Recent Submissions

  • Aromatics Production via Methanol-Mediated Transformation Routes

    Li, Teng; Shoinkhorova, Tuiana; Gascon, Jorge; Ruiz-Martinez, Javier (ACS Catalysis, American Chemical Society (ACS), 2021-06-13) [Article]
    The methanol-to-aromatics (MTA) process is regarded as a promising route to produce aromatic commodities through non-petroleum carbon resources, such as biomass, waste, coal, natural gas, and CO2. In contrast with the industrially implemented methanol-to-olefin (MTO) process, most MTA studies are still in the laboratory-scale stage. Recently, a few demonstration plants of MTA have been successfully launched, indicating the importance and the gradual industrial maturity of this technology. However, there are still many fundamental questions and technological challenges that must be addressed. In this Review, we summarize the recent advances in mechanistic understanding on the reaction and catalyst deactivation during MTA, elaborate the available strategies to improve the catalytic performance, and correlate MTA studies with other important catalytic aromatization processes. With this knowledge in hand, we share our views on future research directions in this field.
  • Molecular sieving using metal–polymer coordination membranes in organic media

    Hardian, Rifan; Pogany, Peter; Lee, Young Moo; Szekely, Gyorgy (Journal of Materials Chemistry A, Royal Society of Chemistry (RSC), 2021-06-10) [Article]
    Improving the chemical resistance of membranes without sacrificing their molecular sieving performance is highly challenging. Herein, a novel scalable methodology was developed for fabricating solvent-resistant nanofiltration membranes based on metal–polymer coordination (MPC) through a facile yet highly effective method. The controlled deposition of copper(I) iodide enabled the fine-tuning of the molecular sieving performance of MPC membranes by altering both their chemistry and morphology. Spectroscopic and morphological analyses were conducted to elucidate the microscopic and macroscopic properties of the membranes. The formation of coordination bonds between the metal and polybenzimidazole chains protected the membranes from dissolving in harsh organic solvents. Additionally, computational modeling was performed to reveal the stabilization energy and fractional free volume (FFV). Our work opens more sustainable avenues for robust membrane fabrication without conventional crosslinking, which requires reactive chemicals.
  • Nanoporous polyethersulfone membranes prepared by mixed solvent phase separation method for protein separation

    Li, Peipei; Thankamony, Roshni; Li, Xiang; Li, Zhen; Liu, Xiaowei; Lai, Zhiping (Journal of Membrane Science, Elsevier BV, 2021-06-08) [Article]
    Nanoporous polyethersulfone (PES) membranes with high surface porosity and uniform pore size distribution were prepared by combining the phase separation in NMP/nonane mixed solvent system with the traditional nonsolvent induced phase inversion process. The effects of PES concentration, nonane concentration, evaporation time, casting solution temperature, and varied mixed solvent systems on the porous PES membrane surface morphology were thoroughly investigated and optimized. The optimized nanoporous PES membrane showed a high surface porosity with a uniform pore size of 20 nm, rendering an exceptional molecular weight cut-off of as low as 100 k Dalton. In addition, the membrane exhibited a significant molecular size exclusion with water permeance of 121 LMH bar−1, bovine serum albumin (BSA) protein rejection of 60.1%, and γ-globulin protein rejection of 99.5% at 0.5 bar, respectively, demonstrating the potential of the as-prepared nanoporous PES membrane for application in protein separation.
  • Pattern-Potential-Guided Growth of Textured Macromolecular Films on Graphene/High-Index Copper

    Zhou, Dikui; Zhang, Zhihong; Zhu, Yihan; Xiao, Yiqun; Ding, Qingqing; Ruan, Luoyuan; Sun, Yiran; Zhang, Zhibin; Zhu, Chongzhi; Chen, Zongping; Wu, Yongjun; Huang, Yuhui; Sheng, Guan; Li, Jixue; Yu, Dapeng; Wang, Enge; Ren, Zhaohui; Lu, Xinhui; Liu, Kaihui; Han, Gaorong (Advanced Materials, Wiley, 2021-06-06) [Article]
    Macromolecular films are crucial functional materials widely used in the fields of mechanics, electronics, optoelectronics, and biology, due to their superior properties of chemical stability, small density, high flexibility, and solution-processing ability. Their electronic and mechanical properties, however, are typically much lower than those of crystalline materials, as the macromolecular films have no long-range structural ordering. The state-of-the-art for producing highly ordered macromolecular films is still facing a great challenge due to the complex interactions between adjacent macromolecules. Here, the growth of textured macromolecular films on a designed graphene/high-index copper (Cu) surface is demonstrated. This successful growth is driven by a patterned potential that originates from the different amounts of charge transfer between the graphene and Cu surfaces with, alternately, terraces and step edges. The textured films exhibit a remarkable improvement in remnant ferroelectric polarization and fracture strength. It is also demonstrated that this growth mechanism is universal for different macromolecules. As meter-scale graphene/high-index Cu substrates have recently become available, the results open a new regime for the production and applications of highly ordered macromolecular films with obvious merits of high production and low cost.
  • On the origins of lubricity and surface cleanliness in ethanol-diesel fuel blends

    Hong, Frank T.; Singh, Eshan; Sarathy, Mani (Fuel, Elsevier BV, 2021-06-04) [Article]
    Ethanol is the most used bio-derived fuel additive. However, adding ethanol in diesel fuel may negatively impact lubricity or surface cleanliness, which is critical for high-pressure fuel injection systems employed in compression ignition engines. This work investigates surfaces lubricated by ethanol–diesel blends. Adding 5 wt% ethanol in diesel showed negligible changes in fuel lubricity, while blending 10, 20, and 40 wt% ethanol increased wear rates by 46, 81, and 239% respectively. These increases in wear rates (with increases in ethanol by wt%) correlate with the evolution of electrical contact resistance (ECR) values over time. As more ethanol was added, the ECR values signaled thinner fuel films, more metal-to-metal contacts, and a delayed onset of frictional product growth. Raman spectra showed that forming frictional species produced by tribochemical reactions enhanced fuel lubricity. The absence of some frictional species in ethanol lubricated surfaces points to simultaneously improved surface cleanliness and reduced lubricity.
  • The Current Status of MOF and COF Applications

    Freund, Ralph; Zaremba, Orysia; Arnauts, Giel; Ameloot, Rob; Skorupskii, Grigorii; Dincă, Mircea; Bavykina, Anastasiya; Gascon, Jorge; Ejsmont, Aleksander; Gościańska, Joanna; Kalmutzki, Markus; Lächelt, Ulrich; Ploetz, Evelyn; Diercks, Christian; Wuttke, Stefan (Angewandte Chemie International Edition, Wiley, 2021-05-14) [Article]
    The amalgamation of different disciplines is at the heart of reticular chemistry and has broadened the boundaries of chemistry by opening up an infinite space of chemical composition, structure, and material properties. Reticular design has enabled the precise prediction of crystalline framework structures, tunability of chemical composition, incorporation of various functionalities onto the framework backbone, and as a consequence, fine-tuning of metal-organic framework (MOF) and covalent organic framework (COF) properties beyond that of any other material class. Leveraging the unique properties of reticular materials has resulted in significant advances from both a fundamental and an applied perspective. Here, we wish to review the milestones in MOF and COF research and give a critical view on progress in their real-world applications. Finally, we briefly discuss the major challenges in the field that need to be addressed to pave the way for industrial applications.
  • Pyrolysis of Waste Tires in a Twin-Auger Reactor Using CaO: Assessing the Physicochemical Properties of the Derived Products

    Campuzano, Felipe; Cardona-Uribe, Natalia; Agudelo, Andrés F.; Sarathy, Mani; Martínez, Juan Daniel (Energy & Fuels, American Chemical Society (ACS), 2021-05-11) [Article]
    This work assesses the effect of adding CaO during the pyrolysis of waste tires (WT) using a twin-auger reactor on the properties of the pyrolysis derived products. Pyrolysis was conducted in a lab-scale facility at a reactor temperature of 475 °C, solid residence time of 3.5 min, WT mass flow rate of 1.16 kg/h, and N2 flow rate of 300 mL/min. CaO was continuously fed at ratios of 10, 15, and 20 wt %, according to the WT mass flow rate, using two particle size ranges: fine (105-149 μm) and coarse (149-841 μm). The resulting tire pyrolysis oil (TPO) was initially characterized in terms of sulfur content, and the sample with the lowest sulfur content, named TPO[CaO], was further studied by different analytical techniques, including GC-MS and 1H NMR. The tire pyrolysis gas (TPG) and the tire pyrolysis solid (TPS) related to TPO[CaO], so-called TPG[CaO] and TPS[CaO], respectively, were also characterized by gas chromatography, and elemental, proximate, and XRF analyses, respectively. Lastly, an acid demineralization process was carried out to remove some of the inorganic elements in the TPS[CaO]. The addition of 15 wt % of coarse CaO during the pyrolysis of WT resulted in a sulfur reduction in TPO of 26.10%, while viscosity and water content were significantly reduced. The GC-MS analysis revealed a significant presence of benzene, toluene, xylene, and limonene in both TPO and TPO[CaO]. Likewise, 1H NMR suggested an increase of hydrogen atoms in aromatic, naphthenic, and olefin structures in the TPO[CaO], and a decrease of these atoms in paraffinic structures. Similarly, H2 and some CxHy compounds increased, while CO2, CO, and H2S decreased in TPG[CaO], which supports the hypothesis of the participation of CaO in several reactions during the pyrolysis of WT. Although the ash content in TPS[CaO] was significantly high after pyrolysis (57.5 wt %), the acid demineralization process was effective at removing 80% of its inorganic content, improving its surface area and porosity. The information presented in this work aims at providing some insights toward the advancement of in situ upgrading strategies for the resulting products derived from pyrolysis of WT.
  • Selective Conversion of Carbon Dioxide to Formate with High Current Densities

    Yang, Xiulin; Liu, Defei; Zhong, Shenghong; Zhou, Xiaofeng; Huang, Kuo-Wei; Li, Lain-Jong; Lai, Zhiping (Journal of Molecular and Engineering Materials, World Scientific Pub Co Pte Lt, 2021-05-10) [Article]
    Selective conversion of CO2 to formate with high current densities is highly desirable but still challenging. Copper hollow fibers with interconnected pore structures were fabricated via a facile method and used as a stand-alone cathode for highly efficient electrochemical reduction of CO2 to formate. Our studies revealed that delivering the reactant CO2 gas to the inner space of the hollow fiber could build up a higher CO2 partial pressure in the pores and presumably reduce the concentration of H[Formula: see text] from the electrolyte to effectively suppress the major competing reaction, hydrogen evolution reaction (HER), from 46.9% faradaic efficiency (FE) to 15.0%. A high selectivity for CO2 reduction to formate with a maximum FE of 77.1% was achieved with a high current density of 34.7[Formula: see text]mA cm[Formula: see text], which is one of the highest FEs on Cu-based materials. Mechanistic studies suggest that the abundant active sites along with the unique crystal facets induced by the high pressure of CO2 at the pore surface in the “gas in” mode are attributed to the superior electroactivity and selectivity for the CO2 reduction to formate. The Cu hollow fiber electrodes exhibit an outstanding long-term stability at high current density, showing great potential for large-scale practical applications.
  • A Reinforcement Learning-based Economic Model Predictive Control Framework for Autonomous Operation of Chemical Reactors

    Alhazmi, Khalid; Albalawi, Fahad; Sarathy, Mani (arXiv, 2021-05-06) [Preprint]
    Economic model predictive control (EMPC) is a promising methodology for optimal operation of dynamical processes that has been shown to improve process economics considerably. However, EMPC performance relies heavily on the accuracy of the process model used. As an alternative to model-based control strategies, reinforcement learning (RL) has been investigated as a model-free control methodology, but issues regarding its safety and stability remain an open research challenge. This work presents a novel framework for integrating EMPC and RL for online model parameter estimation of a class of nonlinear systems. In this framework, EMPC optimally operates the closed loop system while maintaining closed loop stability and recursive feasibility. At the same time, to optimize the process, the RL agent continuously compares the measured state of the process with the model's predictions (nominal states), and modifies model parameters accordingly. The major advantage of this framework is its simplicity; state-of-the-art RL algorithms and EMPC schemes can be employed with minimal modifications. The performance of the proposed framework is illustrated on a network of reactions with challenging dynamics and practical significance. This framework allows control, optimization, and model correction to be performed online and continuously, making autonomous reactor operation more attainable.
  • Atomistic simulations of syngas oxy-combustion in supercritical CO2

    Grajales Gonzalez, Edwing; Monge Palacios, Manuel; Sarathy, Mani (Journal of CO2 Utilization, Elsevier BV, 2021-04-30) [Article]
    The growing energy demand worldwide is currently supplied by the direct use of fossil fuels, which are limited in nature and represent an environmental concern. Syngas/oxy-combustion technologies have become popular due to recent advances in carbon capture and storage and the possibility to avoid NOX formation by replacing N2 with supercritical CO2. However, the successful implementation of these systems faces several drawbacks: variability in syngas composition and lack of understanding of the chemical kinetics at elevated temperature and pressures in the presence of CO2. In this work, we carried out a molecular dynamics study of syngas oxy-combustion using ReaxFF force field. Three main initiation reactions were identified: H2 + O2 → HO2 + H, H2 → H + H, and CO2 → CO + O, with the last being dominant at high temperatures and high concentrations of CO2. We also found that increasing the initial CO2 concentration and decreasing that of O2 delays ignition. However, for enriched CO2 mixtures, this substrate exerts a catalytic effect in the reactions H2 → H + H and H2O → OH + H by forming the intermediate HCO2. In the absence of initial CO2, formyl radical (HCO) chemistry is lacking due to the prominent consumption of H species by molecular oxygen via O2 + H → OH + O and H + O2 (+M) → HO2 (+M). However, we observed the association between HCO and OH radicals to form stable formic acid, a reaction not implemented in syngas mechanisms.
  • Nano-Confinement Effects on Structural Development and Organic Solvent-Induced Swelling of Ultrathin Carbon Molecular Sieve Films

    Ogieglo, Wojciech; Song, Kepeng; Chen, Cailing; Lei, Qiong; Han, Yu; Pinnau, Ingo (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2021-04-28) [Article]
    Successful implementation of carbon molecular sieve (CMS) membranes in large scale chemical processes inevitably relies on fabrication of high performance integrally skinned asymmetric or thin-film composite membranes. In principle, to maximize separation efficiency the selective CMS layer should be as thin as possible which requires its lateral confinement to a supporting structure. In this work, we studied pyrolysis-induced structural development as well as ethanol vapor-induced swelling of ultrathin CMS films made from a highly aromatic polyimide of an intrinsic microporosity (PIM-PI) precursor. Utilization of a light polarization-sensitive technique, spectroscopic ellipsometry, allowed for the identification of an internal orientation within the turbostratic amorphous CMS structure driven by the laterally constraining support. Our results indicated a significant thickness dependence both in the extent of pyrolytic collapse and response to organic vapor penetrant. Thinner, substrate-confined films (∼30 nm) collapsed more extensively leading to a reduction of microporosity in comparison to their thicker (∼300 nm) as well as self-supported (∼70 μm) counterparts. The reduced microporosity in the thinner films induced changes in the balance between penetrant-induced dilation (swelling) and filling of micropores. In comparison to thicker films, the initial lower microporosity of the thinner films was accompanied by slightly enhanced organic vapor-induced swelling. The presented results are anticipated to generate the fundamental knowledge necessary to design optimized ultrathin CMS membranes. In particular, our results reinforce previous findings that excessive reduction of the selective layer thickness in amorphous microporous materials (such as PIMs or CMS) beyond several hundred nanometers may not be optimal for maximizing their fluid transport performance.
  • Unlocking mixed oxides with unprecedented stoichiometries from heterometallic metal-organic frameworks for the catalytic hydrogenation of CO2

    Castells-Gil, Javier; Ould-Chikh, Samy; Ramírez, Adrian; Ahmad, Rafia; Prieto, Gonzalo; Gómez, Alberto Rodríguez; Garzon Tovar, Luis Carlos; Telalovic, Selvedin; Liu, Lingmei; Genovese, Alessandro; Padial, Natalia M.; Aguilar-Tapia, Antonio; Bordet, Pierre; Cavallo, Luigi; Martí-Gastaldo, Carlos; Gascon, Jorge (Chem Catalysis, Elsevier BV, 2021-04-26) [Article]
    Their complex surface chemistry and high oxygen lattice mobilities place mixed-metal oxides among the most important families of materials. Modulation of stoichiometry in mixed-metal oxides has been shown to be a very powerful tool for tuning optical and catalytic properties. However, accessing different stoichiometries is not always synthetically possible. Here, we show that the thermal decomposition of the recently reported metal-organic framework MUV-101(Fe, Ti) results in the formation of carbon-supported titanomaghemite nanoparticles with an unprecedented Fe/Ti ratio close to 2, not achievable by soft-chemistry routes. The resulting titanomaghemite phase displays outstanding catalytic activity for the production of CO from CO2 via the reverse water-gas shift (RWGS) reaction with CO selectivity values of ca. 100% and no signs of deactivation after several days on stream. Theoretical calculations suggest that the reaction proceeds through the formation of COOH* species, favoring in this way CO over other byproducts.
  • A facile approach to synthesize SSZ-13 membranes with ultrahigh N2 permeances for efficient N2/CH4 separations

    Li, Yanmei; He, Shengnan; Shu, Chaojiu; Li, Xinping; Liu, Bo; Zhou, Rongfei; Lai, Zhiping (Journal of Membrane Science, Elsevier BV, 2021-04-26) [Article]
    Separation of inert nitrogen from natural gas by membranes is much more energy-saving than cryogenic distillation but very challenging because the size difference of both gas molecules is quite small. Herein, high-quality and N2-selective SSZ-13 membranes on α-alumina tubes were prepared using a novel synthesis approach called seeded-gel synthesis. Seeded-gel synthesis was more convenient and credible than the conventional secondary growth because a seeding step on the substrate was omitted for the former method. The effect of calcination atmosphere on the quality of membranes was also discussed. SSZ-13 membranes had the fewest defects when ozone calcination was used. The predicted values of single-component N2 and CH4 permeances by the Maxwell-Stefan equations agreed well with the experimental ones. The SSZ-13 membrane exhibited ultrahigh N2 permeance of 850 × 10−9 mol m−2 s−1 Pa−1 (equals 2500 GPU) and a high N2/CH4 selectivity of 13.5 at 298 K and 0.303 MPa feed pressure (absolute). Membrane preparation by seeded-gel method had good reproducibility. The effects of temperature, pressure drop and feed flow rate on membrane performances were investigated for N2/CH4 mixture separations. The membrane also displayed good separation performance in N2/CH4 system either at 2.6 MPa feed pressure or under humid conditions. The continuous SSZ-13 thin membranes prepared by the simple seeded-gel synthesis showed great potentials for energy-efficient N2 removal from unconventional gases.
  • Unraveling the octane response of gasoline/ethanol blends: Paving the way to formulating gasoline surrogates

    AlRamadan, Abdullah S.; Sarathy, Mani; Badra, Jihad (Fuel, Elsevier BV, 2021-04-24) [Article]
    Ethanol is widely used as a gasoline octane booster, and yet, its blending response is not fully understood. Blending ethanol with gasoline most often leads to a synergistic effect (higher than expected relative to linear blending), but can also lead to a linear or antagonistic blending (lower than expected relative to linear blending). To address the knowledges gap in ethanol blending, this study provides new research octane number (RON) and motor octane number (MON) measurements of ethanol blended with various gasoline surrogates. The first set of blends are ternary mixtures, designed to study the interactions between primary reference fuels (PRFs) and certain gasoline components when blended with ethanol. These gasoline components are 1-hexene, 1,2,4-trimethylbenzene and cyclopentane, which, represents the olefin, aromatic and naphthenes classes in commercial gasoline fuels, respectively. The second set represents multicomponent surrogates for Fuels for Advanced Combustion Engines (FACE) gasolines, developed in our previous work (Badra et al., Applied Energy 2017 p. 778-793). This study developes an octane blending model of ethanol/gasoline surrogates that utilize the new measurements along with datasets available in literature. The model consists of the conventional linear by ethanol molar fraction correlation, with the addition of non-linearity terms that depend on base fuel properties, namely, the octane sensitivity and the mole fraction of gasoline components. The model can predict the octane numbers (RON and MON) of blends containing gasoline surrogates composed of n-heptane, n-pentane, iso-octane, iso-pentane, toluene, 124-trimethylbenzene, cyclopentane, cyclohexane (for RON only) and 1-hexene. To ensure the generality of the developed model and avoid over-fitting, the model is trained using 85% of the available dataset while the remaining measurements have been used to test the model. The proposed model outperforms many ethanol blending models available in literature with 87% of the RON and 83% of the MON measurements being within the reproducibility limits. This model can be integrated to the process of designing gasoline surrogates that contain ethanol.
  • A multi-parametric catalyst screening for CO2 hydrogenation to ethanol

    Goryachev, Andrey; Pustovarenko, Alexey; Shterk, Genrikh; Alhajri, Nawal S.; Jamal, Aqil; Albuali, Mohammed; van Koppen, Luke; Khan, Il Son; Russkikh, Artem; Ramirez, Adrian; Shoinkhorova, Tuiana; Hensen, Emiel J. M.; Gascon, Jorge (ChemCatChem, Wiley, 2021-04-21) [Article]
    The direct hydrogenation of CO 2 to higher alcohols has the potential to turn the main contributor of global warming into a valuable feedstock. However, for this technology to become attractive, more efficient and, especially, selective catalysts are required. Here we present a high throughput study on the influence of different promoters on the CO 2 hydrogenation performance of Rh-SiO 2 catalysts. Fe and K promoters were found to improve ethanol selectivity at the expense of undesired CH 4 . The best-performing catalyst, with a composition 2 wt.% K, 20 wt.% Fe, and 5 wt.% Rh, displays an EtOH selectivity of 16% at CO 2 conversion level of 18.4% and CH 4 selectivity of 46%. The combination of different characterization techniques and catalyst screening allowed us to unravel the role of each catalyst component in this complex reaction mechanism.
  • Covalent Assembly of Two-Dimensional COF-on-MXene Heterostructures Enables Fast Charging Lithium Hosts

    Guo, Dong; Ming, Fangwang; Shinde, Digambar; Cao, Li; Huang, Gang; Li, Chunyang; Li, Zhen; Yuan, Youyou; Hedhili, Mohamed N.; Alshareef, Husam N.; Lai, Zhiping (Advanced Functional Materials, Wiley, 2021-04-16) [Article]
    2D heterostructured materials combining ultrathin nanosheet morphology, defined pore configuration, and stable hybrid compositions, have attracted increasing attention for fast mass transport and charge transfer, which are highly desirable features for efficient energy storage. Here, the chemical space of 2D–2D heterostructures is extended by covalently assembling covalent organic frameworks (COFs) on MXene nanosheets. Unlike most COFs, which are generally produced as solid powders, ultrathin 2D COF-LZU1 grows in situ on aminated Ti3C2Tx nanosheets with covalent bonding, producing a robust MXene@COF heterostructure with high crystallinity, hierarchical porosity, and conductive frameworks. When used as lithium hosts in Li metal batteries, lithium storage and charge transport are significantly improved. Both spectroelectrochemical and theoretical analyses demonstrate that lithiated COF channels are important as fast Li+ transport layers, by which Li ions can be precisely nucleated. This affords dendrite-free and fast-charging anodes, which would be difficult to achieve using individual components.
  • Early Chemistry of Nicotine Degradation in Heat-Not-Burn Smoking Devices and Conventional Cigarettes: Implications for Users and Second- and Third-Hand Smokers

    Chavarrio Cañas, Javier Eduardo; Monge Palacios, Manuel; Grajales Gonzalez, Edwing; Sarathy, Mani (The Journal of Physical Chemistry A, American Chemical Society (ACS), 2021-04-09) [Article]
    Nicotine exposure results in health risks not only for smokers but also for second- and third-hand smokers. Unraveling nicotine's degradation mechanism and the harmful chemicals that are produced under different conditions is vital to assess exposure risks. We performed a theoretical study to describe the early chemistry of nicotine degradation by investigating two important reactions that nicotine can undergo: hydrogen abstraction by hydroxyl radicals and unimolecular dissociation. The former contributes to the control of the degradation mechanism below 800 K due to a non-Arrhenius kinetics, which implies an enhancement of reactivity as temperature decreases. The latter becomes important at higher temperatures due to its larger activation energy. This change in the degradation mechanism is expected to affect the composition of vapors inhaled by smokers and room occupants. Conventional cigarettes, which operate at temperatures higher than 1000 K, are more prone to yield harmful pyridinyl radicals via nicotine dissociation, while nicotine in electronic cigarettes and vaporizers, with operating temperatures below 600 K, will be more likely degraded by hydroxyl radicals, resulting in a vapor with a different composition. Although low-temperature nicotine delivery devices have been claimed to be less harmful due to their nonburning operating conditions, the non-Arrhenius kinetics that we observed for the degradation mechanism below 873 K suggests that nicotine degradation may be more rapidly initiated as temperature is reduced, indicating that these devices may be more harmful than it is commonly assumed.
  • Scavenging organic micropollutants from water with nanofibrous hypercrosslinked cyclodextrin membranes derived from green resources

    Topuz, Fuat; Holtzl, Tibor; Szekely, Gyorgy (Chemical Engineering Journal, Elsevier BV, 2021-03-27) [Article]
    As a principal constituent of living organisms, water is crucial to sustain life on Earth. However, its pollution by major human activities leading to clean water scarcity is a significant issue. Industrial activities release toxic pollutants, such as textile dyes and polycyclic aromatic hydrocarbons (PAHs), which pollute water resources and endanger the marine ecosystem and human life. To address this issue, we developed a highly effective sorbent platform based on a nanofibrous membrane, comprising hypercrosslinked cyclodextrin networks (HCNs). Cyclodextrins (CDs) are cyclic oligosaccharides with a truncated cone shape featuring a partially hydrophobic cavity interior, which can form complexes with organic micropollutants. The nanofibrous HCN membrane was produced via the electrospinning of highly concentrated CD solutions containing a naturally occurring graphitic acid linker. The thermal crosslinking of the nanofibrous membrane resulted in a robust covalent polymer network of CD macrocycles, which can retain its shape in aqueous and organic solvents. The membrane was produced by exclusively using green resources including a novel natural crosslinker (i.e., graphitic acid), which has not been previously employed for any CD-based materials. Molecular modeling revealed that the crosslinking had a negligible effect on the host–guest complexation of the nanofibrous CD networks. The HCN membrane was used for scavenging textile dyes and PAHs from polluted water, and it demonstrated high sorption performance (Qmax = 692 mg g−1 dye), and excellent reusability upon the application of acidic methanol treatment. The nanofibrous HCN membrane can be used for rapid and efficient scavenging of organic micropollutants in aqueous environments.
  • High-performance 7-channel monolith supported SSZ-13 membranes for high-pressure CO2/CH4 separations

    Li, Yanmei; Wang, Yulei; Guo, Mingyang; Liu, Bo; Zhou, Rongfei; Lai, Zhiping (Journal of Membrane Science, Elsevier BV, 2021-03-18) [Article]
    Continuous SSZ-13 zeolite membranes were reproducibly synthesized on the inner surface of 7-channel monolith supports for the first time. Packing density and mechanical strength were much greater than those using normal tubular and disc membranes. The membrane in the central channel of monolith was thinner than these of the side channels. The best monolith supported SSZ-13 membrane (with spacers) showed a CO2/CH4 selectivity of 72 and a CO2 permeance of 163 × 10-8 mol/(m2 s Pa) at pressure drop of 2.0 MPa and feed flow rate of 20 standard L/min for an equimolar CO2/CH4 mixture. Such separation performance was higher than most of zeolite membranes prepared on single-channel tubes or discs. The effects of temperature, pressure drop and fluid state on separation performance of the membranes were investigated. The extent of concentration polarization through monolith supported membrane was modelled by the concentration polarization index (CPI). Increasing feed flow rate and inserting spacers into the channels were effective ways to reduce the negative influence of concentration polarization. The latter way was more effective for our monolith supported membranes than the former because the dead volume was reduced greatly. Carbon dioxide permeance and CO2/CH4 selectivity increased by 24% and 85%, respectively, when the CPI increased from 0.79 (without spacer) to 0.89 (with spacer) at feed flow rate of 20 standard L/min.
  • Rapid soot inception via α-alkynyl substitution of polycyclic aromatic hydrocarbons

    Liu, Peng; Jin, Hanfeng; Chen, Bingjie; Yang, Jiuzhong; Li, Zepeng; Bennett, Anthony; Farooq, Aamir; Sarathy, Mani; Roberts, William L. (Fuel, Elsevier BV, 2021-03-17) [Article]
    Soot particles alter global climate and dominate the origin and evolution of carbonaceous interstellar material. Convincing experimental evidence has linked polycyclic aromatic hydrocarbons (PAH) to soot inception under low-temperature astrochemistry and high-temperature combustion conditions. However, significant gaps still remain in the knowledge of PAH and soot formation mechanisms. Here, we report theoretical and experimental evidence for a soot inception and growth pathway driven by peri-condensed aromatic hydrocarbons (PCAH) with an alkynyl substitution. Initially, free radicals attack the α-alkynyl substitution of PCAHs to form covalently bound compounds yielding resonantly stabilized radicals (RSRs), which promote further clustering through repeated addition reactions with negligible energy barriers. The proposed pathway is shown to be competitive at temperatures relevant to astrochemistry, engine exhaust manifold and flames because it does not require H-abstraction reactions, the requisite reaction precursors are in abundance, and the reaction rate is high. Such addition reactions of PCAHs with α-alkyne substituents create covalently bound clusters from moderate-size PAHs that may otherwise be too small to coagulate.

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