Efficient CO2 Removal Research Articles

Experimental research on chemical desorption based on CO2-rich absorption solutions

Although CO2 capture by chemical absorption can achieve highly efficient removal of CO2 from flue gas, the energy consumption of absorbent regeneration is high, and the CO2 after desorption need to be compressed, transported and sequestrated. To reduce energy consumption and sequestrate CO2 at low cost, an CO2 desorption process was developed, in which the CO2-rich solutions was regenerated and CO2 was sequestrated in the form of CaCO3. Five kinds of CO2-rich solutions, monoethanolamine (MEA), methyldiethanolamine (MDEA), potassium glycinate (PG), MDEA/MEA and MDEA/PG were investigated by adding calcium hydroxide. The optimum reaction condition, which CO2 loading was 0.621 mol/L and Ca(OH)2 dosage was 1:1 for desorption of CO2-rich solution, was determined. And the effects of three parameters (time, temperature and stirring rate) on CO2 desorption rate were further analyzed. The optimum reaction temperature for the amine absorbents and the amino acid salt solvents were 20℃ and 50℃, respectively. The optimum reaction time and standing time were 30 min, respectively, and the optimum stirring rate was 800 r/min. MEA exhibited the highest desorption rate (85.31%) among the five solutions. In addition, the results of multicycle-cycle experiments showed that the MEA lean solution desorbed by chemical desorption still had excellent absorption capacity. Compared with the conventional thermal desorption process, the chemical desorption process had great advantages for CO2-rich solutions regeneration and did not require further treatment of CO2.

CO2 sorption using encapsulated imidazolium-based fluorinated ionic liquids

The development and testing of new sorbents for the efficient removal of CO2 from flue gases is essential. Encapsulated room-temperature ionic liquids (RTILs) can be potentially employed in CO2 capture. In this work, we report the preparation and characterization of encapsulated imidazolium-based fluorinated RTILs for CO2 capture. [Emim][TF2N], [Bmim][TF2N], and [Hmim][TF2N] RTILS were encapsulated in polysulfone (PSF) using an emulsification method and characterized by several techniques. The pressure-decay technique was used to assess the CO2 sorption capacity and reusability. Encapsulated RTILs showed improved utility for CO2 capture processes compared with non-encapsulated RTILs, including higher CO2 sorption capacity and faster CO2 sorption/desorption. The CO2 absorption/desorption cycles demonstrated the reuse capacity of all microcapsules under mild conditions. The highest CO2 sorption capacity was noted for encapsulated [Emim][TF2N] (39.5 mg CO2 g−1 at 298.15 K and 1 bar; 62.7 mg CO2 g−1 at 298.15 K and 10 bar). It is worth emphasizing that the encapsulated [Emim][TF2N] contained a lower ionic liquid (IL) content (37.5. ± 0.6) when compared to other encapsulated samples. Moreover, encapsulated [Emim][TF2N] presented a higher CO2 affinity than the encapsulated ILs reported in the literature.

A Ca-Cu Chemical Loop Process for CO2 Capture in Steel Mills: System Performance Analysis

The conceptual design and modelling of the Calcium Assisted Steel-mill Off-gas Hydrogen (CASOH) process for the conversion of blast furnace gas (BFG) into H2-rich stream and CO2-rich stream at a large scale is discussed in this work. High temperature reactors packed with CaO- and Cu-based materials are used to remove CO2 from the gaseous phase and simultaneously shifting the WGS equilibrium towards H2-rich products. The incorporation of a Cu/CuO chemical loop to such sorption process allows an efficient regeneration of the CO2 sorbent. In this case, the heat needed for the calcination of the CaCO3 is supplied in situ by the exothermic reduction of CuO to Cu with a gaseous fuel (e.g. CH4, CO or H2). The Cu-based solid is firstly converted to CuO(s) during the oxidation step with air and later reduced during the regeneration step, which involves the combination of the endothermic reaction of CaCO3(s) calcination and the exothermic gas-solid reduction of CuO(s) to Cu(s) using a gaseous fuel (typically BFG or natural gas producing a highly concentrated stream of CO2 and H2O(v)). In this paper, the three reaction stages of the CASOH process are modelled with a new 1-D reactor model that integrates state of the art kinetic information on the gas solid reactions, predicting the molar composition of the product gases (dry basis) at the outlet of the packed-bed reactor and maximum temperature achieved in each stage. The 1-D reactor modelling results confirm that process allows the conversion of up to 99% of the inlet CO to H2 at intermediate temperatures (about 650 °C), because of the efficient and continuous removal of CO2 from the gas phase. The high pressure (10 bar) during the Cu-oxidation step causes a very low leakage of CO2 (1.1 vol. %) due to the partial calcination of CaCO3, i.e. only 8 wt. % of the CaCO3 is calcined in this stage. Finally, the feed of BFG as reducing gas during the regeneration stage leads to a maximum temperature of 850 °C in the bed, which allows the complete calcination of the sorbent and gives as a result a CO2-rich stream ready for purification and subsequent use or storage.

Alkalinization Scenarios in the Mediterranean Sea for Efficient Removal of Atmospheric CO2 and the Mitigation of Ocean Acidification

It is now widely recognized that in order to reach the target of limiting global warming to well below 2°C above pre-industrial levels (as the objective of the Paris agreement), cutting the carbon emissions even at an unprecedented pace will not be sufficient, but there is the need for development and implementation of active Carbon Dioxide Removal (CDR) strategies. Among the CDR strategies that currently exist, relatively few studies have assessed the mitigation capacity of ocean-based Negative Emission Technologies (NET) and the feasibility of their implementation on a larger scale to support efficient implementation strategies of CDR. This study investigates the case of ocean alkalinization, which has the additional potential of contrasting the ongoing acidification resulting from increased uptake of atmospheric CO2 by the seas. More specifically, we present an analysis of marine alkalinization applied to the Mediterranean Sea taking into consideration the regional characteristics of the basin. Rather than using idealized spatially homogenous scenarios of alkalinization as done in previous studies, which are practically hard to implement, we use a set of numerical simulations of alkalinization based on current shipping routes to quantitatively assess the alkalinization efficiency via a coupled physical-biogeochemical model (NEMO-BFM) for the Mediterranean Sea at 1/16° horizontal resolution (~6 km) under an RCP4.5 scenario over the next decades. Simulations suggest the potential of nearly doubling the carbon-dioxide uptake rate of the Mediterranean Sea after 30 years of alkalinization, and of neutralizing the mean surface acidification trend of the baseline scenario without alkalinization over the same time span. These levels are achieved via two different alkalinization strategies that are technically feasible using the current network of cargo and tanker ships: a first approach applying annual discharge of 200 Mt Ca(OH)2 constant over the alkalinization period and a second approach with gradually increasing discharge proportional to the surface pH trend of the baseline scenario, reaching similar amounts of annual discharge by the end of the alkalinization period. We demonstrate that the latter approach allows to stabilize the mean surface pH at present day values and substantially increase the potential to counteract acidification relative to the alkalinity added, while the carbon uptake efficiency (mole of CO2 absorbed by the ocean per mole of alkalinity added) is only marginally reduced. Nevertheless, significant local alterations of the surface pH persist, calling for an investigation of the physiological and ecological implications of the extent of these alterations to the carbonate system in the short to medium term in order to support a safe, sustainable application of this CDR implementation.

Low viscosity superbase protic ionic liquids for the highly efficient simultaneous removal of H2S and CO2 from CH4

CO2 and H2S are considered impurities in natural gas that moderate the pace of environmental health. Developing highly efficient and cost-effective absorbents is of significance for sweetening natural gas. Herein, four superbase protic ionic liquids (SPILs) were prepared in this study. Typical physical properties (density, viscosity, and decomposition temperature) were also examined at ambient pressure. These SPILs show low viscosity values at ranging from 5.1 cP to 18.3 cP at 313.2 K. The solubility of H2S (0–1.0 bar), CO2 (0–1.0 bar), and CH4 (0–5.0 bar) was systematically measured at temperatures in the range of 298.2 K to 333.2 K. Impressively, the absolute solubility of H2S under 0.1 bar was found to be located at 4.31–5.15 mol/kg at 313.2 K, which is the highest value obtained among the reported results in the literature. The ideal selectivity of H2S/CH4 and CO2/CH4 (H2S or CO2 solubility at 0.1 bar vs CH4 solubility at 1 bar) at 313.2 K are in the ranges of 367–653 and 92.4–240, respectively. The interaction mechanism we explored was characterized by NMR and FT-IR spectroscopy. Thermodynamic parameters, such as enthalpy, Gibbs free energy, and entropy of dissolution were calculated from the temperature dependent solubility using the “deactivated model”. These SPILs are promising alternative candidates for the simultaneous removal of H2S and CO2 in natural gas upgrading.

Efficient removal of Co(II) and Sr(II) from aqueous solution using polyvinyl alcohol/graphene oxide/MnO2 composite as a novel adsorbent

In this study, a novel adsorbent, polyvinyl alcohol/graphene oxide/MnO2 composite was prepared, characterized and used for efficient removal of Co2+ and Sr2+ from aqueous solution. Polyvinyl alcohol (PVA) and Mn2+ played a synergistic role in the gelation of PVA/GO/Mn2+, while Mn2+ can be further converted into oxide to achieve functionalized aerogel (PVA/GO/MnO2). The spectroscopy analysis manifested that hydrogen bonds and electrostatic attraction were responsible for the formation of PVA/GO/MnO2. The functionalization of MnO2 enhanced the adsorption capacity for Co2+ (2.1 folds) and Sr2+ (1.3 folds) by PVA/GO/MnO2. The composite showed high adsorption capacity at broad pH range of 4.0–9.0. For competitive adsorption test, Ni2+/Zn2+ exerted the most interfering effect on Co2+ adsorption, while Mg2+/Ca2+ showed severe interfering effect on Sr2+ adsorption. Both electrostatic attraction and oxygen-containing groups contributed to the adsorption mechanism. This study may provide a new adsorbent for separation of Co2+ and Sr2+ from aqueous solution.

One-step synthesis of microporous nitrogen-doped biochar for efficient removal of CO2 and H2S

It is still a great challenge to prepare an ideal adsorbent for the removal of CO2 and H2S from biogas efficiently. In this study, urea phosphate (UP) was selected as both activator and nitrogen (N) source to prepare the biochar adsorbent from plant biomass with microporous structure and N-rich functional groups through “one-step” synthesis. The results show that the yield of biochar increased from about 20% to 50%, and the SBET and Vmic of the obtained biochar were 1189 m2/g and 0.433 cm3/g, respectively, which was much higher than those without UP addition (524 m2/g and 0.17 cm3/g). Moreover, N was successfully doped on the surface of biochar, and the N content was up to 4.24 at.% with the majority of basic species such as pyridinic and pyrrolic N. This could be attributed to a large amount of N-containing functional groups and phosphoric acid released gradually at the presence of UP during the heating process. The prepared biochar exhibited good CO2 and H2S adsorption capacities up to 1.34 mmol/g and 54.8 mg/g, respectively, which was much higher than those without UP addition (0.958 mmol/g and 0.24 mg/g). The excellent adsorption properties of CO2 and H2S were tightly related to the improved microporous structure and surface basic N-containing functional groups on the biochar.

Magnetically Functionalized Moss Biomass as Biosorbent for Efficient Co2+ Ions and Thioflavin T Removal.

Microwave synthesized iron oxide nanoparticles and microparticles were used to prepare a magnetically responsive biosorbent from Rhytidiadelphus squarrosus moss for the rapid and efficient removal of Co2+ ions and thioflavin T (TT). The biocomposite was extensively characterized using Fourier transformed infrared (FTIR), XRD, SEM, and EDX techniques. The magnetic biocomposite showed very good adsorption properties toward Co2+ ions and TT e.g., rapid kinetics, high adsorption capacity (218 μmol g−1 for Co and 483 μmol g−1 for TT), fast magnetic separation, and good reusability in four successive adsorption–desorption cycles. Besides the electrostatic attraction between the oxygen functional moieties of the biomass surface and both Co2+ and TT ions, synergistic interaction with the –FeOH groups of iron oxides also participates in adsorption. The obtained results indicate that the magnetically responsive biocomposite can be a suitable, easily separable, and recyclable biosorbent for water purification.

Efficient removal of CO2 from indoor air using a polyethyleneimine-impregnated resin and its low-temperature regeneration

Aminated adsorbents are efficient in capturing high concentrations of CO2, while their efficiency in air purifier for the removal of low concentrations of CO2 from indoor air remains unclear. In this study, a polyethyleneimine-impregnated resin (PEI-MR10) was prepared and used to remove indoor CO2, and its regeneration at low temperatures was evaluated. PEI loading narrowed the pore size distribution but increased the average pore size of the PEI-MR10. The PEI-MR10 with small particle size (0.250–0.425 mm) exhibited higher adsorption capacity and faster adsorption rate than the bigger one. The PEI-MR10 was able to remove all CO2 during the first 2 h with an initial CO2 concentration of 1000 ppm. Under variable indoor conditions, the adsorbed amounts of CO2 could maintain high values from 90 to 136 mg/g. At a relative humidity of 50%, the adsorbed amount on the PEI-MR10 for 1000 ppm CO2 reached 128.4 mg/g. In consideration of real application in air purifier, a cost-effective regeneration method using ambient air was adopted, and the spent PEI-MR10 was regenerated at low temperatures no more than 70 °C. The desorption efficiency of CO2 increased with increasing temperatures, and the best regeneration was obtained at 70 °C. The adsorbed amount of CO2 on the first-regenerated PEI-MR10 decreased significantly, but the adsorbent maintained stable adsorption capacity of about 80 mg/g after three adsorption-regeneration cycles. This study demonstrated that PEI-MR10 was an effective adsorbent for CO2 removal from indoor air.

A hydrostable cage-based MOF with open metal sites and Lewis basic sites immobilized in the pore surface for efficient separation and purification of natural gas and C2H2.

Design and construction of stable adsorbents for efficient separation and purification of natural gas and C2H2 is fundamentally important in the chemical industry, and hierarchical cage-based MOFs are attractive in this regard due to their intrinsic structural advantages. In this work, a cage-based MOF (termed ZJNU-15) assembled from a tetranuclear Cu4O-based SBU and an amine-functionalized N,O-mixed donor ligand was solvothermally constructed. Single-crystal X-ray diffraction studies showed that the resulting MOF incorporates two different types of polyhedral cages in the entire network and bears incompatible open copper sites and uncoordinated amine groups immobilized in the pore surface. In view of its intriguing structural features, its gas adsorption properties with respect to C2 hydrocarbons, CO2, and CH4 were systematically investigated, revealing that it could achieve efficient removal of C2 hydrocarbons and CO2 from CH4 as well as separation of a binary C2H2-CO2 mixed gas, which is associated with natural gas and C2H2 separation and purification. At 298 K and 1 atm, for equimolar binary components, the IAST-predicted adsorption selectivities for C2 hydrocarbons over CH4 are above 17.7, while the CO2/CH4 and C2H2/CO2 adsorption selectivities are 5.0 and 4.4, respectively. Notably, stability studies showed that the framework maintained its structural integrity after being immersed in HCl/NaOH aqueous solutions within a pH range of 4-11 at ambient temperature for 24 h, indicating its good hydrolytic stability under harsh chemical conditions, which might lay a solid foundation for its practical applications.

Intrinsic Thermal Desorption in a 3D Printed Multifunctional Composite CO2 Sorbent with Embedded Heating Capability.

Efficient removal of CO2 from enclosed environments is a significant challenge, particularly in human space flight where strict restrictions on mass and volume are present. To address this issue, this study describes the use of a multimaterial, layer-by-layer, additive manufacturing technique to directly print a structured multifunctional composite for CO2 sorption with embedded, intrinsic, heating capability to facilitate thermal desorption, removing the need for an external heat source from the system. This multifunctional composite is coprinted from an ink formulation based on zeolite 13X, and an electrically conductive sorbent ink formulation, which includes metal particles blended with the zeolite. The composites are characterized using analytical and imaging tools and then tested for CO2 adsorption/desorption. The resistivity of the conductive sorbent is <2 mΩ m, providing a temperature increase up to 200 °C under 7 V applied bias, which is sufficient to trigger CO2 desorption. The CO2 adsorption capability of the conductive zeolite ink appears to be unaffected by the presence of the conductive particles, meaning a large fraction of the total mass of the structured composite device is functional.

Membrane gas-solvent contactors undergoing oscillating solvent flow for enhanced carbon dioxide capture

Membrane gas-solvent contactors are a hybrid approach that combine membrane gas separation with solvent absorption to undertake highly efficient CO2 removal. However, solvent boundary layer in many gas-solvent membrane contactors has a high mass transfer resistance to CO2 capture. Here, for the first time, an oscillating solvent flow was applied to a polydimethylsiloxane (PDMS) membrane contactor system to enhance the absorption of CO2. The oscillating solvent flow enhanced the overall mass transfer coefficient of CO2 (Kov) compared to the non-oscillating solvent flow. The effect of the oscillating solvent frequency and amplitude on Kov was investigated. Increasing the oscillating frequency from 0.83 Hz to 2.03 Hz resulted in 53% enhancement in Kov. Doubling the value of the oscillating amplitude increased Kov by 30%. An oscillating Reynolds number (Reos) was introduced to the oscillating solvent flow described by the root mean square oscillating solvent velocity (uos,rms). Using this Reynolds number, a Sherwood number correlation (Shos) was proposed for the hollow fibre membrane contactor, which accounted for the enhancement effects of solvent oscillation on the performance of gas-solvent membrane contactor.

Selective Gas Permeation in Mixed Matrix Membranes Accelerated by Hollow Ionic Covalent Organic Polymers

Mixed matrix membranes (MMMs) have gained great attention for the efficient CO2 removal from raw nature gas or biogas (CO2/CH4 separation) and flue gas (CO2/N2 separation). Nevertheless, the development of high-performance MMMs for industrial applications is largely limited by the lack of suitable porous fillers. Herein, a novel ionic covalent organic polymer (ICOP-1) consisting of gas selective pores and hollow cavities is facilely fabricated using a metal triflate catalyzed condensation reaction. Considering its unique structural properties, ICOP-1 is explored as a novel filler to enhance the gas separation properties of polysulfone (PSf) membranes. Defect-free MMMs are successfully prepared owing to the high polymer–filler affinity originating from the organic nature of these two phases. Besides, the large cavities and size-selective pores of ICOP-1 lead to a simultaneous increase in membrane CO2 permeability and CO2/CH4, CO2/N2 selectivities. With the addition of only 0.5 wt % of ICOP-1 fillers, the a...

Experimental Investigation of the Gas/Liquid Phase Separation Using a Membrane-Based Micro Contactor

The gas/liquid phase separation of CO2 from a water-methanol solution at the anode side of a µDirect-Methanol-Fuel-Cell (µDMFC) plays a key role in the overall performance of fuel cells. This point is of particular importance if the µDMFC is based on a “Lab-on-a-Chip” design with transient working behaviour, as well as with a recycling and a recovery system for unused fuel. By integrating a membrane-based micro contactor downstream into the µDMFC, the efficient removal of CO2 from a water-methanol solution is possible. In this work, a systematic study of the separation process regarding gas permeability with and without two-phase flow is presented. By considering the µDMFC working behaviour, an improvement of the overall separation performance is pursued. In general, the gas/liquid phase separation is achieved by (1) using a combination of the pressure gradient as a driving force, and (2) capillary forces in the pores of the membrane acting as a transport barrier depending on the nature of it (hydrophilic/hydrophobic). Additionally, the separation efficiency, pressure gradient, orientation, liquid loss, and active membrane area for different feed inlet temperatures and methanol concentrations are investigated to obtain an insight into the separation process at transient working conditions of the µDMFC.

Efficient CO2 removal using extracorporeal lung and renal assist device.

We developed a novel system comprising acid infusion, membrane lung, and a continuous renal replacement therapy console for efficient CO2 removal at a low blood flow. To evaluate the new system, we used an ex vivo experimental model using swine blood. A liter of aliquoted blood adjusted to pH 7.25 and pCO2 65mm Hg was mixed with acid (0, 10, or 20mL of lactic or hydrochloric acid [1mol/L]) and was immediately delivered to the system in a single pass. We collected blood samples at each point of the circuit and calculated the amount of CO2 eliminated by the membrane lung. The new system removed 13.2 ± 0.8, 32.0 ± 2.1, and 51.6 ± 3.7mL/min of CO2 (with 0, 10, and 20mEq/L of lactic acid) and 21.2 ± 1.2, 27.3 ± 0.3, and 42.0 ± 1.3mL/min (with 0, 10, and 20mEq/L of hydrochloric acid), respectively. The levels of lactate and Cl- ions for acid-base equilibrium were restored after continuous hemodiafiltration. Thus, the amount of CO2 eliminated by the membrane lung was 3.9 times higher with lactic acid and 2.0 times higher with hydrochloric acid compared with non-acid controls. In conclusion, this easy-to-setup CO2 removal system was safe, effective, and removed CO2 at a low blood flow.

Molecular Dynamics Study of the Solution Structure, Clustering, and Diffusion of Four Aqueous Alkanolamines.

CO2 sequestration from anthropogenic resources is a challenge to the design of environmental processes at a large scale. Reversible chemical absorption by amine-based solvents is one of the most efficient methods of CO2 removal. Molecular simulation techniques are very useful tools to investigate CO2 binding by aqueous alkanolamine molecules for further technological application. In the present work, we have performed detailed atomistic molecular dynamics simulations of aqueous solutions of three prototype amines: monoethanolamine (MEA) as a standard, 3-aminopropanol (MPA), 2-methylaminoethanol (MMEA), and 4-diethylamino-2-butanol (DEAB) as potential novel CO2 absorptive solvents. Solvent densities, radial distribution functions, cluster size distributions, hydrogen-bonding statistics, and diffusion coefficients for a full range of mixture compositions have been obtained. The solvent densities and diffusion coefficients from simulations are in good agreement with those in the experiment. In aqueous solution, MEA, MPA, and MMEA molecules prefer to be fully solvated by water molecules, whereas DEAB molecules tend to self-aggregate. In a range from 30/70-50/50 (w/w) alkanolamine/water mixtures, they form a bicontinuous phase (both alkanolamine and water are organized in two mutually percolating clusters). Among the studied aqueous alkanolamine solutions, the diffusion coefficients decrease in the following order MEA > MPA = MMEA > DEAB. With an increase of water content, the diffusion coefficients increase for all studied alkanolamines. The presented results are a first step for process-scale simulation and provide important qualitative and quantitative information for the design and engineering of efficient new CO2 removal processes.

Clay honeycomb monoliths as low cost CO2 adsorbents

Clay honeycomb monoliths were manufactured from a natural montmorillonite and used for CO2 adsorption, their performance being compared with that of the same clay but in the form of powder. Volumetric adsorption isotherms, thermogravimetric studies, temperature-programmed desorption experiments and transient kinetic analysis, the two latter followed by mass spectrometry, were employed to investigate the interaction of the samples with CO2, both under static and dynamic conditions, and at different temperatures. This research demonstrated that the honeycomb monoliths kept the adsorptive properties of the starting material in terms of capture capacity (around 15 mg/g), Henry constant, heat of adsorption and activation energy. Most of retained CO2 was weakly adsorbed, the temperature needed for its release being 130 °C, an appropriate value which is sufficiently high to avoid undesirable desorption while being low enough to minimize the costs derived from controlled regeneration for further CO2 reuse. The kinetics of the CO2 uptake over the monolith (though of second order like over the powder) was slightly different, allowing a wider operative window for a highly efficient CO2 removal. These results suggest the potential of the honeycomb monolithic design for an even more competitive use of clays as low cost CO2 filters.

Correction: Efficient Removal of Co2+ from Aqueous Solution by 3-Aminopropyltriethoxysilane Functionalized Montmorillonite with Enhanced Adsorption Capacity

[This corrects the article DOI: 10.1371/journal.pone.0159802.].

Supported lithium hydroxide for carbon dioxide adsorption in water-saturated environments

Rebreather-type personal protective equipment requires efficient removal of CO2 from the air that the user exhales. The required operating conditions of low CO2 partial pressure, low temperature, and water saturation create a challenging environment for developing high capacity CO2 adsorbents. Biphasic adsorbents of lithium hydroxide supported on high surface area carbons were synthesized and tested for CO2 capacity under water-saturated conditions. The LiOH phase provides high CO2 capacity through chemisorption while the porous carbon structure helps prevent the formation of diffusion barriers that limit the effectiveness of pure LiOH pellets. Several carbons with different pore morphology were tested, and it was determined that the ideal support has a high degree of mesoporosity that balances the need for high surface area without excess blockage of pore volume upon deposition of LiOH. The activated carbon Norit SX Ultra was chosen based on this criterion. It was found that the maximum achievable loading of LiOH on Norit SX Ultra was 30 wt%, and the highest CO2 capacity under water-saturated conditions at atmospheric pressure with one mole percent CO2 in the gas phase was 3.4 mol/kg.

Efficient Removal of Co2+ from Aqueous Solution by 3-Aminopropyltriethoxysilane Functionalized Montmorillonite with Enhanced Adsorption Capacity.

To achieve a satisfactory removal efficiency of heavy metal ions from wastewater, silane-functionalized montmorillonite with abundant ligand-binding sites (-NH2) was synthesized as an efficient adsorbent. Ca-montmorillonite (Ca-Mt) was functionalized with 3-aminopropyl triethoxysilane (APTES) to obtain the APTES-Mt products (APTES1.0CEC-Mt, APTES2.0CEC-Mt, APTES3.0CEC-Mt, APTES4.0CEC-Mt) with enhanced adsorption capacity for Co2+. The physico-chemical properties of the synthesized adsorbents were characterized by spectroscopic and microscopic methods, and the results demonstrated that APTES was successfully intercalated into the gallery of Ca-Mt or grafted onto the surface of Ca-Mt through Si-O bonds. The effect of solution pH, ionic strength, temperature, initial concentrations and contact time on adsorption of Co2+ by APTES-Mt was evaluated. The results indicated that adsorption of Co2+ onto Ca-Mt, APTES1.0CEC-Mt and APTES2.0CEC-Mt can be considered to be a pseudo-second-order process. In contrast, adsorption of Co2+ onto APTES3.0CEC-Mt and APTES4.0CEC-Mt fitted well with the pseudo-first-order kinetics. The adsorption isotherms were described by the Langmuir model, and the maximum adsorption capacities of APTES1.0CEC-Mt, APTES2.0CEC-Mt, APTES3.0CEC-Mt and APTES4.0CEC-Mt were 25.1, 33.8, 61.6, and 61.9 mg·g-1, respectively. In addition, reaction temperature had no impact on the adsorption capacity, while both the pH and ionic strength significantly affected the adsorption process. A synergistic effect of ion exchange and coordination interactions on adsorption was observed, thereby leading to a significant enhancement of Co2+ adsorption by the composites. Thus, APTES-Mt could be a cost-effective and environmental-friendly adsorbent, with potential for treating Co2+-rich wastewater.