Fabrication and in-situ fouling mitigation of a supported carbon nanotube/γ-alumina ultrafiltration membrane

Recent Advances in Responsive Membrane Functionalization Approaches and Applications

In recent years, significant advances have been made in the field of functionalized membranes. With the functionalization using various materials, such as polymers and enzymes, membranes can exhibit property changes in response to an environmental stimulation, such as heat, light, ionic strength, or pH. The resulting responsive nature allows for an increased breadth of membrane uses, due to the developed functionalization properties, such as smart-gating filtration for size-selective water contaminant removal, self-cleaning antifouling surfaces, increased scalability options, and highly sensitive molecular detection. In this review, new advances in both fabrication and applications of functionalized membranes are reported and summarized, including temperature-responsive, pH-responsive, light-responsive, enzyme-functionalized, and two-dimensional material-functionalized membranes. Specific emphasis was given to the most recent technological improvements, current limitations, advances in characterization techniques, and future directions for the field of functionalized membranes.

Efficient removal of dextran in sugar juice by immobilized α-dextranase from Chaetomium gracile

Dextran problem restricts the development of the sugar industry. Although the enzymatic treatment based on α-dextranase from Chaetomium gracile (α-dextranase (CG)) has been effective in solving this issue, the lack of immobilization products hinder its industrial applications. This research described a novel and suitable method to immobilize α-dextranase (CG). The purified α-dextranase (CG) was immobilized via cross-linking using modified chitosan as carriers. In addition, this study used a deep eutectic solvent that greatly improved the enzymatic properties of immobilized α-dextranase (CG). α-dextranase (CG) was immobilized by adding deep eutectic solvent (DES-IM-α-dextranase (CG)) showed better temperature tolerance and storage properties than free and ordinary immobilized counterparts. It can eliminate dextran by 59.71% in mixed sugarcane juice and 38.71% in clarified sugarcane juice. The achieved results were considerably better than those obtained using free and other immobilized enzymes. Altogether, these findings confirmed that DES-IM-α-dextranase (CG) displayed great potential in solving the dextran problem.

Influence of various shapes of alumina nanoparticle in integrated polysulfone membrane for separation of lignin from woody biomass and salt rejection

Lignin valorization is essential in proposing an economic perspective as a raw material for valuable compounds. The bio-refineries require adequate processing to improve the high purity of lignin. Meanwhile, nanofiltration is fascinated attention to obtain high purity value-added products. The effect of alumina nanoparticles on the fabrication of mixed matrix membranes (MMM) has contributed to improvising filtration performance. However, incorporating nanoparticles is a significant issue regarding appropriate size and shape integrated into membrane for better filtration efficiency. The influence of shapes of alumina nanoparticles has been investigated into polysulfone (PSf) membranes for salt and lignin separation. The morphology of alumina was tailored with spindle, cubic, and spherical shapes synthesized at a different calcination temperature of 250, 500, 700 and 900 °C, respectively. The phase transitions were confirmed in X-ray diffraction (XRD) analysis, and the shape of the nanoparticles was observed in a high-resolution transmission electron microscope (HRTEM). The separation efficiency of membranes was tested with salt rejection using sodium sulfate, calcium chloride, potassium sulfate, and sodium chloride. The lignin was extracted from prehydrolysed sawdust, and the synthetic lignosulfonic acid sodium salt solution was separated. The higher lignin rejection of 98.6% and 97.9% were obtained for cubic shaped gamma phase alumina mixed matrix membrane. The high rejection of lignin occurred due to narrow pores channels that could resist the transfer of lignin through the membrane. The results proved that the controllable organization of PSf/alumina mixed matrix membranes could apply for lignocellulose compounds with good efficiency.

One-Step Water-Induced Phase Separation Simultaneously Triggering Polymer Solidification and Polyelectrolyte Complexation for Porous Ultrafiltration Membranes

Functional additives have been widely utilized for the membrane structure modulation and performance improvement during the nonsolvent-induced phase separation process, but the resulted membranes easily suffer from additives' inhomogeneous dispersity and compatibility with the polymer matrix. Herein, a facile and robust strategy, i.e., one-step water-induced phase separation, was proposed for the preparation of polyelectrolytes-contained composite membranes. Polyanion (dopamine modified polyacrylic acid) and polycation (quaternized chitosan paired with bis(trifluoromethane-sulfonyl)imide) were first premixed in dimethyl sulfoxide and used as polyelectrolyte additives in a polysulfone (PSF) solution, and then a uniform PSF-based casting solution was readily obtained. During the solvent-water exchange process, polymer solidification and polyelectrolyte complexation were simultaneously triggered, in situ generating a polyelectrolyte complex fixed within the membrane matrix. Ultrafiltration membranes with hierarchical structures were notably tailored through altering the concentration, molecular weight, and type of polyelectrolytes. The obtained membrane exhibited a water flux of 672 L·m^-2·h^-1, three times over the raw PSF membrane, while almost maintaining high bovine serum albumin (BSA) rejection. This work paves a straightforward and convenient path for the preparation of composite membranes with tunable architecture and properties.

Preparation and Characterization of the Forward Osmosis Membrane Modified by MXene Nano-Sheets

The Forward Osmosis (FO) membrane was the core of FO technology. Obtaining a high water flux while maintaining a low reverse solute flux has historically been considered the gold standard for a perfect FO membrane. In a thin-film composite FO membrane, the performance of the membrane was determined not only by the material and structure of the porous support layer but also by the structural and chemical properties of the active selective layer. Researchers have selected numerous sorts of materials for the FO membranes in recent years and have produced exceptional achievements. Herein, the performance of the modified FO membrane constructed by introducing new two-dimensional nanomaterial MXene nano-sheets to the interfacial polymerization process was investigated, and the performance of these modified membranes was investigated using a variety of characterization and testing methods. The results revealed that the MXene nano-sheets played an important role in improving the performance of the FO membrane. Because of the hydrophilic features of the MXene nano-sheets, the membrane structure may be tuned within a specific concentration range, and the performance of the modified FO membrane has been significantly enhanced accordingly. The optimal membrane water flux was boosted by around 80%, while its reverse solute flux was kept to a minimum of the resultant membranes. It showed that the addition of MXene nanosheets to the active selective layer could improve the performance of the FO membrane, and this method showed promising application prospects.

Review of New Approaches for Fouling Mitigation in Membrane Separation Processes in Water Treatment Applications

This review investigates antifouling agents used in the process of membrane separation (MS), in reverse osmosis (RO), ultrafiltration (UF), nanofiltration (NF), microfiltration (MF), membrane distillation (MD), and membrane bioreactors (MBR), and clarifies the fouling mechanism. Membrane fouling is an incomplete substance formed on the membrane surface, which will quickly reduce the permeation flux and damage the membrane. Foulant is colloidal matter: organic matter (humic acid, protein, carbohydrate, nano/microplastics), inorganic matter (clay such as potassium montmorillonite, silica salt, metal oxide, etc.), and biological matter (viruses, bacteria and microorganisms adhering to the surface of the membrane in the case of nutrients) The stability and performance of the tested nanometric membranes, as well as the mitigation of pollution assisted by electricity and the cleaning and repair of membranes, are reported. Physical, chemical, physico-chemical, and biological methods for cleaning membranes. Biologically induced biofilm dispersion effectively controls fouling. Dynamic changes in membrane foulants during long-term operation are critical to the development and implementation of fouling control methods. Membrane fouling control strategies show that improving membrane performance is not only the end goal, but new ideas and new technologies for membrane cleaning and repair need to be explored and developed in order to develop future applications.

A critical review on ultrasonic-assisted fouling control and cleaning of fouled membranes

Fouling is one of the most challenging problems impacting the performance of membrane-based separation technology. In recent years, ultrasound have been widely applied as an unconventional method to control membrane fouling, as well as to enhance membrane cleaning. The aim of the present work is to review the current literature and the recent developments related to the use of ultrasound as an innovative and alternative approach to improve the fouling behavior of membrane separation processes. The theory underlying ultrasonic-assisted phenomena is reviewed, together with operational factors that influence the effectiveness of the ultrasound treatment, such as frequency, power intensity, pressure, temperature, pH, and operation mode. Ultrasound irradiation effectively aids the cleaning of contaminated surfaces and enhances the permeate flux, owing to cavitation phenomena and powerful convective currents, associated with secondary phenomena, such as microstreamers, shock waves, and heating. However, the lifetime of the membranes should be carefully evaluated when applying ultrasonication as a technique of cleaning or controlling membrane fouling. Indeed, the integrity of membranes after sonication and the control of erosion produced by high ultrasonic intensities are key issues hindering the scale-up of this approach in the membrane industry. This reviews highlights the topics requiring more investigations, specifically to evaluate the economic aspects of ultrasonic assisted fouling control and cleaning in membrane processes.

Next-Generation Multifunctional Carbon-Metal Nanohybrids for Energy and Environmental Applications

Nanotechnology has unprecedentedly revolutionized human societies over the past decades and will continue to advance our broad societal goals in the coming decades. The research, development, and particularly the application of engineered nanomaterials have shifted the focus from "less efficient" single-component nanomaterials toward "superior-performance", next-generation multifunctional nanohybrids. Carbon nanomaterials (e.g., carbon nanotubes, graphene family nanomaterials, carbon dots, and graphitic carbon nitride) and metal/metal oxide nanoparticles (e.g., Ag, Au, CdS, Cu₂O, MoS₂, TiO₂, and ZnO) combinations are the most commonly pursued nanohybrids (carbon-metal nanohybrids; CMNHs), which exhibit appealing properties and promising multifunctionalities for addressing multiple complex challenges faced by humanity at the critical energy-water-environment (EWE) nexus. In this frontier review, we first highlight the altered and newly emerging properties (e.g., electronic and optical attributes, particle size, shape, morphology, crystallinity, dimensionality, carbon/metal ratio, and hybridization mode) of CMNHs that are distinct from those of their parent component materials. We then illustrate how these important newly emerging properties and functions of CMNHs direct their performances at the EWE nexus including energy harvesting (e.g., H₂O splitting and CO₂ conversion), water treatment (e.g., contaminant removal and membrane technology), and environmental sensing and in situ nanoremediation. This review concludes with identifications of critical knowledge gaps and future research directions for maximizing the benefits of next-generation multifunctional CMNHs at the EWE nexus and beyond.

Enhanced Hydrophilicity and Water Flux of Poly(ether sulfone) Membranes in the Presence of Aluminum Fumarate Metal-Organic Framework Nanoparticles: Preparation and Characterization

The aim of this study is to examine the effect of the addition of aluminum fumarate (AlFu) nanoparticles on the properties of poly(ether sulfone) (PES) membranes, where the AlFu nanoparticles were synthesized as the nanofillers with the metal-organic framework and their structure was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRD), and field emission scanning electron microscopy (FESEM) analyses. Subsequently, PES/AlFu mixed-matrix membranes (MMMs) were fabricated in different weight percentages of nanofiller through the phase inversion method and the membrane characterization was accomplished by FTIR, XRD, FESEM, transmission electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy, and elemental mapping analyses. The effect of the addition of nanoparticles on the membrane properties was investigated by measuring the membrane hydrophilicity, pure water flux, solute rejection, and fouling resistance using a dead-end cell under constant pressure and bovine serum albumin as a foulant. The molecular weight cutoff (MWCO) of MMMs was measured by the rejection of poly(ethylene glycol) in various molecular weights, and the membrane surface roughness, porosity, and mean pore radius were calculated. The results showed that AlFu nanoparticles increased the hydrophilicity and porosity of the neat PES membranes and consequently increased the water permeability such that MMM including 0.75 wt % of AlFu possessed the maximum porosity (62.2%), mean pore radius (10.2 nm), and MWCO (154 kDa). Furthermore, this membrane exhibits a superlative flux recovery and minimal total resistance in the antifouling properties examinations.