Intermolecular Interaction-Induced Hierarchical Transformation in 1D Nanohybrids: Analysis of Conformational Changes by 2D Correlation Spectroscopy

We have examined both self-assembly and confinement effect in room-temperature ionic liquid (RTIL)-aluminum hydroxide hybrids (RAHs) to attain a fundamental understanding of special phenomena in nanoscale spaces as well as to design functional nanomaterials for practical applications. Phase-controlled one-dimensional (1D) RAHs were synthesized through a simple ionothermal process. The RAHs were hierarchically transformed in terms of the molecular structures, morphologies, and phases of the materials during the ionothermal process with respect to the concentration of RTIL. In addition to the hierarchical transformation, the RTIL/aluminum hydroxide nanohybrids revealed unexpected physical behaviors, including thermal transition variation of the RTIL in confined environments and a phase transition from nanosolid to nanoliquid affected by changes of the melting points. More importantly, intermolecular interaction induced-self-assembly and confinement effect of RTILs inside an integrated hybrid system, which have not been clearly explained to date, were analyzed by 2D infrared correlation spectroscopy (2D IR COS); dynamic behaviors of RTILs, i.e., sequentially spatial reorientation and kinetically conformational changes, were attributed to the interactions between RTILs and aluminum hydroxides. 2D IR COS offers a new way to interpret highly complex, veiled systems such as the formation mechanism of nanoparticles, biomineralization, self/supramolecular assembly, and nanoconfinement

Facilitated Ion Transport in All-Solid-State Flexible Supercapacitors

The realization of highly flexible and all-solid-state energy-storage devices strongly depends on both the electrical properties and mechanical integrity of the constitutive materials and the controlled assembly of electrode and solid electrolyte. Herein we report the preparation of all-solid-state flexible supercapacitors (SCs) through the easy assembly of functionalized reduced graphene oxide (f-RGO) thin films (as electrode) and solvent-cast Nafion electrolyte membranes (as electrolyte and separator). In particular, the f-RGO-based SCs (f-RGO-SCs) showed a 2-fold higher specific capacitance (118.5 F/g at 1 A/g) and rate capability (90% retention at 30 A/g) compared to those of all-solid-state graphene SCs (62.3 F/g at 1A/g and 48% retention at 30 A/g). As proven by the 4-fold faster relaxation of the f-RGO-SCs than that of the RGO-SCs and more capacitive behavior of the former at the low-frequency region, these results were attributed to the facilitated ionic transport at the electrical double layer by means of the interfacial engineering of RGO by Nafion. Moreover, the superiority of all-solid-state flexible f-RGO-SCs was demonstrated by the good performance durability under the 1000 cycles of charging and discharging due to the mechanical integrity as a consequence of the interconnected networking structures. Therefore, this research provides new insight into the rational design and fabrication of all-solid-state flexible energy-storage devices as well as the fundamental understanding of ion and charge transport at the interface

Interfacial Interactions of Single-Walled Carbon Nanotube/Conjugated Block Copolymer Hybrids for Flexible Transparent Conductive Films

Nanohybrids consisting of single-walled carbon nanotubes (SWCNTs) and a conductive block copolymer, perchlorate-doped poly­(3,4-ethylenedioxythiophene)-<i>block</i>-poly­(ethyleneoxide) (P-PEDOT-<i>b</i>-PEO), were successfully prepared. Individual exfoliation of SWCNTs and high solution processability were simultaneously achieved in the supramolecular assembly. The assembly at the molecular level was driven by the interfacial interaction between SWCNT walls and the PEDOT block, as characterized by various spectroscopic analyses (UV–Vis, FT-IR, PL, and Raman). The exfoliation of SWCNTs and the solubility of the nanohybrids, which are facilitated by the soluble PEO block, were confirmed by Raman spectroscopy and a range of other microscopy techniques (AFM, TEM, and SEM). Flexible transparent conductive films of the nanohybrids were fabricated using a vacuum-assisted filtration method. The films displayed high electrical conductivity with good mechanical integrity due to the strong interaction between the SWCNT and the conductive polymer. The strategy described here opens up promising possibilities for the fabrication of CNT/conjugated polymer hybrids as well as for their use in flexible electronics

Analysis of the CO₂ and NH₃ Reaction in an Aqueous Solution by 2D IR COS: Formation of Bicarbonate and Carbamate

The two-dimensional (2D) infrared correlation spectra obtained from the reaction time- and concentration-dependent IR spectra elucidates the reaction of CO2 and NH3 in an aqueous solution for CO2 absorption. In the synchronous 2D correlation spectra, the interrelation of the proton with carbamate and bicarbonate indicates that the pH level affected the formation reactions of the two products. Furthermore, the interrelation of carbamate with bicarbonate confirmed the conversion of carbamate into bicarbonate with the release of protons (or the decrease of the pH). From the experimental results including the asynchronous 2D correlation spectra, the reaction of the CO2 and aqueous ammonia proceeded through the following steps: formation of carbamate, formation of bicarbonate, release of protons, and conversion of carbamate into bicarbonate. The analysis of the formation of carbamate and bicarbonate by 2D infrared correlation spectroscopy provides useful information on the reaction mechanism of CO2 and NH3 in aqueous solutions

Facile Route to Synthesize Large-Mesoporous γ-Alumina by Room Temperature Ionic Liquids

A large mesoporous γ-alumina was fabricated through a thermal process without postaddition of molecular or organic solvents at ambient pressure in an open container by using the dual functions of 1-hexadecyl-3-methylimidazolium chloride (C16MimCl) as room-temperature ionic liquids (RTILs), i.e., templating and cosolvent functions. In this synthesis, a thermal process with the assistance of RTILs was the key technology for induction of the nanostructure of aluminum hydroxide and transformation to boehmite crystallites by means of intermolecular interaction. Both C16MimCl/boehmite hybrid and γ-alumina displayed the nanostructure consisting of randomly debundled nanofibers embedded in wormlike porous networks. Nanofibers of C16MimCl/boehmite hybrid and γ-alumina exhibited a length of ca. 40−60 nm and a diameter of ca. 1.5−3 nm. In particular, γ-alumina had good thermal stability and reasonable acidic sites. After conversion from boehmite crystallites into γ-phase by calcination, this nanostructured γ-alumina obtained the largest surface area and pore volume among large mesoporous γ-aluminas around 10 nm pore size, i.e., 470 m2 g-1 in surface area, 1.46 cm3 g-1 in pore volume, and 9.9 nm in pore size by calcination at 550 °C. Therefore, this synthetic method is a facile way to synthesize various nanostructured inorganic materials with the enhanced physical properties

3D Macroporous Graphene Frameworks for Supercapacitors with High Energy and Power Densities

In order to develop energy storage devices with high power and energy densities, electrodes should hold well-defined pathways for efficient ionic and electronic transport. Herein, we demonstrate high-performance supercapacitors by building a three-dimensional (3D) macroporous structure that consists of chemically modified graphene (CMG). These 3D macroporous electrodes, namely, embossed-CMG (e-CMG) films, were fabricated by using polystyrene colloidal particles as a sacrificial template. Furthermore, for further capacitance boost, a thin layer of MnO₂ was additionally deposited onto e-CMG. The porous graphene structure with a large surface area facilitates fast ionic transport within the electrode while preserving decent electronic conductivity and thus endows MnO₂/e-CMG composite electrodes with excellent electrochemical properties such as a specific capacitance of 389 F/g at 1 A/g and 97.7% capacitance retention upon a current increase to 35 A/g. Moreover, when the MnO₂/e-CMG composite electrode was asymmetrically assembled with an e-CMG electrode, the assembled full cell shows remarkable cell performance: energy density of 44 Wh/kg, power density of 25 kW/kg, and excellent cycle life

Antisolvent Precipitation of Potassium Bicarbonate from KHCO₃ + H₂O + Ethanol/2-Propanol Systems in the CO₂ Capture Process

For the energy-saving hot carbonate process, which contains a crystallization step, the antisolvent precipitation of potassium bicarbonate was investigated by adding ethanol and 2-propanol in a simulated effluent solution of CO₂ absorption column. The feasibility of using the antisolvent was verified with the equilibrium data of ternary systems and a KHCO₃ recovery. The ternary systems of KHCO₃ + H₂O + ethanol/2-propanol were equilibrated with varying amounts of alcohols at a preset temperature, and the equilibrium concentrations were determined using the cloud point method. In the ethanol system, a homogeneous and a solid–liquid phase were observed, whereas in the 2-propanol system, a liquid–liquid phase as well as the homogeneous and solid–liquid phases were observed. The equilibrium data were correlated with a local concentration parameter in the range of the antisolvent. From the correlation, the amount of antisolvent that has an effect equivalent to a cooling-only method and the optimum concentration of the antisolvent were evaluated. An addition of 17 wt % of ethanol and 57 wt % of 2-propanol had an effect equivalent to cooling the solution from 333 K to 303 K. The optimum concentrations of the ethanol system and the 2-propanol system were found to range from 32.93 wt % to 60.07 wt % and from 6.24 wt % to 17.88 wt %, respectively, and the bicarbonate recovery yield was almost doubled when the optimum concentration of the antisolvent was applied. Considering the antisolvent concentration that has an effect equivalent to cooling crystallization and the optimum concentration of the antisolvent, ethanol was found to be a more feasible antisolvent than 2-propanol

Innovative Polymer Nanocomposite Electrolytes: Nanoscale Manipulation of Ion Channels by Functionalized Graphenes

The chemistry and structure of ion channels within the polymer electrolytes are of prime importance for studying the transport properties of electrolytes as well as for developing high-performance electrochemical devices. Despite intensive efforts on the synthesis of polymer electrolytes, few studies have demonstrated enhanced target ion conduction while suppressing unfavorable ion or mass transport because the undesirable transport occurs through an identical pathway. Herein, we report an innovative, chemical strategy for the synthesis of polymer electrolytes whose ion-conducting channels are physically and chemically modulated by the ionic (not electronic) conductive, functionalized graphenes and for a fundamental understanding of ion and mass transport occurring in nanoscale ionic clusters. The functionalized graphenes controlled the state of water by means of nanoscale manipulation of the physical geometry and chemical functionality of ionic channels. Furthermore, the confinement of bound water within the reorganized nanochannels of composite membranes was confirmed by the enhanced proton conductivity at high temperature and the low activation energy for ionic conduction through a Grotthus-type mechanism. The selectively facilitated transport behavior of composite membranes such as high proton conductivity and low methanol crossover was attributed to the confined bound water, resulting in high-performance fuel cells

Mesoporous Melamine Resins by Soft Templating of Block-co-Polymer Mesophases

Mesoporous melamine resins have been prepared using hexamethoxymethyl melamine (HMMM) as monomer and block-co-polymer Pluronic F127 as template. At acidic conditions, HMMM condenses into melamine resins, replicating the mesophases formed by the block-co-polymer template. The template can be removed by solvent extraction, yielding mesoporous melamine resins with surface areas of up to 258 m2/g and pore diameters of 7.8 nm. At a HMMM/F127 weight ratio of 1:1 an ordered mesoporous melamine resin is observed exhibiting a 2d hexagonal arrangement of cylindrical pores. The simplicity of the synthesis of these mesoporous films allows the large scale production of the materials, for example, in the form of free-standing films

Influence of Additives Including Amine and Hydroxyl Groups on Aqueous Ammonia Absorbent for CO₂ Capture

Aqueous ammonia absorbent (10 wt %) was modified with four kinds of additives (1 wt %) including amine and hydroxyl groups, i.e., 2-amino-2-methyl-1-propanol (AMP), 2-amino-2-methyl-1,3-propandiol (AMPD), 2-amino-2-ethyl-1,3-propandiol (AEPD), and tri(hydroxymethyl) aminomethane (THAM), for CO2 capture. The loss of ammonia by vaporization was reduced by additives, whereas the removal efficiency of CO2 was slightly improved. These results were attributed to the interactions between ammonia and additives or absorbents and CO2 via hydrogen bonding, as verified by FT-IR spectra and computational calculation. Molecular structures as well as binding energies were obtained from the geometries of (ammonia + additives) and (ammonia + additives + CO2) at the optimized state. These experimental and theoretical findings demonstrate that additives including amine and hydroxyl group are suitable for modifying aqueous ammonia absorbent for CO2 removal