More Like this

1. Confinement Effects on the Magnetic Ionic Liquid 1-Ethyl-3-methylimidazolium Tetrachloroferrate(III)

   https://doi.org/10.3390/molecules27175591  

   Burba, Christopher M.; Chang, Hai-Chou (September 2022, Molecules)

   Confinement effects for the magnetoresponsive ionic liquid 1-ethyl-3-methylimidazolium tetrachloroferrate(III), [C2mim]FeCl4, are explored from thermal, spectroscopic, and magnetic points of view. Placing the ionic liquid inside SBA-15 mesoporous silica produces a significant impact on the material’s response to temperature, pressure, and magnetic fields. Isobaric thermal experiments show melting point reductions that depend on the pore diameter of the mesopores. The confinement-induced reductions in phase transition temperature follow the Gibbs–Thomson equation if a 1.60 nm non-freezable interfacial layer is postulated to exist along the pore wall. Isothermal pressure-dependent infrared spectroscopy reveals a similar modification to phase transition pressures, with the confined ionic liquid requiring higher pressures to trigger phase transformation than the unconfined system. Confinement also impedes ion transport as activation energies are elevated when the ionic liquid is placed inside the mesopores. Finally, the antiferromagnetic ordering that characterizes unconfined [C2mim]FeCl4 is suppressed when the ionic liquid is confined in 5.39-nm pores. Thus, confinement provides another avenue for manipulating the magnetic properties of this compound. 

   more » « less
2. Polymorphic Phase Transformation Pathways under Nanoconfinement: Flufenamic Acid

   https://doi.org/http://dx.doi.org/10.1021/acs.cgd.0c01207  

   Zhang, Keke; Fellah, Noalle; López-Mejías, Vilmalí; Ward, Michael D. (January 2020, Crystal growth design)

   null (Ed.)

   Flufenamic acid (FFA) is a highly polymorphic compound, with nine forms to date. When melt crystallization was performed under nanoscale confinement in controlled pore glass (CPG), the formation of the extremely unstable FFA form VIII was favored. Under confinement, form VIII was sufficiently stable to allow the measurement of its melting point, which decreased with decreasing pore size in accord with the Gibbs−Thomson relationship, enabling determination of the otherwise elusive melting point of the bulk form. Moreover, the transformation pathways among the various polymorphs depended on pore size, proceeding as form VIII → form II → form I for nanocrystals embedded in 30−50-nm diameter pores, and form VIII → form IV → form III in 100−200 nm pores. In contrast, form VIII converts directly to form III in the bulk. Whereas previous reports have demonstrated that nanoconfinement can alter (thermodynamic) polymorph stability rankings, these results illustrate that nanoscale confinement can arrest and alter phase transformations kinetics such that otherwise hidden pathways can be observed. 

   more » « less
3. Tailoring Mesopores and Nitrogen Groups of Carbon Nanofibers for Polysulfide Entrapment in Lithium–Sulfur Batteries

   https://doi.org/10.3390/polym14071342  

   Sarkar, Snatika; Won, Jong Sung; An, Meichun; Zhang, Rui; Lee, Jin Hong; Lee, Seung Goo; Joo, Yong Lak (April 2022, Polymers)

   In the current work, we combined different physical and chemical modifications of carbon nanofibers through the creation of micro-, meso-, and macro-pores as well as the incorporation of nitrogen groups in cyclic polyacrylonitrile (CPAN) using gas-assisted electrospinning and air-controlled electrospray processes. We incorporated them into electrode and interlayer in Li–Sulfur batteries. First, we controlled pore size and distributions in mesoporous carbon fibers (mpCNF) via adding polymethyl methacrylate as a sacrificial polymer to the polyacrylonitrile carbon precursor, followed by varying activation conditions. Secondly, nitrogen groups were introduced via cyclization of PAN on mesoporous carbon nanofibers (mpCPAN). We compared the synergistic effects of all these features in cathode substrate and interlayer on the performance Li–Sulfur batteries and used various characterization tools to understand them. Our results revealed that coating CPAN on both mesoporous carbon cathode and interlayer greatly enhanced the rate capability and capacity retention, leading to the capacity of 1000 mAh/g at 2 C and 1200 mAh/g at 0.5 C with the capability retention of 88% after 100 cycles. The presence of nitrogen groups and mesopores in both cathodes and interlayers resulted in more effective polysulfide confinement and also show more promise for higher loading systems. 

   more » « less
4. Effects of Periodic Pore Ordering on Photocatalytic Hydrogen Generation with Mesoporous Semiconductor Oxides

   https://doi.org/10.1002/sstr.202200184  

   Weller, Tobias; Timm, Jana; Deilmann, Leonie; Doerr, Tobias S.; Greve, Christopher; Cherevan, Alexey S.; Beaucage, Peter A.; Wiesner, Ulrich B.; Herzig, Eva M.; Eder, Dominik; et al (October 2022, Small Structures)

   Crystalline and 3D continuous mesoporous quaternary CsTaWO₆semiconductors are prepared with different degrees of long‐range periodic order and local order, respectively, to investigate the influence of periodic pore order on the photocatalytic performance in hydrogen evolution of mesoporous photocatalysts. The degree of long‐range order of the mesopores is changed by modifying the ratio between metal precursors and soft polymer template poly(isoprene‐b‐styrene‐b‐ethylene oxide) (PI‐b‐PS‐b‐PEO; ISO) in the sol–gel synthesis. Long‐range periodic order is found to have no appreciable advantage compared with an only locally ordered continuous pore system. On the contrary, nonperiodically ordered mesopores result in higher activity toward photocatalytic hydrogen evolution, even with slightly smaller pore diameter and lower cumulative pore volume. Most importantly, it is shown that pore connectivity and heterogeneous pore systems in mesoporous photocatalysts play a major role for hydrogen evolution when other parameters are confirmed to be not rate limiting. 

   more » « less
5. Metal-catalyst-free access to multiwalled carbon nanotubes/silica nanocomposites (MWCNT/SiO ₂ ) from a single-source precursor

   https://doi.org/10.1039/C9DT01783F  

   Mera, Gabriela; Kroll, Peter; Ponomarev, Ilia; Chen, Jiewei; Morita, Koji; Liesegang, Moritz; Ionescu, Emanuel; Navrotsky, Alexandra (January 2019, Dalton Transactions)

   The present study introduces a facile single-source precursor preparative access to bamboo-like multiwalled carbon nanotubes (MWCNTs) highly dispersed within a mesoporous silica-rich matrix. The metal-free single-source precursor was synthesized via a one-pot sol–gel process using tetramethyl orthosilicate (TMOS) and 4,4′-dihydroxybiphenyl (DHBP) and converted subsequently via pyrolysis under an argon atmosphere into MWCNT/silica nanocomposites. The in situ segregation of the highly defective bamboo-like MWCNTs was carefully investigated and has been shown to occur within the mesopores of the silica-rich matrix at relatively low temperatures and without the use of a metal catalyst. The experimental results have been supported by extensive computational simulations, which correlate the molecular architecture of the single-source precursor with the structural features of the carbon phase segregating from the silica matrix. Furthermore, the role of hydrogen in the stability of the prepared nanocomposites as well as in the high-temperature evolution and morphology of the segregated MWCNTs has been discussed based on vibrational spectroscopy, calorimetric studies and empirical potential calculations. The results obtained within the present study may allow for designing highly-defined nanocarbon-containing composites with tailored structural features and property profiles. 

   more » « less