Comparative Study on Metal Extraction Properties of Empore SDB‐XC and Amberlite XAD‐4 Grafted by Salicylic Acid and its Derivatives via Different Bridges

Abstract

Among commercially available sorbents, aromatic organic crosslinked copolymers allow to consider numerous ways of linking ligands. In this way, the grafting of salicylic acid and of its derivatives (methylene disalicylic acid and aurintricarboxylic acid) via the ketone, amide and diazo bridges on Amberlite^® XAD‐4 resin and Empore? SDB‐XC membrane have been carried out. The modified sorbents thus obtained have been appraised according to their grafing rate and their efficiency to selectively retain different metallic ions versus pH. The grafting of the sorbents permits to obtain pretty good yields. Extraction yield studies have revealed that the supports have the same behavior whatever the ligand grafted via a diazo or an amide bridge. Thus, increase of salicylic acid entity number does not improve the performance of the supports. However, bridge used during grafting seems to have an influence upon the extraction yields observed.     

Thermal grafting of organic monolayers on amorphous carbon and silicon (111) surfaces: A comparative study

Thermally-assisted (160 °C) liquid phase grafting of linear alkene molecules has been performed simultaneously on amorphous carbon (a-C) and hydrogen passivated crystalline silicon Si(111):H surfaces. Atomically flat a-C films with a high sp³ average surface hybridization, sp³ / (sp² + sp³) = 0.62, were grown using pulsed laser deposition (PLD). Quantitative analysis of X-ray photoelectron spectroscopy, X-ray reflectometry and spectroscopic ellipsometry data show the immobilization of a densely packed (> 3 × 10¹⁴ cm^? 2) single layer of organic molecules. In contrast with crystalline Si(111):H and other forms of carbon films, no surface preparation is required for the thermal grafting of alkene molecules on PLD amorphous carbon. The molecular grafted a-C surface is stable against ambient oxidation, in contrast with the grafted crystalline silicon surface.     

Synthesis and characterization of a polystyrenic resin functionalized by catechol: Application to retention of metal ions

Chelating solid phase extraction is a preconcentration method adapted for metal ions extraction in water and requires functionalization of a solid sorbent by an organic ligand. A new chelating resin has been prepared by grafting catechol on Amberlite^® XAD-4 with an imine bridge and reducing it to enhance stability of the modified resin. Synthesis was first carried out at molecular level to validate experimental conditions, optimize yields and facilitate characterization of solid sorbent (particularly by FTIR). Each synthesis step of grafting on Amberlite^® XAD-4 was characterized by FTIR, Py-GC–MS and TGA-DSC. BET measurements showed a decrease in specific area after grafting from 865 to 425 m² g⁻¹ and in total pore volume from 1.19 to 0.66 cm³ g⁻¹. The grafting rate of 33% was determined by back titration of –OH (0.31 ± 0.03 mmol g⁻¹ of resin) and –NH-functions (0.93 ± 0.02 mmol g⁻¹ of resin). The increase in the sorbent hydrophilicity was confirmed by evaluating the water regain. Finally the retention properties of Cd(II), Cu(II), Ni(II) and Pb(II) were determined by ICP-AES at a pH range from 2 to 9. Retention rates of 94% and 98% were found at pH 8 for Cu(II) and Pb(II), respectively. Sorption capacities of 25.8 ± 2.5 μmol g⁻¹ for Cd(II), 89.7 ± 8.4 μmol g⁻¹ for Cu(II), 49.0 ± 10.5 μmol g⁻¹ for Ni(II) and 31.5 ± 1.6 μmol g⁻¹ for Pb(II) were measured.     

Preparation of poly (ethylene glycol) acrylate grafted polystyrene resin for solid-phase peptide synthesis

The solid-phase synthesis resin with high loading capacity was prepared through grafting poly (ethylene glycol) acrylate monomer from Merrifield resins via activators generated by electron transfer atom transfer radical polymerization. The grafted resins demonstrate well-swellability in both polar and nonpolar solvent such as dichloromethane, dimethylformamide, ethanol, tetrahydrofuran, acetonitrile, methanol and water. Particularly, the swelling ability of the grafted resin has reached two-fold of Merrifield resin in the polar solvent such as acetonitrile, methanol and water, and it enable high functional loadings up to 0.5–1.2 mmol g⁻¹ compared with the conventional polystyrene-grafting-poly (ethylene glycol) (0.15–0.25 mmol g⁻¹). This resin was derived to be used for synthesis of a difficult sequence-acyl carrier protein fragment 65-74 (ACP 65-74). The quantity and purity of peptide obtained from the grafted resin were higher than when the commercial Wang resin was used. The synthesis efficiency enhanced with the increase of grafting chains’ length within the range of hydroxyl capacity at 0.5–1.0 mmol g⁻¹. It was relative that the longer grafting chains were favor to suppress the hydrophobicity of the Merrifield resin.     

Environmentally friendly preparation of a strong basic anion exchange fibers and its application in sugar decolorization

An efficient route for the synthesis of a strong basic anion exchange fibers is described. In this synthesis route, the commercially available p-chloromethylstyrene was directly grafted onto a polypropylene fiber substrate, which eliminated the need of the highly carcinogenic chloromethyl methyl ether in the chloromethylation of grafting fiber. Several interdependent parameters such as monomer concentration, bath ratio and the influence of solvents on the grafting copolymerization were investigated. The removal efficiency of sugar colorants by the anion exchange fibers was evaluated. The results show that simultaneous irradiation and grafting p-chloromethylstyrene onto polypropylene fiber can obtain a good grafting level under appropriate conditions. The optimal monomer concentration and bath ratio are 40% and 1:30 for a moderate grafting degree and the suitable solvent is toluene. The grafted fiber changed from flexible to rigid. And the prepared material maintains stable before 134.5 °C. The static ion exchange capacity of the synthesized anion exchange fiber is up to 4.72 mmol g⁻¹ and the fiber possesses better ability to remove sugar colorants. The experimental results indicate that the decolorization ratio of the product anion exchange fibers was greater than that of commercial material.     

Separation of butyric acid in fixed bed column with solvent impregnated resin containing ammonium ionic liquid

Batch equilibrium and fixed bed column extraction experiments for the extraction of butyric acid (BA) into solvent impregnated resin (SIR) have been done. Microporous Amberlite XAD-1180N was impregnated with an ammonium ionic liquid (IL) trialkylmethylammonium bis(2,4,4-trimethylpentyl)phosphinate. The BA extraction capacity isotherm has not a Langmuir type shape and no finite capacity was observed. The loading of the impregnated IL with the extracted BA at 37 °C is in agreement with the loading from L/L extraction equilibrium of BA at 25 °C. Capacity of freshly prepared SIR particles is superior to classical porous ion-exchangers. Both the temperature and the superficial velocity in column influence the shape of the breakthrough-curve in fixed bed extraction of BA using SIR. Sharpening of the breakthrough curve was observed with the increasing temperature and decreasing superficial velocity. Stripping with water is not efficient for the regeneration of the loaded column after extraction because of low concentration of the product acid in the obtained effluent. Higher BA concentration was achieved by stripping with 0.15 kmol m⁻³ and 0.075 kmol m⁻³ NaOH solutions. The combination of initial water stripping coupled with consecutive stripping by alkali can be beneficial for decreasing the consumption of chemicals and further processing of the product. After two extraction/stripping cycles, a stable capacity was achieved and sustained for 14 cycles, showing the possibility of long-term application of the prepared SIR in real technology.     

Immobilization of [Bmim+Tf2N−] hydrophobic ionic liquid on nano-silica-amine sorbent for implementation in solid phase extraction and removal of lead

A method is described for highly efficient adsorptive removal of lead with a maximum metal capacity value of 1.300 mmol g^?1 by using physically immobilized [Bmim⁺Tf₂N^?] on the surface of nano-silica-amine sorbent. Lead sorption was found to be highly dependent and controlled by several experimental factors. The effect of sorbent dose played a significant role by yielding the maximum lead adsorption capacity when 100 mg sorbent was used. The effect of lead concentration was examined by various adsorption isotherms. The potential applications for removal of Pb(II) were studied and the percentage recovery values were 99.0–100.0 ± 2.0–5.0%.     

Processing of Foturan® glass ceramic substrates for micro-solid oxide fuel cells

The microfabrication of Foturan^® glass ceramic as a potential substrate material for micro-solid oxide fuel cells (micro-SOFC) was investigated. Foturan^® was etched in 10% aqueous hydrofluoric (HF) acid solution at 25 °C with a linear rate of 22 ± 1.7 μm/min to create structures with an aspect ratio of 1:1 in 500 μm-thick Foturan^® substrates for micro-SOFCs. The concentration of the HF etchant was found to influence the etching rate, whereas the UV-exposure time creating nuclei in the glass for subsequent crystallization of the amorphous Foturan^® material had no significant influence on the etching rates. The surface roughness of the crystallized Foturan^® was determined by the crystallite size in the order of 10–15 μm. Free-standing micro-SOFC membranes consisting of a thin film Pt cathode, an yttria-stabilized-zirconia electrolyte and a Pt anode were released by HF etching of the Foturan^® substrate. An open-circuit voltage of 0.57 V and a maximum power density of 209 mW/cm² at 550 °C were achieved.     

Ultrahigh surface area carbon from carbonated beverages: Combining self-templating process and in situ activation

Ultrahigh surface area carbons (USACs, e.g., >2000 m²/g) are attracting tremendous attention due to their outstanding performance in energy-related applications. The state-of-art approaches to USACs involve templating or activation methods and all these techniques show certain drawbacks. In this work, a series of USACs with specific surface areas up to 3633 m²/g were prepared in two steps: hydrothermal carbonization (200 °C) of carbonated beverages (CBs) and further thermal treatment in nitrogen (600–1000 °C). The rich inner porosity is formed by a self-templated process during which acids and polyelectrolyte sodium salts in the beverage formulas make some contribution. This strategy covers various CBs such as Coca Cola®, Pepsi Cola®, Dr. Pepper®, and Fanta® and it enables an acceptable product yield (based on sugars), for example: 21 wt% for carbon (2940 m²/g) from Coca Cola®. Being potential electrode materials for supercapacitors, those carbon materials possessed a good specific capacitance (57.2–185.7 F g⁻¹) even at a scan rate of 1000 mV s⁻¹. Thus, a simple and efficient strategy to USACs has been presented.     

Comparison of the properties of clay polymer nanocomposites prepared by montmorillonite modified by silane and by quaternary ammonium salts

In this work, the silylation of sodium montmorillonite (Na⁺-Mt, Nanofil 757®) was performed using (3-aminopropyl)triethoxy silane (APTES). Different reaction conditions were used varying the reaction time and the amount of the aminosilane. Epoxy-based nanocomposites were prepared with different amounts of silylated Mt or commercial organically modified Mt intercalated with stearylbenzyldimethyl ammonium chloride (Nanofil 2®) and distearyldimethyl ammonium chloride (Nanofil 8®), respectively. The grafting/intercalation of the aminosilane inside the Mt interlayer spaces was studied by means of Fourier transform infrared (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA). After isothermal curing at 90 °C the Mt epoxy nanocomposites were analyzed by means of XRD and dynamic mechanical analysis (DMA). The glass transition temperature of all prepared nanocomposites containing silylated Mt, is slightly higher than that of the neat epoxy (2 to 5 °C). In the presence of 1 to 5 m% of silylated Mt in epoxy matrix the storage modulus increases from about 5 to 15% at 25 °C, respectively, compared to the pristine epoxy matrix, while only 0–4% increase was observed for epoxy nanocomposites with commercial modified Mt.     

Fabrication and application of Nafion®-modified boron-doped diamond electrode as sensor for detecting caffeine

The surface of boron-doped diamond (BDD) electrodes has been modified by Nafion^®. The polymer film was applied onto the BDD electrode surface by solvent evaporation. Nafion^®-BDD electrode was used as a sensor for caffeine detection in e.g. cola beverage samples. In cyclic voltammetric measurements, favorable ionic interaction between the Nafion^® film and caffeine enhances the current response, and thus the sensitivity, compared to that at the bare electrode. The modified electrode exhibits a stable and sensitive response to caffeine and may represent a new analytical tool, offering a significant improvement over other electroanalytical methods (e.g.: Nafion^®-modified glassy carbon electrode) and the accepted method for caffeine analysis (HPLC-MS). The analysis of residuals from the linear regression proved that a linear response exists from 2.0 × 10^? 7 to 1.2 × 10^? 5 M, obtaining a limit of detection of about 1.0 × 10^? 7 M. The findings presented in this study are described and discussed in the light of the existing literature.     

Extraction of hexachloroplatinate from hydrochloric acid solutions with phosphorylated hexane-1,6-diyl polymers

A series of diols (diethylene glycol, triethylene glycol, butane-1,4-diol and hexane-1,6-diol) were immobilized onto Merrifield resin and subsequently phosphorylated with dialkyl chlorophosphate (alkyl = Me, Et, Bu). The resins bearing hexane-1,6-diyl groups exhibited very good extraction abilities in regard to precious metal chloro complexes like platinum(IV), palladium(II) and rhodium(III). In batch experiments, more than 98% of Pt(IV) is extracted even when the metal and the hydrochloric acid concentration is enhanced significantly. Elution can be achieved with a solution of 0.5 mol L⁻¹ thiourea in 0.1 mol L⁻¹ hydrochloric acid. In the presence of other noble metals, platinum(IV) is preferentially bound. The extraction yield decreases in slightly acidic solution in the following order: Pt(IV) ≈ Pd(II) > Rh(III) and changes with increasing hydrochloric acid concentration to Pt(IV) > Pd(II) ≫ Rh(III). At different ratios of metal and acid, the temperature has nearly no influence on the platinum extraction. On slightly acidic media, the extraction of rhodium decreases by 30% when the temperature is increased from 10 °C to 40 °C. When the acid and metal concentration is enhanced, the palladium extraction decreases by 7–9%, depending on the resin.     

Separation and determination of cadmium in water by foam column prior to inductively coupled plasma optical emission spectrometry

The sorption profile of cadmium (II) ions from aqueous iodide media onto procaine hydrochloride (PQ⁺·Cl⁻) treated polyurethane foams (PUFs) solid sorbent was studied. PQ⁺·Cl⁻ treated PUFs solid sorbent was found suitable and fast for Cd²⁺ uptake as [CdI4]_aq²⁻. Thus, removal of Cd²⁺ at trace levels by the sorbent packed columns was achieved. The sorbed Cd²⁺ species onto packed column were recovered with HNO₃ (10.0 mL, 1.0 mol L⁻¹) prior determination by inductively coupled plasma-optical emission spectrometry (ICP-OES). Plot of Cd²⁺ ions concentration was linear in the range 0.05–15 μg L⁻¹. The limits of detection and quantification of Cd²⁺ were found 0.01 μg L⁻¹ and 0.033 μg L⁻¹, respectively. Such limits could be improved to lower values by retention of Cd²⁺ species from large sample volumes of the aqueous phase at the optimized conditions. The relative standard deviation of the packed column for the extraction and recovery of standard aqueous solutions (0.1 L) containing 1.0 and 5.0 μg L⁻¹ (n = 3) of Cd²⁺ ions at flow rate of 5.0 mL min⁻¹ were 1.98 and 2.9%, respectively. The method was validated by analysis of Cd in certified reference materials (CRMs) IAEA-Soil-7 and TMDW water and wastewater samples.     

Chitosan-grafted nonwoven geotextile for heavy metals sorption in sediments

Functionalized polypropylene nonwoven (PP) geotextiles can be used as a new eco-friendly way to trap heavy metals in sediments. Chitosan was chosen as sorbent because of its ability to trap heavy metals, its natural origin (from shells) and its low cost. PP was first functionalized with acrylic acid using a low pressure cold plasma process, in order to bring reactive carboxylic functions onto the surface. Chitosan was then covalently grafted on the acrylic acid modified PP. The functionalized surfaces were characterized by Fourier Transform Infrared Spectroscopy–Attenuated Total Reflectance (FTIR–ATR) and X-ray Photoelectron Spectroscopy (XPS) and evidence of chitosan grafting was given. The ability of the functionalized geotextile to trap heavy metals was then investigated. Copper was chosen as a model heavy metal, and artificial solutions of CuSO₄ were prepared for the experiments. Sorption studies were carried out at 20 °C with Polypropylene-grafted-Acrylic acid-Chitosan (PP-g-AA-chitosan) varying the concentration of copper in polluted solutions to evaluate the maximum of adsorption of the surface: the textile can chelate copper increasingly as a function of the initial copper concentration until 830 ppm. At this concentration, it reaches a plateau at about 30 mg of trapped copper per gram of geotextile. The effects of pH and of the ionic strength (adsorption in a NaCl containing solution) were finally investigated. The trapping of Cu²⁺ decreases slowly when the ionic strength increases. When there are 30 g/L NaCl in the artificial polluted solution (like in seawater), only 20 mg of Cu²⁺ can be trapped per g of geotextile. Finally, the optimum pH to trap the maximum amount of copper was determined to be 4.8, which corresponds to the optimum pH for the chitosan solubility.     

SBA-15 grafted with 3-aminopropyl triethoxysilane in supercritical propane for CO2 capture

Supercritical propane (SC-propane) was found to be a promising solvent for grafting (3-aminopropyl)triethoxysilane (APS) onto synthesized SBA-15 for CO₂ capture. The influence of operating conditions in SC-propane for CO₂ adsorption at different pressures (8.3–13.8 MPa), temperatures (85–120 °C), and periods of time (4–16 h) were evaluated. The CO₂ adsorption conditions under different partial pressures, temperatures and moisture were evaluated. The results showed a reduction in pore characteristics and an increased amount of grafted APS with increasing pressure and temperature after grafting. After grafting in SC-propane at 11.0 MPa and various temperatures for 16 h, a 3–20% increase in the amount of grafted APS and a 6–49% increase in the CO₂ adsorption capacity over the toluene refluxing was observed. The time required for grafting in SC-propane could be reduced while maintaining higher nitrogen content and CO₂ adsorption capacity compared with grafting in toluene refluxing.     

Sintering and crystallisation of 45S5 Bioglass® powder

The sintering process of 45S5 Bioglass^® powder (mean particle size < 5 μm) was investigated by using different thermal analysis methods. Heating microscopy and conventional dilatometry techniques showed that bioactive glass sinters in two major steps: a short stage in the temperature range 500–600 °C and a longer stage in the range 850–1100 °C. The optimal sintering temperature and time were found to be 1050 °C and 140 min, respectively. Differential thermal analysis (DTA) showed that Bioglass^® crystallises at temperatures between 600 and 750 °C. The characteristic crystalline phases were identified by Fourier Transformed Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). The crystallisation kinetics was studied by DTA, using a non-isothermal method. The Kissinger plot for Bioglass^® powder heated at different heating rates between 5 and 30 °C/min yielded an activation energy of 316 kJ/mol. The average value of Avrami parameter determined using the Augis–Bennett method was 0.95 ± 0.10, confirming a surface crystallisation mechanism. After sintering at 1050 °C for 140 min, the main crystalline phase was found to be Na₂Ca₂Si₃O₉. The results of this work are useful for the design of the sintering/crystallisation heat treatment of Bioglass^® powder which is used for fabricating tissue engineering scaffolds with varying degree of bioactivity.     

SBA-15-supported ionic liquid compounds containing silver salts: Novel mesoporous π-complexing sorbents for separating polyunsaturated fatty acid methyl esters

Novel π-complexing sorbents were prepared by covalently immobilizing ionic liquids (ILs) onto mesoporous SBA-15 using a one-pot sol–gel process followed by coating these SBA-15-supported IL compounds with silver salts. The mesoporous π-complexing sorbents were characterized by small angle X-ray scattering (SAXS), FTIR, TEM, SEM, nitrogen adsorption desorption isotherm, NMR, and nitrogen elemental analysis. Two advantages were obtained using these novel mesoporous π-complexing sorbents versus the traditional π-complexing sorbents formed by directly anchoring silver salts onto silica gel. (1) Higher extraction capacities were found. The extraction capacity for the polyunsaturated fatty acid methyl ester (PUFAME), methyl all-cis-5,8,11,14,17-eicosapentaenoate (20:5 or EPA), was 195 mg/g sorbent using the mesoporous AgBF₄/SBA-15 · IL · PF₆ sorbent. The capacity decreased to 121 mg/g sorbent with microporous complexing sorbent AgBF₄/SiO₂ · IL · PF₆. (2) Better reusability was also achieved. The supported IL phase immobilized and retained silver salt on SBA-15 due to the interaction between the ionic liquid’s imidazolium cations and silver ions. Eight successive sorption runs with the AgBF₄/SBA-15 · IL · PF₆ sorbent showed a satisfactory reusability. The traditional π-complexing sorbent has a silver salt directly anchored on silica without the supported ionic liquid phase. Higher silver leaching into organic solution occurred from the AgBF₄/SBA-15 sorbent determined by ICP-AES. The combined percentage (wt%) of the omega-3 PUFAMEs: 20:5 and methyl all-cis-4,7,10,13,16,19-docosahexaenoate (22:6 or DHA) stripped from the AgBF₄/SBA-15 · IL · PF₆ by 1-hexene was significantly enriched from 18% in the original cod liver oil to 90.5%.     

Extraction of ursolic acid from Ocimum sanctum leaves: Kinetics and modeling

Ursolic acid (UA) is a triterpene compound which shows significant biological potential. This study deals with the optimization and kinetics of UA extraction from Ocimum sanctum (OS) leaves in a stirred batch extraction. The influence of various extraction parameters on the extraction yield has been studied. The optimum extraction conditions were extraction time 40 min, speed of agitation 1000 rpm, temperature 323 K, solute to solvent ratio of 1:120. This resulted in 11.21 mg of UA/g of dried leaf powder of OS. The extraction kinetics behavior of UA from OS revealed that the extraction of UA followed a first order kinetics. The kinetic expression developed by Spiro and Siddique was used and the model is in good agreement with the experimental results. The diffusion coefficient determined ranged from 2 × 10^?11 to 6.10 × 10^?11 m²/s for the all set of experiments. The activation energy for the extraction of UA was found to be E_a = 10.45 kJ/mol.     

Polypropylene grafted with NIPAAm and APMA for creating hemocompatible surfaces that load/elute nalidixic acid

Polypropylene (PP) films grafted with N-isopropylacrylamide (NIPAAm) and N-(3-aminopropyl) methacrylamide hydrochloride (APMA) were tested as components of medical devices able to load and to sustain the release of the antimicrobial agent nalidixic acid. A pre-irradiation method was applied for grafting PP films with two NIPAAm:APMA weight ratios and to various extents. The grafting composition was analyzed recording FTIR–ATR spectra. PP-g-(1NIPAAm-r-0.5APMA) exhibited the temperature-responsiveness of PNIPAAm, while the grafting with a greater content in APMA led to that PP-g-(1NIPAAm-r-1APMA) remained highly swollen at 37 °C. The greater the content in APMA on the PP surface, the higher the amount of nalidixic acid loaded (up to 0.036 mg/cm²) and the slower the release rate in phosphate buffer pH 7.4. Coating with carboxymethyl-dextran (CM-dextran) of some drug-loaded films led to minor drug unloading while remarkably high amounts of dextran were deposited (up to 0.50 mg/cm²). This coating did not significantly modify the drug release rate neither the hemocompatibility of the PP-g-(NIPAAm-r-APMA) films, which was per se very good. Drug-loaded films remarkably inhibited the growth of Escherichia coli in in vitro microbiological tests.     

Regenerable solid CO2 sorbents prepared by supercritical grafting of aminoalkoxysilane into low-cost mesoporous silica

The present work examines the functionalization of silica supports via supercritical CO₂ grafting of aminosilanes, which is an important step in the preparation of materials used as solid sorbents in CO₂ capture. Four materials have been considered as solid supports: two commercially available silica gels (4.1 and 8.8 nm pore diameter), the mesoporous silica MCM-41 (3.8 nm pore diameter) and a microporous faujasite of the Y type. Mono- and di-aminotrialkoxysilane were chosen for this study. The optimal operating conditions required to have free aminosilane in solution were first evaluated by studying the phase behavior of the system scCO₂/aminosilane at different pressures and temperatures. FTIR spectroscopy was used to determine the chemical structure of the grafted species. Aminosilane uptake was estimated by thermogravimetric and elemental analysis. Densities up to 3–4 molecules of monoaminosilane per nm⁻² were reached by using a small amount of a cosolvent together with the supercritical CO₂. The samples were characterized in regards of thermal stability, showing that aminosilane groups were covalently attached to the amorphous silica surface in the mesoporous supports, but not in the microporous zeolite. Low temperature N₂ and ambient temperature CO₂ isotherms were recorded to establish the adsorptive behavior of the prepared hybrid materials. The amine functionalized MCM-41 and the 8.8 nm silica gel exhibited a significant higher uptake of CO₂ at low pressures compared with the bare supports. On the contrary, for the 4 nm silica gel and the zeolite the adsorption decreased after impregnation.