421 research outputs found
Theoretical study of adsorption of organic phosphines on transition metal surfaces
<p>The adsorption properties of organic phosphines on transition metal (TM) surfaces (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au) have been studied to explore the possibility of building novel heterogeneous chiral catalytic systems based on organic phosphines. Preferred adsorption sites, adsorption energies and surface electronic structures of a selected set of typical organic phosphines adsorbed on TM surfaces are calculated with density-functional theory to obtain a systematic understanding on the nature of adsorption interactions. All organic phosphines considered are found to chemically adsorb on these TM surfaces with the atop site as the most preferred one, and the TM–P bond is formed via the lone-pair electrons of the P atom and the directly contacted TM atom. These findings imply that it is indeed possible to build heterogeneous chiral catalytic systems based on organic phosphines adsorbed on TM surfaces, which, however, requires a careful design of molecular structure of organic phosphines.</p
Migration of Phosphorus in Sewage Sludge during Different Thermal Treatment Processes
The
utilization of phosphorus (P) in activated sludge discharged
from wastewater treatment plants is an important part of the global
phosphorus circulation. Thermal treatment of excess sludge would become
a promising method for their disposal throughout the world. Herein,
we investigated the transformation and migration of P in sewage sludge
during different thermal treatment conditions. The results indicate
that the temperature can significantly influence the species and content
of P in the sewage sludge char or ash (SSC/A), while the atmosphere
of thermal treatment has a slight effect on the fate of P. <sup>31</sup>P NMR and XRD analysis indicated that P migrated mainly to the medium-term
plant available P pool (pool<sub>NaOH</sub>) on treating the sewage
sludge at a low temperature (673–873 K), while it was prone
to migration to the long-term plant available P pool (pool<sub>HCl</sub>) when treated at a high temperature (873–1073 K)
Theoretical Investigation of Ta<sub>2</sub>O<sub>5</sub>, TaON, and Ta<sub>3</sub>N<sub>5</sub>: Electronic Band Structures and Absolute Band Edges
Early transition
metal oxides, nitrides, and oxynitrides have attracted
a great deal of interest because of their potential applications in
photovoltaics and photocatalysis. In this work, a systematic investigation
is conducted of the electronic band structures of the Ta<sub>2</sub>O<sub>5</sub> polymorphs, β-Ta<sub>3</sub>N<sub>5</sub> and
β-TaON, which are crucial for the understanding of their photocatalytic
properties, based on state-of-the-art first-principles approaches.
The calculated results imply that many-body perturbation theory in
the <i>GW</i> approximation can overcome the severe underestimation
of the band gap caused by standard density functional theory (DFT)
in the local and semilocal approximations and provide a quantitative
agreement with experiment. The effects of the electron–phonon
coupling on the electronic band structure are considered by the Frölich
model, and especially for ϵ-Ta<sub>2</sub>O<sub>5</sub>, a strong
electron–phonon coupling is predicted as a result of small
high-frequency dielectric constants and large effective masses. Based
on an analysis in terms of the phenomenological ionic model, the band-gap
difference between three compounds can be physically attributed to
not only the well-known energy difference between the O 2p and N 2p
orbitals, but also the influences of the Madelung potential on the
conduction-band energy. By comparing the calculated absolute band
edge positions to the redox potentials for water reduction and oxidation,
all three of the compounds are predicted to have potential photocatalytic
properties for unassisted water splitting. In addition, we also analyzed
the stability and band gaps of different Ta<sub>2</sub>O<sub>5</sub> polymorphs and found that the β-Ta<sub>2</sub>O<sub>5</sub>, the phase commonly used in theoretical studies, is actually unstable
and its unusually small band gap can be attributed to the strong overlap
of neighboring atomic orbitals. On the other hand, ϵ-Ta<sub>2</sub>O<sub>5</sub>, which is much less well studied compared to
β-Ta<sub>2</sub>O<sub>5</sub>, leads to calculated properties
that are much more consistent with the experimental findings for Ta<sub>2</sub>O<sub>5</sub> in general. The theoretical analysis and findings
presented in this work have general implications for the understanding
of the electronic band structures of other early transition metal
compounds
Comparative Investigation on Photoreactivity and Mechanism of Biogenic and Chemosythetic Ag/C<sub>3</sub>N<sub>4</sub> Composites under Visible Light Irradiation
A Ag/C<sub>3</sub>N<sub>4</sub> nanocomposite with optimum Ag content
is an efficient and green photocatalyst for pollutant degradation
under visible light irradiation. In this study, we synthesized Ag
NPs using NaBH<sub>4</sub> and the squeezed out liquid (SOL) of plant
biomass. The Ag NPs thus obtained have been loaded to C<sub>3</sub>N<sub>4</sub> to form Ag/C<sub>3</sub>N<sub>4</sub> nanocomposites
that show superior photocatalytic performance toward Rhodamine B (RhB)
under visible light irradiation. The photocatalytic activity of both
biogenic and chemogenic Ag/C<sub>3</sub>N<sub>4</sub> nanocomposites
with different Ag contents is compared. Results show that the biogenically
synthesized Ag/C<sub>3</sub>N<sub>4</sub> exhibits better photocatalytic
performance than the chemosynthetic composite. Of all the different
nanocomposites prepared in this study, Ag<sub>48</sub>/C<sub>3</sub>N<sub>4</sub> (0.048% of Ag content) exhibits excellent photoreactivity,
with a reaction rate constant (<i>k</i>) 7-fold higher that
the chemosynthetic Ag/C<sub>3</sub>N<sub>4</sub>. The observed improvement
in the photoreactivity is mainly attributed to the high dispersion
of Ag NPs on C<sub>3</sub>N<sub>4</sub>, facilitated by the organic
compounds in SOLs. Besides, these organic compounds also enhance the
photoreactivity of the catalyst by providing adsorption sited for
RhB molecules and by shifting the Fermi level to more negative potential
Additional file 3: Figure S2. of Association between periodontal disease and mortality in people with CKD: a meta-analysis of cohort studies
Sensitivity analysis: Forest plot of risk of all-cause death limiting to studies with low risks of bias. (TIFF 252 kb
Robustness tests.
This paper theoretically analyzes and empirically examines the impact and mechanisms of automated machines on employment in manufacturing enterprises, drawing on task-based model and using micro data from listed Chinese manufacturing enterprises between 2012 and 2019. Our findings reveal that: (1) Automated machines in manufacturing enterprises leads to a substitution effect on the total labor force, with a substitution effect on low-skilled labor and a creation effect on high-skilled labor in terms of employment structure. (2) Further analysis indicates that automated machines primarily have a positive effect on R&D and technical staff, a non-significant effect on sales staff, and a negative impact on production, administrative, and financial staff. (3) The primary influencing mechanisms of automated machines on employment in manufacturing firms are productivity effects and output scale effects, based on the mediation effect model. (4) Considering the industry linkage effect, we employ the input-output method and the Input-Output Table and find that automated machines for upstream (downstream) manufacturing enterprises will result in a substitution effect on employment for downstream (upstream) enterprises. The novelties and research contributions are as follows: (1) we conduct a structural decomposition of total employment, and further decompose employment positions into production, R&D, sales, finance, and administration. (2) We try to investigate the industry linkage effect about the impact of automated machines on the employment of upstream and downstream enterprises. (3) We use data from listed manufacturing companies, and the data of existing research are about provincial and industry-level data.</div
Preventing the Release of Cu<sup>2+</sup> and 4‑CP from Contaminated Sediments by Employing a Biochar Capping Treatment
Preventing release of refractory
pollutants from contaminated sediments is of growing concern. In situ
remediation of sediments becomes more popular because of its low cost
and noninterference of benthic ecosystems compared with conventional
sediment dredging. In this study, a low-cost rice husk biochar (RHB)
was used as a capping material to prevent the release of representative
inorganic (Cu<sup>2+</sup>) and organic (4-chlorophenol, 4-CP) pollutants
from synthetic contaminated sediments. In addition, the release dynamics
of pollutants was investigated under different environmentally relevant
conditions. The experimental results indicated that RHB can efficiently
suppress the release of Cu<sup>2+</sup> and 4-chlorophenol from the
sediments and a select thickness of RHB can maintain the concentrations
of these model pollutants below the national criterion at pH = 5 and
7, even when the concentrations of these pollutants are very high
(1600 mg kg<sup>–1</sup> of Cu<sup>2+</sup> or 100 mg kg<sup>–1</sup> of 4-CP). Fitting the release data of pollutants
to the zero order equation, the Elovich equation, the parabolic diffusion
law, and the two-constant rate equation demonstrated that a simple
model cannot precisely describe the complicated release kinetic process
of the pollutants. This study demonstrated a facile remediation application
of RHB and helped to provide the information needed for future risk
assessments and policy-making
Results of industry linkage effects.
This paper theoretically analyzes and empirically examines the impact and mechanisms of automated machines on employment in manufacturing enterprises, drawing on task-based model and using micro data from listed Chinese manufacturing enterprises between 2012 and 2019. Our findings reveal that: (1) Automated machines in manufacturing enterprises leads to a substitution effect on the total labor force, with a substitution effect on low-skilled labor and a creation effect on high-skilled labor in terms of employment structure. (2) Further analysis indicates that automated machines primarily have a positive effect on R&D and technical staff, a non-significant effect on sales staff, and a negative impact on production, administrative, and financial staff. (3) The primary influencing mechanisms of automated machines on employment in manufacturing firms are productivity effects and output scale effects, based on the mediation effect model. (4) Considering the industry linkage effect, we employ the input-output method and the Input-Output Table and find that automated machines for upstream (downstream) manufacturing enterprises will result in a substitution effect on employment for downstream (upstream) enterprises. The novelties and research contributions are as follows: (1) we conduct a structural decomposition of total employment, and further decompose employment positions into production, R&D, sales, finance, and administration. (2) We try to investigate the industry linkage effect about the impact of automated machines on the employment of upstream and downstream enterprises. (3) We use data from listed manufacturing companies, and the data of existing research are about provincial and industry-level data.</div
Slow Pyrolysis Magnetization of Hydrochar for Effective and Highly Stable Removal of Tetracycline from Aqueous Solution
Although
biochar has been intensively studied as an inexpensive
adsorbent for diverse organic pollutants in aqueous solution, synchronously
achieving high adsorption capacity, separability, and stability is
still a challenge. Herein, we partially addressed this issue via an
integrated activation and pyrolytic magnetization of sawdust hydrochar,
during which the surface area of magnetic activated sawdust hydrochar
(M-SDHA) increases from 1.7 to 1710 m<sup>2</sup> g<sup>–1</sup>, and the weight loss decreases from 70 to 5% at 700 °C. Correspondingly,
the maxmium adsorption capacity of M-SDHA toward tetracycline (TC)
reaches 423.7 mg g<sup>–1</sup> and remains constant at pH
5–9. Multiple characterizations show that the fine pore structure
and surface functional groups of M-SDHA were maintained during the
pyrolysis magnetization process, which is responsible for the high
adsorption capacity. In the pyrolysis magnetization process, the FeCl<sub>3</sub> was reduced to Fe<sub>3</sub>O<sub>4</sub> which endowed
M-SDHA with magnetism and may simultaneously improve the thermostability
of M-SDHA. In addition, acidic–basic stability of M-SDHA may
be responsible for the stable adsorption toward TC at different pHs
based on Fourier transform infrared spectroscopic results. These results
along with the column adsorption experiment show that M-SDHA is an
effective and practical adsorbent for TC removal
Estimated coefficients and confidence intervals of column 2 in Table 3.
Estimated coefficients and confidence intervals of column 2 in Table 3.</p
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