scholarly journals Enhanced photodegradation of dimethoxybenzene isomers in/on ice compared to in aqueous solution

2021 ◽  
Author(s):  
Ted Hullar ◽  
Theo Tran ◽  
Zekun Chen ◽  
Fernanda Bononi ◽  
Oliver Palmer ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Light Absorption ◽  
Inorganic Compounds ◽  
Photochemical Reactions ◽  
Quantum Yields ◽  
Experimental Conditions ◽  
Substantial Impact ◽  
Photodegradation Rate ◽  
The Impact

Abstract. Photochemical reactions of contaminants in snow and ice can be important sources and sinks for various organic and inorganic compounds. Snow contaminants can be found in the bulk ice matrix, in internal liquid-like regions (LLRs), or in quasi-liquid layers (QLLs) at the air-ice interface, where they can readily exchange with the firn air. Some studies have reported that direct photochemical reactions occur faster in LLRs and QLLs than in aqueous solution, while others have found similar rates. Here, we measure the photodegradation rate constants of the three dimethoxybenzene isomers under varying experimental conditions, including in aqueous solution, in LLRs, and at the air-ice interface of nature-identical snow. Relative to aqueous solution, we find modest photodegradation enhancements (3- and 6-fold) in LLRs for two of the isomers, and larger enhancements (15- to 30-fold) at the air-ice interface for all three isomers. We use computational modeling to assess the impact of light absorbance changes on photodegradation rate enhancements at the interface. We find small (2–5 nm) bathochromic (red) absorbance shifts at the interface relative to in solution, which increases light absorption, but this factor only accounts for less than 50 % of the measured rate constant enhancements. The major factor responsible for photodegradation rate enhancements at the air-ice interface appears to be more efficient photodecay: estimated dimethoxybenzene quantum yields are 6- to 24-fold larger at the interface compared to in aqueous solution and account for the majority (51–96 %) of the observed enhancements. Using a hypothetical model compound with an assumed Gaussian-shaped absorbance peak, we find that a shift in the peak to higher or lower wavelengths can have a minor to substantial impact on photodecay rate constants, depending on the original location of the peak and the magnitude of the shift. Changes in other peak properties at the air-ice interface, such as peak width and height (i.e., molar absorptivity) can also impact rates of light absorption and direct photodecay.

scholarly journals The Ripple Effect of Graphite Nanofilm on Stretchable Polydimethylsiloxane for Optical Sensing

Nanomaterials ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 2934
Author(s):  
Kossi A. A. Min-Dianey ◽  
Top Khac Le ◽  
Akeel Qadir ◽  
Noé Landry Privace M’Bouana ◽  
Muhammad Malik ◽  
...  
Keyword(s):  
Light Absorption ◽  
Carrier Mobility ◽  
Optical Sensing ◽  
Broad Band ◽  
Ripple Effect ◽  
Experimental Conditions ◽  
Supporting Layer ◽  
Band Absorption ◽  
Hybrid Devices ◽  
The Impact

Graphene-based optical sensing devices have been widely studied for their broad band absorption, high carrier mobility, and mechanical flexibility. Due to graphene’s weak light absorption, studies on graphene-based optical sensing thus far have focused on hybrid heterostructure devices to enhance photo-absorption. Such hybrid devices need a complicated integration process and lead to deteriorating carrier mobility as a result of heterogeneous interfaces. Rippled or wrinkled graphene has been studied in electronic and optoelectronic devices. However, concrete demonstrations of the impact of the morphology of nanofilms (e.g., graphite and graphene) associated with light absorption in optical sensing devices have not been fully examined. This study explored the optical sensing potential of a graphite nanofilm surface with ripples induced by a stretchable polydimethylsiloxane (PDMS) supporting layer under different stretch:release ratios and then transferred onto silicon, both under experimental conditions and via simulation. The optical sensing potential of the rippled graphite nanofilm was significantly enhanced (260 mA/W at the stretch–release state of 30%), as compared to the pristine graphite/PDMS (20 mA/W at the stretch–release state of 0%) under laser illumination at a wavelength of 532 nm. In addition, the results of our simulated computation also confirmed the improved light absorption of rippled graphite nanofilm surface-based optical sensing devices, which was comparable with the results found in the experiment.

Zur Anwendung von Extinktionsdiagrammen des Stillbens in Perfluormethylcyclohexan./Kinetic Analysis of Photochemical Reactions Using Extinction Diagrams

1972 ◽  
Vol 27 (11) ◽  
pp. 1349-1353 ◽  
Author(s):  
Heinz Mauser ◽  
Hans-Joachim Niemann ◽  
Rainer Kretschmer
Keyword(s):  
Kinetic Analysis ◽  
Rate Constants ◽  
Photochemical Reaction ◽  
Photochemical Reactions ◽  
Quantum Yields ◽  
Method Of Calculation

Extinction diagrams are applied for determining the number of partial reactions. In this paper a method is described for the calculation of the concentration of the reacting substances with the aid of extinction diagrams. The concentration values are more suitable for calculation of the rate constants, and in case of photochemical reactions the partial quantum yields, than the directly measured extinction values. The method of calculation is illustrated using the photochemical reaction of stilbene in a perfluorinated solvent as an example.

Kinetics of the photochemical reactions of the croconate dianion in aqueous solution

1992 ◽  
Vol 70 (1) ◽  
pp. 135-143 ◽  
Author(s):  
B Zhao ◽  
M. H. Back
Keyword(s):  
Aqueous Solution ◽  
Electron Transfer ◽  
Quantum Yield ◽  
Rate Constants ◽  
Photochemical Reactions ◽  
Electron Acceptors ◽  
Basic Solution ◽  
Hydroxyl Ion ◽  
Kinetics Of

The kinetics of the photochemical reactions of the dianion of croconic acid (1,2-dihydroxycyclopentenetrione) have been studied in aqueous solution in the presence of electron acceptors. In neutral solutions the quantum yield for disappearance of croconate dianion was small (< 10−3) but was substantially increased in basic solution and in the presence of electron acceptors. At pH 12 in the presence of 4-nitrobenzylbromide and biacetyl a quantum yield of 1 was obtained. The kinetics of the rate of disappearance of croconate dianion as a function of pH and concentration of acceptor showed that the excited dianion is oxidized by acceptors and reacts with hydroxyl ion. A mechanism is proposed that, by assuming reasonable values for the rate constants involved, is shown to be consistent with the results. Keywords: photolysis, kinetics, croconate dianion, electron transfer.

scholarly journals Photodecay of guaiacol is faster in ice, and even more rapid on ice, than in aqueous solution

2020 ◽  
Vol 22 (8) ◽  
pp. 1666-1677
Author(s):  
Ted Hullar ◽  
Fernanda C. Bononi ◽  
Zekun Chen ◽  
Danielle Magadia ◽  
Oliver Palmer ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Photodegradation Rate ◽  
Frozen Solutions

Guaiacol photodegradation rate constants in solution, liquid-like regions in ice (frozen solutions), and at the air–ice interface (vapor-deposited to snow).

Nonylphenols degradation in the UV, UV/H2O2, O3 and UV/O3 processes – comparison of the methods and kinetic study

2015 ◽  
Vol 71 (3) ◽  
pp. 446-453 ◽  
Author(s):  
E. Felis ◽  
K. Miksch
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Peroxide ◽  
Hydroxyl Radicals ◽  
Rate Constants ◽  
Uv Light ◽  
Second Order ◽  
Quantum Yields ◽  
Environmental Significance ◽  
Order Rate ◽  
Technical Mixture

This paper describes the results of experiments on the decomposition of selected nonylphenols (NPs) in aqueous solutions using the UV, UV/H2O2, O3 and UV/O3 processes. The goal of the research was to determine the kinetic parameters of the above-mentioned processes, and to estimate their effectiveness. These substances were selected because of their ubiquitous occurrence in the aquatic environment, resistance to biodegradation and environmental significance. As a result of the experiments, the quantum yields of the 4-n-nonylphenol (4NP) and NP (technical mixture) photodegradation in aqueous solution were calculated to be 0.15 and 0.17, respectively. The values of the second-order rate constants of the investigated compounds with hydroxyl radical and NP with ozone were also determined. The estimated second-order rate constants of 4NP and NP with hydroxyl radicals were equal to 7.6 × 108–1.3 × 109 mol−1 L s−1. For NP, the determined rate constant with ozone was equal to 2.01 × 106 mol−1 L s−1. The performed experiments showed that NP was slightly more susceptible to degradation by the UV radiation and hydroxyl radicals than 4NP. The study demonstrated also that the polychromatic UV-light alone and also in combination with selected oxidizers (i.e. hydrogen peroxide, ozone) may be successfully used for the removal of selected NPs from the aqueous medium.

scholarly journals Photolysis and oxidation by OH radicals of two carbonyl nitrates: 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone

2020 ◽  
Vol 20 (1) ◽  
pp. 487-498 ◽  
Author(s):  
Bénédicte Picquet-Varrault ◽  
Ricardo Suarez-Bertoa ◽  
Marius Duncianu ◽  
Mathieu Cazaunau ◽  
Edouard Pangui ◽  
...  
Keyword(s):  
Cross Sections ◽  
Rate Constants ◽  
Branching Ratio ◽  
Quantum Yields ◽  
Organic Nitrates ◽  
Oh Radicals ◽  
Experimental Conditions ◽  
Important Species ◽  
Photolysis Rates ◽  
Photolysis Frequencies

Abstract. Multifunctional organic nitrates, including carbonyl nitrates, are important species formed in NOx-rich atmospheres by the degradation of volatile organic compounds (VOCs). These compounds have been shown to play a key role in the transport of reactive nitrogen and, consequently, in the ozone budget; they are also known to be important components of the total organic aerosol. However, very little is known about their reactivity in both the gas and condensed phases. Following a previous study that we published on the gas-phase reactivity of α-nitrooxy ketones, the photolysis and reaction with OH radicals of 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone (which are a β-nitrooxy ketone and γ-nitrooxy ketone, respectively) were investigated for the first time in simulation chambers. The photolysis frequencies were directly measured in the CESAM chamber, which is equipped with a very realistic irradiation system. The jnitrate/jNO2 ratios were found to be (5.9±0.9)×10-3 for 4-nitrooxy-2-butanone and (3.2±0.9)×10-3 for 5-nitrooxy-2-pentanone under our experimental conditions. From these results, it was estimated that ambient photolysis frequencies calculated for typical tropospheric irradiation conditions corresponding to the 1 July at noon at 40∘ N (overhead ozone column of 300 and albedo of 0.1) are (6.1±0.9)×10-5 s−1 and (3.3±0.9)×10-5 s−1 for 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone, respectively. These results demonstrate that photolysis is a very efficient sink for these compounds with atmospheric lifetimes of few hours. They also suggest that, similarly to α-nitrooxy ketones, β-nitrooxy ketones have enhanced UV absorption cross sections and quantum yields equal to or close to unity and that γ-nitrooxy ketones have a lower enhancement of cross sections, which can easily be explained by the larger distance between the two chromophore groups. Thanks to a product study, the branching ratio between the two possible photodissociation pathways is also proposed. Rate constants for the reaction with OH radicals were found to be (2.9±1.0)×10-12 and (3.3±0.9)×10-12 cm3 molecule−1 s−1, respectively. These experimental data are in good agreement with rate constants estimated by the structure–activity relationship (SAR) of Kwok and Atkinson (1995) when using the parametrization proposed by Suarez-Bertoa et al. (2012) for carbonyl nitrates. Comparison with photolysis rates suggests that the OH-initiated oxidation of carbonyl nitrates is a less efficient sink than photodissociation but is not negligible in polluted areas.

scholarly journals A Novel Approach to the Fabrication of CdSe Quantum Dots in Aqueous Solution: Procedures for Controlling Size, Fluorescence Intensity, and Stability over Time

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
M. J. Almendral-Parra ◽  
A. Alonso-Mateos ◽  
J. F. Boyero-Benito ◽  
S. Sánchez-Paradinas ◽  
E. Rodríguez-Fernández
Keyword(s):  
Aqueous Solution ◽  
Quantum Dots ◽  
Mercaptoacetic Acid ◽  
Quantum Yields ◽  
Cdse Quantum Dots ◽  
Cdse Qds ◽  
Experimental Conditions ◽  
Synthesis Of Nanoparticles ◽  
Novel Approach ◽  
High Fluorescence

This paper report a straightforward approach for the synthesis of CdSe quantum dots (CdSe QDs) in aqueous solution. This method, performed in homogeneous phase, affords optimal sizes and high quantum yields for each application desired. It is ana la carteprocedure for the synthesis of nanoparticles aimed at their later application. By controlling the experimental conditions, CdSe QDs of sizes ranging between 2 and 6 nm can be obtained. The best results were achieved in an ice-bath thermostated at 4°C, using mercaptoacetic acid as dispersant. Under these conditions, a slow growth of quantum nanocrystals was generated and this was controlled kinetically by the hydrolysis ofSeSO32-to generateSe2-  in situ, one of the forming species of the nanocrystal. The organic dispersant mercaptoacetate covalently binds to the Cd2+ion, modifying the diffusion rate of the cation, and plays a key role in the stabilization of CdSe QDs. In optimum conditions, when kept in their own solution CdSe QDs remain dispersed over 4 months. The NPs obtained under optimal conditions show high fluorescence, which is a great advantage as regards their applications. The quantum efficiency is also high, owing to the formation under certain conditions of ananoshellof Cd(OH)2, values of 60% being reached.

scholarly journals Adsorption kinetics for the removal of copper(II) from aqueous solution by adsorbent PSTM-3T

2014 ◽  
Vol 12 ◽  
pp. 1-6
Author(s):  
G Burmaa ◽  
O Nasantogtokh ◽  
N Narantsogt ◽  
A Perlee-Oidov
Keyword(s):  
Aqueous Solution ◽  
Thermodynamic Parameters ◽  
Adsorption Kinetics ◽  
Rate Constants ◽  
Condensation Reaction ◽  
Sorption Kinetics ◽  
Order Reaction ◽  
Experimental Conditions ◽  
First Order ◽  
Poly Condensation

The batch removal of copper (II) from aqueous solution under different experimental conditions using silicon-organic sorbent poly[N,N’-bis(3-silseskquioxanilpropyl)thiocarbamide] (PSTM-3T) was investigated in this study. This sorbent was produced from the hydrolytic poly-condensation reaction. The removal was favoured at pH = 5 for PSTM-3T. The effects of concentration and temperature have been reported. PSTM-3T was found to efficiently remove Cu(II) from solution. The batch sorption kinetics have been tested for a first-order reaction. The rate constants of adsorption have been calculated. The thermodynamic parameters (ΔG0, Kc) obtained to indicate the endothermic nature of Cu(II) adsorption on PSTM-3T.DOI: http://dx.doi.org/10.5564/mjc.v12i0.162 Mongolian Journal of Chemistry Vol.12 2011: 1-6

The Digital Divide and K-12 Student Computer Use

10.28945/2926 ◽  
2005 ◽  
Author(s):  
James N. Morgan ◽  
Craig A. VanLengen
Keyword(s):  
Digital Divide ◽  
Computer Use ◽  
Census Data ◽  
Internet Access ◽  
Demographic Characteristics ◽  
The Internet ◽  
Substantial Impact ◽  
Limited Basis ◽  
K 12 ◽  
The Impact

The divide between those who have computer and Internet access and those who do not appears to be narrowing, however overall statistics may be misleading. Measures of computer availability in schools often include cases where computers are only available for administration or are available only on a very limited basis (Gootman, 2004). Access to a computer and the Internet outside of school helps to reinforce student learning and emphasize the importance of using technology. Recent U.S. statistics indicate that ethnic background and other demographic characteristics still have substantial impact on the availability and use of computers by students outside of the classroom. This paper examines recent census data to determine the impact of the household on student computer use outside of the classroom. Encouragingly, the findings of this study suggest that use of a computer at school substantially increases the chance that a student will use a computer outside of class. Additionally, this study suggests that computer use outside of the classroom is positively and significantly impacted by being in a household with adults who either use a computer at work or work in an industry where computers are extensively used.

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