17 research outputs found
DFT Study of Gold Surfaces–Ligand Interactions: Alkanethiols versus Halides
The
variation in the surface reactivity of gold nanorods (GNR) is explored
by density functional theory (DFT) simulations of the different facets.
The physical and chemical properties of Au310 and Au520 surfaces,
recently detected on the GNR tips, were compared with conventional
Au100 and Au111 surfaces. Due to the tight gold packing, the sloped
Au111 surfaces have the highest binding energy with rigid ligands,
whereas the Au310 have the lowest. The observed correspondence between
the ligand binding energies and the surface moduli of elasticity demonstrates
that the overall monolayer structure, stability and reactivity is
a balance between the ligand induced surface strain and the interligand
strain. The GNR tips are able to distribute the ligand induced strain
with minimal surface reorganization due to a high modulus of elasticity
combined with extra free volume within the ligand shell. A simulation
of the halide-surface interaction, consisting of multiple bond breaking
and forming points, showed that the halides will induce the same surface
strain but halides with reduced ligand-to-ligand interaction can move
freely around the gold surface. More importantly, the charge transfer
between halide to gold depends mainly on this mobility and is a factor
in the role of halides as shape directing agents in gold nanoparticle
synthesis. These simulations reveal some of the key factors that must
be considered to effectively functionalize GNRs for specific applications
Mechanistic Aspects of deNO<sub><i>x</i></sub> Processing over TiO<sub>2</sub> Supported Co–Mn Oxide Catalysts: Structure–Activity Relationships and In Situ DRIFTs Analysis
Anatase
TiO<sub>2</sub>-supported manganese and cobalt oxide catalysts
with different Co/Mn molar ratios were synthesized by a conventional
impregnation method and used for selective catalytic reduction (SCR)
of NO<sub><i>x</i></sub> with NH<sub>3</sub>. The catalysts
were characterized by N<sub>2</sub> adsorption/desorption, X-ray diffraction,
X-ray photoelectron spectroscopy, and temperature-programmed desorption
with NH<sub>3</sub> and NO<sub><i>x</i></sub>. Characterization
of the catalyst confirmed that by using Co<sub>3</sub>O<sub>4</sub> over Mn/TiO<sub>2</sub>, we enhanced NO oxidation ability. From
in situ diffuse reflectance infrared transform spectroscopy (DRIFTs)
analysis of desorption and the transient reaction, we concluded that
the addition of Co could remarkably lower the activation energy of
NO<sub><i>x</i></sub> chemisorption on the catalyst surface.
In addition, low-temperature SCR activity mainly results from a “fast
SCR” reaction. We observed four NO<sub><i>x</i></sub> species (bidentate nitrates, gaseous NO<sub>2</sub>, linear nitrites,
and monodentate nitrites) on the surface of Mn/TiO<sub>2</sub> and
Co–Mn/TiO<sub>2</sub> catalysts that all participated in the
SCR reaction in the high temperature range. Doping of cobalt greatly
improved the reactivity of gaseous NO<sub>2</sub>, linear nitrites,
and monodentate nitrites, which makes Co–Mn/TiO<sub>2</sub> a highly effective NH<sub>3</sub>–SCR catalyst
In Situ DRIFTs Investigation of the Low-Temperature Reaction Mechanism over Mn-Doped Co<sub>3</sub>O<sub>4</sub> for the Selective Catalytic Reduction of NO<sub><i>x</i></sub> with NH<sub>3</sub>
The Co<sub>3</sub>O<sub>4</sub> and
Mn-doped Co<sub>3</sub>O<sub>4</sub> nanoparticle were synthesized
by a co-precipitation method
and used as selective catalytic reduction of NO with NH<sub>3</sub> (NH<sub>3</sub>-SCR) catalysts. After the doping of manganese oxides,
the NH<sub>3</sub>-SCR activity of Mn<sub>0.05</sub>Co<sub>0.95</sub>O<sub><i>x</i></sub> catalyst is greatly enhanced. The
NO oxidation ability of two catalysts is compared, and the X-ray diffraction
results demonstrate that Mn has been successfully doped into the lattice
of Co<sub>3</sub>O<sub>4</sub>. The X-ray photoelectron spectroscopy
and temperature-programmed reduction with H<sub>2</sub> results confirmed
that there is a strong interaction between Mn and Co in the Mn<sub>0.05</sub>Co<sub>0.95</sub>O<sub><i>x</i></sub> catalyst.
Their adsorption and desorption properties were characterized by temperature-programmed
desorption with NH<sub>3</sub> or NO + O<sub>2</sub> and in situ diffuse
reflectance infrared Fourier transform spectroscopy (in situ DRIFTs).
These results indicated that the doping of manganese could provide
more acid sites on the catalysts, and bidentate nitrates species originated
from NO<sub><i>x</i></sub> adsorption are obviously activated
on the Mn<sub>0.05</sub>Co<sub>0.95</sub>O<sub><i>x</i></sub> catalyst surface. Moreover, the transient reaction studied by in
situ DRIFTs found that the “fast SCR” reaction participated
by gaseous NO<sub>2</sub> and the standard SCR reaction participated
by bidentate nitrates contribute to the low-temperature SCR activity
In Situ DRIFTs Investigation of Promotional Effects of Tungsten on MnO<sub><i>x</i></sub>‑CeO<sub>2</sub>/meso-TiO<sub>2</sub> Catalysts for NO<sub><i>x</i></sub> Reduction
In
this work, mesoporous TiO<sub>2</sub> spheres supported MnCeW
mixed oxide catalysts (MnCeW/m-TiO<sub>2</sub>) for selective catalytic
reduction of NO<sub><i>x</i></sub> with NH<sub>3</sub> were
prepared by a wet impregnation method. It is interesting that the
MnCeW/m-TiO<sub>2</sub> catalysts exhibited excellent SCR activity
and N<sub>2</sub> selectivity in a wide temperature range, even under
the high gas hourly space velocity. From in situ diffuse reflectance
infrared transform spectroscopy (in situ DRIFTs) studies of desorption,
it could be concluded that the addition of tungsten brought about
more Brønsted acid sites and reduced the energy barrier of NO<sub><i>x</i></sub> species adsorbed on the surface. At high
temperature range, there were still some Brønsted acid sites
and NO<sub><i>x</i></sub> species including bidentate nitrate
and nitro compounds in MnCeW/m-TiO<sub>2</sub>, therefore more intermediates
could take part in the SCR reactions as well as better catalytic performance.
Besides, the in situ DRIFTs of transient reactions indicated that
the formed NH<sub>3</sub> species and NO<sub><i>x</i></sub> species of MnCeW/m-TiO<sub>2</sub> were more reactive due to the
promotional effects of tungsten. A series of traditional characterizations
also revealed the promotional effects of tungsten for surface active
elements, catalytic redox properties, and acid sites of NH<sub>3</sub> adsorption. In a word, all the results confirmed that the introduction
of W could enhance active NH<sub>3</sub> and NO<sub><i>x</i></sub> species as well as surface active elements, thus contributing
to the catalytic performance. The present investigations may open
a path for design and application of catalysts with outstanding catalytic
activity and selectivity
Nanospray Desorption Electrospray Ionization (Nano-DESI) Mass Spectrometry Imaging with High Ion Mobility Resolution
Untargeted separation
of isomeric and isobaric species in mass
spectrometry imaging (MSI) is challenging. The combination of ion
mobility spectrometry (IMS) with MSI has emerged as an effective strategy
for differentiating isomeric and isobaric species, which substantially
enhances the molecular coverage and specificity of MSI experiments.
In this study, we have implemented nanospray desorption electrospray
ionization (nano-DESI) MSI on a trapped ion mobility spectrometry
(TIMS) mass spectrometer. A new nano-DESI source was constructed,
and a specially designed inlet extension was fabricated to accommodate
the new source. The nano-DESI-TIMS-MSI platform was evaluated by imaging
mouse brain tissue sections. We achieved high ion mobility resolution
by utilizing three narrow mobility scan windows that covered the majority
of the lipid molecules. Notably, the mobility resolution reaching
up to 300 in this study is much higher than the resolution obtained
in our previous study using drift tube IMS. High-resolution TIMS successfully
separated lipid isomers and isobars, revealing their distinct localizations
in tissue samples. Our results further demonstrate the power of high-mobility-resolution
IMS for unraveling the complexity of biomolecular mixtures analyzed
in MSI experiments
Teflon: A Decisive Additive in Directly Fabricating Hierarchical Porous Carbon with Network Structure from Natural Leaf
Hierarchically porous
carbons are of increasing importance due
to their special physicochemical properties. The state-of-the-art
approaches for synthesizing hierarchical porous carbon with network
structure normally suffer from specific chemistries, rigid reaction
conditions, high cost, and multiple tedious steps that limit their
large scale production. Herein, we present an interesting insight
into the important role of Teflon additive in fabrication of hierarchical
porous carbon derived from biomass and, thus, use natural Indicalamus
leaves for the first time to successfully synthesize hierarchical
porous carbon with a three-dimensional morphology of interconnected
nanoparticle units by using a facile and post-treatment-free carbonization
technique. It is surprisingly found that the addition of Teflon not
only reduces the synthesis procedure by combining post-removal of
silica and carbonization in a single step but also plays a decisive
role in generating the hierarchical carbonaceous network structure
with a specific surface area as high as 1609 m<sup>2</sup>/g without
any extra activation procedures. Benefiting from the combination of
well-developed porosity and valuable hierarchical porous morphology,
this type of hierarchical porous carbon has demonstrated attractive
liquid-phase adsorption properties toward organic molecules
Enhancing Doxorubicin Delivery toward Tumor by Hydroxyethyl Starch‑<i>g</i>‑Polylactide Partner Nanocarriers
Doxorubicin (DOX),
a kind of wide-spectrum chemotherapeutic drug,
can cause severe side effects in clinical use. To enhance its antitumor
efficacy while reducing the side effects, two kinds of nanoparticles
with desirable compositions and properties were assembled using optimally
synthesized hydroxyethyl starch-grafted-polylactide (HES-<i>g</i>-PLA) copolymers and utilized as partner nanocarriers. The large
empty HES-<i>g</i>-PLA nanoparticles (mean size, <i>ca.</i> 700 nm), at an optimized dose of 400 mg/kg, were used
to block up the reticuloendothelial system in tumor-bearing mice 1.5
h in advance, and the small DOX-loaded HES-<i>g</i>-PLA
nanoparticles (mean size, <i>ca.</i> 130 nm) were subsequently
applied to the mice. When these partner nanocarriers were administered
in this sequential mode, the released DOX had a significantly prolonged
plasma half-life time and much slower clearance rate as well as a
largely enhanced intratumoral accumulation as compared to free DOX. <i>In vivo</i> antitumor studies demonstrated that the DOX-loaded
HES-<i>g</i>-PLA nanoparticles working together with their
partner exhibited remarkably enhanced antitumor efficacy in comparison
to free DOX. In addition, these HES-<i>g</i>-PLA partner
nanocarriers showed negligible damage to the normal organs of the
treated mice. Considering safe and efficient antitumor performance
of DOX-loaded HES-<i>g</i>-PLA nanoparticles, the newly
developed partner nanocarriers in combination with their administration
mode have promising potential in clinical cancer chemotherapy
Facile Synthesis of Highly Porous Carbon from Rice Husk
Highly porous carbon
materials have attracted great interest for
a wide range of important applications. Many examples for their synthesis
exist, but these synthetic processes can be quite complex and also
very time-consuming. There is still a major challenge to develop a
facile yet versatile conceptual approach to produce them. Here, we
present an efficient, activation-free, post-treatment-free strategy
for the synthesis of highly porous carbon by a simple carbonization
of a mixture of rice husk and polytetrafluoroethylene (PTFE) powder.
PTFE employed here can <i>in situ</i> generate HF to etch
out natural silica during the carbonization treatment of rice husk.
This strategy not only reduces the synthesis procedure by combining
carbonization and post-removal of silica into a single step but also
eliminates completely the usage of hazardous HF or corrosive NaOH
or KOH. The as-synthesized carbon materials exhibit a BET surface
area as high as 2051 m<sup>2</sup>/g without any activation treatment,
which is about 20 times enhanced in porosity compared to that of the
traditional carbon material from rice husk. With the combination of
the high porosity and the valuable hierarchical porous structure,
the as-prepared porous carbon materials serve well as electrodes for
supercapacitive energy storage, including a large capacitance of 317
F/g, good rate performance, and high capacitances per surface area.
These findings could provide a new avenue for the facile production
of high-performance porous carbon materials with promising applications
in various areas
Nanocolloidosomes with Selective Drug Release for Active Tumor-Targeted Imaging-Guided Photothermal/Chemo Combination Therapy
Selective drug release
is highly desirable for photothermal/chemo combination therapy when
two or even more theranostic agents are encapsulated together within
the same nanocarrier. A conventional nanocarrier can hardly achieve
this goal. Herein, doxorubicin and indocyanine green (DOX/ICG)-loaded
nanocolloidosomes (NCs), with selective drug release, were fabricated
as a novel multifunctional theranostic nanoplatform for photothermal/chemo
combination therapy. Templating from galactose-functionalized hydroxyethyl
starch-polycaprolactone (Gal-HES-PCL) nanoparticles-stabilized Pickering
emulsions, the resultant DOX/ICG@Gal-HES-PCL NCs had a diameter of
around 140 nm and showed an outstanding tumor-targeting ability, preferable
tumor penetration capability, and promotion of photothermal effect.
Moreover, these NCs can be used for NIR fluorescence imaging and thus
render real-time imaging of solid tumors with high contrast. Collectively,
such NCs achieved the best in vivo antitumor efficacy combined with
laser irradiation compared with DOX/ICG@HES-PCL NCs and DOX/ICG mixture.
These NCs are valuable for active tumor-targeted imaging-guided combination
therapy against liver cancer and potentially other diseases
Redox-Sensitive Hydroxyethyl Starch–Doxorubicin Conjugate for Tumor Targeted Drug Delivery
Doxorubicin (DOX)
is one of the most potent anticancer agents in cancer chemotherapy,
but the clinical use of DOX is restricted by its severe side effects
caused by nonspecific delivery. To alleviate the side effects and
improve the antitumor efficacy of DOX, a novel redox-sensitive hydroxyethyl
starch–doxorubicin conjugate, HES-SS-DOX, with diameter of
19.9 ± 0.4 nm was successfully prepared for tumor targeted drug
delivery and GSH-mediated intracellular drug release. HES-SS-DOX was
relatively stable under extracellular GSH level (∼2 μM)
but released DOX quickly under intracellular GSH level (2–10
mM). In vitro cell study confirmed the GSH-mediated cytotoxicity of
HES-SS-DOX. HES-SS-DOX exhibited prolonged plasma half-life time and
enhanced tumor accumulation in comparison to free DOX. As a consequence,
HES-SS-DOX exhibited better antitumor efficacy and reduced toxicity
as compared to free DOX in the in vivo antitumor activity study. The
redox-sensitive HES-SS-DOX was proved to be a promising prodrug of
DOX, with clinical potentials, to achieve tumor targeted drug delivery
and timely intracellular drug release for effective and safe cancer
chemotherapy