19 research outputs found
Emerging advanced oxidation processes for the elimination of micro-pollutants
Emerging advanced oxidation processes for the elimination of micro-pollutant
Hydrothermal Carbon-Mediated Fenton-Like Reaction Mechanism in the Degradation of Alachlor: Direct Electron Transfer from Hydrothermal Carbon to Fe(III)
As
Fenton systems suffer from the undesirable FeÂ(III)/FeÂ(II) cycle, great
efforts were made to realize the effective reduction of FeÂ(III) to
FeÂ(II). The effects of hydrothermal carbon (HTC) on the FeÂ(III)/H<sub>2</sub>O<sub>2</sub> Fenton-like reaction and the subsequent degradation
of alachlor in water was systematically investigated, and the results
indicated that HTC could enhance alachlor degradation in FeÂ(III)/H<sub>2</sub>O<sub>2</sub> by promoting the FeÂ(III)/FeÂ(II) cycle via electron
transfer from HTC to FeÂ(III) ions. The apparent alachlor degradation
rate constant in the HTC-G/FeÂ(III)/H<sub>2</sub>O<sub>2</sub> system
(7.02 × 10<sup>–2</sup> min<sup>–1</sup>) was about
3 times higher than that in the FeÂ(III)/H<sub>2</sub>O<sub>2</sub> system (2.25 × 10<sup>–2</sup> min<sup>–1</sup>). The electron spin resonance spectra analysis revealed that HTC
consists of abundant carbon-centered persistent free radicals to act
as the electron donor. Meanwhile, the hydroxyl groups on the surface
of HTC also played an important role in the enhanced alachlor degradation
because the decrease in the surface hydroxyl groups on HTC significantly
decreased the degradation of alachlor. On the basis of these results,
an FeÂ(III) complex with surface hydroxyl groups on HTC was proposed
to favor the electron transfer from the hydroxyl groups to FeÂ(III),
and then, the simultaneously produced FeÂ(II) could accelerate the
catalytic decomposition of H<sub>2</sub>O<sub>2</sub> to facilitate
alachlor degradation. These findings shed new light on the possible
roles of carbon materials in a natural aquatic environment and provide
a new pathway for environmental pollutant control and remediation
of organic contaminants by HTC
Adsorption Mechanisms of Typical Carbonyl-Containing Volatile Organic Compounds on Anatase TiO<sub>2</sub> (001) Surface: A DFT Investigation
The
carbonyl-containing compounds (CCs) are typical volatile organic
compounds (VOCs) and ubiquitously present in the environment. Therefore,
the adsorption structures and properties of typical CCs on the anatase
TiO<sub>2</sub> (001) surface were investigated systematically with
density functional theory (DFT) to understand their further catalytic
degradation mechanisms. The adsorption mechanisms show that three
selected typical CCs, acetaldehyde, acetone, and methyl acetate, can
easily be trapped on the anatase TiO<sub>2</sub> (001) surface via
the interaction between the carbonyl group with Ti<sub>5c</sub> sites
of catalyst surface. Especially for acetaldehyde with the bare carbonyl
group and the strongest adsorption energy, it is the most stable on
the surface, because the bare carbonyl group can interact with not
only the Ti<sub>5c</sub> atom, but also the O<sub>2c</sub> atom of
the surface. The substituent effect of different CCs has less impact
on its adsorption models in this studied system and the bare carbonyl
group is the key functional group within studied CCs. The Ti<sub>5c</sub> atoms of anatase TiO<sub>2</sub> (001) surface are active sites
to trap CCs. Our theoretical results are expected to provide insight
into the adsorption mechanisms of these carbonyl-containing VOCs on
TiO<sub>2</sub> catalyst and also to help understand the further catalytic
degradation mechanisms of air pollutants at the molecular level
Spontaneous Iodide Activation at the Air–Water Interface of Aqueous Droplets
We present experimental evidence that atomic and molecular
iodine,
I and I2, are produced spontaneously in the dark at the
air–water interface of iodide-containing droplets without any
added catalysts, oxidants, or irradiation. Specifically, we observe
I3– formation within droplets, and I2 emission into the gas phase from NaI-containing droplets
over a range of droplet sizes. The formation of both products is enhanced
in the presence of electron scavengers, either in the gas phase or
in solution, and it clearly follows a Langmuir–Hinshelwood
mechanism, suggesting an interfacial process. These observations are
consistent with iodide oxidation at the interface, possibly initiated
by the strong intrinsic electric field present there, followed by
well-known solution-phase reactions of the iodine atom. This interfacial
chemistry could be important in many contexts, including atmospheric
aerosols
Can Silica Particles Reduce Air Pollution by Facilitating the Reactions of Aliphatic Aldehyde and NO<sub>2</sub>?
This
study investigated the heterogeneous atmospheric reactions
of acetaldehyde, propanal, and butanal with NO<sub>2</sub> onto silica
(SiO<sub>2</sub>) clusters using a theoretical approach. By analyzing
spectral features and adsorption parameters, the formation of hydrogen
bonds and negative adsorption energies provide evidence that an efficient
spontaneous uptake of aliphatic aldehydes onto SiO<sub>2</sub> could
occur. The atmospheric reaction mechanisms show that when aldehydes
and NO<sub>2</sub> react on the surface model, the H atom abstraction
reaction from the aldehydic molecule by NO<sub>2</sub> is an exclusive
channel, forming nitrous acid and acyl radicals. This study included
kinetics exploring the reaction of aldehydes with NO<sub>2</sub> using
a canonical variational transition state theory. The reaction rate
constants are increased in the presence of SiO<sub>2</sub> between
the temperatures 217 and 298 K. This may explain how aldehydes can
temporarily stay on mineral particles without chemical reactions.
The results suggest that silica can depress the rate at which the
studied aldehydes react with NO<sub>2</sub> and possibly reduce air
pollution generated by these atmospheric reactions
Kinetics and Mechanism of <sup>•</sup>OH Mediated Degradation of Dimethyl Phthalate in Aqueous Solution: Experimental and Theoretical Studies
The hydroxyl radical (<sup>•</sup>OH) is one of the main
oxidative species in aqueous phase advanced oxidation processes, and
its initial reactions with organic pollutants are important to understand
the transformation and fate of organics in water environments. Insights
into the kinetics and mechanism of <sup>•</sup>OH mediated
degradation of the model environmental endocrine disruptor, dimethyl
phthalate (DMP), have been obtained using radiolysis experiments and
computational methods. The bimolecular rate constant for the <sup>•</sup>OH reaction with DMP was determined to be (3.2 ±
0.1) × 10<sup>9</sup> M<sup>–1</sup>s<sup>–1</sup>. The possible reaction mechanisms of radical adduct formation (RAF),
hydrogen atom transfer (HAT), and single electron transfer (SET) were
considered. By comparing the experimental absorption spectra with
the computational results, it was concluded that the RAF and HAT were
the dominant reaction pathways, and OH-adducts (<sup>•</sup>DMPOH<sub>1</sub>, <sup>•</sup>DMPOH<sub>2</sub>) and methyl
type radicals <sup>•</sup>DMPÂ(-H)Âα were identified as
dominated intermediates. Computational results confirmed the identification
of transient species with maximum absorption around 260 nm as <sup>•</sup>DMPOH<sub>1</sub> and <sup>•</sup>DMPÂ(-H)Âα,
and these radical intermediates then converted to monohydroxylated
dimethyl phthalates and monomethyl phthalates. Experimental and computational
analyses which elucidated the mechanism of <sup>•</sup>OH-mediated
degradation of DMP are discussed in detail
Relationship between the mutagenic ratio on TA98 without S9 activation and IR by SOS/<i>umu</i> test without S9 activation.
<p>Relationship between the mutagenic ratio on TA98 without S9 activation and IR by SOS/<i>umu</i> test without S9 activation.</p
Genotoxic activity of organic extracts in water samples detected by SOS/<i>umu</i> test from six sampling locations in Guangzhou drinking water source.
<p>Lower-case letters indicated pair-wise comparison in the dry season in different sampling regions at the same water level and upper-case letters indicated pair-wise comparison in the wet season in different sampling regions at the same water level. *indicated the significant difference from the wet season.</p
Synthesis of Carbon Nanotube–Anatase TiO<sub>2</sub> Sub-micrometer-sized Sphere Composite Photocatalyst for Synergistic Degradation of Gaseous Styrene
The carbon nanotube (CNT)–sub-micrometer-sized
anatase TiO<sub>2</sub> sphere composite photocatalysts were synthesized
by a facile
one-step hydrothermal method using titanium tetrafluoride as titanium
source and CNTs as structure regulator. Various technologies including
X-ray diffraction, UV–visible absorption spectra, N<sub>2</sub> adsorption–desorption, scanning electron microscopy, and
transmission electron microscopy were employed to characterize the
structure properties of the prepared composite photocatalysts. The
results indicated that the composite photocatalysts consisted of CNTs
wrapping around the sub-micrometer-sized anatase TiO<sub>2</sub> spheres
with controllable crystal facets and that the aggregated particles
with average diameter ranged from 200 to 600 nm. The fabricated composite
photocatalysts were used to degrade gaseous styrene in this work.
As expected, a synergistic effect that remarkably enhancing the photocatalytic
degradation efficiency of gaseous styrene by the prepared composite
photocatalysts was observed in comparison with that the degradation
efficiency using pure anatase TiO<sub>2</sub> and the adsorption of
CNTs. Similar results were also confirmed in the decolorization of
liquid methyl orange. Further investigation demonstrated that the
synergistic effect in the photocatalytic activity was related to the
structure of the sub-micrometer-sized anatase TiO<sub>2</sub> spheres
and the significant roles of CNTs in the composite photocatalysts.
By controlling the content of CNTs, the content of TiO<sub>2</sub> or the temperature during the hydrothermal synthesis process, anatase
TiO<sub>2</sub> spheres with controllable crystallite size and dominant
crystal facets such as {001}, {101}, or polycrystalline could be obtained,
which was beneficial for the increase in the synergistic effect and
further enhancement of the photocatalytic efficiencies
Evaluation of Genotoxic and Mutagenic Activity of Organic Extracts from Drinking Water Sources - Fig 2
<p><b>Mutagenicity of TA98 (a) and TA100 (b) detected by Ames test without S9 mix in organic extracts from source water at dose 0.25L (c), 0.5L (d), 1.0L (e) and 2.0L (f) collected during the dry season at six sampling locations in Guangzhou drinking water source</b>. Lower-case letters and upper-case letters indicated pairwise comparison in the TA98 and TA100 in the different sampling regions at the same water level, respectively. *indicated the significant difference compared with the strain TA100 at the same water level in the same sampling regions.</p