In this paper, we compare and contrast the four most promising (
i.e.
commercially viable in the near future) technologies for the post-combustion capture (PCC) of CO
2
that can be retrofitted to a ...conventional pulverised-coal power plant. These are CO
2
capture using: (i) chilled ammonia, (ii) alkali-metal carbonates, (iii) membranes and (iv) calcium looping. These four technologies are compared to the benchmark monoethanolamine (MEA) scrubbing process in terms of efficiency penalty and cost indicators. We first review the relevant CO
2
capture chemistry and typical process flow schematics, and then discuss energy- and mass-balance considerations. We consider 18 published techno-economic studies on these technologies and highlight the key measures, including net CO
2
capture rate, net power output, net plant efficiency, capital costs, cost of electricity and cost of CO
2
avoided. Calcium looping technology results in the lowest efficiency penalty (4.6%-points) and cost of PCC (36.3% increase in levelised cost of electricity). In addition, the cost of CO
2
avoided by employing calcium looping for PCC can be as low as 29 USD
2010
per tCO
2
. On all three of these criteria, calcium looping performs more than twice as well as the benchmark MEA PCC process.
This review compares four promising post-combustion CO
2
-capture technologies to the benchmark (monoethanolamine scrubbing) in terms of technological and economic indicators.
An amino-functionalised metal-organic framework (MOF), aluminium aminoterephthalate (amino-MIL-101(Al)), has been applied to the adsorptive removal of dyes (cationic methylene blue, MB, and anionic ...methyl orange, MO) from aqueous solutions in order to examine the effect of the amino group on sorption behaviour. Adsorption isotherms and thermodynamic studies indicated the spontaneous adsorption of MB with a maximum adsorption capacity at 30 degree C (762 plus or minus 12 mg g sub(MOF) super(-1)) higher than those observed for MB on other MOFs and most other materials. In contrast, lower adsorption capacities were observed in the adsorption of the same dye on the analogous non-amino-functionalised framework (MIL-101(Al), 195 mg g super(-1)) and in the adsorption of MO by amino-MIL-101(Al) (188 plus or minus 9 mg g super(-1)), suggesting that an electrostatic interaction between the amino groups of the MOF and the cationic dye MB may have contributed to the high adsorption capacity. The adsorptions of both dyes on amino-MIL-101(Al) were spontaneous, endothermic, and entropy-driven, as is common for dye adsorptions. However, the Delta Svalue obtained for the adsorption of MB (346 J mol super(-1) K super(-1)) was extreme. Further analysis demonstrated that after exposure to MB, the ordered amino-MIL-101(Al) structure was absent, similar to 30% of the Al super(3+) was lost to solution, and significant changes occurred in the X-ray photoelectron spectrum of the MOF. On the other hand, the MOF structure was intact following the adsorption of MO. Several groups have exploited electrostatic interactions to improve dye adsorption; however, these proved excessive in the case of MB (but not MO) adsorption on amino-MIL-101(Al).
A facile synthesis method to produce nitrogen-doped graphene containing a high atomic percentage of pyridinic N and graphitic N via the thermal annealing of graphene oxide and uric acid is reported. ...The method yielded N-doped graphene nanosheets that had high surface areas and that contained 9.22 at% nitrogen, which was present in four bonding configurations with a high ratio of pyridinic N and graphitic N. The synthesized N-doped graphene showed excellent capacitance properties, which led to the fabrication of a stacked electrode supercapacitor cell of 2-electrode configuration with a specific capacitance of 230 F g −1 at a current density of 1 A g −1 and with a remarkably high energy density of 62.6 W h kg −1 in aqueous electrolyte. Additionally, this material showed superior properties as an electrocatalyst for both the oxygen-reduction reaction (ORR) and oxygen evolution reaction (OER), producing high current density primarily via the four-electron pathway for ORR at a current density of −4.3 mA cm −2 and OER activity of a generating current density of 10 mA cm −2 at 1.74 V vs. RHE in alkaline media. Hence, this dual-natured N-doped graphene could provide a platform for developing nanostructured graphene-based advanced energy storage and conversion devices.
A mobile robotic chemist Burger, Benjamin; Maffettone, Phillip M; Gusev, Vladimir V ...
Nature,
07/2020, Letnik:
583, Številka:
7815
Journal Article
Recenzirano
Odprti dostop
Technologies such as batteries, biomaterials and heterogeneous catalysts have functions that are defined by mixtures of molecular and mesoscale components. As yet, this multi-length-scale complexity ...cannot be fully captured by atomistic simulations, and the design of such materials from first principles is still rare
. Likewise, experimental complexity scales exponentially with the number of variables, restricting most searches to narrow areas of materials space. Robots can assist in experimental searches
but their widespread adoption in materials research is challenging because of the diversity of sample types, operations, instruments and measurements required. Here we use a mobile robot to search for improved photocatalysts for hydrogen production from water
. The robot operated autonomously over eight days, performing 688 experiments within a ten-variable experimental space, driven by a batched Bayesian search algorithm
. This autonomous search identified photocatalyst mixtures that were six times more active than the initial formulations, selecting beneficial components and deselecting negative ones. Our strategy uses a dexterous
free-roaming robot
, automating the researcher rather than the instruments. This modular approach could be deployed in conventional laboratories for a range of research problems beyond photocatalysis.
Raman spectroscopy is among the primary techniques for the characterisation of graphene materials, as it provides insights into the quality of measured graphenes including their structure and ...conductivity as well as the presence of dopants. However, our ability to draw conclusions based on such spectra is limited by a lack of understanding regarding the origins of the peaks. Consequently, traditional characterisation techniques, which estimate the quality of the graphene material using the intensity ratio between the D and the G peaks, are unreliable for both GO and rGO. Herein we reanalyse the Raman spectra of graphenes and show that traditional methods rely upon an apparent G peak which is in fact a superposition of the G and D' peaks. We use this understanding to develop a new Raman characterisation method for graphenes that considers the D' peak by using its overtone the 2D'. We demonstrate the superiority and consistency of this method for calculating the oxygen content of graphenes, and use the relationship between the D' peak and graphene quality to define three regimes. This has important implications for purification techniques because, once GO is reduced beyond a critical threshold, further reduction offers limited gain in conductivity.
A facile synthesis of three-dimensional (3D) network of copper confined nitrogen-doped graphene (NG)/carbon nanotube (CNT) with high atomic percentage of nitrogen (10.1 at.%) has been reported. The ...homogenous intercalation of the CNT network in-between the graphene layers decorated with copper nanoparticles take place which inhibits the self-agglomeration within the lattice and enhance the volumetric storage capability. The composite electrode demonstrates exceptionally high specific capacitance of 1250 mA h/g obtained at a current density of 0.1 A/g which is 3.4 times greater than the theoretical capacity of graphite (372 mA h/g). The discharge-charge profiles (from 0.002 to 3 V) with reversible battery capacity exhibit a stable state of the lithium-ion batteries which were observed at high rate capability of 420 mA h/g at a current density of 1 A/g even after 500 cycles. The enhancement of the electrochemical performance could be attributed to the 3D electrically conductive networks of copper confined nitrogen-doped graphene/carbon nanotubes (Cu@N-Gr/CNT).
•3-dimensional nanostructured copper confined nitrogen-doped graphene/carbon nanotube.•Contains high nitrogen content of 10.1 atomic wt.%.•Investigated as anode for lithium ion battery.•Specific capacitance of 1250 mA h/g at a current density of 0.1 A/g.•High rate capacitance of 420 mA h/g at a current density of 1 A/g after 500 cycles.
Abstract
Dense cores are the final place where turbulence is dissipated. It has been proposed from theoretical arguments that the nonthermal velocity dispersion should be narrower both for molecular ...ions (compared to neutrals) and for transitions with higher critical densities. To test these hypotheses, we compare the velocity dispersion of
(1–0) (
= 6 × 10
4
) and
(
= 2 × 10
3
), in the dense core Barnard 5. We analyze well-resolved and high signal-to-noise observations of
(1,1) and (2,2) obtained with combining Robert C. Byrd Green Bank Telescope (GBT) and Very Large Array (VLA) data, and
(1–0) obtained with GBT Argus, which present a similar morphology. Surprisingly, the nonthermal velocity dispersion of the ion is systematically higher than that of the neutral by 20%. The derived sonic Mach number,
, has peak values
and
for
and
, respectively. This observed difference may indicate that the magnetic field even deep within the dense core is still oscillating, as it is in the turbulent region outside the core. The ions should be more strongly dynamically coupled to this oscillating field than the neutrals, thus accounting for their broader line width. If corroborated by further observations, this finding would shed additional light on the transition to quiescence in dense cores.
Abstract
The C
ii
fine-structure transition at 158
μ
m is frequently the brightest far-infrared line in galaxies. Due to its low ionization potential, C
+
can trace the ionized, atomic, and ...molecular phases of the ISM. We present velocity-resolved C
ii
and N
ii
pointed observations from SOFIA/GREAT on ∼500 pc scales in the nearby galaxies M101 and NGC 6946 and investigate the multiphase origin of C
ii
emission over a range of environments. We show that ionized gas makes a negligible contribution to the C
ii
emission in these positions using N
ii
observations. We spectrally decompose the C
ii
emission into components associated with the molecular and atomic phases using existing CO (2–1) and H
i
data and show that a peak signal-to-noise ratio of 10–15 is necessary for a reliable decomposition. In general, we find that in our pointings ≳50% of the C
ii
emission arises from the atomic phase, with no strong dependence on star formation rate, metallicity, or galactocentric radius. We do find a difference between pointings in these two galaxies, where locations in NGC 6946 tend to have larger fractions of C
ii
emission associated with the molecular phase than in M101. We also find a weak but consistent trend for fainter C
ii
emission to exhibit a larger contribution from the atomic medium. We compute the thermal pressure of the cold neutral medium through the C
ii
cooling function and find
log
(
P
th
/
k
)
=
3.8
–
4.6
K
cm
−
3
, a value slightly higher than similar determinations, likely because our observations are biased toward star-forming regions.
Abstract We report observations of the ground state transitions of 12 CO, 13 CO, C 18 O, HCN, and HCO + at 88–115 GHz in the inner region of the nearby galaxy IC 342. These data were obtained with ...the 16 pixel spectroscopic focal plane array Argus on the 100 m Robert C. Byrd Green Bank Telescope (GBT) at 6″–9″ resolution. In the nuclear bar region, the intensity distributions of 12 CO(1–0) and 13 CO(1–0) emission trace moderate densities, and differ from the dense gas distributions sampled in C 18 O(1–0), HCN(1–0), and HCO + (1–0). We observe a constant HCN(1–0)-to-HCO + (1–0) ratio of 1.2 ± 0.1 across the whole ∼1 kpc bar. This indicates that the HCN(1–0) and HCO + (1–0) lines have intermediate optical depth, and that the corresponding n H 2 of the gas producing the emission is of order 10 4.5−6 cm −3 . We show that HCO + (1–0) is thermalized and HCN(1–0) is close to thermalization. The very tight correlation between the HCN(1–0) and HCO + (1–0) intensities across the 1 kpc bar suggests that this ratio is more sensitive to the relative abundance of the two species than to the gas density. We confirm an angular offset (∼10″) between the spatial distribution of molecular gas and the star formation sites. Finally, we find a breakdown of the L IR – L HCN correlation at high spatial resolution due to the effect of incomplete sampling of star-forming regions by HCN emission in IC 342. The scatter of the L IR – L HCN relation decreases as the spatial scale increases from 10″ to 30″ (170–510 pc), and is comparable to the scatter of the global relation at a scale of 340 pc.
A simple, surfactant-free assembly process was used to prepare multi-wall carbon nanotube (CNT) buckypapers using a highly efficient purification, sonication, and filtration process. To achieve ...effective dispersion of CNT into ethanol, a minimum 5-min sonication time was required. Here, we fabricated a buckypaper with pore size of 41±10nm and porosity of 72.9% with a 10-min sonication. The as-prepared buckypaper was used as a membrane for humic acid (HA) removal from water. During purification process, carboxylic and hydroxylic functional groups were introduced onto the CNT surface. The functional groups increased the hydrophilicity of the CNTs and improved the removal efficiency of HA by the buckypaper. The buckypaper prepared from purified CNTs exhibited excellent removal of HA (>93%) and a long lifetime for filtration.
PDF
