Adsorption Of Nitric Oxide Research Articles

Photo-induced reversible nitric oxide capture by Fe-M(CO2H)4 (M = Co, Ni, Cu) as a building block of mixed-metal BTC-based MOFs.

Metal-organic frameworks incorporating mixed-metal sites (MM-MOFs) have emerged as promising candidates in the development of sensing platforms for the detection of paramagnetic species. In this context, the present study explores the photo-induced switching behavior of mixed-metal Fe-M (M = Co, Ni, Cu) formate (Fe-M(CO2H)4), as an experimentally feasible strategy for the reversible capture of nitric oxide (NO). Using Fe-M(CO2H)4 as a building block of synthesized MOFs based on BTC (benzene-1,3,5-tricarboxylic acid), molecular simulations of NO adsorption on Fe-M(CO2H)4 were conducted to provide a template for evaluating the behavior of BTC-based MOFs towards NO. Accordingly, the relationship between the magnetic properties and adsorption behaviors of Fe-M(CO2H)4 towards NO gas molecules was evaluated before and after photoexcitation. We show that the photo-induced effect on the magnetic properties of Fe-M(CO2H)4 changes the interaction strength between NO and the Fe-M(CO2H)4 systems. NO chemisorption over Fe-Ni(CO2H)4 indicates that nickel-doped Fe-BTC MOFs can be efficiently applied for capturing purposes. Moreover, our calculations show a switching behavior between physisorption and chemisorption of the NO molecules over Fe-Co(CO2H)4, occurring through magnetic modulation under UV-Vis irradiation. As far as we know, this is the first study that proposes light-controlled reversible NO capture using MOFs. The present study provides a promising platform for reversible NO capture using MM-MOF-incorporated BTC building blocks.

Catalytic Reduction of Nitric Oxide with Hydrogen Using Carbon-Supported d-Metal Catalysts

Technologies for the reduction of nitric oxide are well established and are a critical resource in reducing the emission of nitrogen oxides released during combustion. Herein, we demonstrate a more sustainable approach, utilising Earth-abundant metals supported on waste-derived carbon to facilitate this reaction. Selective catalytic reduction, whereby a reductant is used to convert NO over a catalytic bed into nitrogen, is regarded as the best available technology for NO reduction. Here, we have investigated the use of H2, which has the potential to be produced from sustainable resources, as the reductant. Three selected d-metals (copper, iron and manganese) were impregnated over palm kernel shell activated carbons via incipient wetness. The characteristics of the carbon support and the derivative catalysts were analysed to investigate structure-performance relationships. H2-SCR was performed in a fixed-bed reactor; the results showed that the supported-copper catalyst converted NO completely at temperatures of 250 °C and above. This is attributed to the high reducibility and acidity of the catalyst as demonstrated via temperature-programmed reduction, ammonia-temperature programmed desorption, Fourier-transform infra-red spectroscopy and nitric oxide adsorption–desorption experiments. It is concluded that the carbon-supported d-metal catalysts are viable for use in H2-SCR, thereby promoting a more sustainable approach to mitigating NOx emissions.Graphic Abstract

Coverage-dependent adsorption of nitrous oxide (N2O) on perfect and defective Cu(0 0 1) surfaces: A DFT investigation with and without van der Walls forces

The adsorption of the harmful nitrous oxide (N2O) on the perfect and defective Cu(001) surfaces was studied using self-consistent periodic density functional theory (DFT) with the GGA-PBE functional and vdW-DF dispersion correction. We have considered Cu adatom on Cu(001) surface as a model of defective Cu(001) surface. On the perfect Cu(001) surface, our GGA-PBE results show that the N2O molecule adsorbs very weakly onto the Cu(001) surface for 0.25 and 0.50 ML coverages, but a desorption is observed at 0.75 and 1.0 ML coverages. The inclusion of the vdW-DF correction increases the adsorption energies relative to values obtained from pure GGA-PBE functional, however, both types of processes, i.e., adsorption and desorption are retained with respect to the coverages. The dissociative adsorption of N2O on the bare Cu(001) surface is energetically preferred to the molecular adsorption, using the GGA-PBE functional. Regarding the defective surface, we note that the presence of a Cu adatom stabilize the adsorption of N2O better than a flat surface using the GGA-PBE functional, while the opposite effect is observed with vdW-DF correction. The electronic structure was analyzed in terms of the projected density of states (PDOS).

Thermal Treatment Effect on CO and NO Adsorption on Fe(II) and Fe(III) Species in Fe3O-Based MIL-Type Metal-Organic Frameworks: A Density Functional Theory Study.

The properties of metal–organic frameworks (MOFs) based on triiron oxo-centered (Fe3O) metal nodes are often related to the efficiency of the removal of the solvent molecules and the counteranion chemisorbed on the Fe3O unit by postsynthetic thermal treatment. Temperature, time, and the reaction environment play a significant role in modifying key features of the materials, that is, the number of open metal sites and the reduction of Fe(III) centers to Fe(II). IR spectroscopy allows the inspection of these postsynthetic modifications by using carbon monoxide (CO) and nitric oxide (NO) as probe molecules. However, the reference data sets are based on spectra recorded for iron zeolites and oxides, whose structures are different from the Fe3O one. We used density functional theory to study how the adsorption enthalpy and the vibrational bands of CO and NO are modified upon dehydration and reduction of Fe3O metal nodes. We obtained a set of theoretical spectra that can model the modification observed in previously reported experimental spectra. Several CO and NO bands were previously assigned to heterogeneous Fe(II) and Fe(III) sites, suggesting a large defectivity of the materials. On the basis of the calculations, we propose an alternative assignment of these bands by considering only crystallographic iron sites. These findings affect the common description of Fe3O-based MOFs as highly defective materials. We expect these results to be of interest to the large community of scientists working on Fe(II)- and Fe(III)-based MOFs and related materials.

Dynamic Adsorption of Nitric Oxide (NO) in a Fixed-bed Reactor Using Rubber Seed Shell-derived Biochar

Control of nitric oxide emission (NO) as the main constituent of nitrogen oxides (NOx) from combustion sources is a global concern. In this context, this study investigates the adsorption of NO using some biomass-derived adsorbents. Rubber seed shell (RSS) was used as a lignocellulosic residue to develop biochar, modified by metal-doping and alkali activation. The prepared adsorbents, namely, pristine biochar, cerium-loaded biochar and KOH-activated biochar, were used to capture NO in a dynamic fixed-bed adsorption system. The effect of different initial NO feed concentrations (200 and 350 ppm), total gas flow rates (100, 150 and 200 ml/min), and adsorption temperatures (30, 70 and 110 oC) on the adsorption capacity of the adsorbents was investigated. The most suitable operating condition for NO adsorption was found to be the NO feed concentration of 200 ppm, inlet gas flow rate of 100 ml/min and the adsorption temperature of 30 oC at which the high NO adsorption capacity of 81.67, 142.53 and 470.50 mg/g was attained for pristine, Ce-loaded, and KOH-activated biochars, respectively. The adsorbents showed high sustainability in the regeneration process within 5 cycles of NO adsorption-desorption. These results highlight the high potential of RSS-derived biochar for the control of NOx emission from flue gases.

Improved therapeutic nitric oxide delivery by microporous Cu-bearing titanosilicate

Copper was incorporated into microporous titanosilicate ETS-4 framework via the in situ hydrothermal synthesis to achieve a more controlled and extended nitric oxide (NO) release profile. Exogeneous delivery of this gasotransmitter may be effective in the therapeutic setting and titanosilicates, in particular ETS-4, has already evidenced its potential as a NO carrier. Copper ions have high affinity for NO coordination and their substitution within the ETS-4 framework was confirmed by energy dispersive X-ray spectrometry (EDS). Samples were also characterized by PXRD, SEM microscopy, UV–Vis and Raman spectroscopy, TG and DSC. ETS-4Cu presents higher NO adsorption capacity (up to 4.5 mmol g−1 solid) comparing with the parent material, excellent stability in biological media and exhibits high compatibility in different cell lines, including primary keratinocytes (HEKn). Its NO release profile in biological conditions demonstrated a controlled release over at least 4 h, never achieved by any other porous materials so far. This may be reflected by its peculiar NO adsorption mechanism through the formation of stable nitro species on the framework.

Controlled Synthesis of Large Single Crystals of Metal-Organic Framework CPO-27-Ni Prepared by a Modulation Approach: In situ Single-Crystal X-ray Diffraction Studies.

The size of single crystals of the metal‐organic framework CPO‐27‐Ni was incrementally increased through a series of modulated syntheses. A novel linker modulated synthesis using 2,5‐dihydroxyterephthalic acid and the isomeric ligand 4,6‐dihydroxyisophthalic acid yielded large single crystals of CPO‐27‐Ni (∼70 μm). All materials were shown to have high crystallinity and phase purity through powder X‐ray diffraction, electron microscopy methods, thermogravimetry, and compositional analysis. For the first time single‐crystal structure analyses were carried out on CPO‐27‐Ni. High BET surface areas and nitric oxide (NO) release efficiencies were recorded for all materials. Large single crystals of CPO‐27‐Ni showed a prolonged NO release and proved suitable for in situ single‐crystal diffraction experiments to follow the NO adsorption. An efficient activation protocol was developed, leading to a dehydrated structure after just 4 h, which subsequently was NO‐loaded, leading to a first NO loaded single‐crystal structural model of CPO‐27‐Ni.

On-chip electrocatalytic NO sensing using ruthenium oxide nanorods

Online, on-chip measurement of nitric oxide (NO) in organ-on-chip devices is desired to study endothelial (dys)function under dynamic conditions. In this work, ruthenium oxide (RuOx) is explored as an amperometric NO sensor and its suitability for organ-on-chip applications. For testing purposes, diethylamine NONOate was used as chemical NO donor. The NONOate’s NO generation and electrochemical oxidation of generated NO were confirmed by real-time electrochemical/mass-spectrometry. Using RuOx nanorods electrodes, we show that NO oxidation occurred at a lower onset potential (+675 mV vs. Ag/AgCl) than on bare Pt electrode (+800 mV vs. Ag/AgCl). Due to NO adsorption on the RuOx surface, NO oxidation also delivered a higher current density (33.5 nA.μM−1. cm-2) compared to bare Pt (19.6 nA.μM−1. cm-2), making RuOx nanorods a favourable electrode for NO sensing applications. The RuOx electrode’s suitability for organ-on-chip applications was successfully tested by using the electrode to detect a few micromolar concentration of NO generated by endothelial cell culture. Overall, the RuOx nanorods proved to be suitable for organ-on-chip studies due to their high sensitivity and selectivity. Our chip-integrated electrode allows for online NO monitoring in biologically relevant in vitro experiments.

Influence of Water on Nitrous Oxide Adsorption and Desorption on Coals

Oxygen-enriched coal-combustion flue gas geologic sequestration in unmineable coal seams is a promising option to mitigate gaseous pollutant emissions and recover coalbed methane (CH4). Water (H2O) always exists in practical coal seams and shows significant impact on fluid adsorption, desorption, diffusion, and flow behaviors. Thus, this study mainly addressed the influence of H2O on nitrous oxide (N2O) adsorption and desorption, a typical component that existed in oxygen-enriched coal-combustion flue gas, on different rank coals. Results indicate that the N2O adsorption equilibrium and kinetic behaviors within moist coals can be well-predicted using the Sips model and the simplified bidisperse kinetic model, respectively. The H2O dramatically hinders the adsorption and diffusion capability of N2O within coals, which is attributed to the fact that H2O molecules occupy pore channels, induce coal matrix swelling, and compete with N2O molecules for the same adsorption sites, particularly the oxygen-containing functional groups. The H2O impairs the physisorption and chemisorption of N2O on coals. Furthermore, the H2O enhances the chemical transformation among the four main nitrogen-containing species within coals, that is, pyridine-N, pyrrole/pyridone-N, quaternary-N, and oxide-N. Particularly, the abundant −H groups of H2O molecules inhibit the decomposition of pyrrole/pyridone-N and accelerate the transformation of pyridine-N, while −OH groups of H2O molecules promote the formation of oxide-N. To sum up, the practical N2O geologic sequestration should focus on the effects of in-situ H2O within coal reservoirs.

First principle study of transition metals codoped MoS2 as a gas sensor for the detection of NO and NO2 gases

Exposure to nitrogen oxides (NO x ) has been reported to seriously affect the respiratory systems. More precisely, breathing NO x may lead to the appearance of asthma symptoms, and may also result in the infection with asthma over long intervals. This study is devoted to finding novel systems to detect nitric oxide (NO) and nitrogen dioxide (NO 2 ) with improved sensitivity. Consequently, gold (Au) and silver (Ag) codoped molybdenum disulfide (MoS 2 ) (Au–Ag–MoS 2 ) is proposed as NO and NO 2 gas sensor based on density functional theory (DFT) calculations. The variations of the electronic properties as well as the adsorption parameters of the new proposed sensor upon the adsorption of NO and NO 2 gases are compared with pristine, Au-doped, and Ag-doped MoS 2 . The results reflect a remarkable change in the band gap of the developed systems upon the adsorption of NO and NO 2 gases. Meanwhile, the adsorption parameters demonstrate that the Au doped MoS 2 system is selective to NO, while the codoped MoS 2 system is selective to NO 2 . Specifically, the Au-doped MoS 2 exhibits its maximum adsorption energy (E ads ) towards NO of −0.721 eV. Moreover, the highest adsorption energy and charge transfer ( Δ Q) are found to be −2.603 eV and 0.448 e, respectively, for the case of NO 2 /Au–Ag-codoped MoS 2 . Hence, our investigation suggests that Au–Ag-codoped MoS 2 can be utilized as a gas sensor for the detection of NO 2 gas. • MoS 2 sensor materials were investigated for NO and NO 2 sensors using DFT calculation. • The effect of codoping of MoS 2 by Au and Au on adsorption of NO and NO 2 gases was investigated. • The response was analyzed using: adsorption energy and distance, band structure, density of states, and charge transfer. • Doping enhanced of the adsorption energy towards both NO and NO 2 gases. • The adsorption energy and charge transfer were maximum for the NO 2 /Au-Ag-codoped MoS 2 .

Nitric oxide removal by zinc chloride activated oil palm empty fruit bunch fibre

Nitric oxide (NO) emission is known to pose detrimental effects towards the environment and human beings. Low-temperature NO removal by activated carbon from agricultural waste materials is affordable due to the use of low-cost materials as precursor and elimination of the need for flue gas reheating. The use of chemical agents in activated carbon production improves the performance of waste materials in NO removal. The performance of NO removal was investigated via breakthrough experiment using oil palm empty fruit bunch (EFB) activated with zinc chloride (ZnCl2) at different concentrations (0.1, 0.5, and 1.5 M). Activation of EFB with 0.5 M ZnCl2 resulted in the formation of well-defined micropores, but the use of higher concentration of ZnCl2 resulted in widening of developed pores and intense pore blockage which reduce the accessibility of NO molecules to the adsorption sites. An adsorption isotherm study conducted using 0.5 M ZnCl2/EFB sample with varying NO concentration between 300-1000 ppm indicated that the adsorption process was best defined by Langmuir isotherm model. In addition, adsorption kinetic was investigated at different temperatures; i.e. 100, 150, 200, 250 and 300 °C. NO removal was found to follow Avrami kinetic model at T=100 °C, while upon further increase in temperature, the process was better fitted to the pseudo-second order kinetic model. NO adsorption capacity increases significantly beyond 250 °C up to 1000 mg/g. The activation energy of NO adsorption fell into two distinct regions: -4.73 kJ/mol at 100-200 °C and 84.04 kJ/mol at 200-300 °C. At lower temperature, the adsorption process was exothermic and followed physisorption path, while the increase in reaction temperature led to slower rate of reaction. It was concluded that the removal of NO using EFB modified with ZnCl2 at optimized condition could be a promising alternatives for treating NO-containing flue gas.

Analytic expressions for the isosteric heat of adsorption from adsorption isotherm models and two‐dimensional SAFT‐VR equation of state

AbstractThe isosteric heat of adsorption is an important thermodynamic property used to characterize and optimize adsorption processes. In this work, analytic expressions for isosteric heats of adsorption are derived for a collection of commonly used isotherm models and a two‐dimensional molecular equation of state based on the SAFT‐VR approach. The use of these expressions is presented with an example of adsorption of nitrous oxide, N2O, on biochar, which is a waste biomass charcoal that exhibits high adsorption potential. The results show that accurate fitting of the adsorption isotherms leads to consistent results obtained with different approaches; however, the predicted isosteric heat of adsorption exhibits strong variations in the regions where experimental data is insufficient such in the region of low pressure/low coverage. Convergence on the prediction of the isosteric heat of adsorption by the different models is only observed in the region where no extrapolation of experimental data is needed.

Influence of the primary and secondary coordination spheres on nitric oxide adsorption and reactivity in cobalt(ii)-triazolate frameworks.

Nitric oxide (NO) is an important signaling molecule in biological systems, and as such, the ability of porous materials to reversibly adsorb NO is of interest for potential medical applications. Although certain metal–organic frameworks are known to bind NO reversibly at coordinatively unsaturated metal sites, the influence of the metal coordination environment on NO adsorption has not been studied in detail. Here, we examine NO adsorption in the frameworks Co2Cl2(bbta) (H2bbta = 1H,5H-benzo(1,2-d:4,5-d′)bistriazole) and Co2(OH)2(bbta) using gas adsorption, infrared spectroscopy, powder X-ray diffraction, and magnetometry. At room temperature, NO adsorbs reversibly in Co2Cl2(bbta) without electron transfer, with low temperature data supporting spin-crossover of the NO-bound cobalt(ii) centers of the material. In contrast, adsorption of low pressures of NO in Co2(OH)2(bbta) is accompanied by charge transfer from the cobalt(ii) centers to form a cobalt(iii)–NO− adduct, as supported by diffraction and infrared spectroscopy data. At higher pressures of NO, characterization data indicate additional uptake of the gas and disproportionation of the bound NO to form a cobalt(iii)–nitro (NO2−) species and N2O gas, a transformation that appears to be facilitated by secondary sphere hydrogen bonding interactions between the bound NO2− and framework hydroxo groups. These results provide a rare example of reductive NO binding in a cobalt-based metal–organic framework, and they demonstrate that NO uptake can be tuned by changing the primary and secondary coordination environment of the framework metal centers.

Carbon deposition enhanced selective catalytic reduction of nitric oxide by a new catalytic process as well as increasing reducibility of catalyst

Carbon deposition usually hinders catalytic activity in one catalysis. In this work, carbon-deposition influence was investigated on selective catalytic reduction (SCR) of nitric oxide (NO) by a theoretical−experimental method. Density-functional-theory calculations showed that carbon deposition increased adsorption energy of NO on oxide. For example, adsorption energy on Fe2O3 increased from 1.70 to 5.27 eV. Carbon deposition increased activity by following processes: NO adsorption, NO dissociation, oxygen transmittance, CO-group formation, and N2/CO2 evolutions. Among these stages, CO-group formation was a key step. Based on these computational predictions, an experimental SCR was carried out for the verification. As a result, a carbon-deposited catalyst had a better SCR activity (20% higher) than the corresponding oxide catalyst. Characterizations showed that carbon deposition increased the amounts of medium/strong acidic sites as well as the reducibility of the catalytic center. The main result of this article helps to understand the interface behavior of carbon on a catalyst during SCR. Above results are also in favor of designing a more effective SCR reactor to ensure a more stable running.

Zinc imidazolate framework-8 as a promising nitric oxide carrier

Uncontrollable release and unexpected release limit the use of nitric oxide (NO). To overcome this problem, we introduce ZIF-8 as a pH-responsive NO carrier. The flexible framework of ZIF-8 under the high-pressure condition causes the physically NO adsorption inside the SOD cage. ZIF-8 maintain the excellent gas storage ability under the physiological environment. The results show good pH-responsive ability. The gas could not be released out until the particle is in an acid condition. At low pH conditions, half of the gas is released in 1% of the total release duration. Interestingly, the half-release (t1/2) increases to 10% when the phosphate species exist in the acid surrounding. The gradual release can occur under neutral conditions with the existence of phosphate (t1/2 33%). From these results, we expect this ZIF-8 loading NO nanoparticles is lead to the design of innovative gas therapeutic delivery platforms using the advantage of the flexible framework for loading and releasing the gas molecule.

INFLUENCE OF CARBONISATION TEMPERATURE ON THE SURFACE PORE CHARACTERISTICS OF ACID-TREATED OIL PALM EMPTY FRUIT BUNCH ACTIVATED CARBON

Carbonisation process affects the surface physical and chemical properties of an activated carbon. Therefore, this work aims to investigate the influence of carbonisation temperature from 400 to 550°C during activation with 85% phosphoric acid (H3PO4) on the surface pore characteristics of activated carbon produced from oil palm empty fruit bunch (EFB) for nitric oxide (NO) removal from gas streams. Pore and morphological characterisation showed that EFB carbonised at 400°C (EFBC-400) is microporous and has a uniform pore structure with 98% micropore volume. Increasing carbonisation temperature resulted in pore enlargement from 2.8 to 4.7 nm and increment in pore heterogeneity and BET surface area from 215 to 759 m2/g. However, the NO breakthrough experiment indicated that EFBC-400 is more favourable for low-temperature NO removal, due to the importance of microporosity in adsorption of NO. Further study will look at the kinetics of NO removal and the adsorbent regeneration.

First-principle insights of CO and NO detection via antimonene nanoribbons

First-principle investigations under the flagship of density functional theory have been performed to analyze the prospects of antimonene nanoribbons (SbNR) for carbon mono-oxide (CO) and nitric oxide (NO) sensing applications. We have explored various adsorption configurations of gas molecules on the edges of bare and silicon-doped SbNR with zigzag and armchair edge states. Based on adsorption energy ( $$E_{\text{ads}}$$ ) calculations, it is revealed that CO and NO molecules tend to physisorbed on SbNRs substrate. However, upon the introduction of silicon impurity, gas molecules prefer to chemisorb on SbNRs. The electronic properties’ calculations based on band structures and density of states (DOS) profile predict substantial modification in the band structures of the SbNRs after CO and NO adsorption. Charge transfer analysis indicates that gas molecules act as an acceptor on undoped SbNRs whereas act as a donor on a substitutionally doped substrate. To explore deep into the interaction between the gas molecule and SbNRs’ substrate, charge difference density and projected DOS have been plotted and examined. Furthermore, to determine the feasibility, I–V characteristics have been calculated using a standard two-probe model. It is evident from I–V characteristics that gas adsorption has a prominent impact on the current-carrying capability of SbNR. Finally, the recovery time is calculated to analyze the desorption performance of CO/NO adsorbed on bare and Si-doped SbNRs, henceforth projecting the potential of SbNRs for CO and NO sensor applications.

Catalytic activity of Rhn/MegO-nanotube for NO adsorption and dissociation: A van der waals density functional study

We have studied the adsorption and dissociation of nitric oxide (NO) on a series of interfaces consisting of a rhodium cluster (Rhn, n = 1–5) and an MgO nanotube, using van der Waals density functional theory calculations and have found that the Rhn clusters can tightly adhere to an MgO (100) nanotube. The change in the configuration of the nanotube substrate induces differences in the energetically preferred structures for some Rhn clusters (n > 2). With an MgO-nanotube substrate, the low dimensional Rhn clusters tend to be stable, and provide additional active sites to the NO. Hence they have an excellent ability to trap and dissociate NO. We see strong hybridization between N/O 2p and Rh 4d. Moreover, NO dissociation is activated, with the transition state below the reference state, indicating the possibility of the NO dissociating. Binding to NO also yields a change in the total magnetic moment of the Rhn/MgO-NT system, and this affects the adsorption energy of NO. Finally, we propose that the morphology of the metal clusters could be directly regulated by the configuration of the nanotube substrate, which encourages us to explore and design various types of nanotubes for different catalytic purposes.

Partial substitution of magnesium in lanthanum manganite perovskite for nitric oxide oxidation: The effect of substitution sites

Lanthanum manganite (LaMnO3) with magnesium (Mg) substituted the A- and B-sites were reported for the first time in this work. The Mg substituted LaMnO3 catalysts were prepared by means of citric acid sol–gel method. The impact of partial substitution of Mg and its substitution site on the catalytic performance of LaMnO3 in nitric oxide (NO) oxidation was investigated. Through series of characterizations, it was found that Mg substitution at both A- and B-sites improves the specific surface area, Mn4+ content, reactivity of surface oxygen species, redox property and NO adsorption capacity of LaMnO3. However, Mg substitution at the A-site of LaMnO3 can cause the total charge imbalance of B-site, which significantly improves the amount and reactivity of surface active oxygen species. Therefore, the catalytic activity of the samples decreases in the order: La0.9Mg0.1MnO3 > LaMn0.9Mg0.1O3 > LaMnO3. This study will shed more light on the fundamental understanding and designing of perovskite catalyst.

Preventing Undesirable Structure Flexibility in Pyromellitate Metal Organic Frameworks

Removal of coordinated water molecules from the porous Zn‐pyromellitate metal organic framework Zn5(OH)2(PMA)2(H2O)4·xH2O (PMA = pyromellitic acid or 1,2,4,5‐benzene tetracarboxylic acid) should generate coordinatively unsaturated metal sites suitable for gas adsorption. However, reports of instability towards dehydration have restricted the study and utility of this MOF. Here we examine in more detail the nature of the structural transformation that occurs upon dehydration. This study reveals that a fully reversible crystalline‐crystalline transformation from a porous to a non‐porous homologue takes place, proceeding through a partially dehydrated intermediate. We show that doping the structure with Ni2+ ions at greater than 30 % prevents structural rearrangement, thereby maintaining porosity, and rendering the material effective for gas (nitric oxide) adsorption applications. These results indicate that doping can be an effective means to increase the utility of otherwise unserviceable structures.