Sorption Of Molecules Research Articles

Two-Dimensional Cu-Based MOF for Selective Staining of the Cellular Nucleus through Fluorescence Imaging and Selective Sorption of Dye Molecules in Aqueous Medium.

A two-dimensional copper-based metal-organic framework, [Cu(C23H14O6)(C10H8N2)2]·H2O·DMSO, 1, was synthesized using pamoic acid (C23H16O6) and 4,4'-bipyridine (C10H8N2) as an organic ligand and Cu(II) as a metal ion. Single-crystal structure X-ray diffraction studies of the as-synthesized compound showed a two- dimensional structure with free hydroxyl groups. Upon excitation at 370 nm, the aqueous dispersion of [Cu(C23H14O6)(C10H8N2)2]·H2O·DMSO, 1, showed emission centered at 525 nm resulting from the intraligand energy transfer. Fluorescence microscopic experiments using a human epithelioid cervix carcinoma HeLa cell line were carried out, clearly showing that our compound selectively stained the cellular nucleus. To utilize the porous nature of [Cu(C23H14O6)(C10H8N2)2]·H2O·DMSO, 1, its dye sorption behavior in aqueous solution was determined, and a high affinity for methylene blue (MB) dye was confirmed. Our synthesized compound sorbed 88% MB dye with an initial concentration of 32 mg L-1, and its sorption capacity for MB was found to be 29.79 mg g-1. The possible mechanism of the dye sorption behavior was discussed in terms of the size and charge of dye molecules with respect to molecular-level interactions between the framework and the dye molecules.

(Invited) Application of Metal Oxide Active Supports for Enhancement of Electrocatalytic Reduction of Carbon Dioxide

Of particular interest to the preparation of advanced catalytic materials is efficient utilization of catalytic sites (metal and metal oxide nanostructures, their stabilization and intentional activation, as well as organization into two-dimensional arrays, ultra-thin films or three-dimensional networks (e.g. through sequential deposition) on electrode surfaces. They can form nanosized materials with well-defined composition, structure and thickness that exhibit desirable electrocatalytic properties (e.g. toward reduction of CO2). We explore here the ability of polynuclear inorganic metal oxo systems to stabilize and functionalize metal (e.g. copper) nanostructures. Here certain nanostructured metal oxides of zirconium, titanium, zinc or tungsten have been demonstrated to influence supported metal (e.g. Cu, Fe, Ag) centers in ways other than simple dispersion over electrode area. Evidence is presented that the support can modify activity (presumably electronic nature) of the above mentioned catalytic metal nanocenters thus affecting their chemisorptive and catalytic properties. Metal oxide cocatalysts can generate –OH groups at low potentials that induce proton mobility at the photo(electro)chemical interface.Our research interests concern development of systems for the electrocatalytic reduction of carbon dioxide not only in neutral but also in acid media. For example, nanosized Cu or Fe catalytic centers immobilized within ultra-thin films of tungsten oxide or mixed ZrO2-WO3 films have been considered and demonstrated to exhibit synergism during CO2-reduction. Selectivity of the catalytic systems largely depends on the activing adsorptive (CO2) phenomena and the affinity of catalytic centers to the adsorbed carbon monoxide (CO) type intermediates leading to their protonation or hydrogenation. Reduction of carbon dioxide begins now at less negative potentials and is accompanied by significant enhancement of the CO2-reduction current densities relative to the competitive hydrogen evolution. Among other important issues is the ability of certain metal oxides (e.g., WO3) to affect hydrogen via intra-structural sorption of hydrogen molecules or atoms.

Ions-Induced Alginate Gelation According to Elemental Analysis and a Combinatorial Approach.

This study considers the potential of elemental analysis of polysaccharide ionotropic gels in elucidating the junction zones for different divalent cations. The developed algorithm ensures the correct separation of contributions from physically adsorbed and structure-forming ionic compounds, with the obtained results scaled to alginate C12 block. Possible versions of chain association into dimers and their subsequent integration into flat junction zones were analyzed within the framework of the "egg-box" model. The application of combinatorial analysis made it possible to derive theoretical relations to find the probability of various types of egg-box cell occurrences for alginate chains with arbitrary monomeric units ratio μ = M/G, which makes it possible to compare experimental data for alginates of different origins. Based on literature data and obtained chemical formulas, the possible correspondence of concrete biopolymer cells to those most preferable for filling by alkaline earth cations was established. The identified features of elemental composition suggest the formation of composite hydrated complexes with the participation of transition metal cations. The possibility of quantitatively assessing ordered secondary structures formed due to the physical sorption of ions and molecules from environment, correlating with the sorption capabilities of Me2+ alginate, was established.

Importance of inner-sphere P-O-Fe bonds in natural and synthetic mineral-organic associations

Sorption of organic molecules on mineral surfaces can occur through several binding mechanisms of varying strength. Here, we investigated the importance of inner-sphere P-O-Fe bonds in synthetic and natural mineral-organic associations. Natural organic matter such as water extracted soil organic matter (WESOM) and extracellular polymeric substances (EPS) from liquid bacterial cultures were adsorbed to goethite and examined by FTIR spectroscopy and P K-edge NEXAFS spectroscopy. Natural particles from a Bg soil horizon (Gleysol) were subjected to X-ray fluorescence (XRF) mapping, NanoSIMS imaging, and NEXAFS spectro-microscopy at the P K-edge. Inner-sphere P-O-Fe bonds were identified for both, adsorbed EPS extracts and adsorbed WESOMs. Characteristic infrared peaks for P-O-Fe stretching vibrations are present but cannot unambiguously be interpreted due to possible interferences with mono- and polysaccharides. For the Bg horizon, P was only found on Fe oxides, covering the entire surface at different concentrations, but not on clay minerals. Linear combination fitting of NEXAFS spectra indicates that this adsorbed P is mainly a mixture of orthophosphate and organic P compounds. By combining atomic force microscopy (AFM) images with STXM-generated C and Fe distribution maps, we show that the Fe oxide surfaces were fully coated with organic matter. In contrast, clay minerals revealed a much lower C signal. The C NEXAFS spectra taken on the Fe oxides had a substantial contribution of carboxylic C, aliphatic C, and O-alkyl C, which is a composition clearly different from pure adsorbed EPS or aromatic-rich lignin-derived compounds. Our data show that inner-sphere P-O-Fe bonds are important for the association of Fe oxides with soil organic matter. In the Bg horizon, carboxyl groups and orthophosphate compete with the organic P compounds for adsorption sites.

Evaluation of synergistic adsorption approach for terbinafine removal by cotton shell powder immobilized zerovalent copper: Adsorption kinetics and DFT simulation

Cotton shell powder (CS), nano zerovalent copper (nZVC) and cotton shell powder immobilized zerovalent copper (ZVC@CS) were evaluated for their adsorption efficiencies towards terbinafine hydrochloride (TBH), an antifungal drug. The nZVC and ZVC@CS synthesized via one pot redox precipitation method were characterized by FTIR, XRD, BET, FESEM and TGA analysis. The TGA and AAS analysis confirmed the loading of nearly 10% of nZVC on cotton shell powder in ZVC@CS. The effect of operational parameters (pH, adsorbent dose, initial drug concentration, time, etc.) determining the extent of terbinafine hydrochloride adsorption on ZVC@CS were investigated to ascertain the optimal experimental conditions to achieve maximum adsorption efficiencies. To investigate the adsorption behavior of TBH on ZVC@CS, the experimental data were fitted for five different adsorption models viz. Langmuir, Freundlich, Temkin, Redlich-Peterson and Hill isotherms. The TBH adsorption data was best fit with Hill isotherm model indicating cooperative sorption of TBH molecules on ZVC@CS surface. Among the five kinetic equations namely the pseudo-first-order (PFO), the pseudo-second-order (PSO), Elovich model, the intraparticle diffusion model, and Boyd kinetic model used to estimate the adsorption mechanism, the PFO kinetic model give best fit with a good correlation for the physisorption of TBH on ZVC@CS composite. The mechanism of the adsorption process was observed to be complex, consisting of both surface adsorption and pore diffusion. However, the Boyd plot confirms external mass transport as the rate limiting step for the adsorption of TBH on ZVC@CS. The synergistic adsorption of TBH on ZVC@CS was hypothesized, and the idea was supported by structure optimization results from DFT studies. The ZVC@CS exhibits equilibrium TBH adsorption efficiency (qmax) of 285.3 mg.g−1, significantly higher than adsorbents used in literature for the TBH removal.It is suggested that ZVC@CS may serve as sustainable adsorbents for the removal of cationic contaminants from acidic medium.

An efficient eco-friendly water depollution process based on electrodeposited birnessite thin films coupled to electrochemistry: Application to methylene blue degradation as phenothiazines model molecule

This paper describes successful use of nanostructured birnessite thin films as electrode to remediate aqueous solutions containing methylene blue, which can be a model molecule of phenothiazines largely used in industries. Such electrodeposited thin films, noted HB1, can spontaneously degrade dye, but the reactivity is limited by organic molecules sorption. The use as electrode improves largely efficiency for total discoloring in very soft conditions with very low energy inputs, even at high concentrations. The discolored solutions analyses by ion chromatography report the significant presence of non-toxic small organic compounds and inorganic ions confirming the degradation. Characterization of materials by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Raman spectroscopy confirm that no organic compound were adsorbed onto surface, with no modification of birnessite due to an efficient regeneration by electrochemistry in continuous. For better understanding reactions in real time, in situ measurements by UV–Visible spectroscopy were performed on solution confirming the real interest of coupling to electrochemistry. In complement, another type of sample with lower birnessite amount, noted HB4, was tested with success. These HB1 and HB4 samples used as electrodes present high degradation capacities towards methylene blue equal to 934 mg g−1 of HB1 and 2222 mg g−1 of HB4, without any modification of material. These results are very promising for future eco-friendly applications due to good efficiencies, very simple conditions, without toxic products and wastes, and with low energy needs, both for synthesis and depollution processes.

Adsorption of Water Vapour on the Microstructure and Stability of Cu-Zn Bimetallic Coordination Polymer

A current challenge in the design of synthesis lies in the incorporation of two or more transition metals into a coordination polymer. The most widely used approach has been to incorporate a second metal as a generally innocent (coordinatively saturated) part of a linear linker as in the case of multifunctional carboxylated porphyrins (MCPs). The empirical method has been used to obtain many other types of MCPs; however, the selective, direct replacement of one transition metal within a monometallic coordination polymer via controlled stoichiometry has not generally led to maintained structural fidelity. In this present work, three pyromellitic acid complexes were synthesized at room temperature and characterized by Elemental analysis, Powder X-ray diffraction, Fourier transform infrared spectroscopy, Scanning electron microscopy, N2 adsorption-desorption Isotherm, and Thermal analysis. The reaction in water-methanol between pyromellitic acid and copper ions by ambient precipitation method formed [CuH2B4C]·5H2O. When zinc is combined with copper and the ligand, [Cu2Zn(B4C)1.5(H2O)4.5]·9H2O is formed. A repeat of this step under solvothermal condition produced Solvo-[Cu2Zn(B4C)1.5(H2O)5]·2H2O. The N2-adsorption isotherm of these compounds showed them to be Type III according to the IUPAC classification, with small pores only capable of small molecule sorption.
 Keywords: Coordination, microporous, polymer, pyromellitic, sorption

Microwave treatment effect on the enhanced basicity of porous clay heterostructured composites derived from Laponite

Porous clay heterostructured composites (PCH) derived from layered hydrous magnesium silicate, Laponite, were functionalized by Fe(NO3)3x9H2O with the use of mechano-chemical impregnation followed by microwave irradiation or hydrothermal treatment to evoke new base properties, active in CO2 sorption. It resulted in the progressive leaching of the Mg2+ from the octahedral sheets of the Laponite structure and their capture on the surface of PCH composites increasing the Mg/Si ratio. The increase of Mg/Si ratio was accompanied by the decline of the (Mg3OH) absorption bands intensity attributed to Laponite and discussed regarding the formation of dispersed nanostructured MgO moieties capable of adsorbing CO2. CO2-TPD temperature-programmed desorption technique revealed that sorption and stabilization of CO2 molecules are related to the coordination of oxygen sites in the formed MgO lattice and that edge and corner sites facilitate the interaction of CO2 molecules with O2− sites on MgO. Doping of PCH resulted also in the nucleation of nanocrystalline α-Fe2O3 able to capture CO2 with strength and stability higher than MgO. Microwave irradiation resulted in significant development of the surface basicity as part of the transformation of clay structure. This study confirms the importance of clay minerals in the uptake and retention of CO2.

Pressure-mediated crystal-fluid interaction in the zeolite offretite

The high-pressure behaviour and the crystal-fluid interaction of a natural offretite have been investigated by in situ single-crystal synchrotron X-ray diffraction, using a diamond anvil cell. Five different P-transmitting fluids have been employed: the non penetrating daphne oil 7575 and the potentially penetrating methanol:ethanol:H2O ​= ​16:3:1 mixture, ethanol:water ​= ​1:1 mixture, distilled H2O and liquid Ne. The daphne oil 7575 experiment allowed to describe the intrinsic compressional behaviour of offretite, without any pressure-induced crystal-fluid interaction, with an isothermal bulk modulus KV0 ​= ​59(2) GPa (βV0 ​= ​0.0170(9) GPa−1) for the range Pamb-1.83(5) GPa. All the experiments in potentially penetrating P-transmitting fluids showed the P-induced sorption of extra molecules within the large 12 ​mRs channel of offretite, obtained on the basis of X-ray structure refinements. For the aqueous mixtures, the magnitude of the adsorption appears to be governed by the H2O content of the P-transmitting fluid. Ne atoms are also able to penetrate into the 12 ​mRs channel in response to the applied pressure, interacting with the extraframework population via weak Van der Waals attraction. A comparative analysis of the P-mediated crystal-fluid interaction phenomena between offretite and the structurally similar erionite is provided.

Structure sensitivity in gas sorption and conversion on metal-organic frameworks

Many catalytic processes depend on the sorption and conversion of gaseous molecules on the surface of (porous) functional materials. These events often preferentially occur on specific, undercoordinated, external surface sites. Here we show the combination of in situ Photo-induced Force Microscopy (PiFM) with Density Functional Theory (DFT) calculations to study the site-specific sorption and conversion of formaldehyde on the external surfaces of well-defined faceted ZIF-8 microcrystals with nanoscale resolution. We observed preferential adsorption of formaldehyde on high index planes. Moreover, in situ PiFM allowed us to visualize unsaturated nanodomains within extended external crystal planes, showing enhanced sorption behavior on the nanoscale. Additionally, on defective ZIF-8 crystals, structure sensitive conversion of formaldehyde through a methoxy- and a formate mechanism mediated by Lewis acidity was found. Strikingly, sorption and conversion were influenced more by the external surface termination than by the concentration of defects. DFT calculations showed that this is due to the presence of specific atomic arrangements on high-index crystal surfaces. With this research, we showcase the high potential of in situ PiFM for structure sensitivity studies on porous functional materials.

Adsorption mechanism of the N2 and NRR intermediates on oxygen modified MnN4-graphene layers - a single atom catalysis perspective.

In the present work the adsorption of N2 and the nitrogen reduction reaction (NRR) intermediates have been investigated on oxygen modified MnNxOy (x + y = 4, x ≠ 0)/graphene layers through periodic density functional theory calculations. Various number of oxygen atoms substitute nitrogen atoms within the MnNxOy, with their effect on the layer stability, chemical bonding and N2 adsorption being explored. As the oxygen amount increases in the porphyrin unit, Mn-O interactions weaken with reference to that of Mn-N, bonding orbitals become less populated while the antibonding orbitals between Mn-N-O atoms become partially occupied, as evidenced by the Crystal orbital Hamiltonian population (COHP) and integrated crystal orbital bond index (ICOBI) analyses. During N2 adsorption on the different layers, the substitution of two and three nitrogen atoms by oxygen leads to the longest NN molecular bond length. Two main orientations for the N2 molecules sorption have been investigated: side-on and end-on which are perpendicular and parallel to the surface normal, respectively. When the interaction of N2 with MnNO3 layer is considered, d-band center variation of the Mn with reference to the pre-adsorbed state is more obvious after side-on adsorption configuration. For the selected layers based on initial N2 adsorption energies, the adsorption energies of nitrogen reduction reaction intermediates follow a trend based on the number of oxygen atoms in the porphyrin units. Charge density difference (CDD) maps and partial density of states (PDOS) analysis reveal that the interaction of N2 with oxygen modified layers takes place through electron acception-donation mechanism between the partially occupied Mn-d orbitals and the 2p orbitals of the N2 molecule. DDEC6-derived bond orders and atomic charges support the PDOS and adsorption/formation energy trends, and further clarify the bonding strengths of the atoms in the porphyrin units, as well as the Mn-N2 interactions in the adsorbed systems.

Neutron reflectivity study on the nanostructure of PMMA chains near substrate interfaces based on contrast variation accompanied with small molecule sorption.

In the case of poly(methyl methacrylate) (PMMA) thin films on a Si substrate, thermal annealing induces the formation of a layer of PMMA chains tightly adsorbed near the substrate interface, and the strongly adsorbed PMMA remains on the substrate, even after washing with toluene (hereinafter called adsorbed sample). Neutron reflectometry revealed that the concerned structure consists of three layers: an inner layer (tightly bound on the substrate), a middle layer (bulk-like), and an outer layer (surface) in the adsorbed sample. When an adsorbed sample was exposed to toluene vapor, it became clear that, between the solid adsorption layer (which does not swell) and bulk-like swollen layer, there was a "buffer layer" that could sorb more toluene molecules than the bulk-like layer. This buffer layer was found not only in the adsorbed sample but also in the standard spin-cast PMMA thin films on the substrate. When the polymer chains were firmly adsorbed and immobilized on the Si substrate, the freedom of the possible structure right next to the tightly bound layer was reduced, which restricted the relaxation of the conformation of the polymer chain strongly. The "buffer layer" was manifested by the sorption of toluene with different scattering length density contrasts.

A New Insight into the Mechanisms Underlying the Discoloration, Sorption, and Photodegradation of Methylene Blue Solutions with and without BNOx Nanocatalysts.

Methylene blue (MB) is widely used as a test material in photodynamic therapy and photocatalysis. These applications require an accurate determination of the MB concentration as well as the factors affecting the temporal evolution of the MB concentration. Optical absorbance is the most common method used to estimate MB concentration. This paper presents a detailed study of the dependence of the optical absorbance of aqueous methylene blue (MB) solutions in a concentration range of 0.5 to 10 mg·L-1. The nonlinear behavior of optical absorbance as a function of MB concentration is described for the first time. A sharp change in optical absorption is observed in the range of MB concentrations from 3.33 to 4.00 mg·L-1. Based on the analysis of the absorption spectra, it is concluded that this is due to the formation of MB dimers and trimers in the specific concentration range. For the first time, a strong, thermally induced discoloration effect of the MB solution under the influence of visible and sunlight was revealed: the simultaneous illumination and heating of MB solutions from 20 to 80 °C leads to a twofold decrease in the MB concentration in the solution. Exposure to sunlight for 120 min at a temperature of 80 °C led to the discoloration of the MB solution by more than 80%. The thermally induced discoloration of MB solutions should be considered in photocatalytic experiments when tested solutions are not thermally stabilized and heated due to irradiation. We discuss whether MB is a suitable test material for photocatalytic experiments and consider this using the example of a new photocatalytic material-boron oxynitride (BNOx) nanoparticles-with 4.2 and 6.5 at.% of oxygen. It is shown that discoloration is a complex process and includes the following mechanisms: thermally induced MB photodegradation, MB absorption on BNOx NPs, self-sensitizing MB photooxidation, and photocatalytic MB degradation. Careful consideration of all these processes makes it possible to determine the photocatalytic contribution to the discoloration process when using MB as a test material. The photocatalytic activity of BNOx NPs containing 4.2 and 6.5 at.% of oxygen, estimated at ~440 μmol·g-1·h-1. The obtained results are discussed based on the results of DFT calculations considering the effect of MB sorption on its self-sensitizing photooxidation activity. A DFT analysis of the MB sorption capacity with BNOx NPs shows that surface oxygen defects prevent the sorption of MB molecules due to their planar orientation over the BNOx surface. To enhance the sorption capacity, surface oxygen defects should be eliminated.

Constructing high-efficiency transport pathways via incorporating DP-POSS into PEG membranes for pervaporative desulfurization

Constructing high-efficiency transport pathways in polymeric membranes by incorporation of porous fillers has become one of the most prospective methods to break the trade-off effect between membrane selectivity and permeability. Herein, nanoscale dodecyl phenyl polyhedral oligomeric silsesquioxane (DP-POSS) were incorporated into polyethylene glycol (PEG) polymer to fabricate DP/PEG mixed matrix membranes (MMMs) for pervaporation desulfurization. The large internal diameter (0.68 nm) of cage-like DP-POSS particles facilitated the sorption and diffusion of thiophene molecules, and the phenyl groups of DP-POSS might also enhance the preferential sorption of thiophene due to p-π conjugation. The decrease of PEG crystallinity and enhancement of polymer chain mobility contributed to the larger free volume of MMMs, which was also favorable to the mass transfer for small molecules. Accordingly, the resultant DP/PEG-5 MMMs exhibited separation performance with an optimum enrichment factor of 28.9 and permeation flux of 355.3 g/(m2h), achieving 86.5% and 65.0% higher than the pristine membrane. This study might extend strategies to design high-performance MMMs by immobilization nanoscale POSS into polymers for desulfurization.

Al2O3 Dot and Antidot Array Synthesis in Hexagonally Packed Poly(styrene-block-methyl methacrylate) Nanometer-Thick Films for Nanostructure Fabrication.

Nanostructured organic templates originating from self-assembled block copolymers (BCPs) can be converted into inorganic nanostructures by sequential infiltration synthesis (SIS). This capability is particularly relevant within the framework of advanced lithographic applications because of the exploitation of the BCP-based nanostructures as hard masks. In this work, Al2O3 dot and antidot arrays were synthesized by sequential infiltration of trimethylaluminum and water precursors into perpendicularly oriented cylinder-forming poly(styrene-block-methyl methacrylate) (PS-b-PMMA) BCP thin films. The mechanism governing the effective incorporation of Al2O3 into the PMMA component of the BCP thin films was investigated evaluating the evolution of the lateral and vertical dimensions of Al2O3 dot and antidot arrays as a function of the SIS cycle number. The not-reactive PS component and the PS/PMMA interface in self-assembled PS-b-PMMA thin films result in additional paths for diffusion and supplementary surfaces for sorption of precursor molecules, respectively. Thus, the mass uptake of Al2O3 into the PMMA block of self-assembled PS-b-PMMA thin films is higher than that in pure PMMA thin films.

Fluorescent Zn(II)-Based Metal-Organic Framework: Interaction with Organic Solvents and CO2 and Methane Capture.

Adsorption of carbon dioxide (CO2), as well as many other kinds of small molecules, is of importance for industrial and sensing applications. Metal-organic framework (MOF)-based adsorbents are spotlighted for such applications. An essential for MOF adsorbent application is a simple and easy fabrication process, preferably from a cheap, sustainable, and environmentally friendly ligand. Herein, we fabricated a novel structural, thermally stable MOF with fluorescence properties, namely Zn [5-oxo-2,3-dihydro-5H-[1,3]-thiazolo [3,2-a]pyridine-3,7-dicarboxylic acid (TPDCA)] • dimethylformamide (DMF) •0.25 H2O (coded as QUF-001 MOF), in solvothermal conditions by using zinc nitrate as a source of metal ion and TPDCA as a ligand easy accessible from citric acid and cysteine. Single crystal X-ray diffraction analysis and microscopic examination revealed the two-dimensional character of the formed MOF. Upon treatment of QUF-001 with organic solvents (such as methanol, isopropanol, chloroform, dimethylformamide, tetrahydrofuran, hexane), interactions were observed and changes in fluorescence maxima as well as in the powder diffraction patterns were noticed, indicating the inclusion and intercalation of the solvents into the interlamellar space of the crystal structure of QUF-001. Furthermore, CO2 and CH4 molecule sorption properties for QUF-001 reached up to 1.6 mmol/g and 8.1 mmol/g, respectively, at 298 K and a pressure of 50 bars.

PVA-Based MMMs for Ethanol Dehydration via Pervaporation: A Comparison Study between Graphene and Graphene Oxide

Two different types of 2D nanosheets, including hydrophobic graphene (GR) and hydrophilic graphene oxide (GO), were filled into poly (vinyl alcohol) (PVA) polymers to prepare mixed matrix membranes (MMMs) for ethanol dehydration via pervaporation. The relationship between the physical/chemical properties of graphene and pervaporation performance of MMMs was investigated by a comparison of GR/PVA and GO/PVA MMMs in microstructure and PV performance. The incorporation of GO nanosheets into PVA reduced PVA crystallinity and enhanced the membrane hydrophilicity, while the incorporation of GR into PVA led to the opposite results. The incorporation of GR/GO into PVA depressed the PVA membrane swelling degree, and the incorporation of GR showed a more obvious depression effect. GR/PVA MMMs showed a much higher separation factor than GO/PVA MMMs, while they exhibited a much lower permeation flux than GO/PVA MMMs and pristine PVA membranes. The huge difference in microstructure and performance between GO/PVA and GR/PVA MMMs was strongly associated with the oxygen-containing groups on graphene lamellae. The higher permeation flux of GO/PVA MMMs was ascribed to the facilitated transport of water molecules induced by oxygen-containing groups and exclusive channels provided by GO lamellae, while the much lower permeation flux and higher separation factor GR/PVA MMMs was resulted from the smaller GR interplanar spacing (0.33 nm) and hydrophobicity as well as barrier effect of GR lamellae on the sorption and diffusion of water molecules. It was presumed that graphene intercalated with an appropriate number of oxygen-containing groups might be a good choice to prepare PVA-based MMMs for ethanol dehydration, which would combine the advantages of GR’s high interlayer diffusion selectivity and GO’s high permeation properties. The investigation might open a door to achieve both of high permeation flux and separation factor of PVA-based MMMs by tuning the microstructure of graphene.

Small angle x-ray scattering to investigate the specific surface of hydrated alginate microbeads

Encapsulation of active substances in biopolymer beads becomes a widely developed approach to gain efficiency for many applications. However, the characterization of such aqueous materials in their early stage of production is very delicate regarding their textural properties. The classical tools such as gas adsorption and Hg porosimetry can hardly provide relevant information since they require the removal of water, which is yet a fundamental part of the sample that drives its structure. In this article, we used small angle x-ray scattering (SAXS) as a tool in order to determine the specific surface area (SSA) of alginate microbeads in solution. This has been made possible by a careful procedure of SAXS measurements, involving calibration samples, allowing writing intensities in absolute units. Therefore, the Porod limit theory was used to calculate the SSA from the scattering length contrast and the measured absolute intensity. In addition, we compared the SSA of microbeads obtained from pure water and from a widely used cell culture medium, and we followed the textural evolution of a water alginate sample during the first step of a gentle drying process. Our results show that SAXS should be considered as a valuable tool for physico-chemists and food formulators in order to extract in situ dimensional and textural information of hydrogels during the formulation. It enables them to figure out the real surface available for the sorption of additive or active molecules in the formulation of biopolymers such as alginates, empowering them to better control encapsulation processes.

Study of Hydrophilic Properties of Polysaccharides

In this research, the structural characteristics, specific surface area, sorption of water vapor, and wetting enthalpy of various polysaccharides (cellulose, hemicelluloses, starch, pectin, chitin, and chitosan) have been studied. It was confirmed that crystallites are inaccessible for water, and therefore water molecules can interact only with polar groups in noncrystalline (amorphous) domains of biopolymers. The isotherms of water vapor sorption for various polysaccharides had sigmoid shapes, which can be explained by the absorption of water molecules in heterogeneous amorphous domains having clusters with different packing densities. The method of contributions of polar groups to sorption of water molecules was used, which allowed to derivate a simple calculating equation to describe the shape of sorption isotherms. The wetting of biopolymers with water was accompanied by a high exothermic thermal effect, in direct proportion to the amorphicity degree. The sorption values and wetting enthalpies of amorphous domains of biopolymers were calculated, which allowed to find the hydrophilicity index and compare the hydrophilicity of the various polysaccharides.

Adsorption of Fulvic Acid and Water Extractable Soil Organic Matter on Kaolinite and Muscovite

The interaction of organic matter with mineral components of the solid phase of soils is the most important process that regulates the cycle and balance of carbon in the biosphere. The adsorption of humic acids on minerals is accompanied by their fractionation in size, composition, and amphiphilicity, thus decreasing their heterogeneity. Despite a strong interest in studying the regularities and mechanisms of the interaction between natural organic matter and layered aluminosilicates, it is necessary to take into account the natural diversity of soil organic matter, adsorption conditions, and mineral composition. This study was designed to investigate the adsorption regularities of fulvic acid (FA) and water-extractable organic matter (WEOM) isolated from horizon H of peaty-podzolic-gleyic soil on kaolinite and muscovite. Sorbates and sorbents were examined by the following methods: high-pressure size exclusion chromatography (HPSEC), high-performance liquid chromatography (HPLC), and potentiometric titration. The specific surface areas of the sorbents were determined by the sorption of N2 molecules. We found that hydrophobic components of FA and WEOM are mainly adsorbed on mineral surfaces. The adsorption of FA and WEOM on kaolinite and muscovite is followed by decreased hydrophobicity of organic matter and decreased heterogeneity of its amphiphilic properties in an equilibrium solution. At pH levels around 6, sorption of organic matter from FA solution containing 19% and 81% hydrophilic and hydrophobic components, respectively, onto kaolinite and muscovite occurs mainly due to hydrophobic components. Hydrophobic interactions on siloxane surfaces are the main mechanism to fix FA on both minerals. Kaolinite adsorbs slightly more organic carbon per unit area than muscovite. The adsorption of WEOM from a solution with 41% hydrophilic and 59% hydrophobic components results not only from hydrophobic and hydrophilic components but also from hydrophobic and electrostatic interactions and depends on pH. The most hydrophobic fractions of organic matter are adsorbed from the hydrophobic components on the surface of both minerals. Under conditions of the performed experiments at pH < 5, more WEOM is adsorbed on muscovite than on kaolinite.