Metal-Organic Frameworks (MOFs) are highly porous materials built from inorganic nodes joined by organic linkers forming extended crystalline networks. One of the distinguishing features of metal-organic frameworks is the ability to adaptively change their crystal structure in response to external stimuli with significant porosity switching. Such structural switchability of MOFs offers new opportunities in gas separation, selective recognition, sensing, and energy storage. However, there are still open questions in understanding factors affecting switchability. The electronic structure of the metal in the building blocks, host-guest interactions, but also particle size, morphology, surface, desolvation conditions are involved into the responsiveness of the system. One of the representative of switchable metal-organic frameworks is pillared-layer DUT-8 (M2(2,6-ndc)2(dabco), M = Ni, Co, Cu, Zn, 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane). Depending on the metal node and particle size, it is possible to synthesize either switchable or rigid materials differing in physisorption isotherm profiles. In order to understand switching behaviour of DUT-8, the important parameters influencing structural switchability are addressed in my work. For this purpose, the impact of crystal size and morphology, as well as crystal surface on adsorption-induced structural transformations of DUT-8(Ni) were investigated. DUT-8(Ni) shows reversible structural transition between open (op) and closed pore phase (cp) upon adsorption/removal of guest molecules. To understand which particular crystal surfaces dominate the phenomena observed, crystals similar in size and differing in morphology were involved in a systematic study. The analysis of the data shows that the width of the rods (corresponding to the crystallographic directions along the layer) represents a critical parameter governing the dynamic properties upon adsorption of nitrogen at 77 K. This observation is related to the anisotropy of the channel-like pore system and the nucleation mechanism of the solid-solid phase transition triggered by gas adsorption. To investigate the influence of external surface on adsorption-induced switchability, DUT-8(Ni) samples were exposed to different treatment techniques. By means of analytical methods, it was revealed that the surface of samples was modified leading to a significant increase of the gate-opening pressure, reflecting the increase of activation barrier for phase switching form cp to op upon adsorption of nitrogen at 77 K. Furthermore, the properties of DUT-8(Zn) were studied precisely, focusing on the variation of particle size and morphology, host-guest interactions, desolvation conditions, selectivity and thermoresponsivity. Depending on the synthesis conditions, DUT-8(Zn) can be synthesised in macro-sized regime (150 µm) and micron-sized regime (0.5 µm). The solvent removal process (pore desolvation stress contracting the framework) significantly controls the cp/op ratio after desolvation and, subsequently, the adsorption induced switchability characteristics of the system. Among the applied desolvation techniques, the solvent exchange with subsequent heating causes phase transition from open (op) to closed pore phase (cp). After desolvation, the dense cp phase of DUT-8(Zn) shows no adsorption-induced reopening and therefore is non-porous for N2 at 77 K and CO2 at 195 K. However, polar molecules with a higher adsorption enthalpy, such as chloromethane at 249 K and dichloromethane (DCM) at 298 K can reopen the macro-sized crystals upon adsorption, while micron-sized crystals retain the cp phase. For macro-sized particles (160 µm), the outer surface energy is negligible and only the type of metal (Zn, Co, Ni) controls the DCM-induced gate opening pressure. The node hinge stiffness increases from Zn to Ni as confirmed by DFT calculations, X-ray crystal structural analysis, and low frequency Raman spectroscopy. This softer Zn-based node hinges and overall increased stabilization of cp vs. op phase shift the critical particle size at which switchability starts to become suppressed to even lower values. Hence, the three factors affecting switchability (energetics of the empty host, (Eop–Ecp) (i), particle size (ii), and desolvation stress (iii)) appear to be of the same order of magnitude and should be considered collectively, not individually. Crystal downsizing (0.5 µm) facilitates the responsivity of DUT-8(Zn) towards different guest molecules, not opening for macro-sized crystals. Among investigated adsorptives, the alcohols are in the center of attention due to ability to induce so called shape-memory effect in micron-sized crystals. The adsorption of alcohols stimulates the change of initial shape of pores (cp) into a temporary shape (op) which is maintained even after desorption. To brighten the crystal size range and to study the dependence of gate opening pressure from crystal size and morphology, differently shaped crystals in micron-sized regime were produced by face-selective coordination modulation. Morphology modification allowed to determine the critical parameter controlling switchable transformations in DUT-8(Zn). Thus, the crystal size engineering and morphology modification provide an opportunity not only to control the structural dynamics of MOFs, but also to tailor responsivity towards guest molecules, influencing the selective adsorption behaviour.

<p>Various transition metal oxides with interesting magnetic properties (often based on the perovskite structure) were prepared using conventional solid-state methodologies and fully characterized using a variety of techniques such as powder X-ray diffraction, variable temperature neutron diffraction, SEM-EDS, TEM-EDS, SQUID magnetometry and heat capacity measurements.</p> <p>One family of compounds that was investigated intensively were the 'pillared perovskites'. In this structure type, perovskite-like layers of comer shared octahedra are separated. by about 10 A by diamagnetic edge-shared octahedral dimer 'pillars'. Despite this long distance between layers, long-range order is present in both the La5Re3Co016 and La5Re3Ni016 members. In fact, a new magnetic structure was discovered for the Ni compound consisting of ferromagnetically ordered layers, coupled antiferromagnetically.</p> <p>In addition, for the first time, substitution of the 5+ ion within the layer was successful, yielding compounds with general formula, La5Re3-xTaxB016 (B =Mn, Fe, Co, Ni; x ~ 0.5). Surprisingly, despite replacing about half of the magnetic ions within the perovskite layers with non-magnetic tantalum, the materials had the same ordering temperatures and magnetic structures as their unsubstituted analogues. This observation is evidence that the longer interlayer coupling pathway is the key to long-range ordering in this structure type.</p> <p>The lanthanum rhenium oxide, La3Re20 10, involves the edge-shared octahedral dimer 'pillar' unit from the pillared perovskite structure, but with one unpaired electron per dimer unit. Prepared for the first time by solid-state synthesis, and studied magnetically in depth, long-range order was evident at 18 K. Theoretical investigations hinted that the magnetic structure consists of antiferromagnetically coupled chains of dimers, coupled antiferromagnetically.</p> <p>The magnetic properties of the double perovskite, SrLaRuNi06, were also explored for the first time. This study demonstrates the power of neutron diffraction at elucidating magnetic information, such as the ordering temperature and magnetic structure, despite the presence of a ferromagnetic impurity that dominated much of the measurements.</p> <p>The candidate's examination of the magnetism of the rock-salt oxides, Na2Cu2Te06 and Na3Cu2Sb06 has raised some controversy in the literature, as the exact nature of the one-dimensional order (either antiferromagnetic-antiferromagnetic or antiferromagnetic-ferromagnetic alternating linear chains) is uncertain. Again, theoretical calculations and comparison with other magnetic data can aide in the ultimate understanding of the overriding magnetism.</p> <p>This thesis has focused on the synthesis and study of transition metal oxides with interesting or unusual magnetic properties. In many cases, the compounds exhibited long-range magnetic order despite convoluted or non-existent magnetic superexchange pathways.</p> / Thesis / Doctor of Philosophy (PhD)

No description available.

Pillared-graphene structure (PGS) is a novel three-dimensional structure consists of parallel graphene sheets that are separated by carbon nanotube (CNT) pillars that is proposed for efficient thermal management of electronics. For microscale simulations, finite element analyses were carried out by imposing a heat flux on several PGS configurations using a Gaussian pulse. The temperature gradient and distribution in the structures was evaluated to determine the optimum design for heat transfer. The microscale simulations also included conducting a mesh-independent study to determine the optimal mesh element size and shape. For nanoscale simulations, Scienomics MAPS software (Materials And Processes Simulator) along with LAMMPS (Large-scale Atomic/ Molecular Massively Parallel Simulator) were used to calculate the thermal conductivity of different configurations and sizes of PGS. The first part of this research included investigating PGS when purely made of carbon atoms using non-equilibrium molecular dynamics (NEMD). The second part included investigating the structure when supported by a copper foil (or substrate); mimicking production of PGS on copper. The micro- and nano-scale simulations show that PGS has a great potential to manage heat in micro and nanoelectronics. The fact that PGS is highly tunable makes it a great candidate for thermal management applications. The simulations were successfully conducted and the thermal behavior of PGS at the nanoscale was characterized while accounting for phonon scattering the graphene/CNT junction as well as when PGS is supported by a copper substrate.

Unique layered structure with excellent electrical, mechanical, thermal, and optical properties gives graphene widespread application. Graphene based materials are extensively studied in the field of energy storage such as batteries, hydrogen storage and supercapacitors (SC’s). High surface area, electrical conductivity and mechanical flexibility are notable properties for the materials used in energy conversion systems. Porous spaced graphene oxide (PGO) structures were synthesized by hydrothermal and solvothermal reaction between GO and various pillaring molecules include Tetrakis (4-aminophenyl) methane (TKAm), Ethylenediamine (EDA), 2-Amino-5-diethylaminopentane (ADAP) and 2-Aminoethyl trimethylammonium chloride hydrochloride (ATA). Pristine GO shows interlayer distance of 7.2 Å. Characterisation techniques such as XRD, SEM, FTIR, BET and TGA were used understand the properties of these PGO. In contrast, these pillared structures show interlayer distance greater than of the pristine GO. Notably, GO/TKAm show interlayer distance of 14.30 Å. These pillared structures are considered to solve the restacking and aggregation issues found in 2D porous structures. Since these pillaring molecules help to achieve 3D porous network. Pristine GO shows only surface area of 14 m2/g whereas these materials also show excellent surface area as well. GO/TKAm shows high surface area of 450 m2/g. Followed it GO/ATA shows surface area of 106 m2/g. GO/pillared structures show low sheet resistance which means good electrical conductivity. Ultimately, these pillared structures not only solve the issues in 2D porous systems but also improve the surface area, mechanical stability, and electrical conductivity of those systems by means of 3D porous interconnected structures. All these excellent properties make them a great candidate for the energy conversion systems. / Unik skiktad struktur med utmärkta elektriska, mekaniska, termiska och optiska egenskaper ger grafen en utbredd tillämpning. Grafenbaserade material studeras omfattande inom området energilagring såsom batterier, vätelagring och superkondensatorer (SC). Hög yta, elektrisk ledningsförmåga och mekanisk flexibilitet är anmärkningsvärda egenskaper för de material som används i energiomvandlingssystem. Porösa grafenoxidstrukturer (PGO) syntetiserades genom hydrotermisk och solvotermisk reaktion mellan GO och olika pelarmolekyler inkluderar tetrakis (4-aminofenyl) metan (TKAm), etylendiamin (EDA), 2-amino-5-dietylaminopentan (ADAP) och 2 Aminoetyltrimetylammoniumkloridhydroklorid (ATA). Pristine GO visar mellanskiktsavstånd på 7,2 Å. Karakteriseringstekniker som XRD, SEM, FTIR, BET och TGA användes för att förstå egenskaperna hos dessa PGO. Däremot visar dessa pelarstrukturer mellanskiktsavståndet större än det för den orörda GO. Noterbart visar GO / TKAm mellanskiktsavstånd på 14.30 Å. Dessa pelarstrukturer anses lösa omstaplings- och aggregeringsproblemen som finns i 2D-porösa strukturer. Eftersom dessa pelarmolekyler hjälper till att uppnå 3Dporöst nätverk. Pristine GO visar endast en yta på 14 m2 / g medan dessa material också visar utmärkt yta också. GO / TKAm visar hög yta på 450 m2 / g. Följde den visar GO/ATA en yta på 106 m2/g. GO / pelarstrukturer visar lågt plåtmotstånd vilket innebär god elektrisk ledningsförmåga. I slutändan löser dessa pelarstrukturer inte bara problemen i 2D-porösa system utan förbättrar också ytarean, den mekaniska stabiliteten och den elektriska ledningsförmågan hos dessa system med hjälp av 3D-porösa sammankopplade strukturer. Alla dessa utmärkta egenskaper gör energiomvandlingssystem.

<p>A series of layered perovskite-based compounds were synthesized and studied as follows.</p> <p>La₅Mo_2.76(4)V_1.25(4)O₁₆ is a new pillared-perovskite synthesized by solid state chemistry method. It has layers of corner-sharing octahedra separated by dimers of edge-sharing octahedra, and is the first Mo-based pillared-perovskite whose magnetic structure was determined by neutron diffraction.</p> <p>Ca₂FeMnO₅ is an oxygen-deficient-perovskite with a brownmillerite-type ordering of oxygen vacancies, resulting in layers of corner-sharing octahedra separated by chains of corner-sharing tetrahedra. The octahedral layer contains mostly (~87%) Mn, while the tetrahedral layer is mainly (~91%) occupied by Fe. Long-range G-type magnetic ordering is present, where the moment on each site is coupled antiferromagnetically relative to all nearest neighbors.</p> <p>Ca₂FeCoO₅ has a brownmillerite superstructure with space group <em>Pcmb</em>, a rare space group for brownmillerites that requires doubling of one unit cell axis. Ca₂FeCoO₅is the first brownmillerite to contain intra-layer cation ordering. It has a long-range G-type ordering, and is the first brownmillerite to show spin re-orientation as function of temperature.</p> <p>Sr₂FeMnO_5+y was synthesized in both air (y~0.5) and argon (y~0), both of which resulted in vacancy-disordered cubic structures. The argon compound has a local brownmillerite structure, i.e. local ordering of vacancies. It has a superparamagnetic state below ~55K, with domains of short range (50Å) G-type ordering at 4K. For the air synthesized compound, y~0.5, long range G-type ordering is observed in ~4% of the sample.</p> <p>Sr₂Fe_1.9M_0.1O_5+y (M=Mn, Cr, Co; y= 0, 0.5) were synthesized in both air(y~0.5), and argon(y~0). All argon materials are brownmillerites with G-type magnetic ordering, but T_N’s are significantly different. The air-synthesized Co-material has long range vacancy ordering and magnetic ordering, while the Mn and Cr-materials (air) lack such orderings and both show spin-glass-like transitions.</p> <p>Sr₂Fe_1.5Cr_0.5O₅ has a vacancy-disordered cubic structure, but contains long range G-type magnetic ordering, unlike the other vacancy-disordered materials studied.</p> / Doctor of Philosophy (PhD)

Neste trabalho, fracionou-se e tratou-se a argila Brasgel. Esta argila foi pilarizada em vários estágios de facionamento e/ou tratamento com 5 meq de Al / g de argila: (i) Al-PILC, a argila passou por todos os estágios de fracionamento e tratamento (ARG), (ii) Al-PILCFe, a argila não passou pela etapa de retirada de Fe livre (ARGFe) e (iii) Al-PILCFe/silte, a argila não passou pelas etapas de retirada de silte e Fe livre (ARGFE/silte). Em análise por DRX observou-se que as Al-PILCs apresentaram uma distância basal maior que as argilas de partida. A análise textural indicou que as argilas Al-PILCs e ARGs são materiais mesoporosos, com poros do tipo fenda estreita e do tipo fenda, respectivamente. Além disso, as Al-PILCs apresentaram área superficial razoavelmente maior que as ARGs correspondentes. Outras análises feitas nas argilas foram: teor de Si, Fe e Al; CTC; FTIR; TGA e TGD. As argilas Brasgel pilarizadas foram usadas como catalisador na reação de isomerização do óxido de estireno em hexano sob refluxo. A reação foi seletiva na formação de fenilacetaldeído. As argilas Al-PILCFe e Al-PILCFe/silte apresentaram melhor desempenho catalítico (100 % de conversão em 20 min de reação). Assim, as argilas Brasgel pilarizadas se apresentaram como uma Tecnologia Limpa na reação de isomerização do óxido de estireno ao fenilacetaldeído. Palavras-chave: Desenvolvimento Sustentável. Tecnologia Limpa. Química Verde. Argilas Pilarizadas. Isomerização de Epóxidos. / This work, the Brasgel clay was fractionated and treated. The clay was pillared in several stages of fractionation and / or treatment with Al 5 meq / g of clay: (i) Al- PILC, the clay has passed through all stages of treatment and fractionation (ARG), (ii) Al-PILCFe, the clay would not pass the step of removal of free Fe (ARGFe) and (iii) Al-PILCFe/silt, clay has not gone through the steps of removing silt and free Fe (ARGFE/silt). XRD analysis showed that the Al-PILCs showed a basal spacing greater than the starting clays. The textural analysis indicated that the Al-PILCs and ARGs are mesoporous materials, with pore narrow slit type and slit type, respectively. Moreover, the Al-PILCs showed reasonable surface area greater than the corresponding ARGs. Other analyzes were made on clays: the content of Si, Fe and Al; CEC, FTIR, TGA and TGD. Brasgel pillared clays have been used as catalyst in the isomerization reaction of the styrene oxide in refluxing. The reaction was selective for the formation of phenylacetaldehyde. Al-PILCFe and Al-PILCFe/silt clays showed better catalytic performance (100% conversion in 20 min of reaction). Thus, the pillared clays Brasgel presented as a Clean Technology in the isomerization reaction of styrene oxide to phenylacetaldehyde. Keywords: Sustainable Development. Clean Technology. Green Chemistry. Pillared Clays. Isomerization of Epoxides.

Neste trabalho, fracionou-se e tratou-se a argila Brasgel. Esta argila foi pilarizada em vários estágios de facionamento e/ou tratamento com 5 meq de Al / g de argila: (i) Al-PILC, a argila passou por todos os estágios de fracionamento e tratamento (ARG), (ii) Al-PILCFe, a argila não passou pela etapa de retirada de Fe livre (ARGFe) e (iii) Al-PILCFe/silte, a argila não passou pelas etapas de retirada de silte e Fe livre (ARGFE/silte). Em análise por DRX observou-se que as Al-PILCs apresentaram uma distância basal maior que as argilas de partida. A análise textural indicou que as argilas Al-PILCs e ARGs são materiais mesoporosos, com poros do tipo fenda estreita e do tipo fenda, respectivamente. Além disso, as Al-PILCs apresentaram área superficial razoavelmente maior que as ARGs correspondentes. Outras análises feitas nas argilas foram: teor de Si, Fe e Al; CTC; FTIR; TGA e TGD. As argilas Brasgel pilarizadas foram usadas como catalisador na reação de isomerização do óxido de estireno em hexano sob refluxo. A reação foi seletiva na formação de fenilacetaldeído. As argilas Al-PILCFe e Al-PILCFe/silte apresentaram melhor desempenho catalítico (100 % de conversão em 20 min de reação). Assim, as argilas Brasgel pilarizadas se apresentaram como uma Tecnologia Limpa na reação de isomerização do óxido de estireno ao fenilacetaldeído. Palavras-chave: Desenvolvimento Sustentável. Tecnologia Limpa. Química Verde. Argilas Pilarizadas. Isomerização de Epóxidos. / This work, the Brasgel clay was fractionated and treated. The clay was pillared in several stages of fractionation and / or treatment with Al 5 meq / g of clay: (i) Al- PILC, the clay has passed through all stages of treatment and fractionation (ARG), (ii) Al-PILCFe, the clay would not pass the step of removal of free Fe (ARGFe) and (iii) Al-PILCFe/silt, clay has not gone through the steps of removing silt and free Fe (ARGFE/silt). XRD analysis showed that the Al-PILCs showed a basal spacing greater than the starting clays. The textural analysis indicated that the Al-PILCs and ARGs are mesoporous materials, with pore narrow slit type and slit type, respectively. Moreover, the Al-PILCs showed reasonable surface area greater than the corresponding ARGs. Other analyzes were made on clays: the content of Si, Fe and Al; CEC, FTIR, TGA and TGD. Brasgel pillared clays have been used as catalyst in the isomerization reaction of the styrene oxide in refluxing. The reaction was selective for the formation of phenylacetaldehyde. Al-PILCFe and Al-PILCFe/silt clays showed better catalytic performance (100% conversion in 20 min of reaction). Thus, the pillared clays Brasgel presented as a Clean Technology in the isomerization reaction of styrene oxide to phenylacetaldehyde. Keywords: Sustainable Development. Clean Technology. Green Chemistry. Pillared Clays. Isomerization of Epoxides.

Στην παρούσα διατριβή ειδίκευσης παρασκευάσθηκαν νανοσύνθετα υλικά αργιλικών ορυκτών/διοξειδίου του τιτανίου (TiO2) για την περιγραφή και μελέτη των νέων βελτιωμένων χαρακτηριστικών τους και την εφαρμογή τους σαν φωτοκαταλύτες στη διάσπαση ανόργανων αέριων ρύπων οξειδίων του αζώτου (NOX). Τρία αργιλικά ορυκτά (σαπωνίτης, παλυγορσκίτης και αλλοϋσίτης) χρησιμοποιήθηκαν για την διεξαγωγή των πειραμάτων. Δείγματα σαπωνίτη και παλυγορσκίτη συλλέχθηκαν από τη λεκάνη του Βεντζίου στα Γρεβενά και αλλοϋσίτη από τη νήσο Λήμνο. Δύο διαφορετικές μορφές νανοσύνθετων αργιλικού ορυκτού/TiO2 παρήχθησαν με δύο διαφορετικές μεθόδους και χρησιμοποιήθηκαν για τη μελέτη της φωτοαποικοδόμησης ανόργανων αέριων ρύπων NOX : Υποστυλωμένα με TiO2 νανοσύνθετα σαπωνίτη (Ti-sap1, Ti-sap2) παρήχθησαν με τη μέθοδο της «solvothermal synthesis” χρησιμοποιώντας TiCl3 σαν πρόδρομο TiO2 και νανοσύνθετα TiO2/ παλυγορσκίτη (Ti-pal) και TiO2/ αλλοϋσίτη (Ti-hall) παρήχθησαν με τη μέθοδο κολλοειδούς διαλύματος σε πήκτωμα (sol-gel) χρησιμοποιώντας Titanium Tetraisopropoxide (Ti(OC3H7)4) σαν διάλυμα διασποράς-επικάθησης. Για τον χαρακτηρισμό των ιδιοτήτων των φυσικών και τροποποιημένων δειγμάτων εφαρμόστηκαν διαφορετικές τεχνικές (XRD, FTIR-ATR, SEM-EDS, TEM, DLS, BET, porosimetry). Τα νανοσύνθετα αποδείχθηκαν αρκετά αποτελεσματικά για τη φωτοδιάσπαση των αέριων ρύπων NOX συγκριτικά με τον standard τύπο διοξειδίου του τιτανίου, Degussa P25, που χρησιμοποιείται γιαυτό το σκοπό. Tα υποστυλωμένα νανοσύνθετα Ti-sap1 και Ti-sap2 (με αναλογίες μάζας TiO2:σαπωνίτη = 0.2:1 και 0.1:1 αντίστοιχα) έδειξαν αύξηση της ειδικής τους επιφάνειας συγκριτικά με το φυσικό δείγμα σαπωνίτη και μεσοπορώδη δομή με κατανομή πόρων 5.7-9.8nm για το Ti-sap1 και 3.8nm για το Ti-sap2. Και τα δύο νανοσύνθετα απέκτησαν αυξημένη φωτοκαταλυτική ικανότητα βάση του περιεχόμενου ποσοστού TiO2 συγκριτικά με τον standard P25 λόγω της ομοιογενούς διασποράς των σωματιδίων TiO2 στον σαπωνίτη αλλά συγκρίνοντας τα δύο δείγματα Tisap1 και Tisap2, το Tisap2 είχε καλύτερη φωτοκαταλυτική δράση από το Tisap1. Όσον αφορά τα νανοσύνθετα TiO2-pal και TiO2-hall τα αποτελέσματα έδειξαν τη δημιουργία μεσοπορώδους δομής με πόρους 6.5 και 5.6 nm αντίστοιχα για το κάθε υλικό ενώ η μακροπορώδης δομή (lumen) του αλλοϋσίτη δεν υπήρχε στο τροποποιημένο δείγμα λόγω του ότι καλύφθηκε από τα νανοσωματίδια του TiO2 με αποτέλεσμα να προκύψει ένα υλικό με μικρότερο μέγεθος πόρων. Τα δύο δείγματα έδειξαν υψηλή φωτοκαταλυτική ικανότητα στη διάσπαση των αέριων ρύπων NOX υπό την επίδραση ορατής (λ>510nm) και υπεριώδους (λ>290nm) ακτινοβολίας σε σύγκριση με τα αποτελέσματα που έδωσε ο standard τύπος TiO2 P25. / In this thesis TiO2/clay nanocomposites have been synthesized and characterized as photocatalysts in the decomposition of NOx gases. Three different clay minerals (saponite, palygorskite and halloysite) have been used. The saponite and palygorskite samples were collected from Western Macedonia (Grevena, Ventzia basin) and halloysite from Lemnos island. The two different forms of nanocomposites that synthesized by two different methods were: TiO2 -pillared saponite (Ti-sap1, Tisap2) were successfully prepared by solvothermal synthesis using titanium trichloride as the precursor and TiO2- Palygorskite (Ti-pal) and TiO2-Halloysite (Ti-hall) nanocomposites were prepared by deposition of anatase form of TiO2 on the clay surfaces using a sol–gel method with titanium isopropoxide as a precursor. The characterization of the natural and modified samples was done by using different techniques (XRD, FTIR-ATR, SEMEDS, TEM, DLS, BET, porosimetry) The photocatalytic properties of the TiO2-clay nanocomposites were found to be better than that of the standard titania, Degussa P25 in decomposing NOX gases. The pillared TiO2 nanocomposites Ti-sap1, Tisap2 (mass ratio of TiO2:saponite= 0.2:1 and 01:1 respectively) showed a mesoporous structure compared to the natural saponite, with the distribution of pore diameters centered at 5.7-9.8 and at 3.8 nm, with high specific surface areas. Both TiO2-saponite nanocomposites showed higher photocatlytic activity than the standard (Degussa P25) based on TiO2 content because the TiO2 was well dispersed on saponite. By comparing the two modified samples Ti-sap1, Ti-sap2, the second one showed better photocatalytic activity than Ti-sap1 The results of the other two nanocomposites, Ti-hall and Ti-pal, showed mesopores of about 5.6 and 6.5 nm, respectively, while the macropores of halloysite (lumen) disappeared. The latter is attributed to the covering of the lumen of halloysite tubes by TiO2 nanoparticles and for that reason the pore size of the TiO2–treated halloysite was significantly smaller. The clay minerals- TiO2 samples showed significantly higher activity in decomposing NOx gas under visible-light irradiation (λ> 510 nm) and UV light irradiation (λ> 290 nm) compared to that of the standard commercial TiO2, P 25.

DUT-8(Ni) metal–organic framework (MOF) belongs to the family of flexible pillared layer materials. The desolvated framework can be obtained in the open pore form (op) or in the closed pore form (cp), depending on the crystal size regime. In the present work, we report on the behaviour of desolvated DUT-8(Ni) at elevated temperatures. For both, op and cp variants, heating causes a structural transition, leading to a new, crystalline compound, containing two interpenetrated networks. The state of the framework before transition (op vs. cp) influences the transition temperature: the small particles of the op phase transform at significantly lower temperature in comparison to the macroparticles of the cp phase, transforming close to the decomposition temperature. The new compound, confined closed pore phase (ccp), was characterized by powder X-ray diffraction and spectroscopic techniques, such as IR, EXAFS, and positron annihilation lifetime spectroscopy (PALS). Thermal effects of structural transitions were studied using differential scanning calorimetry (DSC), showing an overall exothermic effect of the process, involving bond breaking and reformation. Theoretical calculations reveal the energetics, driving the observed temperature induced phase transition.