Sorption Studies Research Articles

Hybrid Chitosan Biosorbents: Tunable Adsorption at Surface and Micropore Domains

Herein, we report a study that provides new insight on the knowledge gaps that relate to the role of biopolymer structure and adsorption properties for chitosan adsorbents that are cross-linked with glutaraldehyde. The systematic modification of chitosan cross-linked with glutaraldehyde (CG) and its quaternized forms (QCG) was studied in relation to the reaction conditions: mole ratios of reactants and pH conditions. Complementary adsorbent characterization employed 13C NMR/FTIR spectroscopy, TGA and DSC, point-zero-charge (PZC), solvent swelling, and sorption studies using selected dye probes. The spectral and thermal techniques provide complementary evidence that affirm the key role of cross-linker content and quaternization on variation of the physicochemical properties of chitosan. The PZC results reveal a neutral surface charge for the modified materials between pH 6.0 to 6.3 ± 0.3, as compared with pH 8.7 ± 0.4 for pristine chitosan. Solvent swelling in water decreased with greater cross-linking, while the QCG materials had greater swelling over CG materials due to enhanced hydration. The adsorption results reveal variable dye uptake properties according to the cross-linker content. Similarly, surface versus micropore adsorption was demonstrated, according to the nature and ionization state of the dye for the modified adsorbents, where the CG and QCG materials had tunable sorption properties that exceeded that of unmodified chitosan. A key step in tuning the structure and surface chemical properties of cross-linked chitosan involves pH control during synthesis. The facile tunability of the physicochemical properties of the modified biopolymers reported herein means that they possess features of biomimetics that are relevant to advanced drug delivery, antimicrobial materials for wound healing, biosensors, and biosorbents for biomedical applications.

Design of some ferrite-based nanoparticles for uranium removal from Sella leach liquor

ABSTRACT Uranium is a non-biodegradable, toxic and radioactive inorganic pollutant that can cause serious human health impacts. This work aims to dip magnesium and lanthanum in ferrite nanoparticles and study their ability to bind uranium ions from uranium leach liquor. MgFe2O4, LaFe2O4 and CeFe2O4 nano-adsorbents were synthesised and characterised. Comparative studies of uranium sorption on the synthesised nano-adsorbents were achieved through a series of experiments at different adsorption conditions. The results show fast uranium sorption on the nanoparticles (with a high efficiency of 86.4 to 91.6), which reflects their higher affinities towards uranium ions. There is a clear improvement in the adsorption capacities of the nanoparticles for uranium binding in adsorption systems at higher temperatures. The maximum adsorption capacity of the MgFe2O4, LaFe2O4 and CeFe2O4 nano-adsorbents was obtained at pH 5, 0.5 g/L (S/L), 400 mg/L (Ci), 333 K and 90 min. The maximum adsorption capacities of uranium on MgFe2O4, LaFe2O4 and CeFe2O4 nanoparticles are 160.4, 118.8 and 129.2 mg/g, respectively. The assessment of the kinetic, isotherm and thermodynamic models was studied to evaluate the reliability and accuracy of these models in predicting the behaviour of uranium adsorption onto the used nanoparticles under various conditions. The outcome of these models confirms the hypothesis of the Elovich, pseudo-second order, Bangham, Langmuir, Dubinin and Radushkevich models to describe the adsorption process. Additionally, it suggests that uranium removal by the nanoparticles takes place through endothermic and spontaneous physio-chemical adsorption reactions. The nanoparticles show high capacity (115.7–142.3 mg/g) and efficiency (78.1–81.7%) for the uranium ions from different uranium-containing samples. These results confirm the high affinity of the synthesised nanoparticles for uranium adsorption in different media.

Construction of a Fluorinated-Anion Pillared Metal-Organic Framework Exhibiting Dual-Pore Architecture for Simultaneous Enhancement of C2H2 Adsorption Capacity and Selectivity.

Physisorption-based separation processes represents a promising alternative to the conventional thermally driven methods, such as cryogenic separation. However, a significant challenge lies in balancing the trade-off between adsorption capacity and selectivity of adsorbents. In this study, we introduce a novel fluorinated-anion pillared metal-organic frameworks (APMOFs) featuring a dual-pore architecture, constructed using a pyridine-oxazole bifunctional ligand. The inherent low symmetry of the ligand leads to significant distortion of the fluorinated-anion pillars, resulting in a distinctive type of APMOFs characterized by dual-pore architecture. On pore structure with constrict pore width is enriched with a high density of anion fluorinated pillars, offering numerous active sites advantageous for enhancing separation selectivity. Concurrently, the other pore structure exhibits larger dimensions, facilitating increased gas molecule accommodation and thereby augmenting adsorption capacity. Gas sorption studies reveal a substantial C2H2 adsorption capacity and a high C2H2/CO2 separation selectivity. Breakthrough experiments confirm its exceptional separation performance, while theoretical investigations elucidate a sequential adsorption process within these APMOFs, underscoring the efficacy of this strategy in overcoming trade-off limits in adsorbents.

Vertically Expanded Crystalline Porous Covalent Organic Frameworks.

Covalent organic frameworks (COFs) can be developed for molecular confinement and separation. However, their proximate π stacks limit the interlayer distance to be only 3-6 Å, which is too small for guests to enter. As a result, COFs block access to the x-y space and limit guest entry/exit strictly to only the pores along the z direction. Therefore, the extended faces of each layer are hidden between layers, precluding any interactions with guest molecules. Here, we report a strategy for opening interlayer spaces of COFs to attain newly accessible nanospaces between layers. This becomes possible using coordination bonds to replace the conventional π-π stacks between layers. We demonstrate this concept by synthesizing two-dimensional covalent cobalt(II) porphyrin layers through topology-guided polymerization, which were piled up by bidentate axial pillars through coordination bonds with cobalt(II) porphyrin along the z direction, assembling vertically expanded COFs via a one-pot reaction. The resultant frameworks separate the layers with axial pillars and create discrete apertures between layers defined by the molecular length of the pillars. Consequently, the originally inaccessible interlayers are open for guest access, while the polygonal π planes are exposed to trigger various supramolecular interactions. Vapor sorption, breakthrough experiments, and computational studies mutually revealed that the vertically expanded frameworks with optimal interlayer slits induce additional interactions to discriminate benzene and cyclohexane and separate their mixtures efficiently under ambient conditions.

Theoretical and experimental study on efficient thorium removal from aquatic environment using phosphate-modified graphene oxide polymeric beads

AbstractThorium is an element of immense importance in nuclear industry due to lower environmental impact compared to fossil fuels and conventional nuclear power. In the present study, highly selective adsorption of Th4+ on phosphate modified graphene oxide polymeric beads was investigated. The interaction of –PO4, –OH and –O– functional groups of graphene oxide with thorium ion was thoroughly investigated using Density Functional Theory. The adsorption induced density difference was utilized to investigate the bonding characteristics. The affinity of the Th4+ ions was obtained as –PO4 > –OH > –O– group of the phosphate modified graphene oxide. Phosphate modified Graphene oxide embedded in Calcium alginate matrix was characterized using ATR-FTIR, XRD, SEM and Raman spectroscopy. Highly efficient (> 93%) uptake of thorium at pH 5 with fast rate of sorption (< 5 min) was observed in the batch sorption studies.

Study on the Effect of Emulsifiers on the Properties of Oleogels Based on Olive Oil Containing Lidocaine

Oleogels are semi-solid materials that consist primarily of liquid oil immobilized in a network of organized structural molecules, which provide stability and maintain the oil in the desired shape. Due to their structure, oleogels can stabilize large amounts of liquid, making them excellent carriers for active substances, both lipophilic and hydrophilic. This study presents the synthesis methodology and investigations of olive oil-based oleogels, which are among the healthiest and most valuable vegetable fats, rich in unsaturated fatty acids and antioxidants such as vitamin E. Two types of surfactants were used: TWEEN 80, which lowers surface tension and stabilizes emulsions, and SPAN 80, which acts in oil-dominated phases. The oleogels were enriched with lidocaine, an active substance commonly used as a pain reliever and local anesthetic. This research characterized the obtained oleogels regarding their medical applications, paying particular attention to the influence of surfactant type and amount as well as the active substance on their physicochemical properties. Structural analyses were also conducted using Fourier transform infrared (FTIR) spectroscopy, alongside rheological and sorption studies, and the wettability of the materials was evaluated. The stability of the obtained oleogels was verified using the MultiScan MS20 system, allowing for an assessment of their potential suitability for long-term pharmaceutical applications. The results indicated that SPAN-stabilized oleogels exhibited better stability and favorable mechanical properties, making them promising candidates for medical applications, particularly in pain relief formulations.

Green synthesis of graphene oxide and magnetite nanoparticles and their arsenic removal efficiency from arsenic contaminated soil

Graphene-based nanomaterials have been proved to be robust sorbents for efficient removal of environmental contaminants including arsenic (As). Biobased graphene oxide (bGO-P) derived from sugarcane bagasse via pyrolysis, GO-C via chemical exfoliation, and magnetite nanoparticles (FeNPs) via green approach using Azadirachta indica leaf extract were synthesized and characterized by Ultraviolet-Visible Spectrophotometer (UV-vis.), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), mean particle size and Scanning electron microscopy (SEM) along with Energy dispersive spectroscopy (EDX) analysis. Compared to cellulose and hemicellulose, the lignin fraction was less in the precursor material. The GOC, bGO-P and FeNPs displayed maximum absorption at 230, 236, and 374 nm, respectively. FTIR spectrum showed different functional groups (C-OH, C-O-C, COOH and O-H) modifying the surfaces of synthesized materials. Graphene based nanomaterials showed clustered dense flakes of GO-C and thin transparent flakes of bGO-P. Elemental composition by EDX analysis of GO-C (71.26% C and 27.36% O), bGO-P (74.54% C and 24.61% O) and FeNPs (55.61% Fe, 4.1% C and 35.72% O) confirmed the presence of carbon, oxygen, and iron in synthesized nanomaterials. Sorption study was conducted with soil amended with different doses of synthesized nanomaterials (10, 50 and 250 mg) and exposed to 100, 300 and 500 ppm of As. Arsenic concentrations were estimated by colorimetry and atomic absorption spectroscopy (AAS). GO-C, bGO-P, and FeNPs showed substantial As removal efficiency i.e., 81 to 99.3%, 65 to 98.8% and 73.1–89.9%, respectively. Green synthesis of bGO-P and magnetite nanoparticles removed substantial amounts of As compared to GO-C and can be effectively deployed for As removal or immobilization. Higher and medium sorbent doses (250 and 50 mg) exhibited greater As removal and data was best fitted for Freundlich isotherm evidencing favorable sorption. Nevertheless, at low sorbent doses, data was best fitted for both models. Newly synthesized nanomaterials emerged as promising materials for As removal strategy for soil nano-remediation and can be effectively deployed in As contaminated soils.

A polyhedron-based metal-organic framework with electronegative donor sites for efficient C2H6/C2H4 separation

Ethylene is an important chemical raw material which is widely used in the production of chemical fibers, plastics, rubber, coatings, as well as medicines, and its separation from the gas mixtures of C2H6/C2H4 is of great importance but a challenging task due to their similar physical properties and molecular dimensions. Herein, we report the C2H6 and C2H4 sorption studies on a robust anionic metal-organic framework (MOF) {(NH2Me2)[Co3(μ3OH)(TPT)(TZB)3](H2O)6(DMA)6}n (Co-MOF) formed by connection of Co3(OH) clusters by two N-rich organic ligands 2,4,6-tri(4-pyridyl)-1,3,5-triazine (TPT) and 4-(1H-Tetrazol-5-yl)benzoic acid (H2TZB). The prepared Co-MOF features a polyhedron stacking network structure composed of trigonal bipyramidal cages and octahedral cage which both contribute to a high C2H6 uptake capacity of 6.48 mmol/g and a decent C2H6/C2H4 selectivity of 1.54 at 298 K and 1 bar. Grand Canonical Monte Carlo (GCMC) simulation results agree well with the experimental tendency, both in the adsorption isotherms and sorption heats, which demonstrated that the suitable pore surfaces with electronegative donor sites generated multiple CH ⋅⋅⋅O/N and CH ⋅⋅⋅π interactions between the framework and C2H6, resulting in a stronger interaction between the MOF skeleton and C2H6 molecule than C2H4 as reflected by the dispersion-corrected density functional theory (DFT) calculation.

Non-isothermal crystallization kinetics and activation energy modeling of carbon nanotubes dispersed high-density polyethylene and polypropylene blends

The study presents the effect of the reinforcement of carbon nanotubes (CNT) into high-density polyethylene (HDPE) and polypropylene (PP) blends. The Avrami exponent of CNT blends ranges within the 1.3–1.6 range. It demonstrates the 3D growth of crystals and nucleation activity during crystallization. The change in the Ozawa exponent indicates a two-stage crystallization process. The values of the Mo exponent show that the nucleation activity is affected by changing temperatures during the cooling process and the formation of high-quality crystal growth. The activation energy of the HDPE/PP matrix is 420.5 kJ/mol and adding 1.5% CNT resulted in 369.9 kJ/mol for Run-3. The polymer chains encounter difficulties in transitioning during the cooling process and release a significant amount of energy. The composition of the nanofiller in the blend affects the nucleation activity of the crystals. The permeability of the pure HDPE/PP sample obtained from sorption studies is 1.05 × 10−5 m2/s and adding 1.5% CNT in Run-3 provides a permeability of 5.2 × 10−5 m2/s. The CNT has a homogeneous dispersion in the matrix to form a net-like morphology. The crystallinity index calculated using the Seagal method for HDPE/PP, Run-3, Run-4 and Run-5 is 75%, 75.8%, 77.34% and 78%, respectively.

Encapsulation of Bamboosa vulgaris culms derived activated biochar into hierarchical permeable, phosphate rich and functionalized alginate aerogel composites and its contribution in U(VI) adsorption

In this study, a facile methodology was designed to encapsulate Bamboosa vulgaris culms derived activated biochar (BVC) in a variable mass ratio, into a three-dimensional hierarchical porous and permeable and amino-thiocarbamated alginate (TSC) to prepare hybrid biosorbents (BVC-MSA). These ultralight and lyophilized phosphate rich macroporous sorbents were rationally characterized through FTIR, XRD, BET, SEM-EDS, elemental mapping, XPS techniques and employed for efficient UO22+ adsorption from aqueous solutions. The phytic acid (PA) was found to be a suitable hydrophilic and phosphorylating agent for the TSC matrix through hydrogen-bonded crosslinking when employed in a correct mass ratio (1:3). The SEM-EDS and XPS analyses confirmed the UO22+ sorption onto BVC-MSA-3 (the most suitable composite with a BVC/TSC mass ratio of 30.0 % w/w) and provided evidence of heteroatom involvement in developing the physico-chemical interactions. The BCV-MSA-3 exhibited the best response as a sorbent during kinetics/sorption process, therefore, it was selected to study the equilibrium sorption studies. The BCV-MSA-3 removal efficiency increased from 12.1 to 94.2 % using 0.2 to 1.8 g/L sorbent dose at pH (4.5). The mentioned sorbent displayed a significant maximum sorption capacity qm (309.55 mg/g at 35 °C) calculated through the best-fitted Langmuir and Temkin models (R2 ≈ 0.99). The sorption kinetics followed the pseudo-second-order (PSORE) model and exhibited fast sorption rate teq (180 min). Thermodynamic parameters clarified that the sorption process is feasible ΔGo (−25.3 to −27.6 kJ/mol kJ/mol), endothermic ΔHo (27.17 kJ/mol), and proceeds with a positive entropy (0.176 kJ/mol.K). The study shows that BCV-MSA-3 could be an alternative and auspicious sorbent for uranium removal from aqueous solution.

Diffusion and sorption of water vapor by polyamide‐imides

AbstractThe study of sorption and diffusion characteristics of glassy polymers based on polyamide‐imides was carried out using the methods of static sorption, dilatometry, electron microscopy. Water sorption isotherms of polyamide‐imides based on trimellitimido‐N‐acetic acid (PAI‐A) and trimellitimido‐N‐p‐benzoic acid (PAI‐B) with different intramolecular ‘hinges’ in the diamine fragment were obtained. The isotherms are S‐shaped and occupy an intermediate position between polyheteroarylenes and aliphatic polyamides. The dual sorption model was used to interpret the results. It is shown that the Langmuir component of the isotherms is determined by the thermal prehistory of glassy polymers, while the sorption component associated with water dissolution according to Flory‐Huggins is determined by the chemical nature of the functional groups included in the monomeric unit. The diffusion coefficients of water and the temperature and concentration dependences of the diffusion coefficients of sorbed water molecules were determined.

Comparative study on dehydration of isopropanol and acetonitrile by pervaporation using PEBA/PANI/zeolite mixed matrix membranes

ABSTRACT Isopropanol (IPA) and Acetonitrile (ACN) solvents form azeotrope with water and separation by conventional processes is energy intensive. So, Pervaporation (PV) process became quite prominent and an alternative technique for dehydration of azeotropic mixtures. The selection of membrane places a crucial role in pervaporative separation and Mixed Matrix Membranes (MMMs) were widely employed. In this context, MMMs designated as PEBA-PANI and PEBA-PANI-4A were prepared by embedding PANI, zeolite 4A fillers in PEBA matrix. The synthesised zeolite particles, pristine PEBA and MMMs were characterised by XRD, FTIR, as well as contact angle measurements. Further, surface morphology and average particle size of zeolite particles are observed using SEM. Sorption studies with varying composition of isopropanol, and acetonitrile aqueous mixtures were correlated with their PV performances. The PEBA-PANI-4A MMMs showed higher % sorption of 11.34 and 8.57 for IPA–Water and ACN–Water systems respectively. Similarly greater pervaporation flux and selectivity of 0.28 kg/m2h and 720 were obtained for IPA–Water and 0.068 kg/m2h and 564 for ACN–Water systems at 10 wt. % water concentration. The PV results revealed that the MMMs exhibited better performance than pristine PEBA. All three membranes showed greater sorption, flux and selectivity for IPA-Water system than ACN-Water system.

Separation of Nd(III) from Nd(III)/Co(II) Mixture Using Poly (Carboxymethyl Cellulose.starch-g-acrylic Acid/Al2O3) Nanocomposite

AbstractThe separation of neodymium from the Nd(III)/Co(II) mixture is crucial for producing high-purity neodymium, which is essential in industries like electronics. A new nanocomposite, Poly(carboxymethyl cellulose.starch-g-acrylic acid/Al2O3), P(CMC-St-g-AA/Al2O3), was prepared and applied for the sorption and separation of Nd(III) from the Nd(III)/Co(II) mixture. This nanocomposite, synthesized with γ-irradiation of 60Co at 35 kGy, was extensively characterized using SEM, FTIR spectroscopy, and TGA-DTA. Parameters affecting neodymium separation were studied, revealing optimal conditions. Kinetic experiments showed agreement with a pseudo-nth-order kinetic model. Isothermal sorption studies indicated multilayer adsorption, with Co(II) and Nd(III) adsorption capacities of 2.781 mg/g and 8.825 mg/g, respectively, at pH 3.0. Thermodynamic analysis confirmed spontaneous and endothermic sorption. Separation factor values peaked at pH 3.0, shaking for 120 min, 0.1 adsorbent dosage, and ambient temperature, highlighting effective Nd-Co separation under these conditions. In conclusion, the comprehensive analysis and successful application of P(CMC-St-g-AA/Al2O3) nanocomposite underscore its potential as a highly efficient and selective sorbent for neodymium separation.

The role of carboxyl and cationic groups in low-level cationised cellulose fibres investigated by zeta potential and sorption studies

The anionic nature of both cellulose fibres and reactive dyes prevents substantial exhaustion of dye from the dyebath, which is at neutral pH before alkali is added to initiate dye fixation. Conventionally, salt is added to minimize the electrostatic repulsions that interfere with dye sorption, but that increases salt loads in effluents. An alternative is to affix cationic agents on the cellulose to overcome the inherent anionic charge, but that has generally been observed to result in uneven dye sorption. The focus of investigations in this work is to examine the influence of the ratio of charges on cellulose (of affixed cationic charges to inherent anionic charges) on the extents and evenness of dye sorption. The cationisation agent 3-chloro-2-hydroxypropyl-N,N,N-trimethylammonium chloride (CHPTAC) was grafted on loose viscose fibres to yield 12 to 185 mmol kg−1 cationic group content on the fibre that exhibited an inherent carboxyl group content of 68 mmol kg−1. Three different dyes (of varying molecular sizes and anionic group content) were employed for examination of sorption profiles. The results from both zeta potential measurements and dye sorption profiles showed evidence of limited dye uptake until the cationic group content in fibres exceeded that of the inherent carboxyl groups. Thereafter, an uptick in dye sorption was observed, with dye sorption levels increasing with rise in degree of cationisation. There were differences between the dyes in their degrees of sorption, which appear correlated with their molecular sizes.

Sorption behavior of strontium and europium ions from aqueous solutions using fabricated inorganic sorbent based on talc

Sorption of Sr(II) and Eu(III) from aqueous solutions was studied using tin molybdate talc sorbent synthesized by the precipitation technique. The synthesized sorbent was characterized using different analytical tools, such as; FT-IR, SEM, XRD, XRF, TGA, and DTA. The sorption studies applied to Sr(II) and Eu(III) include the effects of shaking time, pH, concentrations, and saturation capacity. The sorption of Sr(II) and Eu(III) depends on pH, reaction kinetics obey the pseudo-2nd-order model, and the Langmuir model is better suited for the sorption isotherm. The thermodynamic parameters reflect an endothermic and spontaneous sorption process. Desorption studies showed that 0.1 M HCl was the best desorbing agent for the complete recovery of Sr(II) (96.8%) and Eu(III) (92.9%). Finally, the obtained data illustrates that the synthesized sorbent can be applied and used as an efficient sorbent for the sorption of Sr(II) and Eu(III) from aqueous solutions and can be used as a promising sorbent to remove Sr(II) and Eu(III).

Bryophyllum pinnatum activated biochar for competent removal of fluoride from water: sorption and equilibrium studies

Bryophyllum pinnatum activated biochar for competent removal of fluoride from water: sorption and equilibrium studies

Small Organic Molecule‐Assisted Mesoscopic Self‐Assembly of SnO2 Nanoparticles: An Efficient Catalyst for the Synthesis of β‐Nitroaldol

AbstractOver the past few decades, huge number of mesoporous materials have been synthesized by using supramolecular assembly of ionic/non‐ionic surfactants as structure‐directing agents (SDAs). Here, we report a facile synthetic strategy to fabricate self‐assembled SnO2 nanoparticles with well‐defined nanocrystalline spherical morphology and mesoporosity using sodium salicylate as a SDA and stabilizing agent. The mesophases of the materials were investigated by powder X‐ray diffraction, TEM and N2 sorption studies. TEM results show that the mesopores are formed by the assembly of ultrasmall SnO2 NPs with broad range of interparticle voids and N2 sorption studies agreed well with this TEM data. This synthesis strategy facilitated the generation of SnO2 NPs with increased surface area and pores of nanoscale dimensions with a large number of exposed surface‐active sites. The photoinduced electron transfer in these materials was investigated by the fluorescence quenching study with pyranine, which suggested the presence of surface Lewis basicity. The materials showed excellent catalytic activity for the synthesis of β‐nitroaldol through the reaction of benzaldehyde and nitromethane. The heterogeneous nature of the catalyst could be attributed to the high surface area, presence of numerous surface active sites, and structural robustness of the self‐assembled SnO2 nanostructure. The catalysts exhibited negligible loss in activity after several catalytic cycles.

Carboxylate bridging Cd(II)-based 1D coordination polymer: Structure, fabrication of Schottky device and selective sorption of Bromocresol Green

Phenyl-1,3-diacetate (1,3-PDAt) bridging Cd(II)-based 1D coordination polymer {[Cd(1,3-PDAt)(phen)]⋅(MeOH)⋅(H2O)0.5}n, (CP) where 1,10-phenanthroline (phen) serves as chelating ligand has been structurally confirmed by Single Crystal X-Ray Diffraction measurements along with other spectral data. The thermal treatment releases MeOH at ∼90 °C and the final product ends at CdO. The Tauc’s plot evaluates the band gap, 3.87 eV (calculated value, 3.76 eV) using absorption spectral data which marks the semiconducting nature of the material. This has motivated us to fabricate Schottky Diode device and the measured conductance is 8.87 × 10−6 S/m in the dark. Interestingly, 1D CP shows selective and specific sorption of Bromocresol Green (BG) out of four common dyes (Methylene blue, Methyl orange, Rhodamine B, and Bromocresol Green (BG)). Besides, the sorbed BG in the CP is leached out on treating with water and the CP has been re-used for further sorption studies. Thus, the CP is economically recycled which is the first principle of Sustainable Development Goals.

An isostructural series of metal-organic frameworks: selective gas adsorption and sensing studies

The solvothermal reaction of Ln(NO3)3•6H2O (Ln = Nd, Sm, Eu, Tb, and Dy) with 9,10-bis(4-carboxylatopyridinium-1-methylene)anthracene dibromide (H2L)Br2 resulted in the formation of an isostructural series of lanthanide-based metal organic frameworks (Ln-MOFs), {[Nd(L)3/2(H2O)2]·(NO3)3·(S)}n (1), {[Sm(L)3/2(H2O)2]·(NO3)3·(S)}n (2), {[Eu(L)3/2(H2O)2]·(NO3)3·(S)}n (3), {[Tb(L)3/2(H2O)2]·(NO3)3·(S)}n (4) and {[Dy(L)3/2(H2O)2]·(NO3)3·(S)}n (5), where S denotes squeezed disordered solvent molecules and out of three nitrate ions in the voids, one nitrate is squeezed due to the high disorder. These MOFs were characterized with various techniques and single crystal X-ray analysis revealed a three dimensional (3D) (4,4,6)-connected metal organic framework with mononuclear metallic nodes in bicapped trigonal prismatic geometry. From the present series, we selected {[Sm(L)3/2(H2O)2]·(NO3)3·(S)}n (2) as a representative example for structural description and gas adsorption study whereas {[Dy(L)3/2(H2O)2]·(NO3)3·(S)}n (5) was used for the sensing of nitro compounds. All MOFs showed stability up to 200 °C. 2 demonstrates a higher CO2 uptake, despite exhibiting a low specific surface area (SABET) in N2 sorption studies. The sensing result shows that 5 act as selective sensors towards TNP with quenching efficiency greater than 99%.

Uptake of Cm (III) and Eu (III) by C–S–H phases under saline conditions in presence of EDTA: A batch sorption and TRLFS study

Eu (III) and Cm (III) uptake by calcium silicate hydrate phases (C–S–H) was investigated in presence of EDTA in NaCl and CaCl2 solutions. Different experimental parameters, i.e., ionic strength (0.1 m ≤ I'm ≤ 5.05 m), ligand concentration (10−5 m ≤ [EDTA] ≤ 10−2 m), calcium-to-silicon ratio (0.6 ≤ C/S ≤ 1.3) and sorption time (7 d ≤ t ≤ 365 d) were varied in the frame of batch sorption experiments and Time Resolved Laser Fluorescence spectroscopy (TRLFS) measurements. No effect of EDTA on the retention of Eu(III)/Cm(III) by C–S–H phases in NaCl or CaCl2 systems was observed at ligand concentrations ≤ 10−3 M. In NaCl solutions with [EDTA] = 10−2 M and C/S < 1.3, low retention (log Rd = 2–3, with Rd in L∙kg−1) of Eu(III) was detected after 7 d of sorption time, while strong retention (log Rd = 5–6) was observed after 50 d. This behaviour was explained by the initial stabilization of Eu(III)/Cm(III) in the aqueous phase due to the formation of two aqueous Eu(III)/Cm(III)-(OH)n-EDTA complexes, followed by the slow incorporation of Eu(III)/Cm(III) into the C–S–H structure. In CaCl2 solutions for all C/S ratios, as well as in NaCl solutions for C/S ∼ 1.3, the presence of [EDTA] = 10−2 M led to a significant decrease of the uptake (log Rd = 2–3) after 7 and 50 d of contact time. This effect was explained by the formation of stable aqueous Ca–Eu(III)/Cm(III)-EDTA complexes triggered by the presence of moderate to high Ca concentrations. No evident effect caused by increased ionic strength conditions could be confirmed in our sorption experiments.Results obtained in batch sorption experiments are underpinned by TRLFS data, with the observation of three main aqueous species, tentatively defined as Cm(OH)(EDTA)2-, Cm(OH)x (EDTA)-(x+1) and Ca–Cm(III)-EDTA, as well as a fourth species corresponding to Cm(III) incorporated in the CaO-layer of the C–S–H phases. In spite of the thermodynamic stability of the CaEDTA2− complex, which reduces the concentration of free EDTA, the formation of ternary Ca–Eu(III)/Cm(III)-EDTA complexes is expected to result in a significant impact of EDTA on the uptake of An (III)/Ln (III) by cement at high ligand concentrations. The assumption that Ca outcompetes actinides for the complexation with EDTA in cementitious systems may need to be revisited under these conditions.