Showing papers by "Nasser A.M. Barakat published in 2013"

Influence of temperature on the photodegradation process using Ag-doped TiO2 nanostructures: Negative impact with the nanofibers

Abstract: In this study, the influence of the temperature on the photodegradation process using Ag-doped TiO2 nanostructures was investigated. Two morphologies were used; nanoparticles and nanofibers. The nanofibers were synthesized by electrospinning of a sol–gel consisting of titanium isopropoxide, silver nitrate and poly(vinyl acetate). The silver nitrate amount was changed to produce nanofibers having different silver contents. Typically, sol–gels containing 0.5, 1.0, 1.5, 2.0 and 2.5 wt% silver nitrate were utilized. Calcination of the electrospun mats at 700 °C led to produce well morphology Ag-doped TiO2 nanofibers for all formulations. The nanoparticles were prepared from the same sol–gels, however, instead of spinning the gels were dried, grinded and sintered at 700 °C. Photodegradation under UV irradiation for the rhodamine B at 5, 15, 25, 45 and 55 °C were performed. For the nanoparticles, increasing the temperature has positive impact as the best degradation was obtained at 55 °C. In contrast to the known influence of the temperature on the chemical reactions, in case of the nanofibrous morphology, the temperature has negative impact as the experimental work indicated that the optimum temperature is 25 °C. The observed strange effect of the temperature in case of the nanofibrous morphology indicates instant degradation of the dye molecules in the active zones surrounding the nanofibers. Therefore, the increase of temperature results in increase the kinetic energy of the dye molecules so the molecules escape from the active thin film surrounding the photocatalyst. Overall, this study shows that the nanofibrous morphology strongly enhances the surface activity of the photocatalyst which generates negative influence of the temperature.

Influence of the nanofibrous morphology on the catalytic activity of NiO nanostructures: an effective impact toward methanol electrooxidation.

Abstract: In this study, the influence of the morphology on the electrocatalytic activity of nickel oxide nanostructures toward methanol oxidation is investigated. Two nanostructures were utilized: nanoparticles and nanofibers. NiO nanofibers have been synthesized by using the electrospinning technique. Briefly, electrospun nanofiber mats composed of polyvinylpyrolidine and nickel acetate were calcined at 700°C for 1 h. Interestingly, compared to nanoparticles, the nanofibrous morphology strongly enhanced the electrocatalytic performance. The corresponding current densities for the NiO nanofibers and nanoparticles were 25 and 6 mA/cm2, respectively. Moreover, the optimum methanol concentration increased to 1 M in case of the nanofibrous morphology while it was 0.1 M for the NiO nanoparticles. Actually, the one-dimensional feature of the nanofibrous morphology facilitates electrons' motion which enhances the electrocatalytic activity. Overall, this study emphasizes the distinct positive impact of the nanofibrous morphology on the electrocatalytic activity which will open a new avenue for modification of the electrocatalysts.

Development of multi-channel carbon nanofibers as effective electrosorptive electrodes for a capacitive deionization process

Abstract: Among the various carbonaceous materials, carbon nanofibers (CNFs) are widely utilized in different applications because of their superior mechanical and physicochemical characteristics. However, due to the low surface area compared to other nanocarbonaceous materials, CNFs performance as an electrode in capacitive deionization (CDI) units is comparatively low. In this study, this problem has been overcome by preparing multi-channel carbon nanofibers having a total surface area 10 times more than the conventional CNFs, by creating numerous channels on the nanofibers surface. The modified CNFs have been synthesized using a low cost, high yielding and facile method; an electrospinning technique. Typically, the stabilization and graphitization of electrospun nanofiber mats composed of polyacrylonitrile (PAN) and poly(methyl methacrylate) (PMMA) leads to the formation of multi-channel CNFs due to the difference in the physicochemical characteristics of the two polymers and the complete thermal decomposition of the PMMA during the graphitization step. Three formulations were prepared; 0, 25 and 50 wt% PMMA with respect to the PAN. To properly evaluate the introduced modified CNFs, graphene was prepared using the chemical route. The utilized characterizations indicated that the CNFs obtained from the electrospun solution having 50% PMMA possess a surface area of 181 m2 g−1, which is more than all the investigated formulations including graphene. Accordingly, these nanofibers revealed a salt removal efficiency of ∼90% and a specific capacitance of 237 F g−1. Overall, the present study introduces an effective and simple strategy to distinctly improve the surface area of CNFs, which can strongly enhance their application in CDI technology.

Ethanol electro-oxidation using cadmium-doped cobalt/carbon nanoparticles as novel non precious electrocatalyst

Abstract: Novel electrocatalyst based on non precious metals (Co and Cd) is introduced to be used as anode in the ethanol fuel cells. Cd-doped Cobalt nanoparticles encapsulated in graphite shell have been synthesized using simple sol–gel technique. The introduced electrocatalyst can be prepared from a sol–gel composed of cadmium acetate, cobalt acetate and poly(vinyl alcohol) based on the polycondensation possibility of the acetates. Grinding and calcination in Ar atmosphere of the prepared gel leads to produce Cd-doped Co nanoparticles encapsulated in a thin graphite layer. High current density (70 mA cm −2 ) and considerably low onset potential (∼585 mV vs. NHE) were obtained when the synthesized nanoparticles have been exploited as electrocatalyst for ethanol (concentration 1 M) oxidation in basic media (1 M KOH). Considering that the introduced nanoparticles composed of non precious metals and the obtained electrochemical results are satisfactory, the introduced study might open new avenues to the cobalt-based nanostructures to be used as novel electrocatalysts in the fuel cells applications.

Electrospun Cu-doped titania nanofibers for photocatalytic hydrolysis of ammonia borane

Abstract: Among reported hydrogen storage materials, ammonia borane is a promising candidate to be utilized in many industrial applications. The high chemical resistance of the ceramic catalysts makes them one of the most stable classes of catalytic materials. In this study, CuO nanoparticles (NPs) -doped TiO2 nanofibers (NFs) are introduced as a highly effective and reusable catalyst for ammonia borane complex hydrolysis. The incorporation of CuO NPs inside the TiO2 NFs provided distinct advantages for the introduced catalyst; the aggregation problem of the CuO NPs was overcome and a synergistic effect was created as the synthesized CuO NPs-doped TiO2 revealed higher activity compared to the individual components. Typically, after 10 min, the obtained hydrogen equivalent was 2.7, 0.9 and 0.95 when CuO NPs-doped TiO2 nanofibers, CuO NPs and pristine TiO2 nanofibers were used as the catalyst, respectively. The catalytic activity of the introduced nanofibers did not change after being used for three successive cycles. Moreover, the catalytic performance was strongly modified when the hydrolysis process was performed under sunlight irradiation because of the photocatalytic activity of the TiO2 and CuO. The introduced nanofibers were prepared by the simple, effective, low cost and high yielding technique of electrospinning. The present study introduces TiO2 nanofibers as a promising catalyst for the ammonia borane complex, as well as an interesting support used for functional materials.

Catalytic and photo hydrolysis of ammonia borane complex using Pd-doped Co nanofibers

Abstract: Due to the axial ratio feature, bimetallic nanofibers are expected to have novel characteristics. In this study, Pd-doped Co nanofibers could be successfully prepared using simple, low cost, high yield and effective technique; electrospinning. The introduced nanofibers have been synthesized by calcination of electrospun nanofibers composed of Pd NPs/cobalt acetate tetrahydrate/poly(vinyl alcohol) in a vacuum atmosphere. The utilized physicochemical characterizations indicated that the introduced bimetallic nanofibers are chemically protected by a sheath of graphite layer. Interestingly, the introduced nanofibers can be utilized in hydrolysis of ammonia borane in an aqueous solutions using two different simultaneous mechanisms; normal and photo catalysis. The solar radiation improves the performance as the stoichiometric hydrogen has been obtained within few minutes under the sunlight because of the photohydrolysis influence. Reusability is a distinct feature for the introduced nanofibers as they could be utilized for several successive times with the same efficiency. Moreover, due to the carbon sheathing, no metallic ions release was observed in the final solution. Photohydrolysis mechanism of ammonia borane might open a new avenue to utilize different class of materials to release the embedded hydrogen in the ammonia borane complex.

Potential Contribution of Retama raetam (Forssk.) Webb & Berthel as a Forage Shrub in Sinai, Egypt

Abstract: The shortage of forage in arid areas is an important concern and it leads us to explore alternative options as nonconventional feed resources. Among potential forage species, samples of Retama raetam (R. raetam) were collected from six different locations representing four habitat types in two diverse phytogeographical regions in Egypt during the summer and winter seasons. Soil characteristics, growth performance, and nutritional traits of R. raetam were evaluated to assess the potential value of this legume as an alternative forage source in the Mediterranean ecosystem. Data showed that soil texture across the study sites had sandy, loamy, and clayey textures, whereas pH ranged from neutral to alkaline and organic carbon was low at all sites. Growth and production of R. raetam were significantly affected by seasonal variation in rainfall and, based on our study results, this effect was more important than specific site property variations such as soil texture and organic matter contents. Moreover, data i...

Development of Cd-doped Co Nanoparticles Encapsulated in Graphite Shell as Novel Electrode Material for the Capacitive Deionization Technology

Abstract: Because of the low energy requirement and the environmentally safe byproducts, the capacitive deionization water desalination technology has attracted the attention of many researchers. The important requirements for electrode materials are good electrical conductivity, high surface area, good chemical stability and high specific capacitance. In this study, metallic nanoparticles that are encapsulated in a graphite shell (Cd-doped Co/C NPs) are introduced as the new electrode material for the capacitive deionization process because they have higher specific capacitance than the pristine carbonaceous materials. Cd-doped Co/C NPs perform better than graphene and the activated carbon. The introduced nanoparticles were synthesized using a simple sol-gel technique. A typical sol-gel composed of cadmium acetate, cobalt acetate and poly(vinyl alcohol) was prepared based on the polycondensation property of the acetates. The physiochemical characterizations that were used confirmed that the drying, grinding and calcination in an Ar atmosphere of the prepared gel produced the Cd-doped Co nanoparticles, which were encapsulated in a thin graphite layer. Overall, the present study suggests a new method to effectively use the encapsulated bimetallic nanostructures in the capacitive deionization technology.

Inactivation of Foodborne Pathogens by NiO/TiO2 Composite Nanofibers: A Novel Biomaterial System

Abstract: This study presents the fabrication and characterization of novel NiO/TiO2 composite nanofibers and their antibacterial activity. The utilized NiO/TiO2 composite nanofibers were prepared by electrospinning of a sol–gel composed of nickel nitrate hexahydrate, titanium isopropoxide and poly(vinyl acetate). The obtained electrospun nanofiberous mat was vacuum dried at 80 °C and then calcined at 600 °C in air for 2 h. The physicochemical properties of the synthesized nanofibers were determined by X-ray diffraction pattern, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron probe microanalysis and transmission electron microscopy. The antibacterial activity was tested against four common foodborne pathogenic bacteria viz., Staphylococcus aureus, Escherichia coli, Salmonella typhimurium and Klebsiella pneumoniae by minimum inhibitory concentration (MIC) method taking five different concentrations (5–45 μg/ml). Our investigation reveals that the lowest concentration of NiO/TiO2 composite solution inhibiting the growth of tested strains was found to be 5 μg/ml. TEM analysis demonstrated that the exposure of the selected microbial strains to the composite nanofibers led to disruption of cell membranes and depressed the activity of some membranous enzymes, which caused bacteria to die eventually. Furthermore, the results illustrate that the combination of NiO and TiO2 can be synergistic and resulted in superior antimicrobial activity of NiO/TiO2 composite nanofibers. To sum up, novel NiO/TiO2 composite nanofibers that possess large surface-to-volume ratio with excellent antimicrobial activity were fabricated that can be used to inhibit the microbial growth associated with food stuff.

Preparation and characterization of nylon-6/gelatin composite nanofibers via electrospinning for biomedical applications

Abstract: Easy fabrication, porosity, good mechanical properties, and composition controllable of the electrospun nanofiber mat make this material a promising candidate for wound dressing applications. In the present study, nylon6/gelatin electrospun nanofiber mats are introduced as novel wound dressing materials. The introduced mats were synthesized by electrospinning of nylon6 and gelatin mixtures, three mats containing different gelatin content were prepared; 10, 20 and 30 wt%. Interestingly, addition of the gelatin did not affect the mechanical properties of the nylon 6, moreover the mat containing 10 wt% gelatin revealed higher mechanical properties due to formation of spider-net like structure from very thin nanofibers (∼10 nm diameter) bonding the main nanofibers. Biologically study indicates that gelatin incorporation strongly enhances the bioactivity performance as increasing the gelatin content linearly increases the MC3T3-E1 cell attachment. Overall, the obtained results recommend exploiting the introduced mats as wound dressing material.

Interior synthesizing of ZnO nanoflakes inside nylon‐6 electrospun nanofibers

Abstract: Doping of the polymeric electrospun nanofibers by metal oxides nanoparticles is usually performed by electrospinning of a colloidal solution containing the metal oxide nanoparticles. Besides the economical aspects, electrospinning of colloids is not efficient compared with spinning of sol–gels, moreover well attachment of the solid nanoparticles is not guaranteed. In this study, reduction of zinc acetate could be performed inside the nylon-6 electrospun nanofibers; so polymeric nanofibers embedding ZnO nanoflakes were obtained. Typically, zinc acetate/nylon-6 electrospun nanofibers were treated hydrothermally at 150°C for 1 h. Besides the utilized characterization techniques, PL study affirmed formation of ZnO. The produced nanofibers showed a good antibacterial activity which improves with increasing ZnO content. Overall, the present study opens new avenue to synthesize hybrid nanofibers by a facile procedure. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The physiological mechanisms of calcium chloride application on broad bean plants grown under salinity stress

Abstract: Salinity stress decreases the dry mass of shoot and root, the percentage of this decrease varied between the two plant organs. Roots seemed to be more salt sensitive than shoots. This was accompanied with a lower Na+ content in the shoots than roots. The organic cytosolutes (soluble carbohydrates, soluble proteins and proline) were much higher in shoots than roots. Treatment plants with CaCl2 retarded the Na+ and proline contents considerably in both plant organs. The amount of inorganic cytosolutes (K+ and Ca++) in general increased markedly. The amount of organic cyto-solutes (soluble carbohydrates, soluble proteins and proline) is also enhanced markedly which in turn could increase the water status and consequently the dry matter yield when compared with the only salinized plants. Cell wall degrading enzymes cellulase, polygalacturnase (PG) and polymethylglacturnase (PMG) is significantly increased as salinity increases in tested plants. CaCl2 treatments induced a significant decrease in the activity of cellulase, PG, and PMG. Key words: Broad bean, salinity, CaCl2 , cell wall degrading enzymes.

Influences of Morphology and Doping on the Photoactivity of TiO2 Nanostructures

Abstract: Compared to the bulk, the nanoscale provides special characteristics for the functional materials. Moreover, the nanostructural morphology has also distinct influences. Enormous efforts have been devoted to the research of TiO2 material, which has led to many promising applications. Beside the morphology impact, doping of titanium dioxide nanostructures by pristine metal nanoparticles (e.g. Ag, Pt, … etc.) revealed distinct improvement in the photocatalytic activity. Although the doping process can remarkably improve the photoactivity, it has also noticeable influences on the crystal structure. In this chapter, the important parameters affecting the photocatalytic activity of TiO2 are discussed; morphology and silver doping. Also, effect of sliver-doping on the crystal structure and the nanofibrous morphology is investigated. Moreover, the influence of the temperature on the photodegradation process using Ag-doped TiO2 nanostructures will be addressed. Two morphologies were introduced; nanoparticles and nanofibers. The nanofibers were synthesized by electrospinning of a sol–gel consisting of titanium isopropoxide, silver nitrate and poly(vinyl acetate). The silver nitrate amount was changed to produce nanofibers having different silver contents. The nanoparticles were prepared from the same sol-gels, however instead of spinning the gels were dried, grinded and sintered. The experimental and analytical studies indicate that doping by silver reveals to form anatase and rutile when the silver nitrate content in the mother solution was more than 3 wt%. The rutile phase content is directly proportional with the AgNO3 concentration. Negative impact of the silver-doping on the nanofibrous morphology was observed as increase the silver content caused to decrease the aspect ratio, i.e. producing nanorods rather nanofibers. However, silver-doping leads to modify the surface roughness. In contrast to the known influence of the temperature on the chemical reactions, in case of the nanofibrous morphology of Ag-doped TiO2, the temperature has negative impact on the photoactivity.