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.

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.

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.

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.

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.

Different Extracellular ß-Amyloid (1-42) Aggregates Differentially Impair Neural Cell Adhesion and Neurite Outgrowth through Differential Induction of Scaffold Palladin.

Extracellular amyloid ß-protein (1-42) (Aß42) aggregates have been recognized as toxic agents for neural cells in vivo and in vitro. The aim of this study was to investigate the cytotoxic effects of extracellular Aß42 aggregates in soluble (or suspended, SAß42) and deposited (or attached, DAß42) forms on cell adhesion/re-adhesion, neurite outgrowth, and intracellular scaffold palladin using the neural cell lines SH-SY5Y and HT22, and to elucidate the potential relevance of these effects. The effect of extracellular Aß42 on neural cell adhesion was directly associated with their neurotrophic or neurotoxic activity, with SAß42 aggregates reducing cell adhesion and associated live cell de-adherence more than DAß42 aggregates, while causing higher mortality. The reduction in cell adhesion due to extracellular Aß42 aggregates was accompanied by the impairment of neurite outgrowth, both in length and number, and similarly, SAß42 aggregates impaired the extension of neurites more severely than DAß42 aggregates. Further, the disparate changes of intracellular palladin induced by SAß42 and DAß42 aggregates, respectively, might underlie their aforementioned effects on target cells. Further, the use of anti-oligomeric Aß42 scFv antibodies revealed that extracellular Aß42 aggregates, especially large DAß42 aggregates, had some independent detrimental effects, including physical barrier effects on neural cell adhesion and neuritogenesis in addition to their neurotoxicity, which might be caused by the rigid C-terminal clusters formed between adjacent Aß42 chains in Aß42 aggregates. Our findings, concerning how scaffold palladin responds to extracellular Aß42 aggregates, and is closely connected with declines in cell adhesion and neurite outgrowth, provide new insights into the cytotoxicity of extracellular Aß42 aggregates in Alzheimer disease.

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.

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.

Carbon Nanotube-Coupled Seaweed-like Cobalt Sulfide as a Dual-Functional Catalyst for Overall Water Splitting.

Preparation of high-efficiency dual-functional catalysts remains the bottleneck for electrochemical water splitting. To prepare a non-precious metal catalyst with high activity and stability, here, we present a seaweed-like structure consisting of transition-metal sulfide nanoplates self-assembled on carbon nanotube sponge networks (SW-CoS@CNT). By adjusting the key parameters during synthesis (e.g., the loading amount and ratio of Co and S precursors), the microstructure can be tailored in a wide range, and sulfur defects can be introduced into the nanoplates by thermal annealing. The resulting SW-CoS@CNT serves as a freestanding dual-functional catalytic electrode, showing low overpotentials of 105 and 218 mV for the hydrogen evolution reaction and the oxygen evolution reaction, respectively, which are superior to most reported transition-metal-sulfide-based catalysts in alkaline solution. Rational design of this hierarchical biomimetic structure may be useful in developing high-performance electrochemical catalysts in renewable energy and environmental fields.

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.

Synergistic CNFs/CoS2/MoS2 Flexible Films with Unprecedented Selectivity for NO Gas at Room Temperature.

Recently, room-temperature flexible gas sensors have been widely studied because they can operate without being heated and create low-cost, low-power-consumption devices with long-term stability. Here, by designing the active material composition and structure, we report an electrospun carbon nanofiber (CNF) network grafted by two-dimensional MoS2 nanosheets and embedded CoS2 nanoparticles, which serves as a flexible gas sensor for various toxic or hazardous gases working at room temperature. In particular, the CNFs/CoS2/MoS2 hybrid films exhibit very high selectivity toward NO over other gases including NO2 and CH4, with selectivity coefficients (|SNO/SNO2| and |SNO/SCH4|) as high as 43 and 42 (defined as the ratio of responses between two gases). The sensor shows a linear relationship in the gas concentration range of 1-100 ppm and a stable response during repeated bending. Theoretical calculations suggest that MoS2 can be selectively n-doped by NO, while CoS2 can effectively capture NO molecules, leading to enhanced selectivity and sensitivity. Our large-area flexible sensors made by synergistic design have potential applications in biological and environmental areas for low-cost, selective detection of toxic or targeted gases.

Nonlinear and mixed inhibitory effect of matrine on the cytotoxicity of oligomeric amyloid-ß protein.

The formation of amyloid ß-protein (1-42) (Aß42) oligomers and Aß42 oligomer cytotoxicity are two defining characteristics of the etiology of Alzheimer's disease (AD). In this study, we found that matrine (Mat) could maintain or even enhance the cytotrophic effect of Aß42 monomers by inhibiting their aggregation and by working in a manner similar to synergy with Aß42 monomers. Moreover, Mat could also exert a cytoprotective effect by actively promoting the disaggregation of immature Aß42 oligomers in a concentration-dependent manner. Although Mat at intermediate concentrations (1-50 µM) exhibited both cytotrophic and cytoprotective effects on SH-SY5Y cells, Mat at higher concentrations (100 µM) only exhibited a cytoprotective effect. Molecular docking studies reveal that these differences are a result of the different interactions between Mat and Aß42 oligomers that occur at different molecular ratios. Our results support the hypothesis that there may be a Mat-like metabolite in the human brain that acts as a molecular chaperone for Aß42 monomers. A deficiency in this chaperone would result in the gradual aggregation of Aß42 monomers, and eventually, formation of toxic Aß42 oligomers. In addition, reduction or clearance of Aß42 aggregates or deposits and inhibition or elimination of the toxicity of oligomeric Aß42, were not always directly correlated. Finally, the site(s) responsible for cytotoxicity in Aß42 oligomers may be located in the integrated region of the N-terminal fragments of Aß42 chains. This study provides valuable insights into the mechanisms involved in the development of natural drugs for the treatment of Alzheimer's disease.

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 Mode of Action of an Anti-Oligomeric Amyloid ß-Protein Antibody Affects its Protective Efficacy.

The process of developing antibody drugs for Alzheimer's disease therapy has been both long and difficult; however, recent advances suggest that antibodies against neurotoxic Αß42 can suppress the progression of AD, especially on its early stage. Here, we obtained and characterized a novel anti-oligomeric Aß42 aggregate scFv antibody, HT7, which could induce the significant disaggregation of Aß42 aggregates through the release of stable and non-cytotoxic hexameric complexes that were composed of three scFv HT7s and one Aß42 trimer, the latter being found to serve as the assembled subunit within larger Aß42 aggregates in addition to existing freely between the cells. The docking model of the scFv HT7-Aß42 complex revealed that only the N-terminal peptide of the Aß42 molecule was bound into the groove between the VH and VL domains of scFv HT7. Thus, it was suggested that the hydrophobic interaction between the C-terminal peptides of Aß42 molecules maintained the stability of the Aß42 trimers or the Aß42 trimer subunits. The saturation of Aß42 trimer subunits by scFv HT7 and the subsequent dissociation of the scFv HT7-saturated Aß42 trimer subunits from larger Aß42 aggregates constituted the primary mechanisms underlying the high efficacy of scFv HT7. Our findings revealed that it was not sufficient for an anti-oligomeric Aß42 antibody to exhibit high specificity and high affinity to the oligomeric Aß42 aggregates in order to promote Aß42 aggregate clearance and neutralize their cytotoxic effects. Here, for the first time, we proposed a "post-saturation dissociation" mechanism of Aß42 oligomeric subunits for effective anti-Aß42 antibodies.

Novel antibody against oligomeric amyloid-ß: Insight into factors for effectively reducing the aggregation and cytotoxicity of amyloid-ß aggregates.

Amyloid-beta 42 (Aß42) aggregates represent a prominent histopathological feature in Alzheimer's disease (AD); thus, immunotherapy against oligomeric Aß42 aggregates is considered to be a potentially safe and specific therapeutic strategy. In this study, we identified an anti-oligomeric Aß42 aggregate single-chain variable fragment (scFv) antibody, HT6, that is capable of efficiently binding to medium-sized Aß42 aggregates (mainly 18-45 kDa) in vitro with an equilibrium dissociation constant (KD) of 3.0 × 10-6 M, whether they were derived from Aß42 monomer, larger Aß42 oligomers, or even fibrils. This ability allowed scFv HT6 to induce the gradual disassembly of large Aß42 aggregates into small Aß42 oligomers while simultaneously effectively inhibiting the further development of Aß42 aggregates. Moreover, the scFv HT6-targeted conformational region on Aß42 aggregates was found to be more local and relatively close to the N-terminus of Aß42; thus, scFv HT6 significantly delayed or even prevented the aggregation of Aß42 protofibrils, while significantly reducing the cytotoxicity of Aß42 oligomers. Overall, this study demonstrate that even though the decrease in the cytotoxicity of Aß42 aggregates might be closely related to the reduction in Aß42 aggregates and vice versa, the reduction in Aß42 aggregates might not necessarily be accompanied by or followed by the reduction or even elimination of the cytotoxicity of Aß42 aggregates. This insight enriches the diversity of anti-oligomeric Aß42 antibodies, further providing a new understanding into the relationship between their binding pattern to Aß42 aggregates and the efficacy against their formation, offering a therapeutic strategy to delay the progression of AD.

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.

NiCo2S4@NiMoO4 Core-Shell Heterostructure Nanotube Arrays Grown on Ni Foam as a Binder-Free Electrode Displayed High Electrochemical Performance with High Capacity.

Core-shell-structured system has been proved as one of the best architecture for clean energy products owing to its inherited superiorities from both the core and the shell part, which can provide better conductivity and high surface area. Herein, a hierarchical core-shell NiCo2S4@NiMoO4 heterostructure nanotube array on Ni foam (NF) (NiCo2S4@NiMoO4/NF) has been successfully fabricated. Because of its novel heterostructure, the capacitive performance has been enhanced. A specific capacitance up to 2006 F g-1 was obtained at a current density of 5 mA cm-2, which was far higher than that of pristine NiCo2S4 nanotube arrays (about 1264 F g-1). More importantly, NiCo2S4@NiMoO4/NF and active carbon (AC) were congregated as positive electrode and negative electrode in an asymmetric supercapacitor. As-fabricated NiCo2S4@NiMoO4/NF//AC device has a good cyclic behavior with 78% capacitance retention over 2000 cycles, and exhibits a high energy density of 21.4 Wh kg-1 and power density of 58 W kg-1 at 2 mA cm-2. As displayed, the NiCo2S4@NiMoO4/NF core-shell herterostructure holds great promise for supercapacitors in energy storage.

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.

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.