Adjustable Charge Density Research Articles

Surface functionalized porous MXene (Ti3C2Tx)/Polyethyleneimine membrane for efficient osmotic energy conversion

The development of ion-selective membranes is crucial for achieving efficient osmotic power conversion in reverse electrodialysis system. However, balancing ion selectivity and ion permeability in membranes remains a challenge, limiting improvements in energy conversion efficiency for practical applications. In this study, we develop efficient cation exchange membranes by integrating versatile aromatic hydroxyl groups with MXene nanosheets and polyethyleneimine (PEI) into their lamellar structure. This approach holds promise for achieving non-swelling, high selectivity, and enhanced power density for osmotic energy conversion. The abundance positive surface charge within PEI molecules, combined with the 2D sub-nanochannels of MXene nanosheets, facilitates the biomimetic replication of channel size, chemical groups, and adjustable charge density in the resulting membranes. The fabrication of these membranes is easily achieved through simple hydrothermal, functionalization, and surface-charged techniques, suggesting promising scalability. These membranes exhibit remarkable stability against swelling in aqueous solutions for up to 25 days and demonstrate a high selectivity of 0.95 and a superior output power density of 18.3 W/m2 in artificial river water and seawater.

Scalable bacterial cellulose biofilms with improved ion transport for high osmotic power generation

The manufacture of large-sized material with tunable nanochannel size and high ion selectivity is always a challenge for osmotic power generation. Herein, we develop negatively charged carboxymethyl bacterial cellulose membranes (BC-CMC) and positively charged chitosan quaternary ammonium bacterial cellulose membranes (BC-HACC) with adjustable charge density and nanochannel size by in situ culture. The scalable membranes are suitable for rapidly ion selective transmission process. When applying the charged BC membranes for an osmotic energy harvesting device, an output power density of 2.25 W m −2 can be reached. Further connecting 15 units of the charged BC device, the output voltage can reach up to 2.53 V, which can directly power the electronic devices. This work highlights the advantage of large-scale preparation by the biosynthesis method, which can simultaneously tune the surface properties and nanochannel size of BC to regulate the ion transport behavior. We offer an easy and scalable method to obtain low-cost membranes for high osmotic energy conversion device, providing the feasibility for their large-scale application. • This paper offers a simple in situ biosynthetic modification to obtain charged BC membranes. • The scalable membranes are suitable for ion selective transmission process. • The BC-RED device can achieve an output power density of 2.25 W m −2 . • Our work develops low-cost, large-scale charged BC membranes potential in practical osmotic energy collection.

Morphology, Thermal Stability, and Flammability Properties of Polymer-Layered Double Hydroxide (LDH) Nanocomposites: A Review

The utilization of layered nanofillers in polymer matrix, as reinforcement, has attracted great interest in the 21st century. This can be attributed to the high aspect ratios of the nanofillers and the attendant substantial improvement in different properties (i.e., increased flammability resistance, improved modulus and impact strength, as well as improved barrier properties) of the resultant nanocomposite when compared to the neat polymer matrix. Amongst the well-known layered nanofillers, layered inorganic materials, in the form of LDHs, have been given the most attention. LDH nanofillers have been employed in different polymers due to their flexibility in chemical composition as well as an adjustable charge density, which permits numerous interactions with the host polymer matrices. One of the most important features of LDHs is their ability to act as flame-retardant materials because of their endothermic decomposition. This review paper gives detailed information on the: preparation methods, morphology, flammability, and barrier properties as well as thermal stability of LDH/polymer nanocomposites.

Enhanced monovalent selectivity of cation exchange membranes via adjustable charge density on functional layers

Electrodialysis (ED) technique is a typical and promising membrane process, for applications like water treatment and ion separation. Especially, the separation between monovalent and multivalent cations is a current central issue in many industries and academic researches. Herein, a series of novel cation exchange membranes were prepared from quaternized polyaniline modified sulfonated polyphenyl sulfone (SPPSU) by in-situ polymerization-deposited polyaniline followed by quaternizing with methyl iodide. Restricted divalent cation penetration and regulated monovalent cation transport were achieved by elevating the kinetic effect of electrostatic repulsion and narrowing water channel. Importantly, positive charge density of modification layer could be adjusted by controlling the degree of quaternization, which was accompanied by the change of water channel. When evaluated in a simulated mixed salt system (Mg2+/Na+ and Mg2+/Li+), the optimal quaternized polyaniline membrane exhibited a higher perm-selectivity (PNaMg=4.1, PLiMg=1.75) than initial polyaniline modified cation exchange membrane (PNaMg=0.8, PLiMg=0.75), and commercial monovalent-selective cations exchange membrane CIMS (PNaMg=3.56, PLiMg=1.11). This presented strategy is straightforward and effective, demonstrating the effect of surface positive charge layer on perm-selectivity.

Quaternized polysulfone and graphene oxide nanosheet derived low fouling novel positively charged hybrid ultrafiltration membranes for protein separation

Low fouling positively charged hybrid UF membranes with adjustable charge density fabricated from a blend of PSf/QPSf and GO nanosheets by solution casting and NIPS method. Cross-section SEM image and observed lysozyme transport values at varied pH.

Preparation and characterization of negatively charged organic–inorganic hybrid ultrafiltration membranes for protein separation

Negatively charged organic–inorganic hybrid ultrafiltration membranes with adjustable charge density were fabricated from blends of water soluble poly vinyl alcohol and N-O-sulfonic acid benzyl chitosan (NSBC) in combination with tetraethyl orthosilicate (TEOS) silica precursor by the sol–gel method and precipitation in a mixture of methanol and water (80wt%:20wt%) solvent. The porous hybrid membrane morphologies, structures and surface properties were characterized comprehensively using scanning electron microscopy, Fourier transform infrared spectroscopy in the attenuated total reflection mode, as well as contact angle measurements. The results confirmed that the fabricated membranes were porous, hydrophilic and mildly charged in nature. The water flux and flux recovery ratio (i.e. protein fouling resistance) of the membranes were highly dependent on the fraction of NSBC. The protein transmission as a function of pH and the fraction of NSBC was studied for two model proteins (bovine serum albumin; BSA and lysozyme; LYZ) and found to be controlled by size exclusion and the fraction of NSBC, and therefore the membrane charge density. The highest transmission of proteins at their isoelectric points was obtained for the membrane containing 40wt% of NSBC. The best separation of LYZ from BSA in the model mixture solution was obtained at pH=11 when membrane C-40 was used in ultrafiltration of protein solution.

Low fouling negatively charged hybrid ultrafiltration membranes for protein separation from sulfonated poly(arylene ether sulfone) block copolymer and functionalized multiwalled carbon nanotubes

Low fouling negatively charged hybrid ultrafiltration membranes with adjustable charge density were fabricated from blends of poly(arylene ether sulfone) (PAES) block copolymer and the sulfonated copolymer (S-PAES) in combination with different fractions of sulfonic acid functionalized multiwalled carbon nanotubes (MWCNT-SO3H) by non-solvent induced phase separation method. Porous hybrid membrane morphologies, structure and surface properties were characterized comprehensively using scanning electron microscopy, Fourier transform infrared spectroscopy in the attenuated total reflection mode, as well as contact angle and zeta potential measurements. Results confirmed that the fabricated membranes were hydrophilic and negatively charged in the studied pH range 3–10. The water permeabilities and increased protein fouling resistances of the membranes were dependent on the fraction of MWCNT-SO3H in the membranes. The protein transmission as function of pH value and fraction of MWCNT-SO3H was studied for two model proteins (bovine serum albumin and myoglobin) and found to be controlled by size exclusion and the content of MWCNT-SO3H. The highest transmission of proteins at their isoelectric points was obtained for the membrane containing 2wt% of MWCNT-SO3H relative to total membrane polymer. The selectivity of the hybrid membranes for the separation of the binary protein mixture could be systematically increased by increasing surface charge density by increasing fraction of MWCNT-SO3H. Consequently, the trade-off relationship between permeability and selectivity for conventional ultrafiltration membranes where separation is based on size exclusion solely could be overcome and performance be tuned by a small fraction of a functional additive.

Novel ultrafiltration membranes with adjustable charge density based on sulfonated poly(arylene ether sulfone) block copolymers and their tunable protein separation performance

A novel poly(arylene ether sulfone) (PAES) block copolymer was prepared from previously synthesized fluoride terminated oligomer (A16) and hydroxyl terminated oligomer (B12) by aromatic nucleophilic substitution polycondensation reaction. PAES was subsequently sulfonated under controlled conditions to yield a copolymer (S-PAES) with sulfonic acid groups selectively in the B12 segments and without chain degradation. Non-solvent induced phase separation method was used to prepare a series of ultrafiltration membranes from blends of S-PAES and PAES with varied ratios and, hence, sulfonic acid group densities. Porous membrane morphologies, structure and surface properties were characterized comprehensively using scanning electron microscopy, Fourier transform infrared spectroscopy in the attenuated total reflection mode, as well as contact angle and zeta potential measurements. Studies of membrane performance revealed systematically increasing water permeabilities and reduced protein fouling tendencies with increasing fraction of S-PAES in the membrane. The protein transmission as function of pH value (and hence protein charge) was studied for two model proteins (bovine serum albumin and lysozyme) and found to be controlled by combined size exclusion and charge effects. The selectivity for the separation of the binary protein mixture could be systematically increased with increasing membrane charge density (by increasing S-PAES fraction). Consequently, the trade-off relationship between permeability and selectivity for conventional ultrafiltration membranes where separation is based on size exclusion solely could be overcome. Due to their high stability and tunable functionality, the PAES block copolymers have also large potential as membrane material for other applications.