Photo-enhanced electrocatalytic hydrogen evolution reaction coupled semiconductor with plasma in neutral solution.

A gold-ruthenium/zinc oxide nanorod composite was synthesized. The electrochemical catalytic efficiency of the noble metal-semiconductor nanostructure increased by nearly 30% under the irradiation of an external light source. It provides an efficient way of thinking for the design of electrocatalysts with a photoresponse.

Chitosan-sodium alginate-based coatings for self-strengthening anticorrosion and antibacterial protection of titanium substrate in artificial saliva.

A self-strengthening coating with silver nanoparticles (Ag NPs) doped chitosan (CHI) and sodium alginate (SA) polyelectrolytes was constructed on the surface of polydopamine (PDA) coated Ti substrate by a layer-by-layer assembly method. The PDA coating exhibited an excellent bond with Ti substrate, and also can uniformly deposit Ag NPs via a mild method without introducing any exogenous reductant. The CHI coating was assembled through a spin-coating method for controlling Ag+ release. The SA was introduced to enhance the anticorrosion performance by forming calcium alginate (CA) in a corrosive medium. The corrosion protection was investigated with electrochemical impedance spectroscopy and polarization curves tests in fluorine-containing artificial saliva. During immersion, the charge-transfer resistance and the protection efficiency (ŋ) presented a continuous increase with the immersion time, demonstrating that this coating possessed a remarkable self-strengthening capability, and the compositions of the outermost film changed from SA to CA with the Ca2+ cations of the corrosive medium as a crosslinker by SEM and EDS analysis. Furthermore, the ŋ remained up to 96.8% after immersion of 30 days, and then the coating also displayed a distinct inhibition zone on S. mutans. These results prove this coating possesses an excellent anticorrosion performance and antibacterial property.

How Stabilizers and Reducing Agents Affect the Formation of Nanogold Amalgams.

The influence of mercury on the morphology and formation mechanism of gold amalgams in the presence of different reducing agents (ascorbic acid and sodium borohydride) was systematically studied. In the presence of cetyltrimethylammonium bromide (CTAB), chemical reducing agents not only reduced mercury ions in the solution but also replaced the CTAB molecules on the surface of the gold nanorod. The stability of the reducing agents in the colloidal system and the combining capacity of the reducing agent to the gold nanoparticles can affect the alloying process of mercury and gold, thereby forming a rod-shaped or spherical gold amalgam. Once CTAB was removed, a similar transformation process occurs between the gold nanorods and mercury. In addition, without the presence of a stabilizer, mercury that cannot be dispersed undergoes Ostwald ripening growth, which causes the gold amalgam nanoalloys to form a tip-to-tip structure as a result of mercury enrichment because of the weak shielding effects occurring at the tips of the gold nanorods. After the CTAB molecules were substituted with ascorbic acid and alkylthiol molecules, the question of whether the shielding effect weakened or disappeared was also investigated. By investigation, this research found that, in comparison to the blocking effect of CTAB molecules, the binding ability of the reducing agent to gold plays a dominant role in the nanoamalgam formation process.

Molybdenum-containing polypyrrole self-supporting hollow flexible electrode for hydrogen peroxide detection in living cells.

A flexible electrode based on polypyrrole-supported free-standing molybdenum oxide-molybdenum disulfide/polypyrrole nanostructure (MoO3-MoS2/PPy) was synthesized. The petal-like MoO3-MoS2 sheets grown on PPy were prepared step by step through simple electrodeposition and hydrothermal methods. The corresponding surface morphological and structural characterizations were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that the prepared petal MoO3-MoS2 hybrid nanomaterials were uniformly distributed on the PPy skeleton and exhibited a three-dimensional porous network structure. The flexible electrode was used for non-enzymatic detection of hydrogen peroxide (H2O2), and the developed MoO3-MoS2/PPy nanomaterials exhibited high electrochemical sensing performance in the range of 0.3-150 µM, with the detection limit of 0.18 µM (S/N = 3). The excellent detection properties enabled the MoO3-MoS2/PPy flexible electrode to detect H2O2 released by living cells. The resulting MoO3-MoS2/PPy flexible electrode also has the advantages of customizable shape and adjustability, which provides a potential platform for constructing clinically diagnosed in vivo portable instruments and real-time environmental monitoring.

Hollow Multiple Noble Metallic Nanoalloys by Mercury-Assisted Galvanic Replacement Reaction for Hydrogen Evolution.

Hollow multimetallic noble nanoalloys with high surface area/volume ratio, abundant active sites, and relatively effective catalytic activity have attracted considerable research interest. Traditional noble nanoalloys fabricated by hydro-/solvothermal methods usually involve harsh synthetic conditions such as high temperatures and intricate processing. We proposed a simple and mild strategy to synthesize platinum- and palladium-decorated hollow gold-based nanoalloys by the galvanic replacement reaction (GRR) at room temperature using hollow gold nanoparticles as templates and mercury as an intermediate. The hollow gold nanoparticles were essential for increasing the number of surface-active sites of the obtained multimetallic nanoalloys, and the introduction of mercury can eliminate the influence of the electrochemical potential of Pt/Pd with Au in the GRRs, increase alloying degrees, and maintain the nanoalloys that exhibit the hollow nanostructures. The structural characterizations of the hollow nanoalloys were studied by means of high-angle annular dark-field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. On the basis of the electrochemical catalytic measurements, the platinum-exposed nanoalloys were found to have excellent electrocatalytic activities. Especially in the presence of palladium, owing to the synergistic effect, the quaternary AuHgPdPt hollow nanoalloy displayed a low overpotential of 38 mV at 10 mA cm-2 with a small Tafel slope of 56.23 mV dec-1 for the alkaline hydrogen evolution reaction. In addition, this approach not only expands the application range of the galvanic replacement reaction but also provides new ideas for the preparation of multialloys and even high-entropy alloys at room temperature.

Bismuth-induced synthesis of Au-X (X = Pt, Pd) nanoalloys for electrocatalytic reactions.

Bismuth was introduced as an intermediate to produce Au-X (X = Pt and Pd) bimetallic nanoalloys using the galvanic replacement reaction. The results showed that the Au-X nanoalloys have good activity for electrocatalytic reactions in alkaline media. This strategy can provide an option for the formation of multimetal nanoalloys with similar electrochemical potentials and compositions.

Electrochemical endotoxin aptasensor based on a metal-organic framework labeled analytical platform.

An electrochemical aptasensor for the lipopolysaccharide (LPS) detection was constructed by using copper-based metal-organic framework (Cu-MOF) as a label and the LPS aptamer of specific single-stranded DNA as a probe. The carboxyl-functionalized polypyrrole nanowires (PPy NWs) were synthesized by electrochemical polymerization method, and the amino-terminated aptamer covalently coupling with the carboxyl group of the PPy NWs was immobilized onto the modified electrode. The aptamer can specifically combine with the target LPS molecules, and Cu-MOF was labeled by adsorption based on specific interactions of LPS carbohydrate portions with anionic groups. The fabrication processes of the aptasensor were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Differential pulse voltammetry (DPV) was used to measure electrochemical performance of the aptasensor, and the electrochemical signal can be directly measured by the electrochemical redox reaction of Cu(II)/Cu(I) existed in the Cu-MOF. The electrochemical aptasensor exhibited a high sensitivity toward LPS ranging from 1.0 pg/mL to 1.0 ng/mL with a detection limit of 0.29 pg/mL. Moreover, the developed sensor was found to have good selectivity, stability and regeneration properties, and the sensor also successfully detected LPS in real tap water samples.

Spectroscopic evidence for electrochemical effect of mercury ions on gold nanoparticles.

We demonstrated an interesting phenomenon that the electrochemical reduction of mercury ions (Hg2+) caused distinctly different morphology of gold nanorods (Au NRs) depending on the concentration of Hg2+. Specifically, in the case of low concentration, mercury formed through electrochemical reduction only deposited onto the gold surface, and then could be reversibly removed from the gold surface by electrochemical stripping process without causing obvious changes of Au NRs in shape and size. But in the case of high concentration, the reduced Hg not only deposited onto the gold surface but also entered into the interior of Au NRs making them change into gold nanospheres (Au NSs) in an irreversible manner due to the alloying effect of gold with Hg. In this situation, even though the most of Hg was removed, the Au NSs can no long return to the previous rod shape. The changing trend of Au NRs was characterized well by measuring the corresponding UV-Visible spectra. The formation of the Au/Hg nanoalloy was confirmed by high-resolution transmit electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS) results. The present study is helpful for having better understanding of the mechanism of electrochemical mercury-analysis by Au nanoparticles, and necessary to optimize the Au nanoparticles-based Hg sensing strategies.

Copper ion-assisted gold nanoparticle aggregates for electrochemical signal amplification of lipopolysaccharide sensing.

A signal amplification electrochemical aptasensor for ultrasensitive detection of lipopolysaccharide (LPS) was fabricated. The sensor was constructed with a probe of LPS aptamer and a copper ions-mediated gold nanoparticles aggregate (Cu/Au NA) as a signal amplification material. The Cu/Au NAs comprising copper ions (Cu2+) and L-cysteine modified AuNPs were fabricated by a self-assembly process. For functionalization of the electrode, the carboxylic group of a mercaptoacetic acid self-assembly layer was covalently coupled with the amine group of the aptamer. The aptamer with high specificity and affinity can effectively gather the dissociative LPS firstly, and the Cu/Au NAs were captured by anionic groups of the carbohydrate portions from LPS molecules based on the specific interactions. With the employment of the sandwich-type biosensor, the strategy can significantly amplify the electrochemical signal for determination of trace amount of LPS. The sensing performance of the electrochemical sensor was investigated by differential pulse voltammetry (DPV) and the stripping peak currents of Cu re-oxidized to Cu2+ was used to monitor the level of LPS. The electrochemical aptasensor exhibited excellent sensitivity toward LPS with a detection limit of 0.033 pg/mL (S/N = 3). The biosensor also exhibited a high specificity toward LPS in the presence of other common interfering substances and was easily regenerated. Furthermore, the fabricated biosensor showed a good practical application for LPS determination in human serum samples.

High rate and stable symmetric potassium ion batteries fabricated with flexible electrodes and solid-state electrolytes.

Aqueous batteries designed with K-ions have outstanding potential for future energy storage applications. When coupled with cathode and anode materials both operating with the intercalation mechanism, K-ion batteries could have kinetics and stability similar to Li-ion batteries in principle but with a much lower cost. However, the electrode materials developed so far still suffer from poor stability and limited activity, especially from the anode side. Herein, a new concept of symmetric K-ion batteries was developed by using potassium Prussian blue (KPB) as a bipolar material. The KPB particles were grown on flexible and strong wiper cloth substrates that were pre-coated with polypyrrole (PPy). The use of PPy as an interlayer not only boosted electrical conductivity but also ensured uniform growth of KPB particles. The synthesized KPB@PPy@wiper electrodes have superior flexibility and stability, and exhibited two redox pairs both with remarkable kinetics. When used as bipolar electrodes in combination with a gel solid-state electrolyte, they delivered a well-defined discharge voltage plateau at ∼0.6 V with superior rate capability and cycling stability. This work could provide new insights into the design of K-ion batteries, and give new options for developing flexible solid-state devices.

Continuous wave and ReS2 passively Q-switched Er : SrF2 laser at ∼3 µm.

We report on an efficient Er:SrF2 laser at 2.79 µm. A continuous wave output power of 1.06 W was obtained with a slope efficiency of 41%, significantly exceeding the Stokes efficiency of 35%. Stable Q-switched laser operation was realized by using an ReS2 saturable absorber, generating an average output power of 0.58 W with a pulse duration of 508 ns at a repetition rate of 49 kHz, corresponding to a pulse energy of 12.1 µJ.

A rechargeable iodine-carbon battery that exploits ion intercalation and iodine redox chemistry.

Graphitic carbons have been used as conductive supports for developing rechargeable batteries. However, the classic ion intercalation in graphitic carbon has yet to be coupled with extrinsic redox reactions to develop rechargeable batteries. Herein, we demonstrate the preparation of a free-standing, flexible nitrogen and phosphorus co-doped hierarchically porous graphitic carbon for iodine loading by pyrolysis of polyaniline coated cellulose wiper. We find that heteroatoms could provide additional defect sites for encapsulating iodine while the porous carbon skeleton facilitates redox reactions of iodine and ion intercalation. The combination of ion intercalation with redox reactions of iodine allows for developing rechargeable iodine-carbon batteries free from the unsafe lithium/sodium metals, and hence eliminates the long-standing safety issue. The unique architecture of the hierarchically porous graphitic carbon with heteroatom doping not only provides suitable spaces for both iodine encapsulation and cation intercalation but also generates efficient electronic and ionic transport pathways, thus leading to enhanced performance.Carbon-based electrodes able to intercalate Li+ and Na+ ions have been exploited for high performing energy storage devices. Here, the authors combine the ion intercalation properties of porous graphitic carbons with the redox chemistry of iodine to produce iodine-carbon batteries with high reversible capacities.

3 D Porous Nickel-Cobalt Nitrides Supported on Nickel Foam as Efficient Electrocatalysts for Overall Water Splitting.

Exploring highly efficient and durable bifunctional electrocatalysts from earth-abundant low-cost transition metals is central to obtaining clean hydrogen energy through large-scale electrolytic water splitting. Porous nickel-cobalt nitride nanosheets on macroporous Ni foam (NF) are synthesized through facile electrodeposition followed by a one-step annealing process in a NH3 atmosphere. The transformation from a metal hydroxide into a metal nitride could efficiently enhance the electrocatalytic performance for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Interestingly, the incorporation of nickel further boosts the catalytic activity of cobalt nitride. When used as bifunctional electrocatalysts, the obtained nickel-cobalt nitride electrocatalyst shows good stability and superior catalytic performance toward both HER and OER with low overpotentials of 0.29 and 0.18 V, respectively, to achieve a current density of 10 mA cm-2 . The good electrocatalytic performance was also evidenced by the fabrication of an electrolyzer for overall water splitting, which exhibits a high gas generation rate for hydrogen and oxygen with excellent stability during prolonged alkaline water electrolysis. The present work provides an efficient approach to prepare a 3 D interconnected porous nickel-cobalt nitride network with exposed inner active sites for overall water splitting.

Determination of copper ions using a phytic acid/polypyrrole nanowires modified glassy carbon electrode.

This study reports a sensitive electro-analytical method for the determination of trace amounts of Cu2+ using a phytate functionalized polypyrrole nanowires (PPy NWs) modified glass carbon electrode. The phytic acid/polypyrrole (PA/PPy) NWs were prepared by an electrostatic adsorption and ultrasonic mixing. The results showed that both PPy NWs and PA/PPy NWs modified glassy carbon electrodes have electrochemical responses toward Cu2+. However, owing to the synergistic contribution between the PPy NWs and PA, the PA/PPy NWs modified electrode exhibited higher sensitivity than that of PPy NWs modified electrode. The PA/PPy NWs composites functionalized electrodes showed a good linear relationship with Cu2+ at concentration ranges of 10-60µg·L-1, and the limit of detection (S/N=3) was 3.33µg·L-1. In addition, the electrochemical sensor was applied to assay Cu2+ in real water samples.

Transition metal ions regulated oxygen evolution reaction performance of Ni-based hydroxides hierarchical nanoarrays.

Nickel-based hydroxide hierarchical nanoarrays (NiyM(OH)x HNAs M = Fe or Zn) are doped with non-noble transition metals to create nanostructures and regulate their activities for the oxygen evolution reaction. Catalytic performance in these materials depends on their chemical composition and the presence of nanostructures. These novel hierarchical nanostructures contain small secondary nanosheets that are grown on the primary nanowire arrays, providing a higher surface area and more efficient mass transport for electrochemical reactions. The activities of the NiyM(OH)x HNAs for the oxygen evolution reaction (OER) followed the order of Ni2.2Fe(OH)x > Ni(OH)2 > Ni2.1Zn(OH)x, and these trends are supported by density functional theory (DFT) calculations. The Fe-doped nickel hydroxide hierarchical nanoarrays (Ni2.2Fe(OH)x HNAs), which had an appropriate elemental composition and hierarchical nanostructures, achieve the lowest onset overpotential of 234 mV and the smallest Tafel slope of 64.3 mV dec-1. The specific activity, which is normalized to the Brunauer-Emmett-Teller (BET) surface area of the catalyst, of the Ni2.2Fe(OH)x HNAs is 1.15 mA cm-2BET at an overpotential of 350 mV. This is ~4-times higher than that of Ni(OH)2. These values are also superior to those of a commercial IrOx electrocatalyst.

Temperature-dependent surface nanomechanical properties of a thermoplastic nanocomposite.

In polymer nanocomposites, particle-polymer interactions influence the properties of the matrix polymer next to the particle surface, providing different physicochemical properties than in the bulk matrix. This region is often referred to as the interphase, but detailed characterization of its properties remains a challenge. Here we employ two atomic force microscopy (AFM) force methods, differing by a factor of about 15 in probing rate, to directly measure the surface nanomechanical properties of the transition region between filler particle and matrix over a controlled temperature range. The nanocomposite consists of poly(ethyl methacrylate) (PEMA) and poly(isobutyl methacrylate) (PiBMA) with a high concentration of hydrophobized silica nanoparticles. Both AFM methods demonstrate that the interphase region around a 40-nm-sized particle located on the surface of the nanocomposite could extend to 55-70nm, and the interphase exhibits a gradient distribution in surface nanomechanical properties. However, the slower probing rate provides somewhat lower numerical values for the surface stiffness. The analysis of the local glass transition temperature (Tg) of the interphase and the polymer matrix provides evidence for reduced stiffness of the polymer matrix at high particle concentration, a feature that we attribute to selective adsorption. These findings provide new insight into understanding the microstructure and mechanical properties of nanocomposites, which is of importance for designing nanomaterials.

Graphitic C3N4 as a new saturable absorber for the mid-infrared spectral range.

The saturable absorption properties of few-layer graphitic carbon nitride (g-C3N4) nanosheets near 3 µm were investigated. A stable Q-switched Er:Lu2O3 laser at 2.84 µm was realized by using a home-made g-C3N4 saturable absorber (SA), generating a pulse duration of 351 ns and an average output power of 1.09 W at a repetition rate of 99 kHz, corresponding to a pulse energy of 11.1 µJ. Our result indicates a great potential of g-C3N4 as a new SA in the 3 µm wavelength range.

Synthesis of a novel electrode material containing phytic acid-polyaniline nanofibers for simultaneous determination of cadmium and lead ions.

The development of nanostructured conducting polymers based materials for electrochemical applications has attracted intense attention due to their environmental stability, unique reversible redox properties, abundant electron active sites, rapid electron transfer and tunable conductivity. Here, a phytic acid doped polyaniline nanofibers based nanocomposite was synthesized using a simple and green method, the properties of the resulting nanomaterial was characterized by electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). A glassy carbon electrode modified by the nanocomposite was evaluated as a new platform for the simultaneous detection of trace amounts of Cd2+ and Pb2+ using differential pulse anodic stripping voltammetry (DPASV). The synergistic contribution from PANI nanofibers and phytic acid enhances the accumulation efficiency and the charge transfer rate of metal ions during the DPASV analysis. Under the optimal conditions, good linear relationships were obtained for Cd2+ in a range of 0.05-60 µg L-1, with the detection limit (S/N = 3) of 0.02 µg L-1, and for Pb2+ in a range of 0.1-60 µg L-1, with the detection limit (S/N = 3) of 0.05 µg L-1. The new electrode was successfully applied to real water samples for simultaneous detection of Cd2+ and Pb2+ with good recovery rates. Therefore, the new electrode material may be a capable candidate for the detection of trace levels of heavy metal ions.

Cation Intercalation in Manganese Oxide Nanosheets: Effects on Lithium and Sodium Storage.

The rapid development of advanced energy-storage devices requires significant improvements of the electrode performance and a detailed understanding of the fundamental energy-storage processes. In this work, the self-assembly of two-dimensional manganese oxide nanosheets with various metal cations is introduced as a general and effective method for the incorporation of different guest cations and the formation of sandwich structures with tunable interlayer distances, leading to the formation of 3D Mx MnO2 (M=Li, Na, K, Co, and Mg) cathodes. For sodium and lithium storage, these electrode materials exhibited different capacities and cycling stabilities. The efficiency of the storage process is influenced not only by the interlayer spacing but also by the interaction between the host cations and shutter ions, confirming the crucial role of the cations. These results provide promising ideas for the rational design of advanced electrodes for Li and Na storage.

General Preparation of Three-Dimensional Porous Metal Oxide Foams Coated with Nitrogen-Doped Carbon for Enhanced Lithium Storage.

Porous metal oxide architectures coated with a thin layer of carbon are attractive materials for energy storage applications. Here, a series of porous metal oxide (e.g., vanadium oxides, molybdenum oxides, manganese oxides) foams with/without nitrogen-doped carbon (N-C) coating have been synthesized via a general surfactant-assisted template method, involving the formation of porous metal oxides coated with 1-hexadecylamine (HDA) and a subsequent thermal treatment. The presence of HDA is of importance for the formation of a porous structure, and the successive pyrolysis of such a nitrogen-containing surfactant generates nitrogen-doped carbon (N-C) coated on the surface of metal oxides, which also provides a facile way to adjust the valence states of metal oxides via the carbothermal reduction reaction. When used as electrode materials, the highly porous metal oxides with N-C coating exhibited enhanced performance for lithium ion storage, thanks to the unique 3D structures associated with highly porous structure and thin N-C coating. Typically, the porous metal oxides (V2O5, MoO3, MnO2) exhibited discharge capacities of 286, 303, and 463 mAh g(-1) at current densities of 30 and 100 mA g(-1), respectively. In contrast, the metal oxides with low valences and carbon coating (VO2@N-C, MoO2@N-C, and MnO@N-C) exhibited improved capacities of 461, 613, and 892 mAh g(-1). The capacity retentions of about 87.5, 80.2, and 85.0% for VO2@N-C, MoO2@N-C, and MnO@N-C were achieved after 600 cycles, suggesting the acceptable cycling stability. The present strategy would provide general guidance for preparing porous metal oxide foams with enhanced lithium storage performances.