The Boost of Toluene Capture in UiO-66 Triggered by Structural Defects or Air Humidity

This work aimed to investigate the adsorption of toluene in UiO-66 materials. Toluene is a volatile, aromatic organic molecule that is recognized as the main component of VOCs. These compounds are harmful to the environment as well as to living organisms. One of the materials that allows the capture of toluene is the UiO-66. A satisfactory representation of the calculated isotherm steep front and sorption capacity compared to the experiment was obtained by reducing the force field σ parameter by 5% and increasing ϵ by 5%. Average occupation profiles, which are projections of the positions of molecules during pressure increase, as well as RDFs, which are designed to determine the distance of the center of mass of the toluene molecule from organic linkers and metal clusters, respectively, made it possible to explain the mechanism of toluene adsorption on the UiO-66 material.</p

Carbon dioxide capture enhanced by pre-adsorption of water and methanol in UiO-66

The rapidly rising level of carbon dioxide in the atmosphere resulting from human activity is one of the greatest environmental problems facing our civilization today. Most technologies are not yet sufficiently developed to move existing infrastructure to cleaner alternatives. Therefore, techniques for capturing carbon dioxide from emission sources may play a key role at the moment. The structure of the UiO‐66 material not only meets the requirement of high stability in contact with water vapor but through the water pre‐adsorbed in the pores, the selectivity of carbon dioxide adsorption is increased. We successfully applied the recently developed methodology for water adsorption modelling. It allowed to elucidate the influence of water on CO(2) adsorption and study the mechanism of this effect. We showed that water is adsorbed in octahedral cage and stands for promotor for CO(2) adsorption in less favorable space than tetrahedral cages. Water plays a role of a mediator of adsorption, what is a general idea of improving affinity of adsorbate. On the basis of pre‐adsorption of methanol as another polar solvent, we have shown that the adsorption sites play a key role here, and not, as previously thought, only the interaction between the solvent and quadrupole carbon dioxide. Overall, we explained the mechanism of increased CO(2) adsorption in the presence of water and methanol, as polar solvents, in the UiO‐66 pores for a potential post‐combustion carbon dioxide capture application

Defect-induced tuning of polarity-dependent adsorption in hydrophobic–hydrophilic UiO-66

Structural defects in metal–organic frameworks can be exploited to tune material properties. In the case of UiO-66 material, they may change its nature from hydrophobic to hydrophilic and therefore affect the mechanism of adsorption of polar and non-polar molecules. In this work, we focused on understanding this mechanism during adsorption of molecules with different dipole moments, using the standard volumetric adsorption measurements, IR spectroscopy, DFT + D calculations, and Monte Carlo calculations. Average occupation profiles showed that polar and nonpolar molecules change their preferences for adsorption sites. Hence, defects in the structure can be used to tune the adsorption properties of the MOF as well as to control the position of the adsorbates within the micropores of UiO-66.</p

Polypropylene cracking on embryonic and ZSM-5 catalysts : an operando study

International audienceA series of ZSM-5 zeolites (embryonic, microporous, hierarchical) is studied in the catalytic cracking of polypropylene in the framework of its chemical recycling. Two important zeolite features impact their catalytic performances and allow their design as efficient catalysts: porosity and acidity. They also play a key role in catalyst deactivation and regeneration. A detailed thermogravimetric and spectroscopic (operando FT-IR) analysis of the reaction, including catalyst coking and regeneration, shows the emergence of rules to design fit-for-purpose catalysts to be used in existing or grass-roots FCC units

Pyrazolins as fluorescent sensors sensitive to anions

W niniejszej pracy zbadano właściwości fotofizyczne dwóch sensorów opartych na strukturze pirazolu. Określono wpływ polarności rozpuszczalnika oraz różnych anionów na właściwości absorpcyjne i emisyjne badanych cząsteczek. W toku badań stwierdzono, że oba związki wykrywają aniony siarczynowe i siarczkowe. Mechanizm detekcji siarczynu sodu opiera się na reakcji Michaela do wiązania podwójnego. W przypadku pochodnej z tiofenem, czas reakcji w obecności 30 ekwiwalentów analitu ustalono na 1 minutę, a limit detekcji wynosi 1.43μM. Zaletą stosowanej sondy jest możliwość przeprowadzania detekcji w wodzie (bez buforu pH=7.4 jak w większości tego typu sensorów) co umożliwia szerokie zastosowanie sondy w przemyśle i analityce środowiska.In this work we investigated the photophysical properties of two pyrazole-based sensors. The influence of the polarity of the solvent and various anions on the absorption and emission properties of the molecules tested was determined. The study found that both compounds detect sulfite and sulfide anions. The mechanism of sodium sulfite detection is based on Michael's reaction to the double bond. In the case of a thiophene derivative, the reaction time in the presence of 30 equivalents of an analyte was set to 1 minute and the detection limit was 1.43 μM. The advantage of using the probe is the ability to perform detection in water (without buffer pH = 7.4 as in most such sensors), which enables a wide range of applications in industry and environmental analytics

Searching for intermediate species of xylenes isomerisation on selected zeolite frameworks - DFT modeling

Niniejsza praca magisterska obejmuje w części teoretycznej ogólną charakterystykę zeolitów oraz możliwości ich modyfikacji w kontekście wykorzystywanych właściwości, w szczególności wpływ rodzaju i położeniu miejsca aktywnego na selektywność i reaktywność katalizatorów zeolitowych. Część badawcza ma charakter teoretyczny, ale prowadzone obliczenia są weryfikowane wynikami eksperymentalnymi, a jednocześnie pozwalają na uzyskanie dodatkowych informacji o badanych układach. Skupiłam się w niej na wpływie struktury na możliwy przebieg reakcji izomeryzacji ksylenów, w szczególności układu i rozmiaru kanałów na tworzenie produktów przejściowych. Badanymi związkami były ksyleny, ponieważ dużym wyzwaniem dla współczesnej chemii jest optymalizacja procesów tak, aby zapewniały one możliwie skuteczną ochronę środowiska naturalnego. W ostatnich czasach duża część badań koncentruje się na odnawialnych źródłach energii, w szczególności paliwach, gdyż to ich spalanie wywołuje najwięcej zanieczyszczeń. Wiele biopaliw tworzonych jest na bazie metanolu i etanolu. Udowodnione zostało, że w procesach konwersji tych dwóch związków do węglowodorów, reakcja prowadzi m.in. do powstawania ksylenów. Aby jeszcze lepiej poznać ten proces, ważne jest poznanie mechanizmów reakcji, a więc także produktów przejściowych ich izomeryzacji. Dzięki zastosowaniu zeolitów jako katalizatorów, ten proces może być jeszcze lepiej kontrolowany, a co za tym idzie – zastosowany w produkcji paliw nowej generacji.This master thesis includes the characterization of the properties of zeolites and the possibility of modifying their structure. It has a theoretical character, but the calculations have experimental confirmation. I have focused in particular on the influence of the type and location of the active site on the selectivity and reactivity of zeolite catalysts. In addition, I discussed the distribution of pores and channels inside for the creation of intermediates.The tested compounds were xylenes, because the major challenge for modern chemistry is the optimization of processes so that they provide the most effective protection of the natural environment. In recent times, a large part of research focuses on renewable energy sources, in particular fuels, because their combustion causes the most pollution. Many biofuels are made on the basis of methanol and ethanol. It has been proved that in the processes of conversion of these two compounds to hydrocarbons, the reaction proceeds through the formation of xylenes. To get to know this process even better, it is important to know the transition products of their isomerization, as the para isomer is the most desirable. Thanks to the use of zeolites as catalysts, this process can be even better controlled and, as a result, used in the production of new generation fuels

Trojan horse thiocyanate : induction and control of high proton conductivity in CPO-27/MOF-74 metal : organic frameworks by metal selection and solvent-free mechanochemical dosing

[Image: see text] Proton-conducting metal–organic frameworks (MOFs) have been gaining attention for their role as solid-state electrolytes in various devices for energy conversion and storage. Here, we present a convenient strategy for inducing and tuning of superprotonic conductivity in MOFs with open metal sites via postsynthetic incorporation of charge carriers enabled by solvent-free mechanochemistry and anion coordination. This scalable approach is demonstrated using a series of CPO-27/MOF-74 [M(2)(dobdc); M = Mg(2+), Zn(2+), Ni(2+); dobdc = 2,5-dioxido-1,4-benzenedicarboxylate] materials loaded with various stoichiometric amounts of NH(4)SCN. The modified materials are not achievable by conventional immersion in solutions. Periodic density functional theory (DFT) calculations, supported by infrared (IR) spectroscopy and powder X-ray diffraction, provide structures of the modified MOFs including positions of inserted ions inside the [001] channels. Despite the same type and concentration of proton carriers, the MOFs can be arranged in the increasing order of conductivity (Ni < Zn < Mg), which strongly correlates with amounts of water vapor adsorbed. We conclude that the proton conductivity of CPO-27 materials can be controlled over a few orders of magnitude by metal selection and mechanochemical dosing of ammonium thiocyanate. The dosing of a solid is shown for the first time as a useful, simple, and ecological method for the control of material conductivity