Tuning the Pore Size in Gradient Poly(ionic liquid) Membranes by Small Organic Acids

Highly charged porous polymer membranes with adjustable pore size and gradient pore structure along the membrane cross-section were prepared by ammonia-triggered electrostatic complexation between an imidazolium-based cationic poly­(ionic liquid) (PIL) and multivalent benzoic acid derivatives. The PIL and the acid compound were first dissolved homogeneously in DMSO, cast into a thin film onto a glass plate, dried, and finally immersed into an aqueous ammonia solution. The diffusion of ammonia from the top to the bottom into the film neutralized the acid and introduced the gradient pore structure and in situ electrostatic cross-linking to fix the pores. The pore size and its distribution of the membranes were found controllable in terms of the multivalency of the acids, the imidazolium/carboxylate ratio, and the nature of the PIL counteranion

Poly(ionic liquid) Complex with Spontaneous Micro-/Mesoporosity: Template-Free Synthesis and Application as Catalyst Support

A facile, template-free synthetic route is reported toward poly­(ionic liquid) complexes (PILCs) which for the first time exhibit stable micro-/mesoporous structure. This is accomplished via <i>in situ</i> ionic complexation between imidazolium-based PILs and poly­(acrylic acid) in various alkaline organic solvents. The PILC can be highly loaded with copper salts and can be used as a catalytic support for effective aerobic oxidation of activated hydrocarbons under mild conditions

Thermodynamic Description of the LCST of Charged Thermoresponsive Copolymers

The dependence of the lower critical solution temperature (LCST) of charged, thermosensitive copolymers on their charge fraction and the salt concentration is investigated by employing systematic cloud-point experiments and analytical theory on a macroscopic thermodynamic level. The latter is based on the concept of the Donnan equilibrium incorporated into a thermodynamic expansion of a two-state free energy around a charge-neutral reference homopolymer and should be applicable for weakly charged (or highly salted) polymer systems. Very good agreement is found between the theoretical description and the experiments for aqueous solutions of the responsive copolymer poly­(NIPAM-<i>co</i>-EVImBr) for a wide range of salt concentrations and charge fractions up to 8%, using only two global, physical fitting parameters. Our model could be useful as a guide for the optimization of thermoresponsive copolymer architectures in the future design of soft, polymer-based materials

Enhanced Carbon Dioxide Adsorption by a Mesoporous Poly(ionic liquid)

The synthesis of a mesoporous poly­(ionic liquid) network via a hard-templating pathway is presented. Structure analysis was carried out using gas adsorption, small-angle X-ray scattering, and electron microscopy. The mesoporous poly­(ionic liquid) showed a significantly faster CO₂ adsorption than its nonporous counterpart. We found the adsorption is accompanied by strong interactions, which are also reflected in a high CO₂ over N₂ selectivity

Enhanced Generation of Reactive Oxygen Species via Piezoelectrics based on p–n Heterojunctions with Built-In Electric Field

Tuning the charge transfer processes through a built-in electric field is an effective way to accelerate the dynamics of electro- and photocatalytic reactions. However, the coupling of the built-in electric field of p–n heterojunctions and the microstrain-induced polarization on the impact of piezocatalysis has not been fully explored. Herein, we demonstrate the role of the built-in electric field of p-type BiOI/n-type BiVO4 heterojunctions in enhancing their piezocatalytic behaviors. The highly crystalline p–n heterojunction is synthesized by using a coprecipitation method under ambient aqueous conditions. Under ultrasonic irradiation in water exposed to air, the p–n heterojunctions exhibit significantly higher production rates of reactive species (·OH, ·O2–, and 1O2) as compared to isolated BiVO4 and BiOI. Also, the piezocatalytic rate of H2O2 production with the BiOI/BiVO4 heterojunction reaches 480 μmol g–1 h–1, which is 1.6- and 12-fold higher than those of BiVO4 and BiOI, respectively. Furthermore, the p–n heterojunction maintains a highly stable H2O2 production rate under ultrasonic irradiation for up to 5 h. The results from the experiments and equation-driven simulations of the strain and piezoelectric potential distributions indicate that the piezocatalytic reactivity of the p–n heterojunction resulted from the polarization intensity induced by periodic ultrasound, which is enhanced by the built-in electric field of the p–n heterojunctions. This study provides new insights into the design of piezocatalysts and opens up new prospects for applications in medicine, environmental remediation, and sonochemical sensors

Lightweight, Room-Temperature CO₂ Gas Sensor Based on Rare-Earth Metal-Free CompositesAn Impedance Study

We report a light, flexible, and low-power poly­(ionic liquid)/alumina composite CO₂ sensor. We monitor the direct-current resistance changes as a function of CO₂ concentration and relative humidity and demonstrate fast and reversible sensing kinetics. Moreover, on the basis of the alternating-current impedance measurements we propose a sensing mechanism related to proton conduction and gas diffusion. The findings presented herein will promote the development of organic/inorganic composite CO₂ gas sensors. In the future, such sensors will be useful for numerous practical applications ranging from indoor air quality control to the monitoring of manufacturing processes

Thiazolium Poly(ionic liquid)s: Synthesis and Application as Binder for Lithium-Ion Batteries

We report a synthetic route to thiazolium-type poly­(ionic liquid)­s (PILs), which can be applied as a polymeric binder in lithium-ion batteries. The ionic liquid monomers were first synthesized by quaternization reaction of 4-methyl-5-vinyl thiazole with methyl iodide, followed by anion exchange reactions to replace iodide by fluorinated anions to access a liquid state below 100 °C. Subsequently, these monomers bearing thiazolium cations in their structure underwent radical polymerizations in bulk to produce corresponding polymers. The dependence of solution and thermal properties of such monomeric and polymeric materials on the choice of the counteranion was investigated. Finally, the thiazolium-type PIL bearing a bis­(trifluoromethanesulfonyl)­imide (TFSI) anion was proven to be a high performance binder for lithium-ion battery electrodes

Smart Hydrogen Atoms in Heterocyclic Cations of 1,2,4-Triazolium-Type Poly(ionic liquid)s

ConspectusDiscovering and constructing molecular functionality platforms for materials chemistry innovation has been a persistent target in the fields of chemistry, materials, and engineering. Around this task, basic scientific questions can be asked, novel functional materials can be synthesized, and efficient system functionality can be established. Poly(ionic liquid)s (PILs) have attracted growing interest far beyond polymer science and are now considered an interdisciplinary crossing point between multiple research areas due to their designable chemical structure, intriguing physicochemical properties, and broad and diverse applications. Recently, we discovered that 1,2,4-triazolium-type PILs show enhanced performance profiles, which are due to stronger and more abundant supramolecular interactions ranging from hydrogen bonding to metal coordination, when compared with structurally similar imidazolium counterparts. This phenomenon in our view can be related to the smart hydrogen atoms (SHAs), that is, any proton that binds to the carbon in the N-heterocyclic cations of 1,2,4-triazolium-type PILs. The replacement of one carbon by an electron-withdrawing nitrogen atom in the broadly studied heterocyclic imidazolium ring will further polarize the C–H bond (especially for C5–H) of the resultant 1,2,4-triazolium cation and establish new chemical tools for materials design. For instance, the H-bond-donating strength of the SHA, as well as its Bro̷nsted acidity, is increased. Furthermore, polycarbene complexes can be readily formed even in the presence of weak or medium bases, which is by contrast rather challenging for imidazolium-type PILs. The combination of SHAs with the intrinsic features of heterocyclic cation-functionalized PILs (e.g., N-coordination capability and polymeric multibinding effects) enables new phenomena and therefore innovative materials applications.In this Account, recent progress on SHAs is presented. SHA-related applications in several research branches are highlighted together with the corresponding materials design at size scales ranging from nano- to micro- and macroscopic levels. At a nanoscopic level, it is possible to manipulate the interior and outer shapes and surface properties of PIL nanocolloids by adjusting the hydrogen bonds (H-bonds) between SHAs and water. Owing to the interplay of polycarbene structure, N-coordination, and the polymer multidentate binding of 1,2,4-triazolium-type PILs, metal clusters with controllable size at sub-nanometer scale were successfully synthesized and stabilized, which exhibited record-high catalytic performance in H2 generation via methanolysis of ammonia borane. At the microscopic level, SHAs are found to efficiently catalyze single crystal formation of structurally complex organics. Free protons in situ released from the SHAs serve as organocatalysts to activate formation of C–N bonds at room temperature in a series of imine-linked crystalline porous organics, such as organic cages, macrocycles and covalent organic frameworks; meanwhile the concurrent “salting-out” effect of PILs as polymers in solution accelerated the crystallization rate of product molecules by at least 1 order of magnitude. At the macroscopic scale, by finely regulating the supramolecular interactions of SHAs, a series of functional supramolecular porous polyelectrolyte membranes (SPPMs) with switchable pores and gradient cross-sectional structures were manufactured. These membranes demonstrate impressive figures of merit, ranging from chiral separation and proton recognition to switchable optical properties and real-time chemical reaction monitoring. Although the concept of SHAs is in the incipient stage of development, our successful examples of applications portend bright prospects for materials chemistry innovation

Polyelectrolyte as Solvent and Reaction Medium

A poly­(ionic liquid) with a rather low glass transition temperature of −57°C was synthesized via free radical polymerization of an acrylate-type ionic liquid monomer. It exhibits fluidic behavior in a wide temperature range from room temperature to the threshold of the thermal decomposition. We demonstrate that it could act as a unique type of macromolecular solvent to dissolve various compounds and polymers and separate substances. In addition, this poly­electrolyte could serve successfully as reaction medium for catalysis and colloid particle synthesis. The synergy in the solvation and stabilization properties is a striking character of this polymer to downsize the <i>in situ</i> generated particles

Iron Nitride and Carbide: from Crystalline Nanoparticles to Stable Aqueous Dispersions

Iron nitride and carbide nanoparticles were synthesized using iron oxide particles as template. They were furthermore dispersed in aqueous solution via stabilization with a poly­(ionic liquid). They provide a great potential combining a high saturation magnetization with low toxicity compared to the iron based compounds that are currently used in several applications such as cell-sorting and hyperthermia or as contrast enhancers for magnetic resonance imaging. We here present a sustainable and green procedure to synthesize iron nitride and carbide by resorting to the variety of iron oxide template nanoparticles. In this way the shape and the size can be precisely controlled and tuned within the nanometer range. During calcination, urea enables to control the composition of the product material, whereas a biopolymer agar protects the particles from agglomeration. We dispersed the particles in water by using poly­(1-ethyl-3-vinylimidazolium bromide) as stabilizing agent. Magnetic measurements of the converted particles show that particles with a diameter of 18 nm are located at the border of superparamagnetic and ferromagnetic behavior. As expected after conversion the saturation magnetization of the particles was notably increased. The herein presented synthetic approach can be applied to other metals and has thus the potential to be important for the synthesis of nitrides and carbides in general