CO_2 adsorption performance of different amine-based siliceous MCM-41 materials

A series of amine-based adsorbents were synthesized using siliceous MCM-41 individually impregnated with four different amines（ethylenediamine（EDA）,diethylenetriamine（DETA）,tetraethylenepentamine（TEPA） and pentaethylenehexamine（PEHA）） to study the effect of amine chain length and loading weight on their CO2 adsorption performances in detail.The adsorbents were characterized by FT-IR,elemental analysis,and thermo-gravimetric analysis to confirm their structure properties.Thermo-gravimetric analysis was also used to evaluate the CO2 adsorption performance of adsorbents.Longer chain amine-based materials can achieve higher amine loadings and show better thermal stability.The CO2 adsorption capacities at different temperatures indicate that the CO2 adsorption is thermodynamically controlled over EDAMCM41 and DETA-MCM41,while the adsorption over TEPA-MCM41 and PEHA-MCM41 is under kinetic control at low temperature.The chain length of amines affects the CO2 adsorption performance and the adsorption mechanism significantly.The results also indicate that CO2 adsorption capacity can be enhanced despite of high operation temperatures,if appropriate amines（TEPA and PEHA） are applied.However,adsorbents with short chain amine exhibit higher adsorption and desorption rates due to the collaborative effect of rapid reaction mechanisms of primary amines and less diffusion resistance of shorter chain length amines.

Enhancement of CO_2 adsorption on nanoporous chromium terephthalate(MIL-101) by amine modification

Carbon dioxide （CO2） adsorption on a standard metal-organic framework MIL-101 and a pentaethylenehexamine modified MIL-101 （PEHA- MIL-101） are investigated and compared in this study. The adsorbent samples were characterized by XRD, FT-IR and nitrogen adsorption- desorption isotherms analysis. CO2 adsorption capacity was measured by a volumetric method. MIL-101 and PEHA-MIL-101 exhibited CO2 adsorption capacities of 0.85 and 1.3 mmO1CO2/gadsorbent at 10 bar and 298 K, respectively. It is observed that CO2 adsorption capacity was fairly improved about 50% after amine modification.

Review on porous nanomaterials for adsorption and photocatalytic conversion of CO_2

Photocatalytic conversion of“greenhouse gas”CO2is considered to be one of the most effective ways to alleviate current energy and environmental problems without additional energy consumption and pollutant emission.The performance of many traditional semiconductor photocatalysts is not efficient enough to satisfy the requirements of practical applications because of their limited specific surface area and low CO2adsorption capacity.Therefore,the exploration of photocatalysts with high CO2uptake is significant in the field of CO2conversion.Recently the porous materials appeared to be a kind of superior candidate for enriching the CO2molecules on the surface of photocatalysts for catalytic conversion.This paper first summarizes the advances in the development of nanoporous adsorbents for CO2capture.Three main classes of porous materials are considered:inorganic porous materials,metal organic frameworks,and microporous organic polymers.Based on systematic research on CO2uptake,we then highlight the recent progress in these porous‐material‐based photocatalysts for CO2conversion.Benefiting from the improved CO2uptake capacity,the porous‐material‐based photocatalysts exhibited remarkably enhanced efficiency in the reduction of CO2to chemical fuels,such as CO,CH4,and CH3OH.Based on reported recent achievements,we predict a trend of development in multifunctional materials with both high adsorption capability and photocatalytic performance for CO2utilization.

Construction of a Pillared-layer Framework Based on Charge Balance:CO2 Adsorption and Luminescence

Via the strategy of charge balance,one new pillared layered metal-organic framework [Zn2（TNB）（2-nim）]（H3TNB = 4,4？,4？？-nitrilotribenzoicacid,2-nim = 2-nitroimidazole）（1） was successfully synthesized based on mixed ligands,where binuclear [Zn2（CO2）3]~＋ cluster-based cationic layers [Zn2（TNB）]~＋ are connected by deprotonated 2-nitroimidazole.Meanwhile,CO2 adsorption bahaviors and luminescent property of compound 1 were investigated.

Direct Synthesis of Amine-functionalized Mesoporous Silica for CO_2 Adsorption

Amine-functionalized mesoporous silica was prepared by using lauric acid and N-stearoyl-l-glutamic acid as structure directing agents via the S-N+-I- mechanism and applied to CO2 adsorption at room temperature. With γ-aminopropyltriethoxysilane as co-structure directing agent and due to the direct electrostatic interaction with anionic surfactant, most of the amino groups were uniformly distributed at the inner surface of pores and the per- formance was stable. The amine-functionalized mesoporous silica was characterized by Fourier transform infrared spectrometer, X-ray diffraction, nitrogen physisorption and thermogravimetric analysis. The CO2 adsorption capacity was measured by digital recording balance. At the room temperature and under the atmospheric pressure, the adsorption capacity of LAA-AMS-0.2 for CO2 and N2 is 1.40 mmol·g-1 and 0.03 mmol·g-1, respectively, indicating high separation coefficient of CO2/N2.

A Doubly Interpenetrated Co(Ⅱ) Framework：Synthesis,Crystal Structure and Selective Adsorption of CO_2

A novel,porous and doubly interpenetrated MOF（FJU-29） was synthesized and characterized by FT-IR,TGA and X-ray single-crystal/powder diffraction.FJU-29 crystallizes in monoclinic,space group C2/c with a = 22.2890（7）,b = 10.9175（2）,c = 21.5601（7） ？,β = 112.908（4）o,V = 4832.7（3） ？~3,Z = 8,Mr = 450.26,D_c = 1.238 g/cm^3,F（000） = 1832,μ（CuKα） = 5.885 mm^（-1）,R = 0.0585 and wR = 0.1544 for 4789 observed reflections（I 〉 2s（I））,and R = 0.0726 and wR = 0.1627 for all data.FJU-29 possesses paddle-wheel {Co_2（COO）_4} clusters bridged by bi-pyrazolate naphthalene diimide ligands（H_2NDI） and H_2BDC to from a 3D framework with a pcu-topology.The desolvated FJU-29a shows the BET surface area of 560.44 m^2·g^（-1） accompanies with discriminating uptakes in CO_2 and N_2.The adsorption selectivity determined by ideal adsorbed solution theory（IAST） indicated that FJU-29 a has high CO_2/N_2（18/85） selectivity（75.5） at 296 K and 100 kPa.The relatively high selectivity further implies that FJU-29 a is a potential material for practical flue gas purification.

Synthesis,gas adsorption and reliable pore size estimation of zeolitic imidazolate framework-7 using CO_2 and water adsorption

Reliable estimation of the pore size distribution(PSD) in porous materials such as metal–organic frameworks(MOFs) and zeolitic imidazolate frameworks(ZIFs) is crucial for accurately assessing adsorption capacity and corresponding selectivity. In this study, the so-called zeolitic imidazolate framework-7(ZIF-7) is successfully synthesized via relatively fast and convenient microwave technique. The morphology and structure of the obtained MOF were characterized by XRD, SEM and N_2 and CO_2adsorption/desorption isotherms at 77 K and0 °C respectively. Then, to determine the PSD of the fabricated MOF, carbon dioxide isotherms are experimentally measured at various temperatures up to atmospheric pressure. Afterward, the experimental CO_2 isotherms data are utilized in two recently proposed in-house algorithms of SHN1 and SHN2 to extract the true PSD of manufactured ZIF-7. The obtained results revealed that median pore diameter of the fabricated ZIF-7 is estimated around 0.404 nm and 0.370 nm by using CO_2 isotherms at 273 K and 298 K respectively. These values are in good agreement with the real pore diameter of 0.42 nm. Moreover, experimental data of water adsorption isotherms over four different MOFs, borrowed from literature, are employed to illustrate further effectiveness of the above algorithms on successful determination of the corresponding pore size distributions. All predicted PSDs are proved to be in good agreement with those obtained from independent methods such as topology and morphology studies.

Preferential adsorption behaviour of CH_4 and CO_2 on high-rank coal from Qinshui Basin,China

In order to better understand the prevailing mechanism of CO2 storage in coal and estimate CO2 sequestration capacity of a coal seam and enhanced coalbed methane recovery （ECBM） with CO2 injection into coal, we investigated the preferential adsorption of CH4 and CO2 on coals. Adsorption of pure CO2, CH4 and their binary mixtures on high-rank coals from Qinshui Basin in China were employed to study the preferential adsorption behaviour. Multiple regression equations were presented to predict CH4 equi- librium concentration from equilibrium pressure and its initial-composition in feed gas. The results show that preferential adsorption of CO2 on coals over the entire pressure range under competitive sorption conditions was observed, however, preferential adsorption of CH4 over CO2 on low-volatile bituminous coal from higher CH4-compostion in source gas was found at up to 1O MPa pressure. Preferential adsorp- tion of CO2 increases with increase of CH4 concentration in source gas, and decreases with increasing pressure. Although there was no systematic investigation of the effect of coal rank on preferential adsorp- tion, there are obvious differences in preferential adsorption of gas between low-volatile bituminous coal and anthracite. The obtained preferential adsorption gives rise to the assumption that CO2 sequestration in coal beds with subsequent CO2-ECBM might be an ootion in Qinshui Basins, China.

MgO-decorated carbon nanotubes for CO_2 adsorption:first principles calculations

The global greenhouse effect makes it urgent to deal with the increasing greenhouse gases. In this paper the performance of MgO-decorated carbon nanotubes for CO2 adsorption is investigated through first principles calculations. The results show that the MgO-decorated carbon nanotubes can adsorb CO2 well and are relatively insensitive to O2 and N2 at the same time. The binding energy arrives at 1.18 eV for the single-MgO-decorated carbon nanotube adsorbing one CO2 molecule, while the corresponding values for O2 and N2 are 0.55 eV and 0.06 eV, respectively. In addition, multi-molecule adsorption is also proved to be very satisfactory. These results indicate that MgO-decorated carbon nanotubes have great potential applications in industrial and environmental processes.

CO2 Capture by Adsorption on MCM-68 Solid Sorbent Materials

Solid sorbents adsorption is considered as one of the potential options for CO2 capture process. CO2 adsorption on MCM-68 （Si/AI ratio 22） sorbent material was investigated. MCM-68 was synthesized using N,N,N＇,N＇-tetraethylbicyclo [2.2.2] oct-7-ene-2,3：5,6-dipyrrolidinium diiodide （TEBOP^2＋（I^＋）2） as a structure-directing agent （SDA）. CO2 adsorption capacity on MCM-68 sorbent was measured at a broad temperature window i.e. 60 ℃, 300 ℃ and at 400 ℃. The presence of ordered mesoporous structure, high surface area （456 me/g） and high thermal stability （TGA analysis up to 900℃） in MCM-68 are thought to be to be advantageous for the CO2 adsorption in broad temperature window.

Molten salts-modified MgO-based adsorbents for intermediate-temperature CO_2 capture: A review

Carbon dioxide（CO2） capture using magnesium oxide（MgO）-based adsorbents at intermediate temperatures has been regarded as a very prospective technology for their relatively high adsorption capacity,low cost, and wide availability. During the past few years, great effort has been devoted to the fabrication of molten salts-modified MgO-based adsorbents. The extraordinary progress achieved by coating with molten salts greatly promotes the COcapture capacity of MgO-based adsorbents. Therefore, we feel it necessary to deliver a timely review on this type of COcapturing materials, which will benefit the researchers working in both academic and industrial areas. In this work, we classified the molten saltsmodified MgO adsorbents into four categories:（1） homogenous molten salt-modified MgO adsorbents,（2） molten salt-modified double salts-based MgO adsorbents,（3） mixed molten salts-modified MgO adsorbents, and（4） molten salts-modified MgO-based mixed oxides adsorbents. This contribution critically reviews the recent developments in the synthetic method, adsorption capacity, reaction kinetics, promotion mechanism, operational conditions and regenerability of the molten salts-modified MgO COadsorbents. The challenges and prospects in this promising field of molten salts-modified MgO COadsorbents in real applications are also briefly mentioned.

Development of a pentaethylenehexamine-modified solid support adsorbent for CO_2 capture from model flue gas

A novel solid support adsorbent for CO2capture was developed by loading pentaethylenehexamine(PEHA)on commercially available mesoporous molecular sieve MCM-41 using wet impregnation method.MCM-41 samples before and after PEHA loading were characterized by X-ray powder diffraction,N2adsorption/desorption,thermal gravimetric analysis and scanning electron microscope to investigate the textural and thermo-physical properties.CO2adsorption performance was evaluated in a fixed bed adsorption system.Results indicated that the structure of MCM-41 was preserved after loading PEHA.Surface area and total pore volume of PEHA loaded MCM-41 decreased with the increase of loading.The working adsorption capacity of CO2could be significantly improved at 60%of PEHA loading and 75°C.The effect of the height of adsorbent bed was investigated and the best working adsorption capacity for MCM-41-PEHA-60 reached 165 mg·(g adsorbent)-1at 75°C.Adsorption/desorption circle showed that the CO2working adsorption capacity of MCM-41-PEHA kept stable.

An Effective Method to Improve the Performance of Fixed Carrier Membrane via Incorporation of C02-selective Adsorptive Silica Nanopartlcles

Fixed carrier membrane exhibits attractive CO2 permeance and selectivity due to its transport mechanism of reaction selectivity （facilitated transport）. However, its performance needs improvement to meet cost targets for CO2 capture. This study attempts to develop membranes with multiple permselective mechanisms in order to enhance CO2 separation performance of fixed carder membrane. In this study, a novel membrane with multiplepermselective mechanisms of solubility selectivity and reaction selectivity was developed by incorporating CO2-selective adsorptive silica nanoparticles in situ into the tertiary amine containing polyamide membrane formed by interfacial polymerization （IP）. Various techniques were employed to characterize the polyamide and polyam-ide-silica composite membranes. The TGA result shows that nanocomposite membranes exhlbit superior-thermal stability than pure polyamide membranes. In addition, gas permeation experiments show that both nanocomposite membranes have larger CO2 permeance than pure polyamide membranes. The enhanced CO2/N2 separation performance for nanocomposite membranes is mainly due to the thin film thickness, and multiple permselective mechanisms of solubility selectivity and reaction selectivity.

Parametric study and effect of calcination and carbonation conditions on the CO_2 capture performance of lithium orthosilicate sorbent

The world is currently facing the challenges of global warming and climate change. Numerous efforts have been taken to mitigate CO2 emission, among which is the use of solid sorbents for CO2 capture. In this work, Li4SiO4 was synthesised via a sol-gel method using lithium nitrate （LiNO3） and tetraethylorthosilicate （SiC8H20O4） as precursors. A parametric study of Li：Si molar ratio （1-5）, calcination temperature （600-800℃） and calcination time （1-8 h） were conducted during sorbent synthesis. Calcination temperature （700-800℃） and carbonation temperature （500-700℃） during CO2 sorption activity were also varied to confirm the optimum operating temperature. Sorbent with the highest CO2 sorption capacity was finally introduced to several cyclic tests to study the durability of the sorbent through 10 cycles of CO2 sorption-desorption test. The results showed that the calcination temperature of 800℃ and carbonation temperature of 700℃ were the best operating temperatures, with CO2 sorption capacity of 7.95 mmol CO2·（g sorbent）^-1 （93% of the theoretical yield）. Throughout the ten cyclic processes, CO2 sorption capacity of the sorbent had dropped approximately 16.2% from the first to the tenth cycle, which was a reasonable decline. Thus, it was concluded that Li4SiO4 is a potential CO2 solid sorbent for high temperature CO2 capture activity.

Smart adsorbents for CO2 capture:Making strong adsorption sites respond to visible light

Due to the good controllability and high energy efficiency in adsorption processes,photoresponsive adsorbents are intriguing for CO2 capture.Nevertheless,most reported photoresponsive adsorbents are designed based on weak adsorption sites,regulating CO2 adsorption through structural change or steric hindrance.In addition,ultraviolet(UV)light is commonly involved in the regulation of adsorption capacity.Here we report for the first time the smart adsorbents for CO2 capture,which makes strong adsorption sites respond to visible(Vis)light.The adsorbents were fabricated by introducing primary amine and Dispersed Red 1(DR1,a kind of push-pull azobenzene that responds to Vis light rapidly)units to mesoporous silica,which act as strong adsorption sites and triggers,respectively.The primary amine sites make the adsorbents highly selective in the adsorption of CO2 over CH4.Without light irradiation,azobenzene is in the form of trans configuration,which leads to decreased electrostatic potential of primary amines and subsequently,exposure of active sites and liberal adsorption of CO2.Upon Vis-light irradiation,cis isomers are formed,which results in increased electrostatic potential of primary amines and subsequently shelter of active sites.Even on such strong adsorption sites,the alteration of CO2 adsorption capacity can reach 40%for the adsorbent with and without Vis-light irradiation.Moreover,the trans/cis isomerization of DR1 units can be triggered reversibly by Vis light.The present smart system endows adsorbents with selective adsorption capacity and avoids the employment of UV light,which is unlikely to be achieved by conventional photoresponsive adsorbents.

Breakthrough CO_2 adsorption in bio-based activated carbons

In this work, the effects of different methods of activation on CO2 adsorption performance of activated carbon were studied. Activated carbons were prepared from biochar, obtained from fast pyrolysis of white wood, using three different activation methods of steam activation, CO2 activation and Potassium hydroxide（KOH） activation. CO2 adsorption behavior of the produced activated carbons was studied in a fixed-bed reactor set-up at atmospheric pressure, temperature range of 25–65°C and inlet CO2 concentration range of10–30 mol% in He to determine the effects of the surface area, porosity and surface chemistry on adsorption capacity of the samples. Characterization of the micropore and mesopore texture was carried out using N2 and CO2 adsorption at 77 and 273 K, respectively.Central composite design was used to evaluate the combined effects of temperature and concentration of CO2 on the adsorption behavior of the adsorbents. The KOH activated carbon with a total micropore volume of 0.62 cm3/g and surface area of 1400 m2/g had the highest CO2 adsorption capacity of 1.8 mol/kg due to its microporous structure and high surface area under the optimized experimental conditions of 30 mol% CO2 and 25°C. The performance of the adsorbents in multi-cyclic adsorption process was also assessed and the adsorption capacity of KOH and CO2 activated carbons remained remarkably stable after50 cycles with low temperature（160°C） regeneration.

Mesoporous carbon adsorbents from melamine–formaldehyde resin using nanocasting technique for CO_2 adsorption

Mesoporous carbon adsorbents, having high nitrogen content, were synthesized via nanocasting technique with melamine-formaldehyde resin as precursor and mesoporous silica as template. A series of adsorbents were prepared by varying the carbonization temperature from 400 to 700°C. Adsorbents were characterized thoroughly by nitrogen sorption, X-ray diffraction（XRD）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, thermogravimetric analysis（TGA）, elemental（CHN） analysis, Fourier transform infrared（FTIR） spectroscopy and Boehm titration. Carbonization temperature controlled the properties of the synthesized adsorbents ranging from surface area to their nitrogen content, which play major role in their application as adsorbents for CO2 capture.The nanostructure of these materials was confirmed by XRD and TEM. Their nitrogen content decreased with an increase in carbonization temperature while other properties like surface area, pore volume, thermal stability and surface basicity increased with the carbonization temperature. These materials were evaluated for CO2 adsorption by fixed-bed column adsorption experiments. Adsorbent synthesized at 700°C was found to have the highest surface area and surface basicity along with maximum CO2 adsorption capacity among the synthesized adsorbents. Breakthrough time and CO2 equilibrium adsorption capacity were investigated from the breakthrough curves and were found to decrease with increase in adsorption temperature. Adsorption process for carbon adsorbent-CO2 system was found to be reversible with stable adsorption capacity over four consecutive adsorption-desorption cycles. From three isotherm models used to analyze the equilibrium data, Temkin isotherm model presented a nearly perfect fit implying the heterogeneous adsorbent surface.

CO_2 adsorption using TiO_2 composite polymeric membranes:A kinetic study

CO2is the main greenhouse gas which causes global climatic changes on larger scale. Many techniques have been utilised to capture CO2. Membrane gas separation is a fast growing CO2 capture technique, particularly gas separation by composite membranes. The separation of CO2 by a membrane is not just a process to physically sieve out of CO2 through the controlled membrane pore size. It mainly depends upon diffusion and solubility of gases, particularly for composite dense membranes. The blended components in composite membranes have a high capability to adsorb CO2. The adsorption kinetics of the gases may directly affect diffusion and solubility. In this study, we have investigated the adsorption behaviour of CO2 in pure and composite membranes to explore the complete understanding of diffusion and solubility of CO2 through membranes. Pure cellulose acetate（CA） and cellulose acetatetitania nanoparticle（CA-TiO2） composite membranes were fabricated and characterised using SEM and FTIR analysis. The results indicated that the blended CA-TiO2 membrane adsorbed more quantity of CO2 gas as compared to pure CA membrane. The high CO2 adsorption capacity may enhance the diffusion and solubility of CO2 in the CA-TiO2 composite membrane, which results in a better CO2 separation. The experimental data was modelled by Pseudo first-order, pseudo second order and intra particle diffusion models.According to correlation factor R2, the Pseudo second order model was fitted well with experimental data. The intra particle diffusion model revealed that adsorption in dense membranes was not solely consisting of intra particle diffusion.

Microporous Hypercross-linked Conjugated Quinonoid Chromophores of Anthracene: Novel Polymers for CO_2 Adsorption

Microporous hypercross-linked conjugated quinonoid chromophores represent a novel class of amorphous polymers, synthesized by the reaction of anthracene with dimethoxy methane in the presence of FeCl3 catalyst. Their N2 adsorption isotherms confirm their microporous nature. Diffuse reflectance UV-Visible（DRS UV-Vis） spectroscopy confirms their matrix built with the conjugated quinonoids by their broad light absorption characteristics extending from 1000 nm to 200 nm with the absorbance maximum close to 400 nm. The catalyst cross-linked anthracene with ―CH2― bridges and subsequently dehydrogenating them to form quinonoids. Their Fourier transform infrared（FTIR） spectra showed their characteristic quinonoid vibrations between 1600 and 1700 cm-1. The synthesis of polymers was carried out at 30, 40, 50, 60, 70 and 80 ℃, but the quinonoid content of the polymer obtained at 80 ℃ was higher than that of the others. Their scanning electron microscopy（SEM） images showed microspheres of 1 to 5 μm size built with tiny particles. Their surfaces were not smooth. The polymer synthesized at 80 ℃ showed 5.1 wt% CO2 sorption at 25 ℃ and 0.1 MPa, but when it was recross-linked, the CO2 sorption increased to 8 wt%. Hence, hypercross-linked conjugated quinonoid chromophores of anthracene are good for sorption of CO2.

Impact of the flexibility of pillar linkers on the structure and CO_2 adsorption property of ‘‘pillar-layered'' MOFs

A new metal–organic framework {[Zn2（bpta）（bpy-ee）（H2O）2]·x solve}n（1）（H4bpta = biphenyl-2,20,6,60-tetracarboxylic acid and bpy-ee = 1,2-bis（4-pyridyl）ethylene） has been obtained under hydrothermal condition, and structurally characterized by single-crystal X-ray diffraction. Complex 1 reveals a threedimensional（3D） “pillar-layered” framework with non-flexible linker, in which some different structure characters can be found compared to that of some related other “pillar-layered” MOFs based on flexible pillar linkers. It demonstrates the impact of the flexibility of pillar linker on the final structure in this system. In addition, the selective CO2 adsorption performance of 1 was also investigated.