606 research outputs found
Simple Synthetic Method Toward Solid Supported C<sub>60</sub> Visible Light-Activated Photocatalysts
Solid
supported fullerene materials are prepared in aims of creating
a fullerene-based photocatalyst that is capable of producing <sup>1</sup>O<sub>2</sub> in the aqueous phase. Past studies of using
fullerene as a photocatalyst in water have exclusively focused on
using water soluble fullerene derivatives and employed sophisticated
chemistry to create immobilized fullerene materials. The method presented
herein is much less synthetically complex and utilizes pristine fullerene,
providing a drastically simpler route to supported fullerene materials
and furthering their potential for use in environmental applications.
Covalent immobilization was achieved through the nucleophilic addition
of a terminal amine (located on a solid support) across a [6,6] fullerene
double bond, resulting in attachment directly to C<sub>60</sub>’s
cage. Immobilization allowed supported fullerene moieties to produce <sup>1</sup>O<sub>2</sub> in water under various illumination conditions
and inactivate MS2 bacteriophages. In a water with natural organic
matter, supported fullerene materials produced <sup>1</sup>O<sub>2</sub> under visible light irradiation without exhibiting significant loss
of photocatalytic activity after successive cycling
Sorbic Acid as a Triplet Probe: Triplet Energy and Reactivity with Triplet-State Dissolved Organic Matter via 1O2 Phosphorescence
Sorbic acid (2,4-hexadienoic acid; HDA) is commonly used as a probe and quencher for triplet-excited chromophoric dissolved organic matter (3CDOM*), an important transient species in natural waters, yet much remains unknown about its reactivity with 3CDOM* and its triplet energy. To better understand the quenching behavior of HDA, we measured HDA quenching rate constants for various humic substance isolates and whole waters with singlet oxygen (1O2) phosphorescence and determined the triplet energy of HDA. Low-temperature phosphorescence measurements determined the triplet energy of HDA to be 217 kJ mol–1, whereas a complementary method based on triplet quenching kinetics found a triplet energy of 184 ± 7 kJ mol–1. Time-resolved 1O2 phosphorescence measurements yielded different HDA quenching rate constants depending on the fitting method. Using an approach that considered the reactivity of the entire triplet pool produced values of (∼1–10) × 108 M–1 s–1, while an approach that considered only the reactivity of the high-energy triplets output higher rate constants ((∼7–30) × 108 M–1 s–1). In addition, the model based on high-energy triplet reactivity found that ∼30–60% of 3CDOM* is not quenched by HDA. Findings from this study provide a more comprehensive view on the use of HDA as a probe for 3CDOM*.ISSN:0013-936XISSN:1520-585
Sorbic Acid as a Triplet Probe: Reactivity of Oxidizing Triplets in Dissolved Organic Matter by Direct Observation of Aromatic Amine Oxidation
Sorbic acid (2,4-hexadienoic acid; HDA) isomerization is frequently used to probe triplet-state dissolved organic matter (3CDOM*) reactivity, but there remain open questions about the reaction kinetics of 3CDOM* with HDA due to the difficulties of directly measuring 3CDOM* quenching rate constants. Using our recently developed approach based on observing the radical cation of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) formed through oxidation of TMPD by 3CDOM*, we studied 3CDOM* quenching kinetics with HDA monitored via transient absorption spectroscopy. A competition kinetics-based approach utilizing formation yields of TMPD•+ was developed, validated with model sensitizers, and used to determine bimolecular rate constants between 3CDOM* oxidants and HDA for diverse DOM isolates and natural waters samples, yielding values in the range of (2.4–7.7) × 108 M–1 s–1. The unquenchable fraction of TMPD-oxidizing triplets showed that, on average, 41% of 3CDOM* oxidants cannot be quenched by HDA. Conversely, cycloheptatriene quenched nearly all TMPD•+-forming triplets in CDOM, suggesting that most 3CDOM* oxidants possess energies greater than 150 kJ mol–1. Comparing results with our companion study, we found slight, but noticeable differences in the 3CDOM* quenching rate constants by HDA and unquenchable triplet fractions determined by oxidation of TMPD and energy transfer to O2 (1O2 formation) methods.ISSN:0013-936XISSN:1520-585
Differential Photoactivity of Aqueous [C<sub>60</sub>] and [C<sub>70</sub>] Fullerene Aggregates
Many
past studies have focused on the aqueous photochemical properties
of colloidal suspensions of C<sub>60</sub> and various [C<sub>60</sub>] fullerene derivatives, yet few have investigated the photochemistry
of other larger cage fullerene species (e.g., C<sub>70</sub>, C<sub>74</sub>, C<sub>84</sub>, etc.) in water. This is a critical knowledge
gap because these larger fullerenes may exhibit different properties
compared to C<sub>60</sub>, including increased visible light absorption,
altered energy level structures, and variable cage geometries, which
may greatly affect aggregate properties and resulting aqueous photoactivity.
Herein, we take the first steps toward a detailed investigation of
the aqueous photochemistry of larger cage fullerene species, by focusing
on [C<sub>70</sub>] fullerene. We find that aqueous suspensions of
C<sub>60</sub> and C<sub>70</sub>, nC<sub>60</sub> and nC<sub>70</sub>, respectively, exhibit many similar physicochemical properties,
yet nC<sub>70</sub> appears to be significantly more photoactive than
nC<sub>60</sub>. Studies are conducted to elucidate the mechanism
behind nC<sub>70</sub>’s superior <sup>1</sup>O<sub>2</sub> generation, including the measurement of <sup>1</sup>O<sub>2</sub> production as a function of incident excitation wavelength, analysis
of X-ray diffraction data to determine crystal packing arrangements,
and the excited state dynamics of aggregate fullerene species via
transient absorption spectroscopy
Dual-Functionality Fullerene and Silver Nanoparticle Antimicrobial Composites via Block Copolymer Templates
We present the facile
prepartion of C<sub>70</sub> and Ag nanoparticle (NP) loaded block
copolymer (BCP) thin films, with C<sub>70</sub> and Ag NPs working
in tandem to provide virucidal and bactericidal activities, respectively.
Polystyrene-<i>block</i>-poly-4-vinylpyridine (PS-P4VP)
was used as a template, allowing C<sub>70</sub> integration into PS
domains and in situ formation of Ag NPs in P4VP domains, while providing
control of the nanoscale spatial distribution of functionality as
a function of BCP molecular weight (MW). C<sub>70</sub> loaded PS-P4VP
films were found to generate significant amounts of <sup>1</sup>O<sub>2</sub> under visible light illumination with no apparent dependence
on BCP MW. An analogous C<sub>70</sub> loaded PS homopolymer film
produced notably less <sup>1</sup>O<sub>2</sub>, highlighting a possible
critical role of morphology on C<sub>70</sub> photoactivity. The antimicrobial
activity of Ag NP and C<sub>70</sub> loaded composites against the
model PR772 bacteriophage and Escherichia coli was assessed, finding synergistic inactivation afforded by the dual
functionality. BCPs were demonstrated as versatile platforms for the
preparation of multifunctional antimicrobial coatings toward combating
diverse microbial communities
Dissolved Organic Matter Singlet Oxygen Quantum Yields: Evaluation Using Time-Resolved Singlet Oxygen Phosphorescence
Singlet oxygen (1O2) generation quantum yields from chromophoric dissolved organic matter (CDOM) have been reported for many samples over the past 4 decades. Yet even for standardized isolates such as those from the International Humic Substance Society (IHSS), wide-ranging values exist in the literature. In this manuscript, time-resolved 1O2 phosphorescence was used to determine the 1O2 quantum yields (ΦΔ) of a variety of dissolved organic matter (DOM) isolates and natural waters. In general, the 1O2 quantum yield values in this study are in the middle, although below the median of the range of past reported values (e.g., for Suwannee River Natural Organic Matter IHSS isolate: 1.8% vs 0.23–2.89%). Notably, hydrophobic neutral fractions of DOM isolates were found to possess the highest 1O2 quantum yields, an interesting result given that these fractions are not retained in typical humic and fulvic acid isolation procedures that use XAD resins. The excitation wavelength dependence of 1O2 generation from CDOM was also examined, and an approximate linear decrease with longer excitation wavelength was observed. This work advances the understanding of CDOM photoprocesses, especially in relation to wavelength-dependent 1O2 production, which is valuable for assessing real-world environmental behavior.ISSN:0013-936XISSN:1520-585
Singlet Oxygen Phosphorescence as a Probe for Triplet-State Dissolved Organic Matter Reactivity
Triplet-state chromophoric dissolved organic matter (3CDOM*) plays an important role in aquatic photochemistry, yet much remains unknown about the reactivity of these intermediates. To better understand the kinetic behavior and reactivity of 3CDOM*, we have developed an indirect observation method based on monitoring time-resolved singlet oxygen (1O2) phosphorescence kinetics. The underpinning principle of our approach relies on the fact that O2 quenches almost all triplets with near diffusion limited rate constants, resulting in the formation of 1O2, which is kinetically linked to the precursors. A kinetic model relating 1O2 phosphorescence kinetics to triplet excited states produced from isolated humic substances and in whole natural-water samples (hereafter referred to as 3CDOM*) was developed and used to determine rate constants governing 3CDOM* natural lifetimes and quenching by oxygen and 2,4,6-trimethylphenol (TMP), a common triplet probe molecule. 3CDOM* was found to exhibit smaller O2 and TMP quenching rate constants, ∼9 × 108 and ∼8 × 108 M–1 s–1, respectively, compared with model sensitizers, such as aromatic ketones. Findings from this report shed light on the fundamental photochemical properties of CDOM in organic matter isolates and whole waters and will help refine photochemical models to more accurately predict pollutant fate in the environment.ISSN:0013-936XISSN:1520-585
Improving the Visible Light Photoactivity of Supported Fullerene Photocatalysts through the Use of [C<sub>70</sub>] Fullerene
We
herein present the first instance of employing [C<sub>70</sub>] fullerene
for photocatalytic <sup>1</sup>O<sub>2</sub> production
in water, through covalent immobilization onto a mesoporous silica
support via nucelophilic amine addition directly to fullerene’s
cage. This attachment approach prevents the aggregation of individual
fullerene molecules in water, thus allowing fullerene to retain its
photoactivity, yet is much less complex than other techniques commonly
pursued to create such supported-fullerene materials, which typically
rely on water-soluble fullerene derivatives and elaborate immobilization
methods. The solid-supported C<sub>70</sub> material exhibits significantly
improved aqueous visible-light photoactivity compared to previous
C<sub>60</sub>- and C<sub>60</sub>-derivative-based supported fullerene
materials. Further, this material rapidly inactivates MS2 bacteriophage
under sunlight illumination, oxidizes various organic contaminants,
and does not appear to be significantly fouled by natural organic
matter (NOM), highlighting the potential of these materials in real-world
applications. Collectively, the ease of preparation and significantly
enhanced visible-light photoactivity of these materials advance fullerene-based
technologies for water treatment
Functionalized Fullerenes in Water: A Closer Look
The excellent photophysical properties
of C<sub>60</sub> fullerenes
have spurred much research on their application to aqueous systems
for biological and environmental applications. Spontaneous aggregation
of C<sub>60</sub> in water and the consequent diminution of photoactivity
present a significant challenge to aqueous applications. The mechanisms
driving the reduction of photoactivity in fullerene aggregates and
the effects of functionalization on these processes, however, are
not well understood. Here, we take a closer look at the molecular
phenomena of functionalized fullerene interactions in water utilizing
simulation and experimental tools. Molecular dynamic simulations were
performed to investigate time-evolved molecular interactions in systems
containing fullerenes with water, oxygen, and/or neighboring fullerene
molecules, complimented by physical and chemical characterizations
of the fullerenes pre- and postaggregation. Aggregates with widely
different photoactivities exhibit similar fullerene–water interactions
as well as surface and aggregation characteristics. Photoactive fullerene
aggregates had weaker fullerene–fullerene and fullerene–O<sub>2</sub> interactions, suggesting the importance of molecular interactions
in the sensitization route
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