Silver nanoparticle decorated poly(2-aminodiphenylamine) modified carbon paste electrode as a simple and efficient electrocatalyst for oxidation of formaldehyde

This work describes the promising activity of silver nanoparticles on the surface of a poly(2-amino diphenylamine) modified carbon paste electrode (CPE) towards formaldehyde oxidation. Electrodeposition of the conducting polymer film on the CPE was carried out using consecutive cyclic voltammetry in an aqueous solution of 2-aminodiphenylamine and HCl. Nitrogen groups in the polymer backbone had a Ag ion accumulating effect, allowing Ag nanoparticles to be electrochemically deposited on the surface of the electrode. The electrochemical and morphological characteristics of the modified electrode were investigated. The electro-oxidation of formaldehyde on the surface of electrode was studied using cyclic voltammetry and chronoamperometry in aqueous solution of 0.1 mol/L NaOH. The electro-oxidation onset potential was found to be around -0.4 V, which is unique in the literature. The effect of different concentrations of formaldehyde on the electrocatalytic activity of the modified electrode was investigated. Finally, the diffusion coefficient of formaldehyde in alkaline media was calculated to be 0.47 × 10^-6 cm²/s using chronoamperometry.     

PVT properties of imidazolium-, phosphonium-, pyridinium- and pyrrolidinium-based ionic liquids using critical point constants

Song and Mason equation of state (EOS) with a simple modification has been extended to modelling PVT properties of ionic liquids (ILs). The considered ILs are [C₁mim][MeSO4], [C₁mim][CH₃OC₂H₅SO₄], [C₁mim][(CH₃)₂PO₄], [C₂mim][MeSO4], [C₂mim][BF₄], [C₂mim][SCN], [C₂eim][NTf₂], [C₄mim][C(CN)₃], [C₄mim][CF₃SO₃], [C₄mim][SCN], [C₅mim][NTf₂], [C₈mim][NTf₂], [(C₆H₁₃)₃P(C₁₄H₂₉)][Cl], [(C₆H₁₃)₃P(C₁₄H₂₉)][NTf₂], [(C₆H₁₃)₃P(C₁₄H₂₉)][Ac], [C₃mpyr][NTf₂], [C₄mpyr][NTf₂] and [Py][C₂H₅OC₂H₄SO₄]. Three temperature-dependent parameters in the proposed EOS have been scaled as functions of reduced temperature with the use of the law of corresponding states. It is shown that the knowledge of just critical temperature and critical density is sufficient to predict the PVT properties of these ILs. The overall average absolute deviation of calculated densities from literature values for 1347 data points of 18 ILs was found to be 0.58%. The predicted density of ILs from proposed EOS has been compared with those obtained by other literature work. Moreover, we indicate that the Zeno line regularity can well be predicted by proposed model for ILs.     

A new PVC matrix membrane sensor for determination of praseodymium(III) ion based on bis(salicylaldehyde)thiocarbohydrazone as an ion carrier

The sufficient amounts of bis(salicylaldehyde) thiocarbohydrazone (STCH) as a lipophilic selective element (3%, w/w), sodium nitrobenzene (NB) as a plasticizer (64%, w/w), tetraphenyl borate (NaTPB) as an anionic additive (3%, w/w), and poly vinyl chloride (PVC) as a polymeric matrix (30%, w/w) was employed to form a PVC membrane of a new Pr³⁺ ions selective sensor to apply as an indicator electrode in analytical applications. The best electrode response was observed in the slope (19.5 ± 0.7 mV per decade) over a wide concentrations from lower (1.0 × 10^?6 mol L^–1) to higher (1.0 × 10^?2 mol L^–1) of Pr³⁺ ion solution with a detection limit of 8.5 × 10^–7 mol L^–1. This electrode showed the fast response time about 10 second for praseodymium ion concentration range of 1.0 × 10^–6 to 1.0 × 10^–2 mol L^–1, in the pH range of 2.3–7.9. The matched potential method was applied to study the selectivity of electrode toward Pr³⁺ ions in comparison with many common cations. The results showed the negligible disturbance of all other cations on the proposed praseodymium(III) electrode. The making sensor has been employed successfully as an indicator electrode in the potentiometric titration of praseodymium(III) solution with EDTA at pH 6.0. Moreover the applicability of the sensor was studied in determination of Pr³⁺ ion in mixtures of different ions.     

Application of the localized surface plasmon resonance of gold nanoparticles for the determination of 1,1-dimethylhydrazine in water: Toward green analytical chemistry

Localized surface plasmon resonance (LSPR) is an optical phenomena generated by light when it interacts with conductive nanoparticles that are smaller than the incident wavelength. In this work, we proposed a simple, fast, and green method for spectrophotometric determination of unsymmetrical 1,1-dimethylhydrazine (UDMH) based on LSPR property of gold nanoparticles (AuNPs). An LSPR band is produced via reduction of Au³⁺ ions in solution by UDMH as active reducing agent in the presence of cetyltrimethylammonium chloride as a capping agent. Some important parameters in the formation of LSPR including Au(III) concentration, pH, concentration of stabilizer, and reaction time were studied and optimized. Under optimum conditions, the LSPR intensity displays linear response with the increasing UDMH concentration in the range from 0.5–10 μg/mL at 550 nm with a detection limit of 0.2 μg/mL. Also, the relative standard deviation for ten replicate determination of 5.0 μg/mL of UDMH was 3%. Usage of AuNPs as new nontoxic reagent instead of hazardous reagents in the spectrophotometric determination of UDMH is a step toward green analytical chemistry. The proposed method was successfully applied for determination of UDMH in water and wastewater samples.     

Fluorescence based turn-on strategy for determination of microRNA-155 using DNA-templated copper nanoclusters

The authors report on a new approach for the determination of the breast cancer biomarker microRNA-155 (miRNA-155). It is based on the measurement of the fluorescence shift of oligonucleotide-templated copper nanoclusters (DNA-CuNC). A probe DNA was designed that acts as a template for the preparation of CuNC which, under 400 nm excitation, exhibit strong fluorescence enhancement at 490 nm and a 90 nm Stokes shift after binding to target miRNA-155 and formation of a DNA-RNA heteroduplex. Under the optimal conditions, the fluorescence of the DNA-CuNC increases with increasing concentration of miRNA-155 in the range from 50 pM to 10 nM, with a 11 pM detection limit. The assay has excellent selectivity over noncomplementary RNA. The method was applied to the determination of miRNA-155 in the presence of human plasma and saliva.

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Graphical abstract Schematic of the detection strategy that relies on the fluorescence shift of DNA-CuNCs resulting from the specific binding of DNA-CuNCs with target miRNA-155. Fluorescence intensities are linearly proportional to the concentrations of target RNA from 50 pM to 10 nM.

     

Highly selective fluorescent recognition of Zn2+ based on naphthalene macrocyclic derivative

A new macrocyclic chemosensor containing two naphthalene fluorophores has been synthesized. The fluorescent properties of this receptor has been studied in the presence of various metal ions such as Na⁺, Ag⁺, Cr³⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺. When increasing concentrations of Zn²⁺ ions were introduced, the emission of L was drastically increased (EFE = 4.34). This special change was not observed when other metal ions were used; such highly selective fluorescent response indicates that this receptor can easily discriminate Zn²⁺ ions from other similar species. Model calculations at DFT level further suggest the possible interaction mode, and relatively steric position between the host and guest also influence the optical response.     

Improved photonic crystal directional coupler with short length

We investigate a photonic crystal (PC) waveguide coupler which is formed by two closely spaced linear waveguides in a two-dimensional triangular lattice of air holes. Our study shows that shifting one row of the air holes between the waveguides affects the dispersion curves of the guided modes and if the triangular lattice of air holes between the waveguides is replaced by a rectangular lattice, this modification results in an ultra-short coupling structure with coupling length less than 3a, where a is the lattice constant. Also, we investigate the effect of changing the radii of air holes that are adjacent to or between the waveguides on the coupling length and show that increasing the radius of air holes between the waveguides decreases the coupling length. We analyze the output spectrum of an ultra-short channel drop filter designed based on this structure.