Integrated Catalyst-Substrate Electrodes for Electrochemical Water Splitting: A Review on Dimensional Engineering Strategy.

Water splitting (or, water electrolysis) is considered as a promising approach to produce green hydrogen and relieve the ever-increasing energy consumption as well as the accompanied environmental impact. Development of high-efficiency, low-cost practical water-splitting systems demands elegant design and fabrication of catalyst-loaded electrodes with both high activity and long-life time. To this end, dimensional engineering strategies, which effectively tune the microstructure and activity of electrodes as well as the electrochemical kinetics, play an important role and have been extensively reported over the past years. Here, a type of most investigated electrode configurations is reviewed, combining particulate catalysts with 3D porous substrates (aerogels, metal foams, hydrogels, etc.), which offer special advantages in the field of water splitting. It is analyzed the design principles, structural and interfacial characteristics, and performance of particle-3D substrate electrode systems including overpotential, cycle life, and the underlying mechanism toward improved catalytic properties. In particular, it is also categorized the catalysts as different dimensional particles, and show the importance of building hybrid composite electrodes by dimensional control and engineering. Finally, present challenges and possible research directions toward low-cost high-efficiency water splitting and hydrogen production is discussed.

Extracellular Amyloid ß-protein (1-42) Oligomers Anchor Brain Cells and Make them inert as an Unconventional Integrin-Coupled Ligand.

This study aimed to investigate the effect of extracellular Aß42 on neural cell migration, and the possible molecular mechanisms. Extracellular Aß42 monomers did not negatively affect the motility of neural cells; however, they could promote cell migration from toxic extracellular Aß42 oligomers. Contrastingly, extracellular Aß42 aggregates, especially Aß42 oligomers, significantly decreased neural cell migration while reducing their survival. Further, their soluble and deposited states showed different effects in causing the neural cells to become inert (incapable of moving). These findings were consistent with that of binding of Aß42 oligomers to the plasma membrane or integrin receptors of the inert cells. By combining the protection of cell migratory capability by anti-oligomeric Aß42 scFv antibody with the information obtained from our docking model of the Aß42 trimer and integrin molecule, our findings suggest that extracellular Aß42 aggregates disrupt the function of integrins mainly through the RHDS motif of Aß42 chain, which eventually causes neural cells to become inert. Thus, we propose an "anchor" opinion, where Aß42 aggregates in the ECM serve as the adverse "anchors" in the brain for anchoring neurons and for making neural cells inert, which causes their dysfunction. The neural cells with damaged motility could be restored or repaired if these anchoring effects of extracellular Aß42 aggregates on the neural cells were severed or reduced, even if the "anchors" themselves were not completely eliminated. Medicines targeting soluble and deposited anchors of Aß42 aggregates could be developed into effective treatments for Alzheimer disease.

Electrocatalytic activity of a ß-Sb two-dimensional surface for the hydrogen evolution reaction.

Hydrogen energy is considered to be one of the most promising clean energy sources. The development of highly active, low-cost catalysts, and good stability is essential for hydrogen production. Herein, the catalytic activity of a two-dimensional ß-Sb surface doped with main-group elements (N, P, As, O, S, Se, and Te) for the hydrogen evolution reaction (HER) was investigated by density functional theory, and the catalytic activity of the ß-Sb monolayer can be improved by doping group VIA atoms. The catalytic activity of Se@Sb and O@Sb structures at the doping concentration of 2.78% and the S@Sb structure at the doping concentration of 5.56% may be as good as the Pt(111) surface, while keeping energetically stable. In addition, the catalytic performance could be optimized under biaxial strain. Further analysis suggests that the activity is caused by hole states in the lone pair electrons, which are created by the group VIA atom dopants. And our work also reveals that the density of states at the Fermi level could be an appropriate descriptor of the hydrogenation Gibbs free energy. This work not only proposes a novel non-platinum HER catalyst but also provides physical foundations for further application on antimonene-based catalysts.

Conformational Essentials Responsible for Neurotoxicity of Aß42 Aggregates Revealed by Antibodies against Oligomeric Aß42.

Soluble aggregation of amyloid ß-peptide 1-42 (Aß42) and deposition of Aß42 aggregates are the initial pathological hallmarks of Alzheimer's disease (AD). The bipolar nature of Aß42 molecule results in its ability to assemble into distinct oligomers and higher aggregates, which may drive some of the phenotypic heterogeneity observed in AD. Agents targeting Aß42 or its aggregates, such as anti-Aß42 antibodies, can inhibit the aggregation of Aß42 and toxicity of Aß42 aggregates to neural cells to a certain extent. However, the epitope specificity of an antibody affects its binding affinity for different Aß42 species. Different antibodies target different sites on Aß42 and thus elicit different neuroprotective or cytoprotective effects. In the present review, we summarize significant information reflected by anti-Aß42 antibodies in different immunotherapies and propose an overview of the structure (conformation)-toxicity relationship of Aß42 aggregates. This review aimed to provide a reference for the directional design of antibodies against the most pathogenic conformation of Aß42 aggregates.

Highly Sensitive, Selective, Flexible and Scalable Room-Temperature NO2 Gas Sensor Based on Hollow SnO2/ZnO Nanofibers.

Semiconducting metal oxides can detect low concentrations of NO2 and other toxic gases, which have been widely investigated in the field of gas sensors. However, most studies on the gas sensing properties of these materials are carried out at high temperatures. In this work, Hollow SnO2 nanofibers were successfully synthesized by electrospinning and calcination, followed by surface modification using ZnO to improve the sensitivity of the SnO2 nanofibers sensor to NO2 gas. The gas sensing behavior of SnO2/ZnO sensors was then investigated at room temperature (~20 °C). The results showed that SnO2/ZnO nanocomposites exhibited high sensitivity and selectivity to 0.5 ppm of NO2 gas with a response value of 336%, which was much higher than that of pure SnO2 (13%). In addition to the increase in the specific surface area of SnO2/ZnO-3 compared with pure SnO2, it also had a positive impact on the detection sensitivity. This increase was attributed to the heterojunction effect and the selective NO2 physisorption sensing mechanism of SnO2/ZnO nanocomposites. In addition, patterned electrodes of silver paste were printed on different flexible substrates, such as paper, polyethylene terephthalate and polydimethylsiloxane using a facile screen-printing process. Silver electrodes were integrated with SnO2/ZnO into a flexible wearable sensor array, which could detect 0.1 ppm NO2 gas after 10,000 bending cycles. The findings of this study therefore open a general approach for the fabrication of flexible devices for gas detection applications.

The crucial role of bacterial laccases in the bioremediation of petroleum hydrocarbons.

Laccases (EC 1.10.3.2) are a class of metallo-oxidases found in a variety of fungi, plants, and bacteria as well as in certain insects. They can oxidize a wide variety of organic compounds and can be widely applied in many fields, especially in the field of biodegradation and detoxification of environmental pollutants. The practical efficacy of laccases depends on their ability to capture the target substance as well as their catalytic activity, which is related to their catalytic center, substrate selectivity, and substrate tolerance. Over the past few decades, many laccases have been identified in plants and fungi. Concurrently, bacterial laccases have received increasing attention because of their high thermostability and high tolerance to organic compounds. The aim of this review is to summarize the role of bacterial laccases in the bioremediation of petroleum hydrocarbons and to outline the correlation between the molecular structure of the mononuclear T1 Cu center of bacterial laccases and their substrate preference.

Study of pre-treatment of quinoline in aqueous solution using activated carbon made from low-cost agricultural waste (walnut shells) modified with ammonium persulfate.

Activated carbon made from agricultural waste (walnut shells) was investigated as a suitable adsorbent for effectively removing quinoline from industrial wastewater. The activated carbon was treated with phosphoric acid and oxidized by ammonium persulfate and its ability to adsorb pyridine and quinoline in aqueous solution was investigated. Kinetic parameters for the adsorption process were determined through pseudo-first-order and pseudo-second-order kinetic models and intraparticle diffusion models. Equilibrium experiments and adsorption isotherms were analyzed using Langmuir and Freundlich adsorption isotherms. After reaching equilibrium, the activated carbon adsorbed quinoline in preference to pyridine: the equilibrium adsorptions from individual aqueous solutions (200 µL L-1) of quinoline and pyridine were 166.907 mg g-1 and 72.165 mg g-1, respectively. Thermodynamic studies of quinoline adsorption were conducted at different temperatures and indicated that quinoline adsorption was an endothermic and spontaneous process. The column-adsorption of quinoline and pyridine was consistent with the Thomas model and the Yoon-Nelson model. The removal efficiency of quinoline reached more than 97% for a velocity of 6 mL min-1 at the initial adsorption stage.

The second conserved motif in bacterial laccase regulates catalysis and robustness.

Laccase (EC1.10.3.2), an oxidase that binds multiple copper ions, is heterogeneous in different species, implying diversity in its function. Nevertheless, the four copper-binding motifs are conserved in most laccases, especially bacterial forms. In order to exploit laccase more widely and more effectively in industrial processes, we investigated the regulatory effects, if any, of the second conserved copper-binding motif in the bacterial laccases CAR2 and CAHH1. The data suggested that three critical amino acid residues His155, His157, and Thr/Ala158 in this motif strongly regulated laccase's catalysis, substrate range, and robustness. Indeed, these residues were essential for laccase's catalytic activity. The data also suggested that laccase's catalytic efficiency and activity are not completely consistent with its stability, and that the enzyme might have evolved naturally to its favor stability. This study provides important insights into the second conserved copper-binding motif and defines some of the previously undefined amino acid residues in this conserved motif and their significances.

High-loading Fe2O3/SWNT composite films for lithium-ion battery applications.

Single-walled carbon nanotube (SWNT) films are a potential candidate as porous conductive electrodes for energy conversion and storage; tailoring the loading and distribution of active materials grafted on SWNTs is critical for achieving maximum performance. Here, we show that as-synthesized SWNT samples containing residual Fe catalyst can be directly converted to Fe2O3/SWNT composite films by thermal annealing in air. The mass loading of Fe2O3 nanoparticles is tunable from 63 wt% up to 96 wt%, depending on the annealing temperature (from 450 °C to 600 °C), while maintaining the porous network structure. Interconnected SWNT networks containing high-loading active oxides lead to synergistic effect as an anode material for lithium ion batteries. The performance is improved consistently with increasing Fe2O3 loading. As a result, our Fe2O3/SWNT composite films exhibit a high reversible capacity (1007.1 mA h g-1 at a current density of 200 mA g-1), excellent rate capability (384.9 mA h g-1 at 5 A g-1) and stable cycling performance with the discharge capacity up to 567.1 mA h g-1 after 600 cycles at 2 A g-1. The high-loading Fe2O3/SWNT composite films have potential applications as nanostructured electrodes for various energy devices such as supercapacitors and Li-ion batteries.

Meter-Long Spiral Carbon Nanotube Fibers Show Ultrauniformity and Flexibility.

Conventional straight fibers spun from carbon nanotubes have rather limited deformability; creating a spiral structure holds the promise to break this shape restriction and enhance structural flexibility. Here, we report up to one meter-length threads containing purely single-walled nanotubes twisted into spiral loops (about 1.3 × 10(5) loops per meter) with tunable fiber diameters and electrical conductivity. Because of significant increase of the loop number and long-range homogeneity, the fibers display many unique properties (e.g., self-shrinking and forming extremely entangled structure, fast stretching with great resilience, large-degree axial and lateral deflection, and excellent fatigue resistance) that are difficult to achieve in straight yarns or short helical segments. They also have potential applications as macroscopic fiber-shaped temperature sensors and deformable gas sensors. Our long spiral fibers may be configured into versatile structures such as nanotextiles for developing wearable electronics and multifunctional fabrics.

Growth of GaN micro/nanolaser arrays by chemical vapor deposition.

Optically pumped ultraviolet lasing at room temperature based on GaN microwire arrays with Fabry-Perot cavities is demonstrated. GaN microwires have been grown perpendicularly on c-GaN/sapphire substrates through simple catalyst-free chemical vapor deposition. The GaN microwires are [0001] oriented single-crystal structures with hexagonal cross sections, each with a diameter of ∼1 µm and a length of ∼15 µm. A possible growth mechanism of the vertical GaN microwire arrays is proposed. Furthermore, we report room-temperature lasing in optically pumped GaN microwire arrays based on the Fabry-Perot cavity. Photoluminescence spectra exhibit lasing typically at 372 nm with an excitation threshold of 410 kW cm(-2). The result indicates that these aligned GaN microwire arrays may offer promising prospects for ultraviolet-emitting micro/nanodevices.

Reverse osmosis desalination of chitosan cross-linked graphene oxide/titania hybrid lamellar membranes.

With excellent mass transport properties, graphene oxide (GO)-based lamellar membranes are believed to have great potential in water desalination. In order to quantify whether GO-based membranes are indeed suitable for reverse osmosis (RO) desalination, three sub-micrometer thick GO-based lamellar membranes: GO-only, reduced GO (RGO)/titania (TO) nanosheets and RGO/TO/chitosan (CTS) are prepared, and their RO desalination performances are evaluated in a home-made RO test apparatus. The photoreduction of GO by TO improves the salt rejection, which increases slowly with the membrane thickness. The RGO/TO/CTS hybrid membranes exhibit higher rejection rates of only about 30% (greater than threefold improvement compared with a GO-only membrane) which is still inferior compared to other commercial RO membranes. The low rejection rates mainly arise from the pressure-induced weakening of the ion-GO interlayer interactions. Despite the advantages of simple, low-cost preparation, high permeability and selectivity of GO-based lamellar membranes, as the current desalination performances are not high enough to afford practical application, there still remains a great challenge to realize high performance separation membranes for water desalination applications.

SERS investigation of ciprofloxacin drug molecules on TiO2 nanoparticles.

In this paper, TiO2 nanoparticles (NPs) with different crystallinity served as SERS-active substrates for SERS detection of ciprofloxacin (CIP) drug molecules for the first time. CIP is close to the surface of the TiO2 substrate through the carboxyl group. The mutual SERS enhancement behaviors between CIP molecules and TiO2 NPs were discovered, which are attributed to the contribution of the TiO2-to-molecule charge-transfer mechanism. The crystallinity of TiO2 NPs, the pH value of adsorption solution and the adsorption time have significant influences on the interaction and the SERS behavior between CIP and TiO2. When the calcination temperature of TiO2 NPs is 450 °C, the pH value of adsorption solution is 6 and the adsorption time is 9 h, the CIP molecules on TiO2 NPs exhibit the largest SERS enhancement.

Trp358 is a key residue for the multiple catalytic activities of multifunctional amylase OPMA-N from Bacillus sp. ZW2531-1.

The oligosaccharide-producing multifunctional amylase-N (OPMA-N) is a novel multifunctional amylase and exhibits both hydrolytic and transglycosyl activities, but the molecular mechanism for its multiple catalytic activities is still unknown. Our research investigates the possible catalytic roles of a Trp residue in OPMA-N (Trp358) which is not only near the catalytic site Glu356 but also highly conserved in glycoside hydrolase subfamily 20 (the neopullulanase subfamily). Site-directed mutageneses at this site reveal that the size and charge of the occupying amino acid directly affect substrate binding, orientation of other crucial catalytic residues, the catalytic specificity, the oligomer formation, as well as the thermal stability of the enzyme. These findings may be useful in elucidating the different mechanisms of the multiple catalytic activities of multifunctional amylase OPMA-N and hence for developing an improved multifunctional amylase for the preparation of isomaltooligosaccharides.

Distinct functional diversity of branched oligosaccharides as chaperones and inhibitory-binding partners of amyloid beta-protein and its aggregates.

Aggregation and deposition of amyloid beta-protein 1-42 (Aß42) in the brain, primarily owing to hydrophobic interactions between Aß42 chains, is a common pathology in all forms of Alzheimer's disease (AD). Hydrophilic oligosaccharides are widely present in the extracellular matrix and on the cytoplasmic membrane. To determine if oligosaccharides bind to Aß42 or its aggregates and consequently affect their aggregation and cellular function, this study examined the interaction of typical functional oligosaccharides with Aß42 or its aggregates. Isomaltooligosaccharides (IMOs), particularly isomaltotriose, panose, and isomaltotetraose, functioned as molecular chaperones for Aß42 by binding directly to Aß42, preserving Aß42's active conformation and cytotrophic activity. Oral IMOs reduced total plasma Aß level and indirectly caused a slight reduction in the load of Aß42 spots/plaques in the brain of AD model mice (male). Another branched oligosaccharide, bianntennary core pentasaccharide (BCP), had a relatively high binding specificity for Aß42 oligomers (Aß42O) and acted as an antagonistic binding partner for Aß42O. Free BCP effectively blocked/prevented further assembly of Aß42O and their toxicity to neural and vascular endothelial cell lines. Since BCP is also a signaling component of membrane targets (glycolipids, glycoproteins or receptors), it seemed that BCP had two opposing effects on the binding of Aß42O to target cells. This study's findings suggest that these branched oligosaccharides may be potential candidates for blocking or preventing Aß42 aggregation and Aß42O cytotoxicity/neurotoxicity, respectively, and that IMO-like or free BCP-like oligosaccharide deficiencies in the brain may be one of the underlying mechanisms for Aß42 aggregation and Aß42O cytotoxicity.

Mechanistic insights into the conversion of flavin adenine dinucleotide (FAD) to 8-formyl FAD in formate oxidase: a combined experimental and in-silico study.

Formate oxidase (FOx), which contains 8-formyl flavin adenine dinucleotide (FAD), exhibits a distinct advantage in utilizing ambient oxygen molecules for the oxidation of formic acid compared to other glucose-methanol-choline (GMC) oxidoreductase enzymes that contain only the standard FAD cofactor. The FOx-mediated conversion of FAD to 8-formyl FAD results in an approximate 10-fold increase in formate oxidase activity. However, the mechanistic details underlying the autocatalytic formation of 8-formyl FAD are still not well understood, which impedes further utilization of FOx. In this study, we employ molecular dynamics simulation, QM/MM umbrella sampling simulation, enzyme activity assay, site-directed mutagenesis, and spectroscopic analysis to elucidate the oxidation mechanism of FAD to 8-formyl FAD. Our results reveal that a catalytic water molecule, rather than any catalytic amino acids, serves as a general base to deprotonate the C8 methyl group on FAD, thus facilitating the formation of a quinone-methide tautomer intermediate. An oxygen molecule subsequently oxidizes this intermediate, resulting in a C8 methyl hydroperoxide anion that is protonated and dissociated to form OHC-RP and OH-. During the oxidation of FAD to 8-formyl FAD, the energy barrier for the rate-limiting step is calculated to be 22.8 kcal/mol, which corresponds to the required 14-hour transformation time observed experimentally. Further, the elucidated oxidation mechanism reveals that the autocatalytic formation of 8-formyl FAD depends on the proximal arginine and serine residues, R87 and S94, respectively. Enzymatic activity assay validates that the mutation of R87 to lysine reduces the kcat value to 75% of the wild-type, while the mutation to histidine results in a complete loss of activity. Similarly, the mutant S94I also leads to the deactivation of enzyme. This dependency arises because the nucleophilic OH- group and the quinone-methide tautomer intermediate are stabilized through the noncovalent interaction provided by R87 and S94. These findings not only explain the mechanistic details of each reaction step but also clarify the functional role of R87 and S94 during the oxidative maturation of 8-formyl FAD, thereby providing crucial theoretical support for the development of novel flavoenzymes with enhanced redox properties.

Wet-Spinning Carbon Nanotube/Shape Memory Polymer Composite Fibers with High Actuation Stress and Predesigned Shape Change.

Actuators based on shape memory polymers and composites incorporating nanomaterial additives have been extensively studied; achieving both high output stress and precise shape change by low-cost, scalable methods is a long-term-desired yet challenging task. Here, conventional polymers (polyurea) and carbon nanotube (CNT) fillers are combined to fabricate reinforced composite fibers with exceptional actuation performance, by a wet-spinning method amenable for continuous production. It is found that a thermal-induced shrinkage step could obtain densified strong fibers, and the presence of CNTs effectively promotes the tensile orientation of polymer molecular chains, leading to much improved mechanical properties. Consequently, the CNT/ polyurea composite fibers exhibit stresses as high as 33 MPa within 0.36 s during thermal actuation, and stresses up to 22 MPa upon electrical stimulation enabled by the built-in conductive CNT networks. Utilizing the flexible thin fibers, various shape change behavior are also demonstrated including the conversion between different structures/curvatures, and recovery of predefined simple patterns. This high-performance composite fibers, capable of both thermal and electrical actuation and produced by low-cost materials and fabrication process, may find many potential applications in wearable devices, robotics, and biomedical areas.

Fast gelling, high performance MXene hydrogels for wearable sensors.

Hydrogel-based functional materials had attracted great attention in the fields of artificial intelligence, soft robotics, and motion monitoring. However, the gelation of hydrogels induced by free radical polymerization typically required heating, light exposure, and other conditions, limiting their practical applications and development in real-life scenarios. In this study, a simple and direct method was proposed to achieve rapid gelation at room temperature by incorporating reductive MXene sheets in conjunction with metal ions into the chitosan network and inducing the formation of a polyacrylamide network in an extremely short time (10 s). This resulted in a dual-network MXene-crosslinked conductive hydrogel composite that exhibited exceptional stretchability (1350 %), remarkably low dissipated energy (0.40 kJ m-3 at 100 % strain), high sensitivity (GF = 2.86 at 300-500 % strain), and strong adhesion to various substrate surfaces. The study demonstrated potential applications in the reliable detection of various motions, including repetitive fine movements and large-scale human body motions. This work provided a feasible platform for developing integrated wearable health-monitoring electronic systems.

High-Strength, Antiswelling Directional Layered PVA/MXene Hydrogel for Wearable Devices and Underwater Sensing.

Hydrogel sensors are widely utilized in soft robotics and tissue engineering due to their excellent mechanical properties and biocompatibility. However, in high-water environments, traditional hydrogels can experience significant swelling, leading to decreased mechanical and electrical performance, potentially losing shape, and sensing capabilities. This study addresses these challenges by leveraging the Hofmeister effect, coupled with directional freezing and salting-out techniques, to develop a layered, high-strength, tough, and antiswelling PVA/MXene hydrogel. In particular, the salting-out process enhances the self-entanglement of PVA, resulting in an S-PM hydrogel with a tensile strength of up to 2.87 MPa. Furthermore, the S-PM hydrogel retains its structure and strength after 7 d of swelling, with only a 6% change in resistance. Importantly, its sensing performance is improved postswelling, a capability rarely achievable in traditional hydrogels. Moreover, the S-PM hydrogel demonstrates faster response times and more stable resistance change rates in underwater tests, making it crucial for long-term continuous monitoring in challenging aquatic environments, ensuring sustained operation and monitoring.

Dual Efficacy of a Catalytic Anti-Oligomeric Aß42 scFv Antibody in Clearing Aß42 Aggregates and Reducing Aß Burden in the Brains of Alzheimer's Disease Mice.

One of the primary pathological mechanisms underlying Alzheimer's disease (AD) is the deposition of amyloid ß-protein (Aß42) aggregates in the brain. In this study, a catalytic anti-oligomeric Aß42 scFv antibody, HS72, was identified by screening a human antibody library, its ability to degrade Aß42 aggregates was defined, and its role in the reduction of Aß burden in the AD mouse brain was evaluated. HS72 specifically targeted Aß42 aggregates with an approximately 14-68 kDa range. Based on molecular docking simulations, HS72 likely catalyzed the hydrolytic cleavage of the His13-His14 bond of Aß42 chains in an Aß42 aggregate unit, releasing N/C-terminal fragments and Aß42 monomers. Degradation of Aß42 aggregates by HS72 triggered a considerable disassembly or breakdown of the Aß42 aggregates and greatly reduced their neurotoxicity. Aß deposit/plaque load in the hippocampus of AD mice was reduced by approximately 27% after 7 days (once daily) of intravenous HS72 administration, while brain neural cells were greatly restored and their morphology was drastically improved. The above efficacies of HS72 were all greater than those of HT7, a simple anti-oligomeric Aß42 scFv antibody. Although a catalytic anti-oligomeric Aß42 antibody may have a slightly lower affinity for Aß42 aggregates than a simple anti-oligomeric Aß42 antibody, the former may display a stronger overall efficacy (dual efficacy of induction and catalysis) than the latter (induction alone) in clearing Aß42 aggregates and improving histopathological changes in AD brain. Our findings on the catalytic antibody HS72 indicate the possibility of functional evolution of anti-oligomeric Aß42 antibodies and provide novel insights into the immunotherapy of AD.