Copper-based metal–organic framework decorated by CuO hair-like nanostructures: Electrocatalyst for oxygen evolution reaction

We report a Cu-based metal–organic framework (MOF) decorated by CuO nanostructures as an efficient catalyst for the oxygen evolution reaction (OER). MIL-53(Cu) was synthesized by a hydrothermal approach using 1,4-bezenedicarboxylic acid as organic precursor and further annealed at 300°C to form CuO nanostructures on its surface. The produced electrocatalyst, CuO@MIL-53(Cu), was characterized using various techniques. Under alkaline conditions, the developed electrocatalyst exhibited an overpotential of 801 and 336 mV versus RHE at 10 and 1 mA cm⁻², respectively. The reproducibility of the catalytic performance was validated using several electrodes. It was confirmed that the CuO hair-like nanostructures grown on MIL-53(Cu) using thermal treatment exhibit high OER activity, good kinetics and durability. CuO@MIL-53(Cu) is an economic noble-metal-free OER electrocatalyst. It has potential for application as anode material for sustainable energy technologies like batteries, fuel cells and water electrolysis.     

The synthesis of silica-supported chiral BINOL: Application in Ti-catalyzed asymmetric addition of diethylzinc to aldehydes

Chiral BINOL was covalently anchored on two different pore sized mesoporous silica (SBA-15 (7.5 nm) and MCF (14 nm)). These heterogenized ligands were used in Ti-catalyzed asymmetric addition of diethylzinc to aldehydes. High catalytic activity with excellent enantioselectivity (up to 94% ee) for secondary alcohols was achieved using MCF supported chiral BINOL under heterogeneous reaction conditions. Good to excellent enantioselectivity (ee, 68–91%) was also achieved with various small to bulkier aldehydes. The MCF supported catalyst was reused in multiple catalytic runs without loss of enantioselectivity.     

Adsorption of acid yellow dye on flakes of chitosan prepared from fishery wastes

Chitosan flakes, extracted from prawns and labeo rohita scales, with high adsorption capacity were prepared after chemical treatment and were used to remove acid yellow dye from water. The results showed that adsorption capacity is dependent on pH, initial concentration of dye, BET, Langmuir surface area and pore volume of the adsorbent. In acidic conditions, the polymer amino groups were protonated (positively charged polymer chain), which showed attraction with negative ions of anionic dye. Chitosan from prawns scales showed higher dye adsorption under the same experimental conditions. Adsorption isotherms were developed and equilibrium data fitted well to Langmuir and Freundlich isotherm models.     

Online thorium determination after preconcentration in a minicolumn having XAD-4 resin impregnated with N-benzoylphenylhydroxylamine by FI-spectrophotometry

A very sensitive and selective flow injection on-line determination method of thorium (IV) after preconcentration in a minicolumn having XAD-4 resin impregnated with N-benzoylphenylhydroxylamine is described. Thorium (IV) was selectively adsorbed from aqueous solution of pH 4.5 in a minicolumn at a flow rate of 13.6 mL min^?1, eluted with 3.6 mol dm^?3 HCl (5.6 mL min^?1), mixed with arsenazo-III (0.05% in 3.6 mol dm^?3 HCl stabilized with 1% Triton X-100, 5.6 mL min^?1) at confluence point and taken to the flow through cell of spectrophotometer where its absorbance was measured at 660 nm. Peak height was used for data analyses. The preconcentration factors obtained were 32 and 162, detection limits of 0.76 and 0.150 ??g L^?1, sample throughputs of 40 and 11 h^?1 for preconcentration times of 60 and 300 s, respectively. The tolerance levels for Zr(IV) and U(VI) metal ions is increased to 50-folds higher concentration to Th(IV). The proposed method was applied on different spiked tap water, sea water and biological sample and good recovery was obtained. The method was also applied on certified reference material IAEA-SL1 (Lake Sediment) for the determination of thorium and the results were in good agreement with the reported value.     

Determination of europium(III) in environmental samples using a flow injection analysis system with on-line preconcentration and spectrophotometric detection

A simple and accurate flow injection analysis system coupled with spectrophotometric detector was developed for preconcentration and determination of europium(III) in aqueous samples. The developed flow system includes a europium preconcentration step in a column packed with Amberlite XAD-4 resin impregnated with nalidixic acid at pH 7.0. The europium complex was desorbed from the resin by 0.1 mol L^?1 HCl and mixed with arsenazo-III solution (0.05 % solution in 0.1 mol L^?1 HCl) and taken to the flow through cell of spectrophotometer where its absorbance was measured at 661 nm. The optimum preconcentration system, chemical and FIA variables were investigated. The preconcentration factors obtained were 115 and 500, detection limits of 0.43 and 0.1 μg L^?1, sample throughputs of 40 and 10 were obtained for preconcentration time of 60 and 300 s respectively. The proposed system showed good precision and accuracy with relative standard deviation of 1.5 %. The method has been applied to the determination of europium(III) in real water samples and certified reference material IAEA-SL-1 (Lake sediment).     

Output-feedback lag-synchronization of time-delayed chaotic systems in the presence of external disturbances subjected to input nonlinearity

In this paper, an adaptive output error feedback control scheme is proposed for the lag-synchronization of two time-delayed chaotic systems in the presence of channel time-delay, external disturbances and input nonlinearity. Using the Lyapunov theory, stability of the proposed adaptive controller is proved. Lyapunov-Krasovskii approach is used to deal with the existence of time-delay in the system dynamics. Finally, two numerical simulations are presented to illustrate the effectiveness of the developed method.     

Liquid-liquid extraction of palladium(II) from hydrobromic acid media by hexadecylpyridinium bromide.

A simple and rapid liquid-liquid extraction of palladium has been studied involving ion-pairing of bromocomplexes of palladium(II) with hexadecylpyridinium bromide (HDPB) dissolved in chloroform. The stoichiometry and distribution of (HDP)2PdBr4 between the aqueous and organic phase was investigated by spectrophotometric mole ratio method. The extraction efficiency of palladium(II) by HDPB was studied as a function of several variables: acid, salt, surfactant concentration and equilibrium time. The results showed that PdBr4(2-) extraction could be explained by assuming the formation of (HDP)2PdBr4 complexes in the aqueous solution and transfer to organic phase. The extraction was fast and the shaking time was only a few min. The average recovery of palladium(II) from an aqueous solution containing 10 microg/ml of analyte was 99% with an RSD% of 0.95. The percentage recovery of 0.2 microg/ml palladium(II) was 96%.     

Efficient functionalization of aqueous CdSe/ZnS nanocrystals using small-molecule chemical activators

Small molecular reagents that can efficiently functionalize water soluble CdSe/ZnS nanocrystals (NCs) are reported. These reagents do not cause quenching or precipitation of NCs as seen with commercially available activators. The results demonstrate that controlling the electrostatic character of the materials is critical in the design of functionalization schemes.     

Synthesis and Characterization of Ligand-Linked Pt Nanoparticles: Tunable,Three-Dimensional,Porous Networks for Catalytic Hydrogen Sensing

Porous networks of Pt nanoparticles interlinked by bifunctional organic ligands have shown high potential as catalysts in micro-machined hydrogen gas sensors. By varying the ligand among p-phenylenediamine, benzidine, 4,4‘‘-diamino-p-terphenyl, 1,5-diaminonaphthalene, and trans-1,4-diaminocyclohexane, new variants of such networks were synthesized. Inter-particle distances within the networks, determined via transmission electron microscopy tomography, varied from 0.8 to 1.4 nm in accordance with the nominal length of the respective ligand. While stable structures with intact and coordinatively bonded diamines were formed with all ligands, aromatic diamines showed superior thermal stability. The networks exhibited mesoporous structures depending on ligand and synthesis strategy and performed well as catalysts in hydrogen gas microsensors. They demonstrate the possibility of deliberately tuning micro- and mesoporosity and thereby transport properties and steric demands by choice of the right ligand also for other applications in heterogeneous catalysis.     

Quartic Thue equations

We will give upper bounds upon the number of integral solutions to binary quartic Thue equations. We will also study the geometric properties of a specific family of binary quartic Thue equations to establish sharper upper bounds.