Immobilization of 2,2'-dipyridyl onto bentonite and its adsorption behavior of copper(II) ions

In this study, the immobilization of 2,2'-dipyridyl onto bentonite was firstly carried out and it was then used for the adsorption of copper(II) ions from aqueous solutions. The variation of the parameters of pH, contact time, initial copper(II) concentration and temperature were investigated in the adsorption experiments. The XRD, FTIR, elemental and thermal analyses were performed to observe the immobilization of 2,2'-dipyridyl onto natural bentonite. The adsorption data obtained were well described by the Langmuir adsorption isotherm model at all studied temperatures. The results indicated that the maximum adsorption capacity was 54.07 mg g(-1) from the Langmuir isotherm model at 50 degrees C. The thermodynamic parameters indicated that the adsorption process is spontaneous, endothermic and chemical in nature. The kinetic parameters of the adsorption were calculated from the experimental data. According to these parameters, the best-fit was obtained by the pseudo-second-order kinetic model. The results showed that 2,2'-dipyridyl-immobilized bentonite can be used as the effective adsorbent for the removal of heavy metal contaminants.     

Phenolic compositions and antioxidant activities of Maya nut (Brosimum alicastrum): Comparison with commercial nuts

The goal of the present study was to investigate the antioxidant activity and total phenolic content (TPC) of Maya nut (Brosimum alicastrum) in comparison with commercially available nuts (i.e. walnut, almond, and peanut). Results indicated that Maya nut had the highest TPCs among these nuts. Maya nut also possessed strong 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and 2.2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) scavenging activities and ferric reducing antioxidant power (FRAP) (p < 0.05) as compared to walnut, almond, and peanut. Five phenolic acids (gallic acid, p-hydroxybenzoic acid, vanillic acid, caffeic acid, and p-coumaric acid) and one flavonoid ((-)-epicatechin) were identified and the phenolic content ranged from 6.5 to 326.2 µg/g.     

Comparison of the Influence of Silica‐rich Supplementary Cementitious Materials on Cement Mortar Composites: Mechanical and Microstructural Assessment

Silicon - The silica-rich supplementary cementitious materials (SCMs) are the key components of mechanical and microstructural properties. The use of SCMs results in improving the mechanical and...     

A critique of master sintering curve analysis

In this work, we explore factors affecting the accuracy of the master sintering curve (MSC) approach for analyzing the complete sintering profile of ceramic powders. We show that the instantaneous anisotropic shrinkage must be accounted for to develop an accurate MSC. The MSC diverges at >90% density because of basic assumptions that oversimplify the analysis of the densification process. We also show that powder chemistry and forming techniques can affect the fitting parameter Q. Q should not be interpreted as the sintering activation energy, or used to interpret mechanistic differences since it is comprised of several mechanisms that influence densification throughout the sintering cycle. Despite these limitations, the MSC is a useful and practical tool for predicting thermal load (i.e. time and temperature) effects on the densification of a ceramic part fabricated from a singular powder that is fabricated by a singular forming process.     

Effects of sandblasting metal bracket base on the bond strength of a resin-modified glass ionomer cement: an in vitro study

The introduction of air abrasion (sandblasting) technology to orthodontics may allow reaching optimum bond strength between the metal bracket and resin-modified glass ionomer cement. This study examined the effects of sandblasting metal bracket bases on the in vitro tensile bond strength of a resin-modified glass ionomer cement. Two-hundred foil-mesh based brackets were divided into ten groups and combinations of three sizes of aluminum oxide powder (25, 50 and 110 μm) and three sandblasting times (3, 6 and 9 seconds) were tested. One group was not sandblasted and used as control. Analysis of variance showed that bond strength was significantly affected by the sandblasting time (p < 0.001) and size of the aluminum oxide powder (p < 0.001). Only the group (SO₂₅) sandblasted with 25 μm aluminum oxide powder for 3 seconds yielded higher mean bond strength than that of the control group. The bond strength values were also analyzed using a Weibull analysis, which showed the most favorable size (25 μm) and time combination (3 seconds), and the 5% and 90% probabilities of failures. This study suggests that sandblasting time and particle size have and important effect on the bond between the metal bracket and resin-modified glass ionomer cement.     

Investigation of two ultrafiltration membranes for treatment of olive oil mill wastewater

In this study, a promising treatment method is given for the olive oil mill wastewater (OMWW). Although the same steps of this method have been used in different studies before, flow scheme is novel. The membrane filtration of pretreated OMWW was investigated by using two ultrafiltration membranes in this study. Pretreatment steps were pH adjustment (pH = 2) and cartridge filter filtration, and pH adjustment (pH = 6) and cartridge filter filtration. Each step of cartridge filter filtration was batch process and effluent from the filter was recycled back to OMWW tank. Pretreated OMWW was sent to feed vessel of experimental set-up. Recovery of olive oil in the OMWW was realized collecting it from the top of pretreated OMWW. Ultrafiltration membranes used were JW and MW membranes supplied by Osmonics. The effects of main operating parameters (transmembrane pressure, feed flow rate, pH and membrane type) on the permeate flux and membrane fouling were examined. The effectiveness of the different membranes and operating conditions was evaluated using retention coefficients calculated from COD and TOC of experimental studies. The highest permeate flux (25.9 l/m² h) was obtained using MW membrane under operational conditions of Qf = 200 l/h flow rate and TMP = 4 bar, while the highest removals were obtained at Qf = 100 l/h flow rate and TMP = 1 bar. COD, TOC, SS, oil and grease concentrations of MW membrane effluent were 6400 mg/l, 2592 mg/l, 320 mg/l, and 270 mg/l, respectively.     

Enrichment of probiotic ice cream with different dietary fibers: Structural characteristics and culture viability

This study evaluated the effect of 5 dietary fibers (apple, orange, oat, bamboo, and wheat) on the physicochemical, rheological, and textural characteristics; sensory properties; and culture viability of probiotic ice cream stored at ?18°C for 180 d. The presence of orange and apple fibers increased the titratable acidity, decreased the lightness (color) value of the ice creams, and enhanced the red and yellow coloration. Compared with the control sample, the consistency indices and apparent viscosities of the experimental samples increased with the addition of all dietary fibers except oat fiber. The highest viscosity was obtained in the sample fortified with apple fiber, whereas the ice cream containing orange fiber showed the highest hardness after d 60 of storage. The addition of orange and apple fibers significantly increased melting resistance; however, panelists did not generally like these samples in terms of taste-flavor. All ice creams had viable counts of Lactobacillus acidophilus of ≥7 log cfu/g during storage except the samples with orange and bamboo fiber. Bifidobacterium lactis counts were also found to be >6 log cfu/g in those samples until d 150 of storage.     

Mechanics of bio-inspired attachment systems contacting with rough surface: effect of spring orientation angle on hierarchical spring model

It is known that due to the asymmetrically designed structure of seta, gecko makes an attachment at 30° and detachment at 90° and achieves its detachment by changing orientation angle of seta from 30° to 90°. In this study, it is shown how pulling orientation affects pull-off force for gecko hierarchy using spring model during detachment from rough surface and then how to achieve easy and quick switch between attachment and detachment. This study adds the change of spring orientation angle to hierarchical spring model and extends it for determining the effect of orientation angle on the pull-off force. One-, two-, and three-level hierarchical models for gecko lamella consisting of seta, branches, and spatula contacting with the rough surface have been used. This study will provide us information about pull-off forces from rough surfaces and help to imitate and produce in particular gecko-like devices, reusable products and in general nanomaterials and nanodevices.     

Investigation of the photocatalytic activity of TiO2--polyoxometalate systems

The present study reports the investigation of polyoxometalate catalyzed electron transfer from the conduction band of photoexcited TiO2 to molecular oxygen. The oxidation of 1,2-dichlorobenzene (DCB) was used as an index reaction for evaluating the photocatalyst systems TiO2-PW12O40(3-), TiO2-SiW12O40,4- and TiO2-W10O32(4-) in oxygenated aqueous solution. Addition of these polyoxometalate (POM) anions to TiO2 suspensions resulted in significant rate enhancement for DCB oxidation. Photodegradation kinetics exhibited [POM] dependence, experiencing different maximum (k = 0.0318 min(-1), 0.0108 min(-1), and 0.0066 min(-1)) for each POM at different [POM] (0.1 mM PW12O40(3-), 0.07 mM SiW12O40,4- and 1 mM W10O32,4-respectively). The probability that the difference in the adsorption affinity of POMs on TiO2 surface could account for the observed ranking of photodegradation rates was ruled out by adsorption isotherm experiments that revealed similar binding constants for each POM (467 M(-1), 459 M(-1), and 417 M(-1) for PW12O40(3-), SiW12O40(4-), and W10O32(4-), respectively). DCB degradation over TiO2 with O2 or POM+O2 systems can be modeled by the Langmuir-Hinshelwood (saturation kinetics) model. The concentration-independent rate constants (kL-H) for TiO2-O2, TiO2-W10O32(4-), TiO2-SiW12O40(4-), and TiO2-PW12O40(3-) were 0.0818, 0.152, 0.421, and 0.638 min(-1), respectively. An analysis of deltaG for electron transfer from the conduction band of TiO2 to POMs in this study shows that the electron transfer takes place even when it is endothermic.     

A moderated mediation model of the relationship between organizational citizenship behaviors and job performance.

Addressing numerous calls for future research on understanding the theoretical mechanisms that explain the relationship between organizational citizenship behaviors (OCBs) and job performance, this study focused on how an employee's relationships with coworkers mediate the relationship between his or her OCBs and his or her job performance. It also looked at how task autonomy might moderate this mediated relationship. The results of an empirical study involving 364 jewelry designers, 310 coworkers, and 284 supervisors indicated that coworker relations mediated the relationship between OCBs and job performance. In addition, task autonomy positively moderated both paths of this mediated relationship. Finally, these results hold for OCBs that are targeted at individuals but not for OCBs that are targeted toward organizations. (PsycINFO Database Record (c) 2011 APA, all rights reserved)