Adsorbent Trap Research Articles

Molecular dynamics simulations of shale wettability alteration and implications for CO2 sequestration: A comparative study

Geological CO2 sequestration (GCS) in shale reservoirs is considered an imperative approach to reducing CO2 emissions and mitigating greenhouse gas effects, with the wettability of reservoir rocks playing a critical role in this process. In this study, we comparatively investigated the wetting characteristics of H2O on the organic matter (graphene) and inorganic matter (hydroxylated quartz) surfaces of shale in a CO2 atmosphere utilizing molecular dynamics (MD) simulations and focused on elucidating the effects of CO2 pressure, temperature, and salinity on wettability from the perspectives of the H2O droplet contact angle (CA), gas-water density distributions and interaction energy. The results demonstrate that the H2O droplet is gradually stripped from the graphene surface by CO2 with increasing CO2 pressure, inducing a wetting transition from intermediate-wet to strongly CO2-wet, while the hydroxylated quartz surface consistently exhibits a strongly H2O-wet state. This significant discrepancy in wetting behaviors can be attributed to the differential adsorption capabilities of CO2. The hydrophilicity of graphene and quartz surfaces is enhanced with increasing temperature for the given CO2 pressure condition, and the wettability alteration is more pronounced above the CO2 critical temperature for graphene, while the opposite is observed for quartz. The H2O CA in the CO2-H2O-shale systems only slightly increases with increasing salinity, which is related to the spatial effect of ions in the brine. The results of this work indicate that the CO2-wet feature of shale organic matter during GCS is favorable for the adsorption trapping of CO2 but unfavorable for capillary trapping, while the opposite is true for inorganic matter. This study sheds light on the phenomena and regularity of the wettability alterations of shale organic and inorganic matter by CO2 injection, and the results gained are expected to furnish new insights into CO2 sequestration-enhanced gas recovery (CS-EGR) and gas-water two-phase flow at the nanoscale.

Migration and transformation mechanisms of Pb/Cd with HCl in organic solid waste incineration flue gas on the composite-modified kaolinite surface

Cadmium/lead (Cd/Pb) pollutants from organic solid wastes (OSW) incineration are of global concern due to high volatility and biotoxicity. The strong interaction between modified kaolinite and Cd/Pb species inspires its utilization for the elimination of heavy metals. However, the specific mechanism of the migration and transformation of Cd/Pb species is yet unclear. Consequently, the migration and transformation mechanisms of Cd/Pb species on the modified kaolinite (001) surface are examined by density functional theory (DFT), considering the effect of HCl. The outcomes show that the HCl significantly alters the characteristics of the kaolinite, which enhances the surface activity of kaolinite and promotes the adsorption and transformation of Cd/Pb species. Furthermore, the chlorination routes of Cd0/Pb0 are fully elucidated in both 2-step and 1-step routes. The first step of the 2-step route obeys the Langmuir-Hinshelwood mechanism and the second step obeys the Eley-Rideal mechanism, while the 1-step chlorination route obeys the Eley-Rideal mechanism. In addition, the oxidation route of Cd0/Pb0 follows the Mars-van Krevelen mechanism. The comparison of the energy barriers shows that the 1-step Cd0/Pb0 chlorination route has the lowest energy barrier. The kaolinite surface is found to have elevated activity for the adsorptive trapping of Cd/Pb species in the presence of HCl, which offers a preliminary theoretical framework for pollutant control on the modified kaolinite surface.

Pore-scale flow simulation of CO2 sequestration in deep shale based on thermal-hydro-mechanical coupled model

The technology of sequestering CO2 in deep shale has shown great potential due to the low permeability of shale and the high adsorption of CO2 by organic-rich characteristics. Deep shale is characterized by high temperature and high pressure with a significant hydro-mechanical coupling effect. The Darcy–Brinkman–Stokes method was integrated with heat transfer equations to simulate thermal-hydro-mechanical coupled single-phase steady-state flow, combined with multiphase flow equations to simulate hydro-mechanical coupled transient flow under high-temperature conditions. This study aims to reveal the effect of temperature difference between CO2 and reservoir, Reynolds number, and formation pressure on the flow process of CO2 geological storage in deep shale based on the constructed real core structure consisting of organic pore, organic matter, and inorganic matter. The results indicate that low-temperature CO2 is conducive to giving full play to the role of convection heat transfer, improving the CO2 saturation and the swept volume of organic pores. The Reynolds number has a negligible impact on the transition of convective and conduction heat transfer. At higher Reynolds numbers, CO2 flows extensively and deeply, and CO2 clusters occupy a higher proportion in organic pores. At higher confining pressures, the Nusselt number is higher and convective heat transfer is more dominant. Shallower reservoirs are favorable conditions for adsorption trapping, as their cores are subjected to slightly lower confining pressure, resulting in higher CO2 saturation in the organic matter and higher sweep efficiency of organic pores. Our main finding is that low-temperature CO2, a higher Reynolds number, and shallower buried depth favor carbon sequestration.

Adsorptive avidity of Prussian blue polypyrrole nanocomposite for elimination of water contaminants: a case study of malachite green and isoniazid.

Persistent water contaminants include a variety of substances that evade natural cleaning processes posing severe risks to ecosystems. Their adsorptive elimination is a key approach to safer attenuation. Herein we present the design and development of Prussian blue incorporated polypyrrole (PPY/PB) hybrid nanocomposite as a high-performance adsorbent for the elimination of malachite green (M.G.), isoniazid (INH) and 4-nitrophenol (4-NP) water contaminants. The nanocomposite synthesis was favored by strong dopant-polymer interactions, leading to a PPY/PB material with enhanced electro-active surface area compared to pristine PPY. The structure-activity response of the nanocomposite for the adsorption of target contaminants was unveiled by evaluating its maximum adsorption capacities under environmentally viable conditions. In-depth analysis and optimization of adsorption influencing factors (pH, temperature, and adsorbent dose) were performed. Using equilibrium studies, kinetic model fitting, aided with FTIR analysis, a multi-step mechanism for the adsorption of target contaminants on the nanocomposite was proposed. Furthermore, the PPY/PB nanocomposite also acts as a catalyst, enabling contaminant elimination following a synergistic scheme that was demonstrated using 4-NP contaminant. The synergetic adsorption and catalytic degradation of 4-NP using PPY/PB as adsorbent and catalyst was demonstrated in the presence of NaBH4 as a reducing agent in absence of light. In summary, this work highlights the targeted design of adsorbent, its optimization for adsorptive avidity, and the synergistic role of adsorption trapping in the catalytic degradation of persistent contaminants.

Boosting in-situ Fenton-like degradation on bifunctional CoFe-CoFe2O4@N-C via constructing “adsorption trap”: Unveiling the role of pyrrolic N

The rational design and construction of bifunctional catalysts with excellent adsorption and catalytic activity are meaningful but challenging. Herein, a core–shell magnetic CoFe-CoFe2O4@N-C catalyst with dual sites was constructed to shorten the migration distance between the target contaminant of ofloxacin (OFX), a typical antibiotic, and reactive oxygen species (ROS) in Fenton-like degradation. The characterization results and theory calculations indicated that abundant pyrrolic N sites on shells served as “adsorption traps” for OFX and encapsulated CoFe2O4 as activation sites for peroxymonosulfate (PMS). The unique reaction pathway between in-situ generated ROS and adjacent adsorbed OFX enhanced the catalytic ability, showing 100% removal of OFX (20 mg/L) with a high rate constant (0.422 min−1). Meanwhile, the system presented excellent anti-interference capability to inorganic (Cl–, NO3–, and H2PO4–), organic (humic acid), actual aqueous matrices (tap water and river water), and good stability proved by the continuous flow experiment. The work will provide ideas for designing bifunctional catalysts and supply an eco-friendly process for boosting in-situ Fenton-like degradation.

Organic-rich source rock/H2/brine interactions: Implications for underground hydrogen storage and methane production

There is increasing global interest in the attainment of a carbon dioxide-free global economy by replacement of carbon-based fossil fuels with clean hydrogen. But huge volume of hydrogen needs to be stored to address the imbalance between energy demand and supply due to low volumetric energy content of H2. Underground Hydrogen Storage (UHS) is an integral part of the hydrogen economy value chain and an appealing technology for the attainment of global decarbonization. The Jordan oil shale (Upper Cretaceous, organic-rich source rock sequence) has been proposed as a promising geological storage medium for hydrogen due to its exceptionally high organic content because methane can be produced from the reaction of trapped hydrogen with the kerogen. However, the extraction of methane from kerogen during hydrogen storage in organic-rich shale has not yet been reported. In this study, pressurized hydrogen was injected into high TOC shale samples for 80 days at 1500 psi and 75 °C to assess the extent of hydrogen-rock reaction and possible methane production. We also measured H2/brine and CH4/brine interfacial tensions (IFT), as well as the contact angles of H2/brine/shale and CH4/brine/shale systems at 75 °C and varying pressure (500–1500 psi) to understand the shale-fluid interaction at subsurface conditions. Results indicate some reaction of H2 with the shale after 80 days. No hydrogen sulfide was detected from gas chromatography analysis at the end of the experiment, but traces of methane (0.018 %) were detected. The reaction between hydrogen and organic matter of the shale yielded only a little methane under the conditions investigated in this research, possibly because the experimental temperature and reaction time was insufficient for copious methane generation. Furthermore, contact angle values of CH4/brine were found to be higher than of H2/brine. This means that under geo-storage conditions, the surface becomes fully CH4-wet condition (131o-149o) but remains only intermediate-wet in the presence of the H2/brine system (94o -106o) with increasing pressure, confirming that the interaction of methane with the shale surface is higher than hydrogen-shale surface interaction at similar conditions. The opposite trend was observed for IFT values. The hydrogen/brine IFT was 69.4 mN/m at 500 psi but decreased to 67.9 mN/m at 1500 psi. Likewise, the methane/brine IFT decreased from 69.7 mN/m to 58.3 mN/m with increasing pressure from 500 to 1500 psi. The findings of this study contribute to a better understanding of the adsorption trapping potential of organic-rich source rocks.

Impact of nanoparticles–surfactant solutions on carbon dioxide and methane wettabilities of organic-rich shale and CO2/brine interfacial tension: Implication for carbon geosequestration

Rock wetting behaviour and CO2/brine interfacial tension (IFT) have significant impacts on enhanced hydrocarbon recovery (EOR) and carbon geo-sequestration (CGS) projects. Influence of nanoparticles/surfactant solutions (NPS) flooding on EOR and CGS in sandstone and carbonate formation have been examined in recent studies. But the impact of NPS on carbon dioxide (CO2) and methane (CH4) wettabilities of organic-rich shale and CO2/brine IFT is presently unclear. Thus, we measured contact angles, [advancing (θa) and receding (θr)] for CO2/brine and CH4/brine on Marcellus shale with high total organic carbon (14.8 wt%), as well as CO2/brine IFT with Krüss drop shape analyzer (DSA 100) through the sessile drop and pendant drop techniques. Prior to IFT and contact angles measurement, the shale samples were aged in NPS solutions to evaluate the impact of NPS treatment on CO2 geo-storage. Low-cost rice husk silica nanoparticles and saponin surfactant were used for the study due to their environmental friendliness and economic attractiveness. At geo-storage conditions (25 MPa and 353 K), the advancing contact angle of untreated shale was measured as θa=116.22° (CO2-wet condition), whereas the receding contact angle was measured as θr=82.88° (near neutral wettability). However, θa reduced by 56.34° whereas θr reduced by 56.76° when the shale substrate was treated with 0.1 wt% SiO 2 and 0. 2 wt% saponin solutions. CO2/NPS IFT were lower than CO2/brine IFT and the CH4 wettability of the Marcellus shale was significantly lower than the CO2 wettability at all investigated conditions. Contact angles decreased with temperature and increased with CO2/CH4 pressure, whereas CO2/NPS IFT exhibited an opposite trend. The reduction in contact angles and CO2/brine IFT by NPS have significant impacts on adsorption trapping of CO2 in organic-rich shale and hydrocarbon recovery from unconventional shale reservoirs.

The impact of humic acid on hydrogen adsorptive capacity of eagle ford shale: Implications for underground hydrogen storage

Hydrogen is a clean fuel that is anticipated to play a key role to phase-out fossil fuels and consequently decline the global warming challenges. Large-scale Underground Hydrogen Storage (UHS) is a critical link in hydrogen economy, but it is yet to be successfully achieved at industrial scale, and this is presently a main drawback in the hydrogen economy. Organic-rich shale pores have been suggested as promising geo-storage media for underground storage of hydrogen through the adsorption trapping mechanism. The hydrogen (H2) could be stored as an adsorbed phase on the kerogen surface or clay minerals, thus replacing methane (CH4) on adsorption sites during competitive adsorption. Moreover, methane has been suggested as a promising cushion gas for hydrogen. Experimental measurement of the H2 and CH4 adsorptive capacity of shale is essential for precise description of competitive adsorption behavior between CH4 and H2 in shale, as well as in designing of UHS in shale. Thus, adsorption capacities of methane and hydrogen were measured using a PCTpro adsorption analyzer in this study. Since organic acids are inherently present in geo-storage media, H2 and CH4 adsorption capacities in the fresh shale and shale aged with humic acid (Shale-HA) were compared to evaluate the impacts of adsorbed organic acids on their gas adsorption affinities. Our results showed that at 303 K, the adsorption of hydrogen increased by almost 170 % at 2.5 MPa and 350 % at 4.28 MPa in Shale-HA. The H2 adsorption trends on both shale samples are type IV isotherm adsorption curves that increased steeply with pressure but levelled beyond 3.5 MPa. The low-pressure N2 adsorption-desorption isotherms showed a type II adsorption isotherm. The CH4 adsorption capacity in raw shale was uniformly increased more than that of hydrogen, but there is no significant difference in CH4 adsorption capacity in shale-HA. This work provides fundamental data for hydrogen storage in shale reservoirs, thus facilitates full-scale implementation of hydrogen economy.

Cable Bacteria Activity Modulates Arsenic Release From Sediments in a Seasonally Hypoxic Marine Basin.

Eutrophication and global change are increasing the occurrence of seasonal hypoxia (bottom-water oxygen concentration <63 μM) in coastal systems worldwide. In extreme cases, the bottom water can become completely anoxic, allowing sulfide to escape from the sediments and leading to the development of bottom-water euxinia. In seasonally hypoxic coastal basins, electrogenic sulfur oxidation by long, filamentous cable bacteria has been shown to stimulate the formation of an iron oxide layer near the sediment-water interface, while the bottom waters are oxygenated. Upon the development of bottom-water anoxia, this iron oxide “firewall” prevents the sedimentary release of sulfide. Iron oxides also act as an adsorption trap for elements such as arsenic. Arsenic is a toxic trace metal, and its release from sediments can have a negative impact on marine ecosystems. Yet, it is currently unknown how electrogenic sulfur oxidation impacts arsenic cycling in seasonally hypoxic basins. In this study, we presented results from a seasonal field study of an uncontaminated marine lake, complemented with a long-term sediment core incubation experiment, which reveals that cable bacteria have a strong impact on the arsenic cycle in a seasonally hypoxic system. Electrogenic sulfur oxidation significantly modulates the arsenic fluxes over a seasonal time scale by enriching arsenic in the iron oxide layer near the sediment-water interface in the oxic period and pulse-releasing arsenic during the anoxic period. Fluxes as large as 20 μmol m−2 day−1 were measured, which are comparable to As fluxes reported from highly contaminated sediments. Since cable bacteria are recognized as active components of the microbial community in seasonally hypoxic systems worldwide, this seasonal amplification of arsenic fluxes is likely a widespread phenomenon.

Wettability of shale–brine–H2 system and H2-brine interfacial tension for assessment of the sealing capacities of shale formations during underground hydrogen storage

Replacement of fossil fuels with clean hydrogen has been recognized as the most feasible approach of implementing CO2-free hydrogen economy globally. However, large-scale storage of hydrogen is a critical component of hydrogen economy value chain because hydrogen is the lightest molecule and has moderately low volumetric energy content. To achieve successful storage of buoyant hydrogen at the subsurface and convenient withdrawal during the period of critical energy demand, the integrity of the underground storage rock and overlying seal (caprock) must be assured. Presently, there is paucity of information on hydrogen wettability of shale and the interfacial properties of H2/brine system. In this research, contact angles of shale/H2/brine system and hydrogen/brine interfacial tension (IFT) were measured using Krüss drop shape analyzer (DSA 100) at 50 °C and varying pressure (14.7–1000 psi). A modified form of sessile drop approach was used for the contact angles measurement, whereas the H2-brine IFT was measured through the pendant drop method. H2-brine IFT values decreased slightly with increasing pressure, ranging between 63.68° at 14.7 psia and 51.29° at 1000 psia. The Eagle-ford shale with moderate total organic carbon (TOC) of 3.83% attained fully hydrogen-wet (contact angle of 99.9°) and intermediate-wet condition (contact angle of 89.7°) at 14.7 psi and 200 psi respectively. Likewise, the Wolf-camp shale with low TOC (0.30%) attained weakly water-wet conditions, with contact angles of 58.8° and 62.9°, at 14.7 psi and 200 psi respectively. The maximum height of hydrogen that can be securely trapped by the Wolf-camp shale was approximately 325 meters whereas the value was merely 100 meters for the Eagle-ford shale. Results of this study will aid in assessment of hydrogen storage capacity of organic-rich shale (adsorption trapping), as well as evaluation of the sealing potentials of low TOC shale (caprock) during underground hydrogen storage.

CleanEx: A Versatile Automated Methane Preconcentration Device for High-Precision Analysis of 13CH4, 12CH3D, and 13CH3D.

The relative abundance of methane isotopologues offers key insights into the global methane (CH4) cycle. Advances in laser spectroscopy enable routine high-precision measurements even for rare deuterated methane isotopologues, 12CH3D and 13CH3D, provided there are sufficiently high methane amount fractions and reproducible measurement conditions, which can be achieved by CH4 adsorption-desorption techniques. We present a new cryogen-free automated preconcentration device─CleanEx─designed for quantitative extraction of CH4 from large volumes of sample gas and for cleaning by stepwise temperature-controlled desorption to separate interferant gases. We show that CleanEx has the capability to preconcentrate methane by almost 2000-fold from ∼18 L of air. The performance is demonstrated in a range of methane amount fractions between 2 ppm (μmol mol-1), which corresponds to the present-day ambient air, up to 1000 ppm, representative for close to source or process conditions. Advantages over existing devices are a significantly larger primary adsorption trap and a secondary cryo-focusing step, which ensures separation of methane from major atmospheric compounds, i.e., O2, Ar, and CO2. We have demonstrated quantitative extraction of methane, with no significant isotopic fractionation and high repeatability of 0.2‰, 0.6‰, and 0.8‰ (n = 42) for the studied isotopologue ratios, 13CH4/12CH4, 12CH3D/12CH4, and 13CH3D/12CH4, during cryogenic adsorption-desorption on HayeSep D material. The developed device in combination with a suitable laser spectrometer offers a robust and autonomous method for precise continuous monitoring of δ13C-CH4 and δD-CH4 in ambient air and optionally Δ13CH3D in process-derived methane.

Predicted CO2 water rock reactions in naturally altered CO2 storage reservoir sandstones, with interbedded cemented and coaly mudstone seals

Geological storage of CO2 captured from industrial processes such as coal combustion or from direct air capture is part of the transition to low emissions. The Jurassic Precipice Sandstone of the southern Surat Basin, Queensland, Australia, is undergoing feasibility studies for industrial scale CO2 geological storage, however regional data has so far been lacking. Precipice Sandstone reservoir drill core samples from the Southwood 1 and Tipton 153 wells in the southern Surat Basin include favourably quartz rich sandstone regions with quartz grain fracturing. A mudstone layer is also present in the reservoir. The overlying lower section of the Evergreen Formation seals consist of clay rich sandstones, interbedded mudstones, coal layers, Fe-Mg-Mn siderite, and Mg-calcite cemented sandstones. K-feldspars are weathered creating localised secondary porosity and pore filling kaolinite and illite. Layers of coal, pore filling cements, and framework grain compaction introduce vertical heterogeneity. Heavy minerals including pyrite, mixed composition sulphides, and barite are associated with disseminated coals in mudstones. Precipice Sandstone mercury intrusion porosities (MIP) ranged from 9 to 22% with favourably low reservoir injection threshold pressures, and the QEMSCAN measured open porosity between 2 and 22%. Evergreen Formation seal porosities were 7.5 to 16% by MIP or 1 to 19% by QEMSCAN, with the smallest pore throat distribution associated with the low permeability coal rich mudstone. Synchrotron XFM shows Rb mainly hosted in K-feldspars and muscovite, with metals including Mn mainly hosted in siderite. Zn and As are present in sulphides; and calcite and apatite cements mainly hosted Sr. Twenty kinetic geochemical CO2-water-rock models were run for 30 and 1000 years with Geochemist Workbench, with calcite and siderite initially dissolving. In the Precipice Sandstone reservoir variable alteration of carbonates, feldspars and chlorite to kaolinite, silica, siderite and smectite were predicted with the pH remaining below 5.5. CO2 was mineral trapped through alteration of chlorite to siderite in three of the four cases, with −0.02 to 1.43 kg/m3 CO2 trapped after 1000 years. In the calcite and siderite cemented Evergreen Formation seal, plagioclase conversion to ankerite trapped the most CO2 with 2.6 kg/m3 trapped after 1000 years. The Precipice Sandstone in both wells appears to be generally suitable as a storage reservoir, with mineral trapping predicted to mainly occur in the overlying lower Evergreen Formation and in interbedded mudstones. Heterogeneity in interbedded sandstone, mudstone, and coal layers are likely to act as baffles to CO2 and encourage mineral trapping. Quartz grain fractures may influence preferential migration pathways in the reservoir but this would need future experimental investigation. Experimental CO2 water rock reactions to understand porosity and permeability changes were out of scope here but are recommended in future validation, along with investigating the potential for CO2 adsorption trapping in coal and mudstone layers.

Synergetic adsorption–photocatalysis process for water treatment using TiO2 supported on waste stainless steel slag

This study presents an economical and efficient method to decolourise dye wastewater using industrial waste stainless steel slag (SSS). Titanium dioxide was immobilised on SSS by a precipitation–calcination method. Samples with different TiO2 loadings (prepared using either titanium isopropoxide precursor or commercial TiO2 nanoparticles) were used to decolourise an organic contaminant (methylene blue) under dark and UV conditions in aqueous solution, and their adsorption and photocatalytic performances were compared. Samples with 15 and 25 TiO2 wt% prepared by the precursor method had normalised photocatalytic efficiencies per gram close to that of bare TiO2; using an adsorption–photocatalysis process led to efficiencies 4.4 and 1.6 times higher than that of pure TiO2. The improvement in catalytic performance (greater for samples with less than 50% TiO2 content) may be due to better UV absorption ability (related to with the improvement of TiO2 particle dispersion) and the close TiO2 support interaction, which can eventually cause a photocatalysis-enhancing shift towards more negative oxidation potentials. The SSS also acted as an efficient adsorption trap for organic compounds. The pollutant was thus transferred to the TiO2 surface and photodegraded more rapidly and efficiently. The outstanding synergetic adsorption–photocatalysis capacities of TiO2 waste stainless steel slag composites for dye water treatment made the proposed conversion approach have great potential in practical applications.Graphical abstract

Development of Active CO2 Emission Control for Diesel Engine Exhaust Using Amine-Based Adsorption and Absorption Technique

Diesel-powered transportation is considered an efficient method of transportation; this sees the increase in the demand for the diesel engine. But diesel engines are considered to be one of the largest contributors to environmental pollution. The automobile sector accounts for the second-largest source for increasing CO2 emission globally. In this experiment, a suitable postcombustion treatment to control CO2 emission from IC engine exhaust is developed and tested. This work focuses to control CO2 emission by using the chemical adsorbent technique in diesel engine exhaust. An amine-based liquid is used to adsorb the CO2 molecules first and absorb over the amines from the diesel engine exhaust. Three types of amino solutions (L-alanine, L-aspartic acid, and L-arginine) were prepared for 0.3 mole concentrations, and the CO2 absorption investigation is performed in each solution by passing the diesel exhaust. A suitable CO2 adsorption trap is developed and tested for CO2 absorption. The experiments were performed in a single-cylinder diesel engine under variable load conditions. The eddy current dynamometer is used to apply appropriate loads on the engine based on the settings. The AVL DIGAS analyzer was used to measure the CO2, HC, and CO emissions. An uncertainty analysis is carried out on the experimental results to minimize the errors in the results. The effective CO2 reduction was achieved up to 85%, and simultaneous reduction of HC and CO was also observed.

Cost‐Effective Adsorption of Oxidative Coupling‐Derived Ethylene Using a Molecular Sieve

AbstractThe adsorption of ethylene (C2H4) from a mixture simulating the products obtained during the oxidative coupling of CH4 using a commercial molecular sieve (MOS) is investigated. A joint experimental and theoretical approach has been employed. The adsorbent's trapping capacity decreases at higher temperatures, while the breakpoint time drops when the inlet C2H4 concentration increases. The Dubinin‐Radushkevich isotherm model can better describe the adsorption of C2H4 onto the MOS. Pore diffusion is the rate‐determining step given that the Bangham's kinetic model was the more suitable for this adsorption process. Finally, the low activation energy obtained corroborates the predominance of physical adsorption.

Biomass-derived carbon nanospheres decorated by manganese oxide nanosheets, intercalated into polypyrrole, as an inside-needle capillary adsorption trap sorbent for the analysis of linear alkylbenzenes

Carbon nanospheres (CNSs) were derived hydrothermally from biomass (orange peels) and decorated by manganese dioxide (MnO2) nanosheets. The MnO2/CNSs nanocomposite was intercalated into polypyrrole (PPy) during flow-through in-situ electropolymerization of pyrrole on the surface of the inner wall of a stainless-steel needle to prepare an inside-needle capillary adsorption trap (INCAT) device. The surface morphology, thermogravimetric behavior, sorption characteristics, and structure of the MnO2/CNSs@PPy nanocomposite were characterized using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), energy dispersive X-ray analysis (EDX), nitrogen physisorption by the Brunauer-Emmett-Teller (BET) method, dynamic light scattering (DLS) size distribution, and Fourier-transform infrared spectrometry (FT-IR). The INCAT device was coupled with GC-FID and applied for dynamic headspace analysis of linear alkyl benzenes (LABs) in wastewater samples. The effective experimental variables on the extraction efficiency was optimized using a central composite design (CCD) based on response surface methodology (RSM). Under the optimal conditions, the limits of detection (LODs) were in the range of 0.5–1.0 ng mL−1. The calibration plots were linear over the range of 0.01–10 μg mL−1. The relative standard deviations (RSDs%) for intra-day, inter-day, and inter-INCAT precision were calculated 5.3–8.3%, 9.4–13.5%, and 13.6–16.9%, respectively. The developed technique was employed successfully for the analysis of LABs in water and wastewater samples with average recovery values ranging from 92 to 109%. A single INCAT device was used more than 90 times without significant change in its extraction capability.

Hydrolytically Stable and Trifunctional Zirconium-Based Organic Frameworks toward Cr2O72- Detection, Capture, and Photoreduction.

Chromium Cr(VI) is frequently used in many fields and has been intensively researched for detection and/or removal from contaminated water. However, the existing approaches are still of low efficiency, high cost, and cumbersome in operation. It is thus highly imperative to hunt for alternative avenues to get out of the predicament. In this work, two bcu topological and highly stable zirconium-metal-organic frameworks (Zr-MOFs) of 1 and 2 have been deliberately prepared, displaying channel-type interior spaces replete with free bipyridine/biquinoline matrices and Zr-O defect sites. Because of their unique intrinsic features of high porosity and photosensitivity, 1 and 2 were deployed as versatile platforms to sense, adsorb, and catalytically reduce Cr(VI) ions. Indeed, the Zr-MOF of 1 performs excellently in fluorescence sensing and adsorption trapping of Cr(VI), with an ultralow detection limit of 0.0176 ppm and a fairly high saturated adsorption capacity of 145.77 mg/g, while 2 is more powerful than 1 in photochemical removal of Cr(VI), exhibiting a remarkable reduction efficiency of 98.05% just within 70 min and still up to 92.21% even after five consecutive photocatalytic cycles. Furthermore, possible photoluminescence, quenching, and reduction mechanisms were also tentatively proposed. This study may open up a new avenue for addressing some unresolved environmental issues, that is, the decontamination of highly toxic Cr(VI) from water.

Hexagonal Ordered Mesoporous Silica-Coated by Polypyrrole as a Coating for Inside Needle Capillary Adsorption Trap of Polycyclic Aromatic Hydrocarbons

An inside needle capillary adsorption trap based on polypyrrole/hexagonally ordered mesoporous silica was fabricated and used to extract polycyclic aromatic hydrocarbons. Chemical polymerization was used for synthesizing polypyrrole/hexagonally ordered mesoporous silica. Polypyrrole/hexagonally ordered silica was analyzed by scanning electron microscopy and thermo gravimetric methods. The prepared nanoporous material was immobilized into a stainless steel needle to fabrication of the inside needle capillary adsorption trap device. The inside needle capillary adsorption trap device was applied for the extraction of some polycyclic aromatic hydrocarbons from aqueous samples in combination with gas chromatography-mass spectrometry. A simplex method was used for optimization of factors affecting the extraction efficiency of the method. The detection limits of the method under optimized conditions (extraction time of 15 min at 50 °C, sampling flow rate of 5 mLmin−1, NaCl 12% w/v) were in the range of 0.001–0.005 ngmL−1. The relative standard deviations at a concentration level of 1 ngmL−1 were between 3.2% and 10.1% (n = 4).

Evaluation of CO2 Storage in a Shale Gas Reservoir Compared to a Deep Saline Aquifer in the Ordos Basin of China

As a new “sink” of CO2 permanent storage, the depleted shale reservoir is very promising compared to the deep saline aquifer. To provide a greater understanding of the benefits of CO2 storage in a shale reservoir, a comparative study is conducted by establishing the full-mechanism model, including the hydrodynamic trapping, adsorption trapping, residual trapping, solubility trapping as well as the mineral trapping corresponding to the typical shale and deep saline aquifer parameters from the Ordos basin in China. The results show that CO2 storage in the depleted shale reservoir has merits in storage safety by trapping more CO2 in stable immobile phase due to adsorption and having gentler and ephemeral pressure perturbation responding to CO2 injection. The effect of various CO2 injection schemes, namely the high-speed continuous injection, low-speed continuous injection, huff-n-puff injection and water alternative injection, on the phase transformation of CO2 in a shale reservoir and CO2-injection-induced perturbations in formation pressure are also examined. With the aim of increasing the fraction of immobile CO2 while maintaining a safe pressure-perturbation, it is shown that an intermittent injection procedure with multiple slugs of hug-n-puff injection can be employed and within the allowable range of pressure increase, and the CO2 injection rate can be maximized to increase the CO2 storage capacity and security in shale reservoir.

Heating-, Cooling- and Vacuum-Assisted Solid-Phase Microextraction (HCV-SPME) for Efficient Sampling of Environmental Pollutants in Complex Matrices

This research introduces a novel solid-phase microextraction technology, in which the features of heating of sample, cooling of sorbent, and extraction under vacuum condition have been merged. Heating-, cooling- and vacuum-assisted solid-phase microextraction (HCV-SPME) method was developed as an efficient solution for the direct extraction of volatile and semi-volatiles species in complex solid samples. HCV-SPME was coupled with an in-needle capillary adsorption trap (HCV-INCAT) and applied to the direct extraction of polycyclic aromatic hydrocarbons (PAHs) within soil samples. It consisted of polythiophene/carboxylic acid modified multi-walled carbon nanotube nanocomposite, which was synthesized and wall-coated within a platinized stainless-steel needle via electropolymerization. The influential experimental variables (desorption conditions, sample temperature, adsorption temperature, sampling flow rate, and vacuum level) on the extraction efficiency were optimized. The developed HCV-INCAT technique was used in conjunction with GC-FID and applied for the extraction and determination of PAHs in contaminated soil samples, closely matching with those obtained using a validated ultrasonic-assisted solvent extraction procedure. Under the optimal conditions, linear dynamic ranges, limits of detection, and relative standard deviations were obtained 0.007–5 µg g−1, 8–20 pg g−1, and 7.1–12.1%, respectively, for direct extraction of naphthalene, fluorene, phenanthrene, fluoranthene, and pyrene from solid samples.