Immobilized enzymatic membrane surfaces for biocatalytic organics removal and fouling resistance.

This research reported on the immobilization of environmentally friendly enzymes, such as horseradish peroxidase (HRP) and laccase (L), along with the hydrophilic zwitterionic compound l-DOPA on nano-filtration (NF) membranes. This approach introduced biocatalytic membranes, leveraging combined effects between membranes and enzymes. The aim was to systematically assess the efficacy of the enzymatic modified membrane (HRP-NF) in degrading colors in the wastewater, as well as enhancing the membrane resistance toward organic fouling. The enzymatic immobilized membrane demonstrated 96.3 ± 1.8% to 96.6 ± 1.9% removal of colors, and 65.2 ± 1.3% to 67.2 ± 1.3% removal of TOC. This result was underpinned by the insights obtained from the radical scavenger coumarin, which was employed to trap and confirm the formation of PRs through the reaction of enzymes and H2O2. Furthermore, membranes modified with enzymes exhibited significantly improved antifouling properties. The HRP-NF membrane experienced an 8% decline in flux, while the co-immobilized HRP-L-NF membrane demonstrated as low as 6% flux decline, contributed by the synergistic effect of increased hydrophilicity and biocatalytic effects. These findings confirmed that the immobilized enzymatic surface has added function of degrading contaminants in addition to separation function of nanofiltration membrane. These l-DOPA-immobilized enzymatic membranes offered a promising hybrid biocatalytic membrane to eliminate dyes and mitigate membrane fouling, which can be applied in many industrial and domestic water and wastewater treatment.

Graphene Oxide-alginate Hydrogel for Drawing Water through an Osmotic Membrane.

We report the preparation and evaluation of graphene oxide (GO)-enhanced alginate hydrogels for drawing water across an osmotic desalination membrane. GO-incorporated calcium alginate hydrogels (GO-HG) and pure calcium alginate hydrogels (P-HG) were synthesized for this study. Environmental scanning electron microscopy, water contact angle, and water uptake tests showed both samples to be strongly hydrophilic. The synthesized hydrogels demonstrated the ability to successfully and continuously draw water through a selective osmotic membrane in experiments. This was driven by the surface energy gradient-induced negative pressure between the more hydrophilic hydrogel and less hydrophilic membrane surface. The GO-HG was found to draw 21.2% more water than the P-HG, owing to the flexible GO nanosheets, which can be easily incorporated into the hydrogel framework. The GO nanosheets not only offer more hydrophilic functional sites but also enhance the connectivity within the alginate hydrogel framework so as to enhance the water production performance. The average amount of water drawn through the membrane by the GO-HG and the P-HG is 23.4 ± 0.9 g and 19.3 ± 1.8 g, respectively. It was found that no external stimuli were needed as water flows through the hydrogel due to gravitational force. The GO-enhanced alginate hydrogel, combined with the osmotic membrane, is a promising surface energy gradient-driven functional material for water purification and desalination without applying external pressure.

Highly Permeable MoS2 Nanosheet Porous Membrane for Organic Matter Removal.

MoS2 nanosheets were synthesized by a bottom-up green chemical process where l-cysteine was used as a sulfur precursor. With specific concentrations, molar ratio of reactants, and pre-mixing conditions, MoS2 nanosheets of 200-300 nm in size and 4.2 nm in average thickness were successfully obtained. Porous membranes were then prepared by depositing the MoS2 nanosheet suspension on a 0.1 µm pore size poly(vinylidene difluoride) membrane filter in a multiple batch procedure. The membrane deposited with 12 batches of MoS2 nanosheets achieved 93.78% removal of bovine serum albumin. Acid red removal of 95.65% was also achieved after the second filtration pass. The porous MoS2 nanosheet membrane also demonstrated a high water flux of 182 ± 2.0 L/(m2 h). This result overcame the trade-off between selectivity and permeability faced by polymeric ultrafiltration membranes. The MoS2 nanosheets as building blocks formed not only intersheet slit pores with a narrow half-width to restrict the passage of organic molecules but also macro-channels allowing easy passage of water. The assembled MoS2 nanosheet membrane delivered promising separation of protein molecules and a high flux, attributing to its porous nanostructure, and could be a potential membrane for various water applications.

Stereotypes About Political Attitudes and Coalitions Among U.S. Racial Groups: Implications for Strategic Political Decision-Making.

What are people's expectations of interracial political coalitions? This research reveals expectations of flexible interracial coalitions stemming from how policies and racial groups are viewed in terms of perceived status and foreignness. For policies seen as changing societal status (e.g., welfare), people expected Black-Hispanic political coalitions and viewed Asian Americans as more likely to align with Whites than with other minorities. For policies seen as impacting American identity (e.g., immigration), people expected Asian-Hispanic coalitions and that Black Americans would align with Whites more than other minorities. Manipulating a novel group's alleged status and cultural assimilation influenced coalitional expectations, providing evidence of causality. These expectations appear to better reflect stereotypes than groups' actual average policy attitudes and voting behavior. Yet these beliefs may have implications for a diversifying electorate as White Americans strategically amplified the political voice of a racial group expected to agree with their personal preferences on stereotyped policies.

Diversifying neighborhoods and schools engender perceptions of foreign cultural threat among White Americans.

A nationally representative survey (N = 2,213) and five experiments (four preregistered, total N = 1,920) revealed that Whites perceived a foreign cultural threat, or a threat to their American culture and way of life, from the projected growth of racial and ethnic minority populations in their majority-White neighborhoods (Studies 1-5) and schools (Study 6). Whites perceived the increasing presence of Arab Americans, Latinos, and Asian Americans to pose an especially strong degree of perceived foreign cultural threat relative to Black Americans, who were perceived as more threatening than no demographic change. Furthermore, perceptions of foreign cultural threat predicted Whites' desires to move out above and beyond other established intergroup threats (e.g., realistic and symbolic threats). These findings highlight how Whites' concerns about losing their American culture and way of life as racial and ethnic minority groups enter majority-White neighborhoods and schools may contribute to the maintenance of racial segregation. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

2D MoS2 nanoplatelets for fouling resistant membrane surface.

2D Molybdenum disulfide (MoS2) nanoplatelets were synthesized via a green bottom-up strategy using non-toxic l-Cysteine as sulfur source. Thehydrophobic MoS2 nanoplatelets assisted by hydrophilic 3-(3, 4-dihydroxyphenyl)-l-alanine (l-DOPA) were coated on a thin film composite nanofiltration (TFC-NFG) membrane. The accelerated fouling experiments were conducted by usingbovine serum albumin (BSA) asmodel organic foulant,and MoS2 coated membrane demonstrated excellent resistance with almost no flux decline within first hour of filtration, whereas the uncoated membrane showed flux decline immediately from the beginning of the experiment. After 5-hour filtration, the flux reduced by only 26% for MoS2 coated membrane with a higher flux recovery rate of 85.4% after washing by de-ionized (DI) water, whereas 45% flux decline was observed for uncoated membrane with lower flux recovery of 68%.These antifouling effects attributed by MoS2coated membrane were underpinned by combined unique interfacial properties offered by 2D tri-atomic layered MoS2morphology including dispersive surface tension, reduced surface roughness, weaker MoS2-foulant interactive forces, and negatively charged surface. This research positively confirms the role of 2D MoS2 nanoplatelets as an anti-fouling coating on membranes and brings up more possibility for applying other nanomaterials in 2D family in water applications such as desalination and water treatment.

Electrostatically coupled SiO2 nanoparticles/poly (L-DOPA) antifouling coating on a nanofiltration membrane.

In this work, the fouling resistance of TFC (thin film composite) nanofiltration membranes have been enhanced using an electrostatically coupled SiO2 (silica dioxide) nanoparticles/poly(L-DOPA) (3-(3,4-dihydroxyphenyl)-l-alanine) antifouling coating. SiO2 nanoparticles were synthesized in different size ranges and combined with L-DOPA; and then coated as an anti-fouling layer on the membrane surface by recirculated deposition. Membranes were coated with S-NP (silica nanoparticles) in small (19.8 nm), medium (31.6 nm) and large (110.1 nm) sizes. The zwitterionic compound L-DOPA in the form of self-polymerized poly(L-DOPA) (PDOPA) helped with the attachment of the S-NP to the membrane surface. It was confirmed by AFM (atomic force microscopy) measurement that coating of membranes led to an increase in hydrophilicity and reduction in surface roughness, which in turn led to a 60% reduction in the adhesion force of the foulant on the membrane as compared to the neat membrane. The modified membranes experienced almost no flux decline during the filtration experimental period, whereas the unmodified membrane showed a sharp flux decline. The best coating conditions of silica nanoparticles resulting in enhanced anti-fouling properties were identified. The biofouling film formation on the membranes was evaluated quantitatively using the flow cytometry method. The results indicated that the modified membranes had 50% lower microbial population growth in terms of total event count compared to the neat membrane. Overall, the experimental results have confirmed that the coating of electrostatically coupled SiO2 nanoparticles and PDOPA (S-NP/PDOPA) on TFC-NF (nanofiltration) membrane surfaces is effective in improving the fouling resistance of the membranes. This result has positive implications for reducing membrane fouling in desalination and industrial wastewater treatment applications.

Interfacial Force-Assisted In-Situ Fabrication of Graphene Oxide Membrane for Desalination.

Graphene-based membranes have shown great potential application prospects in many fields, especially for water purification. Except for the current relatively low salt rejection rate, another main factor restricting application of such membranes is the lack of applicable preparation processes. In this work, a facile and cost-effective method was developed that can be used to in situ fabricate a graphene oxide (GO)-based membrane inside a filtration apparatus. Novel partial reduction and cross-linking was employed to adjust the surface properties and interlayer distance of GO membranes at the subnanometer range. A simple compacting process was applied to promote the integrity and compactness of the GO-based membranes by making full use of the interfacial tensions of gas/liquid/solid, which enables the in-situ fabrication. The as-prepared PrGO membranes show good water permeability (17.2-86.5 L m-2 h-1 MPa-1), reasonable desalination rates (27.7-62.6% for NaCl and 68.4-86.1% for Na2SO4), and good rejection rates of 92.3-96.8% for methyl orange. The method is appropriate for large-scale preparation and is theoretically not restricted by the shape or texture of the basement membrane, which represents another step forward in the fabrication of GO-based membranes toward wide-ranging applications.

Core/Shell Microstructure Induced Synergistic Effect for Efficient Water-Droplet Formation and Cloud-Seeding Application.

Cloud-seeding materials as a promising water-augmentation technology have drawn more attention recently. We designed and synthesized a type of core/shell NaCl/TiO2 (CSNT) particle with controlled particle size, which successfully adsorbed more water vapor (∼295 times at low relative humidity, 20% RH) than that of pure NaCl, deliquesced at a lower environmental RH of 62-66% than the hygroscopic point (hg.p., 75% RH) of NaCl, and formed larger water droplets ∼6-10 times its original measured size area, whereas the pure NaCl still remained as a crystal at the same conditions. The enhanced performance was attributed to the synergistic effect of the hydrophilic TiO2 shell and hygroscopic NaCl core microstructure, which attracted a large amount of water vapor and turned it into a liquid faster. Moreover, the critical particle size of the CSNT particles (0.4-10 µm) as cloud-seeding materials was predicted via the classical Kelvin equation based on their surface hydrophilicity. Finally, the benefits of CSNT particles for cloud-seeding applications were determined visually through in situ observation under an environmental scanning electron microscope on the microscale and cloud chamber experiments on the macroscale, respectively. These excellent and consistent performances positively confirmed that CSNT particles could be promising cloud-seeding materials.

A Novel Fabrication Approach for Multifunctional Graphene-based Thin Film Nano-composite Membranes with Enhanced Desalination and Antibacterial Characteristics.

A practical fabrication technique is presented to tackle the trade-off between the water flux and salt rejection of thin film composite (TFC) reverse osmosis (RO) membranes through controlled creation of a thinner active selective polyamide (PA) layer. The new thin film nano-composite (TFNC) RO membranes were synthesized with multifunctional poly tannic acid-functionalized graphene oxide nanosheets (pTA-f-GO) embedded in its PA thin active layer, which is produced through interfacial polymerization. The incorporation of pTA-f-GOL into the fabricated TFNC membranes resulted in a thinner PA layer with lower roughness and higher hydrophilicity compared to pristine membrane. These properties enhanced both the membrane water flux (improved by 40%) and salt rejection (increased by 8%) of the TFNC membrane. Furthermore, the incorporation of biocidal pTA-f-GO nanosheets into the PA active layer contributed to improving the antibacterial properties by 80%, compared to pristine membrane. The fabrication of the pTA-f-GO nanosheets embedded in the PA layer presented in this study is a very practical, scalable and generic process that can potentially be applied in different types of separation membranes resulting in less energy consumption, increased cost-efficiency and improved performance.

A Short Review of Membrane Fouling in Forward Osmosis Processes.

Interest in forward osmosis (FO) research has rapidly increased in the last decade due to problems of water and energy scarcity. FO processes have been used in many applications, including wastewater reclamation, desalination, energy production, fertigation, and food and pharmaceutical processing. However, the inherent disadvantages of FO, such as lower permeate water flux compared to pressure driven membrane processes, concentration polarisation (CP), reverse salt diffusion, the energy consumption of draw solution recovery and issues of membrane fouling have restricted its industrial applications. This paper focuses on the fouling phenomena of FO processes in different areas, including organic, inorganic and biological categories, for better understanding of this long-standing issue in membrane processes. Furthermore, membrane fouling monitoring and mitigation strategies are reviewed.

Insights on Tuning the Nanostructure of rGO Laminate Membranes for Low Pressure Osmosis Process.

In this research, rGO laminates were prepared by a controlled partial reduction step, aimed to avoid aggregation and tune the interlayer spacing (d) between the rGO layers. The mild reducing agent vitamin C (l-AA) and cross-linker poly(carboxylic acid)s were used to improve the stability of the assembled rGO laminate membranes. AFM was used for the first time to further investigate the statistical size distribution of spacing between rGO layers. Topographical images of the edges of the rGO layers were obtained with an AFM instrument; interlayer spacing profiles were extracted, and then the data was plotted and fitted with Gaussian curves. We confirmed that the differently sized spacing coexisted, and their size distribution was affected by the reduction degree of rGO. At greater levels of reduction, more interlayer spacing was formed in the smaller size range, while few large gaps were still present. The obtained rGO laminate composite membranes were evaluated in a low pressure osmosis process such as forward osmosis (FO). The water permeation was higher in the rGO membrane prepared with a medium reduction degree (1.2-R) than the sample prepared by higher reduction degree (2.0-R) due to well-balanced nanochannels in hydrophilic regions and hydrophobic walls for fast transport of water molecules. The solute flux of the FO membrane was inversely correlated to the reduction degree. These findings helped in developing future strategies for designing high water flux and low reverse solute flux rGO membranes that are ideal for an FO process.

Two axes of subordination: A new model of racial position.

Theories of race relations have been shaped by the concept of a racial hierarchy along which Whites are the most advantaged and African Americans the most disadvantaged. However, the recent precipitated growth of Latinos and Asian Americans in the United States underscores the need for a framework that integrates more groups. The current work proposes that racial and ethnic minority groups are disadvantaged along 2 distinct dimensions of perceived inferiority and perceived cultural foreignness, such that the 4 largest groups in the United States are located in 4 discrete quadrants: Whites are perceived and treated as superior and American; African Americans as inferior and relatively American compared with Latinos and Asian Americans; Latinos as inferior and foreign; and Asian Americans as foreign and relatively superior compared to African Americans and Latinos. Support for this Racial Position Model is first obtained from targets' perspectives. Different groups experience distinct patterns of racial prejudice that are predicted by their 2-dimensional group positions (Studies 1 and 2). From perceivers' perspectives, these group positions are reflected in the content of racial stereotypes (Study 3), and are well-known and consensually recognized (Study 4). Implications of this new model for studying contemporary race relations (e.g., prejudice, threat, and interminority dynamics) are discussed. (PsycINFO Database Record

Single-Step Assembly of Multifunctional Poly(tannic acid)-Graphene Oxide Coating To Reduce Biofouling of Forward Osmosis Membranes.

Graphene oxide (GO) nanosheets have antibacterial properties that have been exploited as a biocidal agent used on desalination membrane surfaces in recent research. Nonetheless, improved strategies for efficient and stable attachment of GO nanosheets onto the membrane surface are still required for this idea to be commercially viable. To address this challenge, we adopted a novel, single-step surface modification approach using tannic acid cross-linked with polyethylene imine as a versatile platform to immobilize GO nanosheets to the surface of polyamide thin film composite forward osmosis (FO) membranes. An experimental design based on Taguchi's statistical method was applied to optimize the FO processing conditions in terms of water and reverse solute fluxes. Modified membranes were analyzed using water contact angle, adenosine triphosphate bioluminescence, total organic carbon, Fourier transform infrared spectroscopy, ζ potential, X-ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy. These results show that membranes were modified with a nanoscale (<10 nm), smooth, hydrophilic coating that, compared to pristine membranes, improved filtration and significantly mitigated biofouling by 33% due to its extraordinary, synergistic antibacterial properties (99.9%).

Fine-Tuning the Surface of Forward Osmosis Membranes via Grafting Graphene Oxide: Performance Patterns and Biofouling Propensity.

Graphene oxide (GO) nanosheets were attached to the polyamide selective layer of thin film composite (TFC) forward osmosis (FO) membranes through a poly L-Lysine (PLL) intermediary using either layer-by-layer or hybrid (H) grafting strategies. Fourier transform infrared spectroscopy, zeta potential, and thermogravimetric analysis confirmed the successful attachment of GO/PLL, the surface modification enhancing both the hydrophilicity and smoothness of the membrane's surface demonstrated by water contact angle, atomic force microscopy, and transmission electron microscopy. The biofouling resistance of the FO membranes determined using an adenosine triphosphate bioluminescence test showed a 99% reduction in surviving bacteria for GO/PLL-H modified membranes compared to pristine membrane. This antibiofouling property of the GO/PLL-H modified membrane was reflected in reduced flux decline compared to all other samples when filtering brackish water under biofouling conditions. Further, the high density and tightly bound GO nanosheets using the hybrid modification reduced the reverse solute flux compared to the pristine, which reflects improved membrane selectivity. These results illustrate that the GO/PLL-H modification is a valuable addition to improve the performance of FO TFC membranes.

Fabrication and characterisation of an electrospun tubular 3D scaffold platform of poly(vinylidene fluoride-co-hexafluoropropylene) for small-diameter blood vessel application.

In this research, nanofibrous 3D tubular (~4-mm-diameter tube) scaffolds of poly (vinylidene fluoride-co-hexafluoropropylene) were fabricated by electrospinning. The role of surface charge in the success of these scaffolds for potential small-diameter artificial vascular grafts has been investigated using streaming potential study. Prior to endothelial cell culture, surface properties such as wettability and the surface charge of these tubular scaffolds were evaluated using unmodified and fibrinogen-adsorbed surfaces to understand their interaction with surrounding environment. The tubular scaffolds constructed using electrospinning show similar mechanical properties such as tensile strength and elastic modulus as those of native vessels. Whilst endothelial cell proliferation on unmodified tubes, as analysed by scanning electron microscopy, was found to be moderate, a simple process of dynamic fibrinogen adsorption was seen to enhance the endothelialisation of these tubular grafts. The high negative zeta potential values, high strength, robustness and structural reliability of the scaffolds represent them to be promising biomaterials for vascular graft applications.

Assessing the effect of surface modification of polyamide RO membrane by l-DOPA on the short range physiochemical interactions with biopolymer fouling on the membrane.

Theoretical predictions of interaction energies for membrane-biopolymer foulant pairs were used to compare the fouling tendencies of a virgin commercial polyamide reverse osmosis (RO) membrane with a amino acid 3-(3,4-dihydroxyphenyl)-l-alanine (l-DOPA) coated RO membrane. Lifshitz-van der Waals (LW) and Lewis acid-base (AB) surface tension components of the membranes were determined based on contact angle results using the van Oss approach. From these values, the LW and AB components of the free energy of adhesion between membrane and foulants were calculated. Electrostatic (EL) double layer interaction energies between the membrane and foulants were also estimated using the measured surface charge data of the membranes and fouling agents. Bovine serum albumin (BSA) and alginic acid sodium salt (alginate) were used as model biopolymers causing membrane fouling. Based on the calculated adhesion free energies, acid-base interactions were found to have the strongest impact on the adhesion of both BSA and alginate to the either membranes surfaces. It was found that l-DOPA modification has significantly lowered acid-base interaction affinity toward the adhesion of both foulants studied. On the basis of calculated free energies of adhesion, lower fouling tendency of the l-DOPA modified membrane was expected. The accelerated fouling tests indicated a lower flux decline rate for the modified membrane and confirmed the results obtained from theory.

Facile fouling resistant surface modification of microfiltration cellulose acetate membranes by using amino acid L-DOPA.

A major obstacle in the widespread application of microfiltration membranes in the wet separation processes such as wastewater treatment is the decline of permeates flux as a result of fouling. This study reports on the surface modification of cellulose acetate (CA) microfiltration membrane with amino acid L-3,4-dihydroxy-phenylalanine (L-DOPA) to improve fouling resistance of the membrane. The membrane surface was characterised using Fourier transform infrared spectroscopy (FTIR), water contact angle and zeta potential measurement. Porosity measurement showed a slight decrease in membrane porosity due to coating. Static adsorption experiments revealed an improved resistance of the modified membranes towards the adhesion of bovine serum albumin (BSA) as the model foulant. Dead end membrane filtration tests exhibited that the fouling resistance of the modified membranes was improved. However, the effect of the modification depended on the foulant solution concentration. It is concluded that L-DOPA modification is a convenient and non-destructive approach to enable low-BSA adhesion surface modification of CA microfiltration membranes. Nevertheless, the extent of fouling resistance improvement depends on the foulant concentration.

Preparation and capacitance properties of graphene/NiAl layered double-hydroxide nanocomposite.

Graphene/NiAl layered double-hydroxide (LDH) composite with high capacitive properties has been prepared in a friendly one-step process. It is found that NiAl-LDH is formed in the addition of precipitator agent (NaOH and NaNO3) by hydrothermal method, at the same time graphene oxide (GO) is reduced to graphene. The morphology and structure of the obtained material are examined by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), transmission electron microscope (TEM), and scanning electron microscope (SEM) techniques. It is revealed that the NiAl-LDH disperses well on the surface of graphene and the formation of NiAl-LDH nanoparticles is beneficial to the peeling of graphene (RGO). More importantly, the addition of NiAl-LDH to graphene endows the materials with desirable specific surface areas and higher porosity. These structural advantages result in higher specific capacitance compared with pristine graphene. Electrochemical property investigations show that the graphene/NiAl-LDH had a higher specific capacitance than graphene.