Search query: uv water media

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abstract: Photocatalytic conversion of CO2 into carbonaceous feedstock chemicals is a promising strategy to mitigate greenhouse gas emissions and simultaneously store solar energy in chemical form. Photocatalysts for this transformation are typically based on precious metals and operate in nonaqueous solvents to suppress competing H2 generation. In this work, we demonstrate selective visible light driven CO2 reduction in water using a synthetic photocatalyst system that is entirely free of precious metals. We present a series of self assembled nickel terpyridine complexes as electrocatalysts for the reduction of CO2 to CO in organic media. Immobilization on CdS quantum dots allows these catalysts to be active in purely aqueous solution and photocatalytically reduce CO2 with >90% selectivity under UV filtered simulated solar light irradiation (AM 1.5G, 100 mW cm 2, l 400 nm, pH 6.7, 25 degC) Correlation between catalyst immobilization efficiency and product selectivity shows that anchoring the molecular catalyst on the semiconductor surface is key in controlling the selectivity for CO2 reduction over H2 evolution in aqueous solution.
author_names: Moritz F Kuehnel

Katherine L Orchard

Kristian E Dalle

Erwin Reisner
title: Selective Photocatalytic CO2 Reduction in Water through Anchoring of a Molecular Ni Catalyst on CdS Nanocrystals.
venue: Journal of the American Chemical Society
year: 2017

abstract: AbstractDistinguishing the toxic effects of nanoparticles (NPs) themselves from the well studied toxic effects of their ions is a critical but challenging measurement for nanotoxicity studies and regulation. This measurement is especially difficult for silver NPs (AgNPs) because in many relevant biological and environmental solutions, dissolved silver forms AgCl NPs or microparticles. Simulations predict that solid AgCl particles form at silver concentrations greater than 0.18 and 0.58 mg/mL in cell culture media and moderately hard reconstituted water (MHRW) respectively. The AgCl NPs are usually not easily separable from AgNPs. Therefore, common existing total silver techniques applied to measure AgNP dissolution, such as inductively coupled plasma mass spectrometry (ICP MS) or atomic absorption, cannot accurately measure the amount of silver remaining in AgNP form, as they cannot distinguish Ag oxidation states. In this work, we introduce a simple localized surface plasmon resonance (LSPR) UV visible absorbance measurement as a technique to measure the amount of silver remaining in AgNP form for AgNPs with constant agglomeration states. Unlike other existing methods, this absorbance method can be used to measure the amount of silver remaining in AgNP form even in biological and environmental solutions containing chloride because AgCl NPs do not have an associated LSPR absorbance. In addition, no separation step is required to measure the dissolution of the AgNPs. After using ICP MS to show that the area under the absorbance curve is an accurate measure of silver in AgNP state for unagglomerating AgNPs in non chloride containing media, the absorbance is used to measure dissolution rates of AgNPs with different polymer coatings in biological and environmental solutions. We find that the dissolution rate decreases at high AgNP concentrations, 5 kDa polyethylene glycol thiol coatings increase the dissolution rate, and the rate is much higher in cell culture media than in MHRW. Figure
author_names: Justin M Zook

Stephen E Long

Danielle M Cleveland

Carly Lay A Geronimo

Robert I MacCuspie
title: Measuring silver nanoparticle dissolution in complex biological and environmental matrices using UV visible absorbance
venue: Analytical and bioanalytical chemistry
year: 2011

abstract: Abstract M/TiO2 photocatalyst activity for H2 production depends on both the metal co catalyst (M) and the reaction medium. To quantify such effects, we compared the performance of M/TiO2 photocatalysts (M Pd, Pt, Au) for H2 production in different alcohol water mixtures under UV excitation. Photocatalysts were prepared using Degussa P25 TiO2 at metal loadings of 0.5 and 1 wt. for Pd, 1 wt. for Pt and 1 wt. for Au. TEM, UV Vis, XPS and EXAFS analyses confirmed the presence of supported metal nanoparticles of size ~2, 1.3 and 5.4 nm for Pd/TiO2, Pt/TiO2 and Au/TiO2, respectively. Photoluminescence data established that the metal co catalysts effectively suppressed electron hole pair recombination in TiO2 following photo excitation. The activities of the M/TiO2 photocatalysts for H2 production were evaluated in a wide range of alcohol water mixtures (alcohol concentration 10 vol. under UV (365 nm, 5 mW cm 2) H2 production rates in the alcohol water mixtures were dependent on (i) the metal co catalyst; (ii) the co catalyst loading; and (iii) the alcohol type. Co catalyst activity followed the order Pd Pt Au. The highest H2 production rates were achieved for the 1 wt. Pd/TiO2 photocatalyst in glycerol water mixtures (47.5 mmol g 1 h 1) and 1,2 ethanediol water mixtures (44.5 mmol g 1 h 1) H2 production rates decreased in the order glycerol 1,2 ethanediol 1,2 propanediol methanol ethanol 2 propanol tert butanol water. For each M/TiO2 photocatalyst, correlations were established between the rate of H2 production and specific alcohol properties, especially alcohol polarity and the exponential of the alcohol oxidation potential.
author_names: Zakiya H N Al-Azri

Wan-Ting Chen

Andrew Chan

Vedran Jovic

Toshiaki Ina

Hicham Idriss

Geoffrey I N Waterhouse
title: The roles of metal co catalysts and reaction media in photocatalytic hydrogen production: Performance evaluation of M/TiO2 photocatalysts (M Pd, Pt, Au) in different alcohol water mixtures
year: 2015

abstract: Over the last decade, ultraviolet light emitting diodes (UV LEDs) have attracted considerable attention as alternative mercury free UV sources for water treatment purposes. This review is a comprehensive analysis of data reported in recent years (mostly, post 2014) on the application of UV LED induced advanced oxidation processes (AOPs) to degrade organic pollutants, primarily dyes, phenols, pharmaceuticals, insecticides, estrogens and cyanotoxins, in aqueous media. Heterogeneous TiO2 based photocatalysis in lab grade water using UVA LEDs is the most frequently applied method for treating organic contaminants. The effects of controlled periodic illumination, different TiO2 based nanostructures and reactor types on degradation kinetics and mineralization are discussed. UVB and UVC LEDs have been used for photo Fenton, photo Fenton like and UV/H2O2 treatment of pollutants, primarily, in model aqueous solutions. Notably, UV LED activated persulfate/peroxymonosulfate processes were capable of providing degradation in DOC containing waters. Wall plug efficiency, energy efficiency of UV LEDs and the energy requirements in terms of Electrical Energy per Order (EEO) are discussed and compared. Despite the overall high degradation efficiency of the UV LED based AOPs, practical implementation is still limited and at lab scale. More research on real water matrices at more environmentally relevant concentrations, as well as an estimation of energy requirements providing fluence based kinetic data are required.
author_names: Galina Matafonova

Valeriy B Batoev
title: Recent advances in application of UV light emitting diodes for degrading organic pollutants in water through advanced oxidation processes: A review.
venue: Water research
year: 2018

abstract: Abstract This work prepared palladium doped titanium dioxide (Pd doped TiO2) catalysts by a facile sol gel method to enhance degradation of single and binary methylene blue and methyl orange by ultraviolet photocatalysis. The physicochemical properties of Pd doped TiO2 particles were analyzed by a X ray powder diffractometer, X ray photoelectron spectroscope, scanning electron microscope, transmission electron microscope, UV visible diffuse reflectance spectroscope, sorptiometer, and transient photocurrent spectroscope. More efficient degradation was achieved in acidic and basic/neutral media for methyl orange and methylene blue, respectively. Also, methylene blue was always degraded faster than methyl orange. The highest degradation efficiency of both dyes in single and binary systems was obtained using 0.5 wt. and 0.75 wt. Pd TiO2, respectively. The degradation pathways of single methylene blue and methyl orange with Pd doped TiO2 and commercial P25 TiO2 were proposed and compared by identifying reaction intermediates produced during photocatalysis. Recycling tests have confirmed excellent stability of Pd TiO2 materials. Also, the prepared materials were easier to separate from the treated liquid using a simple sedimentation or filtration method than P25 TiO2. In particular, the use of sol gel method could readily synthesize a large number of catalysts, which was beneficial for scale up consideration. All these factors highlighted their potential and prospect in practical applications for water reuse.
author_names: Chi Hieu Nguyen

Chun-Chieh Fu

Ruey-Shin Juang
title: Degradation of methylene blue and methyl orange by palladium doped TiO2 photocatalysis for water reuse: Efficiency and degradation pathways
year: 2018

abstract: Perfluorooctane sulfonate (PFOS) is the environmentally concerned compound because of its persistence and bioaccumulative properties. Since photodegradation of PFOS is not yet experimentally confirmed, photodegradation study of PFOS in water and alkaline 2 propanol solution was conducted. Aqueous and alkaline 2 propanol solution of PFOS (40 microM) was irradiated with a low pressure mercury lamp (254 nm, 32 W) by internal irradiation for 10 d, and then PFOS, fluoride and sulfate ions, and the other degradation products were analyzed. Photodegradation of PFOS was confirmed in both media. PFOS was degraded by 8% after 1 day and by 68% after 10 days irradiation compared to the initial concentration in water. In alkaline 2 propanol, 76 and 92% of PFOS was degraded after 1 and 10 days irradiation, respectively. Photodegradation of PFOS in alkaline 2 propanol was much faster and effective than in water, as the photodegradation rate constants were 0.93 days( 1) in alkaline 2 propanol and 0.13 days( 1) in water, respectively. Formation of fluoride and sulfate was also confirmed by ion chromatography and X ray diffraction analysis. From observation of the degradation products, two major degradation pathways of PFOS were considered: via C8HF17 and C8F17OH, respectively, resulting in short chain fluorinated compounds such as C7HF15 and C7F15OH by stepwise removal of CF2. Formation of short chain fluorocarbons such as CF4, C2F6, and C3F8 were also confirmed. This is the first study to confirm photodegradation of PFOS in water and alkaline 2 propanol.
author_names: Takashi Yamamoto

Yukio Noma

Shin-ichi Sakai

Yasuyuki Shibata
title: Photodegradation of perfluorooctane sulfonate by UV irradiation in water and alkaline 2 propanol.
venue: Environmental science technology
year: 2007

abstract: The pKa values of nine polyphenolic acid substances in water and acetonitrile water mixtures using potentiometric, spectrophotometric, and liquid chromatographic (LC) measurements, have been determined. Also, a new method based on the absorbance spectra at the maximum of chromatographic peaks previously obtained has been applied. This method can be applied to data obtained from LC UV (diode array detection (DAD) instruments and retains all the advantages of LC and spectrophotometric methods, such as the possibility of working with impure samples. Finally, the advantages of the different methods to the determination of pKa values of nine polyphenolic acids have been described in order to verify the applicability of the proposed methods in aqueous and acetonitrile water media. (c) 2003 Elsevier Science B.V. All rights reserved.
author_names: Jose Luis Beltran

Nurullah Sanli

Gemma Fonrodona

Dolores Barron

Guleren Ozkan

Jose Barbosa
title: Spectrophotometric, potentiometric and chromatographic pKa values of polyphenolic acids in water and acetonitrile water media
year: 2003

abstract: Urban wastewater treatment plants (UWTPs) are among the main hotspots of antibiotic resistance (AR) spread into the environment and the role of conventional and new disinfection processes as possible barrier to minimise the risk for AR transfer is presently under investigation. Accordingly, the aim of this work was to evaluate the effect of an advanced oxidation process (AOP) (specifically UV/H2O2) on AR transfer potential. UV/H2O2 disinfection experiments were carried out on real wastewater samples to evaluate the: i) inactivation of total coliforms, Escherichia coli and antibiotic resistant E. coli as well as ii) possible removal of target antibiotic resistance genes (ARGs) (namely, blaTEM, qnrS and tetW) In particular, DNA was extracted from both antibiotic resistant E. coli bacterial cells (intracellular DNA) grown on selective culture media, and the whole water suspension (total DNA) collected at different treatment times. Polymerase chain reaction (PCR) assay was performed to detect the absence/presence of the selected ARGs. Real Time quantitative Polymerase Chain Reaction (qPCR) was used to quantify the investigated ARGs in terms of copiesmL( 1) In spite of the bacterial inactivation and a decrease of ARGs in intracellular DNA after 60min treatment, UV/H2O2 process was not effective in ARGs removal from water suspension (total DNA) Particularly, an increase up to 3.7x10(3)copiesmL( 1) (p>0.05) of blaTEM gene was observed in total DNA after 240min treatment, while no difference (p>0.05) was found for qnrS gene between the initial (5.1x10(4)copiesmL( 1) and the final sample (4.3x10(4)copiesmL( 1) On the base of the achieved results, the investigated disinfection process may not be effective in minimising AR spread potential into the environment. The death of bacterial cells, which results in DNA release in the treated water, may pose a risk for AR transfer to other bacteria present in the receiving water body.
author_names: Giovanna Ferro

Francesco Guarino

Stefano Castiglione

Luigi Rizzo
title: Antibiotic resistance spread potential in urban wastewater effluents disinfected by UV/H2O2 process.
venue: The Science of the total environment
year: 2016

abstract: Unlike that for cadmium based nanocrystals, little research has been found on the synthesis of the UV blue emitting ZnSe based QDs with photoluminescence (PL) quantum yield (QY) superior to 50% In this article, high quality water dispersible ZnSe/ZnS core/shell nanocrystals have been prepared in aqueous media. The epitaxial overgrowth of the ZnS shell was carried out at 90 degC in a reaction flask consisting of the shell precursor compounds (zinc acetae as zinc resource and thiourea as sulfur resource) together with the as prepared ZnSe core nanocrystals and the capping reagent glutathione. The optical features and structure of the obtained ZnSe/ZnS core/shell nanocrystals have been characterized by UV vis, PL spectroscopy, transmission electron microscopy (TEM) X ray diffraction (XRD) and energy dispersive X ray analysis (EDX) The influences of various experimental variables, including amounts of ligand and thiourea as well as pH value, on the growth rate and luminescent properties of the obtained cor.
author_names: Zheng Fang

Yan Li

Hua Zhang

Xinhua Zhong

Linyong Zhu
title: Facile Synthesis of Highly Luminescent UV Blue Emitting ZnSe/ZnS Core/Shell Nanocrystals in Aqueous Media
year: 2009

abstract: Abstract In this work, we evaluate the effect of nanoparticles and nanofluids as viscosity reducers for heavy crude oil (HO) The effect of alumina, silica and acidic silica nanoparticles was evaluated through n C7 asphaltene adsorption and aggregation tests using UV vis spectrophotometry and dynamic light scattering. The nanoparticles of acidic silica were used to prepare a water based nanofluid at different concentrations in distilled water, and also with the addition of 2.0 wt% of a non ionic surfactant. The shear rheological response was obtained as function of nanoparticle concentration, temperature (from 298 to 323 K) and shear rate (ranging from 0 to 100 s 1) Experimental results indicate that increasing the concentration of nanoparticles in the mixture, up to 10,000 ppm, leads to a viscosity reduction of approximately 90% in comparison with the nanoparticle free crude oil. At higher concentration of nanoparticles, the effectiveness of the heavy oil viscosity reduction diminishes. Rheological tests showed a non Newtonian behavior for the mixtures tested at 298 K. However, as the temperature reaches 323 K the specimens behave in a Newtonian fashion. Coreflooding tests were conducted under typical reservoir conditions of pore and overburden pressures, i.e. 2600 and 3600 psi, respectively, and at 360 K. Results indicate that the addition of nanoparticles increases the heavy oil mobility and leads to an improvement in oil recovery of roughly 16%
author_names: Esteban A Taborda

Camilo A Franco

Sergio H Lopera

Vladimir Alvarado

Farid B Cortes
title: Effect of nanoparticles/nanofluids on the rheology of heavy crude oil and its mobility on porous media at reservoir conditions
year: 2016