Asymmetric hydrogel-composite membranes with improved water permeability and self-healing property

Construction of self-repairing polyethersulfone membrane with high density hydrophilic microregions by two dimensional restricted channels for enhanced dyes/salts selective separation

Based on the dye/salts separation efficiency and membrane injury caused by serious pollution of dye/salts wastewater, this study constructed a 2D tight ultrafiltration membrane that could both solve the membrane injury problem and improve the dye/salts separation efficiency, the compatibility of good self-healing performance and penetration performance by 2D material magnesium-aluminum Layered double hydroxide (MgAl-LDH). The self-repairing of physical injury was achieved through the swelling effect of AMPS-PAN, this property was proved by permeate flux, the retention performance of salts in dye/salts solution, the comparison of scanning electron microscope (SEM), and the mechanical strength after physical injury. The healing of chemical injury occured through the reaction of CC and polyethersulfone chain breakage, which was confirmed by X-ray photoelectron spectroscopy (XPS), permeate flux, the retention performance of salts in dye/salts solution, and mechanical property. The high separation efficiency of dye/salts was achieved through 2D material MgAl-LDH, which was proved by separation selectivity ɑ. The compatibility of good self-healing performance and penetration performance was obtained by 2D material MgAl-LDH, which was proved by the penetration and self-healing performance. Morever, the membrane illustrated excellent both permeability and dye/sals separation efficiency, just like the permeate flux, the retention performance of sodium sulfate in methyl blue/sodium sulfate solution, the retention performance of Na2SO4 in methyl blue/Na2SO4 solution, the retention rate of methyl blue were 99.1 L/m2h, 12.5%, 7.9%, 97.7%, respectively. The results of pollution index and contact angle also proved that the membrane had anti-pollution performance.

Naked-Eye Readout Distance Quantitative Lateral Flow Assay Based on the Permeability Changes of Enzyme-Catalyzed Hydrogelation

Traditional lateral flow assay (LFA) is restricted to providing qualitative or semi-quantitative results and often requires special equipment for obtaining quantitative results. Herein, we proposed a naked-eye readout distance quantitative lateral flow assay based on the permeability changes in enzyme-catalyzed hydrogelation, which not only has the advantages of being simple, immediate, of high efficiency and low cost, and accurate in quantification but also avoids the use of special equipment. The developed LFA method includes three principal components of a nitrocellulose (NC) membrane containing a control line (C line) loading goat anti-rabbit (GAR) antibodies and a test line (T line) loading specific antibodies, alginate-tyramine conjugates forming a hydrogel in the presence of hydrogen peroxide (H₂O₂) and horseradish peroxidase (HRP), and the HRP-AuNPs-Ab probe only labeling targets captured on the T line. Hemoglobin A1c (HbA1c) was chosen as a representative example to demonstrate the feasibility of our method. Under the optimal conditions, the developed LFA method shows excellent performance in standard samples and real human blood samples where the results of real human blood samples show a high linear correlation with the clinical data obtained by ion exchange chromatography (R² = 0.9929) and the margin of recovery is only 3.8%. All results demonstrated that our developed LFA method not only has enormous potential in the quantitative detection of HbA1c in clinical complex samples but also can serve as a versatile method for highly efficient detection of other target biomolecules due to the fungibility of antibodies.

Microporous Polyethersulfone Membranes Grafted with Zwitterionic Polymer Brushes Showing Microfiltration Permeance and Ultrafiltration Bacteriophage Removal

Virus removal from water using microfiltration (MF) membranes is of great interest but remains challenging owing to the membranes' mean pore sizes typically being significantly larger than most viruses. We present microporous membranes grafted with polyzwitterionic brushes (N-dimethylammonium betaine) that combine bacteriophage removal in the range of ultrafiltration (UF) membranes with the permeance of MF membranes. Brush structures were grafted in two steps: free-radical polymerization followed by atom transfer radical polymerization (ATRP). Attenuated total reflection Fourier transform infrared (ATR-FTIR) and X-ray photoelectron (XPS) verified that grafting occurred at both sides of the membranes and that the grafting increased with increasing the zwitterion monomer concentration. The log reduction values (LRVs) of the pristine membrane increased from less than 0.5 LRV for T4 (∼100 nm) and NT1 (∼50 nm) bacteriophages to up to 4.5 LRV for the T4 and 3.1 LRV for the NT1 for the brush-grafted membranes with a permeance of about 1000 LMH/bar. The high permeance was attributed to a high-water fraction in the ultra-hydrophilic brush structure. The high measured LRVs of the brush-grafted membranes were attributed to enhanced bacteriophages exclusion from the membrane surface and entrapment of the ones that penetrated the pores due to the membranes' smaller mean pore-size and cross-section porosity than those of the pristine membrane, as seen by scanning electron microscopy (SEM) and measured using liquid-liquid porometry. Micro X-ray fluorescence (μ-XRF) spectrometry and nanoscale secondary ion mass spectrometry showed that 100 nm Si-coated gold nanospheres accumulated on the surface of the pristine membrane but not on the brush-coated membrane and that the nanospheres that penetrated the membranes were entrapped in the brush-grafted membrane but passed the pristine one. These results corroborate the LRVs obtained during filtration experiments and support the inference that the increased removal was due to a combined exclusion mechanism and entrapment. Overall, these microporous brush-grafted membranes show potential for use in advanced water treatment.

Construction of self-healing polyethersulfone ultrafiltration membrane by cucurbit[8]uril hydrogel via RTIPS method and host-guest chemistry

In this work, the self-healing polyethersulfone ultrafiltration membrane constructed by host-guest chemistry between cucurbit [8]uril (CB [8] is a family of macrocyclic compounds comprising 8 glycoluril units) and two guest molecules based on reverse thermally induced phase separation (RTIPS) method was developed, which had excellent self-healing performance, better mechanical properties, and high permeation flux and BSA rejection rate. The membrane autonomously restored it BSA rejection rate up to about 89% from rejection rate levels as low as 21% after damage. The observed self-healing performance were attributed to the swelling of pore-filled CB [8] hydrogel into the damage position, the molecular interdiffusion of the hydrogel chains, the strong hydrogen bond of the hydrogel chains and the host-guest interaction between CB [8] and two guest molecules (HEC-Np and PVA-MV). SEM morphologies illustrated that the prepared pore-filled membrane via the RTIPS method had homogeneous and porous skin surface and sponge-like cross-section, which imparted the prepared membranes with improved permeability and better mechanical properties. Properties of MR-CB [8] membranes, which varied with increased content of CB [8], were evaluated by permeability, water contact angle, thermogravimetric analysis (TGA), mechanical properties, FRR, scanning electron microscope (SEM) and atomic force microscopy (AFM). The contact angle water showed that CB [8] hydrogel enhanced the surface hydrophilicity of the prepared membrane. TGA illustrated that the thermal stability improved with the increased content of CB [8]. The optimal pore-filled CB [8] hydrogel membrane (MR-CB [8]₂) exhibited that the pure water flux reached 2100.5 L/m² h, while the BSA rejection rate remained at 86.0%. The results of this work suggested pore-filled CB [8] hydrogel membrane was a more promising way to develop polyethersulfone ultrafiltration membranes with self-healing performance.

Effects of Cu2+/Zn2+ on the electrochemical performance of polyacrylamide hydrogels as advanced flexible electrode materials

Previously, solid-state electrode materials have been utilized for the fabrication of energy storage devices; however, their application is impeded by their brittle nature and ion mobility problems. To address issues faced in such a modern era where energy saving and utility is of prior importance, a novel approach has been applied for the preparation of electrode materials based on polyacrylamide hydrogels embedded with reduced graphene oxide and transition metals, namely, Cu²⁺ and Zn²⁺. The fabricated hydrogel exhibits high electrical properties and flexibility that make it a favorable candidate to be used in energy storage devices, where both elastic and electrical properties are desired. For the first time, a multi-cross-linked polyacrylamide hydrogel was constructed and compared in the presence of other electro-active materials such as reduced graphene oxide and transition metals. Polyacrylamide hydrogels embedded with reduced graphene oxide demonstrate excellent electrical properties such as specific capacitance, least impedance, low phase angle shift and AC conductivity of 22.92 F g^-1, 2115 Ω, 2.88° and 0.67 μδ m^-1 respectively as compared to Cu²⁺- and Zn²⁺-loaded hydrogels, which block all available active sites causing an increase in impedance with a parallel decrease in capacitance. The capacitance retention and coulombic efficiency calculated were 88.22% and 77.23% respectively, indicating high stability up to 150 cycles at 0.1 A g^-1. Storage moduli obtained were 10.52 kPa, which infers the more elastic nature of the hydrogel loaded with graphene oxide than that of other synthesized hydrogels.

Highly Conductive and Permeable Nanocomposite Ultrafiltration Membranes Using Laser-Reduced Graphene Oxide

Electrically conductive membranes are a promising avenue to reduce water treatment costs due to their ability to minimize the detrimental impact of fouling, to degrade contaminants, and to provide other additional benefits during filtration. Here, we demonstrate the facile and low-cost fabrication of electrically conductive membranes using laser-reduced graphene oxide (GO). In this method, GO is filtered onto a poly(ether sulfone) membrane support before being pyrolyzed via laser into a conductive film. Laser-reduced GO composite membranes are shown to be equally as permeable to water as the underlying membrane support and possess sheet resistances as low as 209 Ω/□. Application of the laser-reduced GO membranes is demonstrated through greater than 97% removal of a surrogate water contaminant, 25 μM methyl orange dye, with an 8 V applied potential. Furthermore, we show that laser-reduced GO membranes can be further tuned with the addition of p-phenylenediamine binding molecules to decrease the sheet resistance to 54 Ω/□.

An engineer's introduction to mechanophores

Mechanophores (MPs) are a class of stimuli-responsive materials that are of increasing interest to engineers due to their potential applications as stress sensors. These mechanically responsive molecules change color or become fluorescent upon application of a mechanical stimulus as they undergo a chemical reaction when a load is applied. By incorporating MPs such as spirolactam, spiropyran, or dianthracene into a material system, the real-time stress distribution of the matrix can be directly observed through a visual response, ideal for damage and failure sensing applications. A wide array of applications that require continuous structural health monitoring could benefit from MPs including flexible electronics, protective coatings, and polymer matrix composites. However, there are significant technical challenges preventing MP implementation in industry. Effective strategies to quantitatively calibrate the photo response of the MP with applied stress magnitudes must be developed. Additionally, environmental conditions, including temperature, humidity, and ultraviolet light exposure can potentially impact the performance of MPs. By addressing these limitations, engineers can work to move MPs from the synthetic chemistry bench to the field. This review aims to highlight recent progress in MP research, discuss barriers to implementation, and provide an outlook on the future of MPs, specifically focused on polymeric material systems. Although the focus is on engineering MPs for bulk materials, a brief overview of mechanochemistry will be discussed followed by methods for activation and quantification of MP photo response (concentrating specifically on fluorescently active species). Finally, current challenges and future directions in MP research will be addressed.

Selective Vapor Permeation Behavior of Crosslinked PAMPS Membranes

The effect of crosslinking on vapor permeation behavior of polyelectrolyte membranes was studied. Poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) membranes were crosslinked by using crosslinkers with different lengths between the reactive ends. Crosslinked membranes with a longer crosslinking length showed lower water vapor permeability due to the lower sorption coefficient. It was also shown that the permeation behavior of PAMPS membranes was more affected by sorption than diffusion. For chemical protection applications, the ratio of water over chemical warfare agent permeability (i.e., selectivity) was measured. Due to the high water solubility of polyelectrolytes, crosslinked PAMPS allowed for the selective permeation of water over harmful chemical vapor, showing a selectivity of 20. The addition of electrospun nylon nanofibers in the membranes significantly improved the selectivity to 80, since the embedded nanofibers effectively reduced both diffusion and sorption coefficients of chemical warfare agents.

Processing and modification of hydrogel and its application in emerging contaminant adsorption and in catalyst immobilization: a review

Due to the wonderful property of hydrogels, they can provide a platform for a wide range of applications. Recently, there is a growing research interest in the development of potential hydrogel adsorbents in wastewater treatment due to their adsorption ability toward aqueous pollutants. It is important to prepare such a hydrogel that possesses appropriate robustness, adsorption capacity, and adsorption efficiency to meet the need of water treatment. In order to improve the property of hydrogels, much effort has been made by researchers to modify hydrogels, among which incorporating inorganic components into the polymeric networks is the most common method, which can reduce the product cost and simplify the preparation procedure. Not only can hydrogel be applied as adsorbent, but it also can be used as matrix for catalyst immobilization. In this review, the key advancement on the preparation and modification of hydrogels is discussed, with special emphasis on the introduction of inorganic materials into polymeric networks and consequential changes in the properties of mechanical strength, swelling, and adsorption. Besides, hydrogels used as adsorbents for removal of dyes and inorganic pollutants have been widely explored, but their use for adsorbing emerging contaminants from aqueous solution has not received much attention. Thus, this review is mainly focused on hydrogels' application in removing emerging contaminants by adsorption. Furthermore, hydrogels can be also applied in immobilizing catalysts, such as enzyme and photocatalyst, to remove pollutants completely and avoid secondary pollution, so their progress as catalyst matrix is overviewed.

Hierarchically Assembled Graphene Oxide Composite Membrane with Self-Healing and High-Efficiency Water Purification Performance

Graphene oxide (GO) with a two-dimensional lamellar structure and single-atom thickness has exhibited advantages in water purification by stacking to a continuous membrane. However, a proper method to further increase the separation property of the GO membrane is still urgently needed. Besides, damage to the membrane during the full-scale application processes and the resulted consequential loss are prevalent problems need to be solved. Here, a hierarchically assembled GO composite membrane was developed that can achieve high-efficiency water purification performance and self-healing property via the synergistic effect of the metal-organic framework (MOF) and the coated hydrophilic layer of chitosan. The intercalated MOF effectively expanded the channel space of GO and endowed the channels with molecular-sieving property. Meanwhile, the coated chitosan layer can selectively adsorb water and achieve self-healing through the cross-linking reaction. The prepared GO composite membrane shows largely improved water flux (14.62 L m^-2 h^-1 bar^-1), increased 344% than the water flux of the GO membrane, high rejection ratio (>99% for dyes), and good antifouling performance. In addition, the damaged GO composite membrane can recover its water flux (95%) and rejection ratio (96%) through a facile self-healing process.