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.

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.

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.

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.

Watt-level passively Q-switched Er:Lu2O3 laser at 2.84 µm using MoS2.

Efficient diode-pumped passively Q-switched Er:Lu2O3 laser operation at 2.84 µm was realized. A few-layer MoS2 nanosheet film on a YAG substrate, was fabricated and employed as saturable absorber (SA) in a short plane-plane cavity. Under an absorbed diode laser pump power of 7.61 W, an average output power of 1.03 W was generated with a pulse duration of 335 ns and a repetition rate of 121 kHz, resulting in a pulse energy of 8.5 µJ.

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.

Surface modification of Pt(100) for electrocatalytic nitrate reduction to dinitrogen in alkaline solution.

Nitrate reduction on a Pt(100) electrode modified by Cu (Cu/Pt(100)) and Rh (Rh/Pt(100)) adatoms have been studied in alkaline media by means of cyclic voltammetry and in situ online electrochemical mass spectrometry (OLEMS). According to the cyclic voltammograms, nitrate reduction is catalyzed by both Cu/Pt(100) and Rh/Pt(100). Ammonia is the main product on the Rh/Pt(100) electrode in alkaline media. On Cu/Pt(100), the selective conversion from NO3(-) to N2 may be achieved. The Cu sites catalyze the reduction of NO3(-) to NO2(-), and the Pt(100) sites catalyze the reduction of NO2(-) to N2, though in different potential windows.

Using graphene nanosheets as a conductive additive to enhance the rate performance of spinel LiMn2O4 cathode material.

Graphene nanosheets (GNs) were directly used as a type of novel but powerful planar conductive additive in spinel LiMn2O4 (LMO)-based electrodes, to improve the low electronic conductivity of LMO. It was found that the specific capacity and cycling performance of LMO were obviously enhanced when GNs co-existed with acetylene black (AB), a conventional carbon-based conductive agent, at an appropriate weight ratio in the LMO-based electrode (GNs and AB were 5 wt% and 10 wt% of the total weight, respectively). The unusual phenomenon was attributed to the following two reasons: (i) the planar GNs could bridge LMO particles more effectively via a "plane-to-point" conducting mode; (ii) AB particles might serve as the fillings in the electrode and connect the isolated LMO particles to GNs through a "filling effect", thereby constructing a novel and more effective conducting network. In this way, the synergy effect between the "plane-to-point" conducting mode (due to GNs) and the "filling" mode (due to AB) significantly decreased the charge-transfer resistance of the LMO-based electrode. With the much faster charge-transfer process, the rate performance of LMO was greatly enhanced. In contrast, when GNs were in excess, the effective conducting network was weakened by the agglomeration of GNs and the absence of AB, so the conductivity and the rate performance of LMO were not improved and even decreased.

Well-defined nanoporous palladium for electrochemical reductive dechlorination.

Well-defined nanoporous palladium (np-Pd) fabricated by a modified electrochemical dealloying procedure is demonstrated to be an excellent electrocatalyst material for reductive degradation of both carbon tetrachloride and chlorobenzene.

Electrocatalytic oxidation of nucleobases by TiO2 nanobelts.

Two kinds of TiO(2) nanobelts were prepared from commercial P-25 powders via an alkaline hydrothermal method with and without an acid etching process. The uncauterized nanobelts (TNs) exhibited a smooth surface, and mixed phases of anatase and TiO(2) (B), whereas the cauterized ones (CTNs) displayed a rough surface and a pure anatase structure. TNs and CTNs were then deposited onto a glassy carbon electrode (GCE) surface with a conductive adhesive (CA), and the resulting chemically modified electrodes exhibited electrocatalytic activities in the oxidation of nucleobases in a 0.1 M phosphate buffer solution (PBS) at pH 7.4. For guanine and adenine, well-defined oxidation peaks were observed in voltammetric measurements at about +0.62 and +0.89 V, respectively, at a potential sweep rate of 100 mV s(-1), whereas for cytosine, uracil and thymine, the voltammetric features were not obvious. The average surface coverages (Γ) of guanine and adenine on the CTNs/CA/GCE electrode were estimated to be 4.75 × 10(-10) and 7.44 × 10(-10) mol cm(-2), respectively, which were about twice those at the TNs/CA/GCE electrode. The enhanced activity of the CTN-based electrode towards purine nucleobase oxidation was ascribed to the large specific surface area and anatase structures with enhanced (001) facets of the CTN that facilitated adsorption of the analytes onto the electrode surface and charge transport through the electrode surface layer.

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.

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.

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.

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.

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.

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.