Formation, morphology and control of high-performance biomedical polyurethane porous membranes by water micro-droplet induced phase inversion

Recent advancements in polyurethane-based membranes for gas separation

Gas separation membranes are critical in a variety of environmental research and industrial applications. These membranes are designed to selectively allow some gases to flow while blocking others, allowing for the separation and purification of gases for a variety of applications. Therefore, the demand for fast and energy-efficient gas separation techniques is of central interest for many chemical and energy production diligences due to the intensified levels of greenhouse and industrial gases. This encourages the researchers to innovate techniques for capturing and separating these gases, including membrane separation techniques. Polymeric membranes play a significant role in gas separations by capturing gases from the fuel combustion process, purifying chemical raw material used for plastic production, and isolating pure and noncombustible gases. Polyurethane-based membrane technology offers an excellent knack for gas separation applications and has also been considered more energy-efficient than conventional phase change separation methodologies. This review article reveals a thorough delineation of the current developments and efforts made for PU membranes. It further explains its uses for the separation of valuable gases such as carbon dioxide (CO2), hydrogen (H2), nitrogen (N2), methane (CH4), or a mixture of gases from a variety of gas spillages. Polyurethane (PU) is an excellent choice of material and a leading candidate for producing gas-separating membranes because of its outstanding chemical chemistry, good mechanical abilities, higher permeability, and variable microstructure. The presence of PU improves several characteristics of gas-separating membranes. Selectivity and separation efficiency of PU-centered membranes are enhanced through modifications such as blending with other polymers, use of nanoparticles (silica, metal oxides, alumina, zeolite), and interpenetrating polymer networks (IPNs) formation. This manuscript critically analyzes the various gas transport methods and selection criteria for the fabrication of PU membranes. It also covers the challenges facing the development of PU-membrane-based separation procedures.

Removal of Iron and Copper Ions and Phenol from Liquid Phase by Membrane Based on Carbonaceous Materials

The present work reports an effective method for the removal of inorganic and organic pollutants using membranes based on different carbonaceous materials. The membranes were prepared based on cellulose acetate (18 wt. %), polyvinylpyrrolidone as a pore-generating agent (2 wt. %) and activated carbon (1 wt. %). Activated carbons were developed from residues after extraction of the mushroom Inonotus obliguus using microwave radiation. It has been demonstrated that the addition of activated carbon to the membranes resulted in alterations to their physical properties, including porosity, equilibrium water content and permeability. Furthermore, the chemical properties of the membranes were also affected, with changes observed in the content of the surface oxygen group. The addition of carbon material had a positive effect on the removal of copper ions from their aqueous solutions by the cellulose-carbon composites obtained. Moreover, the membranes proved to be more effective in the removal of copper ions than iron ones and phenol. The membranes were found to show higher effectiveness in copper removal from a solution of the initial concentration of 800 mg/L. The most efficient in copper ions removal was the membrane containing urea-enriched activated carbon.

Modified nano-SiO2/PU hydrophobic composite film prepared through in-situ coupling by KH550 for oil-water separation

In this study, hydrophobic polymer composite films based on polyurethane (PU) were prepared for oil-water separation. Hydrophilic fumed silica (nano-SiO₂) was introduced as reinforcing filler, and silane coupling agent (KH550) was used to crosslink PU with nano-SiO₂ in situ for enhancing the nano-SiO₂ dispersion in the films. The microscopic morphology, crystalline structure, and hydrophobic properties of the films were characterized by using scanning electron microscopy, X-ray diffraction, FTIR spectroscopy, water contact angle, and water absorption tests. The results showed that the hydrophobicity of the nano-SiO₂/PU composite films increased with the addition of nano-SiO₂. KH550 not only significantly promoted the crosslink action between PU and nano-SiO₂ but also enhanced the dispersion of nano-SiO₂ in the composite films. Moreover, the pore structure of the prepared films was changed with the addition of nano-SiO₂ and KH550, which greatly improved the hydrophobicity. The test results for oil-water separation performance showed that the prepared composite films can efficiently separate the oil from oil-water mixtures with good repeatability.

Ferroelectricity-Coupled 2D-MXene-Based Hierarchically Designed High-Performance Stretchable Triboelectric Nanogenerator

Triboelectric nanogenerators based on the state-of-the-art functional materials and device engineering provide an exciting platform for future multifunctional electronics, but it remains challenging to realize due to the lack of in-depth understanding on the functional properties of nanomaterials that are compatible with microstructural engineering. In this study, a high-performance stretchable (∼60% strain) triboelectric nanogenerator is demonstrated via an interlocked microstructural device configuration sandwiched between silver-nanowire-(Ag-NW) electrodes and hierarchically engineered spongy thermoplastic polyurethane (TPU) polymer composite with ferroelectric barium-titanate-coupled (BTO-coupled) 2D MXene (Ti₃C₂T_x) nanosheets. The use of MXene results in an increase in the dielectric constant whereas the dielectric loss is lowered via coupling with the ferroelectricity of BTO, which increases the overall output performance of the nanogenerator. The spongy nature of the composite film increases the capacitance variation under deformation, which results in improved energy-conversion efficiency (∼79%) and pressure sensitivity (4.6 VkPa^-1 and 2.5 mAkPa^-1) of the device. With the quantum-mechanically calculated electronic structure, the device converts biomechanical energy to electrical energy and generates an open-circuit output voltage of 260 V, short-circuit output current of 160 mA/m², and excellent power output of 6.65 W/m², which is sufficient to operate several consumer electronics. Owing to its superior pressure sensitivity and efficiency, the device enables a broad range of applications including real-time clinical human vital-sign monitoring, acoustic sensing, and multidimensional gesture-sensing functionality of a robotic hand. Considering the ease of fabrication, excellent functionality of the hierarchical polymer nanocomposite, and outstanding energy-harvesting performance of nanogenerators, this work is expected to stimulate the development of next-generation self-powered technology.

Porosity Tunable Poly(Lactic Acid)-Based Composite Gel Polymer Electrolyte with High Electrolyte Uptake for Quasi-Solid-State Supercapacitors

The growing popularity of quasi-solid-state supercapacitors inevitably leads to the unrestricted consumption of commonly used petroleum-derived polymer electrolytes, causing excessive carbon emissions and resulting in global warming. Also, the porosity and liquid electrolyte uptake of existing polymer membranes are insufficient for well-performed supercapacitors under high current and long cycles. To address these issues, poly(lactic acid) (PLA), a widely applied polymers in biodegradable plastics is employed to fabricate a renewable biocomposite membrane with tunable pores with the help of non-solvent phase inversion method, and a small amount of poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) is introduced as a modifier to interconnect with PLA skeleton for stabilizing the porous structure and optimizing the aperture of the membrane. Owing to easy film-forming and tunable non-solvent ratio, the porous membrane possesses high porosity (ca. 71%), liquid electrolyte uptake (366%), and preferable flexibility endowing the GPE with satisfactory electrochemical stability in coin and flexible supercapacitors after long cycles. This work effectively relieves the environmental stress resulted from undegradable polymers and reveals the promising potential and prospects of the environmentally friendly membrane in the application of wearable devices.

Asymmetric Cellulose/Carbon Nanotubes Membrane with Interconnected Pores Fabricated by Droplet Method for Solar-Driven Interfacial Evaporation and Desalination

Solar-driven interfacial water purification and desalination have attracted much attention in environmentally friendly water treatment field. The structure design of the photothermal materials is still a critical factor to improve the evaporation performance such as evaporation rate and energy conversion efficiency. Herein, an asymmetric cellulose/carbon nanotubes membrane was designed as the photothermal membrane via a modified droplet method. Under 1 sun irradiation, the evaporation rate and energy efficiency of pure water can reach up to 1.6 kg m−2 h−1 and 89%, respectively. Moreover, stable reusability and desalination performance made the cellulose/carbon nanotubes membrane a promising photothermal membrane which can be used for solar-driven desalination.

Bioinspired Cellulose Foam with Excellent Water Wicking and Flux Properties Prepared Using Ice Template

The application and functionalization of cellulose has been attracting increased attention in academic and industrial studies because of its wide range of sources, short renewable cycle, and low environmental impact. In order to enhance the application field of cellulose and decrease the environmental pollution for organic solvent associated with its preparation, cellulose foam with a vertically hierarchically porous structure similar to wood was designed and fabricated successfully from a cellulose aqueous solution using an ice templated in this study. The cellulose foam prepared using a 3 wt % concentration possessed a uniform vertical hierarchically porous structure, which could provide a pathway for the flow of water or air based on the capillary effect. The highest water wicking rate and flux were 7.8184 mm·s^-1 and 29.49 mL·min^-1·g^-1, respectively, for the porous foam prepared using a 3 wt % concentration. The mechanical testing experiment showed that the porous structure did not reduce the amount of stress that the sample could endure before being damaged. The compression strength increased with increasing cellulose concentration in solution. Therefore, the hierarchical structure formed in the prepared cellulose foam effectively improved the water flux behavior and provided a structural basis for future applications of cellulose scaffolds.

Effect of poly (lactic acid) porous membrane prepared via phase inversion induced by water droplets on 3T3 cell behavior

Phase inversion induced by water droplets has garnered attention in the field of polymer science as a novel method for preparing porous membranes. This study investigates the effect of the porous structure of poly (lactic acid) (PLA) membranes prepared through phase inversion induced by water droplets at four different temperatures (25, 50, 75, and 100 °C) on the morphology and proliferation of 3T3 cells. The surface properties of the PLA porous membrane, including pore size, pore size distribution, surface roughness, surface hydrophilicity, and cytocompatibility with 3T3 cells, were evaluated. The results indicated that the synthesized PLA membrane had two surfaces with different structures. The upper surface in contact with the water droplets during preparation contained uniformly distributed micropores, whereas the bottom surface was smooth and composed of small particles in contacted with the mold. The upper surface showed high cytocompatibility with 3T3 cells, and the 3T3 cells migrated and grew within the pores at 25 °C. In contrast, the bottom surface exhibited low biocompatibility with the 3T3 cells. Our study has wide-ranging implications and will improve the fabrication and implementation of 3D cultured scaffolds with excellent cytocompatibility.

Three-Dimensional Wood-Inspired Bilayer Membrane Device Containing Microchannels for Highly Efficient Solar Steam Generation

A three-dimensional solar steam generation device with a high water evaporation rate and excellent structural stability was developed and characterized. The design consisted of a bilayer membrane composed of polyacrylonitrile (PAN) and PAN/graphene oxide (GO) segments and contained vertically aligned porous structures similar to that of wood. This distinctive design was used to improve the water evaporation rate by increasing the light absorption and specific surface area. The prepared bilayer membrane exhibited excellent water wicking and flux, and it could continuously supply water from the bottom of the solar steam generation device to the top surface. The device's performance was evaluated by exposing the PAN/GO surface to artificial sunlight with a density of 1, 5, and 10 kW m^-2. The water evaporation rate and steam generation efficiency for the PAN and PAN/GO bilayer membrane were found to be 2.27 kg m^-2 h^-1 and 92.63% at a power density of 1 kW m^-2, respectively. Owing to its facile fabrication, hierarchical pore structure, excellent mechanical and water wicking, and high efficiency, the special bilayer composite device has great potential for solar steam generation and desalination applications in resource-limited settings.