High-performance membranes with full pH-stability

Hybridization of Polymer-Encapsulated MoS2-ZnO Nanostructures as Organic-Inorganic Polymer Films for Sonocatalytic-Induced Dye Degradation

The development of environmentally friendly technology is vital to effectively address the issues related to environmental deterioration. This work integrates ZnO-decorated MoS2 (MZ) to create a high-performing PVDF-based PVDF/MoS2-ZnO (PMZ) hybrid polymer composite film for sonocatalytic organic pollutant degradation. An efficient synergistic combination of MZ was identified by altering the ratio, and its influence on PVDF was assessed using diverse structural, morphological, and sonocatalytic performances. The PMZ film demonstrated very effective sonocatalytic characteristics by degrading rhodamine B (RhB) dye with a degradation efficiency of 97.23%, whereas PVDF only degraded 17.7%. Combining MoS2 and ZnO reduces electron-hole recombination and increases the sonocatalytic degradation performance. Moreover, an ideal piezoelectric PVDF polymer with MZ enhances polarization to improve redox processes and dye degradation, ultimately increasing the degradation efficiency. The degradation efficiency of RhB was seen to decrease while employing isopropanol (IPA) and p-benzoquinone (BQ) due to the presence of reactive oxygen species. This suggests that the active species •O2- and •OH are primarily responsible for the degradation of RhB utilizing PMZ2 film. The PMZ film exhibited improved reusability without substantially decreasing its catalytic activity. The superior embellishment of ZnO onto MoS2 and effective integration of MZ into the PVDF polymer film results in improved degrading performance.

Preparation of heterogeneous cation exchange membrane and its contributions in enhancing the removal of Ni2+ by capacitive deionization system

Capacitive deionization (CDI), an emerging method to eliminate ions from water at a low cost, has garnered significant interest in recent years. This study evaluates the implication of cation exchange resin loading on the membrane via the nonsolvent-induced phase inversion method. After determining the quantity of resins efficiently loaded on the membrane, it was subsequently utilized as a cation exchange membrane in the membrane capacitive deionization (MCDI) unit to examine the performance removal of Ni2+. The results show that the amount of resins influenced the membrane structure and significantly improved the efficiency of Ni2+ removal. The sulfonic acid group show a strong intensity directly proportional to the quantity of resins based on the FTIR measurement. In conjunction with the enhanced resin amount, ion exchange capacity and water content were increased. Simultaneously, there was an observed elevation in the water contact angle and the roughness of the membrane surface with increased resin amount. In the MCDI unit, membrane M20 (20% by weight resin) was employed to elucidate its roles in the CDI unit, encompassing an examination of various concentrations and flow rates, with Ni2+ utilized as a test contaminant. The results demonstrated that using membrane M20 in the MCDI (MCDI-M20) unit consistently exhibited higher adsorption levels than the CDI unit, reaching 19.80 mg g-1 ACC in the MCDI-M20 unit, while CDI unit achieved 10.27 mg g-1 ACC at 200 mg L-1 Ni2+ concentration and a flow rate of 10 mL min-1 at 1.2 V. Additionally, Ni2+ concentrations and flow rates in CDI system had an evident impact on the duration of adsorption due to the mechanisms of ions transport on the membrane. This study suggests that employing the prepared membrane in the MCDI unit enhanced the removal of Ni2+ from the solution, contributing to sustainable development goals.

Redesigning Natural Materials for Energy, Water, Environment, and Devices

The United Nations Framework Convention on Climate Change (UNFCCC) acknowledges that global cooperation is paramount to mitigate climate change and further warming. The global community is committed to renewable energy and natural materials to tackle this challenge for all humankind. The widespread use of natural materials is embraced as one such action to reach net-zero carbon emissions. Given the hierarchical framework and earth abundance, cellulose-based materials extend their negative carbon benefits to our daily products and accelerate our pace toward carbon neutrality. Here, we present an overview of recent developments of cellulose-based materials in upsurging applications in radiative cooling, thermal insulation, nanofluidics, and wearable devices. We also highlight various modifications and functionalized processes that transform massive amounts of cellulose into green products. The prosperous development of functionalized cellulose materials aligns with a circular economy. Expedited interdisciplinary fundamental investigations are expected to make fibrillated cellulose penetrate more into carbon downdraw at speed and scale.

Effect of CuO Nanoparticles on the Optical, Structural, and Electrical Properties in the PMMA/PVDF Nanocomposite

A polymeric nanocomposite film, composed of PMMA/PVDF and different amounts of CuO NPs, was successfully prepared using the casting method to enhance its electrical conductivity. Various techniques were employed to investigate their physicochemical properties. The addition of CuO NPs causes a noticeable difference in the intensities and locations of vibrational peaks in all bands, confirming the incorporation of CuO NPs inside the PVDF/PMMA. In addition, the broadening of the peak at 2θ = 20.6° becomes more intense with increasing amounts of CuO NPs, confirming the increase in the amorphous characteristic of PMMA/PVDF incorporated with CuO NPs in comparison with PMMA/PVDF. Furthermore, the image of the polymeric structure exhibits a smoother shape and interconnection of pore structure associated with spherical particles that agglomerate and give rise to a web-like organization that becomes a matrix. Increasing surface roughness is responsible for an increasing surface area. Moreover, the addition of CuO NPs in the PMMA/PVDF leads to a decrease in the energy band gap, and further increasing the additional amounts of CuO NPs causes the generation of localized states between the valence and conduction bands. Furthermore, the dielectric investigation shows an increase in the dielectric constant, dielectric loss, and electric conductivity, which may be an indication of an increase in the degree of disorder that confines the movement of charge carriers and demonstrates the creation of an interconnected percolating chain, enhancing its conductivity values compared with that without the incorporation of a matrix.

Control over Charge Density by Tuning the Polyelectrolyte Type and Monomer Ratio in Saloplastic-Based Ion-Exchange Membranes

Membranes based on polyelectrolyte complexes (PECs) can now be prepared through several sustainable, organic solvent-free approaches. A recently developed approach allows PECs made by stoichiometric mixing of polyelectrolytes to be hot-pressed into dense saloplastics, which then function as ion-exchange membranes. An important advantage of PECs is that tuning their properties can provide significant control over the properties of the fabricated materials, and thus over their separation properties. This work studies the effects of two key parameters─(a) ratio of mixing and (b) choice of polyelectrolytes─on the mechanical, material, and separation properties of their corresponding hot-pressed saloplastic-based ion-exchange membranes. By varying these two main parameters, charge density─the key property of any IEM─was found to be controllable. While studying several systems, including strong/strong, strong/weak, and weak/weak combinations of polyelectrolytes, it was observed that not all systems could be processed into saloplastic membranes. For the processable systems, expected trends were observed where a higher excess of one polyelectrolyte would lead to a more charged system, resulting in higher water uptake and better permselectivities. An anomaly was the polystyrenesulfonate-polyvinylamine system, which showed an opposite trend with a higher polycation ratio, leading to a more negative charge. Overall, we have found that it is possible to successfully fabricate saloplastic-based anion- and cation-exchange membranes with tunable charge densities through careful choice of polyelectrolyte combination and ratio of mixing.

A Comparison of Unmodified and Sawdust Derived-Cellulose Nanocrystals (CNC)-Modified Polyamide Membrane Using X-ray Photoelectron Spectroscopy and Zeta Potential Analysis

Cellulose nanocrystals (CNC) obtained from waste sawdust were used to modify the polyamide membrane fabricated by interfacial polymerization of m-phenylene-diamine (MPDA) and trimesoyl chloride (TMC). The efficiency of the modification with sawdust-derived CNC was investigated using zeta potential and X-ray photoelectron spectroscopy (XPS). The effect of the modification on membrane mechanical strength and stability in acidic and alkaline solutions was also investigated. Results revealed that the negative zeta potential decreased at a high pH and the isoelectric point shifted into the acidic range for both modified and unmodified membranes. However, the negative charges obtained on the surface of the modified membrane at a pH lower than 8 were higher than the pristine membrane, which is an indication of the successful membrane modification. The XPS result shows that the degree of crosslinking was lowered due to the presence of CNC. Enhanced stability in solution in all pH ranges and the increase in mechanical strength, as indicated by higher Young's modulus, maximum load, and tensile strength, confirmed the robustness of the modified membrane.

A Comparative Study of Gamma-Ray Irradiation-Induced Oxidation: Polyethylene, Poly (Vinylidene Fluoride), and Polytetrafluoroethylene

Radiation techniques are used to modify the physical, chemical and biological properties of polymers. This induces crosslinking and degradation reactions of polymers by utilizing radicals generated through ionizing radiation. However, oxidation products (such as carbonyl) can be formed because oxidation occurs by chain scission in the presence of oxygen. Herein, we demonstrate the gamma-ray irradiation-induced oxidation with and without fluorine using polyethylene, polyvinylidene fluoride and polytetrafluoroethylene under the same conditions. In this study, changes in element-content and chemical-bond structures were analyzed before and after gamma-ray irradiation under air atmosphere. As a result, polytetrafluo-roethylene showed less oxidation and excellent thermal properties after the absorbed dose of 500 kGy. This can be attributed to the generation of stable perfluoroalkylperoxy radicals after gamma ray irradiation in the PTFE structure containing only CF2 groups, thereby hindering the oxidation reaction.

High-Performance Triboelectric Nanogenerators Based on Commercial Textiles: Electrospun Nylon 66 Nanofibers on Silk and PVDF on Polyester

A high-performance textile triboelectric nanogenerator is developed based on the common commercial fabrics silk and polyester (PET). Electrospun nylon 66 nanofibers were used to boost the tribo-positive performance of silk, and a poly(vinylidene difluoride) (PVDF) coating was deployed to increase the tribo-negativity of PET. The modifications confer a very significant boost in performance: output voltage and short-circuit current density increased ∼17 times (5.85 to 100 V) and ∼16 times (1.6 to 24.5 mA/m2), respectively, compared with the Silk/PET baseline. The maximum power density was 280 mW/m2 at a 4 MΩ resistance. The performance boost likely results from enhancing the tribo-positivity (and tribo-negativity) of the contact layers and from increased contact area facilitated by the electrospun nanofibers. Excellent stability and durability were demonstrated: the nylon nanofibers and PVDF coating provide high output, while the silk and PET substrate fabrics confer strength and flexibility. Rapid capacitor charging rates of 0.045 V/s (2 μF), 0.031 V/s (10 μF), and 0.011 V/s (22 μF) were demonstrated. Advantages include high output, a fully textile structure with excellent flexibility, and construction based on cost-effective commercial fabrics. The device is ideal as a power source for wearable electronic devices, and the approach can easily be deployed for other textiles.

Investigation on the feasibility of recycled polyvinylidene difluoride polymer from used membranes for removal of methylene blue: experimental and DFT studies

This study reports the feasibility of recycled polyvinylidene difluoride (PVDF) beads to decolourize methylene blue (MB) from aqueous streams. The beads were characterized using scanning electron microscopy (SEM), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FT-IR) for its morphological and structural analysis. The effect of various process parameters such as adsorbent dose, initial concentration, contact time, and pH was studied. The first principle density functional theory (DFT) calculations were performed to investigate the underlying mechanism behind the adsorption process. The MB dye adsorption on recycled PVDF beads followed the pseudo-second-order kinetics and Langmuir isotherm, indicating the adsorption was chemical and monolayer. The maximum adsorption capacity obtained was 27.86 mg g^-1. The adsorption energy of MB-PVDF predicted from the DFT study was -64.7 kJ mol^-1. The HOMO-LUMO energy gap of PVDF decreased from 9.42 eV to 0.50 eV upon interaction with MB dye due to the mixing of molecular orbitals. The DFT simulations showed that the interaction of the MB dye molecule was from the electronegative N atom of the MB dye molecule, implying that electrostatic interactions occurred between the recycled PVDF beads and the positively charged quaternary ammonium groups in MB dye. The present study demonstrates the potential of recycled PVDF beads for a low-cost dye removal technique from textile wastewater.

Poly(aryl cyanurate)-Based Thin-Film Composite Nanofiltration Membranes

The successful synthesis of poly(aryl cyanurate) nanofiltration membranes via the interfacial polymerization reaction between cyanuric chloride and 1,1,1-tris(4-hydroxyphenyl)ethane (TPE), atop a polyethersulfone ultrafiltration support, is demonstrated. The use of cyanuric chloride allows for the formation of a polymer that does not contain hydrolysis-susceptible amide bonds that inherently limit the stability of polyamide nanofiltration membranes. In order to achieve a thin defect-free cross-linked film via interfacial polymerization, a sufficient number of each monomer should react. However, the reactivities of the second and third chloride groups of the cyanuric chloride are moderate. Here, this difficulty is overcome by the high functionality and the high reactivity of TPE. The membranes demonstrate a typical nanofiltration behavior, with a molecular weight cutoff of 400 ± 83 g·mol-1 and a permeance of 1.77 ± 0.18 L·m-2 h-1 bar-1. The following retention behavior Na2SO4 (97.1%) > MgSO4 (92.8%) > NaCl (51.3%) > MgCl2 (32.1%) indicates that the membranes have a negative surface charge. The absence of amide bonds in the membranes was expected to result in superior pH stability as compared to polyamide membranes. However, it was found that under extremely acidic conditions (pH = 1), the performance showed a pronounced decline over the course of 2 months. Under extremely alkaline conditions (pH = 13), after 1 month, the performance was lost. After 2 months of exposure to moderate alkaline conditions (pH = 12), the MgSO4 retention decreased by 14% and the permeance increased by 2.5-fold. This degradation was attributed to the hydrolysis of the aryl cyanurate bond that behaves like an ester bond.

Treatment of Electroplating Wastewater Using NF pH-Stable Membranes: Characterization and Application

Industrial adoption of nanofiltration (NF) for treatment of low-pH wastewater is hindered by the limited membrane lifetime at strongly acidic conditions. In this study, the electroplating wastewater (EPWW) filtration performance of a novel pH-stable NF membrane is compared against a commercial NF membrane and a reverse osmosis (RO) membrane. The presented membrane is relatively hydrophobic and has its isoelectric point (IEP) at pH 4.1, with a high and positive zeta potential of +10 mV at pH 3. A novel method was developed to determine the molecular weight cut-off (MWCO) at a pH of 2, with a finding that the membrane maintains the same MWCO (~500 Da) as under neutral pH operating conditions, whereas the commercial membrane significantly increases it. In crossflow filtration experiments with simulated EPWW, rejections above 75% are observed for all heavy metals (compared to only 30% of the commercial membrane), while keeping the same pH in the feed and permeate. Despite the relatively lower permeance of the prepared membrane (~1 L/(m2·h·bar) versus ~4 L/(m2·h·bar) of the commercial membrane), its high heavy metals rejection coupled with a very low acid rejection makes it suitable for acid recovery applications.

Nanofiltration of Succinic Acid in Strong Alkaline Conditions

Nanofiltration is considered to be an appropriate separation technique in the production of bio-based materials. For the utilization of process streams from the viscose-fiber production, understanding the separation behavior of organic compounds in highly alkaline solutions is necessary. Experiments with succinic acid in sodium hydroxide (NaOH) solutions with varying concentrations up to 5 mol L-1 were performed with the NP030 membrane from Microdyn Nadir. Furthermore, experiments with aqueous disodium succinate and solutions of sodium sulfate in sodium hydroxide were carried out. The influence of concentration ratios and temperature was studied. The Spiegler and Kedem model as well as the Pusch model were applied to fit the experimental data. Additionally, scanning electron microscopy (SEM) and infrared (ATR-IR) measurements were performed to validate the chemical and thermomechanical stability of the membrane. The succinic acid retention varies with its degree of dissociation. In a fully dissociated form, the NaOH concentration shows no impact on the retention. In contrast, the retention of sulfate decreases with increasing NaOH concentration.