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Cincinnati, OH, United States

Virkutyte J.,Pegasus Technical Services Inc. | Varma R.S.,U.S. Environmental Protection Agency
RSC Advances

To utilize visible light, Ag loaded and C, N-doped nano-TiO 2 was prepared using a "one pot" synthesis utilizing mild reaction conditions and benign precursors. The synthesis was optimized using appropriate experiment design that took the silver content and calcination temperature into account. The optimized nanocatalyst was characterized by XRD, BET, TEM, TGA, XPS as well as UV-DRS. Nanocatalysts were predominantly anatase as confirmed by XRD, thermally stable up to 1100 °C, as revealed by TGA studies and exhibited absorption in the visible light region as verified by UV-DRS analysis. Moreover, XPS results proved that Ag was dispersed on the surface of the TiO 2 nanoparticles and nitrogen, as well as carbon from guanidine nitrate was interlaced into the matrix of TiO 2. Co-doping of TiO 2 suppressed charge recombination and improved the visible light photo-activity up to the complete degradation of dichlorophenol (DCP) in 4 h of the reaction. Degradation followed first order reaction kinetics with k app ranging from 1.1 to as high as 15.1 × 10 -3 min -1 depending on the silver content and calcination temperature. Demineralization of the solution in terms of TOC was up to 92%. A complete elimination of Vibrio fischeri was accomplished with 1 mg L -1 of the nanocatalyst regardless of the Ag content. © 2012 The Royal Society of Chemistry. Source

Virkutyte J.,Pegasus Technical Services Inc. | Varma R.S.,U.S. Environmental Protection Agency
RSC Advances

An excellent visible light activated Ag and garlic loaded TiO 2 nanocatalyst was prepared by using AgNO 3 and garlic (Allium sativum) as the Ag + and sulfur sources, respectively. The catalyst resisted the change from anatase to rutile phase even at high (700 °C) calcination temperature. The photocatalytic efficiency of as-prepared nanocatalysts was evaluated by degrading (100 ppm) azodye, methyl orange (MO), and dichloro phenol (DCP) under visible light irradiation for 3 to 4 h from an incandescent light bulb (300 W). The process followed first order reaction kinetics with reaction rates ranging from 9.5 × 10 -4 to 19.4 × 10 -3 min -1. The dye was decomposed in 3 h and more than 70% DCP degraded in 4 h in the presence of Ag and garlic loaded-TiO 2 calcined at 700 °C. Demineralization of the solution was in the range 40 to 90%. A complete elimination of Vibrio fischeri was accomplished with 1 mg L -1 of nanocatalyst regardless the calcination temperature. The catalyst was used for up to 5 consecutive runs without the significant loss in the photocatalytic activity and could be regenerated by adopting a simple procedure of washing with water and acetone as well as drying at 200 °C for 2 h. © 2012 The Royal Society of Chemistry. Source

Revetta R.P.,U.S. Environmental Protection Agency | Pemberton A.,Pegasus Technical Services Inc. | Lamendella R.,University of Cincinnati | Iker B.,U.S. Environmental Protection Agency | Santo Domingo J.W.,U.S. Environmental Protection Agency
Water Research

Intracellular RNA is rapidly degraded in stressed cells and is more unstable outside of the cell than DNA. As a result, RNA-based methods have been suggested to study the active microbial fraction in environmental matrices. The aim of this study was to identify bacterial populations in drinking water by analyzing 16S rRNA-based clone libraries. Hollow-fiber ultrafiltration was used to concentrate bacterial communities from 40 l of tap water collected at 12 different times during three different summer months from a single point-of-use. Total RNA was extracted from the microbial concentrates and used to develop 16S rRNA-based clone libraries. Phylogenetic analyses of 1231 partial 16S rRNA gene sequences showed that difficult-to-classify bacterial sequences were the most predominant clones, representing 57.6% of the sequences analyzed. Within these unclassified clades, most sequences were closely related to sequences retrieved from previous DNA- and RNA-based drinking water studies. Other bacterial groups represented in this study included Proteobacteria, cyanobacteria, Actinobacteria, Bacteroidetes, and Planctomycetes. Overall, the results suggest that these bacterial groups are amongst potentially active bacteria in drinking water. Diversity analyses of clones generated show that while overall diversity is similar amongst the different months, membership changes with respect to time. The results from this study further improve our understanding of the molecular diversity and bacterial population dynamics of drinking water microbial communities. Moreover, these results provide the sequence foundation for the development of molecular assays that target active drinking water bacteria. Source

Virkutyte J.,Pegasus Technical Services Inc. | Jegatheesan V.,Deakin University | Varma R.S.,U.S. Environmental Protection Agency
Bioresource Technology

Hybrid TiO 2/microcrystalline cellulose (MC) nanophotocatalyst was prepared in situ by a facile and simple synthesis utilizing benign precursors such as MC and TiCl 4. The as-prepared nanocomposite was characterized by XRD, XPS, BET surface area analyzer, UV-vis DRS and TGA. Surface morphology was assessed by the means of SEM and HR-TEM. Statistics-based factorial design (FD) was adopted to investigate the effect of precursors concentrations and therefore to optimize the nanocomposite synthesis through catalytic adsorption of methylene blue (MB) from aqueous solutions. The results indicated that TiO 2/MC nanocomposites were photocatalytically active in diminishing 40-90% of MB in 4h. © 2011 Elsevier Ltd. Source

Venosa A.D.,U.S. Environmental Protection Agency | Holder E.L.,Pegasus Technical Services Inc.
Marine Pollution Bulletin

We recently conducted a laboratory study to measure the dispersion effectiveness of eight dispersants currently listed on the National Contingency Plan Product Schedule. Results are useful in determining how many commercial dispersant products would have been effective for use on South Louisiana crude oil in the Deepwater Horizon oil spill. The test used was a modification of the Baffled Flask Test (BFT), which is being proposed to replace the current Swirling Flask Test (SFT). The modifications of the BFT in this study included use of one oil rather than two, increasing replication from 4 runs to 6, and testing at two temperatures, 5 °C and 25 °C. Results indicated that temperature was not as critical a variable as the literature suggested, likely because of the low viscosity and light weight of the SLC. Of the eight dispersants tested, only three gave satisfactory results in the laboratory flasks at both temperatures. © 2012. Source

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