Review of recent studies on interactions between polymers and nanotubes using molecular dynamic simulation

Nanotubes have extraordinary properties, which have attracted the attention of many researchers from diverse fields. The interaction between carbon nanotube (CNT) or boron nitride nanotube (BNNT) and polymer/copolymer/surfactant has shown potential improvement in properties and performance. This paper reviews the recent studies in this field obtained from molecular dynamics simulation calculations, focusing on the interaction energies between nanostructure and polymer, radial distribution function, diffusion and radius of gyration and some other physical chemistry properties. Recent studies show that the intermolecular interaction in mentioned systems is strongly influenced by the specific monomer structure of polymers. The high values of intermolecular interaction energy of such composites offer that an efficient load transfer exists at the interface between nanotube and polymer, which is of a key role in the composite reinforcement practical applications. Our study reviewed the possibility of wrapping CNT/BNNT/CNT bundles by polymers and also the effects of CNTs/CNT bundles’ length on the conformational behavior of polymer adsorbed on these nanostructures.     

Extraction and determination of flavonoids in fruit juices and vegetables using Fe3O4/SiO2 magnetic nanoparticles modified with mixed hemi/ad‐micelle cetyltrimethylammonium bromide and high performance liquid chromatography

Extraction and determination of three flavonoids (morin, quercetin, and kaempferol) were performed by dispersive magnetic solid phase extraction based on mixed hemi/ad‐micelles and high‐performance liquid chromatography with UV detection. The Fe₃O₄/SiO₂ nanoparticles were synthesized and characterized by X‐ray diffraction, FTIR, scanning electron microscopy, and thermogravimetric analysis. Fe₃O₄/SiO₂ nanoparticles coated with mixed hemi/ad‐micelles cetyltrimethyl ammonium bromide was applied as a sorbent and used for extraction of flavonoids. Effective parameters on the extraction recovery such as amount of magnetic nano particles, volume of cetyltrimethyl ammonium bromide solution with specific concentration, pH of sample solution, adsorption equilibrium time, volume of desorption solvent, and desorption times were evaluated and optimized using fractional factorial design and central composite design. Under the optimum condition limit of detection and linearity were 0.83, 2.7–500.0 for morin, 0.18, 0.7–500.0 for quercetin and, 0.37, 1.3–500.0 µg/L for kaempferol. The extraction recovery with relative standard deviation were 97.88, 1.94 for morin, 95.77, 0.80 for quercetin, and 93.35, 1.45 for kaempferol. The proposed method was applied for simultaneous extraction and determination of flavonoids in several fruit juices and vegetable samples.     

Study of mechanism and kinetic modeling of CO hydrogenation reaction over the impregnated Co-Ni/Al2O3 catalyst

An investigation of the kinetic and mechanism of CO hydrogenation reaction was performed on impregnated Co-Ni/Al₂O₃. Determination of kinetic parameters from the experiments was carried out in a micro fixed-bed reactor. Kinetic evaluations were performed under various operational conditions of T = 473–673 K, p = 1–14 bar, H₂/CO = 1–3, and GHSV = 4,500 hr⁻¹. Kinetic models and rate equations for CO consumption were obtained by using two main-type rate equations of Langmuir-Hinshelwood-Hougen-Watson (LHHW) and Eley-Rideal (ER). Estimation of various kinetic parameters was performed using a nonlinear regression method. According to the obtained experimental results and using statistical criteria, one kinetic expression based on the LHHW mechanism (-r_CO = k_p.b_CO.P_CO. b_H2. P_H2/[1+ b_CO.P_CO + b_H2.P_H2]²) was chosen as the best-fitted model. For this fitted model, the activation energy was found to be 109.2 kJ/mol. Characterization of the catalyst was also performed using X-ray diffraction (XRD), BET, scanning electron microscopy (SEM), and energy-dispersive x-ray spectrometer (EDS) techniques.     

Two effective hybrid conjugate gradient algorithms based on modified BFGS updates

Based on two modified secant equations proposed by Yuan, and Li and Fukushima, we extend the approach proposed by Andrei, and introduce two hybrid conjugate gradient methods for unconstrained optimization problems. Our methods are hybridizations of Hestenes-Stiefel and Dai-Yuan conjugate gradient methods. Under proper conditions, we show that one of the proposed algorithms is globally convergent for uniformly convex functions and the other is globally convergent for general functions. To enhance the performance of the line search procedure, we propose a new approach for computing the initial value of the steplength for initiating the line search procedure. We give a comparison of the implementations of our algorithms with two efficiently representative hybrid conjugate gradient methods proposed by Andrei using unconstrained optimization test problems from the CUTEr collection. Numerical results show that, in the sense of the performance profile introduced by Dolan and Moré, the proposed hybrid algorithms are competitive, and in some cases more efficient.     

Fabrication of SAPO‐34 with Tuned Mesopore Structure

Crystalline SAPO‐34 molecular sieves with hierarchical network were synthesized employing polyethylene glycol (PEG) as the meso‐generating agent via a self‐assembly strategy. XRD, FESEM, N₂ adsorption‐desorption and FT‐IR spectroscopic analyses showed that PEG co‐template has a decisive role in tailoring the pore structure and producing a tuned structure from microporous towards the mesoporous structure. Also, addition of PEG favored the formation of more uniform and smaller crystals than the conventional SAPO‐34. In fact, PEG did not only control the size of crystals due to its crystal growth inhibiting (CGI) effect but also modified the morphology of the crystals and improved CSD (crystal size distribution) along with induction of mesopores into the porous structure. The modified SAPO‐34 would be recommended for selective formation of light olefins through the acid‐catalyzed reactions, such as the conversion of methanol to olefins/propylene (MTO/MTP) and propane dehydrogenation (PDH) to produce olefins with higher selectivity and catalyst stability than the conventional SAPO‐34.     

Post-training on RBF neural networks

Radial basis function neural networks are the most widely used networks due to their rapid training, generality, and simplicity. The nature of these networks necessitates some types of errors which can never be removed by traditional training algorithms. This paper is an attempt to introduce the natural error sources of neural networks such as bias error, iteration-restricted error, and Gibbs error. Moreover, a new method is introduced, called post-training, to reduce these errors as far as desired.     

Extraction optimization of polycyclic aromatic hydrocarbons by alcoholic-assisted dispersive liquid-liquid microextraction and their determination by HPLC

A sensitive method for the extraction and determination of polycyclic aromatic hydrocarbons (PAHs) using alcoholic-assisted dispersive liquid-liquid microextraction (AA-DLLME) and HPLC was developed. The extraction procedure was based on alcoholic solvents for both extraction and dispersive solvents. The effective parameters (type and volume of extraction and dispersive solvents, amount of salt and stirring time) on the extraction recovery were studied and optimized utilizing factorial design (FD) and central composite design (CCD). The best recovery was achieved by FD using 2-ethyl-1-hexanol as the extraction solvent and methanol as the dispersive solvent. The results showed that volume of dispersive solvent and stirring time had no effect on the recovery of PAHs. The optimized conditions were 145 μL of 2-ethyl-1-hexanol as the extraction solvent and 4.2% w/v of salt (NaCl) in sample solution. The enrichment factors of PAHs were in the range of 310-325 with limits of detection of 0.002-0.8 ng/mL. The linearity was 0.01-800 ng/mL for different PAHs. The relative standard deviation (RSD) for intra- and inter-day of extraction of PAHs were in the range of 1.7-7.0 and 5.6-7.3, respectively, for five measurements. The method was also successfully applied for the determination of PAHs in environmental water samples.