7 research outputs found
Effect of Electric Field on Gas Hydrate Nucleation Kinetics: Evidence for the Enhanced Kinetics of Hydrate Nucleation by Negatively Charged Clay Surfaces
Natural
gas hydrates are found widely in oceanic clay-rich sediments,
where clay–water interactions have a profound effect on the
formation behavior of gas hydrates. However, it remains unclear why
and how natural gas hydrates are formed in clay-rich sediments in
spite of factors that limit gas hydrate formation, such as small pore
size and high salinity. Herein, we show that polarized water molecules
on clay surfaces clearly promote gas hydrate nucleation kinetics.
When water molecules were polarized with an electric field of 10<sup>4</sup> V/m, gas hydrate nucleation occurred significantly faster
with an induction time reduced by 5.8 times. Further, the presence
of strongly polarized water layers at the water–gas interface
hindered gas uptake and thus hydrate formation, when the electric
field was applied prior to gas dissolution. Our findings expand our
understanding of the formation habits of naturally occurring gas hydrates
in clay-rich sedimentary deposits and provide insights into gas production
from natural hydrate deposits
Evolution of Compressional Wave Velocity during CO<sub>2</sub> Hydrate Formation in Sediments
While the acoustic wave-based survey is considered to be one of the most effective and promising means for monitoring the behavior of particulate/discrete geomaterials, the P-wave velocity has scarcely been used to monitor the long-term behavior of CO<sub>2</sub> sequestered sediments or to understand the characteristics of CO<sub>2</sub> hydrate formation in sediments. Furthermore, there are still only limited reliable laboratory results quantifying the P-wave velocity change in sediments that results from CO<sub>2</sub> hydrate formation and accumulation processes. This study presents experimental measurements on the evolution of P-wave velocity as CO<sub>2</sub> hydrate saturation increases in unconsolidated sediment. The measured data are compared with the simple yet robust asymptotic Gassmann model to estimate CO<sub>2</sub> hydrate saturation (volume fraction of hydrate in pore space) in sediments. Given that in situ techniques to measure acoustic waves are well-established for the exploration of deep oceanic sediment, the methodology presented in this paper for estimating hydrate saturation is of potential significance in the monitoring of the long-term behavior of CO<sub>2</sub> reservoirs after sequestration in deep marine sediments
Destabilization of Marine Gas Hydrate-Bearing Sediments Induced by a Hot Wellbore: A Numerical Approach
This study addresses a numerical approach for exploring how thermal change destabilizes marine gas hydrate-bearing sediments. The underlying physical processes of hydrate-bearing sediments, such as hydrate dissociation, self-preservation, pore pressure evolution, gas dissolution, and sediment volume expansion, are incorporated with the thermal conduction, pore fluid flow, and mechanical response of sediments. Two-dimensional numerical modeling is conducted using a verified finite difference method, in which a steady-state hot wellbore transfers heat to the surrounding hydrate-bearing sediments, resulting in dissociation of methane hydrate. During gas hydrate dissociation, excess pore fluid pressure is generated such that the sediments undergo plastic deformation in the dissociation region and uplift at the seafloor. Sediment stability in the early stage of heat transfer is governed by the intensity of the heat source and the thermal conductivity of the sediments with gas hydrates in place. Later on, excess pore fluid pressure diffusing from the dissociation region destabilizes the shallower overlying sediments. Case studies show that the stability of sediments experiencing thermal change is worsened by an increase in the intensity of the heat source and the initial hydrate saturation. In addition, a decrease in the permeability, initial free gas saturation, and sediment strength also decreases the stability of sediments. A considerable uplifting deformation of the overlying sediments and a sediment failure in a cylindrical or conical shape around a wellbore are observed when the factor-of-safety becomes less than one
Phosphorescent Sensor for Phosphorylated Peptides Based on an Iridium Complex
A bisÂ[(4,6-difluorophenyl)Âpyridinato-<i>N</i>,<i>C</i><sup>2′</sup>]ÂiridiumÂ(III) picolinate
(FIrpic) derivative
coupled with bisÂ(Zn<sup>2+</sup>–dipicolylamine) (ZnDPA) was
developed as a sensor (<b>1</b>) for phosphorylated peptides,
which are related to many cellular mechanisms. As a control, a fluorescent
sensor (<b>2</b>) based on anthracene coupled to ZnDPA was also
prepared. When the total negative charge on the phosphorylated peptides
was changed to −2, −4, and −6, the emission intensity
of sensor <b>1</b> gradually increased by factors of up to 7,
11, and 16, respectively. In contrast, there was little change in
the emission intensity of sensor <b>1</b> upon the addition
of a neutral phosphorylated peptide, non-phosphorylated peptides,
or various anions such as CO<sub>3</sub><sup>2–</sup>, NO<sub>3</sub><sup>–</sup>, SO<sub>4</sub><sup>2–</sup>, phosphate,
azide, and pyrophosphate. Furthermore, sensor <b>1</b> could
be used to visually discriminate between phosphorylated peptides and
adenosine triphosphate in aqueous solution under a UV–vis lamp,
unlike fluorescent sensor <b>2</b>. This enhanced luminance
of phosphorescent sensor <b>1</b> upon binding to a phosphorylated
peptide is attributed to a reduction in the repulsion between the
Zn<sup>2+</sup> ions due to the phenoxy anion, its strong metal-to-ligand
charge transfer character, and a reduction in self-quenching
Control and Monitoring of Dye Distribution in Mesoporous TiO<sub>2</sub> Film for Improving Photovoltaic Performance
Dye
distribution in a mesoporous TiO<sub>2</sub> film is a key factor
in the performance of dye-sensitized solar cells, but there has been
little research on it. Here we report even dye distribution within
the porous TiO<sub>2</sub> film achieved by a physical driving force
of gas flow. Gas-assisted dye arrangement, gas bubbling soaking (GBS),
significantly accelerates the dye infiltration compared to conventional
overnight soaking (OS). As a demonstration, we investigated the time-dependent
dye infiltration using plasmon sensors. GBS produces an even vertical
dispersion throughout the film, as illustrated by time-of-flight secondary
ion mass spectrometry depth profiles. For devices using a 7-μm-thick
active layer and a ruthenium-based dye (N719), only 15 min of GBS
treatment produced better power conversion efficiency (PCE) than the
optimal result from OS treatment (15 h), despite a lower dye capacity.
Dual-GBS treatment (20 min for N719 and 10 min for YD2, a porphyrin
dye) produced the best PCE (9.0%) in the device, which was ∼17%
higher than that treated with dual-OS (10 h for N719 and 5 h for YD2).
Such improvements are associated with reduced dye-free sites inside
the porous TiO<sub>2</sub> film after GBS treatment, leading to faster
charge transport and slower charge loss
Strategy for Improved Photoconversion Efficiency in Thin Photoelectrode Films by Controlling π‑Spacer Dihedral Angle
BenzoÂ[<i>c</i>]Â[1,2,5]Âthiadiazole (BT) has been used
in dye-sensitized solar cells (DSCs) for its light-harvesting abilities.
However, as a strongly electron deficient unit, BT causes rapid back
electron transfer (BET), which in turn lowers the photoconversion
efficiency (PCE) of devices. Herein, we report a powerful strategy
for retarding BET by controlling both the photoelectrode thickness
and π-spacer dihedral angle. To achieve this, we introduced
planar (<b>BT-T</b>) or twisted π-spacers (<b>BT-P</b>, <b>BT-MP</b>, and <b>BT-HT</b>) between BT units and
anchoring groups and used different photoelectrode thicknesses between
1.8 and 10 μm. Computational and experimental results show that
twisted π-spacers were more efficient at retarding BET than
the planar π-spacer. However, BET was found to be less important
than expected, and light harvesting efficiency (LHE) played a critical
role as the thickness of the photoelectrode decreased because charge
collection efficiency was enhanced. The planar dye <b>BT-T</b> obtained the highest LHE, this value remained unusually high even
in 1.8 μm photoelectrodes. As a result, <b>BT-T</b> gave
a PCE of 6.5% (<i>J</i><sub>sc</sub> = 13.56 mA/cm<sup>2</sup>, <i>V</i><sub>oc</sub> = 0.67 V, and FF = 0.72) in thin
1.8 μm photoelectrodes with 3.5 μm scattering layers,
which represented a roughly 40% enhancement compared to the PCE in
10 μm photoelectrodes (4.76%). Overall, these results provide
a novel approach to achieving ultrathin and highly efficient flexible
DSCs
Influence of the Lithium-Ion Concentration in Electrolytes on the Performance of Dye-Sensitized Photorechargeable Batteries
Dye-sensitized photorechargeable batteries (DSPBs) have
recently
gained attention for realizing energy recycling systems under dim
light conditions. However, their performance under high storage efficiency
(i.e., the capacity charged within a limited time) for practical application
remains to be evaluated. Herein, we varied the lithium (Li)-ion concentration,
which plays a dual role as energy charging and storage components,
to obtain the optimized energy density of DSPBs. Electrochemical studies
showed that the Li-ion concentration strongly affected the resistance
characteristics of DSPBs. In particular, increasing the Li-ion concentration
improved the output capacity and decreased the output voltage. Consequently,
the energy density of the finely optimized DSPB improved from 8.73
to 12.64 mWh/cm3 when irradiated by a 1000-lx indoor light-emitting-diode
lamp. These findings on the effects of Li-ion concentrations in electrolytes
on the performance of DSPBs represent a step forward in realizing
the practical application of DSPBs