Unary Adsorption Equilibria of Hydrogen, Nitrogen, and Carbon Dioxide on Y-Type Zeolites at Temperatures from 298 to 393 K and at Pressures up to 3 MPa.

The equilibrium adsorption of CO2, N2, and H2 on commercially available Zeolite H-Y, Na-Y, and cation-exchanged NaTMA-Y was measured up to 3 MPa at 298.15, 313.15, 333.15, 353.15, and 393.15 K gravimetrically using a magnetic suspension balance. The chemical and textural characterization of the materials was carried out by thermogravimetric analysis, helium gravimetry, and N2 (77 K) physisorption. We report the excess and net isotherms as measured and estimates of the absolute adsorption isotherms. The latter are modeled using the simplified statistical isotherm (SSI) model to evaluate adsorbate-adsorbent interactions and parametrize the data for process modeling. When reported per unit volume of zeolite supercage, the SSI model indicates that the saturation capacity for a given gas takes the same value for the three adsorbents. The Henry's constants predicted by the model show a strong effect of the cation on the affinity of each adsorbate.

Measurement of Physicochemical Properties and CO2, N2, Ar, O2, and H2O Unary Adsorption Isotherms of Purolite A110 and Lewatit VP OC 1065 for Application in Direct Air Capture.

Direct air capture (DAC) using solid adsorbents has gained significant attention as a carbon dioxide removal (CDR) technology to help limit global temperature rise to below 2 °C. One large area of focus is the development of new adsorbent materials for DAC. However, the necessary data needed to employ these materials in process models for adsorbent screening are rarely available. Here, we showcase Purolite A110, a commercially available amine-functionalized polymeric resin, as a new candidate adsorbent for DAC and compare its properties to a current benchmark, Lewatit VP OC 1065. For both materials, we report their chemical features and composition, skeletal, particle, and bed density, total pore volume, particle porosity, BET area, thermal stability, and specific heat capacity. We determine their equilibrium sorption properties by measuring the volumetric CO2 isotherms at 288, 298, 308, 333, 343, 353, and 393 K, N2 and H2O isotherms at 288, 298, and 308 K, and Ar and O2 isotherms at 298 K. For CO2, N2, and H2O, we also present the corresponding isotherm model fitting parameters and heats of adsorption. These data can help facilitate process modeling and optimization studies to properly assess these adsorbents at scale.

A Response Surface Model to Predict and Experimentally Tune the Chemical, Magnetic and Optoelectronic Properties of Oxygen-Doped Boron Nitride.

Porous boron nitride (BN), a combination of hexagonal, turbostratic and amorphous BN, has emerged as a new platform photocatalyst. Yet, this material lacks photoactivity under visible light. Theoretical studies predict that tuning the oxygen content in oxygen-doped BN (BNO) could lower the band gap. This is yet to be verified experimentally. We present herein a systematic experimental route to simultaneously tune BNO's chemical, magnetic and optoelectronic properties using a multivariate synthesis parameter space. We report deep visible range band gaps (1.50-2.90 eV) and tuning of the oxygen (2-14 at.%) and specific paramagnetic OB3 contents (7-294 a.u. g-1 ). Through designing a response surface via a design of experiments (DOE) process, we have identified synthesis parameters influencing BNO's chemical, magnetic and optoelectronic properties. We also present model prediction equations relating these properties to the synthesis parameter space that we have validated experimentally. This methodology can help tailor and optimise BN materials for heterogeneous photocatalysis.

The absolute number of leukocytes per vial as a major cause of early false positive blood cultures: proof-of-concept and application.

Blood cultures detected as positive by the automated system but negative by microscopy and subculture are considered as "false-positives." Several causes have been identified, including hyperleukocytosis or the presence of fastidious bacteria, but as many cases remain unexplained we aimed to investigate the false positives occurring in our laboratory. We retrospectively collected data on blood cultures received over a period of 12 months to determine factors associated with the false-positive vials. We then prospectively validated our findings on the false-positive results occurring over a 3.5-month period. We finally applied scanning electron microscopy (SEM) on 63 false positives and molecular approaches on a subset of them. In the retrospective study, 154 (85%) of the 181 false-positive identified were positive following less than 4 h of incubation and were considered as "early false-positives." By performing ROC curves on these early false positives, we demonstrate that the absolute number of leukocytes is in fact the most discriminating factor of early false positivity (p < 0.001). This phenomenon can be the consequence of either a high blood culture volume (p < 0.001) or hyperleukocytosis (p < 0.001). In the prospective study, the use of a threshold of 219 million of leukocytes per vial enabled the identification of 97% of the early false positives. Finally, SEM and specific qPCR enabled three additional identifications while 16S rRNA/nanopore sequencing enabled the detection of Helicobacter cinaedi bacteremia and a polymicrobial infection. A high absolute number of leukocytes in blood cultures explains most false positives, thereby making it possible to target additional microbiological investigations.

En Route to Zero Emissions for Power and Industry with Amine-Based Post-combustion Capture.

As more countries commit to a net-zero GHG emission target, we need a whole energy and industrial system approach to decarbonization rather than focus on individual emitters. This paper presents a techno-economic analysis of monoethanolamine-based post-combustion capture to explore opportunities over a diverse range of power and industrial applications. The following ranges were investigated: feed gas flow rate between 1-1000 kg ·s-1, gas CO2 concentrations of 2-42%mol, capture rates of 70-99%, and interest rates of 2-20%. The economies of scale are evident when the flue gas flow rate is <20 kg ·s-1 and gas concentration is below 20%mol CO2. In most cases, increasing the capture rate from 90 to 95% has a negligible impact on capture cost, thereby reducing CO2 emissions at virtually no additional cost. The majority of the investigated space has an operating cost fraction above 50%. In these instances, reducing the cost of capital (i.e., interest rate) has a minor impact on the capture cost. Instead, it would be more beneficial to reduce steam requirements. We also provide a surrogate model which can evaluate capture cost from inputs of the gas flow rate, CO2 composition, capture rate, interest rate, steam cost, and electricity cost.

The Effect of Materials Architecture in TiO2 /MOF Composites on CO2 Photoreduction and Charge Transfer.

CO2 photoreduction to C1 /C1+ energized molecules is a key reaction of solar fuel technologies. Building heterojunctions can enhance photocatalysts performance, by facilitating charge transfer between two heterojunction phases. The material parameters that control this charge transfer remain unclear. Here, it is hypothesized that governing factors for CO2 photoreduction in gas phase are: i) a large porosity to accumulate CO2 molecules close to catalytic sites and ii) a high number of "points of contact" between the heterojunction components to enhance charge transfer. The former requirement can be met by using porous materials; the latter requirement by controlling the morphology of the heterojunction components. Hence, composites of titanium oxide or titanate and metal-organic framework (MOF), a highly porous material, are built. TiO2 or titanate nanofibers are synthesized and MOF particles are grown on the fibers. All composites produce CO under UV-vis light, using H2 as reducing agent. They are more active than their component materials, e.g., ≈9 times more active than titanate. The controlled composites morphology is confirmed and transient absorption spectroscopy highlights charge transfer between the composite components. It is demonstrated that electrons transfer from TiO2 into the MOF, and holes from the MOF into TiO2 , as the MOF induces band bending in TiO2 .

Physicochemical Properties, Equilibrium Adsorption Performance, Manufacturability, and Stability of TIFSIX-3-Ni for Direct Air Capture of CO2.

The use of adsorbents for direct air capture (DAC) of CO2 is regarded as a promising and essential carbon dioxide removal technology to help meet the goals outlined by the 2015 Paris Agreement. A class of adsorbents that has gained significant attention for this application is ultramicroporous metal organic frameworks (MOFs). However, the necessary data needed to facilitate process scale evaluation of these materials is not currently available. Here, we investigate TIFSIX-3-Ni, a previously reported ultramicroporous MOF for DAC, and measure several physicochemical and equilibrium adsorption properties. We report its crystal structure, textural properties, thermal stability, specific heat capacity, CO2, N2, and H2O equilibrium adsorption isotherms at multiple temperatures, and Ar and O2 isotherms at a single temperature. For CO2, N2, and H2O, we also report isotherm model fitting parameters and calculate heats of adsorption. We assess the manufacturability and process stability of TIFSIX-3-Ni by investigating the impact of batch reproducibility, binderless pelletization, humidity, and adsorption-desorption cycling (50 cycles) on its crystal structure, textural properties, and CO2 adsorption. For pelletized TIFSIX-3-Ni, we also report its skeletal, pellet, and bed density, total pore volume, and pellet porosity. Overall, our data enable initial process modeling and optimization studies to evaluate TIFSIX-3-Ni for DAC at the process scale. They also highlight the possibility to pelletize TIFSIX-3-Ni and the limited stability of the MOF under humid and oxidative conditions as well as upon multiple adsorption-desorption cycles.

Design and characterization of liquidlike POSS-based hybrid nanomaterials synthesized via ionic bonding and their interactions with CO2.

Liquidlike nanoparticle organic hybrid materials (NOHMs) were designed and synthesized by ionic grafting of polymer chains onto nanoscale silica units called polyhedral oligomeric silsesquioxane (POSS). The properties of these POSS-based NOHMs relevant to CO2 capture, in particular thermal stability, swelling, viscosity, as well as their interactions with CO2, were investigated using thermogravimetric analyses, differential scanning calorimetry, and NMR and ATR FT-IR spectroscopies. The results indicate that POSS units significantly enhance the thermal stability of the hybrid materials, and their porous nature also contributes to the overall CO2 capture capacity of NOHMs. The viscosity of the synthesized NOHMs was comparable to those reported for ionic liquids, and rapidly decreased as the temperature increased. The sorption of CO2 in POSS-based NOHMs also reduced their viscosities. The swelling behavior of POSS-based NOHMs was similar to that of previously studied nanoparticle-based NOHMs, and this generally resulted in less volume increase in NOHMs compared to their corresponding polymers for the same amount of CO2 loading.

How to Tailor Porous Boron Nitride Properties for Applications in Interfacial Processes.

The research of new porous materials for applications in interfacial processes is key to addressing global energy and sustainability challenges. For example, porous materials can be used to store fuels such as hydrogen or methane or to separate chemical mixtures reducing the energy currently required by thermal separation processes. Their catalytic properties can be exploited to convert adsorbed molecules into valuable or less hazardous chemicals, thereby reducing energy consumption or pollutants emissions. Porous boron nitride (BN) has appeared as a promising material for applications in molecular separations, gas storage, and catalysis owing to its high surface area and thermal stability, as well as its tunable physical properties and chemistry. However, the production of porous BN is still limited to the laboratory scale, and its formation mechanism, as well as ways to control porosity and chemistry, are yet to be fully understood. In addition, studies have pointed toward the instability of porous BN materials when exposed to humidity, which could significantly impact performance in industrial applications. Studies on porous BN performance and recyclability when employed in adsorption, gas storage, and catalysis remain limited, despite encouraging preliminary studies. Moreover, porous BN powder must be shaped into macrostructures (e.g., pellets) to be used commercially. However, common methods to shape porous materials into macrostructures often cause a reduction in the surface area and/or mechanical strength. In recent years, research groups, including ours, have started addressing the challenges discussed above. Herein, we summarize our collective findings through a selection of key studies. First, we discuss the chemistry and structure of BN, clarifying confusion around terminology and discussing the hydrolytic instability of the material in relation to its structure and chemistry. We demonstrate a way to reduce the instability in water while still maintaining high specific surface area. We propose a mechanism for the formation of porous BN and discuss the effects of different synthesis parameters on the structure and chemistry of porous BN, therefore providing a way to tune its properties for selected applications. While the syntheses covered often lead to a powder product, we also present ways to shape porous BN powders into macrostructures while still maintaining high accessible surface area for interfacial processes. Finally, we evaluate porous BN performance for chemical separations, gas storage, and catalysis. While the above highlights key advances in the field, further work is needed to allow deployment of porous BN. Specifically, we suggest evaluating its hydrolytic stability, refining the ways to shape the material into stable and reproducible macrostructures, establishing clear design rules to produce BN with specific chemistry and porosity, and, finally, providing standardized test procedures to evaluate porous BN catalytic and sorptive properties to facilitate comparison.

Paramagnetic States in Oxygen-Doped Boron Nitride Extend Light Harvesting and Photochemistry to the Deep Visible Region.

A family of boron nitride (BN)-based photocatalysts for solar fuel syntheses have recently emerged. Studies have shown that oxygen doping, leading to boron oxynitride (BNO), can extend light absorption to the visible range. However, the fundamental question surrounding the origin of enhanced light harvesting and the role of specific chemical states of oxygen in BNO photochemistry remains unanswered. Here, using an integrated experimental and first-principles-based computational approach, we demonstrate that paramagnetic isolated OB3 states are paramount to inducing prominent red-shifted light absorption. Conversely, we highlight the diamagnetic nature of O-B-O states, which are shown to cause undesired larger band gaps and impaired photochemistry. This study elucidates the importance of paramagnetism in BNO semiconductors and provides fundamental insight into its photophysics. The work herein paves the way for tailoring of its optoelectronic and photochemical properties for solar fuel synthesis.

Effect of Band Bending in Photoactive MOF-Based Heterojunctions.

Semiconductor/metal-organic framework (MOF) heterojunctions have demonstrated promising performance for the photoconversion of CO2 into value-added chemicals. To further improve performance, we must understand better the factors which govern charge transfer across the heterojunction interface. However, the effects of interfacial electric fields, which can drive or hinder electron flow, are not commonly investigated in MOF-based heterojunctions. In this study, we highlight the importance of interfacial band bending using two carbon nitride/MOF heterojunctions with either Co-ZIF-L or Ti-MIL-125-NH2. Direct measurement of the electronic structures using X-ray photoelectron spectroscopy (XPS), work function, valence band, and band gap measurements led to the construction of a simple band model at the heterojunction interface. This model, based on the heterojunction components and band bending, enabled us to rationalize the photocatalytic enhancements and losses observed in MOF-based heterojunctions. Using the insight gained from a promising band bending diagram, we developed a Type II carbon nitride/MOF heterojunction with a 2-fold enhanced CO2 photoreduction activity compared to the physical mixture.

Cu-functionalised porous boron nitride derived from a metal-organic framework.

Porous boron nitride (BN) displays promising properties for interfacial and bulk processes, e.g. molecular separation and storage, or (photo)catalysis. To maximise porous BN's potential in such applications, tuning and controlling its chemical and structural features is key. Functionalisation of porous BN with metal nanoparticle represents one possible route, albeit a hardly explored one. Metal-organic frameworks (MOFs) have been widely used as precursors to synthesise metal functionalised porous carbon-based materials, yet MOF-derived metal functionalised inorganic porous materials remain unexplored. Here, we hypothesise that MOFs could also serve as a platform to produce metal-functionalised porous BN. We have used a Cu-containing MOF, i.e. Cu/ZIF-8, as a precursor and successfully obtained porous BN functionalised with Cu nanoparticles (i.e. Cu/BN). While we have shown control of the Cu content, we have not yet demonstrated it for the nanoparticle size. The functionalisation has led to improved light harvesting and enhanced electron-hole separation, which have had a direct positive impact on the CO2 photoreduction activity (production formation rate 1.5 times higher than pristine BN and 12.5 times higher than g-C3N4). In addition, we have found that the metal in the MOF precursor impacts porous BN's purity. Unlike Cu/ZIF-8, a Co-containing ZIF-8 precursor led to porous C-BN (i.e. BN with a large amount of C in the structure). Overall, given the diversity of metals in MOFs, one could envision our approach as a method to produce a library of different metal functionalised porous BN samples.

Simultaneous Estimation of Gas Adsorption Equilibria and Kinetics of Individual Shaped Adsorbents.

Shaped adsorbents (e.g., pellets, extrudates) are typically employed in several gas separation and sensing applications. The performance of these adsorbents is dictated by two key factors, their adsorption equilibrium capacity and kinetics. Often, adsorption equilibrium and textural properties are reported for materials. Adsorption kinetics are seldom presented due to the challenges associated with measuring them. The overarching goal of this work is to develop an approach to characterize the adsorption properties of individual shaped adsorbents with less than 100 mg of material. To this aim, we have developed an experimental dynamic sorption setup and complemented it with mathematical models, to describe the mass transport in the system. We embed these models into a derivative-free optimizer to predict model parameters for adsorption equilibrium and kinetics. We evaluate and independently validate the performance of our approach on three adsorbents that exhibit differences in their chemistry, synthesis, formulation, and textural properties. Further, we test the robustness of our mathematical framework using a digital twin. We show that the framework can rapidly (i.e., in a few hours) and quantitatively characterize adsorption properties at a milligram scale, making it suitable for the screening of novel porous materials.

Evaluation of CO2 and H2O Adsorption on a Porous Polymer Using DFT and In Situ DRIFT Spectroscopy.

Numerous hyper-cross-linked polymers (HCPs) have been developed as CO2 adsorbents and photocatalysts. Yet, little is known of the CO2 and H2O adsorption mechanisms on amorphous porous polymers. Gaining a better understanding of these mechanisms and determining the adsorption sites are key to the rational design of improved adsorbents and photocatalysts. Herein, we present a unique approach that combines density functional theory (DFT), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and multivariate spectral analysis to investigate CO2 and H2O adsorption sites on a triazine-biphenyl HCP. We found that CO2 and H2O adsorb on the same HCP sites albeit with different adsorption strengths. The primary amines of the triazines were identified as favoring strong CO2 binding interactions. Given the potential use of HCPs for CO2 photoreduction, we also investigated CO2 and H2O adsorption under transient light irradiation. Under irradiation, we observed partial CO2 and H2O desorption and a redistribution of interactions between the H2O and CO2 molecules that remain adsorbed at HCP adsorption sites.

Effect of graphite features on the properties of metal-organic framework/graphite hybrid materials prepared using an in situ process.

Metal-organic framework (MOF)/graphite hybrid materials were prepared using an in situ process. Graphites with various chemical and physical features were used, and HKUST-1 was selected as the MOF component. The samples (parent materials and hybrid materials) were characterized by X-ray diffraction, nitrogen sorption, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Then they were tested as ammonia adsorbents in dynamic conditions. The results indicate that the functionalization of graphite is important to build the hybrid materials with synergistic properties. The lack of functional groups on graphite results in the formation of a simple physical mixture. Besides the surface chemistry of the graphitic component, the physical parameters (porosity and size of flakes) also seem to influence the formation of the hybrid materials. It is observed that the graphite particles disturb the formation of HKUST-1 and induce a different crystal morphology (more defects and increased surface roughness) than the one observed when MOF is formed in the absence of a substrate. The latter behavior causes less ammonia to be adsorbed on the hybrid materials than is expected for the simple physical mixture of HKUST-1 and graphite. The MOF structure collapses (in HKUST-1 and the hybrid materials) upon ammonia adsorption and leads to the formation of new species.

Toward understanding reactive adsorption of ammonia on Cu-MOF/graphite oxide nanocomposites.

The adsorption of ammonia on HKUST-1 (a metal-organic framework, MOF) and HKUST-1/graphite oxide (GO) composites was investigated in two different experimental conditions. From the isotherms, the isosteric heats of adsorption were calculated from the Clausius-Clapeyron equation following the virial approach. The results on HKUST-1 were compared with those obtained using molecular simulation studies. All materials exhibit higher ammonia adsorption capacities than those reported in the literature. The ammonia adsorption on the composites is higher than that measured separately on the MOF component and on GO. The strong adsorption of ammonia caused by chemical interactions on different adsorption sites is evidenced by the trends in the isosteric heats of adsorption. The molecular simulations conducted on HKUST-1 support the trends observed experimentally. In particular, the strong chemisorption of ammonia on the metallic centers of HKUST-1 is confirmed. Nevertheless, higher adsorption capacities are predicted compared with the experimental results. This discrepancy is mainly assigned to the partial collapse of the MOF structure upon exposure to ammonia, which is not accounted for in the simulation study.

Material Screening for Gas Sensing Using an Electronic Nose: Gas Sorption Thermodynamic and Kinetic Considerations.

To detect multiple gases in a mixture, one must employ an electronic nose or sensor array, composed of several materials, as a single material cannot resolve all the gases in a mixture accurately. Given the many candidate materials, choosing the right combination of materials to be used in an array is a challenging task. In a sensor whose sensing mechanism depends on a change in mass upon gas adsorption, both the equilibrium and kinetic characteristics of the gas-material system dictate the performance of the array. The overarching goal of this work is twofold. First, we aim to highlight the impact of thermodynamic characteristics of gas-material combination on array performance and to develop a graphical approach to rapidly screen materials. Second, we aim to highlight the need to incorporate the gas sorption kinetic characteristics to provide an accurate picture of the performance of a sensor array. To address these goals, we have developed a computational test bench that incorporates a sensor model and a gas composition estimator. To provide a generic study, we have chosen, as candidate materials, hypothetical materials that exhibit equilibrium characteristics similar to those of metal-organic frameworks. Our computational studies led to key learnings, namely, (1) exploit the shape of the sensor response as a function of gas composition for material screening purposes for gravimetric arrays; (2) incorporate both equilibrium and kinetics for gas composition estimation in a dynamic system; and (3) engineer the array by accounting for the kinetics of the materials, the feed gas flow rate, and the size of the device.

Hypercrosslinked Polymers as a Photocatalytic Platform for Visible-Light-Driven CO2 Photoreduction Using H2 O.

The design of robust, high-performance photocatalysts is key for the success of solar fuel production by CO2 conversion. In this study, hypercrosslinked polymer (HCP) photocatalysts have been developed for the selective reduction of CO2 to CO, combining excellent CO2 sorption capacities, good general stabilities, and low production costs. HCPs are active photocatalysts in the visible light range, significantly outperforming the benchmark material, TiO2 P25, using only sacrificial H2 O. It is hypothesized that superior H2 O adsorption capacities facilitate access to photoactive sites, improving photocatalytic conversion rates when compared to sacrificial H2 . These polymers are an intriguing set of organic photocatalysts, displaying no long-range order or extended π-conjugation. The as-synthesized networks are the sole photocatalytic component, requiring no added cocatalyst doping or photosensitizer, representing a highly versatile and exciting platform for solar-energy conversion.