Synthesis of carbon nanotubes using pre-sintered oil fly ash via a reproducible process with large-scale potential.

Oil fly ash (OFA) is a byproduct generated by the burning of heavy crude oil in factories and power plants. Millions of tons of OFA is produced annually worldwide and is mostly treated as solid waste. Extensive efforts have been made to utilize OFA and reduce its environmental effects. Recently, OFA has been found to be a suitable catalyst and co-precursor for carbon nanotube (CNTs) production. However, the treatment methods used are expensive and time consuming. Here, we describe a new method for OFA treatment and provide optimized growth conditions for CNTs production. Pre-sintering of OFA at elevated temperatures (400-450 °C) in air or vacuum using a chemical vapor deposition (CVD) tube furnace (80-100 min) is a very effective treatment method for CNTs growth under optimum growth conditions. The optimum parameters for CNTs growth were growth temperature, gas pressure, gas flow rate, and growth time. Well-defined, thin nanotubes with diameters of 20-40 nm were produced. Bamboo-like nanotubes with zigzag curved walls were also observed in the produced CNTs. The weight percentage of the produced CNTs was approximately twice that of the treated OFA. Consequently, the pre-sintering method exhibited suitability for the mass production of CNTs. Thus, large quantities of the nanomaterial can be supplied for use in various applications, e.g., polymer composites, the rubber industry, construction materials, and lubricant additives.

Size controlled, antimicrobial ZnO nanostructures produced by the microwave assisted route.

Zinc oxide nanostructures (ZnO-NS) have shown to be of great value for several biological and biomedical applications. In particular, they have been used in bioimaging and delivery applications as well as inhibitors of microbial growth. In this work a new methodology for producing highly crystalline, size controlled ZnO-NS using a chemical microwave assisted synthetic route is described. A wide range of sizes and shapes of ZnO-NS could be controlled by varying the molar ratio of zinc nitrate to hexamethylenetetramine (HMT) from 3:20 to 30:20. The produced ZnO-NS systematically changed from 25 nm spherical nanoparticles to well-shaped micro sized hexagonal nanorods. Pronounced oxygen defects were also noticed, particularly at higher molar ratios. However, this is not the case with the lattice constant c, whose value is found to decrease by increasing this ratio. The produced ZnO-NS were tested as antimicrobial agent against Gram-negative (E. coli), Gram-positive (B. subtilis) bacteria and yeast (S. cerevisiae). Significant inhibition of these microbial strains was noticed even at low concentrations of ZnO-NS. The ZnO-NS with the molar ratio 3:20 was the most effective against the microbes tested. The results showed 80, 71 and 50% inhibition of E. coli, B. subtilis and S. cerevisiae, respectively. Using the "surfactant stress model" we describe the nanostructure formation of ZnO-NS. The antimicrobial activity of ZnO-NS correlated well with lattice constant c and particle size, where smaller particles with higher value of c displayed increase inhibitory activity. No clear correlation between the oxygen defects and bacterial inhibitions was observed. This highly crystalline, size tunable ZnO-NS could prove to be effective antimicrobial agents at low concentrations (e.g. 20 µg per 10 mL) and might be tested against other microorganisms.

Size controlled ultrafine CeO2 nanoparticles produced by the microwave assisted route and their antimicrobial activity.

Cerium oxide (CeO2) nanoparticles (NPs) have a wide range of biological and biomedical applications. This work describes a new methodology for producing ultrafine, highly uniform NPs with controlled sizes using the chemical microwave assisted route. The size of CeO2-NPs decreased from 10 to 5 nm by increasing the molar ratio of cerium nitrate Ce(NO3)3.(6H2O) to that of hexamethylenetetramine (C6H12N) from 1:20 to 20:20. Detailed information about their structural characterization was obtained from the XRD, UV-visible, photoluminescence, Raman spectroscopy, SEM, TEM and AFM. These CeO2-NPs were tested as antimicrobial agent against Gram-negative (Escherichia.coli), Gram-positive (Bacillus.subtilis) bacteria and yeast (Saccharomyces cerevisiae). The obtained results showed significant inhibition of these strain even at low concentration of CeO2-NPs. The CeO2-NPs with the molar ratio 5:20 had the most effective inhibition against E.coli (~70%) at a concentration of 20 µL. The CeO2-NPs with the ratio 12:20 were found to be the most effective against B.subtilis (inhibition ~68%). On the other hand, CeO2-NPs synthesized with the 20:20 molar ratio caused the highest inhibition for S. cerevisiae (~60%). It is observed that at higher NPs concentration (i.e., >20 µL) the inhibition of these strains decreased. The antimicrobial activity may be attributed to the penetrating power of CeO2-NPs size beside the generated oxygen species radicals that caused inhibition of bacterial growth.