Directionally In Situ Self-Assembled, High-Density, Macropore-Oriented, CoP-Impregnated, 3D Hierarchical Porous Carbon Sheet Nanostructure for Superior Electrocatalysis in the Hydrogen Evolution Reaction.

3D ZIF-67-particles-impregnated cellulose-nanofiber nanosheets with oriented macropores are synthesized via directional-freezing-assisted in situ self-assembly, and converted to 3D CoP-nanoparticle (NP)-embedded hierarchical, but macropores-oriented, N-doped carbon nanosheets via calcination and phosphidation. The obtained nanoarchitecture delivers overpotentials at 10 and 50 mA cm-2 and Tafel slope of 82.1 and 113.4 mV and 40.8 mV dec-1 in 0.5 M H2 SO4 , and of 97.1 and 136.6 mV and 51.2 mV dec-1 in 1 M KOH, all of which are superior to those of the most reported non-noble-metal-based hydrogen evolution reaction (HER) catalysts. This catalyst even surpasses commercial Pt/C for a much lower overpotential at high current densities, which is essential for large-scale hydrogen production. Its catalytic activity can be further optimized to become one of the best in both 0.5 M H2 SO4 and 1 M KOH. The outstanding catalytic activity is ascribed to the uniformly-dispersed small CoP NPs in the 3D carbon sheets and the hierarchical nanostructure with rich oriented pores. This work develops a facile, economical, and universal self-assembly strategy to fabricate uniquely nanostructured hybrids to simultaneously promote charge transfer and mass transport, and also offers an inexpensive and high-performance HER catalyst toward industry-scale water splitting.

One-pot synthesis of CO2-responsive magnetic nanoparticles with switchable hydrophilicity.

CO2-responsive nanoparticles have been attracted increasing interest due to their benign reactions with CO2 that give them gas-switchable properties, which can be easily reversed by mild heating or purging with inert gases. In this work, we have prepared CO2-responsive magnetic nanoparticles in a simple one-pot polyol synthesis using diaminoalkanes as the surfactant. The as-synthesized nanoparticles show excellent reversible aggregation and dispersion in response to alternating purging of N2 and CO2 at room temperature. We found that, among the diaminoalkanes with different chain lengths, 1,8-diaminooctane is the best candidate for the synthesis of CO2-responsive nanoparticles, since it allows good dispersity of the nanoparticles after charging with CO2 and also provides effective aggregation and separation following N2 purging. Moreover, the self-assembly of 1,8-diaminooctane-functionalized nanoparticles can be controlled to form linear aggregates with the assistance of N2 and an external magnetic field, demonstrating an effective response to dual stimuli. This work paves the way for the direct synthesis of a wide range of CO2-responsive nanoparticles.

DNA-assisted assembly of carbon nanotubes and MnO2 nanospheres as electrodes for high-performance asymmetric supercapacitors.

A DNA-assisted assembly approach is developed to fabricate a capacitor-type electrode material, DNA-functionalized carbon nanotubes (CNTs@DNA), and a battery-type electrode material, DNA@CNTs-bridged MnO2 spheres (CNTs@DNA-MnO2), for asymmetric supercapacitors. An energy density of 11.6 W h kg(-1) is achieved at a power density of 185.5 W kg(-1) with a high MnO2 mass loading of 4.2 mg cm(-2). It is found that DNA assembly plays a critical role in the enhanced supercapacitor performance. This is because while DNA molecules functionalize carbon nanotubes (CNTs) via π-π stacking, their hydrophilic sugar-phosphate backbones also promote the dispersion of CNTs. The resultant CNTs@DNA chains can link multiple MnO2 spheres to form a networked architecture that facilitates charge transfer and effective MnO2 utilization. The improved performance of the asymmetric supercapacitors indicates that DNA-assisted assembly offers a promising approach to the fabrication of high-performance energy storage devices.

Graphdiyne chelated AuNPs for ultrasensitive electrochemical detection of tyrosine.

Tyrosine (Tyr) is a kind of amino acid that can regulate emotions and stimulate the nervous system, and it is of great importance to realize its ultrasensitive detection. A unique material of graphdiyne chelated AuNPs (GDY@AuNPs) is designed and developed to realize high-performance electrochemical sensing of Tyr. GDY promotes the absorption of Tyr via π-π interaction, and its CC strongly chelates with AuNPs for greatly improved sensitivity. GDY@AuNPs delivers a sensitivity of up to 181.2 µA mM-1 cm-2 and a wide range of 0.1-600 µM, among the best for carbon or AuNPs-based materials for the detection of Tyr. It demonstrates the accurate detection of Tyr in human sweat for potential practical applications.

DNA-directed growth of Pd nanocrystals on carbon nanotubes towards efficient oxygen reduction reactions.

Unique DNA-promoted Pd nanocrystals on carbon nanotubes (Pd/DNA-CNTs) are synthesized for the first time, in which through its regularly arranged PO(4)(3-) groups on the sugar-phosphate backbone, DNA directs the growth of ultrasmall Pd nanocrytals with an average size of 3.4 nm uniformly distributed on CNTs. The Pd/DNA-CNT catalyst shows much more efficient electrocatalytic activity towards oxygen reduction reaction (ORR) with a much more positive onset potential, higher catalytic current density and better stability than other Pd-based catalysts including Pd nanocrystals on carbon nanotubes (Pd/CNTs) without the use of DNA and commercial Pd/C catalyst. In addition, the Pd/DNA-CNTs catalyst provides high methanol tolerance. The high electrocatalytic performance is mainly contributed by the ultrasmall Pd nanocrystal particles grown directed by DNA to enhance the mass transport rate and to improve the utilization of the Pd catalyst. This work may demonstrate a universal approach to fabricate other superior metal nanocrystal catalysts with DNA promotion for broad applications in energy systems and sensing devices.

Microelectrodes with gold nanoparticles and self-assembled monolayers for in vivo recording of striatal dopamine.

Electrochemical determination of in vivo dopamine (DA) using implantable microelectrodes is essential for monitoring the DA depletion of an animal model of Parkinson's disease (PD), but faces substantial interference from ascorbic acid (AA) in the brain area due to similar electroactive characteristics. This study utilizes gold nanoparticles (Au-NPs) and self-assembled monolayers (SAMs) to modify platinum microelectrodes for improving sensitivity and specificity to DA and alleviating AA interference. With appropriate choice of ω-mercaptoalkane carboxylic acid chain length, our results show that a platinum microelectrode coated with Au-NPs and 3-mercaptopropionic acid (MPA) has approximately an 881-fold specificity to AA. During amperometric measurements, Au-NP/MPA reveals that the responsive current is linearly dependent on DA over the range of 0.01-5 µM with a correlation coefficient of 0.99 and the sensitivity is 2.7-fold that of a conventional Nafion-coated electrode. Other important features observed include fast response time (below 2 s), resistance to albumin adhesion and low detection limit (7 nM) at a signal to noise ratio of 3. Feasibility of in vivo DA recording with the modified microelectrodes is verified by real-time monitoring of electrically stimulated DA release in the striatum of anesthetized rats with various stimulation parameters and administration of a DA uptake inhibitor. The developed microelectrodes present an attractive alternative to the traditional options for continuous electrochemical in vivo DA monitoring.

In situ synthesized heteropoly acid/polyaniline/graphene nanocomposites to simultaneously boost both double layer- and pseudo-capacitance for supercapacitors.

It is challenging to simultaneously increase double layer- and pseudo-capacitance for supercapacitors. Phosphomolybdic acid/polyaniline/graphene nanocomposites (PMo(12)-PANI/GS) were prepared by using PMo(12) as a bifunctional reagent for not only well dispersing graphene for high electrochemical double layer capacitance but also in situ chemically polymerizing aniline for high pseudocapacitance, resulting in a specific capacitance of 587 F g(-1), which is ~1.5 and 6 times higher than that of PANI/GS (392 F g(-1)) and GS (103 F g(-1)), respectively. The nanocomposites also exhibit good reversibility and stability. Other kinds of heteropolyacids such as molybdovanadophosphoric acids (PMo(12-x)V(x), x = 1, 2 and 3) were also used to prepare PMo(12-x)V(x)-PANI/GS nanocomposites, also showing enhanced double layer- and pseudo-capacitance. This further proves the proposed concept to simultaneously boost both double layer- and pseudo-capacitance and demonstrates that it could be a universal approach to significantly improve the capacitance for supercapacitors.

Direct electron transfer of glucose oxidase and biosensing of glucose on hollow sphere-nanostructured conducting polymer/metal oxide composite.

A hollow sphere-nanostructured conductive polymer/metal oxide composite was synthesized and used to investigate the electrochemical behavior of glucose oxidase, demonstrating a significantly enhanced direct electron transfer ability of glucose oxidase. In particular, the long-standing puzzle of whether enzymatic glucose sensing involves an enzyme direct electron transfer process was studied. The results indicate the mechanism is indeed a glucose oxidase direct electron transfer process with competitive glucose oxidation and oxygen reduction to detect glucose. A glucose biosensor with the glucose oxidase-immobilized nanomaterial was further constructed, demonstrating superior sensitivity and reliability, and providing great potential in clinical applications.

A high-energy-state biomimetic enzyme of oxygen-deficient MnTiO3 nanodiscs for sensitive electrochemical sensing of the superoxide anion.

It is of great importance to determine the superoxide anion (O2˙-), a kind of active free radical that plays important roles in catalytic and biological processes. We present here a high-energy-state biomimetic enzyme with extraordinary activity for O2˙- by inducing surface oxygen defects in MnTiO3 nanodiscs. Oxygen defects enable surface rich active Mn sites with high oxidation ability, which significantly promote the adsorption and electro-oxidation of O2˙-. The oxygen deficient MnTiO3 towards O2˙- exhibits a sensitivity of 126.48 µA µM-1 cm-2 and a detection limit of 1.54 nM, among the best performance of O2˙- sensing platforms.

Room temperature-formed iron-doped nickel hydroxide on nickel foam as a 3D electrode for low polarized and high-current-density oxygen evolution.

Unique room temperature-formed iron-doped nickel hydroxide on Ni foam as a 3D electrode in alkaline electrolyte offers fast gas dissipation, a high number of active sites and a high oxidation state of Ni for an improved oxidation ability for the oxygen evolution reaction (OER), which delivers an OER current density of 100 mA cm-2 at an overpotential of 0.312 V and 96.3% retention after 100 h at an overpotential of 0.370 V in 1 M KOH, and 1000 mA cm-2 at an overpotential of 0.265 V in 30 wt% KOH.

Au@CdS Core-Shell Nanoparticles-Modified ZnO Nanowires Photoanode for Efficient Photoelectrochemical Water Splitting.

Hydrogen production from water splitting using solar energy based on photoelectrochemical (PEC) cells has attracted increasing attention because it leaves less of a carbon footprint and has economic superiority of solar and hydrogen energy. Oxide semiconductors such as ZnO possessing high stability against photocorrosion in hole scavenger systems have been widely used to build photoanodes of PEC cells but under visible light their conversion efficiencies with respect to incident-photon-to-current conversion efficiency (IPCE) measured without external bias are still not satisfied. An innovative way is presented here to significantly improve the conversion efficiency of PEC cells by constructing a core-shell structure-based photoanode comprising Au@CdS core-shell nanoparticles on ZnO nanowires (Au@CdS-ZnO). The Au core offers strong electronic interactions with both CdS and ZnO resulting in a unique nanojunction to facilitate charge transfer. The Au@CdS-ZnO PEC cell under 400 nm light irradiation without any applied bias provides an IPCE of 14.8%. Under AM1.5 light illumination with a bias of 0.4 V, the Au@CdS-ZnO PEC cell produces H2 at a constant rate of 11.5 µmol h-1 as long as 10 h. This work provides a fundamental insight to improve the conversion efficiency for visible light in water splitting.

Nitrogen doped carbon nanoparticles enhanced extracellular electron transfer for high-performance microbial fuel cells anode.

Nitrogen doped carbon nanoparticles (NDCN) were applied to modify the carbon cloth anodes of microbial fuel cells (MFCs) inoculated with Shewanella oneidensis MR-1, one of the most well-studied exoelectrogens. Experimental results demonstrated that the use of NDCN increased anodic absorption of flavins (i.e., the soluble electron mediator secreted by S. oneidensis MR-1), facilitating shuttle-mediated extracellular electron transfer. In addition, we also found that NDCN enabled enhanced contact-based direct electron transfer via outer-membrane c-type cytochromes. Taken together, the performance of MFCs with the NDCN-modified anode was enormously enhanced, delivering a maximum power density 3.5 times' higher than that of the MFCs without the modification of carbon cloth anodes.

Ethylenediamine-mediated synthesis of Mn3O4 nano-octahedrons and their performance as electrocatalysts for the oxygen evolution reaction.

Mn3O4 octahedrons with well-defined facets exhibit enhanced catalytic activity and sensing characteristics, and have attracted considerable attention in recent years. However, current fabrication methods for Mn3O4 octahedrons generally produce particles of micron and sub-micron sizes, and impurities such as MnO2 and Mn2O3 are often found. We present the synthesis of Mn3O4 nano-octahedrons with a pure Mn3O4 phase and size down to 50 nm based on a hydrothermal method using Mn(NO3)2 as the manganese source and ethylenediamine (EDA) as the structure-mediating agent. It is found that EDA plays a crucial role in the formation of Mn3O4 nano-octahedrons in regulating both the morphology and the crystal structure of the products. The growth process is proposed to follow a "dissolution-recrystallization" and "capping-molecule assisted growth" mechanism. As electrocatalysts towards the oxygen evolution reaction, the 50 nm Mn3O4 nano-octahedrons demonstrate a considerably enhanced activity compared to 160 nm Mn3O4 octahedrons.

Na⁺-functionalized carbon quantum dots: a new draw solute in forward osmosis for seawater desalination.

A new type of biocompatible draw solute, Na(+)-functionalized carbon quantum dots (Na_CQDs) with ultra-small size and rich ionic species, in forward osmosis (FO) is developed for seawater desalination. The aqueous dispersion of Na_CQDs demonstrates a high osmotic pressure, which allows high FO water flux and negligible reverse solute permeation.

Graphene oxide-enabled tandem signal amplification for sensitive SPRi immunoassay in serum.

A tandem signal amplification using bioconjugated graphene oxide and subsequent silver catalytic deposition for surface plasmon resonance imaging (SPRi) to sensitively and specifically immunoassay tumor biomarkers in serum, achieving a limit of detection down to 100 pg mL(-1) with a broad dynamic range for α-Fetoprotein (AFP) is reported.

A new class of fluorescent-dots: long luminescent lifetime bio-dots self-assembled from DNA at low temperatures.

Quantum-dots (QDs) have fuelled up intensive research efforts over the past two decades. Nevertheless, currently developed two classes of fluorescent QDs, colloidal semiconductor QDs and carbonaceous QDs suffer from either toxicity or short luminescence lifetime. Here, we report a new class of fluorescent bio-dots that are derived from DNA via self-assembly at low temperatures down to 80°C, which has an optical bandgap of 3.4 eV, and in particular possesses strong photoluminescence with a much longer luminescence lifetime (τ1 = 10.44 ns) than the carbonaceous QDs (τ1 < 0.5 ns). It is discovered that it is the interactions of base pair cytosines with each other to form sp² carbon-like centers as luminescence centers or chromophores for the photoluminescence. The use of bio-dots in cell imaging with strong photoluminescence signal and good biocompatibility demonstrates great potentials of broad biological and optoelectronic applications.

Graphene quantum-dot-doped polypyrrole counter electrode for high-performance dye-sensitized solar cells.

Herein graphene quantum dot (GQD), a graphene material with lateral dimension less than 100 nm, is explored to dope PPy on F-doped tin oxide glass as an efficient counter electrode for high-performance dye-sensitized solar cells (DSSCs). The GQDs-doped PPy film has a porous structure in comparison to the densely structured plain PPy, and displays higher catalytic current density and lower charge transfer resistance than the latter toward I3(-)/I(-) redox reaction. The highest power conversion efficiency (5.27%) for DSSCs is achieved with PPy doped with10% GQDs, which is comparable to that of Pt counter electrode-based DSSCs. This work provides an inexpensive alternative to replace platinum for DSSCs.

Template-free bottom-up synthesis of yolk-shell vanadium oxide as high performance cathode for lithium ion batteries.

A template-free strategy is exploited to bottom-up synthesize yolk-shell vanadium oxide through a two-step spontaneous assembly of hydrolytically formed subunits in a one-pot process. The unique structured vanadium pentoxide exhibits excellent cathode performance for lithium ion batteries.

Functionalization of SnO2 photoanode through Mg-doping and TiO2-coating to synergically boost dye-sensitized solar cell performance.

Mg-doped SnO2 with an ultrathin TiO2 coating layer was successfully synthesized through a facile nanoengineering art. Mg-doping and TiO2-coating constructed functionally multi-interfaced SnO2 photoanode for blocking charge recombination and enhancing charge transfer in dye-sensitized solar cells (DSC). The designed nanostructure might play a synergistic effect on the reducing recombination and prolonging the lifetime in DSC device. Consequently, a maximum power conversion efficiency of 4.15% was obtained for solar cells fabricated with the SnO2-based photoelectrode, exhibiting beyond 5-fold improvement in comparison with pure SnO2 nanomterials photoelectrode DSC (0.85%).