High Negative Charge Density Research Articles

Surface Charge Effects for the Hydrogen Evolution Reaction on Pt(111) Using a Modified Grand-Canonical Potential Kinetics Method.

Surface charges of catalysts have important influences on the thermodynamics and kinetics of electrochemical reactions. Herein, we develop a modified version of the grand-canonical potential kinetics (GCP-K) method based on density functional theory (DFT) calculations to explore the effect of surface charges on reaction thermodynamics and kinetics. Using the hydrogen evolution reaction (HER) on the Pt(111) surface as an example, we show how to track the change of surface charge in a reaction and how to analyze its influence on the kinetics. Grand-canonical calculations demonstrate that the optimum hydrogen adsorption energy on Pt under the standard hydrogen electrode condition (SHE) is around -0.2 eV, rather than 0 eV established under the canonical ensemble, due to the high density of surface negative charges. By separating the surface charges that can freely exchange with the external electron reservoir, we obtain a Tafel barrier that is in good agreement with the experimental result. During the Tafel reaction, the net electron inflow into the catalyst leads to a stabilization of canonical energy and a destabilization of the charge-dependent grand-canonical component. This study provides a practical method for obtaining accurate grand-canonical reaction energetics and analyzing the surface charge induced changes.

Inner Sphere Adsorption Mechanisms for Arsenate and Lead on Goethite: Theoretical Implications in Contaminated Soil Recovery

ABSTRACT Studies that do not separate the adsorption of toxic elements and compounds by outer and inner spheres can lose precision regarding the potential pollution of the water table. We sought to establish details of inner sphere adsorption (ISA) mechanisms of arsenate (H2AsO4 −) and lead (Pb2+) on synthetic goethite under different experimental conditions: pH 5.0 and 9.0; purified and unpurified samples; different contact times (24 and 240 hours). Goethite (Gt) was saturated separately with Pb and arsenate (noncompetitive adsorption) and the outer sphere forms was previously removed. The ISA of Pb (maximum of 67,682 mg kg−1) was more intense than that of As (maximum of 4,492 mg kg−1). ISA of arsenate on goethite was dependent on the contact time and was more intense in acidic soils due to the greater possibility of the occurrence of biprotonated ferrol groups (Fe-OH2 +0.5) on goethite surface. The high negative charge density at the surface of the H2AsO4 − tetrahedron favored its ISA. On the other hand, the lower the level of ISA, the greater binding energy on goethite or adsorption stability of H2AsO4 −. The highest ISA of Pb occurred at the highest pH, when the hydroxylated species PbOH+ preferentially binds to oxygen from the deprotonated ferrol group (Fe-O−1.5), without the need for ligand exchange. The proposal mechanisms of inner sphere adsorption allow better understanding of the recovery actions of contaminated soils rich in Fe and Al oxides.

Direct Evidence of Electric Double Layer (EDL) Repulsive Force Being Responsible for the Time-Dependent Behavior of Clay Gels in the Structural Rejuvenation Mode.

A strong EDL repulsive force is needed to accentuate the time-dependent behavior of charge and shape anisotropic clay gels at the stepdown shear rate. This force was strengthened by P2O74- adsorption, increasing the negative charge density of the clay particles. At the stepdown shear rate of 10 s-1, it is strong enough to disrupt the flow-aligned structure attained at 1000 s-1 and orient the particles to form more bonds. The resultant outcome is stepdown shear stress increasing with time until these structure disruption and bond formation processes reach an equilibrium state. The number of lower energy approach configurations (-ve face - +ve edge) for bonding is reduced by the strengthened EDL repulsive force, slowing the bonding process. The time to reach the equilibrium stepdown shear stress value increased initially and then decreased and became zero at a high negative charge density where the charge anisotropy of the particles no longer exists. The need of a sufficiently strong EDL repulsive force for the display of time-dependent behavior is true for all clay gels: Laponite, hectorite, NaMnt, sepiolite, and kaolin gels. The untreated NaMnt gel already displayed time-dependent behavior as its EDL repulsive force is sufficiently strong. The same EDL-control time-dependent behavior was obtained if pH was used to vary the negative charge density of the clay particles.

Structurally defined heparin octasaccharide domain for binding to SARS-CoV-2 Omicron BA.4/BA.5/BA.5.2 spike protein RBD

Heparin, a bio-molecule with the highest negative charge density, is pharmaceutically important to prevent SARS-CoV-2 infection due to its strong competitive binding to spike protein compared with cellular heparan sulfate, which was confirmed as a co-receptor for virus-host cell interaction. Hence, the refined structural characterization of heparin targeting viral protein-HS interaction was significant for developing antiviral pharmaceuticals. In our study, heparin oligomers (dp ≥ 4) were prepared using heparinase I. The affinity oligosaccharides binding to Omicron spike protein RBD were separated by affinity chromatography and size exclusion chromatography. HILIC-ESI-FTMS was used for chain mapping analysis. The basic building blocks were analyzed and the binding domain sequence was produced by Seq-GAG software and further measured by SAX chromatography. As results, heparin octasaccharide was found with significantly higher binding ability than hexasaccharide and tetrasaccharide, and the octasaccharide [ΔUA-GlcNS6S-GlcA-GlcNS6S-IdoA2S-GlcNS6S-IdoA2S-GlcNS6S] with 12 sulfate groups showed high binding to RBD. The mechanism of this structurally well-defined octasaccharide binding to RBD was further investigated by molecular docking. The affinity energy of optimal pose was −6.8 kcal/mol and the basic amino acid residues in RBD sequence (Arg403, Arg452, Arg493 and His505) were identified as the major contribution factor to interacting with sulfate/carboxyl groups on saccharide chain. Our study demonstrated that heparin oligosaccharide with well-defined structure could be potentially developed as anti-SARS-CoV-2 drugs.

Abstract A174: Antitumor activity of lipid nanoparticle-delivered anti-miR-21

Abstract Background: MicroRNAs (miRNAs) are small non-coding RNA molecules that play crucial roles in various biological processes, such as growth, development, aging, and apoptosis. Several studies have shown that miRNAs, including miR-21, can function as either oncogenes or tumor suppressor genes, influencing tumor initiation and progression. Aberrant expression of miR-21 has been observed in different cancer cells, indicating its significant involvement as an oncogenic miRNA in the development of various types of tumors. Antisense oligonucleotides (ASOs) have been identified as effective tools for downregulating target genes by either triggering RNase H endonuclease activity to cleave the ASO-target gene heteroduplex or by interfering with splicing and translation regulation of the target RNA sequence. ASOs have the potential to target not only mRNA but also oligonucleotides like miRNAs or small interfering RNAs (siRNAs), making them a promising approach for miRNA inhibition. However, the efficient delivery of freely circulating ASOs to the tumor microenvironment poses a challenge due to their high density of negative charges, impeding cell uptake. To address this issue, a novel lipid nanoparticle (LNP) platform called QTsome has been developed, which combines quaternary amine cationic lipids and tertiary amine ionizable lipids to enhance drug delivery. The utilization of a mixture of cationic and ionizable lipids in QTsome allows for optimal pH-dependent drug loading and release characteristics. In this study, our objective was to employ the QTsome system to deliver an ASO targeting miR-21 (AM-21) for potential tumor therapy. Methods: A total of 8E6 A549 cells were inoculated into mice, and when the tumor volume reached 100mm3, the mice were randomly divided into seven groups based on tumor volume, with each group consisting of five mice.On the day of grouping, drug administration was initiated with the following doses: 1mg/kg, every 3 days (Q3D); 2mg/kg, Q3D; 3mg/kg, Q3D; 4mg/kg, Q3D; 4mg/kg, every 4 days (Q4D); 4mg/kg, every 5 days (Q5D); 4mg/kg, every 7 days (Q7D). The drugs were administered a total of 5 times. Additionally, the A549/MC38 model was constructed using the same method. The antitumor activity of the drug and its therapeutic effect in combination with Erlotinib were evaluated in both the A549 CDX and MC38 syngeneic mouse models through intravenous injection, with a dose of 4mg/kg, Q3D. Results: The study revealed that the optimal dose for achieving the maximum antitumor effect was 4mg/kg, administered 3 times per day. In the A549 model, the tumor growth inhibition rates were 71.91%, 60.93%, and 80.44% for the AM-21/QTsome group, Erlotinib group, and the combination of AM-21/QTsome and Erlotinib group, respectively. In the MC38 mouse model, the tumor inhibition rate of AM-21/QTsome was 33.29%. Conclusion: These results emphasize the potential of miR-21 as a therapeutic target for cancer treatment, demonstrating that AM-21/QTsome holds great promise as a groundbreaking drug in this field. Citation Format: Jing Li, Qiaofang Ma, Xinyue Zhang, Xiaojie Chen, Jialiang Lin, Jun Bai, Fei Su, Xiaobin Zhao, Robert J. Lee, Yongsheng Yang. Antitumor activity of lipid nanoparticle-delivered anti-miR-21 [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A174.

A novel approach to supramolecular Aggregation-Induced emission using tetracationic tetraphenylethylene and sulfated β-Cyclodextrin

The combination of aggregation-induced emission-based luminogens (AIEgens) with supramolecular chemistry has gained significant attention due to its ability to produce intense emission even at low concentrations. In this study, we report a supramolecular arrangement characterized by aggregation-induced emission through the integration of tetracationic tetraphenylethylene with a macrocyclic polyanionic derivative of β-cyclodextrin. Despite the exploration of ionic derivatives of cyclodextrins in pharmaceutical and host–guest supramolecular chemistry, the phenomenon of supramolecular aggregation-induced emission based on non-covalent interactions between the ionic derivative of β-cyclodextrin and derivatives of tetraphenylethyelene, a class of AIEgens, has received limited investigation. Our work explores AIE shown by the allylimidazolium derivative of tetracationic tetraphenylethyelene (ALITPE) induced by complexation with polyanionic sulfated β-cyclodextrin (SCD). The effectiveness of the emission intensity of this supramolecular assembly based on AIE is confirmed by steady-state and time-resolved fluorescence measurements, which are supported by ground-state absorption measurements. We also investigate the effect of changes in external environment, such as temperature, pH, and ionic strength, on the supramolecular assembly. Moreover, the aggregation behavior of ALITPE with SCD is comparatively studied with neutral native β-cyclodextrin, highlighting the contribution of high negative charge density on the surface of SCD for efficient aggregation with ALITPE molecules. Additionally, Molecular Docking calculations are employed to provide insights into the aggregation behavior of ALITPE molecules induced by SCD. Overall, our findings demonstrate the potential applicability of the ALITPE/SCD supramolecular assembly as a potential fluorescent sensing probe for various biological applications.

Efficient Adsorption and Electrochemical Detection of Cd2+ with a Ternary MgZnFe-Layered Double Hydroxides Engineered Porous Biochar Composite.

Their unique layered structure, large specific surface area, good stability, high negative charge density between layers, and customizable composition give layered double hydroxides (LDHs) excellent adsorption and detection performance for heavy metal ions (HMIs). However, their easy aggregation and low electrical conductivity limit the practical application of untreated LDHs. In this work, a ternary MgZnFe-LDHs engineered porous biochar (MgZnFe-LDHs/PBC) heterojunction was proposed as a sensing and adsorption material for the effective detection and removal of Cd2+ from wastewater. The growth of MgZnFe-LDHs in the PBC pores not only reduces the accumulation of MgZnFe-LDHs, but also improves the electrical conductivity of the composite. The synergistic effect between MgZnFe-LDHs and PBC enables the composite to achieve a maximum adsorption capacity of up to 293.4 mg/g for Cd2+ in wastewater. Meanwhile, the MgZnFe-LDHs/PBC-based electrochemical sensor shows excellent detection performance for Cd2+, presenting a wide linear range (0.01 ng/L-1 mg/L), low detection limit (3.0 pg/L), good selectivity, and stability. The results indicate that MgZnFe-LDHs/PBC would be a potential material for detecting and removing Cd2+ from wastewater.

Tuning Multistep Biocatalysis through Enzyme and Cofactor Colocalization in Charged Porous Protein Macromolecular Frameworks.

Spatial organization of biocatalytic activities is crucial to organisms to efficiently process complex metabolism. Inspired by this mechanism, artificial scaffold structures are designed to harbor functionally coupled biocatalysts, resulting in acellular materials that can complete multistep reactions at high efficiency and low cost. Substrate channeling is an approach for efficiency enhancement of multistep reactions, but fast diffusion of small molecule intermediates poses a major challenge to achieve channeling in vitro. Here, we explore how multistep biocatalysis is affected, and can be modulated, by cofactor-enzyme colocalization within a synthetic bioinspired material. In this material, a heterogeneous protein macromolecular framework (PMF) acts as a porous host matrix for colocalization of two coupled enzymes and their small molecule cofactor, nicotinamide adenine dinucleotide (NAD). After formation of the PMF from a higher order assembly of P22 virus-like particles (VLPs), the enzymes were partitioned into the PMF by covalent attachment and presentation on the VLP exterior. Using a collective property of the PMF (i.e., high density of negative charges in the PMF), NAD molecules were partitioned into the framework via electrostatic interactions after being conjugated to a polycationic species. This effectively controlled the localization and diffusion of NAD, resulting in substrate channeling between the enzymes. Changing ionic strength modulates the PMF-NAD interactions, tuning two properties that impact the multistep efficiency oppositely in response to ionic strength: cofactor partitioning (colocalization with the enzymes) and cofactor mobility (translocation between the enzymes). Within the range tested, we observed a maximum of 5-fold increase or 75% decrease in multistep efficiency as compared to free enzymes in solution, which suggest both the colocalization and the mobility are critical for the multistep efficiency. This work demonstrates utility of collective behaviors, exhibited by hierarchical bioassemblies, in the construction of functional materials for enzyme cascades, which possess properties such as tunable multistep biocatalysis.

Nanosized Silk-Magnesium Complexes for Tissue Regeneration.

Metal ions provide multifunctional signals for cell and tissue functions, including regeneration. Inspired by metal-organic frameworks (MOFs), nanosized silk protein aggregates with a high negative charge density are used to form stable silk-magnesium ion complexes. Magnesium ions (Mg ions) are added directly to silk nanoparticle solutions, inducing gelation through the formation of silk-Mg coordination complexes. The Mg ions are released slowly from the nanoparticles through diffusion, with sustained release via tuning the degradation or dissolution of the nanosized silk aggregates. Studies in vitro reveal a dose-dependent influence of Mg ions on angiogenic and anti-inflammatory functions. Silk-Mg ion complexes in the form of hydrogels also stimulate tissue regeneration with a reduced formation of scar tissue in vivo, suggesting potential utility in tissue regeneration.

Assessment of Two Materials as Adsorbents for the Effective Removal and Further Pre-Concentration of Gallium from Aqueous Solutions: Mesoporous Carbon vs. Clinoptilolite

In this research, the adsorption of gallium onto natural zeolite (clinoptilolite) and two mesoporous-activated carbons were compared and evaluated. The clinoptilolite was treated with HCl (HCPL), while mesoporous-activated carbons (MCSG60A and MCO1) were synthesized by replica method, using sucrose as the carbon precursor and silica gel as the template. These carbonaceous materials showed large pore sizes and mesoporous surface, as well as a suitable surface chemistry for cation adsorption, which promotes a high negative charge density. On the other hand, zeolites have narrower pore sizes, which hinders the material diffusion inside the particle; however, its strength is their ion exchange capacity. Regarding the gallium kinetic studies, it is described by Pseudo-second order model for both sorts of adsorbents. MCO1 is the best carbonaceous adsorbent studied, with a capacity of 4.58 mg/g. As for zeolites, between the two zeolites studied, HCPL showed the best results, with a gallium adsorption capacity of 3.1 mg/g. The gallium adsorption mechanism onto MCO1 material is based on physisorption, while HCPL is mainly retained due to an ion-exchange process. Regarding the Giles classification, MCO1 isotherm described an H-4 pattern of high affinity and characteristic of multilayer adsorption. The Double-Langmuir model fits properly within these experimental results. In the case of zeolites, HCPL adsorption isotherm followed an L-2 pattern, typical of monolayer adsorption—the Sips model is the one that better describes the adsorption of gallium onto the zeolite.

Enhanced activity of Fe/Mn nanoparticles using a response surface methodology and mechanism for removing oxytetracycline and copper ion

As feed additives, oxytetracycline (OTC) and copper ion (Cu(II)) are often detected in livestock and poultry farming wastewater. To address this issue, firstly, the synthesis conditions of Fe/Mn nanoparticles (Fe/Mn NPs) were initially optimized using a response surface methodology (RSM) to yield highly active Fe/Mn NPs, where the application of RSM significantly increased the Fe/Mn NPs’ efficiency in removing co-contamination OTC and Cu(II),respectively, from 45.8 to 86.2% and 14.9–67.2%. Secondly, scanning electron microscope and Nitrogen adsorption-desorption isotherms results showed that Fe/Mn NPs were composed of elliptic particles between 20 and 40 nm, a specific surface area of 59.5 m2 g−1, and a mean pore diameter of 5.27 nm. Fourier infrared spectrometer and X-ray photoelectron spectroscopy analysis revealed that amino, carboxyl and hydroxyl functional groups existed on the surface. Zeta potential indicated that Fe/Mn NPs maintained a high negative charge density between pH 1 and 11. These surface properties possessed by the green synthesized Fe/Mn NPs resulted in high adsorption efficiency for co-contamination OTC and Cu(II). Based on this, a removal mechanism based on a combination of complex-bridging effect, pore-filling, hydrogen bonding, surface complexation, ion exchange and electrostatic attraction was proposed. Finally, the assessment of Fe/Mn NPs used in swine wastewater demonstrated that both 99.9% OTC and 55.6% Cu(II) were removed.

Reductionist insights into how chaperone charge influences RNA folding.

Non-coding RNAs are composed of modular secondary and tertiary structural units that themselves must form complex 3D structures for the entire RNA to fold and perform its biological function. However, the high density of negative charges associated with the phosphate backbone gives rise to substantial amounts of electrostatic repulsion, contributing to the large energetic barrier between unfolded and folded states. RNA folding chaperones (RFCs) are proteins that help lower this energy barrier by transiently interacting with RNA. Recent work has shown that some RFCs can function as macromolecular counterions for their RNA clients, thereby screening backbone electrostatic repulsion. However, the fundamental principles associated with how RFCs assist folding is largely unexplored. Here, we reduce RFCs to their smallest cationic constituents and then systematically “re-build” RFCs from these components (e.g., NH4+→ Lys→ polyK10→ RFC). We use single-molecule FRET to determine how these counterions influence both the relative population abundance and mean FRET efficiency of the folded and unfolded states of small model RNAs. From these studies, we have begun to determine aspects of RFCs that contribute to chaperoning RNA folding, such as net cationic charge and charge distribution. Here, we show that cationic amino acids (e.g., Lys and Arg) bind to RNA with apparent Kd values (appKd) on the order of 100 mM, which are comparable to those associated with their characteristic functional groups (e.g., ammonium and guanidinium). Further, increasing the net cationic charge of a counterion systematically decreases the appKd over several orders of magnitude. We also show a correlation between the decrease in appKd and a decrease in the folding free energy barrier. We then compare our observations of these polypeptide chaperones to the behavior of known RFCs (e.g., protamine, H1, and HCV nucleocapsid protein) with the small model RNAs.

Aggrecan and Hyaluronan: The Infamous Cartilage Polyelectrolytes - Then and Now.

Cartilages are unique in the family of connective tissues in that they contain a high concentration of the glycosaminoglycans, chondroitin sulfate and keratan sulfate attached to the core protein of the proteoglycan, aggrecan. Multiple aggrecan molecules are organized in the extracellular matrix via a domain-specific molecular interaction with hyaluronan and a link protein, and these high molecular weight aggregates are immobilized within the collagen and glycoprotein network. The high negative charge density of glycosaminoglycans provides hydrophilicity, high osmotic swelling pressure and conformational flexibility, which together function to absorb fluctuations in biomechanical stresses on cartilageduring movement of an articular joint. We have summarized information on the history and current knowledge obtained by biochemical and genetic approaches, on cell-mediated regulation of aggrecan metabolism and its role in skeletal development, growth as well as duringthe development of joint disease. In addition, we describe the pathways for hyaluronan metabolism, with particular focus on the role as a "metabolic rheostat" during chondrocyte responses in cartilage remodeling in growth and disease.Future advances in effective therapeutic targeting of cartilage loss during osteoarthriticdiseases of the joint as an organ as well as in cartilage tissue engineering would benefit from 'big data' approaches and bioinformatics, to uncover novel feed-forward and feed-back mechanisms for regulating transcription and translation of genes and their integration into cell-specific pathways.

Fabrication of Loose Nanofiltration Membranes with High Rejection Selectivity between Natural Organic Matter and Salts for Drinking Water Treatment.

Loose nanofiltration (LNF) membranes with a molecular weight cut-off (MWCO) of about 1000 Da and high surface negative charge density have great application potential for drinking water treatment pursuing high rejection selectivity between natural organic matter (NOM) and mineral salts. This study was conducted to exploit the novel method coupling non-solvent induced phase separation (NIPS) and interfacial polymerization (IP) for the preparation of high-performance LNF membranes. A number of LNF membranes were synthesized by varying the polyethersulfone (PES) and piperazine (PIP) concentrations in the cast solution for the PES support layer preparation. Results showed that these two conditions could greatly affect the membrane water permeance, MWCO and surface charge. One LNF membrane, with a water permeance as high as 23.0 ± 1.8 L/m2/h/bar, when used for the filtration of conventional process-treated natural water, demonstrated a rejection of NOM higher than 70% and a low rejection of mineral salts at about 20%. Both the mineral salts/NOM selectivity and permselectivity were superior to the currently available LNF membranes as far as the authors know. This study demonstrated the great advantage of the NIPS–IP method for the fabrication of LNF membranes, particularly for the advanced treatment of drinking water.

Loose nanofiltration membranes for selective rejection of natural organic matter and mineral salts in drinking water treatment

Loose nanofiltration (LNF) is a promising technology for advanced treatment of drinking water, primarily owing to the potentially high rejection of natural organic matter (NOM) and high passage of mineral salts, particularly divalent cations, along with the low operating pressure. This study was devoted to relating the performance with the properties of LNF membranes, and obtaining the membrane properties most suitable for drinking water treatment. Cluster analysis indicated that the commercially available LNF membranes would behave quite differently, mainly depending on the molecular weight cut-off (MWCO). By using a treated natural water as the feed, a best-performing membrane had a mineral salts rejection lower than 30% and an NOM rejection higher than 70%, with the membrane water permeance at ∼17 L/m2/h/bar. The LNF membranes with high mineral salts/NOM selectivity should have an MWCO of around 1000 Da, sufficiently uniform pore sizes, and high surface negative charge density. The rejection characteristics for mineral ions by LNF membranes were similar with the relatively dense conventional NF membranes, but with a lower rejection difference among the ions, manifesting less strong co-ion and counter-ion competition effects. The LNF membranes with an MWCO of ∼1000 Da could satisfactorily remove (>80%) disinfection byproduct precursors, with small-sized protein-like and other substances remaining in the permeate water. This study helps to understand the rejection characteristics and mechanisms of LNF membranes, which will benefit the synthesis of high-performance LNF membranes for drinking water treatment and other applications.

Three-Dimensional Quantitative Structure and Activity Relationship of Flavones on Their Hypochlorite Scavenging Capacity.

Flavonoids, a class of polyphenolic substances widely present in the plant realm, are considered as ideal hypochlorite scavengers. However, to our knowledge, little study has focused on the structure-activity relationship between flavonoids and hypochlorite scavenging capacity. Herein, we report for the first time the three-dimensional quantitative structure and activity relationship (3D-QSAR) combined with comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA). Four models derived from CoMFA and CoMSIA with different combinations of descriptors were built and compared; the CoMFA model, which included both steric and electrostatic fields, showed great potential (R2 = 0.989; Q2 = 0.818) in predictive quality according to both internal and external validation criteria. Additionally, the average local ionization energy (ALIE), electrostatic potential (ESP), and orbital weighted dual descriptor (OWDD) were determined to identify the key structural moiety for scavenging capacity of flavonoids against hypochlorite. The computational results indicated that hypochlorous acid (HClO) serves as an electrophile undergoing electrophilic addition to the C6 carbon, which has the highest negative charge density, which are influenced by the functional groups on the flavones. The DFT calculated mechanism revealed the catalytic role of water of mono- and di-chlorination reactions, characterized by low activation barriers, and the involvement of neutral, instead of high-energy carbocation, intermediates.

High zeolite loading mixed matrix membrane for effective removal of ammonia from surface water

While zeolite-based mixed matrix membrane (MMM) has been proven effective to remove the ammonia in the wastewater by adsorption, its adsorption capacity is limited by the low zeolite loading due to the need of a high concentration of polymer matrix to maintain the mechanical strength. To break the bottleneck, in this study we proposed a facile solvent evaporation method instead of conventional phase inversion method to prepare the zeolite-based MMMs. With this new preparation method, the loading of zeolite could reach up to ∼90wt.% while the MMM still maintained a good mechanical property. The zeolite-based MMM could treat 910 L·m−2 of feedwater before reaching the ammonia breakthrough point (0.5 mg-N·L−1) when treating the synthetic wastewater water. In addition, it showed a high rejection of turbidity and natural organic material (NOM) (∼90%), mainly due to its high negative surface charge density. When applied to treat real surface water, the membrane demonstrated a high normalized treatable capacity (∼900 L·m−2) with a high rejection to NOM (87.4%). Moreover, the MMM even showed a higher fouling resistance than the PVDF microfiltration membrane. Regeneration and cleaning with NaClO could efficiently recover the adsorption capacity and water flux of the MMM. After four cycles of operation, the MMM still maintained a high treatable capacity (850 L·m−2) with a high NOM rejection. This study provides a new strategy for the preparation of high-loading zeolite-based MMM for the effective removal of ammonia from surface water.

Preparation of acid-resistant nanofiltration membrane with dually charged separation layer for enhanced salts removal

Acid-resistant nanofiltration (NF) membrane with precise ionic separation performance and high permeability is imperative for acidic wastewater reuse. However, the trade-off between ions rejection and water permeability is especially serious for acid resistant NF membrane because of the uneven separation layer structure. Herein, we dissect the two-layer reverse interfacial polymerization (r-IP) process for the preparation of high-performance acid-resistant membrane by investigating monomer reactions and phase interface properties. Mixed organic monomers of 1,4-phenylene diisocyanate and trimesoyl chloride are used to react with the negatively charged aqueous monomer 3-aminobenzenesulfonamide to fabricate interlayer with high negative charge density, and then performs a secondary r-IP reaction with another positively charged aqueous monomer polyethyleneimine to construct a positively charged top layer. By changing the monomer compositions and concentrations, the relationship between monomer reaction and membrane performance is elucidated. Importantly, when aqueous additives of ethanol and glycerol are used to regulate the monomer diffusion coefficient, the membrane surface properties and permselectivity can be improved. Compared to the blank, the prepared membrane shows a 200% water permeability enhancement (2.6 Lm-2h-1bar−1) and desirable rejections of both Na2SO4 (97.7%) and MgCl2 (93.0%). Moreover, the smooth and hydrophilic surface endows the membrane with excellent anti-fouling performance at acidic pH. Benefiting from the robust structure of poly(amide-sulfonamide) and polyurea in the backbone, the membrane shows impressive acid resistance in 10 wt% H2SO4 and long-term stability in heavy metal removal. This work opens new pathways to prepare acid stable NF membrane with desirable permselectivity.

Enhanced Surface Passivation by Atomic Layer-Deposited Al2O3 for Ultraviolet-Sensitive Silicon Photomultipliers

This article describes a superior passivation of p-type (p^&#x002B;) Si surface by an Al₂O₃ thin film that is synthesized by plasma-assisted atomic layer deposition (ALD) for ultraviolet-sensitive silicon photomultipliers (SiPMs), compared to conventional SiO₂ and SiN_<i>x</i> passivation schemes. The superiority of Al₂O₃ passivation is due not only to a sufficiently low interface defect density, but also to a high density of built-in negative charges. A 7-nm thin Al₂O₃ film can yield an emitter saturation current density of &#x007E;8 fA/cm² on a high sheet resistance p^&#x002B; layer, compared to &#x007E;60 and &#x007E;1480 fA/cm² for thermal SiO₂ and SiN_<i>x</i> passivation. This superior surface passivation allows the photon-generated carriers to have higher probabilities to reach the high-field region to trigger an avalanche event. In addition, the Al₂O₃ thin film provides very low values of effective surface recombination velocity on low resistivity n- and p-type Si surfaces, which can lead to well-passivated surface features on the guard ring and trench isolation regions of SiPM. These demonstrate the potential of the Al₂O₃ thin film passivation to improve the quantum efficiency and thus photo-detection efficiency (PDE) of ultraviolet-sensitive SiPM with p^&#x002B;/n^&#x2212;/n/n^&#x002B; structure.

Preparation of Ligand Brush Nanocapsules for Robust Self-Controlled Antimicrobial Activity with Low Cytotoxicity at Target pH and Humidity.

This study prepared nanocapsules (NCs) with excellent self-controlled antimicrobial activity at pH 6–7 and humidity 45–100%, conditions in which most bacterial and fungal strains thrive. The nanocapsule substrate (NC@SiO2) was 676 nm in diameter, and the ligand-grafted capsule (NC@SiO2-g-MAA) was 888 nm. The large surface area and outer ligand brush of the NCs induced a rapid, self-controlled antibacterial response in the pH and humidity conditions needed for industrial and medical applications. Ligand-brush NCs containing an anionic antimicrobial drug had a rapid release effect because of the repellent electrostatic force and swelling properties of the ligand brushes. Controlled release of the drug was achieved at pH 6 and humidity of 45% and 100%. As many carboxylic acid groups are deprotonated into carboxylic acids at pH 5, the NC@SiO2-g-MAA had a high negative charge density. Carboxylic acid groups are anionized (–COO−) at pH 6 and above and push each other out of the capsule, expanding the outer shell as in a polymer brush to create the release behavior. The surface potential of the NC intermediate (NC@SiO2-MPS) was −23.45 [mV], and the potential of the capsule surface decreased to −36.4 [mV] when the MAA ligand brushes were grafted onto the surface of the capsule intermediate. In an antimicrobial experiment using Escherichia coli, a clear zone of 13–20 mm formed at pH 6, and the E. coli was eradicated completely at pH 6 and pH 7 when the humidity was 100%.