Fabrication of Poly (Trans-3-(3-Pyridyl)Acrylic Acid)/Multi-Walled Carbon Nanotubes Membrane for Electrochemically Simultaneously Detecting Catechol and Hydroquinone.

Herein, conductive polymer membrane with excellent performance was successfully fabricated by integrating carboxylated multi-walled carbon nanotubes (MWCNTs) and poly (trans-3-(3-pyridyl) acrylic acid) (PPAA) film. The drop-casting method was employed to coated MWCNTs on the glassy carbon electrode (GCE) surface, and PPAA was then electropolymerized onto the surface of the MWCNTs/GCE in order to form PPAA-MWCNTs membrane. This enables the verification of the excellent performances of proposed membrane by electrochemically determining catechol (CC) and hydroquinone (HQ) as the model. Cyclic voltammetry experiments showed that the proposed membrane exhibited an obvious electrocatalytic effect on CC and HQ, owing to the synergistic effect of PPAA and MWCNTs. Differential pulse voltammetry was adopted for simultaneous detection purposes, and an increased electrochemical responded to CC and HQ. A concentration increase was found in the range of 1.0 × 10-6 mol/L~1.0 × 10-4 mol/L, and it exhibited a good linear relationship with satisfactory detection limits of 3.17 × 10-7 mol/L for CC and 2.03 × 10-7 mol/L for HQ (S/N = 3). Additionally, this constructed membrane showed good reproducibility and stability. The final electrode was successfully applied to analyze CC and HQ in actual water samples, and it obtained robust recovery for CC with 95.2% and 98.5%, and for HQ with 97.0% and 97.3%. Overall, the constructed membrane can potentially be a good candidate for constructing electrochemical sensors in environmental analysis.

Upconversion nanoparticles anchored MnO2 nanosheets for luminescence "turn on" detecting hydrogen peroxide.

The sensitively and reliably detecting hydrogen peroxide (H2O2) is of significant for biology and environment protection fields. Herein, we reported a high sensitive H2O2 nanoprobe based on upconversion nanoparticles (UCNPs) anchored MnO2 nanosheets. In which, DNA modified NaYF4@NaYF4:Yb,Tm core-shell nanoparticles were anchored onto the MnO2 nanosheets surface via π-π stacking. Owing to the luminescence resonance energy transfer, the blue luminescence of UCNPs was effectively quenched by MnO2 nanosheets, then the luminescence could be restored by adding H2O2 for reducing MnO2 to Mn2+, and achieving a H2O2 concentration-dependent luminescence change, the detection limit could reach to 0.23 nM (S/N = 3). The proposed method could detect H2O2 in serum, lake water and real samples. Thus, a desired upconversion luminescence sensing strategy for detection H2O2 in life and environmental analysis was successfully constructed. It may be provide a potential tool in disease diagnosis and environmental monitoring fields.

Ratiometric and visual determination of copper ions with fluorescent nanohybrids of semiconducting polymer nanoparticles and carbon dots.

Developing nanohybrid composition based fluorescent carbon dots (CDs) for ratiometric detection of copper ions is highly appealing. Herein, a ratiometric sensing platform (GCDs@RSPN) for copper ions detection has been developed by loaded green fluorescence carbon dots (GCDs) on the surface of red emission semiconducting polymer nanoparticles (RSPN) through electrostatic adsorption. The GCDs, featuring abundant amino groups, can selectively bind copper ions to induce the photoinduced electron transfer, leading to fluorescence quenching. A good linearity within the range of 0-100 µM is obtained, and the limit of detection (LOD) is 0.577 µM by using obtained GCDs@RSPN as ratiometric probe to detect copper ion. Moreover, the paper-based sensor derived from GCDs@RSPN was successfully applied for the visual detection of Cu2+.

Correlations of Ion Composition and Power Efficiency in a Reverse Electrodialysis Heat Engine.

The main objective of this study is to explore the influence of ion composition on the trans-membrane potential across the ion exchange membrane (IEM), and thus offers a reference for the deep insight of "reverse electrodialysis heat engine" running in the composite systems. In comparison to the natural system (river water | seawater), the performance of the reverse electrodialysis (RED) stack was examined using NaHCO3, Na2CO3, and NH4Cl as the supporting electrolyte in the corresponding compartment. The effect of flow rates and the concentration ratio in the high salt concentration compartment (HCC)/low salt concentration compartment (LCC) on energy generation was investigated in terms of the open-circuit voltage (OCV) and power density per membrane area. It was found that the new system (0.49 M NaCl + 0.01 M NaHCO3|0.01 M NaHCO3) output a relatively stable power density (0.174 W·m-2), with the open-circuit voltage 2.95 V under the low flow rate of 0.22 cm/s. Meanwhile, the simulated natural system (0.5 M NaCl|0.01 M NaCl) output the power density 0.168 W·m-2, with the open-circuit voltage 2.86 V under the low flow rate of 0.22 cm/s. The findings in this work further confirm the excellent potential of RED for the recovery of salinity gradient energy (SGP) that is reserved in artificially-induced systems (wastewaters).

Dynamical properties of a room temperature ionic liquid: Using molecular dynamics simulations to implement a dynamic ion cage model.

The transport behavior of ionic liquids (ILs) is pivotal for a variety of applications, especially when ILs are used as electrolytes. Many aspects of the transport dynamics of ILs remain to be understood. Here, a common ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BmimNTf2), was studied with molecular dynamics simulations. The results show that BmimNTf2 displays typical structural relaxation, subdiffusive behavior, and a breakdown of the Stokes-Einstein diffusion relation as in glass-forming liquids. In addition, the simulations show that the translational dynamics, reorientation dynamics, and structural relaxation dynamics are well described by the Vogel-Fulcher-Tammann equation like fragile glass forming liquids. Building on previous work that employed ion cage models, it was found that the diffusion dynamics of the cations and anions were well described by a hopping process random walk where the step time is the ion cage lifetime obtained from the cage correlation function. Detailed analysis of the ion cage structures indicated that the electrostatic potential energy of the ion cage dominates the diffusion dynamics of the caged ion. The ion orientational relaxation dynamics showed that ion reorientation is a necessary step for ion cage restructuring. The dynamic ion cage model description of ion diffusion presented here may have implications for designing ILs to control their transport behavior.

Origin of heterogeneous dynamics in local molecular structures of ionic liquids.

Room-temperature ionic liquids (ILs) are generally considered as structurally heterogeneous with inherent polar/apolar phase separation. However, even after a decade of research, local dynamics in the heterogeneous structures of ILs remain neglected. Such local dynamics may influence the ion transport of electrolytes, as well as the reaction rate of solvents. In this study, we performed molecular dynamics simulation to analyze the local dynamics for the structural heterogeneity of ILs. Calculations of the diffusion, reorientation, and association dynamics showed a distinct heterogeneous dynamics between the polar and apolar regions of ILs. Further studies demonstrated that such local dynamic differences originate from local structural heterogeneity. Different energy barriers determine a predominant fast reorientation dynamics in apolar regions and a locally vibrating behavior in polar regions. Additionally, we suggested a new jumping mechanism to clarify the dynamic heterogeneity of ions in the polar regions. The results will help determine the origin of the heterogeneous dynamics in IL local structures and provide a theoretical basis for tuning the dynamic properties of ILs used as electrolytes or reaction solvents.

Dilute or Concentrated Electrolyte Solutions? Insight from Ionic Liquid/Water Electrolytes.

When room-temperature ionic liquids (IL) are used as an electrolyte, their transport behaviors are still under heavy debate due to their complicated ion-associations. In this article, we conducted molecular dynamics simulations to study the molecular scale ion associations from the very dilute 1-butyl-3-methylimidazolium iodide/water solution to the pure IL. It revealed that ions are localized in a multicoordinated ion cage structure with nanoseconds in concentrated IL solutions. Dynamics analyses indicate that the transport of this solution can be depicted by the Debye-Hückel model only in dilute IL/water electrolyte. The velocity and rotational correlation functions showed that the lifetime of translational and rotational motions are at the level of picoseconds and nanoseconds, respectively, because of the ion cage effect. The lifetime of ion association demonstrated that the recombination of association ions was prevalent in IL solutions. It means that the dipolar or stable contact ion-pairs model may not be suitable for depicting the IL transport.

Molecular insights into the electric double layers of ionic liquids on Au(100) electrodes.

The electric double layer structure and differential capacitance of single crystalline Au(100) electrodes in the ionic liquid 1-butyl-3-methyl-imidazolium hexafluorophosphate are investigated using molecular dynamics simulations. Results show strong adsorption on the electrode surface. The potential of zero charge (pzc) and maxima of differential capacitance are strongly dependent on the adsorption layer structure. At potentials near the pzc, cations and anions adjacent to the electrode surface are coadsorbed on the same screening layer. This strong adsorption layer results in overscreening effects on the compact layer and induces both a bell-shaped differential capacitance curve and a positive pzc. Moreover, the potential required for transition from overscreening to overcrowding is about 4.0 V. This transition potential may be attributed to the higher interaction energy between the Au(100) electrode and ions compared with the binding energy in our cation-anion system.

A novel nonenzymatic fluorescent sensor for glucose based on silica nanoparticles doped with europium coordination compound.

Amino-functionalized luminescent silica nanoparticles (LSNPs) doped with the europium(III) mixed complex, Eu(TTA)(3)phen with 2-thenoyltrifluoroacetone (TTA) and 1,10-phenanthroline(phen) were synthesized successfully using an revised Stöber method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR), and fluorescence spectroscopy were performed for characterizing the synthesized nanoparticles. In the presence of glucose, the fluorescence intensity of the amino-functionalized LSNPs was enhanced due to the enhanced fluorescence resonance energy transfer. Based on fluorescence-enhancing effect, a simple and sensitive method for the determination of glucose was proposed. Under the optimized experimental conditions, the enhanced fluorescence intensity ratio (DeltaF/F(0)) was linear with the concentration of glucose (c) in the range of 0.0-180 microg ml(-1) with a detection limit of 0.8 microg ml(-1) (S/N=3). The R.S.D. values were 0.33% and 0.37% at the levels of 22.5 and 100 microg ml(-1), respectively. The proposed method was applied to the determination of glucose in synthetic samples with satisfactory results. The proposed method was also performed to the analysis of blood glucose in human serum samples and the results were in good agreement with clinical data provided by the hospital, which indicates that the method presented here is not only simple, sensitive, but also reliable and suitable for practical applications.

Preparation of aminated core-shell fluorescent nanoparticles and their application to the synchronous fluorescence determination of gamma-globulin.

Amino-modified silica nanoparticles (FSNPs) doped with fluorescein isothiocyanate (FITC) were synthesized by using an aqueous core of reverse-micelle microemulsion as the nanoreactor in an easy one-pot method. Due to the FITC conjugating with (3-aminopropyl)triethoxysilane (APTS), the nanoparticles prevent the FITC from leaching from the silica matrix when immersed in aqueous solution. SEM, FTIR, fluorescence lifetime, a photobleaching experiment and synchronous fluorescence spectra were used to characterize the FSNPs. The synchronous fluorescence signal of FSNPs was enhanced when trace amounts of gamma-globulin (gamma-G) were added. Under the optimal experimental conditions, the enhanced fluorescence intensity (DeltaF) was linear with the concentration of gamma-G (c) in the range 0.3-4.8 microg/mL, with a detection limit of 0.04 microg/mL. The proposed method is simple, sensitive for the determination of trace amounts of gamma-G and used to determine the content of gamma-G in synthetic samples with satisfactory results.

A flow injection chemiluminescence method for the determination of fluoroquinolone derivative using the reaction of luminol and hydrogen peroxide catalyzed by gold nanoparticles.

Based on the enhancement of chemiluminescence (CL) of luminol-hydrogen peroxide-gold nanoparticles system by fluoroquinolones (FQs), a novel and rapid CL method is reported for the determination of FQs derivatives. Under the optimum conditions, the CL intensity is proportional to the concentration of FQs derivative in solution. The corresponding linear regression equations are established over the range of 0.08-1.28mug/mL for norfloxacin, 0.013-1.32mug/mL for ciprofloxacin, 0.014-1.4mug/mL for lomefloxacin, 0.029-1.46mug/mL for fleroxacin, 0.02-1.0mug/mL for ofloxacin and 0.01-1.44mug/mL for levofloxacin, respectively. The limits of detection (S/N=3) are 3.2, 9.5, 7.0, 9.0, 8.0, and 8.0ng/mL with the relative standard deviation (n=11) 4.3, 1.5, 1.9, 1.3, 1.6 and 2.1% for norfloxacin, ciprofloxacin, lomefloxacin, fleroxacin, ofloxacin and levofloxacin, respectively. This proposed method has been applied to detect FQs derivatives in human urine successfully.