In situ Functionalized Mesoporous Silicas for Sustainable Remediation Strategies in Removal of Inorganic Pollutants from Contaminated Environmental Water

Low-cost mesoporous silicas of the SBA-15 family were prepared, aimed for removal of a broad spectrum of both cationic and anionic forms of hazardous metal pollutants (Cr(III, VI), Mn(II, VII), Pb(II), Cd(II), and Cu(II)) from environmental water. Series of mono-and bifunctional materials with immobilized ethylenediaminetriacetic acid (EDTA), primary amine (NH2), and quaternary ammonium (QAS) groups were prepared in a cost-efficient one-step synthesis using two silica sources, low-cost sodium metasilicate (Na2SiO3 9H(2)O) and the conventional source-tetraethylorthosilicate (TEOS). The functionalized SBA-15 samples obtained from both silica sources were highly ordered, as evidenced by TEM and SAXS data. All obtained materials were mesoporous with high surface area values of up to 745 m(2)/g, pore volumes from 0.99 to 1.44 cm(3)/g, and narrow pore distributions near 7 nm. The adsorption affinity of the EDTA-functionalized samples followed the common order Pb(II)> Cd(II)> Cu(II)> Cr(III)> Mn(II), which could be explained based on the Pearson theory. The highest adsorption capacities were observed for samples functionalized by EDTA groups using TEOS for synthesis (TEOS/EDTA): 195.6 mg/g for Pb(II), 111.2 mg/g for Cd(II), 58.7 mg/ g for Cu(II), 57.7 mg/g for Cr(III), and 49.4 mg/g for Mn(II). Moreover, organic matter (humic acid up to 10 mg/L) and inorganic (Na(I), K(I), Mg(II), Ca(II), etc) macrocomponents present in environmental water had almost negligible effect on the removal of these cations. The NaSi/EDTA/NH2 sample revealed a better selectivity compared to the NaSi/NH2 sample towards such species as Cr(III), Mn(II), Cd(II), and Cu(II). The chromate-ions uptake at pH 7.5 by the TEOS/QAS sample turned practically unaffected by the presence of doubly charged anions (CO32-, SO42-). The content of functional groups on the surface of MS decreased only slightly (similar to 1-5%) after several regeneration cycles. The complete desorption of all heavy metal ions can be achieved using 1 mol/L EDTA solution. Reusability tests demonstrated the complete stability of the adsorbent for at least five to six consecutive adsorption/ desorption cycles with no decrease in its adsorption characteristics compared to those obtained by 0.05 mol/L HNO3 treatments. The synthesized mesoporous materials were evaluated for removal of the heavy metal ions from drinking and different natural water samples, proving their potential as sustainable, effective, and cost-efficient adsorbents

Synthesis of Silicas with Carboxyl Functionality Using Template Method

A one-step method of synthesis of new materials with acidic carboxylic groups, based on the template method, has been developed. It was found that the postsynthetic treatment of silicas in boiling HCl leads to changes in structural parameters and changes the nature of functional groups. Efficiency of the methods was demonstrated by powder X-ray diffraction, infrared spectroscopy, and thermal analysis.На основі темплатного методу розроблено методику одностадійного синтезу нових матеріалів з кислотними карбоксильними групами. Встановлено, що процедура постсинтетичної обробки зразків кремнеземів в киплячій соляній кислоті приводить до зміни структурних параметрів і природи функціональних груп. Ефективність розроблених методик була доведена за допомогою дифрактометрії, ІЧ-спектроскопії та термічного аналізу.На основе темплатного метода разработана методика одностадийного синтеза новых материалов с кислотными карбоксильными группами. Установлено, что процедура постсинтетической обработки образцов кремнеземов в кипящей соляной кислоте приводит к изменению структурных параметров и природы функциональных групп. Эффективность разработанных методик была доказана с помощью дифрактометрии, ИК-спектроскопии и термического анализа

Removal of Poly- and Perfluoroalkyl Substances from Natural and Wastewater by Tailored Silica-Based Adsorbents

Per- and polyfluoroalkyl substances (PFAS) are very stable and ubiquitously distributed in terrestrial and aquatic environments, and treatment and remediation techniques for the removal of PFAS are urgently needed. In this study, mesoporous silica matrix SBA-15 grafted with alkyl amino groups was used to remove perfluorooctanoate (PFOA) from aqueous solutions. The amino groups were grafted onto SBA-15 by the condensation of alkyl amino silanes. The synthesized adsorbents were studied by SEM, TEM, IR, low-temperature nitrogen sorption, and XRD. The solid-state and liquid F-19 NMR spectroscopy, EDX, and LC-MS/MS results showed high adsorption efficiency and rapid reaction kinetics. In freshly prepared solutions and on the surface of the sorbents, the presence of PFOA micelles was observed. Furthermore, the introduction of amine-containing groups into the structure of the sorbent allows the sorption of up to 649 mg/g of PFOA from solutions. Results showed that the protonated surface amino groups and PFOA interacted electrostatically. The obtained results open perspectives for producing adsorbents for facile extraction of PFAS

The sol-gel method for preparation of polysiloxane xerogels containing carboxylic functionality

A procedure has been developed for synthesis of new polysiloxane xerogels with propionic and butyric acid-type groups. The procedure is based on the sol-gel method and involves the conversion of 2-cyanoethyltriethoxysilane (or 4-(triethoxysilyl)butyronitrile) to an ester with its subsequent hydrolytic polycondensation reaction.Розроблена методика синтезу нових полісилоксанових ксерогелів, що містять залишки пропіонової і масляної кислот.Разработана методика синтеза новых полисилоксановых ксерогелей, содержащих остатки пропионовой и масляной кислот

Template-free synthesis of hybrid silica nanoparticle with functionalized mesostructure for efficient methylene blue removal

A simple one-pot synthesis process for functionalized mesostructured silica nanoparticles (MSNP) is reported. The novel process demonstrated the possibility to achieve MSNP with a surface area up to 501 m2.g−1 using a phosphonate based nonsilane precursor such as N, N´-bis[4,6-bis(diethylphosphono)-1,3,5-triazin-yl]-1,2-diaminoethane (ED). MSNP obtained by using 20 mol% of ED achieved a surface area of 80 m2.g−1 and increasing the ED content to 30 mol% resulted in a surface area of 501 m2.g−1. Zeta potential of novel MSNPs (−65.5 and 70.0 mV) were much higher than the nanoparticle (NP) prepared from only TEOS (−49 mV), indicating the presence of a large number of –SiOH and phosphonic acid surface functional groups, as confirmed by Fourier-transform infrared spectroscopy (FT-IR) and Nuclear magnetic resonance (NMR) analysis. The functionalized MSNPs were used as an adsorbent for the removal of cationic pollutants like methylene blue (MB). The MSNP with the highest porosity displayed favorable MB adsorption behavior with ~380 mg.g−1 of MB adsorption capacity. Facile regeneration in an acidic medium (~pH 4.5) with easy recyclability (10 cycles) confirmed the practical applicability of this novel functionalized MSNPs

Synthesis of SBA-15 Type Organosilica Sorbents Using Sodium Metasilicate and Phosphonic Acid Residues

The direct template method was used for the synthesis of mesoporous organosilica sorbents of SBA-15 type with phosphonic acid groups using sodium metasilicate (SS) as a source of silica. The presence of functional groups in the synthesized samples was confirmed by IR spectroscopy and elemental analysis. This approach allowed producing relatively cheap materials with ordered structure, developed specific surface (550-700 m2/g) and high sorption volume (0.74-0.81 cm3/g). The optimal sodium metasilicate (SS):diphosphoethyltriethoxysilane (DPTS) ratio for the synthesis of SBA-15 type organosilicas with phosphonic acid residues was found to be 10:2

Recovery of rare earth elements from NdFeB magnet by mono- and bifunctional mesoporous silica: Waste recycling strategies and perspectives

Rare earth elements (REEs) such as Nd3+ and Dy3+ were recovered from simulated and real leaching solution of the NdFeB magnet via solid phase extraction (SPE). Extraction of REEs from simulated solutions was investigated using silica functionalized with NH2-, EDTA and/or phosphonic groups. The effects of several experimental factors (pH, efficiency of adsorbents, selectivity, and elution of metal ions) on extraction of REEs were investigated. Exploiting specific affinities of adsorbents toward REEs in the presence of competing ions, selective separation of REEs was achieved successfully. The affinity of phosphorous/nitrogen containing adsorbents had the descending order of adsorption: Fe3+ > Dy3+ > Nd3+ > Ni2+ > Al3+ for multi-component systems. In the first approach, a procedure based on precipitation of Fe3+ ions combined with SPE was evaluated for the recovery of REEs in two steps. Most of the Fe3+ ions (85%) were efficiently separated by adding an ammonia solution (pH ~ 2.5). Chemical analysis of precipitate showed, though, a high content of REEs. Extraction of REEs from supernatant liquid via bi-functional mesoporous silica with EDTA and/or phosphonic groups recovered ~97.0% of Nd3+ with Ni2+ and Al3+ ions as impurities. Non-ordered silica functionalized with phosphonic groups, showed economical superiority over other mesoporous adsorbents studied for REEs extraction. Complete recovery (97.8%) of REEs was achieved after several stages of SPE with adsorbents functionalized by P/N-containing groups. The in-advance removal of Fe3+ ions was a prerequisite for successful implementation of this approach. Finally, separation of Nd3+ and Dy3+ was performed from nitric acid media using the gradient elution to obtain 98.4% purity Nd3+. The proposed step-by-step SPE procedure by P/N-containing functionalized silica was successfully applied for extraction of REEs (95.5%) in an industrial magnet. This study opens up possibilities for application of the developed approach for the End-of-Life materials recycling

Bridged polysilsequioxane adsorption materials containing phosphonic acid residues

International audienceReactions of hydrolytic polycondensation of bis(triethoxysilane) [(C2H5O)3Si]2C2H4 (or [(C2H5O)3Si]2C6H4) and functional agent (C2H5O)3Si(CH2)2P(O)(OC2H5)2 (alkoxysilanes molar ratio of 2: 1 and 4: 1, fluoride ion catalyst and ethanol solvent) yielded powder-like xerogels that contained phosphonic acid residues in the surface layer. Their treatment with boiling concentrated hydrochloric acid resulted in transformation of functional groups ≡Si(CH2)2P(O)(OC2H5)2 into acid groups ≡Si(CH2)2P(O)(OH)2. The methods of IR, 1H MAS NMRm and 13C, 29Si, 31P MAS NMR spectroscopy showed the following (1) The surface layer in the initial xerogels contains not only phosphorus functional groups, but also some non-hydrolyzed ethoxysilyl groups as well as silanol groups. (2) The hydrochloric acid treatment of the initial xerogels causes the hydrolysis of not only ethoxy groups in the phosphonic acid residues, but also most residual ethoxysilyl groups. (3) Vacuum drying of xerogels after acid treatment forms ≡Si(CH2)2P(O)(OH)-OSi≡ links in their surface layer (not more than 20% of phosphorus-containing groups). (4) According to 29Si CP MAS NMR spectroscopic data, boiling acid treatment relatively enriches the xerogel structure T2 and T3 units and accounts for the higher rigidity of the hybrid framework. These units also account for retention of the porous structure in these xerogels over time, while most initial xerogels have porous structures that collapse in 12–18 months of storage. The acid-treated xerogels were attributed to microporous adsorbents (having specific surface area of 620 to 760 m2/g). According to the AFM data, both initial and acid-treated xerogels contain almost spherical aggregates of the primary particles (globules)