Monometallic Ultrasmall Nanocatalysts via Different Valence Atomic Interfaces Boost Hydrogen Evolution Catalysis.

Synergistic monometallic nanocatalysts have attracted much attention due to their high intrinsic activity properties. However, current synergistic monometallic nanocatalysts tend to suffer from long reaction paths due to restricted nanoscale interfaces. In this paper, we synthesized the interstitial compound N-Pt/CNT with monometallic atomic interfaces. The catalysts are enriched with atomic interfaces between higher valence Ptδ+ and Pt0, allowing the reaction to proceed synergistically within the same component with an ideal reaction pathway. Through ratio optimization, N2.42-Pt/CNT with a suitable ratio of Ptδ+ and Pt0 is synthesized. And the calculated turnover frequency of N2.42-Pt/CNT is about 37.4 s-1 (-0.1 V vs reversible hydrogen electrode (RHE)), six times higher than that of the commercial Pt/C (6.58 s-1), which is the most intrinsically active of the Pt-based catalysts. Moreover, prepared N2.42-Pt/CNT exhibits excellent stability during the chronoamperometry tests of 200 h. With insights from comprehensive experiments and theoretical calculations, Pt with different valence states in monometallic atomic interfaces synergistically accelerates the H2O dissociation step and optimizes the Gibbs free energy of H* adsorption. And the existence of desirable hydrogen transfer paths substantially facilitates hydrogen evolution reaction kinetics.

Au-Co nanoparticles-embedded N-doped carbon nanotube hollow polyhedron modified electrode for electrochemical determination of quercetin.

A core-shell ZIF-8@ZIF-67 was synthesized and pyrolyzed to get a Co nanoparticles-embedded N-doped carbon nanotube hollow polyhedron (Co@NCNHP). Then Au nanoparticles were formed on the surface and core of Co@NCNHP to obtain an Au-Co bimetal decorated NCNHP (Au-Co@NCNHP). The resultant nanocomposite was characterized by various methods including transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The Au-Co@NCNHP-based electrochemical sensor displayed an obviously high electrocatalytic response to the oxidation of quercetin, which was attributed to the synergistic effects of Au-Co bimetal nanoparticles and N-doped carbon nanotube with hollow polyhedron. Under the optimal conditions, the oxidation peak currents exhibited a wide linear dynamic range for quercetin concentration from 0.050 to 35.00 µmol/L, and the detection limit was 0.023 ± 0.002 µmol/L (S/N = 3). The analytical applications of the proposed electrochemical sensor were checked by determining the content of quercetin in medical and onion samples with satisfactory results. Grapical abstract.

Photoelectrochemical aptasensor for lead(II) by exploiting the CdS nanoparticle-assisted photoactivity of TiO2 nanoparticles and by using the quercetin-copper(II) complex as the DNA intercalator.

A photoelectrochemical (PEC) aptasensor for Pb(II) detection is described. A nanocomposite consisting of CdS (2.5 µm) and TiO2 nanoparticles (10 nm) was used as a photoactive material, and gold nanochains (Au NCs) as the support for immobilization of the Pb(II)-binding aptamer. The quercetin-copper(II) complex was further employed as the intercalator for the improvement of the photoactivity by embedding it into dsDNA. In the presence of Pb(II), a Pb(II)-stabilized G-quadruplex was formed between Pb(II) and DNA S1. This is accompanied by unwinding of the dsDNA and the release of the quercetin-copper(II) complex from the surface of the sensor. This results in a decrease of the photocurrent that drops linearly from 5.0 × 10-12 to 1.0 × 10-8 mol·L-1 Pb(II) concentration range with a detection limit of 1.6 × 10-12 mol·L-1. The method was applied to the determination of Pb(II) in various samples and gave satisfactory results. Graphical abstractA photoelectrochemical aptasensor was fabricated for the detection of Pb(II) based on CdS-TiO2 nanocomposite modified indium tin oxide (ITO) electrode. Gold nanochains (AuNCs) were used as anchor to immobilize the aptamers S1 and S2 that form a double helix structure by DNA hybridization. After embedding of quercetin-copper(II) complex as intercalator and electron donor, the concentrations of Pb(II) were determined by the changes of photocurrents.

A biomass-derived porous carbon-based nanocomposite for voltammetric determination of quercetin.

Porous carbon was prepared from wheat flour by alkali treatment and carbonization. The resulting biomass-derived porous carbon (BPC) was employed to prepare a Pt-Au-BPC nanocomposite by a hydrothermal method. The material was then placed on the surface of a carbon ionic liquid electrode (CILE). The Pt-Au-BPC was characterized by SEM, XPS, and the modified CILE by electrochemical methods. They revealed a porous structure, a large specific surface with high conductivity. Pt-Au-BPC/CILE was applied to the sensitive determination of quercetin. Electrochemical response was studied by cyclic voltammetry and differential pulse voltammetry (DPV). Under optimized experimental conditions, the oxidation peak current (measured at 0.48 V vs. Ag/AgCl by DPV) increases linearly in the 0.15 to 6.0 µM and in the 10.0 to 25.0 µM quercetin concentration range. The detection limit is 50.0 nM (at 3σ). The Pt-Au-BPC/CILE was applied to the direct determination of quercetin in ginkgo tablets sample and gave satisfactory results. Graphical abstract A Pt-Au-BPC nanocomposite modified carbon ionic liquid electrode was applied to differential pulse voltammetric determination of quercetin. BPC: biomass-derived porous carbon.

Voltammetric sensing performances of a carbon ionic liquid electrode modified with black phosphorene and hemin.

A black phosphorene (BPE) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) hybrid was used for the immobilization of hemin on a carbon ionic liquid electrode (CILE). BPE inside the PEDOT:PSS film was stable without adverse effects of water and oxygen. The hemin-modified electrode facilitates electrochemical communication with a couple of well-shaped and enhanced redox waves. Therefore BPE exhibits an accelerating function to the electron movement. This sensor exhibits excellent electrocatalytic effects on the reduction of various substrates including trichloroacetic acid (TCA), nitrite and H2O2. As for TCA, the reduction current at -0.36 V (vs. Ag/AgCl) increases linearly in the concentration range from 2.0 to 180 mmol·L-1 with a detection limit of 0.67 mmol·L-1 (at 3σ). As for nitrite, the reduction current at -0.59 Vis linear in the 1.0 to 10.5 mmol·L-1 concentration range, and the detection limit is 0.33 mmol·L-1 (at 3σ). As for H2O2, the reduction current at -0.033 V (vs. Ag/AgCl) is linear in the concentration range from 4.0 to 35.0 mmol·L-1 and the detection limit is 1.3 mmol·L-1 (at 3σ). The real sample was analyzed with satisfactory results, which indicated that BPE had potential applications in the field of electrochemical biosensor. Graphical abstract Photos of (a) black phosphorene (BPE) solution, (b) poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), (c) BPE-PEDOT:PSS (1:5) dispersion, and the fabrication procedure of this electrochemical sensor. It was applied to the determination of trichloroacetic acid, nitrite and hydrogen peroxide.

A graphene modified carbon ionic liquid electrode for voltammetric analysis of the sequence of the Staphylococcus aureus nuc gene.

The authors describe a voltammetric method for the detection of the nuc ssDNA sequence originating from Staphylococcus aureus by using a carbon ionic liquid electrode modified with electrodeposited three-dimensional graphene (3DGR). Probe ssDNA was electrostatically adsorbed on the modified electrode by a potentiostatic method. The porous structure and large surface area of 3DGR greatly increase the amount of immobilized probe ssDNA on the interface, which is beneficial for the reaction with target ssDNA. By using Methylene Blue (MB) as the electrochemical probe, the reduction peak current of MB (best measured at -0.30 V vs. SCE) can be used for detecting hybridization. The differential pulse voltammetric current of MB increases linearly in the 1.0 × 10-12 mol L-1 to 1.0 × 10-6 mol L-1 nuc concentration range, and the detection limit is 3.3 × 10-13 mol L-1 (at 3σ). The DNA sensor was successfully applied to the determination of the PCR product of the gene in pork. Graphical abstract Response of an electrochemical DNA biosensor based on the use of a carbon ionic liquid electrode modified with three-dimensional graphene. It enables sensitive voltammetric detection of the specific sequence of the Staphylococcus aureus nuc gene.

Universal Synthesized Strategy for Amorphous Pd-Based Nanosheets Boosting Ambient Ammonia Electrosynthesis.

The electrocatalytic nitrogen reduction reaction (NRR) is emerging as a great promise for ambient and sustainable NH3 production while it still suffers from the high adsorption energy of N2 , the difficulty of *NN protonation, and inevitable hydrogen evolution, leading to a great challenge for efficient NRR. Herein, we synthesized a series of amorphous trimetal Pd-based (PdCoM (M = Cu, Ag, Fe, Mo)) nanosheets (NSs) with an ultrathin 2D structure, which shows high efficiency and robust electrocatalytic nitrogen fixation. Among them, amorphous PdCoCu NSs exhibit excellent NRR activity at low overpotentials with an NH3 yield of 60.68 µg h-1 mgcat -1 and a corresponding Faraday efficiency of 42.93% at -0.05 V versus reversible hydrogen electrode as well as outstanding stability with only 5% decrease after a long test period of 40 h at room temperature. The superior NRR activity and robust stability should be attributed to the large specific surface area, abundant active sites as well as structural engineering and electronic effect that boosts up the Pd 4d band center, which further efficiently restrains the hydrogen evolution. This work offers an opportunity for more energy conversion devices through the novel strategy for designing active and stable catalysts.

ZnO-reduced graphene oxide composite based photoelectrochemical aptasensor for sensitive Cd(II) detection with methylene blue as sensitizer.

In this paper a photoelectrochemical (PEC) aptasensor based on specific recognition with conformational changed after the target Cd(II) identification was fabricated. A ZnO and reduced graphene oxide (ZnO-rGO) nanocomposite with enhanced PEC activity was designed as photoactive material. After the further incorporation of gold nanoparticles (AuNPs) with ZnO-rGO nanocomposite, the enhanced photocurrent signal could be detected owing to the localized surface plasmon resonance and good conductivity of AuNPs. In addition, AuNPs were used as anchors for immobilization of -SH modified aptamer S1. After that aptamer S2 was paired with S1 sequence to form complementary double stranded DNA (dsDNA) on the electrode surface. Methylene blue (MB) was acted as sensitizer and assembled in dsDNA structure to amplify photocurrent response. When Cd(II) was bound to the aptamer presented on the sensing interface, S2 specifically recognized and captured Cd(II), which resulted in the unwinding of dsDNA structure and the separation of MB molecules from the electrode surface with photocurrent response decreased. The photocurrent was detected by a double-working-electrode system, which used the modified electrode as the first working electrode and glassy carbon electrode (GCE) as the second working electrode. Dopamine (DA) was added to the electrolyte and acted as the electron donor, which could be oxidized on the modified electrode and reduced on the GCE to form a cyclic reaction, leading to the enhanced photocurrent response with improved photocurrent stability. This MB sensitized PEC aptasensor exhibited a high sensitivity with a detection limit of 1.8 × 10-12 mol/L (3σ). Thus, a highly sensitive aptasensor with double-working-electrode detection method for Cd(II) determination were established and further applied to the water samples analysis.

Fabrication of ZIF-67@three-dimensional reduced graphene oxide aerogel nanocomposites and their electrochemical applications for rutin detection.

Three-dimensional reduced graphene oxide aerogel (3D rGA) was synthesized by hydrothermal method and cobalt imidazolate framework-67 (ZIF-67) was further grown in situ on the 3D rGA matrix directly. The resultant ZIF-67@3D rGA nanocomposite was checked by different techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrophotometry (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA). The presence of 3D rGA acted as the backbone for the loading of ZIF-67, and the resultant ZIF-67@3D rGA nanocomposite exhibited an interconnected porous structure with large surface area and high conductivity due to synergistic effects, which was applied to the electrode modification and used for rutin detection. The developed method showed excellent performance with a wider linear range (0.05-200.0 µmol/L) and lower detection limit (0.028 ± 0.0016 µmol/L, S/N=3). Various samples including the compounded rutin tablets and onions were analyzed by this modified electrode with satisfactory results.

A fungus-derived biomass porous carbon-MnO2 nanocomposite-modified electrode for the voltammetric determination of rutin.

In this study, we designed a simple procedure for the synthesis of fungus-derived biomass porous carbon (FBPC), which was further used to prepare a MnO2@FBPC composite by a hydrothermal method. The MnO2@FBPC nanocomposite showed a porous structure, large specific surface area, and high conductivity, and was modified on the carbon ionic liquid electrode (CILE) to obtain a working electrode for the sensitive voltammetric determination of rutin. The electrochemical response of rutin was studied via cyclic voltammetry with electrochemical parameters calculated. Under the optimal conditions, the linear range for the rutin analysis was obtained by the differential pulse voltammetry from 0.008 to 700.0 µmol L-1 with the detection limit of 2.67 nmol L-1 (3σ). This MnO2@FBPC/CILE was applied to directly detect the rutin concentration in drug and human urine samples with satisfactory results.

Synthesis and utilization of Co3O4 doped carbon nanofiber for fabrication of hemoglobin-based electrochemical sensor.

In this paper cobalt oxide (Co3O4) nanoparticles were mixed with polyacrylonitrile to prepare Co3O4 doped carbon nanofiber (CNF) composite by electrospinning and carbonization, which was further used to modify on carbon ionic liquid electrode (CILE). Hemoglobin (Hb) was immobilized on Co3O4-CNF/CILE surface with Nafion acted as the protective film to fabricate an electrochemical biosensor (Nafion/Hb/Co3O4-CNF/CILE). Electrochemical behavior of Hb on the electrode was investigated with a pair of quasi-reversible redox peak appeared on cyclic voltammogram and electrochemical parameters were calculated. Moreover, this biosensor had good analytical capabilities for electrocatalytic reduction of different substrates including trichloroacetic acid, potassium bromate and sodium nitrite with wider detection range from 40.0 to 260.0 mmol L-1, 0.1 to 48.0 mmol L-1 and 1.0 to 12.0 mmol L-1 by cyclic voltammetry, respectively. The proposed method showed excellent anti-interferences ability with good selectivity and was successful used for quantitative detection of real samples, which displayed the potential applications to develop into a new analytical device.

2-(1H-Benzotriazol-1-yl)-1-(4-bromo-benzo-yl)ethyl 2-chloro-benzoate.

In the title compound, C(22)H(15)BrClN(3)O(3), the benzotriazole ring system makes dihedral angles of 2.43 (1) and 71.51 (1)° with the bromo-phenyl and chloro-phenyl rings, respectively; the angle between the latter two rings is 69.26 (1)°. In the crystal structure, mol-ecules are linked into chains by inter-molecular C-H⋯O hydrogen bonds. The crystal packing is further stabilized by π-π (with a centroid-centroid distance of 3.764 Å) and C-H⋯π inter-actions.

3-(1H-Benzotriazol-1-yl)-1-(3-methoxy-phen-yl)propan-1-one.

In the title mol-ecule, C(16)H(15)N(3)O(2), the benzotriazole fragment and the benzene ring form a dihedral angle of 75.02 (1)°. In the crystal structure, mol-ecules related by translation along the a axis are linked into chains via weak C-H⋯π inter-actions.

Electrochemical performance of myoglobin based on TiO2-doped carbon nanofiber decorated electrode and its applications in biosensing.

A new biosensing strategy based on a TiO2-doped carbon nanofiber (CNF) composite modified electrode was developed. TiO2@CNF was prepared by electrospinning with further carbonization, before being characterized by various methods and used for electrode modification on the surface of carbon ionic liquid electrode (CILE). Myoglobin (Mb) was further immobilized on the modified electrode surface. The results of ultraviolet-visible (UV-vis) and Fourier transform infrared (FT-IR) spectroscopy showed that Mb maintained its native structure without denaturation in the composite film. Direct electron transfer and the electrocatalytic properties of Mb on the electrode surface were further investigated. A pair of quasi-reversible redox peaks appeared on the cyclic voltammogram, indicating that direct electrochemistry of Mb was realized in the nanocomposite film. This could be attributed to the specific properties of TiO2@CNF nanocomposite, including a large surface-to-volume ratio, good biocompatibility and high conductivity. Nafion/Mb/TiO2@CNF/CILE exhibited an excellent electrochemical catalytic ability in the reduction of trichloroacetic acid, NaNO2 and H2O2. All results demonstrated potential applications of TiO2@CNF in third-generation electrochemical biosensors.

Myoglobin- and Hydroxyapatite-Doped Carbon Nanofiber-Modified Electrodes for Electrochemistry and Electrocatalysis.

In this paper, a hydroxyapatite (HAp)-doped carbon nanofiber (CNF)-modified carbon ionic liquid electrode (CILE) was prepared and used for the investigation on the direct electrochemistry and electrocatalysis of myoglobin (Mb). HAp nanoparticles were mixed within a polyacrylonitrile (PAN) solution, and a HAp@PAN nanofiber was synthesized by electrospinning process, which was further controlled by carbonization at 800 °C for 2 h in a nitrogen atmosphere to get a HAp@CNF nanocomposite. Various techniques were used to check the physicochemical properties of HAp@CNF. Mb was mixed with a HAp@CNF dispersion solution and casted on the surface of CILE to obtain an electrochemical sensing platform. The direct electrochemistry of Mb on the modified electrode was checked when a pair of enhanced redox waves appeared, indicating the direct electron transfer of Mb. HAp@CNF exhibited high conductivity, good biocompatibility, and large surface area, which was beneficial for Mb immobilization. The modified electrode showed excellent electrocatalytic activity toward the reduction of trichloroacetic acid and sodium nitrite, which was further used to establish a new electroanalytical method. Real samples were analyzed by the proposed method with satisfactory results.

Platinum nanoparticles decorating a biomass porous carbon nanocomposite-modified electrode for the electrocatalytic sensing of luteolin and application.

A sensitive electrochemical method was proposed for the determination of luteolin based on platinum (Pt) nanoparticles decorating a biomass porous carbon (BPC) composite-modified carbon ionic liquid electrode (CILE). For Pt-BPC/CILE, a pair of well-defined redox peaks of luteolin appeared with enhanced peak currents and the positive movement of peak potentials, proving the electrocatalytic activity of the Pt-BPC nanocomposite for redox reaction. The results can be ascribed to the porous structure of BPC, the catalytic activity of Pt nanoparticles and their synergistic effects. Electrochemical parameters were calculated via cyclic voltammetry and differential pulse voltammetry. The results showed that the oxidation peak currents increased linearly with the concentration of luteolin in the range from 0.008 to 100.0 µmol L-1, with a detection limit of 2.6 ± 0.054 nmol L-1. The analytical performance of this sensor was checked by the detection of luteolin contents in a real Duyiwei capsule sample with satisfactory results.

Three-dimensional reduced graphene oxide aerogel modified electrode for the sensitive quercetin sensing and its application.

Quercetin belongs to flavonoid drug that has favorable properties such as antiviral, anticancer, anti-allergic and anti-tumor. Therefore a sensitive method is highly required for quercetin determination. In this paper, a three-dimensional reduced graphene oxide aerogel (3D-rGA) with excellent porous framework was synthesized via one-step hydrothermal technique. The characteristics and performances of 3D-rGA were checked by SEM, TEM, BET, XRD, Raman, FT-IR, XPS and electrochemical methods, which exhibited good properties including unique porous structure, large surface area and excellent conductivity. 3D-rGA was further used as the modifier on carbon ionic liquid electrode (CILE) to construct a modified electrode, which was applied to sensitive and selective determination of quercetin. Electrochemical responses of quercetin were accelerated with a pair of symmetrical cyclic voltammetric peaks in good shape appeared and the electrochemical parameters were calculated. The sensitive oxidation response of quercetin from differential pulse voltammetry was verified. Under the selected conditions, electroanalysis of quercetin was established by plotting the oxidation peak currents against quercetin concentrations with linear regression analysis. A wider linear range from 0.1 µmol/L to 100.0 µmol/L was obtained with a detection limit of 0.065 µmol/L (3S0/S). This as-explored approach could be successfully utilized for quercetin detection in Ginkgo tablets.

Investigation on direct electrochemical and electrocatalytic behavior of hemoglobin on palladium-graphene modified electrode.

Palladium-graphene (Pd-GR) nanocomposite was acted as modifier for construction of the modified electrode with direct electrochemistry of hemoglobin (Hb) realized. By using Nafion as the immobilization film, Hb was fixed tightly on Pd-GR nanocomposite modified carbon ionic liquid electrode. Electrochemical behaviors of Hb modified electrode were checked by cyclic voltammetry and a pair of redox peaks originated from direct electron transfer of Hb was appeared. The Hb modified electrode had excellent electrocatalytic activity to the reduction of trichloroacetic acid and sodium nitrite in the concentration range from 0.6 to 13.0mmol·L-1 and from 0.04 to 0.5 mmol·L-1. Therefore Pd-GR nanocomposite was proven to be a good candidate for the fabrication of third-generation electrochemical biosensor.

Profiling of Extracellular Toxins Associated with Diarrhetic Shellfish Poison in Prorocentrum lima Culture Medium by High-Performance Liquid Chromatography Coupled with Mass Spectrometry.

Extracellular toxins released by marine toxigenic algae into the marine environment have attracted increasing attention in recent years. In this study, profiling, characterization and quantification of extracellular toxin compounds associated with diarrhetic shellfish poison (DSP) in the culture medium of toxin-producing dinoflagellates were performed using high-performance liquid chromatography-high-resolution mass spectrometry/tandem mass spectrometry for the first time. Results showed that solid-phase extraction can effectively enrich and clean the DSP compounds in the culture medium of Prorocentrum lima (P. lima), and the proposed method achieved satisfactory recoveries (94.80%-100.58%) and repeatability (relative standard deviation ≤9.27%). Commercial software associated with the accurate mass information of known DSP toxins and their derivatives was used to screen and identify DSP compounds. Nine extracellular DSP compounds were identified, of which seven toxins (including OA-D7b, OA-D9b, OA-D10a/b, and so on) were found in the culture medium of P. lima for the first time. The results of quantitative analysis showed that the contents of extracellular DSP compounds in P. lima culture medium were relatively high, and the types and contents of intracellular and extracellular toxins apparently varied in the different growth stages of P. lima. The concentrations of extracellular okadaic acid and dinophysistoxin-1 were within 19.9-34.0 and 15.2-27.9 µg/L, respectively. The total concentration of the DSP compounds was within the range of 57.70-79.63 µg/L. The results showed that the proposed method is an effective tool for profiling the extracellular DSP compounds in the culture medium of marine toxigenic algae.

Application of three-dimensional reduced graphene oxide-gold composite modified electrode for direct electrochemistry and electrocatalysis of myoglobin.

In this paper a three-dimensional (3D) reduced graphene oxide (RGO) and gold (Au) composite was synthesized by electrodeposition and used for the electrode modification with carbon ionic liquid electrode (CILE) as the substrate electrode. Myoglobin (Mb) was further immobilized on the surface of 3D RGO-Au/CILE to obtain an electrochemical sensing platform. Direct electrochemistry of Mb on the modified electrode was investigated with a pair of well-defined redox waves appeared on cyclic voltammogram, indicating the realization of direct electron transfer of Mb with the modified electrode. The results can be ascribed to the presence of highly conductive 3D RGO-Au composite on the electrode surface that accelerate the electron transfer rate between the electroactive center of Mb and the electrode. The Mb modified electrode showed excellent electrocatalytic activity to the reduction of trichloroacetic acid in the concentration range from 0.2 to 36.0 mmol/L with the detection limit of 0.06 mmol/L (3σ).