Halloysite Nanotube-Ferrihydrite Incorporated Polyethersulfone Mixed Matrix Membrane: Effect of Nanocomposite Loading on the Antifouling Performance

Recent Advances on the Fabrication of Antifouling Phase-Inversion Membranes by Physical Blending Modification Method

Membrane technology is an essential tool for water treatment and biomedical applications. Despite their extensive use in these fields, polymeric-based membranes still face several challenges, including instability, low mechanical strength, and propensity to fouling. The latter point has attracted the attention of numerous teams worldwide developing antifouling materials for membranes and interfaces. A convenient method to prepare antifouling membranes is via physical blending (or simply blending), which is a one-step method that consists of mixing the main matrix polymer and the antifouling material prior to casting and film formation by a phase inversion process. This review focuses on the recent development (past 10 years) of antifouling membranes via this method and uses different phase-inversion processes including liquid-induced phase separation, vapor induced phase separation, and thermally induced phase separation. Antifouling materials used in these recent studies including polymers, metals, ceramics, and carbon-based and porous nanomaterials are also surveyed. Furthermore, the assessment of antifouling properties and performances are extensively summarized. Finally, we conclude this review with a list of technical and scientific challenges that still need to be overcome to improve the functional properties and widen the range of applications of antifouling membranes prepared by blending modification.

Xylem-Inspired Hydrous Manganese Dioxide/Aluminum Oxide/Polyethersulfone Mixed Matrix Membrane for Oily Wastewater Treatment

Ultrafiltration membrane has been widely used for oily wastewater treatment application attributed to its cost-efficiency, ease of operation, and high separation performance. To achieve high membrane flux, the pores of the membrane need to be wetted, which can be attained by using hydrophilic membrane. Nevertheless, conventional hydrophilic membrane suffered from inhomogeneous dispersion of nanofillers, causing a bottleneck in the membrane flux performance. This called for the need to enhance the dispersion of nanofillers within the polymeric matrix. In this work, in-house-fabricated hydrous manganese dioxide-aluminum oxide (HMO-Al₂O₃) was added into polyethersulfone (PES) dope solution to enhance the membrane flux through a xylem-inspired water transport mechanism on capillary action aided by cohesion force. Binary fillers HMO-Al₂O₃ loading was optimized at 0.5:0.5 in achieving 169 nm membrane mean pore size. Membrane morphology confirmed the formation of macro-void in membrane structure, and this was probably caused by the hydrophilic nanofiller interfacial stress released in PES matrix during the phase inversion process. The superhydrophilic properties of PES 3 in achieving 0° water contact angle was supported by the energy-dispersive X-ray analysis, where it achieved high O element, Mn element, and Al elements of 39.68%, 0.94%, and 5.35%, respectively, indicating that the nanofillers were more homogeneously dispersed in PES matrix. The superhydrophilic property of PES 3 was further supported by high pure water flux at 245.95 L/m².h.bar, which was 3428.70% higher than the pristine PES membrane, 197.1% higher than PES 1 incorporated with HMO nanofiller, and 854.00% higher than PES 5 incorporated with Al₂O₃ nanofillers. Moreover, the excellent membrane separation performance of PES 3 was achieved without compromising the oil rejection capability (98.27% rejection) with 12 g/L (12,000 ppm) oily wastewater.

Influence of the Zeolite ZSM-22 Precursor on a UF-PES Selective Substrate Layer for Salts Rejection

Fabrication of the ZSM-22/Polyethersulfone (ZSM-22/PES) membranes as selective salt filters represent a growing membrane technological area in separation with the potential of high economic reward based on its low energy requirements. The incorporation of ZSM-22 zeolite material as additives into the PES polymer matrix has the prospective advantage of combining both the zeolite and polymer features while overcoming the limitations associated with both materials. This work investigated the influence of the nature of the silica precursor on ZSM-22 zeolite hydrothermally synthesised using colloidal (C60) and fumed (C60) silica to Si/Al of 60. The successful synthesis of the highly crystalline zeolitic materials was confirmed through XRD, FTIR, and SEM with EDX. The ZSM-22 additives were directly dispersed into a PES polymeric matrix to form a casting solution for the preparation of the ZSM-22/PES selective substrate layers via a phase inversion method for salts rejection. The polymeric PES was selected as an organic network in which the content of the ZSM-22 zeolite (ranging between 0 and 1.0 wt.%), was obtained and characterised by XRD, FTIR, and SEM analysis, as well as water contact angle (WCA) measurement and dead-end filtration cell. The phase inversion preparation method has induced the resulting ZSM-22/PES NF substrates anisotropy, as attributed to a high water flux to the above 700 L·m−2·h−1; high selectivity and rejection of salts to above 80% is revealed by the obtained results. The materials also exhibited improved antifouling behavior to above 70% flux recovery ratios. As such, the nature of the silica precursor influences ZSM-22 zeolite synthesis as a potential additive in the PES polymer matrix and led to the enhanced performance of the pure PES ultrafiltration membrane.

Ab initio thermodynamics reveals the nanocomposite structure of ferrihydrite

Ferrihydrite is a poorly crystalline iron oxyhydroxide nanomineral that serves a critical role as the most bioavailable form of ferric iron for living systems. However, its atomic structure and composition remain unclear due in part to ambiguities in interpretation of X-ray scattering results. Prevailing models so far have not considered the prospect that at the level of individual nanoparticles multiple X-ray indistinguishable phases could coexist. Using ab initio thermodynamics we show that ferrihydrite is likely a nanocomposite of distinct structure types whose distribution depends on particle size, temperature, and hydration. Nanoparticles of two contrasting single-phase ferrihydrite models of Michel and Manceau are here shown to be thermodynamically equivalent across a wide range of temperature and pressure conditions despite differences in their structural water content. Higher temperature and water pressure favor the formation of the former, while lower temperature and water pressure favor the latter. For aqueous suspensions at ambient conditions, their coexistence is maximal for particle sizes up to 12 nm. The predictions inform and help resolve different observations in various experiments.

Manufacturing and Characterisation of Polymeric Membranes for Water Treatment and Numerical Investigation of Mechanics of Nanocomposite Membranes

In this study, polyethersulfone (PES) and polyvinylidene fluoride (PVDF) microfiltration membranes containing polyvinylpyrrolidone (PVP) with and without support layers of 130 and 150 μm thickness are manufactured using the phase inversion method and then experimentally characterised. For the characterisation of membranes, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and pore size analysis are performed, the contact angle and water content of membranes are measured and the tensile test is applied to membranes without support layers. Using the results obtained from the tensile tests, the mechanical properties of the halloysite nanotube (HNT) and nano-silicon dioxide (nano SiO₂) reinforced nanocomposite membranes are approximately determined by the Mori–Tanaka homogenisation method without applying any further mechanical tests. Then, plain polymeric and PES and PVDF based nanocomposite membranes are modelled using the finite element method to determine the effect of the geometry of the membrane on the mechanical behaviour for fifteen different geometries. The modelled membranes compared in terms of three different criteria: equivalent stress (von Mises), displacement, and in-plane principal strain. Based on the data obtained from the characterisation part of the study and the numerical analysis, the membrane with the best performance is determined. The most appropriate shape and material for a membrane for water treatment is specified as a 1% HNT doped PVDF based elliptical membrane.