Synthesis of MIL-101@g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanocomposite for enhanced adsorption capacity towards CO<Subscript>2</Subscript>

MIL-101@g-C₃N₄ nanocomposite was prepared by solvothermal synthesis and used for CO₂ adsorption. The parent materials (MIL-101 and g-C₃N₄) and the MIL-101@g-C₃N₄ were characterized by X-ray diffraction, argon adsorption/desorption, Fourier transform infrared spectroscopy, thermal analysis (TG/DTA), transmission electronic microscopy, and Energy-dispersive X-ray spectroscopy. The results confirmed the formation of well-defined MIL-101@g-C₃N₄ with interesting surface area and pore volume. Furthermore, both MIL-101 and MIL-101@g-C₃N₄ were accomplished in carbon dioxide capture at different temperatures (280, 288, 273 and 298 K) at lower pressure. The adsorption isotherms show that the nanocomposite has a good CO₂ adsorption affinity compared to MIL-101. The best adsorption capacity is about 1.6 mmol g^?1 obtained for the nanocomposite material which is two times higher than that of MIL-101, indicating strong interactions between CO₂ and MIL-101@g-C₃N₄. This difference in efficacy is mainly due to the presence of the amine groups dispersed in the nanocomposite. Finally, we have developed a simple route for the preparation of an effective and new adsorbent for the removal of CO₂, which can be used as an excellent candidate for gas storage, catalysis, and adsorption.     

Adsorptive separation of carbon dioxide by polyethyleneimine modified adsorbents

Utilization of carbon dioxide (CO₂) has become an important global issue due to significant and continuous rise in atmospheric CO₂ concentrations. To find a potential solution, two types of mesoporous materials, MCM-41 and MCM-48, were synthesized and impregnated with 30, 50 and 70 wt% of polyethyleneimine (PEI) in methanol to evaluate the performance of the materials in terms of CO₂ adsorption. The materials were characterized by XRD, TGA, FTIR, TEM, SEM, N₂-physisorption and BET techniques. All the PEI-loaded materials exhibited substantially higher reversible CO₂ adsorption-desorption behaviors with >99% recovery. The above study proved that MCM-48 is a better material as compared to MCM-41 for loading of PEI. The material with 50 wt% loading of PEI on MCM-48, showed maximum adsorption of 248 mg/g-PEI at 80 °C which is about 30 times higher than that of MCM-48 and about 2.3 times that of pure PEI.     

Facile synthesis of amine-functionalized MIL-53(Al) by ultrasound microwave method and application for CO<Subscript>2</Subscript> capture

An amine functional MIL-53(Al) material was prepared through a clean, rapid, energy-efficient method of microwave and ultrasound irradiation. The pure phase NH₂-MIL-53(Al) can be formed in 25 min, utilizing the synergistic effect of microwave and ultrasound irradiation. The dramatic acceleration in reaction rates suggested that the removal of a passivation coating on the substrate particles and the resultant enhancement in mass and heat transfer. The porous MOFs exhibited a high thermal and chemical stability, decomposing at temperatures above 410 °C in air. The NH₂-MIL-53(Al) performed an excellent adsorption for CO₂. The CO₂ capacities up to 33.86 cm³ g^?1 at 298 K at low pressures, which suggests chemisorption between CO₂ and pendan amine groups. Measurement of CO₂ adsorption cycles proved that the functionalized materials show good regenerability and stability.     

Nanoporous rice husk derived carbon for gas storage and high performance electrochemical energy storage

We report on the gas storage behaviour and electrochemical charge storage properties of high surface area activated nanoporous carbon obtained from rice husk through low temperature chemical activation approach. Rice husk derived porous carbon (RHDPC) exhibits varying porous characteristics upon activation at different temperatures and we observed high gas uptake and efficient energy storage properties for nanoporous carbon materials activated even at a moderate activation temperature of 500 °C. Various experimental techniques including Fourier transform-infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy and pore size analyser are employed to characterise the samples. Detailed studies on gas adsorption behaviour of CO₂, H₂ and CH₄ on RHDPCs have been performed at different temperatures using a volumetric gas analyser. High adsorption capacities of ~9.4 mmol g^?1 (298 K, 20 bar), 1.8 wt% (77 K, 10 bar) and ~5 mmol g^?1 (298 K, 40 bar) were obtained respectively for CO₂, H₂ and CH₄, superior to many other carbon based physical adsorbents reported so far. In addition, these nanoporous carbon materials exhibit good electrochemical performance as supercapacitor electrodes and a maximum specific capacitance of 112 F g^?1 has been obtained using aqueous 1 M Na₂SO₄ as electrolyte. Our studies thus demonstrate that nanoporous carbon with high porosity and surface area, obtained through an efficient approach, can act as effective materials for gas storage and electrochemical energy storage applications.     

Hydrogen Production from Aqueous Solutions of Glycerol on TiO<Subscript>2</Subscript>/Ru-MCM-41 Photocatalysts Using Solar Light

Ru-MCM-41 molecular sieves were prepared (Si/Ru atomic ratio?=?50 or 100) by a hydrothermal method and impregnated with TiO₂. The materials were characterized by XRD, N₂ physisorption, DRS, SEM and TEM. Their potential application to hydrogen production by photolysis of water using solar light was tested in a batch reactor using mixtures of water and glycerol (0–6.85 mol L^?1) at pH varying from 1 to 11. The photocatalytic efficiency under simultaneous UV (0.05 μW cm^?2) and visible light (90.07 W m^?2) irradiation was compared to the activity of TiO₂/MCM-41 (i.e., no Ru incorporated) and commercial Degussa TiO₂ P25. The most active material was 20%TiO₂/Ru-MCM-41(100) whose performance (220.6 µmol g_Ti ^?1 H₂) was approximately 47 times higher than TiO₂ P25. Characterization results showed the deposition of TiO₂ and revealed the formation of RuO₂ on the surface. Hydrogen generation was improved due to higher charge separation at the TiO₂/RuO₂ heterojunction and to the enhancement of visible light absorption caused by surface plasmon resonance (SPR). Hydrogen production increased with glycerol concentration, tending to stabilize around 40.3 µmol h^?1 g_Ti ^?1 above 4 mol L^?1 of glycerol. Hydrogen generation reached its maximum at extreme values of pH (1 and 11).     

Adsorption of CO<Subscript>2</Subscript> by iron-exchanged heteropolyacid Fe<Subscript>1.5</Subscript>PMo<Subscript>12</Subscript>O<Subscript>40</Subscript> supported on mesoporous cellular foams

Novel low-temperature swing adsorbents that preferably adsorb CO₂ were synthesized by varying loading of heteropolyacid Fe_1.5PMo₁₂O₄₀ (Fe–PMA) supporting on mesoporous cellular foams (MCFs) by wetting impregnation. The synthesized materials were characterized by various physicochemical, thermal and spectral techniques and the CO₂ adsorption capacity of the materials were evaluated. Solid adsorbents showed a significantly high adsorption capacity toward CO₂ due to the chemisorptions of CO₂. The CO₂ adsorption capacities of the materials decreased as the temperature increased. The results showed that the adsorption capacity reached a level of 81.8 mg CO₂/g-adsorbent at 25 °C for the 20 wt% Fe–PMA–MCFs. These results indicated that the iron (Fe²⁺) complexes acted as efficient catalysts for the separation of CO₂. The as-synthesized adsorbents were selective, thermally stable, long-lived, and could be recycled at a temperature of 110 °C.     

Hierarchical porous nitrogen-doped carbon materials derived from one-step carbonization of polyimide for efficient CO<Subscript>2</Subscript> adsorption and separation

Hierarchical porous nitrogen-doped carbon (HPNC) materials are synthesized through one-step carbonization of polyimide using triblock copolymer P123 as mesoporous template. The microstructure, chemical composition and CO₂ adsorption behaviors are investigated in detail. The results show that HPNC materials have hierarchical micro-/mesopore structures, high specific surface area of 579 m²/g, large pore volume of 0.34 cm³/g, and nitrogen functional groups (5.2 %). HPNC materials exhibit high CO₂ uptake of 5.56 mmol/g at 25 °C and 1 bar, which is higher than those of previously reported nitrogen-doped porous carbon materials. After 5 cycles the value of CO₂ adsorption uptakes is 5.28 mmol/g, which is approximately 95 % of the original adsorption capacity. The estimated CO₂/N₂ selectivity of HPNC materials is 17, revealing great promise for practical CO₂ adsorption and separation applications. The efficient CO₂ uptake and enhanced CO₂/N₂ selectivity are due to the combination of nitrogen-doped and hierarchical porous structures of HPNC materials.     

Effects of different structure-directing agents (SDA) in MCM-41 on the adsorption of CO2

CO₂ capturing technologies have attracted significant attention in order to limit emissions and reduce their negative effect on the environment. Mesoporous silica materials (MCM-41) are easily recyclable, affordable, and thermally and mechanically stable, providing added benefits in CO₂ capture. However, further studies are necessary to characterize the effects of MCM-41 pore size, adsorption temperature and surface silylation on CO₂ adsorption efficiency. In this work, mesoporous silica is synthesized using alkyltrimethylammonium bromide with different chain lengths (C_nH_2n + 1 N(CH₃)₃Br, n = 14, 16 and 18) as structure-directing agents, and the adsorption capacity of CO₂ on TTMCM-41 (C₁₇H₃₈NBr), CTMCM-41 (C₁₉H₄₂NBr), DTMCM-41(C₂₁H₄₆NBr) samples was measured gravimetrically at room temperature and pressure up to 40 bar. The silica structures were characterized by X-ray diffraction (XRD), nitrogen adsorption/desorption, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy (TEM). The XRD, N₂ adsorption–desorption and TEM measurements indicated the presence of a well-ordered hexagonal array with uniform mesostructures. The mesoporous silica obtained, denoted as TTMCM-41, CTMCM-41 and DTMCM-41, had distinct physical properties, such as BET surface area, hexagonal unit cell, pore volume, pore diameter and pore wall thickness. CTMCM-41 exhibited an adsorption capacity (0.58 g CO₂/g adsorbent) of more than DTMCM-41 (0.48 g CO₂/g adsorbent) and TTMCM-41 (0.42 g CO₂/g adsorbent). The results suggest that CTMCM-41 can be a better mesoporous adsorbent for CO₂ adsorption .     

Characterization of MCM-41 with Immobilized Bi-functional SH/SO3H Layer

A new approach for quantitative determination of –SH and –SO₃H functional groups on MCM-41 silica with covalently immobilized mercaptopropyl groups is proposed. A set of MCM-41 type samples containing 1 mmol g^?1 of mercaptopropyl groups was oxidized with proportional quantities of hydrogen peroxide and subsequently characterized with different ratios of grafted mercaptopropyl and propylsulfonic acid groups. Data calculated from conductometric titration were correlated with the corresponding X-ray photoelectron spectra and exhibit a linear relationship of results for both techniques. The described method was applied to thiol-containing MCM-41 samples to reveal ambient oxidation of organo-silicas with immobilized thiol groups.     

Effective photoconversion of CO<Subscript>2</Subscript> into CH<Subscript>4</Subscript> over Ti<Subscript>30</Subscript>Si<Subscript>70</Subscript>MCM-41 nanoporous catalyst photosensitized by a ruthenium dye

Nanoporous Ti₃₀Si₇₀MCM-41 was applied as a photocatalyst for effective reduction of CO₂ to CH₄. A ruthenium dye (N₇₁₉) was also introduced onto the surface of Ti₃₀Si₇₀MCM-41 as a photosensitizer to improve its photoabsorption in the visible range. The catalytic performance of N₇₁₉-photosensitized Ti₃₀Si₇₀MCM-41 was superior to that of the non-photosensitized Ti₃₀Si₇₀MCM-41 and N₇₁₉-photosensitized Ti₃₀Si₇₀O₂₀₀ nanomaterials. The photoreduction of CO₂ to CH₄ was remarkably improved on N₇₁₉-(5 h)-photosensitized Ti₃₀Si₇₀MCM-41, with a production of 1,900 μmol g _cat ^?1 L^?1 after an 8 h reaction. The results were attributed to the effective charge separation and the inhibited recombination of photogenerated electron-hole pairs on N₇₁₉-photosensitized Ti₃₀Si₇₀MCM-41. Lastly, a model for the enhanced photoactivity over N₇₁₉-photosensitized Ti₃₀Si₇₀MCM-41 was proposed.     

Synthesis of polyaniline/mesoporous carbon nanocomposites and their application for CO<Subscript>2</Subscript> sorption

Ordered mesoporous carbons (OMC), were synthesized by nanocasting using ordered mesoporous silica as hard templates. Ordered mesoporous carbons CMK-1 and CMK-3 were prepared from MCM-48 and SBA-15 materials with pore diameters of 3.4 nm and 4.2 nm, respectively. Mesoporous carbons can be effectively modified for CO₂ adsorption with amine functional groups due to their high affinity for CO₂. Polyaniline (PANI)/mesoporous carbon nanocomposites were synthesized from in-situ polymerization by dissolving OMC in aniline monomer. The polymerization of aniline molecules inside the mesochannels of mesoporous carbons has been performed by ammonium persulfate. The nanocomposition, morphology, and structure of the nanocomposite were investigated by nitrogen adsorption-desorption isotherms, Fourier Transform Infrared (FT–IR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and thermo gravimetric analysis (TGA). CO₂ uptake capacity of the mesoporous carbon materials was obtained by a gravimetric adsorption apparatus for the pressure range from 1 to 5 bar and in the temperature range of 298 to 348 K. CMK-3/PANI exhibited higher CO₂ capture capacity than CMK-1/PANI owing to its larger pore size that accommodates more amine groups inside the pore structure, and the mesoporosity also can facilitate dispersion of PANI molecules inside the pore channels. Moreover, the mechanism of CO₂ adsorption involving amine groups is investigated. The results show that at elevated temperature, PANI/mesoporous carbon nanocomposites have a negligible CO₂ adsorption capacity due to weak chemical interactions with the carbon nanocomposite surface.     

Preparation of dendrimer polyol/mesoporous silica nanocomposite for reversible CO2 adsorption: Effect of pore size and polyol content

This paper focuses on the synthesis of polyol/MCM-48 nanocomposite materials with different percentages of polyalcohol dendrimer H20. The obtained materials were used for CO₂ adsorption. CO₂-TPD analysis showed that the samples containing 1 and 3 wt% of H20 dendrimer have low CO₂ adsorption capacity due to the occupation of active sites, The sample prepared with 0.5 wt% of H20 dendrimer exhibited higher adsorption capacity and thermal stability. The affinity toward CO₂ was found to be mainly due to the presence of organic moiety within the MCM-48 pores.     

Preparation of amine-modified SiO<Subscript>2</Subscript> aerogel from rice husk ash for CO<Subscript>2</Subscript> adsorption

Amine-modified SiO₂ aerogel was prepared using 3-(aminopropyl)triethoxysilane (APTES) as the modification agent and rice husk ash as silicon source, its CO₂ adsorption performance was investigated. The amine-modified SiO₂ aerogel remains porous, the specific surface area is 654.24 m²/g, the pore volume is 2.72 cm³/g and the pore diameter is 12.38 nm. The amine-modified aerogel, whose N content is up to 3.02 mmol/g, can stay stable below the temperature of 300 °C. In the static adsorption experiment, amine-modified SiO₂ aerogel (AMSA) showed the highest CO₂ adsorption capacity of 52.40 cm³/g. A simulation was promoted to distinguish the adsorption between the physical process and chemical process. It is observed that the chemical adsorption mainly occurs at the beginning, while the physical adsorption affects the entire adsorption process. Meanwhile, AMSA also exhibits excellent CO₂ adsorption–desorption performance. The CO₂ adsorption capacity dropped less than 10 % after ten times of adsorption–desorption cycles. As a result, AMSA with rice husk ash as raw material is a promising CO₂ sorbent with high adsorption capacity and stable recycle performance and will have a broad application prospect for exhaust emission in higher temperature.     

Carbon dioxide capture under postcombustion conditions using amine-functionalized SBA-15: Kinetics and multicyclic performance

ABSTRACT

In this work, ordered mesoporous SBA-15 was synthesized and functionalized by polyethyleneimine (PEI). The morphological properties were characterized by N₂ adsorption/desorption, field–emission scanning electron microscopy (FE-SEM), high–resolution transmission electron microscopy (HR-TEM) and Fourier transform infrared (FTIR) spectroscopy methods. The carbon dioxide (CO₂) uptake on the sorbents, kinetics of CO₂ adsorption/desorption and long-term multicycle stability of PEI-impregnated sorbent were measured. An optimal amine loading of 50 wt.% showed a CO₂ adsorption capacity ~3.09 mmol g^?1 using 10% pre-humidified CO₂ at 75°C. The presence of moisture in flue gas showed a promoting effect in CO₂ sorption capacity. The temperature swing adsorption/desorption cycles showed excellent multicycle stability over 60 cycles during 65 h of operations under humid CO₂.     

Oxidative dehydrogenation of n-butane over bimetallic mesoporous and microporous zeolites with CO2 as mild oxidant

Oxidative dehydrogenation of n-butane was tested using carbon dioxide as a mild oxidant over bimetallic Cr–V supported catalysts (MCM-41, ZSM-5, MCM-22 and mesoZSM-5). The textural properties of the catalysts were measured by means of XRD, N₂ adsorption, SEM-EDX, Raman, H₂-TPR, pyridine FT-IR, NH₃ and CO₂-TPD techniques. The metal content of Cr and V was maintained around 1.2 and 2.8 wt% for the catalytic test in packed bed reactor at different temperatures (525–600 °C) for 180 min. 1.2Cr2.8 V/MCM-41 and 1.2Cr2.8 V/ZSM-5 exhibited maximum conversion of 14 and 13.1 %, respectively at 10 min and 600 °C. Significantly, high butenes selectivity was observed over MCM-41 (86.27 %) than ZSM-5 support (58.1 %). The mesoporosity in ZSM-5 had a negative impact on conversion level (7.1 %) but improved the butenes selectivity slightly. 1.2Cr2.8 V/M-22 showed the highest cracking ability leading to overall reduced butenes selectivity (57.9 %). The study shows that over all catalysts, n-butane conversion is independent of CO₂ conversion. 1.2Cr2.8 V/M-22 showed highest CO₂ conversion in the range 2.35–2.2 % between 525 and 550 °C. The apparent activation energies of dehydrogenation and cracking reaction over the four catalysts were evaluated. The ratio of conversion to coke weight per cent over the four catalysts are observed in the following order: 1.2Cr2.8 V/M-41 > 1.2Cr2.8 V/Z-5 > 1.2Cr2.8 V/mesoZ-5 > 1.2Cr2.8 V/M-22.     

Performance as electrode of electrical double layer capacitor of activated carbon prepared from bamboo using guanidine phosphate and CO<Subscript>2</Subscript> activation

The electrochemical performances of an electrical double layer capacitor were investigated regarding the activated carbon prepared from bamboo by a new approach, that is, the combination of delignification, addition of guanidine phosphate, and CO₂ activation. In this study, a 1 M H₂SO₄ aqueous solution was used as the electrolyte of the capacitor. The physical properties, such as the BET specific surface area of the carbon material, depend on the preparation conditions of the activated carbon. A TEM image indicated that the addition of guanidine phosphate did not facilitate the graphitization and did not prevent activation by CO₂. The apparent reaction equation for the CO₂ activation was first-order, which is reasonable for physical activation. The electrochemical performances of the carbon material depended on the preparation conditions of the carbon material, such as the heat treatment temperature, amount of added guanidine phosphate, and CO₂ activation time. The sample prepared under the following conditions (the amount of added guanidine phosphate: 9 wt%, the heat treatment temperature: 800 °C, CO₂ activation time: 3 h) had the highest performance (153 F g^?1 at 1000 mA g^?1) because the sample had the highest BET specific surface area (2001 m² g^?1).     

Fast and efficient adsorption of azure (II) on nanoporous MCM-41 for its removal,preconcentration and determination in biological matrices

The objective of the present study was to investigate the potential of nanoporous MCM-41 silicate for the azure (II) adsorption from the aqueous solutions. The method is based on the adsorption of azure (II) after passing on MCM-41 in a column. The adsorption with respect to contact time, pH, flow rate of sample, eluent kind and volume was investigated to provide more information about the adsorption characteristics of MCM-41. After elution of the adsorbed dye, the concentrations of dye were determined by UV–Vis spectrophotometer. The method showed good linearity for the determination of azure (II) in the range of 1–200 ng mL^?1 with a regression coefficient of 0.9997. The limit of detection was 0.5 ng mL^?1 and the relative standard deviation for 50 ng mL^?1 of azure (II) was 1.26 %. The adsorption properties of the MCM-41 were investigated using batch method. In order to investigate the efficiency of adsorption, pseudo-first-order, pseudo-second-order and intra particle diffusion kinetic models were studied. It was observed that the pseudo-second-order kinetic model fits better than other kinetic models with good correlation coefficient. Equilibrium data were fitted to the Langmuir model. Adsorption equilibrium reach within 5 min of contact time and adsorption capacity was found to be 66.0 mg g^?1. The method was applied to the determination of azure (II) in river water, broth culture medium and DNA samples.     

Hydrogen storage characteristics of metal oxide doped Al–MCM-41 mesoporous materials

The feasibility and perspectives of Al–MCM-41 as hydrogen storage systems were evaluated. The Al–MCM-41 with varying content of aluminum was synthesized by hydrothermal process. Different metal oxides were impregnated over Al–MCM-41 by incipient wetness impregnation (IWI) method. The crystallnity of the samples were interrogated by powder X-ray diffraction. The textural properties were measured by N₂ sorption method. The structural properties were established by Transmission Electron Microscope (TEM). The gas chromatogram indicates that hydrogen uptake in Al–MCM-41 is strongly dependent on density of Brønsted acid sites and the amount of metal oxide (especially NiO).     

Effect of the Synthesis Method on Co-catalysts Based on MCM-41 for the Fischer–Tropsch Reaction

In this work, cobalt catalysts based on ordered mesoporous materials of the MCM-41 type were synthesized and characterized. The synthesis of the catalysts was performed by using different methods: impregnation; incorporation of the metal in the synthesis gel and ionic exchange of the metal by the template. Different characterization techniques were used (N₂ adsorption–desorption, XRD, TPR, SEM and XPS) to study the textural and structural properties of the samples and the metal-support interaction corresponding to each method of synthesis. These samples were tested in the CO Hydrogenation (Fischer–Tropsch Synthesis) by measuring the CO conversion and the selectivity to CO₂ and some groups of hydrocarbons chains. The results show that structural and textural properties as well as the metal-support interactions are affected by the synthesis method. According to this study, catalytic performance is related to the properties of the samples, observing that the metal support interaction highly affects the activity and selectivity of the catalysts.     

Extraction of Ultra Trace Amounts of Palladium on 9-Acridinylamine Functionalized SBA-15 and MCM-41 Nanoporous Silica Sorbents

The application of the modified MCM-41 and SBA-15 nanporous silicas in extraction of trace amounts of palladium is investigated and developed. Surface of nanoporous silicas, MCM-41 and SBA-15, were modified with 9-acridinylamine ligand and then utilized as solid-phase sorbents for the extraction of palladium. Different experimental conditions such as pH, flow rates of the sample, and eluent solution were studied. The type and the smallest amount of eluent for elution were optimized and the breakthrough volume and the influence of various cationic interferences on the adsorption was investigated. The recovery values in this method are greater than 95% and 98.5%. The obtained limits of detections (LOD) are lower than 0.17 ng mL^?1 and 0.15 ng mL^?1 for SBA-15 and MCM-41, respectively. The pre-concentration factors were calculated to be more than 193 and 187.5 for SBA-15 and MCM-41, respectively. The relative standard deviations (RSD) of the method are lower than 4% and 1.5%, and the adsorption capacities were also obtained to be more than 170 mg g^?1 and 195 mg g^?1 for SBA-15 and MCM-41, respectively. The proposed procedure was applied on real samples and the amount of palladium was successfully derived.