Removal of perfluorooctanoic acid from water by adsorption on high surface area mesoporous materials

Removal of perfluorinated alkylated substances (PFAS) such as perfluorooctanoic acid (PFOA) from aqueous solution is an actual topic in light of their widespread diffusion and their persistence in the environment. The process of adsorption has been identified as an effective technique to eliminate PFAS in water, however the process efficiency strongly depends on the adsorbents employed (silica, alumina, activated carbon, layer doubled hydroxides). In this work three nanostructured mesoporous silica materials of similar pore diameter (~4 nm) featuring high surface area (~900 m²/g) and high pore volume (0.7–1.0 mL/g) were evaluated in PFOA removal: calcined MCM-41 (MCM-41c), calcined hexagonal mesoporous silica (HMSc) and HMSe obtained after ethanol extraction of the amine templates from HMS. Sorption kinetics and isotherms were performed at PFOA concentrations from 10 µg/L to 10 mg/L. It appeared that HMSe showed much faster and higher adsorption capacity for PFOA than the other tested adsorbents (MCM-41c and HMSc) whatever the pH of the solution (5 < pH < 9). Thermogravimetric analysis of HMSe evidenced that the ethanol extraction of the templating amines was not complete (70 %) and HMSe possessed some remaining hexadecylamine (HDA) (0.08 mol amine per mol SiO₂) on the surface conferring some hydrophobic properties to the adsorbent and also some probable complex formation between anionic PFOA^? and protonated HDA. Indeed, the incomplete amine extraction is surely due to the presence of protonated HDA in strong electrostatic interactions with SiO^? avoiding their removal by simple ethanol extraction as for H-bonding amine with Si–OH groups. Considering both adsorption isotherms and adsorption kinetics, PFOA could be efficiently removed from contaminated water in a wide range of concentration by an environmental friendly adsorbent as HMSe.     

Synthesis and evaluation of NiO@MCM-41 core–shell nanocomposite in the CO<Subscript>2</Subscript> reforming of methane

In this paper, the synthesis of core shell structured NiO@MCM-41 nanocomposite via vesicles as soft template is reported for the first time. Its catalytic performance was investigated in the CO₂ reforming of methane (CRM) conversion. Stable vesicles first formed with CTAB/SDBS surfactant ratio of 1:2. Nickle nitrate was added to the vesicle mixture followed by addition of the aqueous solution of vesicle containing Ni cations inside to the MCM-41 gel. After high-temperature calcination, NiO@MCM-41 nanocomposite were obtained. The structural symmetry and the surface morphology were characterized by transmission electron microscope (TEM), low angle X-Ray Diffraction (XRD) and N₂ adsorption/desorption analysis. TEM image confirmed core–shell structure and the hexagonally ordered structure of shell of MCM-41 silica. The results indicated that the average diameter of synthesized core–shell NiO@MCM-41 particles is 70–80 nm and the most of them are of spherical shape. The result of small angle XRD and N₂ isotherm adsorption/desorption analyses indicated successfull formation of mesoporous shell. Hydrogen consumption by the catalyst mainly at 700 °C in TPR profile showed the strong interaction of the most of Nickel content with the support. CRM conversion on the prepared catalyst after 245 min of reaction led to H₂ conversion at 42%, CO₂ conversion at 48% with H₂/CO yield ratio of 0.8.     

CO2 capture of amino functionalized three-dimensional worm-hole mesostructured MSU-J silica

Tetraethylenepentamine (TEPA) was employed to functionalize the large-pore mesoporous silica (denoted MSU-J) with 3D worm-hole framework structures which was prepared through a supramolecular hydrogen-bonding assembly pathway from low-cost H₂NCH(CH₃)CH₂[OCH₂CH(CH₃)]₃₃NH₂ (D2000) as structure-directing porogens and tetraethylorthosilioate as the silica source for capturing CO₂. The resultant adsorbents were characterized by FT-IR, Transmission electron microscopy (TEM), N₂ adsorption/desorption and thermogravimetric analysis. Textural properties, elemental analysis and TEM measurement of the samples showed a severe pore filling of MSU-J as TEPA loading was increased to 70 wt%. CO₂ adsorption isotherms measured at different temperatures revealed the optimal adsorption temperature is 25 °C. The adsorption capacity of MSU-J with different TEPA loading contents was calculated. As a result, 50 wt% of TEPA supported on as-synthesized MSU-J achieved the highest capacity with the value of 164.3 mg/g under the conditions of 99.99 % CO₂ at 25 °C and 0.1 MPa. Repeated adsorption/desorption cycles revealed that amine-impregnated materials was very efficient for less apparent decrease in CO₂ adsorption capacity even after 6 adsorption–regeneration cycles.     

Utilization of mesoporous molecular sieves synthesized from natural source rice husk silica to Chlorinated Volatile Organic Compounds (CVOCs) adsorption

The adsorption of trichloroethylene (TCE), tetrachloroethylene (PCE), and carbon tetrachloride was studied over our synthesized mesoporous material, MCM-41, from rice husk silica source, abbreviated as RH-MCM-41. More than 99% silica for RH-MCM-41 synthesis was extracted from rice husk under refluxing in HBr solution and then calcined at 873 K for 4 hours. RH-MCM-41 possessed surface area around 750-1,100 m²/g with a uniform pore size with an average diameter of 2.95 nm, narrow range of pore distribution and somewhat hexagonal structure, similar to properties of parent MCM-41. The adsorption of CC1₄ to RH-MCM-41 was stronger than that of TCE and PCE. The adsorption capacity of RH-MCM-41 for CVOCs (chlorinated volatile organic compounds) was higher than commercial mordenite and activated carbons.     

Adsorption of CO2 from dry gases on MCM-41 silica at ambient temperature and high pressure. 2: Adsorption of CO2/N2, CO2/CH4 and CO2/H2 binary mixtures

Adsorption equilibrium capacity of CO₂, CH₄, N₂, H₂ and O₂ on periodic mesoporous MCM-41 silica was measured gravimetrically at room temperature and pressure up to 25 bar. The ideal adsorption solution theory (IAST) was validated and used for the prediction of CO₂/N₂, CO₂/CH₄, CO₂/H₂ binary mixture adsorption equilibria on MCM-41 using single components adsorption data. In all cases, MCM-41 showed preferential CO₂ adsorption in comparison to the other gases, in agreement with CO₂/N₂, CO₂/CH₄, CO₂/H₂ selectivity determined using IAST. In comparison to well known benchmark CO₂ adsorbents like activated carbons, zeolites and metal-organic frameworks (MOFs), MCM-41 showed good CO₂ separation performances from CO₂/N₂, CO₂/CH₄ and CO₂/H₂ binary mixtures at high pressure, via pressure swing adsorption by utilizing a medium pressure desorption process (PSA-H/M). The working CO₂ capacity of MCM-41 in the aforementioned binary mixtures using PSA-H/M is generally higher than 13X zeolite and comparable to different activated carbons.     

Highly Stable Amine-modified Mesoporous Silica Materials for Efficient CO2 Capture

A highly efficient and stable solid adsorbent invoking a direct incorporation of tetraethylenepentamine (TEPA) onto the as-synthesized mesocelullar silica foam (MSF) has been developed for CO₂ capture. Unlike most amine-functionalized silicas, which typically exhibit CO₂ adsorption capacities less than 2.0 mmol/g, such organic template occluded mesoporous silica-amine composites exhibited remarkably high CO₂ uptake as high as 4.5 mmol/g at 348 K and 1 atm. Moreover, notable increases in CO₂ adsorption capacities of the composite materials were observed when in the presence of humidity. Durability test performed by cyclic adsorption–desorption revealed that such adsorbents also possess excellent stability, even though a slight decrease in adsorption capacity over time was observed.     

Adsorption of phosphate and nitrate anions on ammonium-functionnalized mesoporous silicas

Surface modified mesostructured silica materials represent potential adsorbents offering an opportunity to remediate several important water pollutants. In the present work, ammonium-functionnalized MCM-41, MCM-48 and SBA-15 mesoporous silica materials were synthesized via post-synthesis grafting and co-condensation. Their efficiency to remove nitrate and phosphate anions in aqueous solutions was investigated. The adsorbent materials showed high adsorption capacities reaching 46.5 mg NO₃⁻/g and 55.9 mg H₂PO₄⁻/g under the operating conditions explored. The mesoporous silica materials functionalized via post-synthesis grafting method exhibited higher performances in terms of percentage pollutant removal and adsorption capacities if compared to their analogs synthesized according to the co-condensation strategy.     

CO<Subscript>2</Subscript> adsorption at high pressures in MCM-41 and derived alkali-containing samples: the role of the textural properties and chemical affinity

The adsorption properties of N₂ and CO₂ of MCM-41 and derived alkali-containing samples were analyzed over a wide range of pressures (up to ~4500 kPa) and temperatures (between 30 and 300 °C). The high-pressure and high-temperature experiments were carried out on pure MCM-41 and K- and Na-impregnated derived samples. It was analyzed the influence of pressure and temperature on the CO₂ capture capacity on pure and impregnated samples. The adsorption performance was correlated to the structure and textural properties of the materials using X-ray diffraction and N₂ adsorption–desorption measurements. The addition of an alkaline element changes the textural properties of the material increasing the pore size, which positively affected the CO₂ adsorption capacity of these materials at high pressure. In addition, the isosteric heats of adsorption gave information about the chemical affinity between the impregnated materials and CO₂. The CO₂ adsorption at ~ 4500 kPa for the samples with 5 wt% Na at 100 and 200 °C were 77.98 and 9.79 mmol g^?1, respectively, while the pure MCM-41 adsorbs only 8.92 mmol g^?1.     

Mixed-amine Modified SBA-15 as Novel Adsorbent of CO2 Separation for Biogas Upgrading

A novel adsorbent of CO₂ from biogas was prepared by synthesizing and modifying the mesoporous molecular silica of SBA-15 with methyl-diethyl-amine (MDEA) and piperazine (PZ). The adsorbent showed good performance in separating CO₂ from biogas. The loaded amines did not change the ordered structure of SBA-15, but enhanced its adsorption of CO₂. The adsorbents were characterized by X-ray powder diffraction (XRD) and N₂ adsorption/desorption. With the increase in MDEA loading, the surface area, pore size, and pore volume of the MDEA-loaded SBA-15 decreased. The modification of amines enlarged the difference between the equilibrium adsorption of CO₂ and CH₄. Quantitatively evaluated on the basis of the breakthrough curves, the separation factors between CO₂ and CH₄, was increased more than seven fold due to the MDEA modification. With mixed-amine (MDEA + PZ) modification, the separation factors between CO₂ and CH₄ was further improved. In addition, not only the adsorbent was regenerable by purging with the purified gas, but also the adsorption performance is stable in adsorption cycles. Effect of moisture on adsorption of CO₂ is investigated and the results show the increase in the adsorption performance.     

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.     

Covalent grafting of polyacrylamide onto mesoporous MCM-41 silica via free radical polymerization

MCM-41 mesoporous silicas were covalently modified with polyacrylamide (PAAm) by a novel grafting strategy. The effect of various parameters such as monomer concentration, reaction time, and temperature on the content of PAAm onto MCM-41 silicas were studied. Modified silicas were characterized by X-ray diffraction (XRD), infrared spectroscopy, FT-IR, thermogravimetric analysis, nitrogen adsorption–desorption analyses, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy which confirmed the grafting process. According to XRD, SEM and TEM results, PAAm-modified MCM-41 silica did not show changes in its morphology and mesostructure by comparing with pristine MCM-41. Nitrogen adsorption–desorption studies showed that the attaching of PAAm onto MCM-41 silica decreased the values of pore size, pore volume and surface area.     

MCM-41介孔材料的合成条件和特性对吸附镉离子的影响

以气相氧化硅为硅源,十六烷基三甲基溴化铵(cetyl trimethyl ammonium bromide,CTAB)为模板剂,分别在碱性[氢氧化钠(NaOH),四乙基氢氧化铵,tetraethyl ammonium hydroxide,(C2Hs)4NOH(TEAOH)]和酸性介质条件[盐酸(HCl)]T水热合成了MCM-41有序介孔材料MCM-41-N,MCM-41-T和MCM-41-H.用X射线衍射、氮气吸附-脱附等手段对比分析了合成的3种MCM-41介孔材料的物相、比表面积、孔径、孔体积等,发现酸性介质中合成的介孔材料的孔径最大.在此基础上,利用MCM-41介孔材料对比研究了处理含镉离子(Cd2 )废水的效果和机理,确定了不同介孔材料用量、不同初始pH值条件下MCM-41介孔材料对水中Cd2 的吸附率和吸附量.结果表明:介孔材料用量相同时,溶液pH值的增大有利于提高3种MCM-41介孔材料对水中Cd2 的处理效果.在pH值从7.0到8.0的过程中,其吸附率有1个突变,MCM-41-T的Cd2 吸附率从35.65%提高到62.15%;MCM-41-N的从38.80%提高到69.40%;MCM-41-H的从50.22%提高到73.47%.孔径最大的MCM-41-H对Cd2 的吸附效果最佳,最大吸附率为89.56%,最大吸附容量为8.57 mg/g.吸附溶液pH值的大小和介孔材料的孔径尺寸是决定吸附量大小的关键因素,因此,重点应通过优化合成工艺提高介孔材料的孔径.     

High loading of C60 in nanochannels of mesoporous MCM-41 materials

Very high loadings of C₆₀ and C₆₀⁻ anions in MCM-41 mesoporous materials have been achieved by modifying the channel surface with amino-functional group. Detailed physical properties of these mesoporous materials containing C₆₀ were characterized by EPR, NMR, XRD, FTIR and UV–vis spectroscopic techniques. The surface area and pore size of mesoporous materials were further determined by N₂ adsorption–desorption isotherms. The mesopores of MCM-41 show sieving behavior in excluding the larger sized C₁₂₀O while absorbing the smaller C₆₀ as indicated in the EPR studies.     

Synthesis and characterization of monolithic carbon/silicon carbide composite aerogels

Resorcinol–formaldehyde/silica composite (RF/SiO₂) aerogels were synthesized using sol–gel process followed by supercritical CO₂ drying. Monolithic carbon/silicon carbide composite (C/SiC) aerogels were formed from RF/SiO₂ aerogels after carbothermal reduction. X-ray diffraction and transmission electron microscopy demonstrate that β-SiC was obtained after carbothermal reduction. Scanning electron microscopy and nitrogen adsorption/desorption reveal that the as-prepared C/SiC aerogels are typical mesoporous materials. The pore structural properties were measured by nitrogen adsorption/desorption analysis. The resulting C/SiC aerogels possess a BET surface area of 564 m²/g, a porosity of 95.1 % and a pore volume of 2.59 cm³/g. The mass fraction of SiC in C/SiC aerogels is 31 %.     

Nitridation of MgO-loaded MCM-41 and its beneficial applications in base-catalyzed reactions

Nitrogen-containing MgO-MCM-41 solid base material is prepared by nitridation of MgO-loaded mesoporous MCM-41. The ordered mesoporous structure and high surface area of MCM-41 are well preserved after MgO impregnation and nitridation, as proved by the XRD, TEM and nitrogen adsorption/desorption analysis. FTIR spectra the bridging -NH- groups and terminal -NH₂ groups are incorporated into the framework of MgO-MCM-41 by nitridation, and the base strength is expected to be enhanced due to the replacement of oxygen by nitrogen with lower electronegativity. FTIR spectra with the adsorption of different probe molecules, e.g. CO, CD₃CN and ¹³CO₂, are employed for the characterization of surface acidic-basic properties of MgO-MCM-41 before and after nitridation. It is revealed that the acidic hydroxyls in MgO-MCM-41 are greatly reduced through nitridation process. Compared with MgO-MCM-41, the nitridized MgO-MCM-41 material exhibits improved basic catalytic performances in Knoevenagel condensation reaction, Claisen-Schmidt reaction and dehydrogenation reaction of 2-propanol.     

Synthesis of chloropropylamine grafted mesoporous MCM-41, MCM-48 and SBA-15 from rice husk ash: their application to CO<Subscript>2</Subscript> chemisorption

Mesoporous siliceous MCM-41, MCM-48 and SBA-15 were synthesized using Rice Husk Ash (RHA) as the silica source. Their defective –OH sites were then grafted with 3-chloropropyl amine hydrochloride (3-CPA) and characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and BET techniques. Those results portrayed their resemblance with that synthesized from conventional silica sources. 3-CPA grafted mesoporous silicas were tested for CO₂ chemisorption over fixed bed reactor at different temperatures. The maximum adsorption of 1.7 mmol/g of CO₂ was observed on 3-CPA grafted SBA-15 (SBA-15/CPA) at 25°C. The chemisorbed CO₂ on amine grafted mesoporous silica was stabilized by weak hydrogen bonds formed during the nucleophilic attack between lone pair of electrons in amine groups and quadrupolar CO₂ with more degree of positive charge to form carbamates. The rapid steep slope which arises due to CO₂ adsorption illustrated a minimal mass transfer effect and extreme fast kinetics. Performance tests such as reproducibility, stability and selectivity towards CO₂ adsorption were also carried out over 3-CPA grafted mesoporous silica and the results were in line with that of well established CO₂ sorbent.     

五乙烯六胺改性制备CO2吸附剂及其对模拟烟气中CO2捕集性能的研究（英文）

A novel solid support adsorbent for CO2 capture was developed by loading pentaethylenehexamine (PEHA) on commercial y available mesoporous molecular sieve MCM-41 using wet impregnation method. MCM-41 sam-ples before and after PEHA loading were characterized by X-ray powder diffraction, N2 adsorption/desorption, thermal gravimetric analysis and scanning electron microscope to investigate the textural and thermo-physical properties. CO2 adsorption 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 CO2 could 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)?1 at 75 °C. Adsorption/desorption circle showed that the CO2 working adsorption capacity of MCM-41-PEHA kept stable. ? 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. Al rights reserved.     

Direct synthesis of bi-modal porous structure MCM-41 and its application in CO2 capturing through amine-grafting

A bi-modal porous structure MCM-41 (BPS-MCM-41) was synthesized and functionalized by 3-[2-(2-Aminoethylamino)ethylamino]propyltrimethoxysilane (TRI); also, its performance in amine grafting and CO₂ capturing was compared with that of pore-expanded MCM-41 [1]. To create larger pores beside the mesoporous structure of MCM-41, carbon black nanoparticles were used as the solid template. Characterizing the BPS-MCM-41 using the BET and BJH techniques resulted in the surface reduction of 29.3 percent and volume increase of 68.46 percent. The pore size distribution showed two peaks: a narrow peak at 2.24 nm diameter, which belonged to micelles, and a wide one at about 50 nm due to the presence of used nanoparticles. The functionalization confirmed that BPS-MCM-41 is capable of accommodating a large quantity of amine groups. The CO₂ adsorption measurement indicated that internal volume of the adsorbent was a critical factor affecting the adsorption capacity of the amine grafted adsorbents.     

Synthesis and characterization of nanocomposite MCM-48-PEHA-DEA and its application as CO2 adsorbent

Three nanocomposites containing MCM-48-35PEHA-15DEA (35 and 15 as weight percent of amine addition), MCM-48-30PEHA-20DEA and MCM-48-25PEHA-25DEA of mesoporous silica MCM-48 modified by the mixture of pentaethylenehexamine (PEHA) and diethanolamine (DEA) have been synthesized and used to study the adsorption of carbon dioxide (CO₂). They are characterized by low angle x-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Brunauer-Emmet-Teller (BET) analysis. MCM-48-35PEHA-15DEA (as optimized adsorbent) shows CO₂ adsorption capacity of 0.51 (m·mol CO₂/g-adsorbent) at 1 bar and 298 K, much higher than CO₂ adsorption capacity on polyethyleneimine, pyrrolidinepropyl and polymerized aminopropyl loaded MCM-48.     

Direct Electrochemistry and Electrocatalysis of Hemoglobin on Bimetallic Au–Pt Inorganic–Organic Nanofiber Hybrid Nanocomposite and Mesoporous Molecular Sieve MCM-41

A glassy carbon electrode modified with MCM-41 and bimetallic inorganic–organic nanofiber hybrid nanocomposite was prepared and used for determination of trace levels of hydrogen peroxide (H₂O₂). The direct electron transfer (DET) and electrocatalysis of hemoglobin (Hb) entrapped in the MCM-41 modified Au–Pt inorganic–organic nanofiber hybrid nanocomposite electrode (Au–PtNP/NF/GCE) were investigated by using cyclic voltammetry in 0.1 M pH 7.0 phosphate buffer solution. Due to its uniform pore structure, high surface area and good biocompatibility, the mesoporous silica sieve MCM-41 provided a suitable matrix for immobilization of biomolecules. The MCM-41 modified Au–Pt inorganic–organic nanofiber hybrid nanocomposite electrode showed significant promotion to DET of Hb, which exhibited a pair of well-defined and quasi-reversible peaks for heme Fe(III)/Fe(II) with a formal potential of ?0.535 V (vs. Ag/AgCl). Additionally, the Hb immobilized on the MCM-41 modified electrode showed excellent electrocatalytic activity toward H₂O₂ reduction.