Hydrated layered polysilicates (HLPSs) have received considerable attention as adsorbents because of their selective adsorption for heavy metal cations. However, the adsorption behavior of kenyaite, ...a HLPS, was not elucidated for heavy metal cations yet. The aim of this study is to investigate adsorption behavior of kenyaite for various heavy metal cations and to elucidate selective adsorption. In the quaternary Cu–Pb–Cd–Zn system, kenyaite exhibited selective adsorption, especially for Pb
2+
and Cu
2+
of which removal rates were 97 and 66%, respectively. It revealed that Pb
2+
was more strongly adsorbed than Cu
2+
through coordination with interlayer silanol groups, resulting in dehydration in the interlayers and severe collapse of the silicate layers. In the presence of NaCl, on the other hand, adsorption for Cu
2+
was less affected showing removal rate of 56% whereas that for Pb
2+
was considerably affected as indicated by remarkably decreased removal rate (42%). Such a preferential adsorption of Cu
2+
in the presence of NaCl could be explained by the role of interlayer Na
+
in inhibiting rapid collapse of the interlayer space to facilitate more adsorption of Cu
2+
with a larger hydrated radius. This study provides an insight into understanding selective adsorption of HLPSs and developing potential adsorbents for water purification.
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•Pore-filling method successfully converted a porous HDPE hollow fiber membrane with large pores into a non-porous membrane for stable water vapor separation.•Pore-filling solution ...used glycerin/PVA/GA, which forms into a hydrogel through physicochemical cross-linking.•Higher the viscosity of the pore-filling solution, more of the large pores were blocked.•However, excess concentration (related to high viscosity) of the pore-filling solution negatively impacted the pore-filling process.•Pore-filled composite membrane consists of a hydrogel that can be washed and recharged, allowing it to be rechargeable.
We propose a new method of using high-density polyethylene (HDPE) ultrafiltration hollow fibers, which are inexpensive but difficult to use as a dehumidification membrane. Dehumidification membranes have a wide range of applications and can also offer the benefit of water recovery. Conventional membranes for gas separation consist of a substrate and a thin layer that selectively permeates a desired gas. However, low-cost substrates such as HDPE are limited in their application due to the presence of large pores that prevent defect-free thin layer formation. To address the issue of large pores, we utilized hydrogels made from viscous solutions, that can be stably positioned in large pores. Specifically, we filled the pores of the HDPE substrate with hydrogels consisting of glycerin, polyvinyl alcohol (PVA), and glutaraldehyde (GA). The pore-filled membranes capable of separating water vapor were 40GPGM and 50GPGM, which were filled with 40GPM (40 wt% glycerin/1 wt% PVA/0.5 wt% GA) and 50GPG (50 wt% glycerin/1 wt% PVA/0.5 wt% GA), respectively. Since the pore-filled membranes were filled with viscous hydrogels, they could be washed and recharged. Accordingly, they showed good rechargeability when measuring properties during multiple pore-filling and washing processes. The water vapor permeance/selectivity/water flux of the pore-filled membranes were measured at various temperatures and feed flow rates. The water vapor permeance/selectivity/water flux of 40GPGM and 50GPGM measured at 35 °C and 3.5 L/min were 3400 GPU/110/0.12 kg/m2∙hr and 2398 GPU/469/0.14 kg/m2∙hr, respectively. After continuous operation for 30 days, it was confirmed that the pore-filled membranes had good long-term stability.
In this study, we focus on the estimation of the regression function in the single-index model based on B-splines using penalization techniques. We adopt a spherical coordinates reparameterization of ...an index vector to deal with an identification problem of the single-index model. To provide a spatially adaptive method, two types of penalties are applied to the estimation of the index vector and the regression function. A special penalty called the localized penalty is introduced to handle the sparsity of the index vector using the spherical coordinates, and the total variation penalty is considered to deal with the smoothing function. Using a coordinate descent algorithm with a grid search of the two tuning parameters, the entire solution paths of the index coefficients and the regression functions for tuning parameters can be obtained efficiently. The performance of the proposed estimator is studied through both numerical simulations and real data sets. An R software package pbssim is available.
An Al13 ϵ-Keggin cluster, AlO4Al12(OH)24(H2O)127+, is a predominant intermediate during the hydrolysis and polymerization of aluminum as well as a highly toxic substance to plants and fishes. ...However, no one could clearly explain why and how a cage-like Al13 ϵ-Keggin cluster is formed even though it could be readily synthesized by the forced hydrolysis of Al3+. We found that the Al13 ϵ-Keggin cluster was spontaneously formed not in monocrystalline octosilicate but in polycrystalline magadiite by the cation-exchange reaction with unhydrolyzed Al3+. Furthermore, the Al13 ϵ-Keggin cluster was hardly detected in disaggregated magadiite crystals whose morphology was changed into monocrystalline crystals like octosilicate. Our findings prove that Al13 formation is necessary to relieve localized inhomogeneity and rationalize that Al13 is formed by the simultaneous co-assembly of four planar trimers and one octahedral monomer. In addition, the spontaneous formation of Al13 in heterogeneous systems could be a vital clue to its evaluation in soils and sediments.
Efficient scale-up processes of gas separation membranes require a thorough assessment of performance across various parameters. Semi-empirical modeling based on theory and empirical data is an ...attractive approach to predict the required performance. Despite numerous studies on the performance of gas separation membranes depending on internal parameters such as morphology and geometry, relatively few studies on performance dependent on external parameters have been reported. In this study, we propose semi-empirical modeling for the performance of membranes as a function of external parameters using a bench-scale pore-filled composite membranes for water vapor separation. As external parameters, we selected temperature, pressure, relative humidity (RH), and feed flow rate. These parameters influence water vapor permeance, water flux, and RH reduction, which are theoretical indicators of the performance of water vapor separation membranes. A power regression analysis was used to find the power of individual parameters (Y = Coefficient (k) ∙ Xpower), and a multiple linear regression analysis (finite power law model, Y = k ∙ X1α ∙ X2β…) was used to develop a semi-empirical model with the correlations of these parameters. The modeling values closely coincided with measured values, suggesting the effectiveness of the proposed modeling. This method is expected to simplify the prediction of membrane performance, offering valuable insights for potential scale-up processes.
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•Successfully scaled up the pore-filled composite membrane (PFCM) for water vapor separation to bench-scale (7.8 m2).•Bench-scale PFCM was stable for long-term operation.•Propose semi-empirical models for performance of water vapor separation related to external parameters.•Semi-empirical models were assembled in the forms of finite power law model by combining power and multiple linear regression analysis.•Proposed semi-empirical models will serve as a robust predictive tool for potential installation sites.
Anion exchange membranes (PE/VBC) are successfully synthesized by pore-filling a porous polyethylene (PE) substrate with poly(4-vinylbenzyl chloride) followed by amination with pyridyl functional ...groups for vanadium redox flow battery (VRFB) applications. The membrane crosslinked with 10% of DVB content (PE/VBC(10)), 33μm in thickness, exhibits a low swelling ratio of 3.4% and a water uptake of 23%. In addition, the vanadium crossover rate of the PE/VBC(10) membrane is lower than Nafion 117 by 48% at a similar electrical area resistance. Electrochemical properties of the PE/VBC membranes are examined in terms of the transport number and migration of ions as well as the electrical area resistance. Transport numbers for anions of the PE/VBC(10) membranes are 0.96 and 0.97 in NaCl and NaOH solutions, respectively. In acidic solutions of HCl and H2SO4, the membrane shows remarkably higher cation transport numbers of 0.20 and 0.72, which imply that the membrane allows high proton permeation and it is advantageous in VRFB operations. Furthermore, the migration of ions reveals reasonably low fluxes of other cations through the anion exchange membrane. Finally, the energy efficiency of the PE/VBC (10) membrane is 90.2%, higher than Nafion 117 by 5.4%.
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► Pore-filled anion exchange membranes were fabricated for redox flow batteries. ► Electrochemical properties of anion exchange membranes were examined for RFB systems. ► The PE/VBC membranes showed high cationic transport numbers in acidic solutions. ► Both H+ and SO42− ions are simultaneously transported through the membranes. ► It is advantageous for operations owing to the lower resistance.
Recently, because of the increase in the number of connections to Distributed Generation (DG), the problem of lowering voltage stability in the distribution system has become an issue. Reactive power ...compensators, such as Static Synchronous Compensators (STATCOM), may be used to solve the problem of voltage stability degradation. However, because of the complexity of the distribution system, it is very difficult to select the installation location for STATCOM. Furthermore, when installed in the wrong location, economical efficiency and availability problems may occur. This paper proposes a Virtual STATCOM Configuration and Control method that would operate like a single STATCOM based on multiple DGs connected to the system. The proposed Virtual STATCOM has the merit of being economical by using existing facilities without adding new power facilities, and it solves the problem of the difficulty of selecting the installation location because of the complexity of the distribution system. In addition, while the conventional STATCOM uses an independent control method in consideration of the power quality of the access point, the Virtual STATCOM performs the Point of Common Coupling (PCC) power quality compensation using the integrated control of multiple DGs connected to the system. In the proposed method, the Virtual STATCOM integrated control algorithm is configured by adopting linear programming, and the compensation is performed while considering the distance between DG and PCC, the inverter’s rated capacity, and the power generation. The performance of the Virtual STATCOM power quality compensation was verified using MATLAB/SIMULINK and Real Time Simulator (OPAL-RT).
We synthesize the anatase TiO2/zinc phthalocyanine (ZnPc) hybrids in various sizes (245–1188 nm) and examine the visible light photocatalytic activity of TiO2/ZnPc hybrids, in conjunction with their ...Mie light scattering ability. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy show that ZnPc molecules are well-incorporated and dispersed on the surface of the TiO2, instead of being aggregates. From the field-emission scanning electron microscopy, dynamic light scattering, and nitrogen adsorption–desorption analysis, we confirm the formation of spherical TiO2/ZnPc hybrids in various sizes (245, 548, 798, 1188 nm in diameter), the large specific surface areas (up to 223.76 m2/g), and the mesoporous structures. The mesoporous TiO2/ZnPc hybrids show excellent photocatalytic efficiency (up to 89.93% after 90 min) toward the degradation of methylene blue under visible light irradiation, which is about 2 times of that of simple nanoparticular P25/ZnPc. Among the mesoporous TiO2/ZnPc hybrids, the hybrid with a size of 548 nm (P123–TiO2/ZnPc) exhibits the highest photocatalytic activity. The highest activity observed on P123–TiO2/ZnPc may be attributed to its efficient cascade Mie scattering effect under visible light irradiation.
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•We synthesized the mesoporous TiO2/phthalocyanice (ZnPc) hybrids in various sizes.•We examine the visible light photocatalytic activity of the TiO2/ZnPc hybrids.•We investigate the effect of Mie scattering on the photocatalytic activity.•Scattering efficiency of the incident light is dependent on the diameter of hybrid.•The hybrid with a size of 548 nm exhibits the highest photocatalytic activity.
Microporous Engelhard titanosilicate-4 (ETS-4) particles are synthesized by means of the hydrothermal method using a gel with the following molar composition: 5H2O2:0.5TiO2:10SiO2:18NaOH:675H2O. The ...as-synthesized ETS-4 product is comprised of large dumbbell-shaped particles consisting of fine needlelike crystallites. These ETS-4 particles are finely ground with a ball mill and added to a 5wt% Nafion solution to produce the Nafion/ETS-4 composite membranes for direct methanol fuel cells (DMFCs). The methanol permeability of the composite membranes decreases with increasing ETS-4 contents up to 15wt% and then increases again upon further addition of ETS-4. The proton conductivity of the composite membranes decreases upon increasing ETS-4 contents. These results show that the best membrane selectivity is achieved with the NE10 membrane (where ‘NEx denotes a Nafion/ETS-4 composite membrane containing xwt% of ETS-4). The proton diffusion coefficients obtained with 1H pulsed field gradient nuclear magnetic resonance (PFG-NMR) are found to be much smaller than that of pure bulk water and to decrease with increasing ETS-4 contents in the membrane, which is in good agreement with the results obtained from the proton conductivity.
► Microporous Engelhard titanosilicate-4 (ETS-4) particles were synthesized by the hydrothermal method. ► Nafion/ETS-4 composite membranes were prepared by the solution casting method. ► The best membrane selectivity was achieved with the NE10 membrane with 10wt% ETS-4. ► The proton diffusion coefficients obtained with 1H PFG-NMR were found to decrease with increasing ETS-4 contents in the membrane.
Remote sensing techniques offer significant potential for generating accurate thick oil slick maps critical for marine oil spill response. However, field validation and methodology assessment ...challenges remain. Here, we report on an approach to leveraging oil emissions from the Coal Oil Point (COP) natural marine hydrocarbon seepage offshore of southern California, where prolific oil seepage produces thick oil slicks stretching many kilometers. Specifically, we demonstrate and validate a remote sensing approach as part of the Seep Assessment Study (SAS). Thick oil is sufficient for effective mitigation strategies and is set at 0.15 mm. The brightness temperature of thick oil, TBO, is warmer than oil-free seawater, TBW, allowing segregation of oil from seawater. High spatial-resolution airborne thermal and visible slick imagery were acquired as part of the SAS; including along-slick “streamer” surveys and cross-slick calibration surveys. Several cross-slick survey-imaged short oil slick segments that were collected by a customized harbor oil skimmer; termed “collects”. The brightness temperature contrast, ΔTB (TBO − TBW), for oil pixels (based on a semi-supervised classification of oil pixels) and oil thickness, h, from collected oil for each collect provided the empirical calibration of ΔTB(h). The TB probability distributions provided TBO and TBW, whereas a spatial model of TBW provided ΔTB for the streamer analysis. Complicating TBW was the fact that streamers were located at current shears where two water masses intersect, leading to a TB discontinuity at the slick. This current shear arose from a persistent eddy down current of the COP that provides critical steering of oil slicks from the Coal Oil Point. The total floating thick oil in a streamer observed on 23 May and a streamer observed on 25 May 2016 was estimated at 311 (2.3 bbl) and 2671 kg (20 bbl) with mean linear floating oil 0.14 and 2.4 kg m−1 with uncertainties by Monte Carlo simulations of 25% and 7%, respectively. Based on typical currents, the average of these two streamers corresponds to 265 g s−1 (~200 bbl day−1) in a range of 60–340 bbl day−1, with significant short-term temporal variability that suggests slug flow for the seep oil emissions. Given that there are typically four or five streamers, these data are consistent with field emissions that are higher than the literature estimates.
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