Now showing items 1-20 of 1098

    • How Reproducible are Surface Areas Calculated from the BET Equation?

      Osterrieth, Johannes W. M.; Rampersad, James; Madden, David; Rampal, Nakul; Skoric, Luka; Connolly, Bethany; Allendorf, Mark D.; Stavila, Vitalie; Snider, Jonathan L.; Ameloot, Rob; Marreiros, João; Ania, Conchi; Azevedo, Diana; Vilarrasa-Garcia, Enrique; Santos, Bianca F.; Bu, Xian-He; Chang, Ze; Bunzen, Hana; Champness, Neil R.; Griffin, Sarah L.; Chen, Banglin; Lin, Rui-Biao; Coasne, Benoit; Cohen, Seth; Moreton, Jessica C.; Colón, Yamil J.; Chen, Linjiang; Clowes, Rob; Coudert, François-Xavier; Cui, Yong; Hou, Bang; D'Alessandro, Deanna M.; Doheny, Patrick W.; Dincă, Mircea; Sun, Chenyue; Doonan, Christian; Huxley, Michael Thomas; Evans, Jack D.; Falcaro, Paolo; Ricco, Raffaele; Farha, Omar; Idrees, Karam B.; Islamoglu, Timur; Feng, Pingyun; Yang, Huajun; Forgan, Ross S.; Bara, Dominic; Furukawa, Shuhei; Sanchez, Eli; Gascon, Jorge; Telalovic, Selvedin; Ghosh, Sujit K.; Mukherjee, Soumya; Hill, Matthew R.; Sadiq, Muhammed Munir; Horcajada, Patricia; Salcedo-Abraira, Pablo; Kaneko, Katsumi; Kukobat, Radovan; Kenvin, Jeff; Keskin, Seda; Kitagawa, Susumu; Otake, Ken-ichi; Lively, Ryan P.; DeWitt, Stephen J. A.; Llewellyn, Phillip; Lotsch, Bettina V.; Emmerling, Sebastian T.; Pütz, Alexander M.; Martí-Gastaldo, Carlos; Padial, Natalia M.; García-Martínez, Javier; Linares, Noemi; Maspoch, Daniel; Suárez del Pino, Jose A.; Moghadam, Peyman; Oktavian, Rama; Morris, Russel E.; Wheatley, Paul S.; Navarro, Jorge; Petit, Camille; Danaci, David; Rosseinsky, Matthew J.; Katsoulidis, Alexandros P.; Schröder, Martin; Han, Xue; Yang, Sihai; Serre, Christian; Mouchaham, Georges; Sholl, David S.; Thyagarajan, Raghuram; Siderius, Daniel; Snurr, Randall Q.; Goncalves, Rebecca B.; Telfer, Shane; Lee, Seok J.; Ting, Valeska P.; Rowlandson, Jemma L.; Uemura, Takashi; Iiyuka, Tomoya; Veen, Monique A.; Rega, Davide; Van Speybroeck, Veronique; Rogge, Sven M. J.; Lamaire, Aran; Walton, Krista S.; Bingel, Lukas W.; Wuttke, Stefan; Andreo, Jacopo; Yaghi, Omar; Zhang, Bing; Yavuz, Cafer T.; Nguyen, Thien S.; Zamora, Felix; Montoro, Carmen; Zhou, Hongcai; Kirchon, Angelo; Fairen-Jimenez, David (Advanced Materials, Wiley, 2022-05-23) [Article]
      Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer–Emmett–Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already-measured raw adsorption isotherms were provided to sixty-one labs, who were asked to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called “BET surface identification” (BETSI), expands on the well-known Rouquerol criteria and makes an unambiguous BET area assignment possible.
    • Modifying the Hydrogenation Activity of Zeolite Beta for Enhancing the Yield and Selectivity to Fuel-Range Alkanes from Carbon Dioxide

      Dokania, Abhay; Ramirez, Adrian; Shterk, Genrikh; Cerrillo, Jose Luis; Gascon, Jorge (ChemPlusChem, Wiley, 2022-05-21) [Article]
      In order to empower a circular carbon economy for addressing global CO2 emissions, the production of carbon-neutral fuels is especially desired, since addressing the global fuel demand via this route has the potential to significantly mitigate carbon emissions. In this study, we report a multifunctional catalyst combination consisting of a potassium promoted iron catalyst (Fe-K) and platinum containing zeolite beta (Pt-beta) which produces an almost entirely paraffinic mixture (up to C10 hydrocarbons) via CO2 hydrogenation in one step. Here, the Fe catalyst is responsible for modified Fischer-Tropsch synthesis from CO2 while Pt-beta is instrumental in tuning the product distribution almost entirely towards paraffins (both linear and branched) presumably via a combination of cracking and hydrogenation. The optimal temperature of operation was estimated to be 325 °C for the production of higher paraffins (C5-C10) with a selectivity of ca. 28% at a CO2 conversion of ca. 31%.
    • Origin of active sites on silica-magnesia catalysts and control of reactive environment in the one-step ethanol-to-butadiene process

      Chung, Sang-Ho; Li, Teng; Shoinkhorova, Tuiana; Ramirez, Adrian; Mukhambetov, Ildar; Abou-Hamad, Edy; Shterk, Genrikh; Telalovic, Selvedin; Dikhtiarenko, Alla; Sirks, Bart; Lavrik, Polina; Tang, Xinqi; Weckhuysen, Bert M.; Bruijnincx, Pieter; Gascon, Jorge; Ruiz-Martinez, Javier (Research Square Platform LLC, 2022-05-18) [Preprint]
      Wet-kneaded silica–magnesia is a benchmark catalyst for the one–step ethanol-to-butadiene Lebedev process. Magnesium silicates, formed during wet-kneading, have been proposed as active sites responsible for butadiene formation, and their catalytic performance has been mainly explained by the variations in the ratio of acid and base sites. While the Lebedev process was developed in the 1930s, However, a detailed insight into how the peculiar, yet essential wet-kneading synthesis leads to the generation, location, and catalytic role of magnesium silicates has not been fully established. Here, we demonstrate that magnesium silicates formation occurs via dissolution of Si and Mg subunits from SiO2 and Mg(OH)2 precursors, initiated by the alkaline pH of the aqueous wet-kneading medium, followed by cross-deposition of the dissolved species on the precursor surfaces. Building on these new insights, two individual model systems (Mg/SiO2 and Si/MgO) were synthesized, representative of the constituents of the wet-kneaded silica–magnesia catalyst, by selective dissolution/deposition induced by pH alteration of the aqueous wet-kneading medium. Using these model catalysts, we demonstrate that the location of the magnesium silicates (i.e., Mg on SiO2 or Si on MgO) governs not only their chemical nature but also the ethanol adsorption configuration, which ultimately cause the catalyst material to be selective mainly for ethylene or butadiene. We demonstrate close proximity at the particle level of the of acid and basic sites is a prerequisite to promote the butadiene formation. The insights gained from the new structure–performance relationships that correlate catalytic activity with types and nature of magnesium silicates can offer new possibilities for the development of next generation Lebedev catalysts.
    • Continuous extraction and concentration of secreted metabolites from engineered microbes using membrane technology

      Overmans, Sebastian; Ignacz, Gergo; Beke, Aron K.; Xu, Jiajie; Saikaly, Pascal; Szekely, Gyorgy; Lauersen, Kyle J. (Green Chemistry, Royal Society of Chemistry (RSC), 2022-05-18) [Article]
      Microalgal cultivation in photobioreactors and membrane separations are both considered sustainable processes. Here we explore their synergistic combination to extract and concentrate a heterologous sesquiterpenoid produced by engineered green algal cells. A hydrophobic hollow-fiber membrane contactor was used to allow interaction of culture broth and cells with a dodecane solvent phase to accumulate algal produced patchoulol. Subsequent continuous membrane extraction of patchoulol from dodecane enabled product concentration in a methanol stream as well as dodecane recovery for its reuse. A structure-based prediction using machine learning was used to model a process whereby 100% patchoulol recovery from dodecane could be achieved with solvent-resistant nanofiltration membranes. Solvent consumption, E-factor, and economic sustainability were assessed and compared with existing patchoulol production processes. Our extraction and product purification process offers six- and two-orders of magnitude lower solvent consumption compared to synthetic production and thermal-based separation, respectively. Our proposed methodology is transferable to other microbial systems for the isolation of high-value isoprenoid and hydrocarbon products.
    • Revisiting low temperature oxidation chemistry of n-heptane

      Xie, Cheng; Lailliau, Maxence; Issayev, Gani; Xu, Qiang; Chen, Weiye; Dagaut, Philippe; Farooq, Aamir; Sarathy, Mani; Wei, Lixia; Wang, Zhandong (Combustion and Flame, Elsevier BV, 2022-05-17) [Article]
      Benefitting from the rapid development of instrumental analysis methods, intermediate products that were difficult to probe in the past can now be measured and quantified in complex reaction systems. To understand low temperature reactions of interest for combustion applications, and reduce the deviations between model predictions and experimental measurements, constant advancement in understanding low temperature oxidation process is necessary. This work examines the oxidation of n-heptane in jet-stirred reactors at atmospheric pressure, with an initial n-heptane mole fraction of 0.005, equivalence ratio of 0.5, a residence time of 1s, and over a temperature range of 500-800 K. Reaction products were analyzed using synchrotron ultra-violet photoionization mass spectrometry, gas chromatography, and Fourier-transform infrared spectroscopy. Ignition delay times of n-heptane/O2/CO2 mixture were measured in a rapid compression machine at 20 and 40 bar over a 600-673 K temperature range. Based on the experimental results, a comprehensive kinetic model of n-heptane low temperature oxidation was developed by considering the sub-mechanisms of keto-hydroperoxide, cyclic ether, heptene isomers, and the third O2 addition reaction, and by updating the rate constants of keto-hydroperoxide decomposition and second oxygen addition reactions. The combination of reaction mechanism development and evaluation of the rate constants of key reactions enabled the model to effectively predict the species concentrations and ignition delay times of n-heptane low temperature oxidation, providing additional insight into alkane low temperature oxidation chemistry.
    • The impact of gasoline formulation on turbulent jet ignition

      Gorbatenko, Inna; Nicolle, Andre; Silva, Mickael; Im, Hong G.; Sarathy, Mani (Elsevier BV, 2022-05-13) [Article]
      Turbulent jet ignition (TJI) is a promising technology for burning ultra-lean mixtures; the process is comprised of hot reactive jets issuing from a pre-chamber (PC) and initiating combustion in the main chamber (MC). The present study employs a simplified zero-dimensional (0D) partially stirred reactor (PaSR) model to describe the complex mixing and reaction progress within the PC and its subsequent impact on the MC combustion in terms of combustion efficiency and pollutant formation characteristics. Full three-dimensional (3D) computational fluid dynamics (CFD) data are used to calibrate the PC model, which is subsequently linked to predict the MC combustion behavior. We propose a model to predict the effects of the fuel formulations with varying research octane number (RON) and octane sensitivities (OS) on the TJI performance. After a careful parametric study, a dedicated merit function for identifying the optimal TJI operating conditions was proposed to assess multiple fuel properties and their influence on MC combustion. The model properly accounts for micro-mixing effects in the early jet expansion phase, and represents the effects of a PC jet on enhancing flammability and pollutant mitigation. It was demonstrated that aromatic content affects not only the progress of the thermokinetic runaway, but also the importance of NO formation paths in MC (N2O vs NNH routes), and the effect of the PC jet on MC flammability limits. Among the jet active species, OH and NO exhibited the greatest chemical impact on MC reactivity, while the chemical effects of CO2 and H2O remained limited. The overall fuel TJI merit function showed optimum performance for fuels with 2 < OS < 6 and high RON, similar to the requirements for spark-ignited engine operation beyond motor octane number (MON) conditions, fuel lean advanced compression ignition operation, and spark-induced compression ignition.
    • The effect of hydrogen bonding on the reactivity of OH radicals with prenol and isoprenol: a shock tube and multi-structural torsional variational transition state theory study

      Mohamed, Samah; Monge Palacios, Manuel; Giri, Binod; KHALED, Fethi; Liu, Dapeng; Farooq, Aamir; Sarathy, Mani (Physical Chemistry Chemical Physics, Royal Society of Chemistry (RSC), 2022-05-11) [Article]
      The presence of two functional groups (OH and double bond) in C5 methyl-substituted enols (i.e., isopentenols), such as 3-methyl-2-buten-1-ol (prenol) and 3-methyl-3-buten-1-ol (isoprenol), makes them excellent biofuel candidates as fuel additives. As OH radicals are abundant in both combustion and atmospheric environments, OH-initiated oxidation of these isopentenols over wide ranges of temperatures and pressures needs to be investigated. In alkenes, OH addition to the double bond is prominent at low temperatures (i.e., below ∼700 K), and H-atom abstraction dominates at higher temperatures. However, we find that the OH-initiated oxidation of prenol and isoprenol displays a larger role for OH addition at higher temperatures. In this work, the reaction kinetics of prenol and isoprenol with OH radicals was investigated over the temperature range of 900–1290 K and pressure of 1–5 atm by utilizing a shock tube and OH laser diagnostic. To rationalize these chemical systems, variational transition state theory calculations with multi-structural torsional anharmonicity and small curvature tunneling corrections were run using a potential energy surface characterized at the UCCSD(T)/jun-cc-pVQZ//M06-2X/6-311++G(2df,2pd) level of theory. A good agreement was observed between the experiment and theory, with both predicting a non-Arrhenius behavior and negligible pressure effects. OH additions to the double bond of prenol and isoprenol were found to be important, with at least 50% contribution to the total rate constants even at temperatures as high as 700 and 2000 K, respectively. This behavior was attributed to the stabilizing effect induced by hydrogen bonding between the reacting OH radical and the OH functional group of isopentenols at the saddle points. These stabilizing intermolecular interactions help mitigate the entropic effects that hinder association reactions as temperature increases, thus extending the prominent role of addition pathways to high temperatures. The site-specific rate constants were also found to be slower than their analogous reactions of OH + n-alkenes.
    • Nerve Network-Inspired Solid Polymer Electrolytes (NN-SPE) for Fast and Single-Ion Lithium Conduction

      Li, Zhen; Guo, Dong; Li, Fan; Hou, Guangjin; Liu, Xiaowei; Li, Chunyang; Cao, Li; Wei, Ruicong; Zhou, Zongyao; Lai, Zhiping (Energy Storage Materials, Elsevier BV, 2022-05-04) [Article]
      The low lithium-ion conductivity is current the bottleneck in developing solid-state electrolytes (SSEs) that are expected to be a key component in the next generation of lithium batteries. Inspired by the high connectivity of the biological nerve network, we designed a mimic architecture inside a polymer electrolyte to provide fast lithium-ion pathways. Detailed experimental and simulation studies revealed that the mimic nerve network could efficiently form the bi-continuous structure at very low percolation threshold, and rendered an unprecedentedly non-linear increment by order of magnitudes in the lithium-ion conductivity, with a superior lithium-ion conductivity up to 0.12 mS•cm−1, transference number up to 0.974 and robust mechanical strength of 10.3 MPa. When applied in lithium metal batteries, good rate and cycling performance were achieved at both room and elevated temperatures.
    • In situ conductive spacers for early pore wetting detection in membrane distillation

      Alpatova, Alla; Qamar, Adnan; Alhaddad, Mohammed; Kerdi, Sarah; Soo Son, Hyuk; Amin, Najat A.; Ghaffour, NorEddine (Separation and Purification Technology, Elsevier BV, 2022-04-30) [Article]
      Membrane distillation (MD) suffers from pore wetting which deteriorates membrane separation properties and causes water protrusion to permeate side. The early detection of pore wetting is a challenge which needs to be addressed to achieve stable MD performance. In this study, electrically-conductive Pt-coated spacers placed inside the feed and coolant channels with a dual purpose of maximizing permeate flux and instantaneous wetting detection once first membrane pores are compromised are proposed. Upon wetting, permeate salt concentration increases thereby initiating redox reactions at two spacer electrodes under the applied electrical potential. As a result, electrical current is produced and measured. The competence of the proposed wetting detection method was explored in MD process in the presence of organic substances with high wetting propensity. An increase in generated electrical current upon wetting development and substantial signal amplification with the voltage increase was demonstrated. The new wetting detection method achieved a faster response comparing to conventional conductivity measurements. Moreover, this method allows to define the wetting onset which can serve as an indication of early membrane impairment. Different spacer geometries and observed no adverse effect of spacer coating on MD performance were further compared. Experimental and numerical simulations accentuated an importance of spacer design by providing specific permeate flux gain for a 1-helical spacer comparing to a spacer with a smooth cylindrical filament. This effect became more evident at higher feed water temperature, condition that favors greater temperature polarization.
    • Accurate thermochemistry prediction of extensive Polycyclic aromatic hydrocarbons (PAHs) and relevant radicals

      Li, Yang; Wang, Tairan; Yalamanchi, Kiran K.; Kukkadapu, Goutham; Sarathy, Mani (Combustion and Flame, Elsevier BV, 2022-04-26) [Article]
      Polycyclic aromatic hydrocarbons (PAHs) are important intermediates to soot formation in combustion. A reliable database of their thermochemistry is required for the development of chemical kinetic models describing the gas-phase chemistry of hydrocarbon fuels. In this study, temperature-dependent thermodynamic properties are consistently determined using high-accuracy quantum chemistry calculations for an extensive set of PAH compounds. The developed database comprehensively consists of 125 C6-C18 PAH molecules and radicals, which are important and commonly included in chemical mechanisms studies. At the M06-2X/6-311++G(d,p) level of theory, geometry optimizations, vibrational frequency calculations, and dihedral angle scans are performed for all PAH species. The G3 method, together with the atomization reaction approach, is selected to derive the average atomization formation enthalpy. This method produces the most accurate thermochemistry quantities for PAHs, as demonstrated in a previous study. The entropy and heat capacity values are calculated using statistical thermodynamics in MultiWell. These results exhibit good agreement with the databases in literature. To examine the application of the group additivity (GA) method for PAHs, the Bland−Altman plot, a statistical analysis approach, is employed to visualize the agreement between the results from the quantum chemical calculations and GA methods. Two GA methods are examined and significant differences are found, which indicates that GA values of relevant groups need to be further updated. The database of thermodynamic quantities developed in this study are of particular value in modeling studies and important for exploring mechanisms of the PAH growth.
    • Plasmonic Titanium Nitride Tubes Decorated with Ru Nanoparticles as Photo-Thermal Catalyst for CO2 Methanation

      Mateo, Diego; Navarro, Juan Carlos; Khan, Il Son; Ruiz-Martinez, Javier; Gascon, Jorge (Molecules, MDPI AG, 2022-04-22) [Article]
      Photo-thermal catalysis has recently emerged as a viable strategy to produce solar fuels or chemicals using sunlight. In particular, nanostructures featuring localized surface plasmon resonance (LSPR) hold great promise as photo-thermal catalysts given their ability to convert light into heat. In this regard, traditional plasmonic materials include gold (Au) or silver (Ag), but in the last years, transition metal nitrides have been proposed as a cost-efficient alternative. Herein, we demonstrate that titanium nitride (TiN) tubes derived from the nitridation of TiO2 precursor display excellent light absorption properties thanks to their intense LSPR band in the visible–IR regions. Upon deposition of Ru nanoparticles (NPs), Ru-TiN tubes exhibit high activity towards the photo-thermal CO2 reduction reaction, achieving remarkable methane (CH4) production rates up to 1200 mmol g−1 h−1. Mechanistic studies suggest that the reaction pathway is dominated by thermal effects thanks to the effective light-to-heat conversion of Ru-TiN tubes. This work will serve as a basis for future research on new plasmonic structures for photo-thermal applications in catalysis.
    • Ionic covalent organic nanosheet (iCON)–quaternized polybenzimidazole nanocomposite anion-exchange membranes to enhance the performance of membrane capacitive deionization

      McNair, Robert; Kumar, Sushil; Wonanke, A. D.Dinga; Addicoat, Matthew A.; Dryfe, Robert A.W.; Szekely, Gyorgy (Desalination, Elsevier BV, 2022-04-19) [Article]
      Membrane capacitive deionization (MCDI) is a promising technique to achieve desalination of low-salinity water resources. The primary requirements for developing and designing materials for MCDI applications are large surface area, high wettability to water, high conductivity, and efficient ion-transport pathways. Herein, we synthesized ionic covalent organic nanosheets (iCONs) containing guanidinium units that carry a positive charge. A series of quaternized polybenzimidazole (QPBI)/iCON (iCON@QPBI) nanocomposite membranes was fabricated using solution casting. The surface, thermal, wettability, and electrochemical properties of the iCON@QPBI nanocomposite membranes were evaluated. The iCON@QPBI anion-exchange membranes achieved a salt adsorption capacity as high as 15.6 mg g−1 and charge efficiency of up to 90%, which are 50% and 20% higher than those of the pristine QPBI membrane, respectively. The performance improvement was attributed to the increased ion-exchange capacity (2.4 mmol g−1), reduced area resistance (5.4 Ω cm2), and enhanced hydrophilicity (water uptake = 32%) of the iCON@QPBI nanocomposite membranes. This was due to the additional quaternary ammonium groups and conductive ion transport networks donated by the iCON materials. The excellent desalination performance of the iCON@polymer nanocomposite membranes demonstrated their potential for use in MCDI applications and alternative electromembrane processes.
    • Understanding Zeolite Desilication by NMR Spectroscopy

      Tsereshko, Nina (2022-04-17) [Thesis]
      Advisor: Ruiz-Martinez, Javier
      Committee members: Gascon, Jorge; Han, Yu
      Today, zeolites play a considerable role in many industrial fields, especially in heterogeneous catalysis. Well-defined microporous structure combined with acidity provides exceptional size and shape selectivity, making zeolites indispensable in petrochemistry. However, the micropores can cause diffusion limitations and, in turn, a drop in reaction rate and selectivity. Hence, the development of modification methodologies on zeolite textural properties is one of the attention-grabbing research topics nowadays. For example, to overcome transport limitations in zeolites, the particle size can be reduced, or a system of larger auxiliary pores can be introduced [1]. One of the most promising methods for introducing secondary pores on a large scale is desilication since it is low-cost, versatile, and easy [2]. Despite its simplicity, the desilication mechanism is still a matter of discussion. In detail, it is not well-understood: 1. The influence of different species on mesopore formation kinetics 2. How aluminum is assembled back into the zeolite 3. Which types of aluminum species form throughout the treatment. The present study tries to answer these questions by relating ex-situ and in-situ NMR. The proposed ex-situ 29Si MAS NMR approach allows monitoring the development of mesoporosity and silicon extraction by analyzing Q3 and Q4 changes. The combination of ex-situ with in-situ 29Si MAS NMR study showed that the limiting step of Si extraction is the transformation of Q3 into Q2. 27Al MAS NMR combined with MQMAS showed the formation of new aluminum species after desilication. It was shown that some of the Al framework T-sites might dissolve during alkaline treatment. In-situ 27Al NMR indicates redistribution of dissolved aluminum upon desilication.
    • Insight into the role of reduced graphene oxide in enhancing photocatalytic hydrogen evolution in disordered carbon nitride.

      Rahman, Mohammad Ziaur; Maity, Partha; Mohammed, Omar F.; Gascon, Jorge (Royal Society of Chemistry (RSC), 2022-04-12) [Article]
      Compared to crystalline carbon nitride, the performance of disordered carbon nitride (d-CN) as a hydrogen production photocatalyst is extremely poor. Owing to its disordered atomic orientation, it is prone to numerous defect states. These energy states are potential sites for trapping and recombination of photogenerated charge carriers. As a result, rapid recombination of photogenerated charge carriers places a fundamental photophysical challenge in charge separation and transport, which inhibits its photocatalytic activity. In the presence of reduced graphene oxide (rGO), d-CN shows enhanced photocatalytic production of hydrogen. However, photophysical insight into the tacit role of rGO is not well understood which limits the rational design of d-CN as a photocatalyst. Particularly, understanding of the early time-scale (in fs to ps) recombination mechanism and the charge transport kinetics has not yet been achieved. With the help of ultrafast transient absorption spectroscopy, femtosecond time-resolved photoluminescence spectroscopy and transient photocurrent measurements, this article deciphers the ultrafast dynamics of the separation and transport of photogenerated charge carriers in d-CN facilitated by rGO. It is found that rGO substantially suppresses the bimolecular and trap-assisted recombination and enables a faster separation of charge carriers. As a result, it increases the lifetime of the charge carriers to be transported to the surface catalytic sites, and therefore, augments the rate of hydrogen production almost by an order of magnitude. Our findings therefore offer a proof-of-concept for overcoming the trap-mediated recombination problems in disordered carbon nitride.
    • Catalytic arene-norbornene annulation (CANAL) ladder polymer derived carbon membranes with unparalleled hydrogen/carbon dioxide size-sieving capability

      Hazazi, Khalid; Wang, Yingge; Bettahalli Narasimha, Murthy Srivatsa; Ma, Xiaohua; Xia, Yan; Pinnau, Ingo (Journal of Membrane Science, Elsevier BV, 2022-04-08) [Article]
      Hydrogen is an emerging energy source with a wide range of applications in transportation, electricity generation, and manufacturing of important chemicals such as ammonia and methanol. Hydrogen is commonly coproduced with CO2 using steam reforming of methane and its purification is typically achieved using energy-intensive processes such as pressure swing adsorption (PSA) and cryogenic distillation. Membrane technology with potentially lower energy consumption and lower carbon footprint could play an important role in developing a more sustainable hydrogen economy. In this study, we prepared carbon molecular sieve (CMS) membranes by the pyrolysis of a highly aromatic catalytic arene-norbornene annulation (CANAL)-Tröger's base ladder polymer of intrinsic microporosity precursor — CANAL-TB-1. CMS membranes obtained by pyrolysis between 600 and 900 °C displayed excellent gas separation performance for hydrogen/carbon dioxide separation and related applications. The CANAL-CMS-800 °C membrane showed a pure-gas hydrogen permeability of 41 Barrer with H2/CO2, H2/N2, and H2/CH4 selectivity values of 39, 1952, and >8200 at 35 °C. Increasing the pyrolysis temperature to 850 and 900 °C further boosted the selectivity. For example, the CANAL-CMS-900 °C exhibited a stable long-term mixed-gas performance over a period of 38 days with an unprecedented H2/CO2 selectivity of 174 and H2 permeability of 8.2 Barrer at 10 bar total feed pressure and 100 °C, which significantly exceeded the performance of previously reported polymers and related CMS membrane materials.
    • Gas separation performance and physical aging of tubular thin-film composite carbon molecular sieve membranes based on a polyimide of intrinsic microporosity precursor

      Ogieglo, Wojciech; Puspasari, Tiara; Alabdulaaly, Abdullah; Nga Nguyen, Thi Phuong; Lai, Zhiping; Pinnau, Ingo (Journal of Membrane Science, Elsevier BV, 2022-04-07) [Article]
      We present a study on the fabrication of tubular thin-film composite CMS membranes based on an intrinsically microporous polyimide of intrinsic microporosity (PIM-PI), PIM-6FDA-OH. Besides the inherent structural similarity between the PIM-PI and CMS membranes (i.e. microporosity with pores <20 Å), the unique feature of the chosen precursor is its ability to undergo a thermal rearrangement (TR) reaction which constitutes an additional mechanism of microporosity evolution in addition to the pyrolysis process. By using Raman spectroscopy and in-situ thermal spectroscopic ellipsometry we tracked the structural TR- and pyrolysis-related evolution in CMS films as thin as 100 nm. Our study revealed a pronounced acceleration of the microstructure collapse (densification) due to physical aging that occurred in ultra-thin films. These, and our previous findings, suggest that excessive reductions in selective layer thickness in microporous amorphous materials, such as PIMs or CMS, may not be beneficial to obtaining highly efficient membranes. Instead, we have shown that excellent and stable separation properties could be achieved by PIM-PI-derived CMS membranes with thicker, ∼3 μm, selective layers (e.g. CO2, H2 permeances of >200 GPU, with CO2/CH4, CO2/N2, and O2/N2 selectivities of 43.0, 41.0, and 7.5, respectively) even after 3 months of aging.
    • Large-Scale Thermochemistry Calculations for Combustion Models

      Yalamanchi, Kiran; Li, Yang; Wang, Tairan; Monge Palacios, Manuel; Sarathy, Mani (Elsevier BV, 2022-04-05) [Preprint]
      Accurate thermochemical properties for chemical species are of vital importance in combustion research. Empirical group additivity approaches are extensively used to generate thermochemistry data used in chemical kinetic models, but the accuracy is limited. In this work, we performed electronic structure calculations to determine reliable thermochemistry data for an extensive set of molecules that were taken from a large and well-established chemical kinetic model. The developed database consists of 1340 species that contain up to 18 and 5 carbon and oxygen atoms, respectively. The M06-2X/aug-cc-pVTZ level of theory was used for the geometry optimizations, vibrational frequency calculations, and dihedral angle scans. The potential energy of the different species was further refined with different composite methods, and the G3 method, together with the atomization reaction approach, was selected to calculate the enthalpy of formation at 0 K. This information was then used in statistical thermodynamics to calculate standard enthalpies of formation and entropy, as well as heat capacities at different temperatures. Our thermochemistry data exhibit good agreement with existing values in the literature, verifying the accuracy of our approach. The group additivity (GA) method is also examined based on the calculated values and significant differences are found, which indicates that GA values of relevant functional groups need to be updated. The database of thermochemistry quantities developed in this study is of particular interest not only for the update of GA values, but also to develop machine learning models for predicting the data of new species, which can assist in the development of combustion models. The impact of the developed dataset is illustrated by examining the variation in ignition delay times with the updated thermochemistry values.
    • Electrospun Nanofibrous Mats Obtained from Green Resources

      Gulyas Oldal , Diana (2022-04) [Thesis]
      Advisor: Szekely, Gyorgy
      Committee members: Nunes, Suzana Pereira; Castaño, Pedro
      The fabrication of electrospun nanofibers has sparked great interest in both academia and industry owing to their unique properties, such as a high surface area to volume ratio, porosity, interconnected porous structure, or controllable fiber morphology. They are highly desired in numerous application areas such as filtration, biotechnology, and energy storage. Cellulose acetate is an ester of cellulose, one of the most abundant natural polymers, that is biodegradable, non-toxic, and has good stability. Electrospinning of cellulose acetate has received significant interest in a broad spectrum of applications, including membranes and air filters, drug-delivery systems, scaffolds for tissue engineering, sensors, and batteries. The electrospinning of cellulose acetate predominantly suffers from the use of toxic and hazardous solvents, which makes the final products less suitable for application in biosystems. In this work, the sustainable electrospinning of cellulose acetate has been shown using renewable-based green solvents, dimethyl carbonate, and cyclopentanone. A binary system consisting of these solvents has been applied. The addition of green salts and biosurfactants substantially improved the spinnability of the cellulose-based solutions. Altering the composition of the solvents allowed tuning of the fiber texture from highly porous to smooth fiber morphology. The thermal analysis revealed that the polymer’s thermal behavior had not been influenced by the salt in nanofibers. Incorporating additives into the polymer matrix resulted in enhanced mechanical properties of nanofibers. Uniform cellulose acetate-based porous nanofibers from green solvents and additives could be successfully fabricated, which has not been reported yet. Based on the reported advantageous properties of electrospun CA nanofibers, it may serve as a possible green and biodegradable porous support layer in thin-film composite membranes replacing the conventional fossil-derived polymeric membrane supports.
    • Thickness-dependent physical aging of a triptycene-based Tröger’s base ladder polymer of intrinsic microporosity (PIM-Trip-TB)

      Albuwaydi, Ahmed Y (2022-04) [Thesis]
      Advisor: Pinnau, Ingo
      Committee members: Lai, Zhiping; Yavuz, Cafer T.
      Gas separation membranes are proving to be a sustainable method to mitigate climate change given the rising energy demand. Polymers of intrinsic microporosity (PIMs) have emerged as a novel material class for such application. Physical aging is a major concern for the growth and commercialization of these glassy polymers. Several factors play an important role in determining the effects of physical aging for a PIM film; one important parameter is its thickness. Gas transport properties of PIM-Trip-TB films of thicknesses between 20-150 µm were monitored over 150 days for physical aging and its dependence on film thickness. Over this period, thicker films had generally higher permeability, and thinner films aged faster. Although fresh films showed higher selectivity during the initial tests, no correlation was found between film thickness and selectivity after aging. In addition, physical aging was more severe and independent of film thickness for larger-sized gases. Film storing environment affected the physical aging of multiply tested samples significantly, whereas films which were not tested periodically showed very minimal aging. A more systematic approach is required to fully analyze and comprehend factors yielding this phenomenon.
    • Intrinsically Microporous Ladder Polymer-based Carbon Molecular Sieve Membranes for Gas Separation Applications

      Hazazi, Khalid (2022-04) [Dissertation]
      Advisor: Pinnau, Ingo
      Committee members: Han, Yu; Koros, William J.; Lai, Zhiping
      Industrial separations – primarily dominated by thermally driven distillation-based processes – consume 10-15% of the global energy production and emit more than 100 million tonnes of CO2 annually. Membrane technology, a 90% thermodynamically more energy-efficient than distillation processes, could be a desirable alternative with potentially lower energy consumption and lower carbon footprint. Industrial implementation of membrane technology, particularly for olefin/paraffin separations and hydrogen purification from syngas, remains challenging due to the substantially low mixed-gas selectivity of the currently available polymeric materials. Carbon molecular sieve (CMS) membranes – formed by high-temperature pyrolysis of solution-processable polymeric-based precursors at an oxygen-free atmosphere – have shown superior gas separation performance far beyond the polymeric upper bounds for many gas-pairs (e.g., CO2/CH4, N2/CH4). The ultimate goal of the research reported in this dissertation was to develop highly performing CMS membranes for industrially important but challenging gas separation applications (e.g., C2H4/C2H6, H2/CO2, etc.). This work successfully introduced a promising approach to fine-tune the pore size distribution of CMS membranes through a systematic modification of the contortion sites of highly aromatic ladder polymer of intrinsic microporosity (PIM) precursors. CMS membranes derived from Trip(Me2)-TB – a precursor with large and thermally stable triptycene units – demonstrated unprecedented pure- and-mixed C2H4/C2H6 selectivities of 96 and 57, respectively, with relatively higher ethylene permeability than other CMS membranes. Similarly, CMS membranes derived from an alternative ladder PIM-based precursor, EA(Me2)-TB, also showed an outstanding performance for C2H4/C2H6 with a pure-gas selectivity up to 77 but with, however, low ethylene permeability of 0.35 barrer. Furthermore, CMS membranes derived from ladder CANAL-TB-1 – a precursor with the smallest contortion site – exhibited superior pure- and-mixed H2/CO2 selectivities of 248 and 174, respectively, due to their tightly packed structure enabled by the lack of any shape-persistence unit such as triptycene. CMS membranes fabricated in this work also showed promising gas separation performance for many other important energy-intensive industrial applications, including CO2/CH4, O2/N2, N2/CH4, H2/CH4, etc. In summary, this dissertation frameworks a facile and effective approach to obtain CMS membranes with exceptional gas separation performance by rational design of the contortion sites of intrinsically microporous ladder polymer-based precursors.