A Versatile Shaping Method of Very-High Loading Porous Solids Paper Adsorbent Composites.

Owing to their high porosity and tunability, porous solids such as metal-organic frameworks (MOFs), zeolites, or activated carbons (ACs) are of great interest in the fields of air purification, gas separation, and catalysis, among others. Nonetheless, these materials are usually synthetized as powders and need to be shaped in a more practical way that does not modify their intrinsic property (i.e., porosity). Elaborating porous, freestanding and flexible sheets is a relevant shaping strategy. However, when high loadings (>70 wt.%) are achieved the mechanical properties are challenged. A new straightforward and green method involving the combination softwood bleached kraft pulp fibers (S) and nano-fibrillated cellulose (NFC) is reported, where S provides flexibility while NFC acts as a micro-structuring and mechanical reinforcement agent to form high loadings porous solids paper sheets (>70 wt.%). The composite has unobstructed porosity and good mechanical strength. The sheets prepared with various fillers (MOFs, ACs, and zeolites) can be rolled, handled, and adapted to different uses, such as air purification. As an example of potential application, a MOF paper composite has been considered for the capture of polar volatile organic compounds exhibiting better performance than beads and granules.

Novel Carbonaceous Adsorbents Prepared from Glycerin Waste and Dopamine for Gas Separation.

Glycerin, a low-valued waste from biodiesel production, and dopamine were used as precursors for adsorbent materials. The study is centered on the preparation and application of microporous activated carbon as adsorbent materials in the separation of ethane/ethylene and of gases that are natural gas or landfill gas components (ethane/methane and carbon dioxide/methane). The activated carbons were produced by the following sequence reactions: facile carbonization of a glycerin/dopamine mixture and chemical activation. Dopamine allowed the introduction of nitrogenated groups that improved the selectivity of the separations. The activating agent was KOH, but its mass ratio was kept lower than one to improve the sustainability of the final materials. The solids were characterized by N2 adsorption/desorption isotherms, SEM, FTIR spectroscopy, elemental analysis, and point of zero charges (pHPZC). The order for adsorption of the different adsorbates (in mmolg-1) on the most well performing material-Gdop0.75-is methane (2.5) < carbon dioxide (5.0) < ethylene (8.6) < ethane (8.9).

Evaluation of an Imine-Linked Polymer Organic Framework for Storage and Release of H2S and NO.

Hydrogen sulfide (H2S) and nitric oxide (NO) are especially known as toxic and polluting gases, yet they are also endogenously produced and play key roles in numerous biological processes. These two opposing aspects of the gases highlight the need for new types of materials to be developed in addition to the most common materials such as activated carbons and zeolites. Herein, a new imine-linked polymer organic framework was obtained using the inexpensive and easy-to-access reagents isophthalaldehyde and 2,4,6-triaminopyrimidine in good yield (64%) through the simple and catalyst-free Schiff-base reaction. The polymeric material has microporosity, an ABET surface area of 51 m2/g, and temperature stability up to 300 °C. The obtained 2,4,6-triaminopyrimidine imine-linked polymer organic material has a higher capacity to adsorb NO (1.6 mmol/g) than H2S (0.97 mmol/g). Release studies in aqueous solution showed that H2S has a faster release (3 h) from the material than NO, for which a steady release was observed for at least 5 h. This result is the first evaluation of the possibility of an imine-linked polymer organic framework being used in the therapeutic release of NO or H2S.

MOFs with Open Metal(III) Sites for the Environmental Capture of Polar Volatile Organic Compounds.

Metal-Organic Frameworks (MOFs) with open metal sites (OMS) interact strongly with a range of polar gases/vapors. However, under ambient conditions, their selective adsorption is generally impaired due to a high OMS affinity to water. This led previously to the privilege selection of hydrophobic MOFs for the selective capture/detection of volatile organic compounds (VOCs). Herein, we show that this paradigm is challenged by metal(III) polycarboxylates MOFs, bearing a high concentration of OMS, as MIL-100(Fe), enabling the selective capture of polar VOCs even in the presence of water. With experimental and computational tools, including single-component gravimetric and dynamic mixture adsorption measurements, in situ infrared (IR) spectroscopy and Density Functional Theory calculations we reveal that this adsorption mechanism involves a direct coordination of the VOC on the OMS, associated with an interaction energy that exceeds that of water. Hence, MOFs with OMS are demonstrated to be of interest for air purification purposes.

Emerging Nitric Oxide and Hydrogen Sulfide Releasing Carriers for Skin Wound Healing Therapy.

Nitric oxide (NO) and hydrogen sulfide (H2 S) have been recognized as important signalling molecules involved in multiple physiological functions, including wound healing. Their exogenous delivery has been established as a new route for therapies, being the topical application the nearest to commercialization. Nevertheless, the gaseous nature of these therapeutic agents and their toxicity at high levels imply additional challenges in the design of effective delivery systems, including the tailoring of their morphology and surface chemistry to get controllable release kinetics and suitable lifetimes. This review highlights the increasing interest in the use of these gases in wound healing applications by presenting the various potential strategies in which NO and/or H2 S are the main therapeutic agents, with focus on their conceptual design, release behaviour and therapeutic performance. These strategies comprise the application of several types of nanoparticles, polymers, porous materials, and composites as new releasing carriers of NO and H2 S, with characteristics that will facilitate the application of these molecules in the clinical practice.

Chitosan Biocomposites for the Adsorption and Release of H2S.

The search for H2S donors has been increasing due to the multiple therapeutic effects of the gas. However, the use of nanoporous materials has not been investigated despite their potential. Zeolites and activated carbons are known as good gas adsorbents and their modification with chitosan may increase the material biocompatibility and simultaneously its release time in aqueous solution, thus making them good H2S donors. Herein, we modified with chitosan a series of A zeolites (3A, 4A and 5A) with different pore sizes and an activated carbon obtained from glycerin. The amount of H2S adsorbed was evaluated by a volumetric method and their release capacity in aqueous solution was measured. These studies aimed to verify which of the materials had appropriate H2S adsorption/release properties to be considered a potential H2S donor. Additionally, cytotoxicity assays using HeLa cells were performed. Considering the obtained results, the chitosan composite with the A zeolite with the larger pore opening was the most promising material to be used as a H2S donor so a further cytotoxicity assay using H2S loaded was conducted and no toxicity was observed.

Unravelling moisture-induced CO2 chemisorption mechanisms in amine-modified sorbents at the molecular scale.

This work entails a comprehensive solid-state NMR and computational study of the influence of water and CO2 partial pressures on the CO2-adducts formed in amine-grafted silica sorbents. Our approach provides atomic level insights on hypothesised mechanisms for CO2 capture under dry and wet conditions in a tightly controlled atmosphere. The method used for sample preparation avoids the use of liquid water slurries, as performed in previous studies, enabling a molecular level understanding, by NMR, of the influence of controlled amounts of water vapor (down to ca. 0.7 kPa) in CO2 chemisorption processes. Details on the formation mechanism of moisture-induced CO2 species are provided aiming to study CO2 : H2O binary mixtures in amine-grafted silica sorbents. The interconversion between distinct chemisorbed CO2 species was quantitatively monitored by NMR under wet and dry conditions in silica sorbents grafted with amines possessing distinct bulkiness (primary and tertiary). Particular attention was given to two distinct carbonyl environments resonating at δ C ∼161 and 155 ppm, as their presence and relative intensities are greatly affected by moisture depending on the experimental conditions. 1D and 2D NMR spectral assignments of both these 13C resonances were assisted by density functional theory calculations of 1H and 13C chemical shifts on model structures of alkylamines grafted onto the silica surface that validated various hydrogen-bonded CO2 species that may occur upon formation of bicarbonate, carbamic acid and alkylammonium carbamate ion pairs. Water is a key component in flue gas streams, playing a major role in CO2 speciation, and this work extends the current knowledge on chemisorbed CO2 structures and their stabilities under dry/wet conditions, on amine-modified solid surfaces.

Decision making based on hybrid modeling approach applied to cellulose acetate based historical films conservation.

Preserving culture heritage cellulose acetate-based historical films is a challenge due to the long-term instability of these complex materials and a lack of prediction models that can guide conservation strategies for each particular film. In this work, a cellulose acetate degradation model is proposed as the basis for the selection of appropriate strategies for storage and conservation for each specimen, considering its specific information. Due to the formulation complexity and diversity of cellulose acetate-based films produced over the decades, we hereby propose a hybrid modeling approach to describe the films degradation process. The problem is addressed by a hybrid model that uses as a backbone a first-principles based model to describe the degradation kinetics of the pure cellulose diacetate polymer. The mechanistic model was successfully adapted to fit experimental data from accelerated aging of plasticized films. The hybrid model considers then the specificity of each historical film via the development of two chemometric models. These models resource on gas release data, namely acetic acid, and descriptors of the films (manufacturing date, AD-strip value and film type) to assess the current polymer degradation state and estimate the increase in the degradation rate. These estimations are then conjugated with storage conditions (e.g., temperature and relative humidity, presence of adsorbent in the film's box) and used to feed the mechanistic model to provide the required time degradation simulations. The developed chemometric models provided predictions with accuracy more than 87%. We have found that the storage archive as well as the manufacturing company are not determining factors for conservation but rather the manufacturing date, off gas data as well as the film type. In summary, this hybrid modeling was able to develop a practical tool for conservators to assess films conservation state and to design storage and conservation policies that are best suited for each cultural heritage film.

MOFs industrialization: a complete assessment of production costs.

The potential of safe and low-cost batch production processes for Metal-Organic Frameworks (MOFs) at an industrial scale has been evaluated based on the prototypical MOF MIL-160(Al), a bio-derived material of high practical interest that can be made with a high space-time yield using green ambient pressure conditions. A simple method to calculate the production cost of this material has been determined based on a simulated process constructed with the data collected from laboratory pilot large-scale tests taking into account for the first time in MOF cost evaluation all the process parameters such as the scale, the cost of the raw materials, recirculation, and washing. The investment for a production plant established the ground for the estimation of the complete cost. The expected cost ranged from ca. 55 $ per kg at 100 tons per year down to 29.5 $ per kg for 1 kton per year production with longer term perspectives of reaching costs below 10 $ per kg once the bio-derived ligand is considered for the large-scale production of bioplastics.

First-Principles Model to Evaluate Quantitatively the Long-Life Behavior of Cellulose Acetate Polymers.

A deep understanding of the degradation of cellulose diacetate (CDA) polymer is crucial in finding the appropriate long-term stability solution. This work presents an investigation of the reaction mechanism of hydrolysis using electronic density functional theory calculations with the B3LYP/6-31++G** level of theory to determine the energetics of the degradation reactions. This information was coupled with the transition-state theory to establish the kinetics of degradation for both the acid-catalyzed and noncatalyzed degradation pathways. In this model, the dependence on water concentration of the polymer as a function of pH and the evaporation of acetic acid from the polymer is explicitly accounted for. For the latter, the dependence of the concentration of acetic acid inside the films with the partial pressure on the surrounding environment was measured by sorption isotherms, where Henry's law constant was measured as a function of temperature. The accuracy of this approach was validated through comparison with experimental results of CDA-accelerated aging experiments. This model provides a step forward for the estimation of CDA degradation dependence on environmental conditions. From a broader perspective, this method can be translated to establish degradation models to predict the aging of other types of polymeric materials from first-principles calculations.

A Comparison of Different Approaches to Quantify Nitric Oxide Release from NO-Releasing Materials in Relevant Biological Media.

The development of solid materials that deliver nitric oxide (NO) are of interest for several therapeutic applications. Nevertheless, due to NO's reactive nature, rapid diffusion and short half-life, reporting their NO delivery characteristics is rather complex. The full knowledge of this parameter is fundamental to discuss the therapeutic utility of these materials, and thus, the NO quantification strategy must be carefully considered according to the NO-releasing scaffold type, to the expected NO-releasing amounts and to the medium of quantification. In this work, we explore and discuss three different ways of quantifying the release of NO in different biological fluids: haemoglobin assay, Griess assay and NO electrochemical detection. For these measurements, different porous materials, namely zeolites and titanosilicates were used as models for NO-releasing platforms. The oxyhaemoglobin assay offers great sensitivity (nanomolar levels), but it is only possible to monitor the NO release while oxyhaemoglobin is not fully converted. On the other hand, Griess assay has low sensitivity in complex biological media, namely in blood, and interferences with media make NO measurements questionable. Nevertheless, this method can measure micromolar amounts of NO and may be useful for an initial screening for long-term release performance. The electrochemical sensor enabled real-time measurements in a variety of biological settings. However, measured NO is critically low in oxygenated and complex media, giving transient signals, which makes long-term quantification impossible. Despite the disadvantages of each method, the combination of all the results provided a more comprehensive NO release profile for these materials, which will help to determine which formulations are most promising for specific therapeutic applications. This study highlights the importance of using appropriate NO quantification tools to provide accurate reports.

Sorption/Diffusion Contributions to the Gas Permeation Properties of Bi-Soft Segment Polyurethane/Polycaprolactone Membranes for Membrane Blood Oxygenators.

Due to their high hemocompatibility and gas permeation capacity, bi-soft segment polyurethane/polycaprolactone (PU/PCL) polymers are promising materials for use in membrane blood oxygenators. In this work, both nonporous symmetric and integral asymmetric PU/PCL membranes were synthesized, and the permeation properties of the atmospheric gases N2, O2, and CO2 through these membranes were experimentally determined using a new custom-built gas permeation apparatus. Permeate pressure vs. time curves were obtained at 37.0 °C and gas feed pressures up to 5 bar. Fluxes, permeances, and permeability coefficients were determined from the steady-state part of the curves, and the diffusion and sorption coefficients were estimated from the analysis of the transient state using the time-lag method. Independent measurements of the sorption coefficients of the three gases were performed, under equilibrium conditions, in order to validate the new setup and procedure. This work shows that the gas sorption in the PU/PCL polymers is the dominant factor for the permeation properties of the atmospheric gases in these membranes.

Tuning Cellular Biological Functions Through the Controlled Release of NO from a Porous Ti-MOF.

Materials for the controlled release of nitric oxide (NO) are of interest for therapeutic applications. However, to date, many suffer from toxicity and stability issues, as well as poor performance. Herein, we propose a new NO adsorption/release mechanism through the formation of nitrites on the skeleton of a titanium-based metal-organic framework (MOF) that we named MIP-177, featuring a suitable set of properties for such an application: (i) high NO storage capacity (3 µmol mg-1solid ), (ii) excellent biocompatibility at therapeutic relevant concentrations (no cytotoxicity at 90 µg mL-1 for wound healing) due to its high stability in biological media (<9 % degradation in 72 hours) and (iii) slow NO release in biological media (≈2 hours for 90 % release). The prospective application of MIP-177 is demonstrated through NO-driven control of mitochondrial respiration in cells and stimulation of cell migration, paving the way for the design of new NO delivery systems for wound healing therapy.

Enhancement of Ethane Selectivity in Ethane-Ethylene Mixtures by Perfluoro Groups in Zr-Based Metal-Organic Frameworks.

A series of zirconium dicarboxylate-based metal-organic frameworks (Zr MOFs) of the UiO-66 (tetrahedral and octahedral cages) or MIL-140 (triangular channels) structure type were investigated for the separation of ethane/ethylene mixtures. The adsorption, investigated both experimentally and computationally, revealed that the size and type of pores have a more pronounced effect on the selectivity than the aromaticity of the linker. The increase in pore size when changing from benzene to naphthalene (NDC) dicarboxylate ligand makes UiO-NDC less selective (1.3-1.4) than UiO-66 (1.75-1.9) within the pressure range (100-1000 kPa), while the three-dimensional (3D) pores of the UiOs favor the adsorption of ethane due to the interactions between ethane with more spacers than in the case of the 1D channels of MIL-140s. The impact of the functionalization revealed a very interesting increase of selectivity when two perfluoro groups are present on the aromatic ring (UiO-66-2CF3) (value of 2.5 up to 1000 kPa). Indeed, UiO-66-2CF3 revealed a unique combination of selectivity and working capacity at high pressures. This is due to a complex adsorption mechanism involving a different distribution of the guest molecules in the different cages associated with changes in the ligand/perfluoro orientation when the pressure increases, favoring the ethane adsorption at high pressures.

New generation of nitric oxide-releasing porous materials: Assessment of their potential to regulate biological functions.

Nitric oxide (NO) presents innumerable biological roles, and its exogenous supplementation for therapeutic purposes has become a necessity. Some nanoporous materials proved to be potential vehicles for NO with high storage capacity. However, there is still a lack of information about their efficiency to release controlled NO and if they are biocompatible and biologically stable. In this work, we address this knowledge gap starting by evaluating the NO release and stability under biological conditions and their toxicity with primary keratinocyte cells. Titanosilicates (ETS-4 and ETS-10 types) and clay-based materials were the materials under study, which have shown in previous studies suitable NO gas adsorption/release rates. ETS-4 proved to be the most promising material, combining good biocompatibility at 180 µg/mL, stability and slower NO release. ETS-10 and ETAS-10 showed the best biocompatibility at the same concentration and, in the case of clay-based materials, CoOS is the least toxic of those tested and the one that releases the highest NO amount. The potentiality of these new NO donors to regulate biological functions was assessed next by controlling the mitochondrial respiration and the cell migration. NO-loaded ETS-4 regulates O2 consumption and cell migration in a dose-dependent manner. For cell migration, a biphasic effect was observed in a narrow range of ETS-4 concentration, with a stimulatory effect becoming inhibitory just by doubling ETS-4 concentration. For the other materials, no effective regulation was achieved, which highlights the relevance of the new assessment presented in this work for nanoporous NO carriers that will pave the way for further developments.

Detecting Proton Transfer in CO2 Species Chemisorbed on Amine-Modified Mesoporous Silicas by Using 13 C†NMR Chemical Shift Anisotropy and Smart Control of Amine Surface Density.

The wealth of site-selective structural information on CO2 speciation, obtained by spectroscopic techniques, is often hampered by the lack of easy-to-control synthetic routes. Herein, an alternative experimental protocol that relies on the high sensitivity of 13 C chemical shift anisotropy (CSA) tensors to proton transfer, is presented to unambiguously distinguish between ionic/charged and neutral CO2 species, formed upon adsorption of 13 CO2 in amine-modified porous materials. Control of the surface amine spacing was achieved through the use of amine protecting groups during functionalisation prior to CO2 adsorption. This approach enabled the formation of either "isolated" or "paired" carbamate/carbamic acid species, providing a first experimental NMR proof towards the identification of both aggregation states. Computer modelling of surface CO2 -amine adducts assisted the solid-state NMR assignments and validated various hydrogen-bond arrangements occurring upon formation of isolated/aggregated carbamic acid and alkylammonium carbamate ion species. This work extends the understanding of chemisorbed CO2 structures formed at pore surfaces and reveals structural insight about the protonation source responsible for the proton-transfer mechanism in such aggregates.

Metal-Organic Frameworks for Cultural Heritage Preservation: The Case of Acetic Acid Removal.

The removal of low concentrations of acetic acid from indoor air at museums poses serious preservation problems that the current adsorbents cannot easily address owing to their poor affinity for acetic acid and/or their low adsorption selectivity versus water. In this context, a series of topical water-stable metal-organic frameworks (MOFs) with different pore sizes, topologies, hydrophobic characters, and functional groups was explored through a joint experimental-computational exploration. We demonstrate how a subtle combination of sufficient hydrophobicity and optimized host-guest interactions allows one to overcome the challenge of capturing traces of this very polar volatile organic compound in the presence of humidity. The optimal capture of acetic acid was accomplished with MOFs that do not show polar groups in the inorganic node or have lipophilic but polar (e.g., perfluoro) groups functionalized to the organic linkers, that is, the best candidates from the list of explored MOFs are MIL-140B and UiO-66-2CF3. These two MOFs present the appropriate pore size to favor a high degree of confinement, together with organic spacers that allow an enhancement of the van der Waals interactions with the acetic acid. We establish in this work that MOFs can be a viable solution to this highly challenging problem in cultural heritage protection, which is a new field of application for this type of hybrid materials.

Vitamin B3 metal-organic frameworks as potential delivery vehicles for therapeutic nitric oxide.

The synthesis and structural characterization of two isostructural metal (M=Ni, Co) 3D framework structure that integrate vitamin B3 building blocks with NO delivery capabilities and low toxicity is presented. The compounds with a formula [M2(µ2-H2O)(µ-vitamin B3)4]·2H2O contain two crystallographic distinct divalent metal centres connected by a bridging water and carboxylate group from vitamin B3. The porous compounds have the capability of storing and releasing nitric oxide (NO) in a slow and reversible manner, with released amounts of 2.6 and 2.0µmol NOmgsolid-1, on the Ni and Co compound, respectively. The NO release followed a convenient slow release kinetic profile in both gas and liquid phases. Haemoglobin tests demonstrated that NO is released to the medium in a biologically active form, thus suitable to trigger the desired response in biological systems. The toxicity of the samples with and without loaded NO was evaluated from cytotoxicity tests in HeLa and HEKn cells, showing low toxicity of the compounds at concentrations below 180µgcm-3. The overall results indicate that these bio based MOFs are of interest for therapeutic applications related with NO delivery. STATEMENT OF SIGNIFICANCE.

Structure of Chemisorbed CO(2) Species in Amine-Functionalized Mesoporous Silicas Studied by Solid-State NMR and Computer Modeling.

Two-dimensional (2D) solid-state nuclear magnetic resonance (SSNMR) experiments on samples loaded with 13C-labeled CO2, "under controlled partial pressures", have been performed in this work, revealing unprecedented structural details about the formation of CO2 adducts from its reaction with various amine-functionalized SBA-15 containing amines having distinct steric hindrances (e.g., primary, secondary) and similar loadings. Three chemisorbed CO2 species were identified by NMR from distinct carbonyl environments resonating at δC ≈ 153, 160, and 164 ppm. The newly reported chemisorbed CO2 species at δC ≈ 153 ppm was found to be extremely moisture dependent. A comprehensive 1H-based SSNMR study [1D 1H and 2D 1H-X heteronuclear correlation (HETCOR, X = 13C, 29Si) experiments] was performed on samples subjected to different treatments. It was found that all chemisorbed CO2 species are involved in hydrogen bonds (HBs) with either surface silanols or neighboring alkylamines. 1H chemical shifts up to 11.8 ppm revealed that certain chemisorbed CO2 species are engaged in very strong HBs. We effectively demonstrate that NMR may help in discriminating among free and hydrogen-bonded functional groups. 13C{14N} dipolar-recoupling NMR showed that the formation of carbonate or bicarbonate is excluded. Density functional theory calculations on models of alkylamines grafted into the silica surface assisted the 1H/13C assignments and validated various HB arrangements that may occur upon formation of carbamic acid. This work extends the understanding of the chemisorbed CO2 structures that are formed upon bonding of CO2 with surface amines and readily released from the surface by pressure swing.

The influence of the textural properties of activated carbons on acetaminophen adsorption at different temperatures.

The influence of temperature (20-40 °C) on the acetaminophen adsorption onto activated carbons with different textures was studied. Different temperature dependences, not explained by kinetic effects, were observed for carbons with different micropore size distribution patterns: adsorption capacity increased for pine gasification residues (Pi-fa) derived carbons and decreased for sisal based materials. No significant variation was seen for carbon CP. The species identified by (1)H NMR spectroscopy on the back-extraction solution proved that during the adsorption process exist the conditions required to promote the formation of acetaminophen oligomers which have constrained access to the narrow microporosity. The rotation energy of the dihedral angle between monomers (estimated by electronic DFT methods) showed that conformations in the planar form are less stable than the non-planar conformation (energy barrier of 70 and 23 kJ mol(-1)), but have critical dimensions similar to the monomer and can access most of the micropore volume. The enthalpy change of the overall process showed that the energy gain of the system (endothermic) for Pi-fa samples (≈40 kJ mol(-1)) was enough to allow a change in the dimer, or even a larger oligomer, conformation to the planar form. This will permit adsorption in the narrow micropores, thus explaining the uptake increase with temperature. Non-continuous micropore size distributions centered at pore widths close to the critical dimensions of the planar form seem to be crucial for a positive evolution of the adsorption capacity with temperature.