Nd(III) and Gd(III) Sorption on Mesoporous Amine-Functionalized Polymer/SiO2 Composite

The strong demand for rare-earth elements (REEs) is driven by their wide use in high-tech devices. New processes have to be developed for valorizing low-grade ores or alternative metal sources (such as wastes and spent materials). The present work contributed to the development of new sorbents for the recovery of rare earth ions from aqueous solutions. Functionalized mesoporous silica composite was synthesized by grafting diethylenetriamine onto composite support. The physical and chemical properties of the new sorbent are characterized using BET, TGA, elemental analysis, titration, FTIR, and XPS spectroscopies to identify the reactive groups (amine groups: 3.25 mmol N g⁻¹ and 3.41 by EA and titration, respectively) and their mode of interaction with Nd(III) and Gd(III). The sorption capacity at the optimum pH (i.e., 4) reaches 0.9 mmol Nd g⁻¹ and 1 mmol Gd g⁻¹. Uptake kinetics are modeled by the pseudo-first-order rate equation (equilibrium time: 30–40 min). At pH close to 4–5, the sorbent shows high selectivity for rare-earth elements against alkali-earth elements. This selectivity is confirmed by the efficient recovery of REEs from acidic leachates of gibbsite ore. After elution (using 0.5 M HCl solutions), selective precipitation (using oxalate solutions), and calcination, pure rare earth oxides were obtained. The sorbent shows promising perspective due to its high and fast sorption properties for REEs, good recycling, and high selectivity.     

Kinetics of the reaction of sodium arylthiolates with nitro-carboxybenzyl halide derivatives

The rate constants for the reactions of 4-halomethyl-3-nitrobenzoic acids, the nonnitro derivatives, and their ethyl esters with arylthiolates were measured at different temperatures. It was found that the retardation in rate constants compared to benzyl halides is due to the electrostatic repulsion between the electronegative substituents (COO⁻ and/or NO₂) in the substrates and thiolate ions. Good correlations between log k₂ values of the acids and carbon basicities of thiolates were found while log k₂ values of the esters show good straight lines with Hammett σ constants, pk_a, and carbon basicities of arylthiolates. © 1996 John Wiley & Sons Inc     

Prediction of rheological behavior of MWCNTs–SiO2/EG–water non-Newtonian hybrid nanofluid by designing new correlations and optimal artificial neural networks

In this paper, at the first, new correlations were proposed to predict the rheological behavior of MWCNTs–SiO₂/EG–water non-Newtonian hybrid nanofluid using different sets of experimental data for the viscosity, consistency and power law indices. Then, based on minimum prediction errors, two optimal artificial neural network models (ANNs) were considered to forecast the rheological behavior of the non-Newtonian hybrid nanofluid. One hundred and ninety-eight experimental data were employed for predicting viscosity (Model I). Two sets of forty-two experimental data also were considered to predict the consistency and power law indices (Model II). The data sets were divided to training and test sets which contained respectively 80 and 20% of data points. Comparisons between the correlations and ANN models showed that ANN models were much more accurate than proposed correlations. Moreover, it was found that the neural network is a powerful instrument in establishing the relationship between a large numbers of experimental data. Thus, this paper confirmed that the neural network is a reliable method for predicting the rheological behavior of non-Newtonian nanofluids in different models.

     

Conformal adhesion enhancement on biomimetic microstructured surfaces

Inspired by the superior adhesive ability of the gecko foot pad, we report an experimental study of conformal adhesion of a soft elastomer thin film on biomimetic micropatterned surfaces (micropillars), showing a remarkable adhesion enhancement due to the surface patterning. The adhesion of a low-surface-energy poly(dimethylsiloxane) tape to a SU-8 micropatterned surface was found be able to increase by 550-fold as the aspect ratio increases from 0 to 6. The dependency of the adhesion enhancement on the aspect ratio is highly nonlinear. A series of peeling experiment coupled with optical interference imaging were performed to investigate the adhesion enhancement as a function of the height of the micropillars and the associated delamination mechanisms. Local elastic energy dissipation, side-wall friction, and plastic deformations were analyzed and discussed in terms of their contributions to the adhesion enhancement. We conclude that the local adhesion and friction events of pulling micropillars out of the embedded polymer film play a primary role in the observed adhesion enhancement. The technical implications of this local friction-based adhesion enhancement mechanism were discussed for the effective assembly of similar or dissimilar material components at small scales. The combined use of the micro/nanostructured surfaces with the van der Waals interactions seem to be a potentially more universal solution than the conventional adhesive bonding technology, which depends on the chemical and viscoelastic properties of the materials.     

Application of PMR Spectrometry in Pharmaceutical Analysis I. Assay of Clofibrate

A new method, involving the application of PMR spectrometry for the assay of clofibrate and its capsules, is proposed. Among other peaks the PMR spectrum of clofibrate has a well-defined singlet system which is chosen for quantitative measurement. The principle of the method involves comparing the integral of this signal to that of the sharp singlet (positioned at 0.00 ppm) of hexamethylcyclotrisilazane which is used as internal standard.     

Electrically conductive epoxy‐based nanocomposite adhesives loaded with silver‐coated copper and silver‐coated reduced graphene oxide nanoparticles

In this research, a conductive adhesive based on epoxy resin as the polymer matrix and silver‐coated copper powder and silver‐coated reduced graphene oxide as conductive fillers was synthesized. Graphene oxide was synthesized by modified Hummer's method. It was reduced and modified by silver powder. Copper particles were coated with silver using the electroless plating method. Finally, conductive nanocomposite adhesives were prepared using conductive fillers with different weight fractions. The structural properties of fillers were identified by Fourier‐transform infrared (FTIR) and induced coupled plasma (ICP) analysis and the morphology of the samples by scanning electron microscopy (SEM). Finally, conductive properties, lap shear strength, and thermal stability of adhesive were evaluated. The conductive adhesive prepared with optimized properties have 70% weight percentage silver‐coated copper powder and 1% weight percentage silver‐coated reduced graphene oxide. The bulk resistivity of the optimum sample was 1.6 × 10^‐2 Ω.cm, and the lap shear strength was 7.10 MPa. Also, thermogravimetric analysis showed that the weight loss of adhesive decreased from 88.72% to 30.55% during heating, which showed the addition of fillers improves the thermal stability of adhesive.     

Anilinolysis of Picryl Benzoate Derivatives in Methanol: Reactivity,Regioselectivity, Kinetics,and Mechanism

The reaction of picryl benzoate derivatives 1a–g with aniline in methanol proceeds through CO? O and Ar? O bond cleavage pathways. Furthermore, the reactivity of these esters toward anilinolysis is correlated to the energy gap between highest occupied molecular orbital aniline and lowest unoccupied molecular orbital of each ester. The regioselectivity of acyl? oxygen versus aryl? oxygen cleavage is also discussed. The overall rate constants k_tot split into k_{CO? O} (the rate constant of acyl‐oxygen cleavage) and k_{Ar? O} (rate constant of aryl‐oxygen cleavage). The CO? O bond cleavage advances through a stepwise mechanism in which the formation of the tetrahedral intermediate is the rate‐determining step. The Ar? O bond cleavage continues through a S_NAr mechanism in which the departure of the leaving group from the Meisenheimer complex occurs rapidly after its formation in the rate‐determining step.     

Silica aerogel-filled PMMA by in situ reverse atom transfer radical polymerization: kinetics and thermal studies

Hydrophobically modified silica aerogel nanoparticles (H-SiANp) were used for in situ polymerization of methyl methacrylate by reverse atom transfer radical polymerization to synthesize well-defined PMMA nanocomposites. Inherent characteristics of the prepared H-SiANp were evaluated by nitrogen adsorption/desorption isotherms, SEM, and TEM. Conversion and molecular weight determinations were carried out using GC and SEC, respectively. Addition of 3 mass% of the H-SiANp leads to decrement of conversion from 92 to 74%. Molecular weight of poly (methyl methacrylate) chains also decreases from 19,737 to 15,662 g mol^?1 by addition of only 3 mass% H-SiANp; however, PDI values increase from 1.36 to 1.82. Linear increase of ln(M₀/M) with time for all the samples shows that polymerization proceeds in a living manner. In addition, suitable agreement between theoretical and experimental molecular weight in combination with low PDI values can appropriately demonstrate the living nature of the polymerization. TG results indicate that by increasing H-SiANp content, improvements in thermal stability of the nanocomposites were obtained. DSC results show a decrease in glass transition temperature from 87.4 to 80.9 °C by addition of 3 mass% H-SiANp.

     

Theoretical prediction of proton and electron affinities,gas phase basicities,and ionization energies of sulfinamides

Structural Chemistry - Sulfinamides, as an asymmetric synthesizer, especially in drug synthesis, play critical roles in organic chemistry. In this study, the gas phase ion energetics data including...