15 research outputs found
Comprehensive defect suppression in perovskite nanocrystals for high-efficiency light-emitting diodes
Electroluminescence efficiencies of metal halide perovskite nanocrystals (PNCs) are limited by a lack of material strategies that can both suppress the formation of defects and enhance the charge carrier confinement. Here we report a one-dopant alloying strategy that generates smaller, monodisperse colloidal particles (confining electrons and holes, and boosting radiative recombination) with fewer surface defects (reducing non-radiative recombination). Doping of guanidinium into formamidinium lead bromide PNCs yields limited bulk solubility while creating an entropy-stabilized phase in the PNCs and leading to smaller PNCs with more carrier confinement. The extra guanidinium segregates to the surface and stabilizes the undercoordinated sites. Furthermore, a surface-stabilizing 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene was applied as a bromide vacancy healing agent. The result is highly efficient PNC-based light-emitting diodes that have current efficiency of 108 cd Aâ1 (external quantum efficiency of 23.4%), which rises to 205 cd Aâ1 (external quantum efficiency of 45.5%) with a hemispherical len
A study on protozoan infections (Giardia, Entamoeba, Isoapora and Cryptosporidium) in stray dogs in Ilam province
Giardia, Entamoeba, Isospora and Cryptosporidium are important protozoan parastites that caused diarrhea in human and animals. In the present study, fecal samples were collected fresh, directly from the rectum of 112 stray dogs in Ilam province. Giardia and Entamoeba were concentrated by using the formalin ether sedimentation method followed by the trichrome and iodine staining technique andCryptosporidium oocysts were concentrated by using the formalin ether sedimentation method followed by the modified Ziehl-Neelsen staining technique. Of 112 stray dogs, protozoan infections were detected from feces of 46 dogs (41.07%) that Giardia infection was detected from feces of 21 dogs (18.75%), Isospora 17 (15.17%), Cryptosporidium 8 (7.14%) and synchronization infection to 2 protozoan in 9 dogs (8.03%) and to 3 protozoan in 3 (2.67%). In the present study not observed to Entamoeba. No statistically significant differences in prevalence of protozoan parasites occurred between female (34.21 %) and male (55.5 %) stray dogs (p>0/05). But statistically significant differences in prevalence occurred between 1âĽ0 and 0 âĽ1 stray dogs (p>0/05). So that stray dogs of Ilam province can cause infection of human water and food sources
Direct Methane to Methanol: The SelectivityâConversion Limit and Design Strategies
Currently,
methane is transformed into methanol through the two-step
syngas process, which requires high temperatures and centralized production.
While the slightly exothermic direct partial oxidation of methane
to methanol would be preferable, no such process has been established
despite over a century of research. Generally, this failure has been
attributed to both the high barriers required to activate methane
as well as the higher activity of the CH bonds in methanol compared
to those in methane. However, a precise and general quantification
of the limitations of catalytic direct methane to methanol has yet
to be established. Herein, we present a simple kinetic model to explain
the selectivityâconversion trade-off that hampers continuous
partial oxidation of methane to methanol. For the same kinetic model,
we apply two distinct methods, (1) using ab initio calculations and
(2) fitting to a large experimental database, to fully define the
model parameters. We find that both methods yield strikingly similar
results, namely, that the selectivity of methane to methanol in a
direct, continuous process can be fully described by the methane conversion,
the temperature, and a catalyst-independent difference in methane
and methanol activation free energies, Î<i>G</i><sup>a</sup>, which is dictated by the relative reactivity of the CâH
bonds in methane and methanol. Stemming from this analysis, we suggest
several design strategies for increasing methanol yields under the
constraint of constant Î<i>G</i><sup>a</sup>. These
strategies include (1) âcollectorsâ, materials with
strong methanol adsorption potential that can help to lower the partial
pressure of methanol in the gas phase, (2) aqueous reaction conditions,
and/or (3) diffusion-limited systems. By using this simple model to
successfully rationalize a representative library of experimental
studies from the diverse fields of heterogeneous, homogeneous, biological,
and gas-phase methane to methanol catalysis, we underscore the idea
that continuous methane to methanol is generally limited and provide
a framework for understanding and evaluating new catalysts and processes
Direct Methane to Methanol: The SelectivityâConversion Limit and Design Strategies
Currently,
methane is transformed into methanol through the two-step
syngas process, which requires high temperatures and centralized production.
While the slightly exothermic direct partial oxidation of methane
to methanol would be preferable, no such process has been established
despite over a century of research. Generally, this failure has been
attributed to both the high barriers required to activate methane
as well as the higher activity of the CH bonds in methanol compared
to those in methane. However, a precise and general quantification
of the limitations of catalytic direct methane to methanol has yet
to be established. Herein, we present a simple kinetic model to explain
the selectivityâconversion trade-off that hampers continuous
partial oxidation of methane to methanol. For the same kinetic model,
we apply two distinct methods, (1) using ab initio calculations and
(2) fitting to a large experimental database, to fully define the
model parameters. We find that both methods yield strikingly similar
results, namely, that the selectivity of methane to methanol in a
direct, continuous process can be fully described by the methane conversion,
the temperature, and a catalyst-independent difference in methane
and methanol activation free energies, Î<i>G</i><sup>a</sup>, which is dictated by the relative reactivity of the CâH
bonds in methane and methanol. Stemming from this analysis, we suggest
several design strategies for increasing methanol yields under the
constraint of constant Î<i>G</i><sup>a</sup>. These
strategies include (1) âcollectorsâ, materials with
strong methanol adsorption potential that can help to lower the partial
pressure of methanol in the gas phase, (2) aqueous reaction conditions,
and/or (3) diffusion-limited systems. By using this simple model to
successfully rationalize a representative library of experimental
studies from the diverse fields of heterogeneous, homogeneous, biological,
and gas-phase methane to methanol catalysis, we underscore the idea
that continuous methane to methanol is generally limited and provide
a framework for understanding and evaluating new catalysts and processes
Nature of Lone-PairâSurface Bonds and Their Scaling Relations
We investigate the (surface) bonding
of a class of industrially and biologically important molecules in
which the chemically active orbital is a 2<i>p</i> electron
lone pair located on an N or O atom bound via single bonds to H or
alkyl groups. This class includes water, ammonia, alcohols, ethers,
and amines. Using extensive density functional theory (DFT) calculations,
we discover scaling relations (correlations) among molecular binding
energies of different members of this class: the bonding energetics
of a single member can be used as a descriptor for other members.
We investigate the bonding mechanism for a representative (H<sub>2</sub>O) and find the most important physical surface properties that dictate
the strength and nature of the bonding through a combination of covalent
and noncovalent electrostatic effects. We describe the importance
of surface intrinsic electrostatic, geometric, and mechanical properties
in determining the extent of the lone-pairâsurface interactions.
We study systems including ionic materials in which the surface positive
and negative centers create strong local surface electric fields,
which polarize the dangling lone pair and lead to a strong âelectrostatically
driven bondâ. We emphasize the importance of noncovalent electrostatic
effects and discuss why a fully covalent picture, common in the current
first-principles literature on surface bonding of these molecules,
is not adequate to correctly describe the bonding mechanism and energy
trends. By pointing out a completely different mechanism (charge transfer)
as the major factor for binding N- and O-containing unsaturated (radical)
adsorbates, we explain why their binding energies can be tuned independently
from those of the aforementioned species, having potential implications
in scaling-driven catalyst discovery