An Eco-Friendly Manner to Prepare Superwetting Melamine Sponges with Switchable Wettability for the Separation of Oil/Water Mixtures and Emulsions

Oil/water separation processes have garnered significant global attention due to the quick growth in industrial development, recurring chemical leakages, and oil spills. Hence, there is a significant demand for the development of inexpensive superwetting materials in an eco-friendly manner to separate oil/water mixtures and emulsions. In this study, a superwetting melamine sponge (SMS) with switchable wettabilities was prepared by modifying melamine sponge (MS) with sodium dodecanoate. The as-prepared SMS exhibited superhydrophobicity, superoleophilicity, underwater superoleophobicity, and underoil superhydrophobicity. The SMS can be utilized in treating both light and heavy oil/water mixtures through the prewetting process. It demonstrated fast permeation fluxes (reaching 108,600 L m-2 h-1 for a light oil/water mixture and 147,700 L m-2 h-1 for a heavy oil/water mixture) and exhibited good separation efficiency (exceeding 99.56%). The compressed SMS was employed in separating surfactant-stabilized water-in-oil emulsions (SWOEs), as well as surfactant-stabilized oil-in-water emulsions (SOWEs), giving high permeation fluxes (reaching 7210 and 5054 L m-2 h-1, respectively). The oil purity for SWOEs' filtrates surpassed 99.98 wt% and the separation efficiencies of SOWEs exceeded 98.84%. Owing to their remarkable capability for separating oil/water mixtures and emulsions, eco-friendly fabrication method, and feasibility for large-scale production, our SMS has a promising potential for practical applications.

Fluorinated photoreduced graphene oxide with semi-ionic C-F bonds: An effective carbon based photocatalyst for the removal of volatile organic compounds

There is much interest in developing metal-free halogenated graphene such as fluorinated graphene for various catalytic applications. In this work, a fluorine-doped graphene oxide photocatalyst was investigated for photocatalytic oxidation (PCO) of a volatile organic compound (VOC), namely gaseous methanol. The fluorination process of graphene oxide (GO) was carried out via a novel and facile solution-based photoirradiation method. The fluorine atoms were doped on the surface of the GO in a semi-ionic C-F bond configuration. This presence of the semi-ionic C-F bonds induced a dramatic 7-fold increment of the hole charge carrier density of the photocatalyst. The fluorinated GO photocatalyst exhibited excellent photodegradation up to 93.5% or 0.493 h-1 according pseudo-first order kinetics for methanol. In addition, 91.7% of methanol was mineralized into harmless carbon dioxide (CO2) under UV-A irradiation. Furthermore, the photocatalyst demonstrated good stability in five cycles of methanol PCO. Besides methanol, other VOCs such as acetone and formaldehyde were also photodegraded. This work reveals the potential of fluorination in producing effective graphene-based photocatalyst for VOC removal.

Microfluidic-Assisted Synthesis of Metal-Organic Framework -Alginate Micro-Particles for Sustained Drug Delivery

Drug delivery systems (DDS) are continuously being explored since humans are facing more numerous complicated diseases than ever before. These systems can preserve the drug's functionality and improve its efficacy until the drug is delivered to a specific site within the body. One of the least used materials for this purpose are metal-organic frameworks (MOFs). MOFs possess many properties, including their high surface area and the possibility for the addition of functional surface moieties, that make them ideal drug delivery vehicles. Such properties can be further improved by combining different materials (such as metals or ligands) and utilizing various synthesis techniques. In this work, the microfluidic technique is used to synthesize Zeolitic Imidazole Framework-67 (ZIF-67) containing cobalt ions as well as its bimetallic variant with cobalt and zinc as ZnZIF-67 to be subsequently loaded with diclofenac sodium and incorporated into sodium alginate beads for sustained drug delivery. This study shows the utilization of a microfluidic approach to synthesize MOF variants. Furthermore, these MOFs were incorporated into a biopolymer (sodium alginate) to produce a reliable DDS which can perform sustained drug releases for up to 6 days (for 90% of the full amount released), whereas MOFs without the biopolymer showed sudden release within the first day.

Effects of Co-Solvent-Induced Self-Assembled Graphene-PVDF Composite Film on Piezoelectric Application

A persistent purpose for self-powered and wearable electronic devices is the fabrication of graphene-PVDF piezoelectric nanogenerators with various co-solvents that could provide enhanced levels of durability and stability while generating a higher output. This study resulted in a piezoelectric nanogenerator based on a composite film composed of graphene, and poly (vinylidene fluoride) (PVDF) as a flexible polymer matrix that delivers high performance, flexibility, and cost-effectiveness. By adjusting the co-solvent in the solution, a graphene-PVDF piezoelectric nanogenerator can be created (acetone, THF, water, and EtOH). The solution becomes less viscous and is more diluted the more significant the concentration of co-solvents, such as acetone, THF, and EtOH. Additionally, when the density is low, the thickness will be thinner. The final film thickness for all is ~25 µm. Furthermore, the- crystal phase becomes more apparent when graphene is added and combined with the four co-solvents. Based on the XRD results, the peak changes to the right, which can be inferred to be more dominant with the β-phase. THF is the co-solvent with the highest piezoelectric output among other co-solvents. Most of the output voltages produced are 0.071 V and are more significant than the rest.

Sustainable, biocompatible, and mass-producible superwetting water caltrop shell biochars for emulsion separations

The separation of oily wastewater, specifically emulsions, is a crucial global issue. Possible strategies for the efficient separation of emulsified oil/water mixtures through sustainable and environmentally friendly materials have recently drawn considerable attention. In our study, we prepared superwetting water caltrop shell biochar (WCSB) via a top-lit-updraft carbonization procedure. The as-prepared WCSB was characterized by superhydrophilicity, underwater superoleophobicity, underoil superhydrophilicity, and underoil water adsorption ability. Because of its superwetting properties, WCSB was used for the separation of both surfactant-stabilized oil-in-water emulsions (SOIWEs) and surfactant-stabilized water-in-oil emulsions (SWIOEs) with very high fluxes (up to 74,700 and 241,000 L m^-2 h^-1 bar^-1 for SOIWE and SWIOE, respectively). The separation performances were excellent, with oil contents in all SOIWE filtrates lower than 10 ppm and oil purities in all SWIOE filtrates higher than 99.99 wt%. Moreover, WCSB was applied to separate dye-spiked emulsions. Due to their high emulsion separation ability, sustainability, good biocompatibility, and ease of mass production, the as-prepared WCSBs have notable potential for utilitarian applications.

Evaluation of the Antibacterial Activity of Eco-Friendly Hybrid Composites on the Base of Oyster Shell Powder Modified by Metal Ions and LLDPE

Transforming biological waste into high-value-added materials is currently attracting extensive research interest in the medical and industrial treatment fields. The design and use of new antibacterial systems are urgently needed. In this study, we used discarded oyster shell powder (OSP) to prepare calcium oxide (CaO). CaO was mixed with silver (Ag), zinc (Zn), and copper (Cu) ions as a controlled release and antibacterial system to test the antibacterial activity. The inhibition zones of various modified metals were between 22 and 29 mm for Escherichia coli (E. coli) and between 21 and 24 mm for Staphylococcus aureus (S. aureus). In addition, linear low-density polyethylene (LLDPE) combined with CaO and metal ion forms can be an excellent alternative to a hybrid composite. The strength modulus at 1% LLDPE to LLDPE/CaO Ag increased from 297 to 320 MPa. In addition, the antimicrobial activity of LLDPE/CaO/metal ions against E. coli had an antibacterial effect of about 99.9%. Therefore, this hybrid composite material has good potential as an antibacterial therapy and biomaterial suitable for many applications.

Polyamide-based membranes with structural homogeneity for ultrafast molecular sieving

Thin-film composite membranes formed by conventional interfacial polymerization generally suffer from the depth heterogeneity of the polyamide layer, i.e., nonuniformly distributed free volume pores, leading to the inefficient permselectivity. Here, we demonstrate a facile and versatile approach to tune the nanoscale homogeneity of polyamide-based thin-film composite membranes via inorganic salt-mediated interfacial polymerization process. Molecular dynamics simulations and various characterization techniques elucidate in detail the underlying molecular mechanism by which the salt addition confines and regulates the diffusion of amine monomers to the water-oil interface and thus tunes the nanoscale homogeneity of the polyamide layer. The resulting thin-film composite membranes with thin, smooth, dense, and structurally homogeneous polyamide layers demonstrate a permeance increment of ~20-435% and/or solute rejection enhancement of ~10-170% as well as improved antifouling property for efficient reverse/forward osmosis and nanofiltration separations. This work sheds light on the tunability of the polyamide layer homogeneity via salt-regulated interfacial polymerization process.

Microporous polymers with cascaded cavities for controlled transport of small gas molecules

In membrane-based separation, molecular size differences relative to membrane pore sizes govern mass flux and separation efficiency. In applications requiring complex molecular differentiation, such as in natural gas processing, cascaded pore size distributions in membranes allow different permeate molecules to be separated without a reduction in throughput. Here, we report the decoration of microporous polymer membrane surfaces with molecular fluorine. Molecular fluorine penetrates through the microporous interface and reacts with rigid polymeric backbones, resulting in membrane micropores with multimodal pore size distributions. The fluorine acts as angstrom-scale apertures that can be controlled for molecular transport. We achieved a highly effective gas separation performance in several industrially relevant hollow-fibrous modular platform with stable responses over 1 year.

Superfast Water Transport Zwitterionic Polymeric Nanofluidic Membrane Reinforced by Metal-Organic Frameworks

Nanofluidics derived from low-dimensional nanosheets and protein nanochannels are crucial for advanced catalysis, sensing, and separation. However, polymer nanofluidics is halted by complicated preparation and miniaturized sizes. This work reports the bottom-up synthesis of modular nanofluidics by confined growth of ultrathin metal-organic frameworks (MOFs) in a polymer membrane consisting of zwitterionic dopamine nanoparticles (ZNPs). The confined growth of the MOFs on the ZNPs reduces the chain entanglement between the ZNPs, leading to stiff interfacial channels enhancing the nanofluidic transport of water molecules through the membrane. As such, the water permeability and solute selectivity of MOF@ZNPM are one magnitude improved, leading to a record-high performance among all polymer nanofiltration membranes. Both the experimental work and the molecular dynamics simulations confirm that the water transport is shifted from high-friction-resistance conventional viscous flow to ultrafast nanofluidic flow as a result of rigid and continuous nanochannels in MOF@ZNPM.

A review of recent progress in polymeric electrospun nanofiber membranes in addressing safe water global issues

With rapid advancement in water filtration materials, several efforts have been made to fabricate electrospun nanofiber membranes (ENMs). ENMs play a crucial role in different areas of water treatment due to their several advantageous properties such as high specific surface area, high interconnected porosity, controllable thickness, mechanical robustness, and wettability. In the broad field of water purification, ENMs have shown tremendous potential in terms of permeability, rejection, energy efficiency, resistance to fouling, reusability and mechanical robustness as compared to the traditional phase inversion membranes. Upon various chemical and physical modifications of ENMs, they have exhibited great potential for emerging applications in environment, energy and health sectors. This review firstly presents an overview of the limiting factors influencing the morphology of electrospun nanofibers. Secondly, it presents recent advancements in electrospinning processes, which helps to not only overcome drawbacks associated with the conventional electrospinning but also to produce nanofibers of different morphology and orientation with an increased rate of production. Thirdly, it presents a brief discussion about the recent progress of the ENMs for removal of various pollutants from aqueous system through major areas of membrane separation. Finally, this review concludes with the challenges and future directions in this vast and fast growing area.

Surface Properties, Free Volume, and Performance for Thin-Film Composite Pervaporation Membranes Fabricated through Interfacial Polymerization Involving Different Organic Solvents

The type of organic solvents used in interfacial polymerization affects the surface property, free volume, and separation performance of the thin-film composite (TFC) polyamide membrane. In this study, TFC polyamide membrane was fabricated through interfacial polymerization between diethylenetriamine (DETA) and trimesoyl chloride (TMC). Four types of organic solvent were explored in the preparation of pervaporation membrane. These are tetralin, toluene, hexane, and isopentane. The solubility parameter distance between organic solvents and DETA follows in increasing order: tetralin (17.07 MPa1/2) < toluene (17.31 MPa1/2) < hexane (19.86 MPa1/2) < isopentane (20.43 MPa1/2). Same trend was also observed between the organic solvents and DETA. The larger the solubility parameter distance, the denser and thicker the polyamide. Consequently, field emission scanning electron microscope (FESEM) and positron annihilation spectroscopy (PAS) analysis revealed that TFCisopentane had the thickest polyamide layer. It also delivered the highest pervaporation efficiency (permeation flux = 860 ± 71 g m-2 h-1; water concentration in permeate = 99.2 ± 0.8 wt%; pervaporation separation index = 959,760) at dehydration of 90 wt% aqueous ethanol solution. Furthermore, TFCisopentane also exhibited a high separation efficiency in isopropanol and tert-butanol. Therefore, a suitable organic solvent in preparation of TFC membrane through interfacial polymerization enables high pervaporation efficiency.

Mechanism of a Self-Assembling Smart and Electrically Responsive PVDF-Graphene Membrane for Controlled Gas Separation

The development of science and technology is accompanied by a complex composition of multiple pollutants. Conventional passive separation processes are not sufficient for current industrial applications. The advent of active or responsive separation methods has become highly essential for future applications. In this work, we demonstrate the preparation of a smart electrically responsive membrane, a poly(vinylidene difluoride) (PVDF)-graphene composite membrane. The high graphene content induces the self-assembly of PVDF with a high β-phase content, which displays a unique self-piezoelectric property. Additionally, the membrane exhibits excellent electrical conductivity and unique capacitive properties, and the resultant nanochannels in the membrane can be reversibly adjusted by external voltage applications, resulting in the tailored gas selectivity of a single membrane. After the application of voltage to the membrane, the permeability and selectivity toward carbon dioxide increase simultaneously. Moreover, atomic-level positron annihilation spectroscopic studies reveal the piezoelectric effect on the free volume of the membrane, which helps us to formulate a gas permeation mechanism for the electrically responsive membrane. Overall, the novel active membrane separation process proposed in this work opens new avenues for the development of a new generation of responsive membranes.

Phosphonium Modification Leads to Ultrapermeable Antibacterial Polyamide Composite Membranes with Unreduced Thickness

Water transport rate in network membranes is inversely correlated to thickness, thus superior permeance is achievable with ultrathin membranes prepared by complicated methods circumventing nanofilm weakness and defects. Conferring ultrahigh permeance to easily prepared thicker membranes remains challenging. Here, a tetrakis(hydroxymethyl) phosphonium chloride (THPC) monomer is discovered that enables straightforward modification of polyamide composite membranes. Water permeance of the modified membrane is ≈6 times improved, give rising to permeability (permeance × thickness) one magnitude higher than state-of-the-art polymer nanofiltration membranes. Meanwhile, the membrane exhibits good rejection (R_Na2SO4 = 98%) and antibacterial properties under crossflow conditions. THPC modification not only improves membrane hydrophilicity, but also creates additional angstrom-scale channels in polyamide membranes for unimpeded transport of water. This unique mechanism provides a paradigm shift in facile preparation of ultrapermeable membranes with unreduced thickness for clean water and desalination.

Polyamide nanofiltration membrane with highly uniform sub-nanometre pores for sub-1 Å precision separation

Separating molecules or ions with sub-Angstrom scale precision is important but technically challenging. Achieving such a precise separation using membranes requires Angstrom scale pores with a high level of pore size uniformity. Herein, we demonstrate that precise solute-solute separation can be achieved using polyamide membranes formed via surfactant-assembly regulated interfacial polymerization (SARIP). The dynamic, self-assembled network of surfactants facilitates faster and more homogeneous diffusion of amine monomers across the water/hexane interface during interfacial polymerization, thereby forming a polyamide active layer with more uniform sub-nanometre pores compared to those formed via conventional interfacial polymerization. The polyamide membrane formed by SARIP exhibits highly size-dependent sieving of solutes, yielding a step-wise transition from low rejection to near-perfect rejection over a solute size range smaller than half Angstrom. SARIP represents an approach for the scalable fabrication of ultra-selective membranes with uniform nanopores for precise separation of ions and small solutes.

Separating molecules or ions with sub-Angstrom scale precision is important but technically challenging. Here, the authors demonstrate that precise solute-solute separation can be achieved using polyamide membranes formed via surfactant-assembly regulated interfacial polymerization.

Zwitterion Co-Polymer PEI-SBMA Nanofiltration Membrane Modified by Fast Second Interfacial Polymerization

Nanofiltration membranes have evolved as a promising solution to tackle the clean water scarcity and wastewater treatment processes with their low energy requirement and environment friendly operating conditions. Thin film composite nanofiltration membranes with high permeability, and excellent antifouling and antibacterial properties are important component for wastewater treatment and clean drinking water production units. In the scope of this study, thin film composite nanofiltration membranes were fabricated using polyacrylonitrile (PAN) support and fast second interfacial polymerization modification methods by grafting polyethylene amine and zwitterionic sulfobutane methacrylate moieties. Chemical and physical alteration in structure of the membranes were characterized using methods like ATR-FTIR spectroscopy, XPS analysis, FESEM and AFM imaging. The effects of second interfacial polymerization to incorporate polyamide layer and ‘ion pair’ characteristics, in terms of water contact angle and surface charge analysis was investigated in correlation with nanofiltration performance. Furthermore, the membrane characteristics in terms of antifouling properties were evaluated using model protein foulants like bovine serum albumin and lysozyme. Antibacterial properties of the modified membranes were investigated using E. coli as model biofoulant. Overall, the effect of second interfacial polymerization without affecting the selectivity layer of nanofiltration membrane for their potential large-scale application was investigated in detail.

Correlating PSf Support Physicochemical Properties with the Formation of Piperazine-Based Polyamide and Evaluating the Resultant Nanofiltration Membrane Performance

Membrane support properties influence the performance of thin-film composite nanofiltration membranes. We fabricated several polysulfone (PSf) supports. The physicochemical properties of PSf were altered by adding polyethylene glycol (PEG) of varying molecular weights (200⁻35,000 g/mol). This alteration facilitated the formation of a thin polyamide layer on the PSf surface during the interfacial polymerization reaction involving an aqueous solution of piperazine containing 4-aminobenzoic acid and an organic solution of trimesoyl chloride. Attenuated total reflectance-Fourier transform infrared validated the presence of PEG in the membrane support. Scanning electron microscopy and atomic force microscopy illustrated that the thin-film polyamide layer morphology transformed from a rough to a smooth surface. A cross-flow filtration test indicated that a thin-film composite polyamide membrane comprising a PSf support (TFC-PEG20k) with a low surface porosity, small pore size, and suitable hydrophilicity delivered the highest water flux and separation efficiency (J = 81.1 ± 6.4 L·m^-2·h^-1, R_Na2SO4 = 91.1% ± 1.8%, and R_NaCl = 35.7% ± 3.1% at 0.60 MPa). This membrane had a molecular weight cutoff of 292 g/mol and also a high rejection for negatively charged dyes. Therefore, a PSf support exhibiting suitable physicochemical properties endowed a thin-film composite polyamide membrane with high performance.

Antibacterial Property and Cytotoxicity of a Poly(lactic acid)/Nanosilver-Doped Multiwall Carbon Nanotube Nanocomposite

A novel method was used to synthesize a nanosilver-doped multiwall carbon nanotube (MWCNT-Ag), and subsequently, the novel poly(lactic acid) (PLA)- and MWCNT-Ag-based biocompatible and antimicrobial nanocomposites were prepared by melt blending. Based on energy dispersive X-ray spectrometry images, an MWCNT-Ag was successfully synthesized. The effect of the MWCNT-Ag on the PLA bionanocomposites was investigated by evaluating their thermal and mechanical properties, antifungal activity, and cytotoxicity. The nanocomposites exhibited a high degree of biocompatibility with the MWCNT-Ag content, which was less than 0.3 phr. Furthermore, tensile strength testing, thermogravimetric analysis, differential scanning calorimetry, and antibacterial evaluation revealed that the tensile strength, thermostability, glass transition temperature, and antibacterial properties were enhanced by increasing the MWCNT-Ag content. Finally, hydrolysis analysis indicated that the low MWCNT-Ag content could increase the packing density of PLA.

Characterization of a Thermoresponsive Chitosan Derivative as a Potential Draw Solute for Forward Osmosis

A thermoresponsive chitosan derivative was synthesized by reacting chitosan (CS) with butyl glycidyl ether (BGE) to break the inter- and intramolecular hydrogen bonds of the polymer. An aqueous solution of the thermoresponsive CS derivative exhibits a lower critical solution temperature (LCST) than CS, and it undergoes a phase transition separation when the temperature changes. Successful incorporation of BGE into the CS was confirmed by FTIR and XPS analyses. Varying the BGE content and the concentration of the aqueous solution produced different LCST ranges, as shown by transmittance vs temperature curves. The particle size was observed by scanning electron microscopy, which revealed that the particles were smaller and well dispersed at 15 °C, whereas the particles became larger and tended to aggregate at 60 °C. A similar trend was observed with the mean particle size measured using dynamic light scattering. Positron annihilation lifetime spectroscopy data also revealed the reversibility of the particle properties as a function of temperature. Microstructure analysis showed that the particles had larger free-volume sizes at 15 °C than at 60 °C. The particles were also found to be nontoxic with 92% cell survival. A simple forward osmosis (FO) test for dye dehydration revealed the potential use of the thermoresponsive chitosan derivative as a draw solute with a flux of 8.6 L/m² h and rejection of 99.8%.

Non-destructive means of probing a composite polyamide membrane for characteristic free volume, void, and chemical composition

Positron annihilation spectroscopy measures free volume in membranes at the sub-nanometer scale (0.1–1 nm).

Biocompatibility and characterization of polylactic acid/styrene-ethylene-butylene-styrene composites

Polylactic acid (PLA)/styrene-ethylene-butylene-styrene (SEBS) composites were prepared by melt blending. Differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WXRD) were used to characterize PLA and PLA/SEBS composites in terms of their melting behavior and crystallization. Curves from thermal gravimetric analysis (TGA) illustrated that thermostability increased with SEBS content. Further morphological analysis of PLA/SEBS composites revealed that SEBS molecules were not miscible with PLA molecules in PLA/SEBS composites. The tensile testing for PLA and PLA/SEBS composites showed that the elongation at the break was enhanced, but tensile strength decreased with increasing SEBS content. L929 fibroblast cells were chosen to assess the cytocompatibility; the cell growth of PLA was found to decrease with increasing SEBS content. This study proposes possible reasons for these properties of PLA/SEBS composites.