Anti-fouling and easy-cleaning PVDF membranes blended with hydrophilic thermo-responsive nanofibers for efficient biological wastewater treatment

Room-temperature fabrication of fluorinated covalent organic polymer @ Attapulgite composite for in-syringe membrane solid-phase extraction and analysis of domoic acid in aquatic products

A novel fluorinated covalent organic polymer @ attapulgite composite (F-COP@ATP) was prepared at room temperature for in-syringe membrane solid-phase extraction (SM-SPE) of domoic acid (DA) in aquatic products. Natural ore ATP has the advantages of low cost, good mechanical strength and abundant hydroxyl group on its surface, and in-situ modified F-COP layer can provide abundant adsorption sites. F-COP@ATP combining the advantages of F-COP and ATP, becomes an ideal adsorbent for DA extracting. Moreover, a high-throughput sample preparation strategy was carried out by using the F-COP@ATP membrane as syringe filter and assembling syringes with a ten-channel injection pump. In addition, the experimental factors were optimized, such as pH of extract, amount of adsorbent, velocity of extraction and desorption, type and volume of desorption solvent. The DA analytical method was established by SM-SPE-HPLC/tandem mass spectrometry. The method had a wide linear range with low limit of detection (0.344 ng/kg) and low limit of quantification (1.14 ng/kg). F-COP@ATP membrane can be reused more than five times. The method realized the analysis of DA in scallop and razor clam samples, which shows its application prospect in practical analysis. This study provided an efficient, low-energy and mild idea for preparing other reusable natural mineral ATP-based composite materials for separation and enrichment, which reduces the experimental cost and is closer to environmental protection and green chemistry to a certain extent.

Anti-fouling PVDF membranes incorporating photocatalytic biochar-TiO2 composite for lignin recycle

In this study, a photocatalytic biochar-TiO₂ (C-Ti) composite was prepared using lignin as carbon precursor, and blended with PVDF polymer to fabricate PVDF/C-Ti MMMs via non-solvent induced phase inversion. The prepared membrane demonstrates both 1.5 times higher initial and recovered fluxes than the similarly prepared PVDF/TiO₂ membrane, suggesting the C-Ti composite can help maintain higher photodegradation efficiency and better anti-fouling performance. In addition, the comparison of PVDF/C-Ti membrane against pristine PVDF membrane show that the reversible fouling and photodegradation reversible fouling of BSA increased from 10.1% to 6.4%-35.1% and 26.6%, respectively. And the FRR of PVDF/C-Ti membrane was 62.12%, 1.8 times that of PVDF membrane. The PVDF/C-Ti membrane was also applied for lignin separation, where the rejection to sodium lignin sulfonate was maintained at about 75%, and the flux recovery ratio after UV irradiation reached 90%. The demonstrated the advantages of PVDF/C-Ti membrane in photocatalytic degradation and antifouling performance.

Research Progress of Water Treatment Technology Based on Nanofiber Membranes

In the field of water purification, membrane separation technology plays a significant role. Electrospinning has emerged as a primary method to produce nanofiber membranes due to its straightforward, low cost, functional diversity, and process controllability. It is possible to flexibly control the structural characteristics of electrospun nanofiber membranes as well as carry out various membrane material combinations to make full use of their various properties, including high porosity, high selectivity, and microporous permeability to obtain high-performance water treatment membranes. These water separation membranes can satisfy the fast and efficient purification requirements in different water purification applications due to their high filtration efficiency. The current research on water treatment membranes is still focused on creating high-permeability membranes with outstanding selectivity, remarkable antifouling performance, superior physical and chemical performance, and long-term stability. This paper reviewed the preparation methods and properties of electrospun nanofiber membranes for water treatment in various fields, including microfiltration, ultrafiltration, nanofiltration, reverse osmosis, forward osmosis, and other special applications. Lastly, various antifouling technologies and research progress of water treatment membranes were discussed, and the future development direction of electrospun nanofiber membranes for water treatment was also presented.

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.

A Simple Approach to Fabricate Composite Ceramic Membranes Decorated with Functionalized Carbide-Derived Carbon for Oily Wastewater Treatment

Membrane-based oil−water separation has shown huge potential as a remedy to challenge oily wastewater with ease and low energy consumption compared to conventional purification techniques. A set of new composite ceramic membranes was fabricated to separate surfactant-stabilized oil/water (O/W) emulsion. Carbide-derived carbon (CDC) was functionalized by 3-aminopropyltriethoxy silane (APTES) and subsequently deposited on a ceramic alumina support and impregnated with piperazine as an additional amine. The APTES functionalized CDC-loaded membrane was then crosslinked using terephthalyol chloride (TPC). Different loadings of functionalized CDC (50 mg, 100 mg and 200 mg) were employed on the ceramic support resulting in three versions of ceramic membranes (M-50, M-100 and M-200). The fabricated membranes were thoroughly characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Attenuated total teflectance Fourier transform infrared (ATR-FTIR) spectroscopy, Energy dispersive x-ray spectroscopy (EDX) and elemental mapping. The highest permeate flux of 76.05 LMH (L m−2 h−1) at 1 bar using 67.5 ppm oil-in-water emulsion (as feed) was achieved by the M-50 membrane, while an oil separation efficiency of >99% was achieved by using the M-200 membrane. The tested emulsions and their respective permeates were also characterized by optical microscopy to validate the O/W separation performance of the best membrane (M-100). The effect of feed concentration and pressure on permeate flux and oil−water separation efficiency was also studied. A long-term stability test revealed that the M-100 membrane retained its performance for 720 min of continuous operation with a minor decrease in permeate flux, but the O/W separation efficiency remained intact.

Alternative methods for cleaning membranes in water and wastewater treatment

Membrane fouling is caused by foulant deposition or adsorption through physical or chemical interactions on the membrane surface, causing the reduction of flux through the membrane. The main drawbacks of chemical agents used for cleaning are cost, damage caused on the membrane, and waste stream making the process unattractive. Alternative, methods such as ultrasound, enzymatic process, and osmotic backwashing were explored for membrane cleaning. Among all mentioned methods, micronanobubbles have been reported as a promising and emergent method for membrane surface cleaning; unfortunately, the information is limited, but preliminary studies have shown it as an efficient, cheap, and environmentally friendly technique. Other methods like electrically and vibratory-enhanced membrane cleaning also could be interesting but currently are unexplored and information is limited. PRACTITIONER POINTS: Chemical cleaning is an efficient option; however, from an environmental point of view, it is not attractive, and high concentrations could cause damage to the membrane. Micronanobubbles are an emergent and suitable technology for membrane and surface cleaning. Membrane modification and functionalization avoid membrane fast fouling, and the cleaning process is easier, but the manufacture cost could be expensive.

Effects of Benzalkonium Chloride Contents on Structures, Properties, and Ultrafiltration Performances of Chitosan-Based Nanocomposite Membranes

The effects of benzalkonium chloride (BKC) contents on the structure, properties, and ultrafiltration performance of chitosan-based nanocomposite membranes containing poly(ethylene glycol) and multi-walled carbon nanotube (chitosan/BKC/PEG/CNT) were examined. The membranes were prepared by a mixing solution method and phase inversion before being characterized with microscopic techniques, tensile tests, thermogravimetric analysis, water contact angle, and porosity measurements. The performance of the nanocomposite membranes in regard to permeability (flux) and permselectivity (rejection) was examined. The results show that the incorporation of BKC produced nanocomposite membranes with smaller pore structures and improved physico-chemical properties, such as an increase in porosity and surface roughness (Ra = 45.15 to 145.35 nm and Rq = 53.69 to 167.44 nm), an enhancement in the elongation at break from 45 to 109%, and an enhancement in the mechanical strength from 31.2 to 45.8 MPa. In contrast, a decrease in the membrane hydrophilicity (water contact angle increased from 56.3 to 82.8°) and a decrease in the average substructure pore size from 32.64 to 10.08 nm were observed. The membrane rejection performances toward Bovine Serum Albumin (BSA) increased with the BKC composition in both dead-end and cross-flow filtration processes. The chitosan/BKC/PEG/CNT nanocomposite membranes have great potential in wastewater treatments for minimizing biofouling without reducing the water purification performance.