Mesoporous Adsorbents Research Articles

Amine-functionalized mesoporous monolithic adsorbents for post-combustion carbon dioxide capture

Amine-functionalized solid adsorbents have significant application potential in post-combustion CO2 capture due to the advantages of high capacity, low regeneration cost and long-term stability. Although the powdery adsorbents exhibit higher CO2 uptake capacity, the poor strength and large pressure drop limit their practicability. Monolithic adsorbent is considered as a good choice to solve these problems, but still facing the bottle-neck of insufficient CO2 capacity. In this work, a facile and feasible gel-casting method was proposed to fabricate monolithic adsorbents with high CO2 capacity, excellent mechanical strength, and good cycling stability. MCM-41 with rich mesoporous structure was immobilized by polymerization of organic polymer to construct monolithic adsorbents supports with high specific surface area (~1088 m2 g−1) and mechanical strength. The 70T-MM-550 monolithic adsorbent impregnated with TEPA achieved high adsorption capacity of 151.1 mg g−1 at 75 ℃ under 1 atm pure CO2. The monolithic adsorbents also showed good reversibility of CO2 adsorption under mild conditions, where the adsorption capacity decreased only by 2.8% after five regeneration cycles. In addition, the radial and axial compressive strength of 70T-MM-550 is over 200 N cm−1 and 4.5 MPa, respectively. In consideration of the high CO2 capture performance and mechanical properties of the monolithic adsorbents, the findings here open a new avenue for designing efficient monolithic CO2 adsorbents with industrially potential.

Microwave and fusion techniques for the synthesis of mesoporous zeolitic composite adsorbents from bagasse fly ash: sorption of p-nitroaniline and nitrobenzene

p-Nitroaniline (PNAN) and nitrobenzene (NB) being important raw materials and intermediates for the production of a wide range of chemical products have the potential of constituting water pollutants. Hence, the development of the means of removing these chemicals from water would go a long way to safeguard the health of the environment. The goal of this research was to transform bagasse fly ash (BFA), solid waste from the sugar industry into porous zeolitic adsorbents MgFZBFA and MgMZBFA and examine them for their adsorptive removal of PNAN and NB from aqueous solutions. The syntheses of the sorbents involve alkali fusion technique and microwave hydrothermal treatment for the desired properties. Advanced characterization techniques such as FTIR (Fourier transform infrared spectroscopy), XRF (X-ray fluorescence spectroscopy), XRD (X-ray diffraction spectroscopy), SEM (scanning electron microscopy), Brunauer–Emmett–Teller (BET)/Barrett–Joyner–Halenda (BJH) Method, and TGA (thermogravimetric analysis) were used for the characterization and evaluation of the sorbents’ properties. The adsorptive removal of PNAN and NB from aqueous solutions by MgFZBFA and MgMZBFA were investigated. Various parameters such as pH, adsorbent dosage, initial sorbate concentration were optimized during the adsorption experiment to achieve best performance. Adsorption isotherm, kinetics and dynamics were studied. It was found that Langmuir adsorption isotherm model better represents the adsorption processes and that the processes follow pseudo-second-order kinetics. More so, the sorption processes were most possibly completed by both surface sorption (liquid-film diffusion) and intra-particle diffusion. The maximum sorption capacities observed with MgFZBFA for PNAN and NB are 30.86 mg g−1 and 19.92 mg g−1, while with MgMZBFA the values are 12.72 mg g−1 and 10.20 mg g−1, respectively. The performances of MgFZBFA and MgMZBFA for the sorption of PNAN and NB were compared with some adsorbents previously studied for the same purpose, and results show that the adsorbents in the present study exhibit better performances. The application as materials of cheap source for the removal of PNAN and NB from contaminated water could be considered.

Entropy in multiple equilibria. Argon and nitrogen adsorption isotherms of nonporous, microporous, and mesoporous materials

Analysis of multiple equilibria of compounds with different coordination sites is extended to the description of adsorption isotherms with focus on the low relative pressure range. The entropy evolution is described using the particle distribution theory which also holds for adsorbents consisting of materials bearing more than one type of sites and applies for the condition that the adsorptive-adsorbent binding strength is larger than the adsorptive-adsorbate binding strength, so that monolayer coverage is favored. This allows to accurately determine the adsorption enthalpy. No assumption concerning the growth mechanism and specifics regarding the structure of the surface is needed. We find on a rigorous basis that this leads to Langmuir's equation for each site independently, that the total fractional amount of bound adsorptive can be described as a linear combination of individual Langmuir isotherms, and that such a linear combination has never the shape of the original Langmuir isotherms. The results are successfully applied to argon and nitrogen adsorption isotherms of nonporous, microporous, and mesoporous adsorbents which allows comparing systems for which the properties of the active surface span a large range. We observe that all experimental data can accurately be described by means of a linear combination of two Langmuir isotherms in the low relative pressure range up to a coverage of 60%–95%. This means that the shape of all adsorption isotherms is essentially determined by the entropy decrease with increasing coverage. The two site interactions involved exhibit substantially different adsorption enthalpies. Interestingly the Ar enthalpy of adsorption Δ a d s H 1 ∅ of the sites 1 for the Stöber-type silica and of the three investigated MCM-41 adsorbents (with pore size of 2.7 nm, 4.1 nm, and 4.4 nm) are similar, namely −11 kJ/mol. The situation is analogous for the enthalpy of adsorption Δ a d s H 2 ∅ for the sites 2, which amounts to −8 kJ/mol. A significantly larger enthalpy of adsorption Δ a d s H 1 ∅ for the sites 1, namely −14.3 kJ/mol, and Δ a d s H 2 ∅ = − 11.7 kJ / mol for the sites 2 is measured for potassium zeolite L thus reflecting the more polar nature of this adsorbent. The measured specific surface area for these samples ranges from 14 m 2 /g for the Stöber-type silica up to 1100 m 2 /g for the MCM-41(4.1 nm) adsorbent. The information provided by the lc2-L (linear combination of 2 Langmuir functions) analysis allows calculating the evolution of the coverage of site 1 and of site 2 as a function of increasing pressure. The inflection points of the isotherms, which mark the point where the curvature changes sign, were determined by numerically evaluating the second derivatives which vanish at this point and are compared with values obtained using BET analysis.

Microwave‐assisted synthesis of mesoporous γ‐Fe2O3for dye removal

The synthesis of mesoporous γ-Fe2O3 nanoparticles by eco-friendly one-step microwave irradiation method in ambient atmospheres without surfactants as described in this Letter. Characterisation of synthesised nanoparticles was performed by X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller surface area & pore volume analyser, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and superconducting quantum interference device. The adsorption behaviour of nanoparticles towards methyl orange, an azo dye, was examined in aqueous solutions under various operational conditions like pH, temperature, contact time, and adsorbent weight. Results suggest that as-synthesised γ-Fe2O3 nanoparticles are mesoporous and superparamagnetic at room temperature. Some characteristics of γ-Fe2O3 nanoparticles, for example, saturation magnetisation, pore diameters, specific surface areas, and pore volumes are 72.0 emu g−1, 7.11 nm, 189.35 m2 g−1, and 0.52 cm3 g−1, respectively. The experimental data of adsorption study fitted with the Langmuir isotherm model and maximum adsorption capacity is 403.23 mg g−1. The reusability of the γ-Fe2O3 nanomaterials was examined, and it can be recycled for ten cycles. In sum, this simple eco-friendly synthesis method of magnetic mesoporous adsorbent is suitable for large scale production without any template or surfactant or inert atmosphere.

Amino-grafted mesoporous MCM-41 and SBA-15 recyclable adsorbents: Desert-rose-petals-like SBA-15 type as the most efficient to remove azo textile dyes and their mixture from water

Amino-grafted Mobil Composition of Matter N. 41 (MCM-41/NH2) and Santa Barbara Amorphous (SBA-15/NH2) type mesoporous adsorbents were successfully used and compared in this work to remove azo dyes (and their mixture) from highly colored solutions. This paper reports a very fast removal and recycle (in 5 min) of great amounts of textile dyes (about the 100%) by materials characterized by high adsorption/desorption capacities. A qmax ≈ 250 mg/g for each adsorption cycle, that should be potentially increase to ≈ 1250 mg/g, under appropriate experimental conditions, was found for the proposed adsorbents. The UV–Vis absorption spectra of dyes were used to support this finding, determining the rate of adsorption. Several parameters affecting the adsorption process were investigated: the contact time, dyes solution pH values and amount of the adsorbent materials, ranging from 0.4 mg to 12 mg, and dyes (5 × 10−5 M and 1 × 10−5 M). Further, the Nitrogen adsorption/desorption isotherms, SAXS patterns, TG analyses, Zeta-potential measurements and microscopic imaging techniques, such as SEM and TEM, were used to detail the nature of interaction between dyes and adsorbents, and to investigate the morphology and the mesoporous array of the amino grafted MCM-41 and SBA-15.

Removal of Cs+ in water by dibenzo-18-crown-6 ether tethered on mesoporous SBA-15 as a reusable and efficient adsorbent

Inadvertent release of radioactive Cs+ to the environment poses a grave threat as it may cause severe health problems to the exposed population. One of the practical solutions is to use effective regenerable Cs+ adsorbents to minimize total waste volume. In this study, a mesoporous adsorbent for Cs+ capture was prepared by tethering a Cs+-selective ligand monoamino-dibenzo-18-crown-6 (MA-DB18C6) ether on chloro-functionalized SBA-15 (Cl-SBA) support. The dispersible adsorbent (DB18C6-SBA) registered a maximum adsorption capacity of 94.54 mg g−1 from non-linear Hill isotherm fitting. The model suggests near Langmuir-type of Cs+ capture as Hill coefficient nH→1. This indicates nearly independent monolayer Cs+ binding with the tethered DB18C6 with no adsorbate interaction. Kinetic study reveals a pseudo-second order of Cs+ uptake rate while thermodynamic analyses show the spontaneity and endothermicity of the process. Compared with conventional ligand impregnation technique, covalently tethered DB18C6 occupy smaller surface space of SBA-15 resulting in higher ligand loading and higher adsorption capacity. DB18C6-SBA is regenerable in mild acid and exhibits consistent adsorption capacity after several reuse cycles. It can selectively capture Cs+ from simulated high level liquid waste, but more effectively from Cs+-contaminated surface water with KD ∼ 1578 mL g−1 and concentration factor CF ∼ 2267 in the presence of Na+, K+, Mg2+ and Ca2+. Cycled batch adsorption shows that DB18C6-SBA can be reused with consistent uptake performance while lab-scale sequential adsorption-nanofiltration system with Cs+ stripping further demonstrates its potential long-term use as Cs+ adsorbent for the treatment of contaminated water.

Silica-based nanomaterials as designer adsorbents to mitigate emerging organic contaminants from water matrices

The abatement of emerging organic contaminants from industrial effluents and wastewater is a key challenge for environmental scientists around the globe. Many industries release their effluents containing organic compounds into water bodies, which make them contaminated and hazardous for the living ecosystem. Controlling water pollution has become challenging in recent years. Adsorption technology has received worldwide acceptance for the removal of various classes of pollutants from water. Though many sorbents like activated carbons and other low-cost materials are used for the elimination of organic pollutants from water, their widespread use is restricted due to high costs and lower removal efficiency. In this context, silica and silica-based adsorbents have gained incredible attention due to their probable applications in the field of catalysis, separation, and green synthesis. This review describes various classes of silica with emphasis on mesoporous silica-based adsorbents and also comprehensively underline an up to date description, development, and their use for the removal of organic pollutants.

Preparation of mesoporous coal-gasification fine slag adsorbent via amine modification and applications in CO2 capture

Here, a novel adsorbent was prepared from coal-gasification fine slag by acid leaching and amine modification and was used for CO2 capture. The fine slag adsorbent (FSA) material was found to have a specific surface area of 541 m2 g−1 and a pore volume of 0.543 cm3 g−1. To improve the CO2 adsorption capacity of the material, the raw FSA was immobilized with amines through physical impregnation. The FSA-based composites were developed using four types of amines: ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), and tetraethylenepentamine (TEPA). The optimum formula was found to be the FSA loaded with 20 wt% TEPA (FSA-TEPA-20), whose theoretical maximum adsorption capacity for CO2 was 132.5 mg g−1 (273 K). The partition coefficient values obtained at 100% breakthrough for FSA and FSA-TEPA-20 were determined as 1.4 × 10−4 and 3.3 × 10−4 mol kg−1 Pa−1, respectively, which were far superior to those of other mesoporous materials (e.g., SBA-PEI). The FSA-TEPA-20 showed good cycling stability. The reaction mechanism was investigated, and the thermodynamic/kinetic parameters for CO2 adsorption were derived; the adsorption was demonstrated to follow the Avrami model. The strength of the preparation strategy is it enables the development of a high-performance adsorbent from low-cost solid wastes.

Microwave-assisted synthesis and characterization of γ-Al2O3/γ-Fe2O3 composite and evaluating its efficiency in fluoride removal

A reclaimable mesoporous adsorbent of γ-Al2O3/γ-Fe2O3 nanocomposite was prepared by microwave irradiation method for fluoride removal from aqueous solution. The chemical constituent and morphology of adsorbent were characterized by XRD, XPS, SEM, and FTIR, and the pore structure and surface area were calculated using BET analyses. BET study revealed surface area is 203.24 m2/g. The adsorbent was superparamagnetic with a saturation magnetization of 27.52 emu/g at 300 K, which improves the magnetic separation of adsorbent using an external magnet. The batch of adsorption experiments was studied to evaluate fluoride removal capacity. The adsorption isotherm follows Langmuir isotherm than Freundlich isotherm, and the maximum adsorption capacity is 105.042 mg/g. The adsorption equilibrium reached within 15 min. The adsorption kinetic well defined by the pseudo-second-order model. Adsorption mechanism study suggested Al3+ ions on the surface of the adsorbent interact with fluoride molecules. Up to the fifth cycle, the adsorbent retains 95 % removal capacity.

A comparative study on methane adsorption onto various adsorbents including activated carbons, zeolites, MWCNT, and MCM-41

ABSTRACT In this study, it was aimed to produce low-cost activated carbons from cornelian cherry stones (CCS) by ultrasound-assisted chemical activation with the use of LiOH, KOH, NaOH, and ZnCl2. In the study, adsorption capacities of the activated carbon samples for CH4 compared with that of commercially obtained activated carbon (AC), multi-walled carbon nanotubes (MWCNT), mesoporous silica (MCM-41), and various zeolites. BET and t-plot analysis have been used for the characterization of adsorbents with the use of N2 adsorption-desorption data and SEM. In the evaluation of the adsorption data, several isotherm models such as DR, Harkins-Jura, Temkin, Freundlich, and Langmuir have been used. It was observed that activated carbons showed higher CH4 adsorption capacity than commercial mesoporous adsorbents and microporous zeolites. The CH4 adsorption capacity of commercial activated carbon was measured to be 0.939 mmol/g, while the CH4 adsorption capacities of activated carbons obtained with the use of NaOH, KOH, LiOH, and ZnCl2 were found to be 2.455, 1.584, 1.477, and 1.433 mmol/g, respectively. Results showed that activated carbons obtained from CCS with the use of KOH, NaOH, LiOH, and ZnCl2 are effective low-cost adsorbents for CH4 adsorption.

Rapid adsorption of As(V) from aqueous solution by ZnO embedded in mesoporous aluminosilicate nanocomposite adsorbent: Parameter optimization, kinetic, and isotherms studies

In this work, ZnO modified mesoporous AlSBA-15 nanocomposite adsorbent was prepared by wet chemical method and employed to adsorption of As(V) from an aqueous solution. The adsorbent was characterized by XRD, SEM (EDS), N2 sorption, and FTIR spectroscopy. The surface area, pore-volume, and pore diameter was estimated to be 373 m2 /g, 1.01 cc/g, 7.31 nm respectively. Arsenic (V) adsorption studies were conducted in the batch model. In optimized condition, the maximum adsorption capacity found to be 123.994 mg /g at pH 4.5, adsorbent dose 4g/L, and temperature 298 K. Rapid adsorption occurs within the first 30 min with adsorption efficiency of 99.13%. The results obtained from the kinetic model showed that the adsorption process followed pseudo-second-order kinetics well with an R2 value of 0.9999. Adsorption isotherm investigation showed the Langmuir model fitted well the experimental data with an R2 value of 0.996. Moreover, the adsorption process occurs through electrostatic attraction between the adsorbent and As(V) ions. Adsorption efficiency decreases with the increase of temperature and hence exothermic.

Adsorption of phosphorus on lanthanum doped carbon films guided by self-assembly of cellulose nanocrystalline

Phosphorus has been an important main reason for water eutrophication. Reducing the concentration of phosphate to prevent eutrophication is one of the crucial goals of sewage engineering and surface water management. For the first time, cellulose nanocrystalline was used as biomass template and tetramethoxysilane as mesoporous template. A highly efficient and selective self-supporting mesoporous composite membrane adsorbent was prepared by one-step method. The film material has a highly ordered chiral nematic phase structure. It adsorbed phosphate well. In batch adsorption test, through lanthanum loading, the adsorbent material can selectively adsorb phosphate, and the adsorption kinetics followed a pseudo second-order model, especially in the case of phosphate. At the same time, cellulose nanocrystalline doped with trace lanthanum have been investigated to achieve high phosphate adsorption performance. The effect of Lanthanum on flocculation of cellulose nanocrystalline was discussed, and the adsorbent material with the best adsorption performance was obtained. The adsorption isotherm Langmuir model of the adsorbent was more representative than the Friedrich model. In addition, the adsorbent was achieved a high adsorption capacity in the range of pH values between 3.0 and 7.0. Phosphate selectivity was also soaring. The mesoporous films adsorbent has the advantages of high cycle times, repeatability and easy separation from solution.

Insights into the CO2 capture over amine-functionalized mesoporous silica adsorbents derived from rice husk ash

The design of high-performance porous adsorbents active for CO2 capture is imperative to mitigate the global climate problems arising from the accumulation of anthropogenic emissions. This work evaluates the CO2 adsorption behavior of a series of amine-functionalized silicas with different pore structures: SBA-15 (2D hexagonal), SBA-11 (3D cubic), and SiO2 (d) (disordered). The materials were synthesized using Rice Husk Ash (RHA) as a silica source and then functionalized with polyethyleneimine (PEI) by wet impregnation. CO2 adsorption performance was found to be quite sensitive to the pore features of the silica supports and the impregnated amount of PEI. Among the prepared adsorbents, the PEI/SBA-15 exhibited the highest amine utilization (0.38 mol CO2/mol N, at 20 wt.% PEI) and CO2 adsorption capacity (61.6 mg CO2/g ads., at 40 wt.% PEI) under mild conditions (40 °C and ambient pressure). The outstanding performance of this adsorbent was attributed to its uniform 2D hexagonal arrangement of cylindrical mesopores that decreases the CO2 mass transfer resistance and favors the PEI distribution through the pore network, enhancing the interaction with the CO2 stream. Further evaluation of the adsorption kinetics indicated that the CO2 capture was influenced by kinetic and thermodynamic regimes to different extents depending on the adsorption temperature.

Sulfonic Acid Derivative-Modified SBA-15, PHTS and MCM-41 Mesoporous Silicas as Carriers for a New Antiplatelet Drug: Ticagrelor Adsorption and Release Studies.

Three mesoporous, siliceous materials, i.e., SBA-15 (Santa Barbara Amorphous), PHTS (Plugged Hexagonal Templated Silica) and MCM-41 (Mobil Composition of Matter), functionalized with a sulfonic acid derivative, were successfully prepared and applied as the carriers for the poorly water-soluble drug, ticagrelor. The siliceous carriers were characterized using nitrogen sorption analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and elemental analysis. The adsorption studies were conducted in acetonitrile. At the highest equilibrium concentrations, the amount of ticagrelor Qe that adsorbed onto the examined silicas was in the range of 83 to 220 mg/g, increasing in the following order: PHTS-(CH2)3-SO3H < SBA-15-(CH2)3-SO3H < MCM-41-(CH2)3-SO3H. The equilibrium adsorption data were analyzed using the Freundlich, Jovanovich, Langmuir, Temkin, Dubinin-Radushkevich, Dubinin-Astakhov and Redlich-Peterson models. In order to find the best-fit isotherm for each model, a nonlinear fitting analysis was carried out. Based on the minimized values of the ARE function, the fit of the isotherms to the experimental points for ticagrelor adsorption onto the modified silicas can be ordered as follows: SBA-15-(CH2)3-SO3H (Redlich-Peterson > Dubinin-Astakhov > Temkin), PHTS-(CH2)3-SO3H (Redlich-Peterson > Temkin > Dubinin-Astakhov), MCM-41-(CH2)3-SO3H (Redlich-Peterson > Dubinin-Astakhov > Langmuir). The values of adsorption energy (above 8 kJ/mol) indicate the chemical nature of ticagrelor adsorption onto propyl-sulfonic acid-modified silicas. The results of release studies indicated that at pH 4.5, modified SBA-15 and MCM-41 carriers accelerate the drug dissolution process, compared to the dissolution rate of free crystalline ticagrelor. Intriguingly, modified PHTS silica provides prolonged drug release kinetics compared to other siliceous adsorbents and to the dissolution rate of crystalline ticagrelor. A Weibull release model was employed to describe the release profiles of ticagrelor from the prepared carriers. The time necessary to dissolve 50% and 90% of ticagrelor from mesoporous adsorbents at pH 4.5 increased in the following order: SBA-15-(CH2)3-SO3H < MCM-41-(CH2)3-SO3H < PHTS-(CH2)3-SO3H.

Unraveling influence of metal species on norfloxacin removal by mesoporous metallic silicon adsorbent.

Metal-modified adsorbent had appreciable adsorption capacity and fast rate toward norfloxacin (NOR), but limited studies focused on the influence of metal species on adsorbents' performance. In this study, Fe and Cu were chosen to be loaded on mesoporous silicon SBA-15 for absorbing NOR and investigating the key function of metal species. An obvious synergy effect was found between active species and supporter. A high adsorption capacity (44.8mgg-1 for Fe/SBA-15 and 78.3mgg-1 for Cu/SBA-15) and short equilibration time (< 2h) were obtained. NOR adsorptions on two processes were described well by pseudo-second-order kinetics, particle diffusion equation, and Langmuir isotherm. The adsorption processes were spontaneous, but NOR adsorption on Cu/SBA-15 was endothermic while its adsorption on Fe/SBA-15 was exothermic. HA had dual effect on the adsorption efficiency, with a promotion at low HA concentration but an inhibition at high concentration. NOR removal increased first and then decreased with pH ascension from 3 to 9 for both Fe/SBA-15 and Cu/SBA-15, achieving maximum at pH = 7. Comparative characterizations and experiments suggested that NOR adsorption processes were dominated by electrostatic interactions, n-π EDA interactions, hydrogen bonds, and surface complex. The greater n-π EDA and complex efficiency of Cu with NOR resulted in the superior performance of Cu/SBA-15. Graphical abstract.

Development of recoverable magnetic mesoporous carbon adsorbent for removal of methyl blue and methyl orange from wastewater

Abstract The novel magnetic mesoporous activated carbon (MMAC) was prepared from activated carbon (AC), produced from rice husk through ZnCl2 chemical activation. Meso-structure was induced via Korea Advanced Institute of Science and Technology-6 (KIT-6) silica formation and magnetic behavior was incorporated by magnetite by wetness impregnation method. KIT-6 silica enhances the porosity and provides a 3D structure to improve the adsorption process. The adsorption of methyl blue (MB) and methyl orange (MO) dyes on MMAC, mesoporous activated carbon (MAC) and AC was investigated and compared. The adsorbents were characterized by SEM, XRD, BET and FTIR analysis techniques. The effect of different process parameters on the adsorption efficiency such as pH of the dye solution, initial dye concentration and dosing of adsorbents were studied. The adsorption efficiency was evaluated by testing aliquot in UV–vis spectroscopy. The experimental data for the MMAC shows that MB followed the Freundlich isotherm while MO was well suited with the Langmuir model. The MMAC removed 82 % MB and 98.5 % MO dye solution in 30 min. The adsorbent was regenerated and reused for MB and MO for 4 cycles without a significant decrease in the adsorption efficiency. The MMAC was found to be the most efficient adsorbent than MAC and AC because of its high surface area and high pore volume. The magnetic behavior of MMAC separates the adsorbent after the adsorption process, making it potential adsorbent for water treatment.

Mesoporous adsorbents for perfluorinated compounds

Abstract Effective adsorbents for polyfluorinated compounds (PFCs) were obtained and successfully tested in adsorption of perfluorooctanoic and perfluorooctanesulfonic acids. Bridged silsesquioxanes containing secondary and tertiary amino groups were synthesized by sol-gel condensation of bis[3-(trimethoxysilyl)propyl]amine and N-methyl-3,3′-bis(trimethoxysilyl)dipropylamine in acidic media in the presence of surfactants. Obtained materials were mesoporous with high BET surface area. They combine high structural stability with high concentration of surface amino groups serving as adsorption sites. Batch adsorption tests demonstrated their high adsorption capacity on PFCs: in some experiments it reached up to 88% of the adsorbent weight. Adsorption of PFCs changed the surfaces of the adsorbent nanoparticles from hydrophilic to hydrophobic thus providing their agglomeration and floatability. Column tests showed fast adsorption of PFCs even at high concentrations and high flow rates. Obtained results can be used in the development of an effective filtration device for clean-up of water contaminated by PFCs.

Heating induced hierarchically mesoporous adsorbent derived from natural hydromagnesite for highly efficient defluoridation of water

Hierarchically mesoporous adsorbent derived from natural hydromagnesite with remarkable adsorption capacity for fluoride (F−) has been synthesized through the facile one-step calcination. Various characterizations confirmed that calcination temperature was directly correlated with their crystallite structures, surface properties, and adsorb ability. The hydromagnesite calcined at 500 °C (CH-5) exhibits the highest adsorption capacity and rate towards F−. The F− adsorption isotherm data was explored by both Langmuir and Freundlich model and the maximum adsorption capacity of CH-5 was 69.6 mg/g. Kinetic study revealed that the adsorption kinetics follows the pseudo-second-order model, suggesting the chemisorption mechanism. Regeneration study showed that the adsorption ability for fluorine can be completely recovered by calcining at 500 °C, and after five cycles, the adsorption ability is not significantly weakened. After detailed evaluation, the enhancement mechanism of the calcined product can be attributed to relatively higher specific surface area and exposed more magnesite active sites due to the maintenance of the intrinsic three-dimensional layer structure during the dehydration and decarbonation, which were responsible for the striking adsorption abilities. The green adsorbent originated from natural mineral with the characteristics of low cost, high adsorption ability and recoverability is advantageous for fluoride-containing wastewater treatment.

High capacity amidic succinic acid functionalized mesoporous silica for the adsorption of uranium

The nuclear reactors operating worldwide are currently using the uranium mined from the resources available on the earth's crust. A significant volume of aqueous waste containing a small quantity of uranium was generated during the processing of ores. There is a growing demand to remove this toxic uranium from these aqueous streams, owing to the limit of tolerable daily intake (15 μg L−1) for uranium imposed by the World Health Organization. This demand throws huge challenges to the separation chemists to engineer the solid phase adsorbents having high capacity, excellent selectivity and satisfactory throughputs for processing a vast quantity of aqueous waste containing traces of uranium. In this context, the task specific amidic succinic acid (SUC) functional groups tailored on mesoporous silica having wide porosity and large surface area have been prepared and characterized by BET surface area, pore and particle size distribution, thermogravimetry, SEM-EDX analysis, FT-IR and Raman spectroscopy. The adsorption behavior of uranium (VI) from the aqueous phase on the tailored adsorbent (MCM-SUC) was studied as a function of pH of the aqueous phase, duration of equilibration, uranium concentration in the aqueous phase, and the results were compared with the adsorbent containing the same functional group but grafted on silica gel (Si-SUC), which exhibited adsorption capacity of 61 mg g−1. The fast kinetics of adsorption and significantly high Langmuir adsorption capacity of uranium (807 mgg −1), as compared to the other mesoporous adsorbents reported in literature, achieved in MCM-SUC was due to controlled synthesis of SUC functionalized mesoporous silica that favoured high degree of SUC number density on the mesoporous material. The adsorbed uranium was recovered using 0.1 M nitric acid.

Luminescence performance of Cerium(III) ions incorporated into organofunctional mesoporous silica

Abstract Series of SBA-15 derived ordered mesoporous silica adsorbents bearing phenylsulfonic, phosphonic groups and their combinations were synthesized by non-grafting approach. Sodium metasilicate was used as precursor for the silica matrix. The materials were characterized using 1H, 31P, 29Si and 13C solid-state NMR spectroscopy, N2-physisorption isotherms, powder XRD, FTIR, TGA, SEM and TEM. It was found that all the samples exhibited typical hexagonal arrangement of mesoporous structure with high surface area. The active organic functions were, at least to some extent, incorporated into the framework of SBA-15, efficiently promoting the uptake of Ce(III) into the produced SBA-15 type matrices. Significant changes in luminescence of the samples were observed with both increasing content of incorporated cation and with change of heteroatoms (O, P, S) in functional groups of silica. The shapes of the peaks at 350–360 nm in the photoluminescence spectra originating from the 4f→5d (2F5/2, 2F7/2) transitions were indicative of the presence of Ce(III) ions in the mesoporous silica matrix with adsorption capacity increasing in the series up to ~2 mmol∙g−1(259.2 mg∙g−1). The Ce-incorporated samples dehydrated in vacuum exhibited decreased photoluminescence with integrated intensities comparable to those of water-containing samples. The high luminescent performances of these luminescent Ce-incorporated mesoporous materials could render attractive potential applications in optical amplification and laser systems, etc.