorine chains to the outer fiber surface, simultaneously advancing membrane scaling and fouling resistance. Nevertheless, excessive temperature or pressure will destroy the interconnected pores and surface wettability of the PVDF FM. Significantly, the hot-pressing-treated F-POSS/PVDF FM shows a high water recovery (∼90%) and robust stability after five rounds of the concentration process toward concentrating natural seawater as a target. Thus, the all-polymer and self-roughened superhydrophobic PVDF FMs constructed via electrospinning combined with the thermal treatment have potential applications in concentrating hypersaline brines, which make up for the other membrane technology, including reverse osmosis and nanofiltration technologies that failed to concentrate hypersaline solutions.

New mechanistic insights into the effect of cations on membrane fouling caused by anionic polyacrylamide

HYPOTHESIS

Understanding the effect of cations on membrane fouling is crucial for the widespread application of the membrane technology. However, contradictory results have been reported based on different studies. Moreover, although the effect of the ionic strength has been studied extensively, limited information is available on the effect of the ion type on membrane fouling.

EXPERIMENTS

The physicochemical properties of the membrane and anionic polyacrylamide (APAM) were evaluated to calculate the APAM-membrane and APAM-APAM interfacial interaction energies under different conditions. Moreover, a series of microfiltration (MF) experiments was conducted to investigate the effects of the ionic conditions on the flux decline, pore blockage and cake layer resistances, and the flux recovery rate of APAM during the MF process.

FINDINGS

As the ionic strength increased, the rate of decrease in the normalized flux increased, the total and cake layer resistances increased significantly, the pore blockage resistance was affected slightly, and the recovery rates of the water flux after physical and chemical cleaning decreased gradually, which could be clearly explained using the Derjaguin-Landau-Verwey-Overbeek theory. Furthermore, compared with Na⁺, Ca²⁺ could effectively mitigate the membrane fouling at an identical ionic strength, which is attributed to the hydration forces of APAM-membrane and APAM-APAM.

Synchronous removal of emulsions and organic dye over palladium nanoparticles anchored cellulose-based membrane

Membrane is a considerable precursor for emulsions separation and organic dyes degradation used in water purification and oil reclamation. However, the tedious preparation method, the surface smears easily, and low degradation efficiency, these characteristics usually significantly hinder its applicability toward wastewater governance. Herein, a green, facile, and efficient fabrication strategy to prepare a bi-functional palladium nanoparticles (PdNPs)-loaded bacterial cellulose membrane (BCMPd) is proposed. A tri-functional bacterial cellulose membrane (BCM) was obtained by percolating bacterial cellulose (BC) on a basal membrane, and BCM served as a support, reducing agent, and stabilizer in the subsequent reduction of PdNPs. Bi-functional BCMPd was successfully obtained and used for continuously removing emulsions and reducing methylene blue (MB) from simulated wastewater via the integration of physical sieving and chemical reaction. Meanwhile, the enhancement factors for the water transfer ability and demulsification capacity correlated directly with the wettability and surface structure of BCMPd. Furthermore, the dosage of BC was adjusted to reveal the mechanism for the enhanced water transferability and demulsification capacity. Notably, PdNPs of BCMPd decreased Fermi potential difference between BH_4- and MB, accelerating the electron transfer of the reduction reaction and thus exhibiting a remarkable MB degradation efficiency. Together, the information obtained in this work can be useful for comprehensively addressing the bottleneck of forming a cost-effective, eco-friendly, and bi-functional membrane reactor, providing an alternative approach for better treatment of complex wastewater.