Effect of Cobalt and Nickel Doping on Structural and Magnetic Properties of Iron Oxide Nanoparticles

Two series samples of Iron Oxide nanoparticles doped with nickel and cobalt with different doping values (x?=?0.01; 0.03; 0.05 and 0.07), were successfully synthesized by using sol–gel method, and then they were characterized by X-ray diffraction, scanning electron and vibrating sample magnetometer (VSM). X-ray diffraction analysis of two series samples showed the formation α-Fe₂O₃ nanoparticles, accompanied by two phases iron spinels, CoFe₂O₄ and NiFe₂O₄. In addition, the variations in grain size were observed for both two series. The observation by scanning electron microscopy reveals a change in the morphology of the grains of all the samples doped, which confirm the cobalt and nickel effect on the morphology of iron oxide nanoparticles. Magnetic measurements which were measured by VSM showed significant magnetic parameters such as coercivity and magnetization besides the ferromagnetic behavior of both two series doped with Cobalt and Nickel.

     

Electrochemical measurements for studying the polymerization process and critical point behaviors of hydrogels

We propose a new technique based on electrochemical measurements for studying the critical point behaviors of the sol–gel transition of acrylamide–N,N′‐methylene bisacrylamide hydrogels. In this technique, no chemical activator is used for accelerating the polymerization reaction. However, a potential difference is applied by means of silver and calomel electrodes placed in the reaction mixture. The silver electrode begins to be ionized and loses its electrons. The free radicals, ^?O₃S? O^?, H^?, and ^?OH, form on the silver electrode via persulfate dissociation. The polymerization is initiated by means of these free radicals. The current measured during the gelation processes passes through a maximum (a Gaussian‐like behavior) and varies linearly with the reaction time during linear polymerization. All the parameters (the monomer, initiator, and crosslinker concentrations, the applied voltage, and the stirring rate of the reacting mixture) affecting the current have been studied in detail. We show that the maxima appearing in the current–time plots correspond to the gelation thresholds, the so‐called sol–gel transition points. We also analytically prove that the current monitors the weight‐average degree of polymerization (DP_w) and the gel fraction (G) below and above the threshold, respectively. The scaling behaviors of DP_w and G have been tested near the gelation thresholds, and we have observed that the critical exponents γ and β, defined for DP_w and G, agree with the predictions by mean‐field theory. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of pH on the survival of Listeria innocua in calcium ascorbate solutions and on quality of fresh-cut apples

Fresh-cut apple slices were dipped in calcium ascorbate (CaA) solution at pH values ranging from 2.5 to 7.0 to inhibit browning. After treatment, the cut apples were stored at 4 and 10 degrees C for up to 21 days. Color and texture of the apples were determined on days 1, 14, and 21. In a separate experiement, the pH of CaA solution was adjusted with acetic acid to six different pH levels, and the solution was inoculated with Listeria innocua. The survival of the bacterium and the stability of CaA were determined at 0, 20, and 96 h. The cut apples maintained fresh quality when the pH of the CaA solution was above 4.5, but slight discoloration of apple slices dipped in pH 4.5 solution was observed after 14 days at 10 degrees C. At pH 5.0, the CaA dip maintained the quality of the apples at both temperatures for at least 21 days. The L. innocua population was reduced by 4 to 5 log CFU/ml at pH 4.5 after 96 h. At pH 5, the bacterial population in the CaA solution was reduced by approximately 2 log CFU/ml during the same period. The CaA solution was stable at pH 5 for at least 96 h. Reduction of the pH to between 4.5 and 5.0 might reduce the risk of foodborne illness due to consumption of fresh-cut apples treated with a CaA solution contaminated with Listeria.     

Investigating 5-hydroxymethylfurfural formation kinetic and antioxidant activity in heat treated honey from different floral sources

The quality and biochemical properties of honey are affected by heating or during storage period. The most important biochemical reaction that occurs in this process is the Maillard reaction. HMF (5-hydroxymethylfurfural) is one of the major intermediate products in the Maillard reaction that can lead to quality reduction in heated honey. In this study, the effect of heating on the antioxidant activity, and colour values as Maillard reaction indicators of three different botanical honeys were investigated; the HMF formation was also determined. Temperatures of 50, 70 and 80 °C were applied on the honeys between 0 and 48 h. Total phenolic content, ferric reducing/antioxidant power and scavenging of 2,2-diphenyl-1-picrylhydrazyl free radical assays are used to determine the antioxidant capacity. Results showed that the formation of HMF and the antioxidant properties of honeys were significantly increased during the heating process. Pure HMF compound also showed lower antioxidant activity. The formation of HMF has higher degree of linearity in the fit of the zero order reaction and also it was the highest in the chestnut honey. Furthermore, it was found that as the biochemical value of the honeys increased, the HMF formation decelerated.     

Immobilization of invertase in conducting polypyrrole/PMMA‐co‐PMTM graft copolymers

In this study, invertase was immobilized in copolymer electrodes constructed. Three different types of polymethyl methacrylate‐co‐polymethyl thienyl methacrylate matrices were used to obtain copolymers that were characterized by FT‐IR spectroscopy. Immobilization of enzymes was carried out by the entrapment of the enzyme in conducting polymer matrices during electrochemical polymerization of pyrrole through thiophene moieties of polymers. Immobilization of the enzyme was achieved by application of 1.0 V constant potential on a platinum electrode for 30 min in solution. The effects of temperature and pH on the activity of the enzyme electrodes were examined and operational stability studies were done. The changes in the maximum reaction rate and the variations in the Michaelis–Menten constant were studied. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 502–507, 2005     

Biodegradation kinetics of the soluble slowly biodegradable substrate in polyamide carpet finishing wastewater

BACKGROUND: Carpet manufacturing and finishing with purely synthetic fibers has received relatively little attention, compared to other textile processing types. This study evaluates the biodegradation kinetics of organic compounds generated from polyamide‐based carpet manufacturing. RESULTS: Experiments were conducted on pre‐washing and dyeing/softening wastewater effluents. Model evaluation of oxygen uptake rate profiles with dual hydrolysis kinetics revealed that the soluble slowly hydrolysable chemical oxygen demand (COD) was the major fraction, constituting nearly 97% of the biodegradable COD and 78% of total COD content. Degradation of the slowly hydrolysable COD fraction was characterized with a rate coefficient of 0.72 day^?1, a significant rate limiting step for substrate utilization. Model simulation of system performance indicated that an unusually long hydraulic retention time was required for an activated sludge system to reduce the effluent COD concentration. CONCLUSION: Compared to domestic wastewater, two additional hydrolysable COD fractions with different degradation kinetics were characterized. The dyeing and softening step had the highest slowly biodegradable organic matter content, with the lowest degradation rate. Simulation results showed that soluble slowly hydrolysable COD degradation did not cause any problem in terms of effluent quality. With the system operated under reduced solids retention time, the effluent COD quality was significantly influenced by the slow hydrolysis rate of soluble hydrolysable matter. Copyright © 2007 Society of Chemical Industry     

Heat-resistance characteristics of ascospores of Eurotium chevalieri isolated from apricot juice

A heat-resistant fungus was isolated from aseptically packaged apricot pulp. The fungus was identified as Eurotium chevalieri. Heat resistance of the fungus was studied at four different temperatures (70, 75, 80 and 83 degrees C) after activation of its ascospores for 30 min at 70 degrees C. D70, D75, D80 and D83 values of ascospores of Eurotium chevalieri were estimated by linear regression (log-survival vs. heating time) as 118.58, 34.15, 5.50 and 3.77 min, respectively. The z-value was determined in the same way (regression of log-D values vs. heating temp.) and was found as 8.23 degrees C.