Mangrove-mediated synthesis of silver nanoparticles using native Avicennia marina plant extract from southern Iran

The development of eco-friendly and nontoxic processes for the synthesis of nanoparticles is one of the most important discussed issues in nanotechnology science. This study reports the green synthesis of silver nanoparticles (AgNPs) using aqueous extract of leaf, stem, and root of Avicennia marina, the native and dominant mangrove plant in southern Iran. Among the different plant parts, the extract of leaves yielded the maximum synthesis of AgNPs. Synthesized AgNPs were investigated using UV–visible spectrophotometry, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and Fourier transform infrared (FTIR) spectroscopy. Absorption spectrum in 420?nm confirmed the synthesis of AgNPs. TEM images revealed that the synthesized AgNPs had the same spherical morphology with a size range between 0 and 75?nm. The distribution size histogram indicated that the most frequent particles were in the range of 10–15?nm and the mean size of nanoparticles was 17.30?nm. The results of SEM image showed nanoparticles with a size range between 15 and 43?nm. XRD pattern indicated the crystalline nature of synthesized nanoparticles. EDS results confirmed the presence of elements like silver, carbon, chlorine, nitrogen, and oxygen in the nanoparticles produced from leaf extract. Silver had the maximum percentage of formation, 51.6%. FTIR indicated the presence of different functional groups such as amines, alcohol, alkanes, phenol, alkyl halides, and aromatic loops in the synthesis process. Green biosynthesis of AgNPs using aqueous extract of native A. marina appears rapid, reliable, nontoxic, and eco-friendly.     

A comprehensive study on wastewater treatment using photo-impinging streams reactor: Continuous treatment

The degradation of phenol was investigated in a continuous flow impinging streams system. In the first step, statistical experimental designs were used to optimize the process of phenol degradation in a photo-impinging streams reactor. The more important factors affecting phenol degradation (p<0.05) were screened by a two-level Plackett-Burman design. Four of the latter parameters, namely phenol concentration, catalyst loading, pH and slurry flow rate, were selected for final process optimization, applying central composite design (CCD). The predicted data showed that the maximum removal efficiency of phenol (99%) could be obtained under the optimum operating conditions (phenol concentration=50 mg l ^?1, catalyst loading=2.1 g l ^?1, pH 6.2 and slurry flow rate=550ml min^?1). These predicted values were then verified by certain validating experiments. A good correlation was observed between the predicted data and those determined by the experimental study. This may confirm the validity of the statistical optimum strategy. Finally, continuous degradation of phenol was performed, and the results indicated a higher efficiency and an increased performance capability of the present reactor in comparison with the conventional processes.     

Kinetic Model for Invertase‐Induced Sucrose Hydrolysis: Initial Time Lag

The kinetics of sucrose hydrolysis by invertase was studied in order to find a comprehensive model for the reaction pathway and mechanism. First, three common models of Michaelis‐Menten (MM), substrate inhibition (S²), and substrate clusters' inhibition (S³(I)) were investigated. The third model was found to better predict the initial sucrose concentration. Then, the S³(I) model was modified to cover the remaining pathway (S³(II)). Finally, a new comprehensive model (S³(III)) was evaluated, which in addition to what is considered in the two previously mentioned models (S³(I) and S³(II)) also involved the initial time lag. The model predictions showed an excellent agreement with the experimental data. The mean absolute error for the MM model is significantly reduced for the S³(III) model.     

Comparison of pristine and polyaniline‐grafted MWCNTs as conductive sensor elements for phase change materials: Thermal conductivity trend analysis

Phase change materials (PCMs) function based on latent heat stored on or released from a substance over a slim temperature range. Multiwalled carbon nanotubes (MWCNTs) and polyaniline are important elements in sensor devices. In this work, pristine and polyaniline‐grafted MWCNTs (PANI‐g‐MWCNTs) were applied as conductive carbon‐based fillers to make PCMs based on paraffin. The attachment of PANI to the surface of MWCNTs was proved by Fourier transform Infrared analysis. Dispersion of MWCNTs in paraffin was studied by wide‐angle X‐ray scattering. Heating and solidification of PCM nanocomposites were investigated by differential scanning calorimetry, while variation in nanostructure of PCMs during heating/solidification process was evaluated by rheological measurements. It was found that after 30 min of sonication, the samples filled with 1 wt % MWCNTs have melting and solidification temperatures of 29 and 42 °C, respectively. It was also found that PANI attachment to MWCNTs significantly changes thermal conductivity behavior of PCM nanocomposites. The developed MWCNTs‐based sensor elements responded sharply at low MWCNTs content, and experienced an almost steady trend in conductivity at higher contents, while PANI‐g‐MWCNTs sensor followed an inverse trend. This contradictory behavior brought insight for understanding the response of PCMs against thermal fluctuations. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45389.     

Effect of oxide and carbide nanoparticles on tribological properties of phenolic-based nanocomposites

The phenolic-based composites and components are widely used because of their excellent thermal, tribological and mechanical behaviors. In the present study, phenolic resin composed of hexamine, novalac, furfural, and furfuryl alcohol has been used. The effects of two carbide nanoparticles (SiC and TiC) and two oxide nanoparticles (TiO₂ and ZrO₂) on the tribological properties of phenolic resin were experimentally investigated. This paper intends to identify the effects of different fillers, fraction of particles and normal load on wear rate and coefficient of friction in dry sliding wear of phenolic-based nanocomposites against hard metal. The proportions of fillers were 0.5, 1 and 2?vol% and experiments were carried out under 40, 50, 60 and 70?N loads and at 0.2?m/s speed. The fillers were mixed with phenolic resin and molded in the form of a cylinder (8.5?mm diameter?×?25?mm height). The samples were cured at 135?°C with a special heating cycle. The wear tests were performed on pin-on-disk testing apparatus at ambient temperature. The composite pins were tested in dry sliding against carbon steel disk. The worn surfaces of samples have been investigated by SEM and the effects of nanometer particles showed different wear mechanisms. Observations showed that carbide particles have better enhancing effect on tribological properties of phenolic resin as compared to the oxide particles. Nanocomposites with SiC particles showed the best tribological properties among the investigated samples. The optimal content of SiC nanoparticles were 1?vol%.     

Interrelationship of thermal and mechanical properties of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate)/graphene nanocomposites

In the present work, attempts were made to investigate the thermal and mechanical properties of melt‐processed poly(ethylene terephthalate) (PET)/poly(ethylene 2,6‐naphthalate) (PEN) blends and its nanocomposites containing graphene by using differential scanning calorimetry and tensile test experimenting. The results showed that crystallinity, which depends on a blend ratio, completely disappeared in a composition of 50/50. By introducing graphene to PET, even in low concentrations, the crystallinity of samples increased, while the nanocomposite of PEN indicated reverse behavior, and the crystallinity was reduced by adding graphene. In the case of PET‐rich (75/25) nanocomposite blends, by increasing the nano content in the blend, the crystallinity of the samples was enhanced. This behavior was attributed to the nucleating effect of graphene particles in the samples. From the results of mechanical experiments, it was found in PET‐rich blends that by increasing the PEN/PET ratio, the modulus of samples decreased, whereas in the case of PEN‐rich blends, a slight increment of modulus is seen as a result of the increment of the PEN/PET ratio. The two contradicting behaviors were attributed to the reduction of crystallinity of PET‐rich blends by enhancement of PEN/PET ratio and the rigid structure of PEN chains in PEN‐rich blends. Unlike the different modulus change of PET‐rich and PEN‐rich blends, the nanocomposites of these blends similarly indicated an increment of modulus and characteristics of rigid materials by increasing the nano content. Furthermore, the same behavior was detected in nanocomposites of each polymer (PET and PEN nanocomposites). The alteration from ductile to rigid conduction was related to the impedance in the role of graphene plates against the flexibility of polymer chains and high values of graphene modulus. J. VINYL ADDIT. TECHNOL., 23:210–218, 2017. © 2015 Society of Plastics Engineers     

Polyurethane-SAPO-34 mixed matrix membrane for CO2/CH4 and CO2/N2 separation

SAPO-34 nanocrystals (inorganic filler) were incorporated in polyurethane membranes and the permeation properties of CO₂, CH_4, and N₂ gases were explored. In this regard, the synthesized PU-SAPO-34 mixed matrix membranes (MMMs) were characterized via SEM, AFM, TGA, XRD and FTIR analyses. Gas permeation properties of PU-SAPO-34 MMMs with SAPO-34 contents of 5 wt%, 10 wt% and 20 wt% were investigated. The permeation results revealed that the presence of 20 wt% SAPO-34 resulted in 4.45%, 18.24% and 40.2% reductions in permeability of CO_2, CH_4, and N₂, respectively, as compared to the permeability of neat polyurethane membrane. Also, the findings showed that at the pressure of 1.2 MPa, the incorporation of 20 wt% SAPO-34 into the polyurethane membranes enhanced the selectivity of CO₂/CH₄ and CO₂/N₂, 14.43 and 37.46%, respectively. In this research, PU containing 20 wt% SAPO-34 showed the best separation performance. For the first time, polynomial regression (PR) as a simple yet accurate tool yielded a mathematical equation for the prediction of permeabilities with high accuracy (R² > 99%).     

Pack Cementation Coatings for High-Temperature Oxidation Resistance of AISI 304 Stainless Steel

Aluminum and titanium are deposited on the surface of steel by the pack cementation method to improve its hot-corrosion and high-temperature oxidation resistance. In this research, coatings of aluminum and titanium and a two-step coating of aluminum and titanium were applied on an AISI 304 stainless steel substrate. The coating layers were examined by carrying out scanning electron microscopy (SEM) and x-ray diffraction (XRD). The SEM results showed that the aluminized coating consisted of two layers with a thickness of 450???m each, the titanized coating consisted of two layers with a thickness of 100???m each, and the two-step coatings of Al and Ti consisted of three layers with a thickness of 200???m each. The XRD investigation of the coatings showed that the aluminized coating consisted of Al₂O₃, AlCr₂, FeAl, and Fe₃Al phases; the titanized layers contained TiO₂, Ni₃Ti, FeNi, and Fe₂TiO₅ phases; and the two-step coating contained AlNi, Ti₃Al, and FeAl phases. The uncoated and coated specimens were subjected to isothermal oxidation at 1050?°C for 100?h. The oxidation results revealed that the application of a coating layer increased the oxidation resistance of the coated AISI 304 samples as opposed to the uncoated ones.