Polymer solubility in ionic liquids: dominated by hydrogen bonding

Deep dewatering of sludge and resource recovery of hydroxyapatite: A recyclable approach via ionic liquid biphasic system and hydrogen bonds reformation

Deep dewatering of Waste Activated Sludge (WAS) through mechanical processes remains inefficient, primarily due to the formation of a stable hydrogen bonding network between the biopolymers and water, which consequently leads to significant water trapped by Extracellular Polymeric Substances (EPS). In this study, a novel and recyclable treatment for WAS based on Ionic Liquids (ILs) was established, named IL-biphasic aqueous system (IL-ABS) treatment. Specifically, the IL-ABS formed in WAS facilitated rapid and efficient in-situ deep dewatering while concurrently recovering hydroxyapatite. The water content decreased from an initial 98.27 % to 65.35 % with IL-ABS, formed by 1-Butyl-3-methylimidazolium bromide (BmimBr) and K3PO4 synthesized from waste H3PO4. Moreover, the recycled BmimBr maintaining the water content of the dewatered sludge consistently between 65.61 % and 67.25 % across five cycles, exhibited remarkable reproducibility. Through three-dimensional excitation-emission matrix, lactate dehydrogenase analyses and confocal laser scanning microscopy, the high concentration of BmimBr in the upper phase effectively disrupted the cells and EPS, which exposed protein and polysaccharide on the EPS surface. Subsequently, the K3PO4 in the lower phase led to an enhanced salting-out effect in WAS. Furthermore, FT-IR analysis revealed that K3PO4 disrupted the original hydrogen bonds between EPS and water. Then, BmimBr formed numerous hydrogen bonds with the sludge flocs, leading to deep dewatering and agglomeration of the sludge flocs during the unique phase separation process of IL-ABS. Notably, sludge-derived hydroxyapatite product exhibited remarkable adsorption capacity for prevalent heavy metal contaminants such as Pb2+, Cd2+ and Cu2+, with efficiencies comparable to those of commercial hydroxyapatite, thereby achieving the resource utilization of waste H3PO4. Moreover, economic calculations demonstrated the suitability of this novel treatment. This innovative treatment exhibits potential for practical applications in the non-mechanical deep dewatering of WAS.

Polymer solubility mechanism in ionic liquids: 1H-NMR spectra and two-parameter hydrogen bonding analysis

Understanding the polymer solubility in ionic liquids (ILs) is important for polymer processing or polymeric material preparation. Previously, two-parameter H-bonding analysis has been proposed to clarify that polymer solubility in ILs is dominated by H-bonding interactions (Y. F. Yuan et al., Phys. Chem. Chem. Phys., 2021, 23, 21893-21900). In the present work, 1H-NMR spectra are adopted to characterize the H-bonding interactions between polymers and ILs, which provide a microscopic relation between polymer solubility and two-parameter H-bonding analysis.

Dilute polyelectrolyte solutions: recent progress and open questions

Polyelectrolytes are a class of polymers possessing ionic groups on their repeating units. Since counterions can dissociate from the polymer backbone, polyelectrolyte chains are strongly influenced by electrostatic interactions. As a result, the physical properties of polyelectrolyte solutions are significantly different from those of electrically neutral polymers. The aim of this article is to highlight key results and some outstanding questions in the polyelectrolyte research from recent literature. We focus on the influence of electrostatics on conformational and hydrodynamic properties of polyelectrolyte chains. A compilation of experimental results from the literature reveals significant disparities with theoretical predictions. We also discuss a new class of polyelectrolytes called poly(ionic liquid)s that exhibit unique physical properties in comparison to ordinary polyelectrolytes. We conclude this review by listing some key research challenges in order to fully understand the conformation and dynamics of polyelectrolytes in solutions.

Solvent Effects on the 1 H-NMR Chemical Shifts of Imidazolium-Based Ionic Liquids

The 1 H nuclear magnetic resonance (1 H-NMR) spectrum is a useful tool for characterizing the hydrogen bonding (H-bonding) interactions in ionic liquids (ILs). As the main hydrogen bond (H-bond) donor of imidazolium-based ILs, the chemical shift (δH2 ) of the proton in the 2-position of the imidazolium ring (H2) exhibits significant and complex solvents, concentrations and anions dependence. In the present work, based on the dielectric constants (ϵ) and Kamlet-Taft (KT) parameters of solvents, we identified that the δH2 are dominated by the solvents polarity and the competitive H-bonding interactions between cations and anions or solvents. Besides, the solvents effects on δH2 are understood by the structure of ILs in solvents: 1) In diluted solutions of inoizable solvents, ILs exist as free ions and the cations will form H-bond with solvents, resulting in δH2 being independent with anions but positively correlated with βS . 2) In diluted solutions of non-ionzable solvents, ILs exist as contact ion-pairs (CIPs) and H2 will form H-bond with anions. Since non-ionizable solvents hardly influence the H-bonding interactions between H2 and anions, the δH2 are not related to βS but positively correlated with βIL .

Ionic-Liquid-Mediated Deconstruction of Polymers for Advanced Recycling and Upcycling

Ionic liquids (ILs) are a promising medium to assist in the advanced (chemical and biological) recycling of polymers, owing to their tunable catalytic activity, tailorable chemical functionality, low vapor pressures, and thermal stability. These unique physicochemical properties, combined with ILs' capacity to solubilize plastics waste and biopolymers, offer routes to deconstruct polymers at reduced temperatures (and lower energy inputs) versus conventional bulk and solvent-based methods, while also minimizing unwanted side reactions. In this Viewpoint, we discuss the use of ILs as catalysts and mediators in advanced recycling, with an emphasis on chemical recycling, by examining the interplay between IL chemistry and deconstruction thermodynamics, deconstruction kinetics, IL recovery, and product recovery. We also consider several potential environmental benefits and concerns associated with employing ILs for advanced recycling over bulk- or solvent-mediated deconstruction techniques, such as reduced chemical escape by volatilization, decreased energy demands, toxicity, and environmental persistence. By analyzing IL-mediated polymer deconstruction across a breadth of macromolecular systems, we identify recent innovations, current challenges, and future opportunities in IL application toward circular polymer economies.

Self-aggregation, H-bonding, and photoresponse in film and solution states of azobenzene containing polyurea

We critically understand the hydrogen bonding interactions and electronic transitions occurring in a thin film as well as in solution of a photo-responsive polymer, azo-polyurea (azo-PU). We synthesize azo-PU by covalent attachment of the azobenzene chromophore to the main chain of polyurea. Azo-PU shows reversible photoisomerization between trans and cis states upon light exposure, the occurrence of which is typically analysed using the π-π* and n-π* electronic transition peaks in the UV-visible absorption spectrum. We find that the π-π* and n-π* bands undergo a redshift and blueshift respectively on dissolving azo-PU in DMF solvent, resulting in a single overlapped peak in the spectrum. However, upon UV irradiation, these bands split into two independent transitions that are characteristic of azo-PU solid films. These observations are explained based on the changes in polymer-polymer and polymer-solvent interactions through hydrogen bonding and self-aggregation tendency. The experimental findings are corroborated using DFT simulations which provide useful insights into electronic orbital transitions, electron distribution, and hydrogen bonding interaction through IR vibrational modes.

Molecular simulation of enhanced separation of humid air components using GO-PVA nanocomposite membranes under differential pressures

Hydrophilic nanocomposite membranes have significant advantages in the separation of water vapor which is the core process in air dehumidification. This paper focuses on exploring the micro-mechanism of enhanced separation using graphene oxide-polyvinyl alcohol (GO-PVA) nanocomposite membranes. The sorption and diffusion behaviors of water vapor and nitrogen in GO-PVA membranes were investigated using molecular dynamics (MD) and Monte Carlo (MC) methods. The study showed that embedding GO into a PVA matrix results in a higher glass transition temperature and fractional free volume. The latter is believed to enhance the diffusivity of gas molecules in polymeric membranes. The interaction between the polymer chains and GO nanoparticles notably promotes the adsorption capacity of water vapor and inhibits nitrogen adsorption in the membrane. A water vapor permeance of 8844.07 Barrer and a separation factor of 3.53 could be achieved with the GO-PVA-0.5 membrane. The analysis confirmed that GO has the same effect on single gas and binary gas mixtures, i.e., increasing the water vapor permeability and selectivity. The calculated water vapor permeance of binary gas is 83% lower than that of single gas permeation. It is expected that this research could provide fundamentals for the optimization and synthesis of gas separation membranes.

Ammonium-, phosphonium- and sulfonium-based 2-cyanopyrrolidine ionic liquids for carbon dioxide fixation

The development of carbon dioxide (CO₂) scavengers is an acute problem nowadays because of the global warming problem. Many groups around the globe intensively develop new greenhouse gas scavengers. Room-temperature ionic liquids (RTILs) are seen as a proper starting point to synthesize more environmentally friendly and high-performance sorbents. Aprotic heterocyclic anions (AHA) represent excellent agents for carbon capture and storage technologies. In the present work, we investigate RTILs in which both the weakly coordinating cation and AHA bind CO₂. The ammonium-, phosphonium-, and sulfonium-based 2-cyanopyrrolidines were investigated using the state-of-the-art method to describe the thermochemistry of the CO₂ fixation reactions. The infrared spectra and electronic and structural properties were simulated at the hybrid density functional level of theory to characterize the reactants and products of the chemisorption reactions. We conclude that the proposed CO₂ capturing mechanism is thermodynamically allowed and discuss the difference between different families of RTILs. Quite unusually, the intramolecular electrostatic attraction plays an essential role in stabilizing the zwitterionic products of the CO₂ chemisorption. The difference in chemisorption performance between the families of RTILs is linked to sterical hindrances and nucleophilicities of the α- and β-carbon atoms of the aprotic cations. Our results rationalize previous experimental CO₂ sorption measurements (Brennecke et al., 2021).