Chemically Activated Covalent Triazine Frameworks with Enhanced Textural Properties for High Capacity Gas Storage

Lee, Yoon Jeong,Talapaneni, Siddulu Naidu,Coskun, Ali American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.36

<P>Chemical activation of porous/nonporous materials to achieve high surface area sorbents with enhanced textural properties is a very promising strategy. The chemical activation using KOH, however, could lead to broad distribution of pores originating from the simultaneous pore deepening and widening pathways. Accordingly, establishing correlation between the chemical/textural properties of starting porous/nonporous materials and various pore formation mechanisms is quite critical to realize superior porosity and gas uptake properties. Here,, we show that the chemical and textural properties of starting porous organic polymers, that is, covalent triazine frameworks (CTF), have profound effect on the resulting porosity of the frameworks. The chemical activation of microporous CTF-1 using KOH at 700 degrees C enabled the preparation of chemically activated CTF-1, caCTF-1-700, which predominantly showed pore deepening, leading to an increased surface area of 2367 m(2) g(-1) and significantly enhanced gas adsorption properties with CO2 uptake capacities up to 6.0 mmol g(-1) at 1 bar and 1.45 mmol g(-1) at 0.15 bar and 273 K along with a isosteric heats of adsorption (Q(st)) of 30.6 kJ mol(-1). In addition, a remarkable H-2 uptake capacity of 2.46 and 1.66 wt % at 77 and 87 K, 1 bar along with the Q(st) value of 10.95 kJ mol-1 at zero coverage was also observed for the caCTF-1-700. Notably, the activation of mesoporous CTF-2 under the same conditions was accompanied by a decrease in its surface area and also in the conversion of mesopores into the micropores, thus leading to a pore deepening/narrowing rather than widening. We attributed this result to the presence of reactive weak spots, triazine moieties, for the chemical activation reaction within the CTF backbone. These results collectively suggest the critical role of chemical and pore characteristics of porous organic polymers in chemical activation to realize solid-sorbents for high capacity gas storage applications.</P>

Tetrathiafulvalene (TTF)-Annulated Calix[4]pyrroles: Chemically Switchable Systems with Encodable Allosteric Recognition and Logic Gate Functions

Park, Jung Su,Sessler, Jonathan L. American Chemical Society 2018 Accounts of chemical research Vol.51 No.10

<P><B>Conspectus</B></P><P>Molecular and supramolecular systems capable of switching between two or more states as the result of an applied chemical stimulus are attracting ever-increasing attention. They have seen wide application in the development of functional materials including, but not limited to, molecular and supramolecular switches, chemosensors, electronics, optoelectronics, and logic gates. A wide range of chemical stimuli have been used to control the switching within bi- and multiple state systems made up from either singular molecular entities or supramolecular ensembles. In general, chemically triggered switching systems contain at least two major functional components that provide for molecular recognition and signal transduction, respectively. These components can be connected to one another via either covalent or noncovalent linkages.</P><P>Of particular interest are switchable systems displaying cooperative or allosteric features. Such advanced control over function is ubiquitous in nature and, in the case of synthetic systems, may allow the capture and release of a targeted chemical entity or permit the transduction of binding information from one recognition site to another. Allosterically controlled complexation and decomplexation could also permit the amplification or deamplification of analyte-specific binding affinity, lead to nonlinear binding characteristics, or permit a magnification of output signals.</P><P>Our own efforts to develop chemically driven supramolecular switches, advanced logic gates, and multifunction cascade systems have focused on the use of tetrathiafulvalene (TTF) annulated calix[4]pyrroles (C4Ps). These systems, TTF-C4Ps, combine several orthogonal binding motifs within what are conformationally switchable receptor frameworks. Their basic structure and host-guest recognition functions can be controlled via application of an appropriate chemical stimulus. Homotropic or heterotropic allosteric molecular recognition behavior is often seen. This has allowed us to (1) produce self-assembled structures, (2) control switching between bi- and multistate constructs, (3) generate chemical logic gates performing chemical-based Boolean logic operations, (4) create ionically controlled three-state logic systems that release different chemical messengers and activate disparate downstream reactions, and (5) encode a variety advanced functional operations into what are relatively simple molecular-scale devices.</P><P>Looking to the future, we believe that exploiting allosteric control will expand opportunities for supramolecular chemists and allow some of the complexity seen in biology to be reproduced in simple constructs. Of particular appeal would be a capacity to release chemical messengers at will, perhaps after a prior capture and chemical modification step, that then encode for further downstream functions as seen in the case of the small molecules, such as neurotransmitters and pheromones, used by nature for the purpose of intraentity communication. Molecular scale logic devices with allosteric functions are thus the potential vanguard of a new area of study involving interactions between multiple discrete components with an emphasis on functional outcomes.</P> [FIG OMISSION]</BR>

Versatile Processing of Metal-Organic Framework-Fluoropolymer Composite Inks with Chemical Resistance and Sensor Applications

Kim, Jin-Oh,Kim, Jin Yeong,Lee, Jeong-Chan,Park, Steve,Moon, Hoi Ri,Kim, Dong-Pyo American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.4

<P>We report a new class of metal-organic framework (MOF) inks with a water-repellent, photocurable fluoropolymer (PFPE) having up to 90 wt % MOF loading. These MOF inks are enabled to process various MOFs through spray coating, pen writing, stencil printing, and molding at room temperature. Upon UV curing, the hydrophobic PFPE matrix efficiently blocks water permeation but allows accessibility of chemicals into the MOF pores, thereby freeing the MOF to perform its unique function. Moreover, by introducing functional MOFs we successfully demonstrated a water-tolerant chemosensor for a class of aromatic pollutants in water and a chemical-resistant thermosensor for visualizing temperature image. This approach would open up innumerable opportunities for those MOFs that are otherwise dormant.</P> [FIG OMISSION]</BR>

Fully Solution-Processed Transparent Conducting Oxide-Free Counter Electrodes for Dye-Sensitized Solar Cells: Spray-Coated Single-Wall Carbon Nanotube Thin Films Loaded with Chemically-Reduced Platinum Nanoparticles

Kim, Sang Yong,Kim, Yesel,Lee, Kyung Moon,Yoon, Woo Sug,Lee, Ho Seok,Lee, Jong Tae,Kim, Seung-Joo,Ahn, Yeong Hwan,Park, Ji-Yong,Lee, Tai Kyu,Lee, Soonil American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.16

<P>We report fully solution-processed fabrication of transparent conducting oxide-free counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) by combining spray-coating of single-wall carbon nanotubes (SWCNTs) and chemical reduction of chloroplatinic acid precursor to platinum nanoparticles (Pt NPs) with formic acid. The power conversion efficiency of a semitransparent DSSC with such SWCNT-based CE loaded with Pt NPs is comparable to that of a control device with a conventional CE. Quantification of Pt loading shows that network morphology of entangled SWCNTs is efficient in forming and retaining chemically reduced Pt NPs. Moreover, electron microscopy and electrochemical impedance spectroscopy results show that mainly Pt NPs, which are tens of nanometers in diameter and reside at the surface of SWCNT CEs, contribute to electrocatalytic activity for triiodide reduction, to which we attribute strong correlation between power conversion efficiency of DSSCs and time constant deduced from equivalent-circuit analysis of impedance spectra.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-16/am5019447/production/images/medium/am-2014-019447_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5019447'>ACS Electronic Supporting Info</A></P>

Achieving Selective and Efficient Electrocatalytic Activity for CO₂ Reduction Using Immobilized Silver Nanoparticles

Kim, Cheonghee,Jeon, Hyo Sang,Eom, Taedaehyeong,Jee, Michael Shincheon,Kim, Hyungjun,Friend, Cynthia M.,Min, Byoung Koun,Hwang, Yun Jeong American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.43

<P>Selective electrochemical reduction of CO<SUB>2</SUB> is one of the most sought-after processes because of the potential to convert a harmful greenhouse gas to a useful chemical. We have discovered that immobilized Ag nanoparticles supported on carbon exhibit enhanced Faradaic efficiency and a lower overpotential for selective reduction of CO<SUB>2</SUB> to CO. These electrocatalysts were synthesized directly on the carbon support by a facile one-pot method using a cysteamine anchoring agent resulting in controlled monodispersed particle sizes. These synthesized Ag/C electrodes showed improved activities, specifically decrease of the overpotential by 300 mV at 1 mA/cm<SUP>2</SUP>, and 4-fold enhanced CO Faradaic efficiency at −0.75 V vs RHE with the optimal particle size of 5 nm compared to polycrystalline Ag foil. DFT calculations enlightened that the specific interaction between Ag nanoparticle and the anchoring agents modified the catalyst surface to have a selectively higher affinity to the intermediate COOH over CO, which effectively lowers the overpotential.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2015/jacsat.2015.137.issue-43/jacs.5b06568/production/images/medium/ja-2015-06568y_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5b06568'>ACS Electronic Supporting Info</A></P>

Photon-Triggered Current Generation in Chemically-Synthesized Silicon Nanowires

Kim, Jungkil,Kim, Ha-Reem,Lee, Hoo-Cheol,Kim, Kyoung-Ho,Hwang, Min-Soo,Lee, Jung Min,Jeong, Kwang-Yong,Park, Hong-Gyu American Chemical Society 2019 NANO LETTERS Vol.19 No.2

<P>A porous Si segment in a Si nanowire (NW), when exposed to light, generates a current with a high on/off ratio. This unique feature has been recently used to demonstrate photon-triggered NW devices including transistors, logic gates, and photodetection systems. Here, we develop a reliable and simple procedure to fabricate porous Si segments in chemically synthesized Si NWs for photon-triggered current generation. To achieve this, we employ 100 nm-diameter chemical-vapor-deposition grown Si NWs that possess an n-type high doping level and extremely smooth surface. The NW regions uncovered by electron-beam resist become selectively porous through metal-assisted chemical etching, using Ag nanoparticles as a catalyst. The contact electrodes are then fabricated on both ends of such NWs, and the generated current is measured when the laser is focused on the porous Si segment. The current level is changed by controlling the power of the incident laser and bias voltage. The on/off ratio is measured up to 1.5 × 10<SUP>4</SUP> at a forward bias of 5 V. In addition, we investigate the porous-length-dependent responsivity of the NW device with the porous Si segment. The responsivity is observed to decrease for porous segment lengths beyond 360 nm. Furthermore, we fabricate nine porous Si segments in a single Si NW and measure the identical photon-triggered current from each porous segment; this single NW device can function as a high-resolution photodetection system. Therefore, our fabrication method to precisely control the position and length of the porous Si segments opens up new possibilities for the practical implementation of programmable logic gates and ultrasensitive photodetectors.</P> [FIG OMISSION]</BR>

Novel Flexible Transparent Conductive Films with Enhanced Chemical and Electromechanical Sustainability: TiO₂ Nanosheet–Ag Nanowire Hybrid

Sohn, Hiesang,Kim, Seyun,Shin, Weonho,Lee, Jong Min,Lee, Hyangsook,Yun, Dong-Jin,Moon, Kyoung-Seok,Han, In Taek,Kwak, Chan,Hwang, Seong-Ju American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.3

<P>Flexible transparent conductive films (TCFs) of TiO2 nanosheet (TiO2 NS) and silver nanowire (Ag NW) network hybrid were prepared through a simple and scalable solution-based process. The as-formed TiO2 NS-Ag NW hybrid TCF shows a high optical transmittance (TT: 97% (90.2% including plastic substrate)) and low sheet resistance (R-s: 40 Omega/sq). In addition, the TiO2 NS Ag NW hybrid TCF exhibits a long-time chemical/aging and electromechanical stability. As for the chemical/aging stability, the hybrid TCF of Ag NW and TiO2 NS reveals a retained initial conductivity (Delta R-S/R-S < 1%) under ambient oxidant gas over a month, superior to that of bare Ag NW (Delta R-s/R-s > 4000%) or RuO2 NS Ag NW hybrid (Delta R-s/R-s > 200%). As corroborated by the density functional theory simulation, the superb chemical stability of TiO2 NS-Ag NW hybrid is attributable to the unique role of TiO2 NS as a barrier, which prevents Ag NW's chemical corrosion via the attenuated adsorption of sulfidation molecules (H2S) on TiO2 NS. With respect to the electromechanical stability, in contrast to Ag NWS (Delta R/R-0 similar to 152.9%), our hybrid TCF shows a limited increment of fractional resistivity (Delta R/R-0 similar to 14.4%) after 200 000 cycles of the 1R bending test (strain: 6.7%) owing to mechanically welded Ag NW networks by TiO2 NS. Overall, our unique hybrid of TiO2 NS and Ag NW exhibits excellent electrical/optical properties and reliable chemical/electromechanical stabilities.</P>

A Photocatalyst–Enzyme Coupled Artificial Photosynthesis System for Solar Energy in Production of Formic Acid from CO₂

Yadav, Rajesh K.,Baeg, Jin-Ook,Oh, Gyu Hwan,Park, No-Joong,Kong, Ki-jeong,Kim, Jinheung,Hwang, Dong Won,Biswas, Soumya K. American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.28

<P>The photocatalyst–enzyme coupled system for artificial photosynthesis process is one of the most promising methods of solar energy conversion for the synthesis of organic chemicals or fuel. Here we report the synthesis of a novel graphene-based visible light active photocatalyst which covalently bonded the chromophore, such as multianthraquinone substituted porphyrin with the chemically converted graphene as a photocatalyst of the artificial photosynthesis system for an efficient photosynthetic production of formic acid from CO<SUB>2</SUB>. The results not only show a benchmark example of the graphene-based material used as a photocatalyst in general artificial photosynthesis but also the benchmark example of the selective production system of solar chemicals/solar fuel directly from CO<SUB>2</SUB>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-28/ja3009902/production/images/medium/ja-2012-009902_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja3009902'>ACS Electronic Supporting Info</A></P>

Including Bioconcentration Kinetics for the Prioritization and Interpretation of Regulatory Aquatic Toxicity Tests of Highly Hydrophobic Chemicals

Kwon, Jung-Hwan,Lee, So-Young,Kang, Hyun-Joong,Mayer, Philipp,Escher, Beate I. American Chemical Society 2016 Environmental science & technology Vol.50 No.21

<P>Worldwide, regulations of chemicals require short-term toxicity data for evaluating hazards and risks of the chemicals. Current data requirements on the registration of chemicals are primarily based on tonnage and do not yet consider properties of chemicals. For example, short-term ecotoxicity data are required for chemicals with production volume greater than 1 or 10 ton/y according to REACH, without considering chemical properties. Highly hydrophobic chemicals are characterized by low water solubility and slow bioconcentration kinetics, which may hamper the interpretation of short-term toxicity experiments. In this work, internal concentrations of highly hydrophobic chemicals were predicted for standard acute ecotoxicity tests at three trophic levels, algae, invertebrate, and fish. As demonstrated by comparison with maximum aqueous concentrations at water solubility, chemicals with an octanolwater partition coefficient (Kow) greater than 106 are not expected to reach sufficiently high internal concentrations for exerting effects within the test duration of acute tests with fish and invertebrates, even though they might be intrinsically toxic. This toxicity cutoff was explained by the slow uptake, i.e., by kinetics, not by thermodynamic limitations. Predictions were confirmed by data entries of the OECDs screening information data set (SIDS) (n = 746), apart from a few exceptions concerning mainly organometallic substances and those with inconsistency between water solubility and Kow. Taking error propagation and model assumptions into account, we thus propose a revision of data requirements for highly hydrophobic chemicals with log Kow > 7.4: Short-term toxicity tests can be limited to algae that generally have the highest uptake rate constants, whereas the primary focus of the assessment should be on persistence, bioaccumulation, and long-term effects.</P>

Coal Chemical Looping Gasification for Syngas Generation Using an Iron-Based Oxygen Carrier

Guo, Qingjie,Cheng, Yu,Liu, Yongzhuo,Jia, Weihua,Ryu, Ho-Jung American Chemical Society 2014 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.53 No.1

<P>The chemical-looping gasification (CLG) of coal is a clean and effective technology for syngas generation. Sharing principles with chemical-looping combustion (CLC), CLG also uses oxygen carriers to transfer lattice oxygen to the fuel. Investigations into CLG with different O/C ratios are carried out in a fluidized bed reactor with steam used as the gasification–fluidization medium. The effect of the active component content of the oxygen carrier on the gas selectivity is performed, and reaction mechanisms between the Fe<SUB>2</SUB>O<SUB>3</SUB> oxygen carrier and coal with steam as the gasification agent are discussed. Moreover, we also assessed the reactivity of the CaO-decorated iron-based oxygen carrier particles in multicycle reactions. The carbon conversion efficiency is increased from 55.74 to 81% with increasing O/C ratio, whereas the content of H<SUB>2</SUB> first decreases and then increases. The addition of CaO can increase the carbon conversion efficiency and the gasification rate substantially and reduce the generation rate of H<SUB>2</SUB>S from 1.89 × 10<SUP>–3</SUP> to 0.156 × 10<SUP>–3</SUP> min<SUP>–1</SUP>. Furthermore, X-ray diffraction (XRD) images indicate that the CaO-decorated iron-based oxygen carrier particles were completely regenerated after six redox cycles. Finally, the peak fitting of gasification reaction rate curves is used to explore the reaction mechanism between coal char and the CaO-decorated iron-based oxygen carrier, indicating that the reactions in the CLG include three stages: the complex reactions involved an oxygen carrier, coal char, and steam; the gasification of coal char; and the reduction of Fe<SUB>3</SUB>O<SUB>4</SUB> to FeO. The two-segment modified random pore model (MRPM) fits the experiment data well.</P>