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Diffusion is an omnipresent, most fundamental phenomenon in nature and thus critical for the performance of numerous technologies. This is in particular true for nanoporous materials with manifold applications for matter upgrading by separation, purification and conversion. The path lengths of molecular transportation within the industrial plants range from the elementary steps of diffusion within the micropores of the individual particles up to the matter flow over macroscopic distances. Each of them might be decisive in determining overall performance so that detailed knowledge of all modes of mass transfer is crucial for a knowledge-based optimization of the devices with reference to their transport properties. The rate of mass transfer is particularly complicated to be assessed within the individual (adsorbent) particles/crystallites with pore sizes of the order of molecular dimensions. We are going to present two powerful techniques exactly for this application, operating under both equilibrium (Pulsed Field Gradient (PFG) NMR) and non-equilibrium (Microimaging by interference microscopy and IR microscopy) conditions. The potentials of these techniques are demonstrated in a few showcases, notably including the options of transport enhancement in pore hierarchies. The contribution concludes with a survey on present activities within an IUPAC initiative aiming at the elaboration of “guidelines for measurements and reporting of diffusion properties of chemical compounds in nanoporous materials”.

Diffusion is an omnipresent, most fundamental phenomenon in nature and thus critical for the performance of numerous technologies. This is in particular true for nanoporous materials with manifold applications for matter upgrading by separation, purification and conversion. The path lengths of molecular transportation within the industrial plants range from the elementary steps of diffusion within the micropores of the individual particles up to the matter flow over macroscopic distances. Each of them might be decisive in determining overall performance so that detailed knowledge of all modes of mass transfer is crucial for a knowledge-based optimization of the devices with reference to their transport properties. The rate of mass transfer is particularly complicated to be assessed within the individual (adsorbent) particles/crystallites with pore sizes of the order of molecular dimensions. We are going to present two powerful techniques exactly for this application, operating under both equilibrium (Pulsed Field Gradient (PFG) NMR) and non-equilibrium (Microimaging by interference microscopy and IR microscopy) conditions. The potentials of these techniques are demonstrated in a few showcases, notably including the options of transport enhancement in pore hierarchies. The contribution concludes with a survey on present activities within an IUPAC initiative aiming at the elaboration of “guidelines for measurements and reporting of diffusion properties of chemical compounds in nanoporous materials”.

This cumulative dissertation is a compilation of eight peer-reviewed, published scientific papers on the subject of two microscopic techniques of diffusion measurement, namely infrared (IR) microimaging and pulsed field gradient (PFG) NMR. The dissertation contains mainly five chapters. The first chapter introduces diffusion phenomena in general and concisely explains the importance and the current challenges of the investigation of molecular diffusion in nanoporous materials, which are the primary motivations behind the present work. To rise the challenges, it proposes an option of employing IR microimaging in parallel with PFG NMR in the measurement of the molecular diffusion. The second chapter describes the basic principles of the two diffusion measurement techniques and what they are capable of. Chapters 3 and 4 deliver convincing demonstrations of their applicability and potential in diffusion studies. Lastly, Chapter 5 concludes the present work by discussing complementary benefits of the two techniques, along with the novel application of the two-region model for assessing mass transfer in hierarchically porous materials.:Table of Contents CHAPTER 1. Introduction CHAPTER 2. Basics of diffusion measurement techniques 2.1. Introduction to infrared microscopy (IRM) 2.1.1. Working principle 2.1.2. Experimental setup 2.2. Introduction to pulsed field gradient nuclear magnetic resonance (PFG NMR) 2.2.1. Self-diffusion and propagator 2.2.2. Theory of PFG NMR CHAPTER 3. Applicability and potential of IRM • Publication 3.1. Anomaly in the chain length dependence of n-alkane diffusion in ZIF 4 metal-organic frameworks • Publication 3.2. Metal-organic framework Co-MOF-74-based host-guest composites for resistive gas sensing • Publication 3.3. Revealing the transient concentration of CO2 in a mixed-matrix membrane by IR microimaging and molecular modeling • Publication 3.4. IR microimaging of direction-dependent uptake in MFI-type crystals CHAPTER 4. Importance of PFG N

This cumulative dissertation is a compilation of eight peer-reviewed, published scientific papers on the subject of two microscopic techniques of diffusion measurement, namely infrared (IR) microimaging and pulsed field gradient (PFG) NMR. The dissertation contains mainly five chapters. The first chapter introduces diffusion phenomena in general and concisely explains the importance and the current challenges of the investigation of molecular diffusion in nanoporous materials, which are the primary motivations behind the present work. To rise the challenges, it proposes an option of employing IR microimaging in parallel with PFG NMR in the measurement of the molecular diffusion. The second chapter describes the basic principles of the two diffusion measurement techniques and what they are capable of. Chapters 3 and 4 deliver convincing demonstrations of their applicability and potential in diffusion studies. Lastly, Chapter 5 concludes the present work by discussing complementary benefits of the two techniques, along with the novel application of the two-region model for assessing mass transfer in hierarchically porous materials.:Table of Contents CHAPTER 1. Introduction CHAPTER 2. Basics of diffusion measurement techniques 2.1. Introduction to infrared microscopy (IRM) 2.1.1. Working principle 2.1.2. Experimental setup 2.2. Introduction to pulsed field gradient nuclear magnetic resonance (PFG NMR) 2.2.1. Self-diffusion and propagator 2.2.2. Theory of PFG NMR CHAPTER 3. Applicability and potential of IRM • Publication 3.1. Anomaly in the chain length dependence of n-alkane diffusion in ZIF 4 metal-organic frameworks • Publication 3.2. Metal-organic framework Co-MOF-74-based host-guest composites for resistive gas sensing • Publication 3.3. Revealing the transient concentration of CO2 in a mixed-matrix membrane by IR microimaging and molecular modeling • Publication 3.4. IR microimaging of direction-dependent uptake in MFI-type crystals CHAPTER 4. Importance of PFG N

This cumulative dissertation is a compilation of eight peer-reviewed, published scientific papers on the subject of two microscopic techniques of diffusion measurement, namely infrared (IR) microimaging and pulsed field gradient (PFG) NMR. The dissertation contains mainly five chapters. The first chapter introduces diffusion phenomena in general and concisely explains the importance and the current challenges of the investigation of molecular diffusion in nanoporous materials, which are the primary motivations behind the present work. To rise the challenges, it proposes an option of employing IR microimaging in parallel with PFG NMR in the measurement of the molecular diffusion. The second chapter describes the basic principles of the two diffusion measurement techniques and what they are capable of. Chapters 3 and 4 deliver convincing demonstrations of their applicability and potential in diffusion studies. Lastly, Chapter 5 concludes the present work by discussing complementary benefits of the two techniques, along with the novel application of the two-region model for assessing mass transfer in hierarchically porous materials.:Table of Contents CHAPTER 1. Introduction CHAPTER 2. Basics of diffusion measurement techniques 2.1. Introduction to infrared microscopy (IRM) 2.1.1. Working principle 2.1.2. Experimental setup 2.2. Introduction to pulsed field gradient nuclear magnetic resonance (PFG NMR) 2.2.1. Self-diffusion and propagator 2.2.2. Theory of PFG NMR CHAPTER 3. Applicability and potential of IRM • Publication 3.1. Anomaly in the chain length dependence of n-alkane diffusion in ZIF 4 metal-organic frameworks • Publication 3.2. Metal-organic framework Co-MOF-74-based host-guest composites for resistive gas sensing • Publication 3.3. Revealing the transient concentration of CO2 in a mixed-matrix membrane by IR microimaging and molecular modeling • Publication 3.4. IR microimaging of direction-dependent uptake in MFI-type crystals CHAPTER 4. Importance of PFG N

This cumulative dissertation is a compilation of eight peer-reviewed, published scientific papers on the subject of two microscopic techniques of diffusion measurement, namely infrared (IR) microimaging and pulsed field gradient (PFG) NMR. The dissertation contains mainly five chapters. The first chapter introduces diffusion phenomena in general and concisely explains the importance and the current challenges of the investigation of molecular diffusion in nanoporous materials, which are the primary motivations behind the present work. To rise the challenges, it proposes an option of employing IR microimaging in parallel with PFG NMR in the measurement of the molecular diffusion. The second chapter describes the basic principles of the two diffusion measurement techniques and what they are capable of. Chapters 3 and 4 deliver convincing demonstrations of their applicability and potential in diffusion studies. Lastly, Chapter 5 concludes the present work by discussing complementary benefits of the two techniques, along with the novel application of the two-region model for assessing mass transfer in hierarchically porous materials.:Table of Contents CHAPTER 1. Introduction CHAPTER 2. Basics of diffusion measurement techniques 2.1. Introduction to infrared microscopy (IRM) 2.1.1. Working principle 2.1.2. Experimental setup 2.2. Introduction to pulsed field gradient nuclear magnetic resonance (PFG NMR) 2.2.1. Self-diffusion and propagator 2.2.2. Theory of PFG NMR CHAPTER 3. Applicability and potential of IRM • Publication 3.1. Anomaly in the chain length dependence of n-alkane diffusion in ZIF 4 metal-organic frameworks • Publication 3.2. Metal-organic framework Co-MOF-74-based host-guest composites for resistive gas sensing • Publication 3.3. Revealing the transient concentration of CO2 in a mixed-matrix membrane by IR microimaging and molecular modeling • Publication 3.4. IR microimaging of direction-dependent uptake in MFI-type crystals CHAPTER 4. Importance of PFG N

With reference to these advantages, the poster goes the other way round and identifies a couple of similarities where, on looking at molecular diffusion in nanoporous materials, one is able to recognize features of spreading, which may occur in quite different fields of research. The examples presented include (i) considering molecular uptake and release with nanoporous particles as a model for, respectively, occupation of a habitat by a new species and, vice versa, for the loss of a species in this habitat [2], (ii) the effect of additional highways on overall mass transfer [3,4], (iii) transport impediment (and enhancement!) by diffusant interference [5], (iv) invader-induced changes in the host system [2] and (v) host-induced changes of the invaders [6].

With reference to these advantages, the poster goes the other way round and identifies a couple of similarities where, on looking at molecular diffusion in nanoporous materials, one is able to recognize features of spreading, which may occur in quite different fields of research. The examples presented include (i) considering molecular uptake and release with nanoporous particles as a model for, respectively, occupation of a habitat by a new species and, vice versa, for the loss of a species in this habitat [2], (ii) the effect of additional highways on overall mass transfer [3,4], (iii) transport impediment (and enhancement!) by diffusant interference [5], (iv) invader-induced changes in the host system [2] and (v) host-induced changes of the invaders [6].

Increasing demands in thefield of sensing, especially for gas detectionapplications, require new approaches to chemical sensors. Metal−organic frameworks (MOFs) can play a decisive role owing to their outstanding performances regardinggas selectivity and sensitivity. The tetrathiafulvalene (TTF)-infiltrated MOF, Co-MOF-74, has been prepared following the host−guest concept and evaluated inresistive gas sensing. The Co-MOF-74-TTF crystal morphology has beencharacterized via X-ray diffraction and scanning electron microscopy, while thesuccessful incorporation of TTF into the MOF has been validated via X-rayphotoemission spectroscopy, thermogravimetric analysis, UV/vis, infrared (IR), andRaman investigations. We demonstrate a reduced yet ample uptake of CO2in thepores of the new material by IR imaging and adsorption isotherms. Thenanocomposite Co-MOF-74-TTF exhibits an increased electrical conductivity incomparison to Co-MOF-74 which can be influenced by gas adsorption from asurrounding atmosphere. This effect could be used for gas sensing.

With reference to these advantages, the poster goes the other way round and identifies a couple of similarities where, on looking at molecular diffusion in nanoporous materials, one is able to recognize features of spreading, which may occur in quite different fields of research. The examples presented include (i) considering molecular uptake and release with nanoporous particles as a model for, respectively, occupation of a habitat by a new species and, vice versa, for the loss of a species in this habitat [2], (ii) the effect of additional highways on overall mass transfer [3,4], (iii) transport impediment (and enhancement!) by diffusant interference [5], (iv) invader-induced changes in the host system [2] and (v) host-induced changes of the invaders [6].

With reference to these advantages, the poster goes the other way round and identifies a couple of similarities where, on looking at molecular diffusion in nanoporous materials, one is able to recognize features of spreading, which may occur in quite different fields of research. The examples presented include (i) considering molecular uptake and release with nanoporous particles as a model for, respectively, occupation of a habitat by a new species and, vice versa, for the loss of a species in this habitat [2], (ii) the effect of additional highways on overall mass transfer [3,4], (iii) transport impediment (and enhancement!) by diffusant interference [5], (iv) invader-induced changes in the host system [2] and (v) host-induced changes of the invaders [6].

A systematic NMR cryo-porometry and -diffusometry study using nitrobenzene as a probe liquid is carried out in order to characterise pore structures of hierarchically-organised porous silica monolith possessing mesopores along with a 3D bicontinuous macropore network. The result obtained from NMR cryoporometry shows the presence of a relatively wide mesopore size distribution of 10-35 nm. Furthermore, NMR cryodiffusometry indicates that whilst the mesopores are highly tortuous (Tmeso ≈6), they have little influence on the overall tortuosity of the material (Tmacro ≈1.5), which is largely dominated by the macropores (Toverall ≈1.7).

A systematic NMR cryo-porometry and -diffusometry study using nitrobenzene as a probe liquid is carried out in order to characterise pore structures of hierarchically-organised porous silica monolith possessing mesopores along with a 3D bicontinuous macropore network. The result obtained from NMR cryoporometry shows the presence of a relatively wide mesopore size distribution of 10-35 nm. Furthermore, NMR cryodiffusometry indicates that whilst the mesopores are highly tortuous (Tmeso ≈6), they have little influence on the overall tortuosity of the material (Tmacro ≈1.5), which is largely dominated by the macropores (Toverall ≈1.7).

A systematic NMR cryo-porometry and -diffusometry study using nitrobenzene as a probe liquid is carried out in order to characterise pore structures of hierarchically-organised porous silica monolith possessing mesopores along with a 3D bicontinuous macropore network. The result obtained from NMR cryoporometry shows the presence of a relatively wide mesopore size distribution of 10-35 nm. Furthermore, NMR cryodiffusometry indicates that whilst the mesopores are highly tortuous (Tmeso ≈6), they have little influence on the overall tortuosity of the material (Tmacro ≈1.5), which is largely dominated by the macropores (Toverall ≈1.7).

A systematic NMR cryo-porometry and -diffusometry study using nitrobenzene as a probe liquid is carried out in order to characterise pore structures of hierarchically-organised porous silica monolith possessing mesopores along with a 3D bicontinuous macropore network. The result obtained from NMR cryoporometry shows the presence of a relatively wide mesopore size distribution of 10-35 nm. Furthermore, NMR cryodiffusometry indicates that whilst the mesopores are highly tortuous (Tmeso ≈6), they have little influence on the overall tortuosity of the material (Tmacro ≈1.5), which is largely dominated by the macropores (Toverall ≈1.7).