Graphene/Ionic liquid composite films and ion exchange.
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ABSTRACT:
SUBMITTER: Mo Y
PROVIDER: S-EPMC4073168 | biostudies-other | 2014
REPOSITORIES: biostudies-other
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Project description:In light of increasing interest in the development of organic-organic multicomponent heterostructures on metals, this molecular-scale study investigates prototypical composite systems of ultrathin porphyrin and ionic liquid (IL) films on metallic supports under well-defined ultrahigh vacuum conditions. By means of angle-resolved X-ray photoelectron spectroscopy, we investigated the adsorption, stability, and thermal exchange of the resulting films after sequential physical vapor deposition of the free-base porphyrin 5,10,15,20-tetraphenylporphyrin, 2H-TPP, and the IL 1-methyl-3-octylimidazolium hexafluorophosphate, [C8C1Im][PF6], on Ag(111) and Au(111). 2H-TPP shows two-dimensional growth of up to two closed molecular layers on Ag(111) and Au(111) and three-dimensional island growth for thicker films. IL films on top of a monolayer of 2H-TPP exhibit Stranski-Krastanov-like growth and are stable up to 385 K. The 2H-TPP layer leads to destabilization of the IL films, compared to the IL in direct contact with the bare metals, by inhibiting the specific adsorption of the ions on the metal surfaces. When the porphyrin is deposited on top of [C8C1Im][PF6] at low temperature, the 2H-TPP molecules adsorb on top of the IL film at first but replace the IL at the IL/metal interfaces upon heating above 240 K. This exchange process is most likely driven by the higher adsorption energy of 2H-TPP on Ag(111) and Au(111) surfaces, as compared to the IL. The behavior observed on Ag(111) and Au(111) is identical. The results are highly relevant for the stability of porphyrin/IL-based thin film catalyst systems and molecular devices, and more generally, stacked organic multilayer architectures.
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Project description:Selective separation of small molecules by membranes is inhibited by the performance gap between nanofiltration and ultrafiltration membranes. In this work, a membrane that can efficiently remove small molecules (> 300 Da) was created by incorporating graphene oxide quantum dots (GQDs) into a cellulose membrane using an ionic liquid (1-ethyl-3-methylimidazolium acetate). Incorporation of GQD into cellulose membranes using an ionic liquid brings several advantages over traditional mixed matrix membranes: 1) GQDs are abundant in peripheral hydroxyl and carboxyl groups, thus GQDs have strong binding with cellulose through hydrogen bonding and forms a stable composite membrane. 2) Negative surface charge of GQDs helps prevent aggregation. 3) The size (5 nm) of GQD is smaller than most nanoparticles used in membranes, allowing for interesting pore forming properties. GQD-cellulose membranes were prepared by non-solvent induced phase separation in water. It was determined that about 45% of GQDs are incorporated from solution to membrane. GQDs were determined to be located on the membrane surface, giving the membrane negative surface charge and improved hydrophilicity. GQDs showed no leaching after convective flow through the membrane. Impact of GQD on membrane permeability and rejection was studied through convective flow experiments, and through longer term permeability studies.
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Project description:This manuscript details a novel and simple approach to achieve surface-tethered co-poly(ionic liquid) (coPIL) films through the exchange of the resident anion of a poly(ionic liquid) (PIL) film with two or more anions. Initially, surface-tethered PIL films were prepared by the surface-initiated ring-opening metathesis polymerization of the ionic liquid monomer 3-[(bicyclo[2.2.1]hept-5-en-2-yl)methyl]-1,2-dimethylimidazol-3-ium hexafluorophosphate ([N1-dMIm][PF6]) whose PF6 - anion was easily interchanged with aqueous solutions containing a binary mixture of the PF6 - anion, along with perchlorate (ClO4 -) or bis(fluorosulfonyl)imide (FSI-) anions. The binary mole fraction of each anion in the film was determined from the infrared spectra of the coPIL films. The thermodynamically driven anion selectivity for exchange from the liquid phase into the coPIL films was determined to follow the order ClO4 - < PF6 - < FSI-. The aqueous wettability of p[N1-dMIm] coPIL films containing both the PF6 - and ClO4 - anions (p[N1-dMIm][PF6][ClO4]) was quantified by contact angle goniometry with the observation that the surface showed an enrichment in the ClO4 - anion compared to the average binary anion mole fraction of ClO4 - in the film (y ClO4 - ). The rate of ion transport through the p[N1-dMIm][PF6][ClO4] coPIL films, quantified by electrochemical impedance spectroscopy, linearly depends on the binary anion mole fraction of ClO4 - in solution (x ClO4 - ), enabling continuous tunability by over three orders of magnitude for ion conductivity in the coPIL films.
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Project description:Polymerized ionic liquids (PIL) are an interesting substance class, which is discussed to transfer the outstanding properties and tunability of ionic liquids into a solid material. In this study we extend our previous research on ammonium based PIL and discuss the influence of additives and their usability as polymer electrolyte membranes for lithium ion batteries. The polymer electrolyte is thereby used as replacement for the commercially widespread system of a separator that is soaked with liquid electrolyte. The influence of the material composition on the ionic conductivity (via electrochemical impedance spectroscopy) and the diffusion coefficients (via pulsed-field-gradient nuclear magnetic resonance spectroscopy) were studied and cell tests with adapted membrane materials were performed. High amounts of the additional ionic liquid (IL) MPPyrr-TFSI (1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide) increased the ionic conductivity of the materials up to 1.3·10-4 S·cm-1 but made the usage of a cross-linker necessary to obtain mechanically stable membranes. The application of liquid electrolyte mixtures with ethylene carbonate (EC) and MPPyrr-TFSI decreased ionic conductivity values down to the 10-9 S·cm-1 range, but increased 7Li diffusion coefficients with increasing amounts of EC up to 1.7·10-10 m2·s-1. Cell tests with two membrane mixtures proofed that it is possible to build electrolyte membranes on basis of the polymerized ionic liquids, but also showed that further research is necessary to ensure stable and efficient cell cycling.
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Project description:Thin ionic liquid (IL) films play an important role in many applications. To obtain a better understanding of the ion distribution within IL mixture films, we sequentially deposited ultrathin layers of two ILs with the same cation but different anions onto Ag(111), and monitored their dynamic behaviour by angle-resolved X-ray photoelectron spectroscopy. Upon depositing [C8 C1 Im][PF6 ] on top of a wetting layer of [C8 C1 Im][Tf2 N] at room temperature (RT), we found a pronounced enrichment of the [Tf2 N]- anions at the IL/vacuum interface, due to a rapid anion exchange at the IL/solid interface. In contrast, at 90?K, the [Tf2 N]- anions remain at the IL/solid interface. Upon heating, we observe a rearrangement of the cations between 140 and 160?K, such that the octyl chains preferentially point towards the vacuum. Above 170?K, the ions start to become mobile, and at 220?K, the anion exchange is completed, with the [Tf2 N]- anions enriched at the IL/vacuum interface in the same way as found for deposition at RT. The temperature range for the anion exchange corresponds well to glass transition temperatures reported in literature. We propose two driving forces to be cooperatively responsible for the replacement/exchange of [Tf2 N]- at the IL/solid interface and its enrichment at the IL/vacuum interface. First, the adsorption energy of [C8 C1 Im][PF6 ] is significantly larger than that of [C8 C1 Im][Tf2 N], and second, the surface tension of [C8 C1 Im][Tf2 N] is lower than that of [C8 C1 Im][PF6 ].
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Project description:One of the most critical challenges for commercialization of sodium-ion battery (SIB) is to develop carbon anodes with high capacity and good rate performance. Graphene would be an excellent SIB anode candidate due to its success in various kinds of batteries. Liquid-phase exfoliation (LPE) method is an inexpensive, facile and potentially scalable method to produce less-defected graphene sheets. In this work, we developed an improved, dispersant-assisted LPE method to produce graphene composite materials from raw graphite with high yield and better quality for SIB anode. Here, bacterial cellulose (BC) was used as a green dispersant/stabilizer for LPE, a "spacer" for anti-restacking, as well as a carbon precursor in the composite. As a result, the carbonized BC (CBC)/LPE graphene (LEGr) presented improved performance compared to composite with graphene prepared by Hummers method. It exhibited a specific capacity of 233 mAh g-1 at a current density of 20 mA g-1, and 157 mAh g-1 after 200 cycles at a high current density of 100 mA g-1 with capacity retention rate of 87.73%. This method not only provides new insight in graphene composites preparation, but also takes a new step in the exploration of anode materials for sodium-ion batteriesSIBs.
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Project description:Ionic liquid (IL) combined with 2D materials has evoked considerable attention in the field of lubrication applications because of their speical structure and outstanding lubrication properties. However, the ambiguous effect of the 2D materials on the friction and anti-wear properties of the IL needs futher study. Here, we have obtained two families of IL composite films with additives of MoS 2 and graphene via a combined process of spin-coated and curing, and the distinction of the effects of two additives on the tribological performance of the IL films was studied. The friction tests showed that the friction coefficient and anti-wear life of the IL films were greatly enhanced after the addition of MoS 2 or graphene, which could be attributed to the improved load-carrying capacity and the second lubrication phase. Under a low addition content, graphene had more advantages to reduce the friction of the films, and MoS 2 was more beneficial to the tribological properties with the additional content increased. The films with low friction and good anti-wear properties may be valuable for the rational design of lubrication films for the practical engineering applications.
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