Martin Hartmann

• Professor
• Professor at Friedrich-Alexander-University Erlangen-Nürnberg

When annealing a 4H silicon carbide (SiC) crystal, a sequence of optically active defect centers occurs among which the TS center is a prominent example. Here, we present low-temperature photoluminescence analyses on the single defect level. They reveal that the three occurring spectral signatures TS1, TS2 and TS3 originate from one single defect....

Enzymatic fuel cells (EFCs) offer renewable energy conversion via highly selective electrode reactions using enzymes as natural catalysts even under mild conditions. Electrochemical impedance spectroscopy (EIS) is a valuable tool for evaluating EFC performance, providing insights into substrate mass transport, enzyme kinetics, and electrode stabili...

In this work, bovine serum albumin (BSA) and Aspergillus sp. laccase (LC) were encapsulated in situ within two lanthanide-based MOFs (TbBTC and GdBTC) through a green one-pot synthesis (almost neutral aqueous solution, T = 25 °C, and atmospheric pressure) in about 1 h. Pristine MOFs and protein-encapsulated MOFs were characterized through wide angl...

Recently, mesoporous bioactive glasses (MBGs) as microparticles or nanoparticles (MBGNs) aroused a great interest owing to their high textural properties and capability to be incorporated with biologically active ions desirable for different stages of wound healing. Considering therapeutic effects of two well-recognized elements (copper and zinc) a...

The flexibility of the MIL-53(M) metal–organic framework (MOF) has been elucidated through various characterization methodologies, particularly in gas and liquid adsorption processes. However, to the best of our knowledge, there has been no prior electron paramagnetic resonance (EPR) characterization of liquid-phase adsorption in the MOF MIL-53(M),...

Separation and reuse of the catalytically active metal complexes are persistent issues in homogeneous catalysis. Supported Ionic Liquid Phase (SILP) catalysts, where the catalytic center is dissolved in a thin film of a stable ionic liquid, deposited on a solid support, present a promising alternative. However, the dissolution of the metal center i...

We have developed a comprehensive strategy for quantitatively assessing the hydrophilicity/ hydrophobicity of nanoporous materials by combining advanced adsorption studies, novel liquid intrusion techniques and solid-state NMR spectroscopy. For this we have chosen a well-defined system of model materials, i.e., the highly ordered mesoporous silica...

Ordered mesoporous carbon CMK-3 sieves with a hexagonal structure and uniform pore size have recently emerged as promising materials for applications as adsorbents and electrodes. In this study, using sucrose as the sustainable carbon source and SBA-15 as a template, CMK-3 sieves are synthesized to form bioelectrocatalytic immobilization matrices f...

Metal‐organic frameworks (MOFs) are microporous adsorbents for high‐throughput gas separation. Such materials exhibit distinct adsorption characteristics owing to the flexibility of the crystal framework in a nanoparticle, which can be different from its bulk crystal. However, for practical applications, such particles need to be compacted into mac...

Silica is widely used as a support material for chemically-bound/bonded stationary phases in chromatographic separations. Tuning of textural properties and surface chemistry of stationary phase materials (SPMs) is crucial to enhance their selectivity to certain compounds. Silica supports are beneficial as surface modifications are possible with a l...

Zeolite A (LTA) was synthesized at 80 °C under hydrothermal conditions from a gel with the molar composition of 2.5 Na 2 O : 2 SiO 2 : Al 2 O 3 : 80 H 2 O. In the present study, we report the use of home‐made ultrasound devices as a real‐time, in situ diagnostic tool for monitoring the progress of zeolite formation. In addition, the specific aim of...

Silica particles are widely used as a support material for chemically-bound stationary phases in chromatographic separation processes. The tuning of textural properties and surface chemistry of stationary phase materials (SPMs) is crucial to enhance their selectivity to certain compounds and the efficiency of the separation process. Silica supports...

We have developed a comprehensive strategy for assessing the surface chemistry of nanoporous materials by combining advanced adsorption studies, novel liquid intrusion techniques and solid-state NMR spectroscopy. For this we have chosen a well-defined system of model materials, i.e., the highly ordered mesoporous silica molecular sieve SBA-15 in it...

The ability to molecularly engineer luminescent metal-organic frameworks is a powerful tool for the design of better performing rational temperature sensors. Lanthanide based MOF stand out as luminescent temperature sensors due to the high luminescence intensity and sharp emission lines of the lanthanides. The use of two different lanthanide cation...

Engineering two cooperative sites into a catalyst implies the onset of synergistic effects related to the existence of short-range electronic interactions between two metal components. However, these interactions and the relative structure-property correlations are often difficult to obtain. Here we show that hyperfine spectroscopy has the potentia...

Silica particles are widely used as a support material for chemically-bound stationary phases in chromatographic separation processes. The tuning of textural properties and surface chemistry of stationary phase materials (SPMs) is crucial to enhance their selectivity to certain compounds and the efficiency of the separation process. Silica supports...

The ability to molecularly engineer luminescent metal-organic frameworks is a powerful tool for the design of better performing rational temperature sensors. Lanthanide based MOF stand out as luminescent temperature sensors due to the high luminescence intensity and sharp emission lines of the lanthanides. The use of two different lanthanide cation...

We have developed a comprehensive strategy for assessing the surface chemistry of nanoporous materials by combining advanced adsorption studies, novel liquid intrusion techniques and solid-state NMR spectroscopy. For this we have chosen a well-defined system of model materials, i.e., the highly ordered mesoporous silica molecular sieve SBA-15 in it...

Laccase from Aspergillus sp. (LC) was immobilized on functionalized silica hierarchical (microporous-macroporous) MFI zeolite (ZMFI). The obtained immobilized biocatalyst (LC#ZMFI) was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (ATR-FTIR), N2 adsorption/desorption isotherms,...

Hydrothermal synthesis is the state-of-the-art technique for the preparation of zeolites and related porous solids. However, when it comes to the preparation of nanosized zeolites, this technique is limited by low yields, separation problems and high amounts of waste. In this work, we utilized the strengths of a combination of spray drying and stea...

Using EPR and HYSCORE spectroscopies in conjunction with ab initio calculations, we assess the structure of framework-bound monomeric hydroxo-CuII in copper-loaded chabazite (CHA). The species is an interfacial distorted square-planar [CuIIOH(O-8MRs)3] complex located at eight-membered-ring windows, displaying three coordinating bonds with zeolite...

Zeolites are very important catalysts in the chemical industry, but their intrinsic narrow micropore system often restricts the mass transport of reactant and product molecules. These mass transport limitations can be overcome by introducing a second larger pore system (meso-/macropores) into the zeolite crystals. Over the past decade, desilication...

Aldol condensation of n -pentanal can lead to pore blocking and hence transport limitations in supported liquid phase (SLP) catalysts. By careful texture optimization this effect can be minimized.

Sol-gel-based silica monoliths with hierarchical mesopores/macropores are promising catalyst support and flow reactors. Here, we report the successful preparation of cylindrically shaped Pt-loaded silica monoliths (length: 2 cm, diameter: 0.5 cm) with a variable mean macropore width of 1, 6, 10, or 27 μm at a fixed mean mesopore width of 17 nm. The...

This chapter provides the basics of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy by the discussion of selected examples demonstrating the potential and limitations of using both techniques in the characterization of metal oxide nanoparticles. It focuses on the (rare) examples directly probing the metal sit...

The pyrolytic treatment of the novel ionic liquid 1-ethyl-3-methyl-imidazolium tetrakis-(1-imidazolyl)borate ([EMIM][BIm4]) allowed the preparation of B/N-doped carbonaceous materials with an exceptional performance in the adsorptive removal of the cationic dye methylene blue (MB) from wastewater. [EMIM][BIm4] was prepared via an easy and scalable...

The bonding of copper ions to lattice oxygens dictates the activity and selectivity of copper exchanged zeolites. By 17O isotopic labelling of the zeolite framework, in conjunction with advanced EPR methodologies and DFT modelling, we determine the local structure of single site CuII species, we quantify the covalency of the metal-framework bond an...

Serotonin (5-HT) plays an important role in human physiology. An excess of this native regulator within the human gut can be partially controlled by orally consuming zeolite. Therefore, this study focuses on the kinetics of the uptake and release of serotonin hydrochloride (5-HT-hc) by natural Cuban zeolite containing clinoptilolite and mordenite a...

Due to its structural features, ZIF-11 is one of the most interesting materials for gas separation applications. Herein, we report a systematic study on the synthesis of ZIF11 as a supported membrane. For this, we adapted optimized conditions for the ZIF-11 powder synthesis, identified in our previous works, to form ZIF layers on symmetric and asym...

Cryogenic adsorption using microporous materials is one of the emerging technologies for hydrogen storage in fuel cell vehicles. Metal–organic frameworks have been identified as suitable adsorbents exhibiting large hydrogen sorption at 77 K. With respect to technical realization, in this work, the deliverable capacity at the optimal storage tempera...

Adsorptive hydrogen storage is a desirable technology for fuel cell vehicles, and efficiently identifying the optimal storage temperature requires modeling hydrogen loading as a continuous function of pressure and temperature. Using data obtained from high-throughput Monte Carlo simulations for zeolites, metal-organic frameworks, and hyper-cross-li...

With a gravimetric hydrogen density of 19.6 wt % and the capability of storing up to 146 kgH2 m-3, ammonia borane (NH3·BH3) possesses excellent hydrogen storage properties. Nanoconfinement in six different porous metal-organic frameworks with MIL-53 topology is shown to reduce the hydrogen release temperature and modify its decomposition pathway. I...

Ordered arrays of parallel, cylindrical silicon nanotubes are obtained by aluminothermic reduction of SiO2 nanotubes generated by atomic layer deposition (ALD) on nanoporous aluminum oxide templates. The reduction to amorphous Si (a-Si) is characterized by a combination of X-ray diffraction (XRD), solid-state cross-polarization magic-angle spinning...

X-/Q-band electron paramagnetic resonance (EPR) and hyperfine sublevel correlation (HYSCORE) spectroscopies have been employed, in conjunction with density functional theory (DFT) modeling, to determine the location of Cr⁵⁺ions in SAPO-5 zeotype materials. The interaction of the unpaired electron of the paramagnetic Cr⁵⁺ species with ²⁷Al could be...

A one‐pot synthesis of aluminium‐containing mesoporous silica particles (Al‐MSPs) utilizing polyvinyl alcohol (PVA) as steric stabilization agent is reported. PVA prevents particle agglomeration even when the ionic aluminium source is present in the synthesis mixture. Silicon and aluminium sources were utilised completely, resulting in high yield a...

Hierarchically‐ordered zeolites have received increasing attention in the last 15 years due to their outstanding properties, which are explored in catalytic reaction with industrial relevance. Up to now, a large number of different synthetic strategies have been reported that allow to introduce an additional meso‐ or macropore system in addition to...

Using ionic liquids (ILs) as linker precursors, the well‐known metal‐organic framework (MOF) UiO‐66 (Universitetet i Oslo) and the recently reported MOF hcp UiO‐66 (hexagonal closed packed) have been successfully synthesized and characterized. The advantage of the applied novel synthesis approach is an economically and environmentally benign work‐u...

The material ZIF-F reported by Jin et al. is not a new structure, but one of the oldest known polymorphs of ZIF-8, viz . ZIF-8 dia. In this comment, we shed some light on the formation of different polymorphs as a function of the synthesis mixture.

A large number of functional and catalytic materials exhibit porosity, often on different length scales and with a hierarchical structure. The assessment of pore sizes, pore geometry, and pore interconnectivity is complex and usually not feasible by classical spectroscopic and diffraction techniques. One of the most powerful methods to probe these...

In this work, a widely applicable routine to characterize the core, surface, stability, and optical properties of CdSe/CdS/ZnS core–shell–shell nanorods after multiple growth steps is established. First, size, shape, and shell thickness of the nanorods are characterized by transmission electron microscopy (TEM), analytical ultracentrifugation (AUC)...

Studying complex processes in solid phases such as adsorption or phase transitions in situ is the best way to obtain detailed and realistic insights on a molecular level. Besides in situ X-ray diffraction techniques, magic angle spinning (MAS) solid-state NMR spectroscopy is one of the most powerful analytical techniques. The implementation of in s...

While it is well-known that the particle size of solvothermally synthesized metal–organic frameworks (MOFs) can be controlled by tuning the solvent composition, which affects the solubility of the linker and metal salt educts, the exact relationship between linker solubility, initial chemical coordination steps occurring in solution, and the result...

In this work, we demonstrate that a well-established and facile ball milling approach using mixtures of commercial anatase nanoparticles and TiH2 introduces noble-metal-free photocatalytic H2 activity to titania. We characterize this synergistic effect in view of the nature of defects, state of hydroxylation, and investigate the effect on the energ...

We present the effect of different combinations of intracrystalline pore systems in hierarchical ZSM‐5 zeolites on their performance as MTO catalysts. We prepared ZSM‐5 zeolites with additional intracrystalline mesoporous, intracrystalline macropores and a novel ZSM‐5 type zeolite with intracrystalline meso and macropores. The catalytic results sho...

The formation of multifunctional materials involves various simultaneous and closely entangled physico‐chemical processes including nucleation, growth, aggregation, and in some cases, also growth by oriented aggregation. These elementary particle formation processes occur in broad size ranges from the molecular to micron level and time scales rangi...

The topological metal-organic framework isomers MIL-53 and MIL-68 form from similar educts but differ in their pore geometries. They have been known for several years, but their synthesis always reported separately. In consequence, the underlying mechanism and decisive synthesis parameters leading to the formation of either MIL-53 or MIL-68 are not...

A facile extrusion approach that can fully retain the breathing behavior of flexible metal‐organic frameworks (MOF) like MIL‐53 and MIL‐53‐NH2 employing methyl cellulose as binder is reported. Shaped MOF extrudates were extensively characterized by nitrogen sorption, X‐ray diffraction, thermogravimetric analysis and scanning electron microscopy. A...

In the context of environmental problems and resource depletion, the chemical industry is challenged with the substitution of fossil feedstock by renewable resources. To reduce the probability of unexpected environmental impacts by new processes using various sources of biomass, LCA methods can provide support for process development. The investiga...

A previously unknown solid phase in the zinc-imidazole system relevant for the synthesis of ZIF8 was obtained by adding a small excess of methylimidazole (Hmim) to a diluted zinc chloride solution. By chemical and thermal analyses, a composition of Zn3(mim)5ClH2O∙xH2O with x = 0.74, was determined and the compound denoted as ZIFyqt hydrate. The cry...

A new germanosilicate structural analogue of AFI zeolite (Ge-AFI) was hydrothermally synthesized. One- and two-step alumination of the Ge-AFI zeolites were used to modify their structure and acidic properties traced using XRD, N 2 adsorption, ICP-OES, ²⁷ Al NMR, and FTIR spectroscopy. Two-step aluminated sample (deGe-Al-AFI) provided a higher Al co...

A detailed model is developed for the separation of strongly adsorbing gas mixtures at semi-pilot scale. It assumes a non-isothermal compressible transport-diffusion mechanism in the adsorber and dispersed compressible flow in the periphery, respectively. A methodology is proposed for efficient system analysis and parameter determination, leading t...

By using a terephthalate containing ionic liquid, a new metal-organic framework, hcp UiO-66, comprising (Zr12O8(OH)14) double clusters and terephthalate ligands has been synthesized. The hydrothermal synthesis of hcp UiO-66 might help to establish metal-organic frameworks for industrial scale applications.

ZIF-8 membranes were fabricated by a two-step procedure consisting of (1) a flexible and simple spray coating process to deposit uniform ZnO layers on different supports and (2) subsequent solvent-free transformation of the ZnO layers into dense ZIF-8 membranes by a vapor-solid reaction. The spray coating offered superior flexibility regarding the...

Chemical and physical processes occurring within the nanochannels of mesoporous materials are known to be determined by both chemical nature of the solution inside the pores/channels as well as the channel surface properties, including surface electrostatic potential. Such properties are important for numerous practical applications such as heterog...

The synthesis of ZIF-11 in N,N-Diethylformamide (DEF) at varying reaction temperatures, times and different molar compositions of the reaction mixture was investigated in detail in order to identify ranges of the formation of phase-pure ZIF-11. Since it is known that water in the solvent DEF leads to the formation of the phase impurity ZIF-7-III du...

In a recently published communication (CrystEngComm, 2018, 20, 402-406), Perea-Cachero et al. stated that the topolgically isomeric metal-organic frameworks MIL-53(Al) and MIL-68(Al) could be reversibly transformed into each other. However, the suggested synthesis procedure for MIL-68 indeed resulted in MIL-53 with DMF entrapped inside of the pores...

A new synthesis route for the zeolitic imidazolate framework ZIF-4 using imidazolium imidazolate is reported. Additionally, the ionic liquid-derived material is compared to conventional ZIF-4 with respect to the powder X-ray diffraction pattern pattern, nitrogen uptake, particle size, and separation potential for olefin/paraffin gas mixtures. Highe...

Adsorption of nitric oxide (NO) in the metal-organic framework MIL-100(Al) is studied by solid-state NMR. Due to a modified synthesis no extra-framework btc is present on the cost of a small amount of extra-framework Al(OH)3 as evident from ²⁷Al, ¹H as well as HETCOR spectra. Five-coordinated aluminum sites represent about 50% of the aluminum in a...

The metal-organic framework MIL-53(Al) serves as a model system in this study. Its formation mechanism in N,N-dimethylformamide (DMF) is elucidated through simultaneous FTIR and Raman spectroscopy and turbidity measurements collected under in-situ synthesis conditions in a custom-designed solvothermal reactor coupled with reaction sampling. Differe...

Zeolite faujasite (FAU) is widely used as a catalyst and adsorbent in many industrial catalytic and separation applications. The high water adsorption capacity of zeolite FAU makes it an attractive adsorbent material for the heat pump and heat storage applications. However, highly alkaline condition, which is required for the synthesis of zeolite F...

In this study, two zeolitic imidazolate frameworks (ZIFs) called ZIF-4 and ZIF-zni (zni is the network topology) were characterized by sorption studies regarding their paraffin/olefin separation potential. In particular, equilibrated pure and mixed gas adsorption isotherms of ethane and ethene were recorded at 293 K up to 3 MPa. ZIF-4 exhibits sele...

Molecular diffusion is commonly found to slow down with increasing molecular size. Deviations from this pattern occur in some host materials with pore sizes approaching the diameters of the guest molecules. A variety of theoretical models have been suggested to explain deviations from this pattern, but robust experimental data are scarcely availabl...

Red mud presents significant environmental problems, so that its incorporation in geopolymers could represent an alternative solution to produce valuable products from this residue. Novel geopolymers using red mud as source of alumina and waste glass as silica supplier were developed, using sodium hydroxide as the only ‘non-waste’ material. The for...

The low-temperature binding of nitric oxide (NO) in the metal-organic framework MIL-100(Al) has been investigated by pulsed electron nuclear double resonance and hyperfine sublevel correlation spectroscopy. Three NO adsorption species have been identified. Among them, one species has been verified experimentally to bind directly to an ²⁷Al atom and...

Investigation of kinetics of the UOV germanosilicate alumination by X-ray diffraction, 27Al and 29Si MAS NMR, ICP/OES and FTIR spectroscopy showed the multi-stage mechanism of the process. The first step consists of degermanation and partial disassembly followed by Al incorporation into UOV germanosilicate framework in the second step. Al atoms sta...

The separation of ethane/ethene mixtures (as well as other paraffin/olefin mixtures) is one of the most important but challenging processes in the petrochemical industry. In this work, we report the synthesis of ZIF-318, isostructural to ZIF-8 but built from the mixed linkers of 2-methylimidazole (L1) and 2-trifluoromethylimidazole (L2) (ZIF-318 =...

A new synthesis route for the zeolitic imidazolate framework ZIF-4 is reported. About 200 g of ZIF-4 are prepared by sonothermal synthesis from ZnO at room temperature. The ZIF-4 prepared by sonothermal synthesis is comparable to the ZIF-4 synthesized by the pathway reported in literature with respect to the powder X-ray diffraction pattern, partic...

Four metal-organic frameworks with similar topology but different chemical environment inside the pore structure, namely IFP-1, IFP-3, IFP-5, and IFP-7, have been investigated with respect to the separation potential for olefin-paraffin mixtures as well as the influence of the different linkers on adsorption properties using experiments and Monte C...

Nanosized materials are expected to play a unique role in the development of future catalytic processes. Herein, pre-prepared and geometrically well-defined amorphous silica spheres are densified into silica-rich zeolites with nanosized dimensions. After the densification, the obtained nanosized zeolites exhibit the same spherical morphology like t...

EMIM][Hbdc] and [EMIM]2[bdc] were synthesized and successfully used in a one-step synthesis procedure of MIL-53(Al)/boehmite composites with unusual properties. The breathing effect typically observed for MIL-53(Al) is not found and scanning electron microscopy confirms the presence of MIL-53 nanoparticles in a boehmite matrix. The completely diffe...

Hierarchical nanosheet assemblies of boron-containing MFI-type zeolites were successfully synthesized using bifunctional surfactant molecules under static conditions. With the optimized Si/B = 50 in the synthesis gel, a material with high specific surface area (483 m(2) g(-1)) and a maximum pore size of 6.5 nm suitable for lipase encapsulation was...

The syntheses of MOFs and ZIFs are often accompanied by the formation of unwanted byproducts. Also for the ZIF-11 synthesis in N,N-Diethylformamide (DEF), phase impurities have been reported. In this systematic study, water residues in the reaction mixture could be identified as one major reason for the formation of the phase impurity ZIF-7-III wit...

An organic imidazolium salt of terephthalic acid has been utilized as a linker precursor for the synthesis of an aluminum-based metal organic framework (MOF) with MIL-53(ht) structure. This material shows the predicted porosity in terms of nitrogen and hydrogen sorption without exhibiting the breathing effect typical for MIL-53(Al) materials.

Ball milling TiO2 anatase together with TiH2 can create an effective photocatalyst. The process changes the lattice and electronic structure of anatase. Lattice deformation created by mechanical impact combined with hydride incorporation yield electronic gap-states close to the conduction band of anatase. These provide longer lifetimes of photogene...

We apply high-energy proton ion-implantation to modify TiO2 nanotubes selectively at their tops. In the proton-implanted region we observe the creation of intrinsic co-catalytic centers for photocatalytic H2-evolution. We find proton implantation to induce specific defects and a characteristic modification of the electronic properties not only in n...

In the present work we show, how a high pressure hydrogenation of commercial anatase or anatase/rutile powder can create a photocatalyst for hydrogen evolution that is highly effective and stable without the need of any additional co-catalyst. This activation effect can not be observed for rutile. For anatase/rutile mixtures, however, a strong syne...

Hierarchical zeolites were prepared by post synthesis treatments of commercial ZSM-5 zeolite (Si/Al = 13) involving alkali treatment, acid treatment, steam treatment, combination of acid-alkali treatments, and combination of steam-acid-alkali treatments. Various characterization techniques were employed to investigate the influence of each post syn...

Two zeolitic imidazolate frameworks, ZIF-9 and ZIF-71, are evaluated by adsorption experiments and molecular simulations with respect to their potential towards olefin/paraffin separation. Pure component adsorption isotherms are measured and compared to grand-canonical Monte–Carlo (GCMC) simulations. The experiments show that the adsorption of the...