Coadsorption Of Water Research Articles

Monte Carlo Simulations of Water Pollutant Adsorption at Parts-per-Billion Concentration: A Study on 1,4-Dioxane.

1,4-dioxane, an emerging water pollutant with high production volumes, is a probable human carcinogen. The inadequacy of conventional treatment processes demonstrates the need for an effective remediation strategy. Crystalline nanoporous materials are cost-effective adsorbents due to their high capacity and selective separation in mixtures. This study explores the potential of all-silica zeolites for the separation of 1,4-dioxane from water. These zeolites are highly hydrophobic and can preferentially adsorb nonpolar molecules from mixtures. We investigated six zeolite frameworks (BEA, EUO, FER, IFR, MFI, and MOR) using Monte Carlo simulations in the Gibbs ensemble. The simulations indicate high selectivity by FER and EUO, especially at low pressures, which we attribute to pore sizes and shapes with a greater affinity to 1,4-dioxane. We also demonstrate a Monte Carlo simulation workflow using gauge cells to model the adsorption of an aqueous solution of 1,4-dioxane at a 0.35 ppb concentration. We quantify 1,4-dioxane and water coadsorption and observe selectivities ranging from 1.1 × 105 in MOR to 8.7 × 106 in FER. We also demonstrate that 1,4-dioxane is in the infinite dilution regime in the aqueous phase at this concentration. This simulation technique can be extended to model other emerging water contaminants such as perfluoroalkyl and polyfluoroalkyl substances (PFAS), chlorofluorocarbons, and others, which are also found in extremely low concentrations.

Co-Adsorption of Alcohols and Water in JUK-8 Studied Using Quasi-Equilibrated Thermodesorption.

JUK-8 ([Zn(oba)(pip)]n, oba2- = 4,4'-oxybis(benzenedicarboxylate), pip = 4-pyridyl-functionalized benzene-1,3-dicarbohydrazide) is a hydrolytically stable flexible metal-organic framework. Owing to its unusual adsorptive properties, JUK-8 can be considered as a promising sensing material for construction of detectors of volatile organic compounds (VOCs) in air. Quasi-equilibrated temperature-programmed desorption and adsorption (QE-TPDA) is a versatile method dedicated to characterization of porous materials. In this work, QE-TPDA was employed to study co-adsorption of water and selected alcohols in JUK-8. For the first time an infrared detector sensitive to organic compounds was used in the QE-TPDA measurements, allowing the study of the influence of water vapor on sorption of VOCs. The QE-TPDA profiles of the studied alcohols, exhibiting two desorption maxima and two adsorption minima, are consistent with the standard sorption isotherms, revealing a two-step adsorption-desorption mechanism. The profiles recorded in the presence of water are noticeably changed in different ways for different alcohols. While at low relative humidity (RH) (ca. 20%) the low temperature adsorption states of ethanol and 1-propanol were only slightly destabilized, for 2-propanol almost complete suppression of adsorption was observed. The results found for moderate RH levels (ca. 50%) indicated that the opening of the JUK-8 structure, responsible for its breathing behavior, was followed by the filling of the just generated pores with a water-alcohol mixture.

Excitonic Effects of the Excited-State Photocatalytic Reaction at the Molecule/Metal Oxide Interface.

Excitonic effects caused by the Coulomb interaction between electrons and holes play a crucial role in photocatalysis at the molecule/metal oxide interface. As an ideal model for investigating the excitonic effect, coadsorption and photodissociation of water and methanol molecules on titanium dioxide involve complex ground-state thermalcatalytic and excited-state photocatalytic reaction processes. Herein, we systemically investigate the excited-state electronic structures of the coadsorption of H2O and CH3OH molecules on a rutile TiO2(110) surface by linear-response time-dependent density functional theory calculations and probe the reaction path for generating HCOOH or CO2, from ground-state and excited-state perspectives. The reaction barriers in excited-state calculations are significantly different from those in ground-state calculations during three processes, with the largest decrease being 0.94 eV for the Ti5c-O-CH2-O-Ti5c formation process.

Electrochemical CO2 reduction on metal-silicon centered single-atom dual site catalyst: A computational study

In this work, we employed density functional theory (DFT) computations to design innovative electrocatalysts for the electrochemical CO2 reduction reaction (ECRR). Specifically, we focused on single-metal dual site catalysts (SM-DSCs) based on monolayer boron nitride (BN) modified with silicon (Si) or carbon (C) coordinating atoms. These materials, denoted as M@BN_D(V) (BN = boron nitride monolayer; D = Si or C atom; M = metal atoms; V = B vacancy or N vacancy), were investigated as the potential electrocatalysts for the ECRR. Our computational results revealed that Fe@BN_Si(B) and Fe@BN_C(N) were the most stable forms for Fe@BN_Si(V) and Fe@BN_C(V), respectively. After that, we proceeded to analyze CO2 adsorption as well as reduction pathways for the ECRR based on the calculated Gibbs energy and the competitive hydrogen evolution reaction (HER). Among the Fe-based catalysts, Fe@BN_Si(B) exhibited a lower limiting potential (UL) of –0.63 V, while Fe@BN_C(N) required a higher UL of –0.72 V for the production of CH4(g). Notably, both Fe@BN_Si(B) and Fe@BN_C(N) catalysts displayed high selectivity compared to the HER. Accordingly, Fe@BN_Si(B) and Fe@BN_C(N) catalysts are emerged as the promising electrocatalyst candidates for the ECRR. In addition, the UL required to overcome was reduced to –0.35 V for WFe@BN_Si(B) in a water co-adsorption environment, suggesting the catalytic performance can be enhanced by water promotion effect.

IMPREGNATED ACTIVATED CARBON MATERIALS FOR RESPIRATORY PURPOSE. CHEMISORPTION OF SULFUR DIOXIDE

The review is devoted to the use of impregnated activated carbon materials as chemisorbents of sulfur (IV) oxide. General methods for obtaining ordinary activated carbon, preparation of raw materials, their chemical activation with alkalis and acids followed by heat treatment (carbonization) in an inert environment or in the presence of a gaseous oxidizer, the role of acid-base and redox catalysts in this process are considered. The influence of the chemical composition of the activated carbon surface, the presence of functional groups, and their acid-base properties, as well as the products of surface reactions on the peculiarities of sulfur (IV) oxide adsorption is analyzed from the point of view of SO2 removal efficiency and the possibility of SO2 regeneration. An important role in these processes is played by the pore size, the possibility of co-adsorption of water, and the presence of an oxidant. The nature of adsorbent-adsorbate interactions on the surface of activated carbon, their ener­gy, in particular, the contribution of so-called "physical" adsorption, van der Waals forces, hydrogen bonding, and the influence of surface functional groups are discussed. The activation of carbon raw materials with nitrogen-containing compounds leads to the N-doping of the surface, which increases the efficiency of SO2 adsorption, facilitating not only van der Waals and electrostatic interactions, but also S←N binding. The influence of oxygen and oxygen-containing functional groups on SO2 adsorption is also discussed. To obtain impregnated activated carbon for SO2 absorption, the original activated carbon of the required quality is impregnated with solutions of inorganic and organic compounds that remain on the inner surface of the activated carbon after drying. Impregnation blocks partly the porosity of activated carbon, but makes it more capable of chemical adsorption. Chemisorption, in which certain chemical bonds are formed between the surface of the activated carbon and the compound being adsorbed, is more selective than physical adsorption, where the size of molecules is critical for an effective capture process. It can be noted that unlike inorganic alkalis, which spoil the porous structure of activated carbon, treatment with a solution of ammonia or organic N-containing bases promotes SO2 absorption. A special place in gas purification is occupied by activated carbon impregnated with ionic liquids, non-aqueous solvents being used for impregnation. A separate issue of the chemisorption of sulfur (IV) oxide by samples of impregnated activated carbon based on d-metals will be discussed in detail below.

First-principles study on the co-adsorption of water and oxygen molecules on chalcopyrite (112)-M surface

Chalcopyrite is a common copper-bearing mineral with antiferromagnetic properties. However, this property has rarely been considered in previous studies for detailed adsorption behaviors of molecules on chalcopyrite. Based on density functional theory (DFT), new adsorption pathways by H2O and O2 on the chalcopyrite metal terminated (112) surface ((112)-M) is found in this work. First, through simulating the adsorption of an isolated water molecule and monolayer water molecules, it is confirmed that H2O molecules tend to adsorb on the surface Fe atoms more than on the surface Cu atoms. Then, we studied various adsorption behaviors of the O2 molecule. It is found that the adsorption on the hollow FeFe site is the most stable case; however, O2 is undissociated. Two adsorption cases will happen when H2OO2 adsorb simultaneously on the surface. For the S site, the H2O molecule thoroughly dissociated and formed SO species, and the other case is H2O undissociated adsorbing at the Cu site. For the former case, it is interesting that H2O is dissociated before O2.

Investigation of CO2-Sorption Characteristics of Readily Available Solid Materials for Indoor Direct Air Capturing

Direct air capturing (DAC) is an energy demanding process for CO2-removal from air. Ongoing research focuses on the potential of indoor air as DAC-feed to profit from currently unused energetic synergies between DAC and the built environment. In this work, we investigated the performance of three different readily available, solid DAC-adsorbers under typical indoor environmental conditions of 16-25°C, 25-60% relative humidity (RH), and CO2-concentrations of less than 800 ppm above atmospheric concentrations. The measured mass-specific CO2-adsorption capacities of K2CO3-impregnated activated carbon, polyethylenimine-snow (PEI-snow), and polyethylenimine (PEI) on silica amount to 6.5 ± 0.3 mg g − 1 , 52.9 ± 4.9 mg g − 1 , and 56.9 ± 4.2 mg g − 1 , respectively. Among the three investigated adsorber materials, PEI on silica is the most promising candidate for DAC-applications as its synthesis is rather simple, the CO2-desorption is feasible at moderate conditions of about 80°C at 100 mbar, and the competing co-adsorption of water does not strongly affect the CO2-adsorption under the investigated experimental conditions.

Cold, Hot, Dry, and Wet: Locations and Dynamics of CO2 and H2O Co-Adsorbed in an Ultramicroporous MOF.

Climate change from anthropogenic carbon dioxide (CO2) emissions poses a severe threat to society. A variety of mitigation strategies currently include some form of CO2 capture. Metal-organic frameworks (MOFs) have shown great promise for carbon capture and storage, but several issues must be solved before feasible widespread adoption is possible. MOFs often exhibit reduced chemical stabilities and CO2 adsorption capacities in the presence of water, which is ubiquitous in nature and many practical settings. A comprehensive understanding of water influence on CO2 adsorption in MOFs is necessary. We have used multinuclear nuclear magnetic resonance (NMR) experiments at temperatures ranging from 173 to 373 K, along with complementary computational techniques, to investigate the co-adsorption of CO2 and water across various loading levels in the ultra-microporous ZnAtzOx MOF. This approach yields detailed information regarding the number of CO2 and water adsorption sites along with their locations, guest dynamics, and host-guest interactions. Guest adsorption and motional models proposed from NMR data are supported by computational results, including visualizations of adsorption locations and the spatial distribution of guests in different loading scenarios. The wide variety and depth of information presented demonstrates how this experimental methodology can be used to investigate humid carbon capture and storage applications in other MOFs.

Experimental Investigation of Sorption-Enhanced CO2 Hydrogenation to Methanol

In this work, we investigate experimentally the use of zeolite 13X as an efficient water sorbent in the sorption-enhanced CO2 hydrogenation reaction over Cu/ZnO/Al2O3 under different operating conditions and over multiple reaction–regeneration cycles. Introduction of the solid sorbent along with the catalyst in the reactor leads to a prominent increase in the CO2 conversion and CH3OH yield. As the reaction proceeds, the sorbent gradually becomes saturated, the enhancement effect reduces, and the system eventually reaches the same steady state as with catalyst only. The CH3OH yield increase is higher than that of the CO2 conversion, indicating preferential enhancement of methanol production. This can be attributed to the partial co-adsorption of both methanol and water on zeolite 13X. The effects of reaction and regeneration temperature on the activity, product distribution, enhancement degree, and recyclability are also examined. The highest sorption enhancement occurs at 225 °C, with the methanol yield increasing by 115% compared to the conventional process. The cyclic stability is investigated by consecutive reaction–regeneration cycles. The correlation between activity reduction and textural properties of both the catalyst and sorbent as well as the zeolite’s ability to regenerate are explored. To that end, the effect of regeneration temperature on the products’ desorption is also examined.

The impact of water co-adsorption on the removal of formaldehyde from the indoor air by oxygen-rich activated carbons: A theoretical and experimental study

Surface oxygen modification of activated carbon has been considered an effective sorbent to remove formaldehyde from indoor air, while the role of co-existing moisture on formaldehyde adsorption by oxygen-rich carbons is unclear. This study investigates the dynamic impact of water on formaldehyde adsorption from simulated indoor air was studied experimentally and theoretically. Among them, the improvement of formaldehyde adsorption on oxygen-rich activated carbon originated from forming stronger hydrogen bonds between oxygen functional groups and formaldehyde compared to conventional van der Waals force. However, the more vital interaction forces between water and oxygen functional groups by forming more hydrogen bonds and the pore blockage by accumulated water molecules around adsorption sites with the increasing adsorption time became the significant barriers of formaldehyde adsorption on carbon surface in a wet environment. Oxygen functional groups with pre-adsorbed water/formaldehyde can accommodate at least one more water while it can hardly adsorb another formaldehyde due to the weak interaction force that can easily be replaced by water molecules. Formaldehyde cannot form hydrogen bonds with the double bond O atom of the carboxyl group, but water can. The sustained adsorption capacity of water is much stronger than that of formaldehyde.

High-Throughput Screening of the CoRE-MOF-2019 Database for CO2 Capture from Wet Flue Gas: A Multi-Scale Modeling Strategy.

Stabilizing the escalating CO2 levels in the atmosphere is a grand challenge in view of the increasing global demand for energy, the majority of which currently comes from the burning of fossil fuels. Capturing CO2 from point source emissions using solid adsorbents may play a part in meeting this challenge, and metal-organic frameworks (MOFs) are considered to be a promising class of materials for this purpose. It is important to consider the co-adsorption of water when designing materials for CO2 capture from post-combustion flue gases. Computational high-throughput screening (HTS) is a powerful tool to identify top-performing candidates for a particular application from a large material database. Using a multi-scale modeling strategy that includes a machine learning model, density functional theory (DFT) calculations, force field (FF) optimization, and grand canonical Monte Carlo (GCMC) simulations, we carried out a systematic computational HTS of the all-solvent-removed version of the computation-ready experimental metal-organic framework (CoRE-MOF-2019) database for selective adsorption of CO2 from a wet flue gas mixture. After initial screening based on the pore diameters, a total of 3703 unique MOFs from the database were considered for screening based on the FF interaction energies of CO2, N2, and H2O molecules with the MOFs. MOFs showing stronger interactions with CO2 compared to that with H2O and N2 were considered for the next level of screening based on the interaction energies calculated from DFT. CO2-selective MOFs from DFT screening were further screened using two-component (CO2 and N2) and finally three-component (CO2, N2, and H2O) GCMC simulations to predict the CO2 capacity and CO2/N2 selectivity. Our screening study identified MOFs that show selective CO2 adsorption under wet flue gas conditions with significant CO2 uptake capacity and CO2/N2 selectivity in the presence of water vapor. We also analyzed the nature of pore confinements responsible for the observed CO2 selectivity.

Density functional theory study of trends in water dissociation on oxygen-preadsorbed and pure transition metal surfaces

Oxygen and water are the most reactive gases of the ambient air. The adsorption of both molecules on transition metal surfaces have been studied extensively, but mostly separately. However, water and oxygen usually co-exist, and therefore realistic systems need to take into consideration both simultaneously. As these adsorption reactions are so common, state-of-the-art results are beneficial as they capture large trends as accurately as possible. A comprehensive study of oxygen and water co-adsorption and dissociation on Ag(111)-, Au(111)-, Pd(111)-, Pt(111)-, Rh(111)- and Ni(111)-surfaces have been performed using density functional theory. We present a very strong general trend, where dissociated oxygen systematically lowers the activation energy of water dissociation on transition metal surfaces. This makes the oxygen dissociation the rate-determining step of the water dissociation reaction. The effect is caused by the additional pathway that the dissociated oxygen enables for the dissociation of water molecule.

One-step synthesis of methanol and hydrogen from methane and water using non-thermal plasma and Cu-Mordenite catalyst

In this study, the copper-mordenite zeolite (Cu-MOR) and non-thermal plasma were used to produce methanol and hydrogen from methane and water at low temperature (120 °C) without CO2 formation. Energy efficiency for methanol and hydrogen were 68.8 mmol·kJ−1 and 562.3 mmol·kJ−1, respectively, and the selectivity of methanol in liquid products reached 86%. The reaction mechanism likely involves methane being excited to methyl (·CH3) and hydrogen radicals (·H) under DBD plasma conditions, which can then adsorb on the catalyst surface at the Cu2-(μ-O)2+ active sites, accompanied by water co-adsorption to facilitate formation and desorption of methanol. XPS analysis showed that with the prolongation of reaction time, Cu2-(μ-O)2+ was reduced to Cu+ and Cu(II) hydroxide, and the catalyst had carbon deposition, resulting in the decrease of catalytic activity. It is also worth noting that in an oxygen atmosphere, Cu2-(μ-O)2+ regenerates rapidly and eliminates catalyst carbon deposits. Trace oxygen was introduced into the reactor, and the reaction was carried out for 30 h, and the catalytic activity did not decrease.

In situ single-crystal synchrotron X-ray diffraction studies of biologically active gases in metal-organic frameworks

Metal-organic frameworks (MOFs) are well known for their ability to adsorb various gases. The use of MOFs for the storage and release of biologically active gases, particularly nitric oxide (NO) and carbon monoxide (CO), has been a subject of interest. To elucidate the binding mechanisms and geometry of these gases, an in situ single crystal X-ray diffraction (scXRD) study using synchrotron radiation at Diamond Light Source has been performed on a set of MOFs that display promising gas adsorption properties. NO and CO, were introduced into activated Ni-CPO-27 and the related Co-4,6-dihydroxyisophthalate (Co-4,6-dhip). Both MOFs show strong binding affinity towards CO and NO, however CO suffers more from competitive co-adsorption of water. Additionally, we show that morphology can play an important role in the ease of dehydration for these two systems.

Environmental Applications of Zeolites: Preparation and Screening of Cu-Modified Zeolites as Potential CO Sensors

This work is focused on the application of Cu-containing zeolites as potential environmental sensors for monitoring carbon monoxide. A number of commercial zeolites with different structural properties (NaX, NaY, MOR, FER, BEA and ZSM-5) were modified using CuSO4, Cu(NO3)2 and Cu(OAc)2 solutions as copper sources to prepare Cu+-containing zeolites, since Cu+ forms stable complexes with CO at room temperature that can be monitored by infrared spectroscopy. Zeolite impregnation with Cu(NO3)2 resulted in the highest total Cu-loadings, while the Cu(OAc)2-treated samples had the highest Cu+/Cutotal ratio. Cu(NO3)2-impregnated MOR, which displayed the highest concentration of Cu+, was subjected to a number of tests to evaluate its performance as a potential CO sensor. The working temperature and concentration ranges of the sensor were determined to be from 20 to 300 °C and from 10 to 10,000 ppm, respectively. The stepwise CO desorption experiments indicated that the sensor can be regenerated at 400 °C if required. Additional analyses under realistic flow conditions demonstrated that for hydrophilic zeolites, the co-adsorption of water can compromise the sensor’s performance. Therefore, a hydrophobic Sn-BEA was utilised as a parent material for the preparation of an impregnated Cu-Sn-BEA zeolite, which exhibited superior resistance to interfering water while maintaining its sensing properties. Overall, the prepared Cu-modified zeolites showed promising potential as environmental CO sensors, displaying high sensitivity and selectivity under representative testing conditions.

Impact of the Si/Al ratio on the ethanol/water coadsorption on MFI zeolites revealed using original quantitative IR approaches.

Advanced IR vibrational spectroscopic techniques, e.g., using a coupled gravimetric-IR surface analyzer (AGIR) and a high-throughput in situ IR cell (Carroucell), have been used for the quantitative studies of the adsorption and coadsorption of ethanol and water on MFI zeolites with different Si/Al ratios. The AGIR coupling is a powerful tool for the accurate determination of the molar adsorption coefficients during coadsorption experiments since their evaluation is based on the measurement of the exact amount of adsorbed species. The use of the Carroucell set up allows characterizing all the samples simultaneously, strictly in the same gaseous and temperature environment. The molar absorption coefficients of pure adsorbed ethanol and water are determined: their values are constant whatever the Si/Al ratio of the MFI zeolites. Moreover, these coefficients are found to be identical in the case of the water-ethanol coadsorption experiments. Their use allows obtaining the exact quantity of each adsorbate specie in the binary system. At low partial pressures, the unary water adsorption experiments suggest that the amount of adsorbed water results mainly from the preferential adsorption on Brønsted acid sites in tetrameric clusters. In contrast, the adsorption of EtOH occurs on both silanol groups and Brønsted acid sites (BASs). The effect of the Si/Al ratio is only observed at relatively low partial pressures. The effect of the Si/Al ratio on the ethanol adsorption capacity is also investigated. This study directs the choice of an appropriate zeolite once it is used in membranes for drying ethanol.

Accelerating effect of water on electroreduction of lanthanide ions in a dicyanamide ionic liquid: A generic phenomenon

• The electroreduction of Ln(III) to Ln(0) is described for six lanthanides in a dicyanamide IL. • Deposited Ln can be partly oxidized during electrodeposition by water in the solution. • Water accelerates the electroreduction of Ln(III) to Ln(0) in the dicyanamide IL. • The water accelerating effect is a generic phenomenon for the electroreduction of Ln. Electroplating is a relatively cheap and processible technique of metal production. In the case of lanthanides (Ln), however, this technology is inapplicable in water solutions due to their pronounced electropositivity. This work studies the electroreduction of lanthanides (Ln) from a dicyanamide ionic liquid (IL) on a model Pt(1 1 1) substrate in dry solutions and upon addition of controlled amounts of water. We demonstrate the possibility of irreversible electrodeposition for six different Ln from the dried IL using a complex set of electrochemical and physical (spectroscopic and microscopic) methods. Addition of water leads to the facilitation of electrodeposition for all the studied Ln, as confirmed by a positive shift in the deposition potentials. We relate this promoting effect to the coadsorption of water on the electrode surface and the relevant changes in the IL|electrode interface structure, e.g., the disordering of the IL multilayer structure at the electrode surface. We believe that this promoting effect of water is a generic phenomenon for Ln electrodeposition in dicyanamide ILs and discuss the possible causes that result in acceleration of deposition. Analysis of the obtained deposits indicates that the deposited Ln are partly oxidized in the course of the deposition even in dry solutions, probably due to interaction with the residual water. The results of this work may be instrumental in developing lanthanide electrowinning techniques based on mixtures of ionic organic solvents with controlled water additives.

Density functional theory study of NO−H2O coadsorption on Cu(111)

The coadsorption and complex formation of nitric oxide (NO) and water $({\mathrm{H}}_{2}\mathrm{O})$ on Cu(111) are studied theoretically using the nonlocal van der Waals density functional method. The energetics, adsorption geometries, and vibrational properties of several $n\mathrm{NO}\text{\ensuremath{-}}{m\mathrm{H}}_{2}\mathrm{O}$ complexes $(n=1--4$, $m=1--3)$ on Cu(111) are reported, and the relative stabilities of those complexes are compared with their respective NO and ${\mathrm{H}}_{2}\mathrm{O}$ clusters on Cu(111). We find that the mixed $n\mathrm{NO}\text{\ensuremath{-}}{m\mathrm{H}}_{2}\mathrm{O}$ complexes on Cu(111) are more stable than separated NO and ${\mathrm{H}}_{2}\mathrm{O}$ clusters due to the attractive $\mathrm{NO}\text{\ensuremath{-}}{\mathrm{H}}_{2}\mathrm{O}$ and NO-NO interactions on the surface. The attractive $\mathrm{NO}\text{\ensuremath{-}}{\mathrm{H}}_{2}\mathrm{O}$ interaction originates mainly from the hydrogen bonding between ${\mathrm{H}}_{2}\mathrm{O}$ and the negatively charged NO upon adsorption. Moreover, hydrogen bonding also induces an additional back donation process from Cu(111), further strengthening the $\mathrm{NO}\text{\ensuremath{-}}{\mathrm{H}}_{2}\mathrm{O}$ coadsorption. In addition to hydrogen bonding, the NO-NO interaction originating from $2{\ensuremath{\pi}}^{*}$ orbital hybridization further stabilizes the formation of the $4\mathrm{NO}\text{\ensuremath{-}}3{\mathrm{H}}_{2}\mathrm{O}$ complex, which is observed in the experiment. Even though the hydrogen bonding strength in $\mathrm{NO}\text{\ensuremath{-}}{\mathrm{H}}_{2}\mathrm{O}$ complexes is slightly weaker than the one in ${\mathrm{H}}_{2}\mathrm{O}$ clusters, due to the saturation of hydrogen bonding and the NO-NO interaction, NO and ${\mathrm{H}}_{2}\mathrm{O}$ tends to form a mixed $\mathrm{NO}\text{\ensuremath{-}}{\mathrm{H}}_{2}\mathrm{O}$ complex on Cu(111), in agreement with experiment. Our findings shed light on the role of intermolecular interactions between NO and ${\mathrm{H}}_{2}\mathrm{O}$ in the formation of the NO complex, which is important for understanding the reaction of NO in three-way catalysts.

Leucine on Silica: A Combined Experimental and Modeling Study of a System Relevant for Origins of Life, and the Role of Water Coadsorption

Leucine on silica constitutes an interesting system from the point of view of origins of life studies since leucine coadsorbed on SiO2 together with glutamic acid can give rise to rather long linear polypeptides upon activation. It is also an ideal system to test methods of molecular characterization of biomolecules deposited on mineral surfaces since it combines a small-scale model of peptides and proteins, which are among the most important components of biodevices, with one of the most widely used inorganic materials. We have deposited l-leucine on a high surface fumed silica in the submonolayer range and characterized it by a multipronged approach including macroscopic information (thermogravimetry, X-ray diffraction), in situ spectroscopic methods (IR, multinuclear solid-state NMR including single-pulse and CP-MAS, 2-D HETCOR), and molecular modeling by density functional theory (DFT), including calculation of NMR parameters. Specific information can be obtained on the adsorption and interaction mechanism. Leucine is rather strongly adsorbed without any covalent bonds, through the formation of a specific lattice of H-bonds that often involve coadsorbed water molecules. Its state is indeed strongly dependent on the drying procedure: insufficient drying results in liquid-like surroundings for the leucine functional groups, while vacuum drying only retains a limited number of waters (of the order of 5 per leucine molecule). The most stable models have zwitterionic leucine interacting directly with surface silanols through their ammonium group, while the carboxylate interacts through bridging waters. Experimental NMR chemical shifts are satisfactorily predicted for these models, and leucine can be viewed as a probe for specific groups of surface sites known as silanol nests.

New insight into the co-adsorption of oxytetracycline and Pb(II) using magnetic metal-organic frameworks composites in aqueous environment: co-adsorption mechanisms and application potentials.

The present study aimed to investigate the co-adsorption and application of water stabilized Fe3O4@ZIF-8 composite with magnetic cubic crystal structure. This new material was successfully prepared by facile modification strategy and rational design, which was used for simultaneous adsorption of oxytetracycline (OTC) and Pb(II) in aqueous solution. The co-adsorption behavior and mechanism of the composite for OTC and Pb(II) were systematically investigated by characterization techniques and batch experiments, and its application potential was effectively evaluated. The results showed that the synthesized Fe3O4@ZIF-8 composite innovatively retained the cubic crystal structure of ZIF-8 and was successfully loaded on the surface of Fe3O4 particles with small particle size to form a core-shell structure. The Fe3O4@ZIF-8 composite possessed a large specific surface area (1722 m2/g), magnetic separation performance (13.4emu/g), and rich functional groups. The co-adsorption of OTC and Pb(II) on Fe3O4@ZIF-8 had fast reaction kinetics (equilibrium within 90min) and large adsorption capacity (310.29mg/g and 276.06mg/g respectively). The adsorption process for both contaminants followed pseudo-second order kinetics and Langmuir isotherm models and had synergistic and competitive effects at the same time. π-π stacking and electrostatic interaction were the main mechanisms of adsorption. Fe3O4@ZIF-8 had good adsorption performance after cyclic adsorption for 4 times and it performed well in the treatment of real waste water. This study provided a new sight for the control of combined pollution of OTC and Pb(II) and proved Fe3O4@ZIF-8 composites have great application potentials for complex wastewater treatment.