Antifouling Fibrous Membrane Enables High Efficiency and High-Flux Microfiltration for Water Treatment

Developments of electrospinning technology in membrane bioreactor: A review

The necessity for effective wastewater treatment and purification has grown as a result of the increasing pollution issues brought on by industrial and municipal wastewater. Membrane bioreactor (MBR) technology stands out when compared to other treatment methods because of its high efficiency, environmental friendliness, small footprint, and ease of maintenance. However, the development and application of membrane bioreactors has been severely constrained by the higher cost and shorter service life of these devices brought on by membrane biofouling issues resulting from contaminants and bacteria in the water. The nanoscale size of the electrospinning products provides unique microstructure, and the technology facilitates the production of structurally different membranes, or the modification and functionalization of membranes, which makes it possible to solve the membrane fouling problem. Therefore, many current studies have attempted to use electrospinning in MBRs to address membrane fouling and ultimately improve treatment efficacy. Meanwhile, in addition to solving the problem of membrane fouling, the fabrication technology of electrospinning also shows great advantages in constructing thin porous fiber membrane materials with controllable surface wettability and layered structure, which is helpful for the performance enhancement of MBR and expanding innovation. This paper systematically reviews the application and research progress of electrospinning in MBRs. Firstly, the current status of the application of electrospinning technology in various MBRs is introduced, and the relevant measures to solve the membrane fouling based on electrospinning technology are analyzed. Subsequently, some new types of MBRs and new application areas developed with the help of electrospinning technology are introduced. Finally, the limitations and challenges of merging the two technologies are presented, and pertinent recommendations are provided for future research on the use of electrospinning technology in membrane bioreactors.

Ultrasonication-assisted synthesis of transition metal carbide of MXene: an efficient and promising material for photocatalytic organic dyes degradation of rhodamine B and methylene blue in wastewater

Water pollutants of non-biodegradable toxic aromatic dye including Methylene blue (MB) and Rhodamine (RhB) are extremely carcinogenic thiazines used in various industries such as leather industry, paper industry, and the dyeing industry. The presence of dyes in wastewater causes severe threats to human health that are responsible for various harmful chronic or acute diseases and also shows an adverse impact on the environment as it reduces transparency and is harmful to water microorganisms. To overcome severe issues, many traditional techniques have been used to remove toxic pollutants, but these methods are insufficient to remove chemically stable dyes that remain in the treated wastewater. However, the photocatalytic degradation process is an efficient approach to degrade the dye up to the maximum extent with improved efficiency. Therefore, in this work, a new class of two-dimensional (2D) transition metal carbide of Titanium Carbide (Ti3C2Tx) MXene material was used for the organic dyes degradation such as MB and RhB using a photocatalytic process. A layered structure of hexagonal lattice symmetry of Ti3C2Tx MXene was successfully synthesized from the Titanium Aluminum Carbide of Ti3AlC2 bulk phase using an exfoliation process. Further, the XRD spectrum confirms the transformation of bulk MAX phase having (002) plane at 9.2° to Ti3C2Tx MXene of (002) plane at 8.88° confirms the successful removal of Al layer from MAX phase. A smooth, transparent, thin sheet-like morphology of Ti3C2Tx nanosheet size were found to be in the range of 70 to 150 nm evaluated from TEM images. Also, no holes or damages in the thin sheets were found after the treatment with strong hydrofluoric acid confirms the formation Ti3C2Tx layered sheets. The synthesized Ti3C2Tx MXene possesses excellent photocatalytic activity for the degradation of dyes MB, RhB, and mixtures of MB and RhB dyes. MB dye degraded with a degradation percentage efficiency of 99.32% in 30 min, while RhB dye was degraded upto 98.9% in 30 min. Also, experiments were conducted for degradation of mixture of MB and RhB dyes by UV light, and the degradation percentage efficiency were found to be 98.9% and 99.75% for mixture of MB and RhB dye in 45 min, respectively. Moreover, reaction rate constant (k) was determined for each dye of MB, RhB, and mixtures of MB and RhB and was found to be 0.0215 min-1 and 0.0058 min-1, and for mixtures, it was 0.0020 min-1 and 0.009 min-1, respectively.

Cross-linking electrospinning

Although electrospinning (e-spinning) has witnessed rapid development in recent years, it has also been criticized by environmentalists due to the use of organic solvents. Therefore, aqueous e-spinning (green e-spinning) is considered a more attractive technique. However, considering the poor water resistance and mechanical properties of electrospun (e-spun) nanofibers, cross-linking is a perfect solution. In this review, we systematically discuss the cross-linking e-spinning system for the first time, including cross-linking strategies (in situ, liquid immersion, vapor, and spray cross-linking), cross-linking mechanism (physical and chemical cross-linking) of e-spun nanofibers, and the various applications (e.g., tissue engineering, drug delivery, water treatment, food packaging, and sensors) of cross-linked e-spun nanofibers. Among them, we highlight several cross-linking methods, including UV light cross-linking, electron beam cross-linking, glutaraldehyde (and other commonly used cross-linking agents) chemical cross-linking, thermal cross-linking, and enzymatic cross-linking. Finally, we confirm the significance of cross-linking e-spinning and reveal the problems in the construction of this system.

A Magneto-Heated Silk Fibroin Scaffold for Anti-Biofouling Solar Steam Generation

Macroscopic 3D porous materials are ideal solar evaporators for water purification. However, the limited sunlight intensity and penetrating depth during solar-driven evaporation cannot prevent the biofouling formation by photothermal effect, thus leading to the deterioration of evaporation rate. Herein, a magnetic heating strategy is reported for anti-biofouling solar steam generation based on a magnetic silk fibroin (SF) scaffold with bi-heating property. Under one sun, the solar-heated top surface of magnetic SF scaffolds accelerates water evaporation at 2.03 kg m^-2 h^-1 , while the unheated inner channels suffer from the formation of biofilm. When exposed to alternating magnetic field (AMF), the magnetic SF scaffold can be integrally heated, leading to an efficient inner temperature to prevent biofouling in channels for water transportation. Accordingly, magneto-heated scaffolds show steady water evaporation rates after exposure to S. aureus and E. coli, which maintained 93.6-94.6% of original performance. In contrast, the evaporation rates of the scaffolds without AMF treatment are reduced to 1.31 (S. aureus) and 1.32 (E. coli) kg m^-2 h^-1 , decreased by 35.5% and 35.0%, respectively. In addition, the magneto-heated scaffold inhibits biofouling formation in natural lake water, maintaining 99.5% original performance.

In situ rapid synthesis of hydrogels based on a redox initiator and persistent free radicals

The development of fast and economical hydrogel manufacturing methods is crucial for expanding the application of hydrogels. However, the commonly used rapid initiation system is not conducive to the performance of hydrogels. Therefore, the research focuses on how to improve the preparation speed of hydrogels and avoid affecting the properties of hydrogels. Herein, a redox initiation system with nanoparticle-stabilized persistent free radicals was introduced to rapidly synthesize high-performance hydrogels at room temperature. A redox initiator composed of vitamin C and ammonium persulfate rapidly provides hydroxyl radicals at room temperature. Simultaneously, three-dimensional nanoparticles can stabilize free radicals and prolong their lifetime, thereby increasing the free radical concentration and accelerating the polymerization rate. And casein enabled the hydrogel to achieve impressive mechanical properties, adhesion, and electrical conductivity. This method greatly facilitates the rapid and economical synthesis of high-performance hydrogels and presents broad application prospects in the field of flexible electronics.

Modification of ultrafiltration membrane with antibacterial agent intercalated layered nanosheets: Toward superior antibiofouling performance for water treatment

Membrane fouling, especially biofouling induced by biofilm formation on membranes, can result in frequent cleaning or even replacement of membranes. Fabrication of membrane with excellent antibiofouling property is quite attractive due to its effectiveness and low-impact on the operation of membrane-based process. Herein, a cationic antibacterial agent, quaternary ammonium compound (QAC), was intercalated into the interlayer spaces of the MgAl layered double hydroxide (QAC/LDH) by self-assembly. The QAC/LDH composite was incorporated into polyethersulfone (PES) ultrafiltration (UF) membrane (PES-QLDH). The QAC/LDH enhanced the hydrophilicity, water flux, and resistance to organic fouling for the PES-QLDH membrane. The PES-QLDH membrane exhibited superior antibiofouling performance than the control PES membrane, with deposition of a thinner biofilm layer consisted of almost dead cells. The superior antibacterial activity inhibits the adhesion and growth of bacteria on the membrane surface, effectively retarding the formation of biofilms. Importantly, the synergistic effect of QAC and LDH in the PES-QLDH membrane resulted in a high biocidal activity based on both direct and indirect killing mechanisms. The PES-QLDH membrane maintained a stable and high antibacterial activity after several fouling-cleaning cycles. These results imply that the PES-QLDH membrane provides an effective and promising strategy for its long-term application in wastewater treatment.