Quantum Mechanical and Molecular Dynamics Simulations of Dual-Amino-Acid Ionic Liquids for CO₂ Capture

Global warming is occurring because of emission of greenhouse gases due to human activities. Capture of CO₂ from fossil-fuel industries and absorption of CO₂ for natural gas sweetening are crucial industrial tasks to address the threat from greenhouse gases. Amino acid ionic liquids (AAILs) are used for reversible CO₂ capture. In this study, the effect of CO₂ chemisorption on tetramethylammonium glycinate ([N₁₁₁₁]­[GLY]), tetrabutylammonium glycinate ([N₄₄₄₄]­[GLY]), and 1,1,1-trimethylhydrazinium glycinate ([aN₁₁₁]­[GLY]) were analyzed using density functional theory (DFT) and molecular dynamics (MD) studies. Density functional theory studies predicted different reaction pathways for CO₂ absorption on [GLY]⁻ and [aN₁₁₁]⁺. The activation energy barriers for CO₂ absorption on [GLY]⁻ and [aN₁₁₁]⁺ are 52.43 and 64.40 kJ/mol, respectively. The MD results were useful for mimicking the reaction mechanism for CO₂ absorption on AAILs and its effect on physical properties such as the fractional free volume, diffusion coefficient, and hydrogen bonding. Dry and wet conditions were compared to identify factors contributing to CO₂ solubility and selectivity at room temperature and elevated temperature. Hydrogen bonding between ion pairs was used to understand the increase in viscosity after CO₂ absorption. The MD studies revealed that glycinate and related products after CO₂ absorption contribute the most to the increase in viscosity

Effect of Surface Modification of Polyamide-Based Reverse Osmosis Membranes by Glycerol Monoacrylate–Butyl Acrylate Copolymers on Antifouling

Suppression of membrane fouling is essential for making reverse osmosis (RO) membrane systems more economical. In the present study, we synthesized polymers bearing a glycerol monoacrylate moiety as an antifouling unit and a butyl acrylate moiety as a membrane-adsorbing unit. We modified RO membranes by immersion in solutions of the synthesized copolymers as a simple antifouling method. We evaluated the membrane antifouling performance by assessing its permeability to bovine serum albumin as a foulant. Compared with the pristine membrane, the copolymer-modified RO membrane had a higher normalized water permeability and longer water retention (24 h). This enhancement was attributed to the hydrophilicity of the glycerol monoacrylate moiety, membrane modification by the butyl acrylate moiety, and the formation of intermediate water with a small quantity of nonfreezing water in the polymer, as determined by differential scanning calorimetry

Tailoring the Affinity of Organosilica Membranes by Introducing Polarizable Ethenylene Bridges and Aqueous Ozone Modification

Bis­(triethoxysilyl)­ethylene (BTESEthy) was used as a novel precursor to develop a microporous organosilica membrane via the sol–gel technique. Water sorption measurements confirmed that ethenylene-bridged BTESEthy networks had a higher affinity for water than that of ethane-bridged organosilica materials. High permeance of CO₂ with high CO₂/N₂ selectivity was explained relative to the strong CO₂ adsorption on the network with π-bond electrons. The introduction of polarizable and rigid ethenylene bridges in the network structure led to improved water permeability and high NaCl rejection (>98.5%) in reverse osmosis (RO). Moreover, the aqueous ozone modification promoted significant improvement in the water permeability of the membrane. After 60 min of ozone exposure, the water permeability reached 1.1 × 10^–12 m³/(m² s Pa), which is close to that of a commercial seawater RO membrane. Meanwhile, molecular weight cutoff measurements indicated a gradual increase in the effective pore size with ozone modification, which may present new options for fine-tuning of membrane pore sizes

Adsorption of Bovine Serum Albumin on Poly(vinylidene fluoride) Surfaces in the Presence of Ions: A Molecular Dynamics Simulation

Adsorption of bovine serum albumin (BSA) on poly­(vinylidene fluoride) (PVDF) surfaces in an aqueous environment was investigated in the presence and absence of excess ions using molecular dynamics simulations. The adsorption process involved diffusion of protein to the surface and dehydration of surface–protein interactions, followed by adsorption and denaturation. Although adsorption of BSA on PVDF surface was observed in the absence of excess ions, denaturation of BSA was not observed during the simulation (1 μs). Basic and acidic amino acids of BSA were found to be directly interacting with PVDF surface. Simulation in a 0.1 M NaCl solution showed delayed adsorption of BSA on PVDF surfaces in the presence of excess ions, with BSA not observed in close proximity to PVDF surface within 700 ns. Adsorption of Cl^– on PVDF surface increased its negative charge, which repelled negatively charged BSA, thereby delaying the adsorption process. These results will be helpful for understanding membrane fouling phenomena in polymeric membranes, and fundamental advancements in these areas will lead to a new generation of membrane materials with improved antifouling properties and reduced energy demands

Preparation of Microfiltration Hollow Fiber Membranes from Cellulose Triacetate by Thermally Induced Phase Separation

For the first time, self-standing microfiltration (MF) hollow fiber membranes were prepared from cellulose triacetate (CTA) via the thermally induced phase separation (TIPS) method. The resultant membranes were compared with counterparts prepared from cellulose diacetate (CDA) and cellulose acetate propionate (CAP). Extensive solvent screening by considering the Hansen solubility parameters of the polymer and solvent, the polymer’s solubility at high temperature, solidification of the polymer solution at low temperature, viscosity, and processability of the polymeric solution, is the most challenging issue for cellulose membrane preparation. Different phase separation mechanisms were identified for CTA, CDA, and CAP polymer solutions prepared using the screened solvents for membrane preparation. CTA solutions in binary organic solvents possessed the appropriate properties for membrane preparation via liquid–liquid phase separation, followed by a solid–liquid phase separation (polymer crystallization) mechanism. For the prepared CTA hollow fiber membranes, the maximum stress was 3–5 times higher than those of the CDA and CAP membranes. The temperature gap between the cloud point and crystallization onset in the polymer solution plays a crucial role in membrane formation. All of the CTA, CDA, and CAP membranes had a very porous bulk structure with a pore size of ∼100 nm or larger, as well as pores several hundred nanometers in size at the inner surface. Using an air gap distance of 0 mm, the appropriate organic solvents mixed in an optimized ratio, and a solvent for cellulose derivatives as the quench bath media, it was possible to obtain a CTA MF hollow fiber membrane with high pure water permeance and notably high rejection of 100 nm silica nanoparticles. It is expected that these membranes can play a great role in pharmaceutical separation

Comparison of Fouling Behavior in Cellulose Triacetate Membranes Applied in Forward and Reverse Osmosis

Membrane fouling is inevitable during the membrane separation process. The difference in the driving force of reverse osmosis (RO) and forward osmosis (FO) affects the behavior of foulants. Thus, in this work, we examined the behavior of different foulants during the FO or RO process, including before and after physical cleaning of the membrane. The foulants used were alginate (Alg-Na), humic acid (HA), bovine serum albumin (BSA), and colloidal silica. The commercial cellulose triacetate membrane was used for both FO and RO processes to investigate the behavior of foulants fairly. During the RO process, the formation of the gel network between alginate and calcium ions tends to accumulate on the surface of the membrane, leading to the formation of a dense layer of the foulant, consequently decreasing the flux. Having HA in the feed, RO and FO processes had a similar flux decline, whereas having alginate and BSA, the flux decline during the RO process was higher than the FO process. When colloidal silica was presented in the feed, the membrane in the RO process had constant flux throughout the testing, whereas the membrane in the FO process had a remarkable decrease in flux. Silicas were adhered more on the membrane tested in FO. It was presumed that the reverse salt diffusion facilitates the aggregation of the silica on the membrane surface, leading to a reduction of flux by cake-enhanced concentration polarization in the foulant layer of silica. Therefore, the foulant properties, type of draw solution, the structure of the foulant layer, and the interaction between the foulant and membrane are important to consider in the fouling behavior in RO and FO processes. This understanding of the fouling behavior in the FO process will lead to the development of the optimum FO process