Reusable Membranes Research Articles

Composite flat-sheet membrane adsorbent of Li2TiO3-Ethylene-co-vinyl alcohol (LTO-EVAL) for lithium extraction

Composite bead adsorbents have been prevalent for the extraction of Li+ from brines. However, adsorbent beads generally demonstrate declining adsorption capacity and require extended equilibrium time when used repeatedly in absorption/desorption cycles. To overcome this challenge, a novel composite flat-sheet membrane adsorbent based on ethylene-co-vinyl alcohol (EVAL) and Li2TiO3 (LTO) is reported herein for highly efficient Li+ extraction from a geothermal brine. At an optimal LTO loading and membrane thickness, the resulting LTO-EVAL membrane was characterized by a large open macrovoid structure for fast ion transport, a fast adsorption rate that reached equilibrium in 0.5 h, and a high capacity of 96 % of that of the powder. The new membrane adsorbent showed adsorption behavior consistent with the Langmuir model and pseudo-second-order kinetic model. For a geothermal brine with a low lithium concentration, the LTO-EVAL membrane showed stable performance in 13 rapid adsorption/desorption cycles, with adsorption capacity at an average adsorption capacity of 7.3 mg/g and a 70 % adsorption efficiency. The average dissolution rate of Ti4+ was below 0.6 % in each cycle. The structure of the adsorbent material showed no discernable changes in chemical structure as confirmed by XRD and SEM results. With the improved extraction efficiency, the reusable membrane adsorbents would be economically viable in the long run and could potentially serve as the next generation of scalable Li+ adsorption material for brines. Further utilization of membrane adsorbent would lead to new design of adsorption modules and systems with reduced footprint. We need to further optimize the stability of the membrane adsorbents so that loss of Li2TiO3 remain at low level to reduce the lost for lithium extraction from the geothermal brine.

The life cycle assessment of temporary reusable membrane structures: Case study analysis

Membrane structures represent lightweight spatial structures composed of a primary framework combined with tensioned membranes. Their popularity has increased due to their lightweight, flexible, and durable characteristics. However, as all constructions, their production and use come with an environmental impact. This study aims to assess the life cycle assessment of membrane structures with temporary use, specially focusing on the Global Warming Potential, a well-recognised indicator of greenhouse gas emissions.Using Life Cycle Assessment methodology, this research evaluates the environmental impact of membrane structures from raw material extraction to disposal. The investigation concentrates on temporary membrane structures installed multiple times across different locations within a 25-year lifespan. Two case studies, Nomad ADD-ON rental sails and Wolke Marienfeld, are analysed. The LCA of a temporary structure involves three distinct LCAs: one for the initial installation, one for each intermediate installation, and a final assessment for the end installation.Results indicate that temporary reusable membrane structures demonstrate a significant environmental impact, primarily due to the high energy consumption during manufacturing and transportation. It is essential to consider the effects of the ‘End-of-Life’ stages and the ‘benefits and loads beyond the system boundaries’ stage, particularly for temporary structures.This research aims to raise awareness about the environmental impact of temporary membrane structures and offers a framework for sustainable design and construction methods. Additionally, it explores potential strategies to reduce the environmental impact including thoughtful material choices, innovative construction practices and effective End-of-Life management.

Natural Clay-Modified Piezocatalytic Membrane for Efficient Removal of Coliform Bacteria from Wastewater.

In the modern era, water pollution, especially from industries, agricultural farms, and residential areas, is caused by the release of a large scale of heavy metals, organic pollutants, chemicals, etc., into the environment, posing a serious threat to aquatic ecosystems and nature. Moreover, untreated sewage waste discharged directly into nearby water bodies can cause various diseases to mankind due to the high load of fecal coliform bacteria. This work demonstrates the development of a biocompatible, cost-effective, highly robust, efficient, flexible, freestanding, and reusable membrane using naturally formed biocompatible kaolinite clay-doped poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) for effective piezodynamic destruction of coliform bacteria. In this study, Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis) have been used to evaluate the mechanical stimulus-responsive antibacterial efficacy of the nanocomposite membrane. The membrane can effectively eradicate nearly 99% viable E. coli and 97% E. faecalis within a span of 40 min under mechanical stimulation (soft ultrasound ∼15 kHz). To further understand the mechanism, an evaluation of reactive oxygen species and bacterial FESEM was performed. These studies revealed that bacterial cells suffered severe visible cell damage after 40 min of piezocatalysis, elucidating the fact that the synthesized membrane is capable of producing a superior piezodynamic antibacterial effect.

Switchable superlyophobic PAN@Co-MOF membrane for on-demand emulsion separation and efficient soluble dye degradation

Developing membrane surfaces with double superlyophobicity properties under liquids for different separation applications poses significant challenges in thermodynamics and material science. Switchable superwettability is usually achieved through complex manipulation means and the application of external stimuli such as light, heat, electrical current, and so on. In this study, a reversible superhydrophobic/superoleophobic membrane (PAN@Co-MOF) was fabricated conveniently by in situ growth of Co(Hmim)2 (Co-MOFs) onto the surfaces of electrospun polyacrylonitrile (PAN). The as-prepared PAN@Co-MOF membrane facilitated the selective passage of water or oil in a unidirectional manner, only when water or oil was prewetted, which enabled the efficient separation of oil-in-water (O/W) or water-in-oil (W/O) emulsions on demand. This novel organic and inorganic hybrid material overcame traditional limitations, resulting in a mechanically robust and reusable membrane. Moreover, the PAN@Co-MOF membrane demonstrated the capability to activate peroxymonosulfate (PMS) for efficient dye degradation through interactions of Co-MOF with diverse liquids. Impressively, the O/W emulsion separation flux surpassed 1600 L·m−2·h−1 with chemical oxygen demand (COD) values of the filtrate below 100 mg·L−1, while the W/O emulsion separation flux exceeded 1040 L·m−2·h−1, maintaining the water content of the filtrate under 50 mg·L−1. Furthermore, the degradation efficiency of methylene blue (MB) (50 ppm) achieved a staggering 99.3% within 10 min. This study offers an innovative idea for the development of multifunctional membrane materials with switchable superwettability in the integrated oil–water treatment.

Recent Combinations of Electrospinning with Photocatalytic Technology for Treating Polluted Water

Dyes, antibiotics, heavy metal ions, and bacteria are important sources of water pollution. How to solve these issues has become a problem in the fields of science and technology. People have developed a variety of technologies to treat pollutants in water. Photocatalytic technology came into being. As a simple and environmentally friendly treatment technology, it has been widely studied by the scientific community. Traditional powder photocatalysts cause secondary pollution to the environment and are not conducive to recycling. Therefore, large specific surface area and reusable membrane photocatalysts built by electrospinning technology have become a favorite of today’s scientific community. Nanofiber membranes prepared by electrospinning technology have a variety of structures, which can meet the needs of different occasions. This review summarizes and discusses research progress in electrospinning technology, the relationship between the structure and treatment of electrospun fiber membranes, and their impacts on the photocatalytic performance of nanofiber membranes. The performance, challenges, and future development directions of nanofiber membranes with different structures, prepared by different kinds of electrospinning techniques using photocatalysis to treat different pollutants, are reviewed.

Fabrication of Anatase TiO2/PVDF Composite Membrane for Oil-in-Water Emulsion Separation and Dye Photocatalytic Degradation

At present, the types of pollutants in wastewater are more and more complicated, however, the multifunctional membrane materials are in short supply. To prepare a membrane with both high efficient oil-in-water emulsion separation performance and photocatalytic degradation performance of organic dyes, the bifunctional separation membrane was successfully prepared by electrostatic spinning technology of PVDF/PEMA and in situ deposition of anatase TiO2 nanoparticles containing Ti3+ and oxygen vacancies (Ov). The prepared composite membrane has excellent hydrophilic properties (WCA = 15.65), underwater oleophobic properties (UOCA = 156.69), and photocatalytic performance. These composite membranes have high separation efficiency and outstanding anti-fouling performance, the oil removal efficiency reaches 98.95%, and the flux recovery rate (FRR) reaches 99.19% for soybean oil-in-water emulsion. In addition, the composite membrane has outstanding photocatalytic degradation performance, with 97% and 90.2% degradation of RhB and AG-25 under UV conditions, respectively. Several oil-in-water separation and dye degradation experiments show that the PVDF composite membrane has excellent reuse performance. Based on these results, this study opens new avenues for the preparation of multifunctional reusable membranes for the water treatment field.

P(VDF-TrFE)/BaTiO3 Nanofibrous Membrane with Enhanced Piezoelectricity for High PM0.3 Filtration and Reusable Face Masks

In the background of air pollution and regular COVID-19 prevention, personal protective masks are necessary for our daily life. However, protective masks with high PM0.3 filtration usually have poor air permeability and are mostly disposable, leading to a heavy burden on the environment. In this work, a reusable membrane based on piezoelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] nanofibers embedded with BaTiO3 nanoparticles (BTO NPs) was developed. The P(VDF-TrFE)/BTO composite nanofibers not only have enhanced piezoelectricity and surface polarity but also have reduced diameters that could be beneficial for electrostatic adhesion, pole-polar interactions, and mechanical sieving to increase the PM0.3 capture capacity. Moreover, the BTO NPs also improved the charge storage capacity of the composite membrane, which could further enhance the PM0.3 filtration efficiency after corona treatment. The piezoelectric mask based on P(VDF-TrFE)/BTO composite nanofibers has high filtration efficiencies of 96% for PM0.3 and 98% for bacteria, while the pressure drop was only 182 Pa, which is lower than the commercial N95 standard of 343.2 Pa. Furthermore, the piezoelectric mask has a long and stable filtration performance after 5 cycles of 75% alcohol disinfection, demonstrating that the P(VDF-TrFE)/BTO composite membrane has a potential application in personal protective masks with comfortable and reusable properties.

Macrocyclic ligand-embedded graphene-in-polymer nanofiber membranes for lithium ion recovery

Ensuring a stable and diverse lithium supply is becoming increasingly important for battery-related industries. Herein, we propose the concept of integrating a molecular receptor and graphene-in-polymer nanofibers to create highly durable and reusable membranes for selective lithium ion recovery. Specifically, macrocyclic chelating ligand (12C4) molecules as ion receptors were incorporated into a graphene-in-polyethersulfone (PES) nanofiber (CGPNF) membrane. The CGPNF membranes with diameters of approximately 100 nm showed an increase in diameter and surface roughness after lithium ion adsorption. Theoretical calculations indicated that the graphene nanosheets provide intermolecular interactions for the uniform dispersion and stable entrapment of the molecular receptors in the nanofibers. In addition, nitrogen sorption tests revealed that the graphene nanosheets improve the stability of the nanofibers, allowing for more effective porosity and surface area. The graphene nanosheets also increased the surface roughness and chemical inhomogeneity of the CGPNF membrane, thereby increasing its hydrophilicity. The adsorption isotherms of the CGPNF membranes were more accurately described by a pseudo second-order model, indicating that the adsorption kinetics are governed by a chemisorption process, namely, host–guest interactions. Finally, in a flow system, the CGPNF membrane showed a maximum adsorption capacity of 86.3 mg g−1 for lithium ions and retained more than 93 % of its initial adsorption capacity after 10 regeneration cycles.

Preparation of adsorptive polyethyleneimine/polyvinyl chloride electrospun nanofiber membrane: Characterization and application

Landfilling and burning plastic waste, especially waste polyvinyl chloride (PVC), can produce highly toxic and carcinogenic by-products that threaten the ecosystem and human health. However, there is still a lack of proper methods for waste PVC recycling. Therefore, developing feasible ways for waste PVC recovery is urgently needed. The purpose of this study is to analyze the characteristics of PVC-based adsorptive nanofiber membranes and test their ability for the treatment of wastewater containing Cibacron Brilliant Yellow 3G-P, a widely used reactive dye. The polyethylenimine/polyvinyl chloride membrane (PEI/PVCM) was characterized by FTIR, FE-SEM, TGA, tensile analysis, water contact angle measurement, and zeta-potential analysis. The FTIR analysis confirmed that the PEI has successfully crosslinked with PVC. The FE-SEM images showed that the nanofibers constituting PEI/PVCM are compact with an average fiber diameter of 181 nm. The TGA results showed that the membrane was able to remain stable in wastewater below 150 °C. The average stress and strain of the PEI/PVCM were 7.64 ± 0.32 MPa and 934.14 ± 48.12%, respectively. The water contact angle and zeta potential analysis showed that after the introduction of PEI, the membrane converted from hydrophobic to hydrophilic, and the pHpzc was increased from 3.1 to 1.08. The pure water flux of the membrane was measured at 0.1 MPa and the result was 3013 ± 60 L/m2‧h. The wastewater purification capability of PEI/PVCM was measured at an initial dye concentration of 10 ppm and pH 4–9 at 0.1 MPa. The reusability of PEI/PVCM was verified through three adsorption-desorption cycles. The results demonstrated that the PEI/PVCM is a reusable membrane for efficient purification of wastewater containing reactive dyes over a wide pH range (pH 4–8).

Highly efficient removal of organic pollutants from wastewater using a recyclable graphene oxide membrane intercalated with g-C3N4@TiO2-nanowires

Membrane fouling has been a major challenge in the practical application of membrane technology for wastewater treatment and purification. In this study, a reusable membrane composed of g-C3N4@TiO2-nanowires modified graphene oxide (GO/CN@TNWs) was successfully fabricated through electrostatic interactions and a vacuum filtration-assisted self-assembly process. The as-fabricated membrane possessed higher photocatalytic activity than the pure TNWs under simulated solar light exposure, attributing to the introduction of GO with high absorption and carrier mobility, and the synergistic effects of TNWs and CN. Furthermore, the π-π stacking interactions between GO and organic pollutant molecules contribute to the excellent enrichment efficiency of GO/CN@TNWs membrane (98.77%) toward tetracycline hydrochloride (TCH). Room-temperature ESR studies indicate that the GO/CN@TNWs membrane can generate more superoxide radical, hydroxyl radical and hole species for photocatalytic degradation. Therefore, the GO/CN@TNWs membrane may be used for TCH removal from waste water and the excellent solar-light-driven photocatalytic performance endows GO/CN@TNWs membrane absorbents with recycling abilities for the realization of large-scale wastewater purification.

Reusable membrane with multifunctional skin layer for effective removal of insoluble emulsified oils and soluble dyes

The organic pollutants, typical of emulsified oils and soluble organic dyes, is commonly found in wastewater, however simultaneous removal of them remains challenging because of their difference in surface charge, molecule size, and solubility in water. Inspired by the water purification of the earth's multilayer strata, a fibrous membrane with multifunctional skin is fabricated by coupling sub-micrometer pores layer of polyaniline (PANI) and nano molecular brush of polyacrylic acid (PAA)/polyethyleneimine (PEI) on polyacrylonitrile membrane, for cross-scale organic pollution/water separation. This ultrathin skin of PANI/PAA/PEI is endowed with sub-micrometer pores and strong hydration, which can effectively prevent tiny oil droplets from entering or adhering the membrane pores. Furthermore, this skin with double electric layer can selectively adsorb and even filtrate anionic/cationic dyes by protonation and deprotonation effect in different pH solutions. The synergy of these features enables this membrane with ultra-high water flux (>3000 L m−2 h−1 bar−1), oil rejection rates (>99.6%), and anionic/cationic dyes adsorbability (>49.1 mg/g). Besides, the membrane also exhibits desirable reusability, excellent mechanical durability and outstanding acid/alkali resistance, promising for removal of insoluble emulsified oils and soluble organic dyes in wastewater.

Intelligent Environmental Sensing: Fabrication of Switchable, Reusable, and Highly Sensitive Gas Sensors with Spiropyran-Grafted Anodic Aluminum Oxide Templates

Monitoring undesired pH deviations in the surroundings is one of the most pervasive issues for environment and industry, and developing efficient, economical, portable, and reusable membranes for p...

A slippery oil-repellent hydrogel coating

Development of oil-repellent coatings that are anti-fouling with water alone is highly desirable, yet still challenging. Herein, to address this challenge, we fabricate a slippery oil-repellent hydrogel coating that exhibits oil repellency when exposed in the air as well as underwater. In the air, water wets the slippery oil-repellent hydrogel coating surface completely, while organic liquid drops such as toluene can slide off the water wetted coating surface easily. When immersed in water, the slippery oil-repellent hydrogel coating surface exhibits excellent underwater superoleophobic property with all oil contact angles more than 159° and oil adhesive forces less than 1 μN. The hydrogel coating keeps its oil repellency after long-term outdoor storage, thermal treatment, knife scratching and other treatments. Exploiting its water-attracting and oil-repelling property, the slippery oil-repellent hydrogel coated copper mesh and filter paper are demonstrated as reusable membranes to separate oil–water mixtures with separation efficiency more than 97%.

Self-cleaning SERS membrane for reusable and ultrasensitive molecular detection via integrating graphitic‑carbon-nitride nanosheets and Ag nanospheres into hierarchical graphene layers that covered with graphitic‑carbon-nitride quantum-dots

Abstract Self-cleaning ability is an attractive parameter for fabricating practical surface enhanced Raman scattering (SERS) substrates. Thus, it is an important issue for searching suitable materials to decompose molecules inside SERS “hot spots”. Here we fabricate a flexible CNs/AgNSs@CNQDs-GLs SERS membrane for visible-light derived reusable molecular detection, via integrating graphitic‑carbon-nitride nanosheets (CNs) and Ag nanospheres (AgNSs) into graphene layers that covered with graphitic‑carbon-nitride quantum-dots (CNQDs-GLs). This membrane exhibits strong SERS activity due to the high pre-concentration ability to analytes via the delocalized π-bond, and well-rounded self-cleaning performance due to: i) the bottomed CNQDs-GLs as photocatalytic platforms degrade molecules inside nanogaps; and ii) the CNs on AgNSs@CNQDs-GLs surfaces decompose molecules outside nanogaps. This reusable membrane can be used for rhodamine B (RhB) or methylene blue (MB) fully-recovered circle-detection with a limit of 10−14 M. The practicability of this membrane is shown by detection-photodegradation cycle-runs of 4-chlorophenol, and no obvious performance loss can be observed. Thus, this membrane provides an effective route to overcome one-off substrates or incomplete self-cleaning substrates, for developing green sensing techniques.

Acrylic acid-grafted pre-plasma nanofibers for efficient removal of oil pollution from aquatic environment

Oily wastewater is a worldwide problem threatening the environment and humans. High flux and low-energy consumption separation of oil and water is urgently required but still faces great challenges. In this study, nanofibrous membranes with superhydrophilic and underwater superoleophobic surfaces were fabricated by grafting acrylic acid onto plasma-treated electrospun polystyrene/polyacrylonitrile (PS/PAN) membranes. The morphologies, chemical compositions, mechanical and surface properties of the membranes were examined in detail. The water contact angles of the PS/PAN membranes were 137.4°, 130.1°, 119.5°, 88.1° and 80.2°, respectively, which decreased to 76.5°, 47.9°, 34.4°, 0° and 0° after grafting treatment, proving that the modification improved the surface hydrophilicity of the membranes due to the introduction of hydrophilic groups. In addition, a gravity-driven filtration device was utilized to investigate the oil/water separation potential of the membranes. The results indicated that the grafted PS/PAN membranes separated the layered oil/water mixtures with permeate flux up to 57509 L m-2 h-1, while high fluxes of 1390-6460 L m-2 h-1 for the separation of different oil-in-water emulsions. Importantly, the membranes still maintained high flux and efficiency even after several cycles of separation. Therefore, the reusable membranes can be expected to be potential cost-effective materials for oil/water treatment.

A reusable electrospun PVDF-PVP-MnO2 nanocomposite membrane for bisphenol A removal from drinking water

In this study, polyvinylidene fluoride (PVDF) nanocomposite membranes with different fillers were fabricated using electrospinning technique. The physico-chemical properties of electrospun membranes such as PVDF (NF1), PVDF-polyvinyl pyrrolidone (PVP) (NF2), PVDF-activated carbon (AC) (NF3), PVDF-MnO2 (NF4), PVDF-PVP-AC (NF5), and PVDF-PVP-MnO2 (NF6) were assessed using field emission scanning electron microscopy-energy dispersive X-ray spectroscopy (FESEM-EDX), tensile tester, contact angle measurement, zeta potential, and attenuated total reflection-fourier transform infrared spectroscopy (ATR-FTIR). The Bisphenol A (BPA) removal efficacy of the membranes was assessed using flat sheet membrane filtration unit. The single layer filtration for BPA removal at 30 min was found to be 27%, 100%, 24%, 54%, 100%, and 100% for NF1, NF2, NF3, NF4, NF5, and NF6, respectively. In particular, NF2 and NF6 membranes exhibited maximum removal of BPA with good retention potential for the entire sampling time. In recyclic application, the regenerated NF6 membrane showed better reusability for BPA removal. During the removal process, BPA attached with PVP and MnO2 present in NF6 membrane through hydrogen bonding interaction. The hydrogen bonding length and energies EH were calculated by density functional theory (DFT). Finally, this study suggests that PVP and MnO2 incorporated PVDF membrane might be an effective and reusable membrane for BPA removal from drinking water sources.

Engineered ZnO‐TiO2 Nanospheres for High Performing Membrane Assimilated Photocatalytic Water Remediation and Energy Harvesting

AbstractThis paper is a study of ZnO doped TiO2 in various percentages ranging from 0% (undoped) up to 10%. The effect of doping was observed via the change in morphological, optical, electrical and physical properties of ZnO‐TiO2 nanospheres. Hydrothermally grown nanospheres are used for removing contaminants photo‐catalytically from waste water and also as photoanodes in dye‐sensitized solar cells (DSSCs) with graphene as counter electrode. Of the many approaches that have been explored for purification of contaminated water, this work presents designing of an environmental friendly solution, based on easily available filter paper membrane and incorporating it with the synthesized catalyst for photodegradation of the harmful toxic substances. These reusable membranes assist in the photodegradation process by creating room for better light‐catalyst‐dye interaction via large surface sites. The spherically structured heterojunction of ZnO‐TiO2 generates excitons that oxidize methyl orange (MO) and reduce harmful Cr(VI) to non‐toxic Cr(III) with high efficacy. Additionally, the agile nanostructures were employed as efficient photoanode material by fabricating dye sensitized solar cells with graphene as counter electrode.

Photocatalytic reusable membranes for the effective degradation of tartrazine with a solar photoreactor

Recalcitrant dyes present in effluents constitute a major environmental concern due to their hazardous properties that may cause deleterious effects on aquatic organisms. Tartrazine is a widely-used dye, and it is known to be resistant to biological and chemical degradation processes and by its carcinogenic and mutagenic nature. This study presents the use of TiO2 (P25) nanoparticles immobilized into a poly(vinylidenefluoride–trifluoroethylene) (P(VDF–TrFE)) membrane to assess the photocatalytic degradation of this dye in a solar photoreactor. The nanocomposite morphological properties were analyzed, confirming an interconnected porous microstructure and the homogeneous distribution of the TiO2 nanoparticles within the membrane pores. It is shown that the nanocomposite with 8wt% TiO2 exhibits a remarkable sunlight photocatalytic activity over five hours, with 78% of the pollutant being degraded. It was also demonstrated that the degradation follows pseudo-first-order kinetics model at low initial tartrazine concentration. Finally, the effective reusability of the produced nanocomposite was also assessed.

High catalytic efficiency of Pd nanoparticles immobilized on TiO2 nanorods‐coated ceramic membranes

In this work, we designed and constructed an efficient and reusable membrane catalyst by loading palladium (Pd) nanoparticles on TiO2 nanorods (NRs)‐coated ceramic membrane. The morphology and structure analysis show that the TiO2 NRs with a width of 200 nm–1000 nm and a length of about 4000 nm can be successfully synthesized on the ceramic membrane by a two‐step hydrothermal method. The Pd nanoparticles with an average particle size of 4 nm can be uniformly distributed on the TiO2 NRs‐coated ceramic membrane. The catalytic performance evaluation highlights that higher catalytic activity and stability are observed for the Pd nanoparticles immobilized on the TiO2 NRs‐coated ceramic membrane compared to the ones loaded on the unmodified ceramic membrane in the liquid‐phase p‐nitrophenol hydrogenation. The TiO2 NRs can provide more areas for the deposition of Pd nanoparticles, and then more Pd nanoparticles with better dispersion can be loaded on the membrane, leading to superior catalytic activity. The interaction between Pd nanoparticles and TiO2 provides less leaching of Pd nanoparticles and higher catalytic stability.

Determination of nanofiltration membranes for reuse of paper mill industry wastewater

Determination of nanofiltration membranes for reuse of paper mill industry wastewater