Computational characterization and prediction of metal-organic framework properties

In this introductory review, we give an overview of the computational chemistry methods commonly used in the field of metal-organic frameworks (MOFs), to describe or predict the structures themselves and characterize their various properties, either at the quantum chemical level or through classical molecular simulation. We discuss the methods for the prediction of crystal structures, geometrical properties and large-scale screening of hypothetical MOFs, as well as their thermal and mechanical properties. A separate section deals with the simulation of adsorption of fluids and fluid mixtures in MOFs

New Synthetic Strategies for Improved Gas separation by Nanoporous Organic Polymers

Abstract NEW SYNTHETIC STRATEGIES FOR IMPROVED GAS SEPARATION BY NANOPOROUS ORGANIC POLYMERS Suha S. Altarawneh, Ph.D. The emission of carbon dioxide (CO2) from fossil fuel combustion is a major cause of climate change. Therefore, the efficient separation of CO2 from mixtures of gases such as flue gas and impure sources of CH4 (e.g. natural gas and landfill gas) is an essential step in meeting the ever increasing demands on natural gas and creating a cleaner environment. Carbon capture and storage technology (CCS) is one of the methods employed for gas separation using chemisorption and/or physisorption processes. Several materials such as porous polymers and amine solutions have been used as gas adsorbents. However, the amount of energy required for the adsorbent regeneration is one of the main concerns that needs to be addressed. In this regard, porous organic polymers (POPs) with defined porosity and preferential binding affinity for CO2 over N2 and CH4 are some of the most attractive materials that could fulfill the above requirement and are also applicable for use in gas storage and separation. Suitable POPs that can be used for gas storage applications need to have high porosity and mechanical stability under high pressure conditions (~100 bar). Alternatively, the most effective POPs in gas separation are those that have preferential binding affinity for CO2 over other gases present at low pressure settings. In all cases, the chemical nature of POPs and their textural properties are key parameters, however, the modest surface area of most POPs limits their efficiency. With the above considerations in mind, the aim of our research is to develop benzimidazole–linked polymers (BILPs) that have variable porosity levels and chemical functionality to enhance gas separation (CO2/CH4, CO2/N2). We have established new synthetic routes that utilize polycondensation reactions between aryl-aldehydes and aryl-o-diamine building units to construct new BILPs with improved gas separation properties. Our strategy targeted structural and textural modifications of BILPs. We used longer linkers (building units) to improve porosity; however, the flexible linkers offered only low porosity due to network interpenetration. To overcome this challenge, a more controlled network growth rate was assessed by adjusting imine-bond formation rates through different acid loading. The acid, HCl, was used to catalyze imine-bond formation. The new resulting acid-catalyzed BILPs have shown an improved porosity up to 92% compared to the non-catalyzed BILPs. We also used the “rational ligand design” approach to introduce new functionalities into BILPs (-OR) to alter the hydrophobic nature of their pores. In this regard, we have illustrated the applicability of this strategy to BILPs containing flexible aryl-o-diamine linkers. The bulky alkoxy groups were incorporated into the aryl-aldehyde building unit prior to polymerization. The resulting polymers have proven that the presence of the bulky pendant alkoxy-chains plays a significant role during the polymerization process which allows for increased control over network formation, and in turn, porosity. Sorption measurements, selectivity, and heats of adsorption data have confirmed the positive impact of the alkoxy-groups and shown that varying the pendant groups is a promising method for designing highly porous BILPs. In addition to pore functionalization with alkoxy-chains, we used pi-conjugated and N-rich building units to prepare new BILPs that have semiconducting properties in addition to their porous nature. This class of BILPs has shown that the extended-conjugated system improved BILPs electronic properties. The other studies performed in this research, involved the use of DFT theory to investigate CO2/BILPs interaction sites and binding affinities. The computational outcomes of DFT have shown that (C-H) bond of the aryl system is a possible site for CO2 interaction beside the free-N side and hydrogen bonding. All new polymers were characterized by spectral and analytical characterization methods and their sorption data were collected to evaluate their capability as candidates for gas separation applications

Metal-Organic Frameworks in Germany: from Synthesis to Function

Metal-organic frameworks (MOFs) are constructed from a combination of inorganic and organic units to produce materials which display high porosity, among other unique and exciting properties. MOFs have shown promise in many wide-ranging applications, such as catalysis and gas separations. In this review, we highlight MOF research conducted by Germany-based research groups. Specifically, we feature approaches for the synthesis of new MOFs, high-throughput MOF production, advanced characterization methods and examples of advanced functions and properties

Modeling structural and electronic properties of nano-scale systems

Computergestütze Modellierung von organischen elektronsichen Materialien durch gezielte Untersuchung mikroskopischer Prozesse und Berechnung molekülspezifischer Materialparameter ermöglicht die effiziente Entwicklung langlebiger, effizienter Bauteile. In dieser Arbeit werden die strukturellen und elektronischen Eigenschaften organischer und metall-organischer Schichten untersucht, sowie effiziente Simulationsmethoden (weiter-)entwickelt

Ruthenium Metal–Organic Frameworks with Different Defect Types: Influence on Porosity, Sorption, and Catalytic Properties

By employing the mixed-component, solid-solution approach, various functionalized ditopic isophthalate (ip) defect-generating linkers denoted 5-X-ipH(2), where X = OH (1), H (2), NH2 (3), Br (4), were introduced into the mixed-valent ruthenium analogue of [Cu-3(btc)(2)](n) (HKUST-1, btc = benzene-1,3,5-tricarboxylate) to yield Ru-DEMOFs (defect-engineered metal-organic frameworks) of the general empirical formula [Ru-3(btc)(2-x)(5-X-ip)(x)Y-y](n). Framework incorporation of 5-X-ip was confirmed by powder XRD, FTIR spectroscopy, ultrahigh-vacuum IR spectroscopy, thermogravimetric analysis, H-1 NMR spectroscopy, N-2 sorption, and X-ray absorption near edge structure. Interestingly, Ru-DEMOF 1c with 32% framework incorporation of 5-OH-ip shows the highest BET surface area (approximate to 1300 m(2) g(-1), N-2 adsorption, 77 K) among all materials (including the parent framework [Ru-3(btc)(2)Y-y](n)). The characterization data are consistent with two kinds of structural defects induced by framework incorporation of 5-X-ip: modified paddlewheel nodes featuring reduced ruthenium sites (Ru delta+, 0 Plus at Ruhr-University Bochum for the support of her PhD project and funding of an internship at UC Berkeley at the group of Prof. Jeffrey. R. Long and collaboration with D.J.X. and M.I.G. including Douglas Reed for the collection of CO isotherms (298 K). W.Z. also thanks Dr. Raghavender Medishetty for the fruitful discussions. P.G. acknowledges the support of the EU innovative Training Network "DEFect NETwork materials science and engineering" (DEFNET). The authors further thank the team at DELTA synchrotron facility at the TU Dortmund for the support with the X-ray absorption spectroscopy experiments performed at beam lines BL8 and the PXRD data collection at beam lines BL9.Zhang, W.; Kauer, M.; Halbherr, O.; Epp, K.; Guo, P.; Gonzalez, MI.; Xiao, DJ.... (2016). Ruthenium Metal–Organic Frameworks with Different Defect Types: Influence on Porosity, Sorption, and Catalytic Properties. Chemistry - A European Journal. 22(40):14297-14307. https://doi.org/10.1002/chem.2016026411429714307224

Metal-organic Framework (MOFs) Derived Nanocomposites: Synthesis and Applications in Photocatalysis

Metal-organic frameworks (MOFs) are exceptionally porous coordination polymers forming highly crystalline reticular networks via the coordination bonds between organic ligands and inorganic metal clusters. In the past 10 years, MOFs have been proved to be excellent rationally designed precursors and sacrificial templates to derive metal compounds, metal compounds/carbon composites, porous carbons and related nanostructures. The inherited morphologies, adjustable structural and textural properties, in-situ modifiable physicochemical and semiconducting properties make MOFs derived composites excellent nanomaterials for a wide variety of applications in chemistry, physics, electronics and medical sciences. This thesis demonstrates the synthesis of selected Zn-MOFs and Ti-MOFs and their derived functionalised nanocomposites for applications in environment and energy. Briefly, this thesis systematically presents the following research findings: The role of pyrolysis temperature and gaseous atmosphere in Zn-MOF derived composites was studied. Homogeneously dispersed crystalline ZnO nanoparticles embedded in a porous carbon matrix were synthesised via simple one-step carbonisation of MOF-5 at 800 °C and 1000 °C in air, argon and water vapour atmospheres. The resulting carbon doped ZnO, ZnO/C or porous carbon, decorated with hydrophilic functional groups retains the inherited cubic morphology of the precursor MOF-5. Built on the finding of the optimal synthesis conditions for best performing ZnO/C composites, a comparative study of 3 different Zn-MOFs including MOF-5, MOF-74 and ZIF-8 derived ZnO/C nanocomposites was carried out to further understand the structure-property-application relationships. The photocatalytic performance of these derived composites was also evaluated for photodegradation of organic dye pollutants and photocatalytic H2 evolution reaction. Moreover, an in-depth in-situ study was carried out to understand the pyrolytic conversion mechanism of Ti-MOF precursors into the desired TiO2/C nanocomposites. The ¬in-situ TGA-MS and in-situ STEM/EDX combined with other characterisation techniques were employed to investigate the evolution of the structural, physicochemical, textural and morphological properties of the NH2-MIL-125(Ti) derived nanocomposites. Based on the understanding of the thermal decomposition mechanism of NH2-MIL-125(Ti), Cu species were loaded into NH2-MIL-125(Ti) via the post-synthetic method to obtain bimetallic NH2-MIL-125(Ti/Cu). The effect of pyrolysis temperature on the thermal decomposition of NH2-MIL-125(Ti/Cu) under water vapour atmosphere and the subsequent in-situ formation of the p-n heterojunction between TiO2 and CuxO nanoparticles were investigated, and their performance in photocatalytic H2 evolution from water splitting was evaluated.Engineering and Physical Sciences Research Council (EPSRC

Confined MOF pyrolysis within mesoporous SiO₂ core–shell nanoreactors for superior activity and stability of electro-Fenton catalysts

Despite the high density and uniform distribution of active sites in metal–organic frameworks (MOFs) and their derivatives, the relatively low stability in water still limits their utilization in heterogeneous catalysis. Herein, the confinement of pyrolyzed MIL-88B(Fe) derivatives within mesoporous SiO2 allowed fabricating core–shell nanoreactors (Fe/C@mSiO2) that served as heterogeneous electro-Fenton (HEF) catalysts for the first time, revealing an excellent performance. The as-prepared catalysts were featured by high specific surface area and dense active sites. During service as core–shell nanoreactors, they behaved as a dual function adsorbent-catalyst, exhibiting superior catalytic activity and recyclability as compared to HEF catalysts without shell. Using 0.2 g/L of catalyst, the complete removal of bisphenol A at pH 6.2 and 100 mA was achieved at 120 min, with extremelylow iron leaching of 0.11 mg/L. The rigid mSiO2 shell not only protected the iron active sites from leaching, but it also provided porous and permeable channels for efficient mass transport. The unique core–shell architecture concentrates the catalytic sites and reactants within a confined space, promoting the fast degradation of bisphenol A. Furthermore, the defect-rich carbon substrate and the high dispersibility of iron-rich sites favor a fast electron transfer. The efficient treatment of several organic micropollutants in consecutive trials corroborated the high activity and stability of the Fe/C@mSiO2. This work contributes to the rational design of HEF catalysts, aiming at consolidating their practical application in advanced wastewater treatment

Multilayer Thin Films

This book, "Multilayer Thin Films-Versatile Applications for Materials Engineering", includes thirteen chapters related to the preparations, characterizations, and applications in the modern research of materials engineering. The evaluation of nanomaterials in the form of different shapes, sizes, and volumes needed for utilization in different kinds of gadgets and devices. Since the recently developed two-dimensional carbon materials are proving to be immensely important for new configurations in the miniature scale in the modern technology, it is imperative to innovate various atomic and molecular arrangements for the modifications of structural properties. Of late, graphene and graphene-related derivatives have been proven as the most versatile two-dimensional nanomaterials with superb mechanical, electrical, electronic, optical, and magnetic properties. To understand the in-depth technology, an effort has been made to explain the basics of nano dimensional materials. The importance of nano particles in various aspects of nano technology is clearly indicated. There is more than one chapter describing the use of nanomaterials as sensors. In this volume, an effort has been made to clarify the use of such materials from non-conductor to highly conducting species. It is expected that this book will be useful to the postgraduate and research students as this is a multidisciplinary subject

Solid-State Nuclear Magnetic Resonance Spectroscopy of Unreceptive Quadrupolar Nuclei in Inorganic Materials

Preparation and characterization of inorganic materials is a crucial practice because understanding the relationship between structure and property is important for improving current performance and developing novel materials. Many metal centers in technologically and industrially important materials are unreceptive low-γ quadrupolar nuclei (i.e., possessing low natural abundance, low NMR frequencies and large quadrupole moments) and they usually give rise to very broad NMR resonances and low signal-to-noise ratios, making it difficult to acquire their solid-state NMR spectra. This thesis focuses on the characterization of inorganic materials using solid-state NMR (SSNMR) spectroscopy at very high magnetic field of 21.1 T in combination with quantum chemical calculations for computational modeling. In the first part of this thesis, 67Zn and 17O SSNMR studies of several microporous materials were reported. The results of 67Zn SSNMR studies from several important metal-organic frameworks (MOFs), in particular, zeolitic imidazolate frameworks (ZIFs) were presented. 67Zn SSNMR spectroscopy was used to gain structural information regarding the desolvation process in MOF-5. Furthermore, 67Zn SSNMR spectroscopy were utilized to study the host-guest interactions in ZIF-8 loaded with different guest molecules. Static 67Zn SSNMR spectra of microporous zinc phosphites (ZnP) and zinc phosphates (ZnPO) were also acquired at natural abundance. The Gaussian calculation results on a model cluster for ZnP indicate that Zn–O bond length is the most dominant factor to the observed quadrupolar coupling constant (CQ) among other geometric parameters around Zn centres. The local structures of the framework oxygen sites in molecular sieve SAPO-34 were directly probed by several 17O SSNMR techniques. The involvement of water vapor during the SAPO-34 formation in dry-gel conversion (DGC) synthesis was also investigated. In the second part, 91Zr and 33S SSNMR spectra of layered zirconium phosphates (ZrP) and transition metal disulfides (MS2) were obtained. The empirical correlations between NMR parameters and various structural parameters were used for obtaining partial structural information in Li+ and Co(NH3)63+ exchanged layered ZrP. For a series of closely related MS2 materials, the observed differences in the CQ(33S) values were rationalized by considering the difference in their geometrical arrangements. The final part of this thesis featured two examples of SSNMR spectroscopy of “exotic” nuclei in some interesting inorganic materials. (i) The experimental 135/137Ba SSNMR spectroscopy and theoretical studies of β-BBO, an important non-linear optical (NLO) material, indicate that the true crystal structure of β-BBO is R3c space group rather than R3. (ii) An ultrahigh field natural abundance 73Ge SSNMR study of two representative germanium containing materials [GeCl2•dioxane and GePh4] demonstrated that acquiring 73Ge wideline NMR spectra of germanium compounds where the Ge experiences an extremely large quadrupolar interaction is feasible and that the small 73Ge chemical shielding anisotropy (CSA) can be directly measured