Sorption in mixed matrix membranes: Experimental and molecular dynamic simulation and Grand Canonical Monte Carlo method

New insight into impact of humidity on direct air capture performance by SIFSIX-3-Cu MOF

Removal of CO2 from air is one of the key human challenges in battling global warming. SIFSIX-3-Cu is a promising metal-organic framework (MOF) suggested for carbon capture even at low CO2 concentrations. However, the impact of humidity on its performance in direct air capture (DAC) is poorly understood. To evaluate the MOF performance for DAC application under humid conditions, we investigate the adsorption of H2O, CO2, and N2 using density functional theory (DFT), grand canonical Monte Carlo (GCMC), and molecular dynamics (MD) simulations. The simulation results show a higher tendency of SIFSIX-3-Cu towards H2O adsorption rather than CO2 (and N2). The results agree with the adsorption isotherms for the pure compounds from the Sips model. The extended Sips model shows 1.34 mmol g-1 CO2 adsorption at the atmospheric pressure and 298 K for the CO2/N2 mixture containing 400 ppm CO2, and low CO2 adsorption (less than 0.75 mmol g-1) at a low relative humidity (RH) of 20%. This finding highlights the efficiency of SIFSIX-3-Cu for DAC in dry air and the negative impact of humidity on the CO2 selective adsorption. Therefore, we suggest to consider the impairing of humidity effects when designing a SIFSIX-3-Cu-based CO2 separation process and removal of any water vapor before introduction of the air to SIFSIX-3-Cu.

A theoretical probe into the separation of CO2/CH4/N2 mixtures with polysulfone/polydimethylsiloxane-nano zinc oxide MMM

In the current investigation, molecular dynamics (MD) and Grand Canonical Monte Carlo (GCMC) simulation as remarkable and competent approaches have been employed for understanding structural and transport properties of MMMs in the realm of gas separation. The two commonly used polymers i.e. polysulfone (Psf) and polydimethylsiloxane (PDMS) as well as zinc oxide (ZnO) nanoparticle (NP) were used to carefully examine the transport properties of three light gasses (CO₂, N₂ and CH₄) through simple Psf, Psf/PDMS composite loaded by different amounts of ZnO NP. Also, the fractional free volume (FFV), X-ray diffraction (XRD), glass transition temperature (T_g), and Equilibrium density were calculated to scrutinize the structural characterizations of the membranes. Moreover, the effect of feed pressure (4-16 bar) on gas separation performance of simulated MMMs was investigated. Results obtained in different experiments showed a clear improvement in the performance of simulated membranes by adding PDMS to PSf matrix. The selectivity of studied MMMs was in the range from 50.91 to 63.05 at pressures varying from 4 to 16 bar for the CO₂/N₂ gas pair, whereas the corresponding value for CO₂/CH₄ system was found to be in the range 27.27-46.24. For 6 wt% ZnO in 80%PSf + 20%PDMS membrane, high permeabilities of 78.02, 2.86 and 1.33 barrers were observed for CO₂, CH₄ and N₂ gases, respectively. The 90%PSf + 10%PDMS membrane with 2% ZnO had a highest CO₂/N₂ selectivity value of 63.05 and its CO₂ permeability at 8 bar was 57 barrer.

A systematic review of the molecular simulation of hybrid membranes for performance enhancements and contaminant removals

Number of research on molecular simulation and design has emerged recently but there is currently a lack of review to present these studies in an organized manner to highlight the advances and feasibility. This paper aims to review the development, structural, physical properties and separation performance of hybrid membranes using molecular simulation approach. The hybrid membranes under review include ionic liquid membrane, mixed matrix membrane, and functionalized hybrid membrane for understanding of the transport mechanism of molecules through the different structures. The understanding of molecular interactions, and alteration of pore sizes and transport channels at atomistic level post incorporation of different components in hybrid membranes posing impact to the selective transport of desired molecules are also covered. Incorporation of molecular simulation of hybrid membrane in related fields such as carbon dioxide (CO₂) removal, wastewater treatment, and desalination are also reviewed. Despite the limitations of current molecular simulation methodologies, i.e., not being able to simulate the membrane operation at the actual macroscale in processing plants, it is still able to demonstrate promising results in capturing molecule behaviours of penetrants and membranes at full atomic details with acceptable separation performance accuracy. From the review, it was found that the best performing ionic liquid membrane, mixed matrix membrane and functionalized hybrid membrane can enhance the performance of pristine membrane by 4 folds, 2.9 folds and 3.3 folds, respectively. The future prospects of molecular simulation in hybrid membranes are also presented. This review could provide understanding to the current advancement of molecular simulation approach in hybrid membranes separation. This could also provide a guideline to apply molecular simulation in the related sectors.

Simulation Study on the Screening of Hydrophobic Surface Materials for Pipeline Drag Reduction Based on Adsorption Properties

Hydrophobic surface drag reduction techniques are effective in reducing the frictional resistance of fluids, the adsorption of liquid molecules on hydrophobic surfaces can reflect the resistance to fluid flow through such solid surfaces. Based on molecular simulation technology, we investigate the adsorption characteristics of water molecules on hydrophobic surfaces to achieve rapid screening of hydrophobic materials in fire-fighting water supply systems. The Monte Carlo method was used to simulate the adsorption process of polymers and to analyze the effects of temperature and fixed adsorption quantity. Contact angle tests were also done to verify polymer hydrophobicity. The isothermal adsorption heat, water molecule distribution, and energy distribution were studied by molecular mechanics and molecular dynamics methods. Then, adsorption localization simulations and electrostatic potential distributions were used to predict possible adsorption sites on hydrophobic surfaces and single-molecule chains. Finally, the interaction energy, diffusion coefficient, and free volume were investigated to explain the adsorption mechanism at the molecular level. Simulation results show that, overall, PTFE was more hydrophobic and PES was more hydrophilic and at 298 K, the number of adsorbed water molecules was ranked as follows: PTFE < PVDF < PVC < PMMA < PPS < CSM < BD-HDI < BD-MDI < BD-TDI < PES. Furthermore, PTFE, PVDF, PVC, PES, and PPS have more stable adsorption configurations on the (0 -1 0) surface. According to the findings, hydrogen bonding dominates the interaction between water molecules and hydrophilic polymers, whereas π-π interactions increase water molecules' diffusion resistance in polymers with benzene rings. In addition, PES contains many sulfone groups and ether bonds, which disorganize the chain arrangement to provide more free volume, whereas the water adsorption rate of PTFE is reduced because its molecular chains are less convoluted and more organized.

The Transport Properties of Semi-Crystalline Polyetherimide BPDA-P3 in Amorphous and Ordered States: Computer Simulations

The effect of polymer chain ordering on the transport properties of the polymer membrane was examined for the semi-crystalline heterocyclic polyetherimide (PEI) BPDA-P3 based on 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and diamine 1,4-bis [4-(4-aminophenoxy)phenoxy]benzene (P3). All-atom Molecular Dynamics (MD) simulations were used to investigate the gas diffusion process carried through the pores of a free volume several nanometers in size. The long-term (~30 μs) MD simulations of BPDA-P3 were performed at T = 600 K, close to the experimental value of the melting temperature (Tm ≈ 577 K). It was found during the simulations that the transition of the PEI from an amorphous state to an ordered one occurred. We determined a decrease in solubility for both the gases examined (CO2 and CH4), caused by the redistribution of free volume elements occurring during the structural ordering of the polymer chains in glassy state (Tg ≈ 487 K). By analyzing the diffusion coefficients in the ordered state, the presence of gas diffusion anisotropy was found. However, the averaged values of the diffusion coefficients did not differ from each other in the amorphous and ordered states. Thus, permeability in the observed system is primarily determined by gas solubility, rather than by gas diffusion.

Experimental and theoretical study for removal of trimethoprim from wastewater using organically modified silica with pyrazole-3-carbaldehyde bridged to copper ions

BACKGROUND

Human and veterinary antibiotics are typically discharged as parent chemicals in urine or feces and are known to be released into the environment via wastewater treatment plants (WWTPs). Several research investigations have recently been conducted on the removal and bioremediation of pharmaceutical and personal care products (PPCPs) disposed of in wastewater.

RESULTS

SiNP-Cu, a chelating matrix, was produced by delaying and slowing 1.5-dimethyl-1H-pyrazole-3-carbaldehyde on silica gel from functionalized with 3-aminopropyltrimethoxysilane. The prepared sorbent material was characterized using several techniques including BET surface area, FT-IR spectroscopy, Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and nitrogen adsorption-desorption isotherm. The pseudo-second-order model provided the best correlation due to the big match between the experimental and theoretical of different adsorption coefficients. The Langmuir and Freundlich adsorption models were used and the study showed a better match with the Freundlich model with a capacity of removal reached up to 420 mg g^-1. The removal capacity was dependent on pH and increased by increasing pH. The removal percentage reached 91;5% at pH = 8. The adsorbent demonstrated a high percentage removal of TMP, reaching more than 94% when increased pH. The sample was simply regenerated by soaking it for a few minutes in 1 N HCl and drying it. The sorbent was repeated five times with no discernible decrease in removal capacity. The thermodynamic study also showed endothermic, increasing randomness and not spontaneous. The free energy was 2.71 kJ/mol at 320 K. The findings of the DFT B3LYP/6-31 + g (d, p) local reactivity descriptors revealed that nitrogen atoms and π-electrons of the benzene and pyrimidine rings in the TMP are responsible for the adsorption process with the SiNP surface. The negative values of the adsorption energies obtained by molecular dynamic simulation indicated the spontaneity of the adsorption process.

CONCLUSION

The global reactivity indices prove that TMP is stable and it can be removed from wastewater using SiNP surface. The results of the local reactivity indices concluded that the active centers for the adsorption process are the nitrogen atoms and the π-electrons of the pyrimidine and benzene rings. Furthermore, the positive value of the maximum charge transfer number (ΔN) proves that TMP has a great tendency to donate electrons to SiNP surface during the process of adsorption.

Mixed Matrix Membrane Tip Extraction Coupled with UPLC–MS/MS for the Monitoring of Nonsteroidal Anti-Inflammatory Drugs in Water Samples

An ultra-performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method, in combination with a mixed matrix membrane microextraction method for the quantification of nonsteroidal anti-inflammatory drugs (NSAIDs) in environmental water samples, is reported. The extraction device was prepared by casting well-dispersed polymeric bonded octadecyl (C18) particles in a cellulose triacetate matrix solution onto commercially available 200 μL micropipette tips. The membrane formed contains 25% of the adsorbent loading amount and was firmly attached to the inner wall of the membrane tip. The dynamic extraction was performed by withdrawing and dispensing the sample solution through the tip device for effective analyte adsorption, followed by the analyte desorption process into 40 μL of methanol and acetonitrile (1:1) prior to UPLC–MS/MS analysis. NSAIDs—namely diclofenac, ibuprofen, indoprofen, naproxen and sulindac—were chosen as targeted analytes. Several extraction parameters were comprehensively optimized, including sample pH value, ionic strength, dynamic extraction cycle, desorption solvent and desorption time. The optimized conditions demonstrated a linear range from 0.25 to 500 ng L−1, with correlation coefficients (r2) from 0.9988 to 0.9992 and detection limits ranging from 0.08 to 0.40 ng L−1. The recoveries of the spiked water samples were between 92% and 99% and exhibited excellent precision relative to standard deviations (RSDs ≤ 4.9%), and enrichment factors (EFs) were at 201–249 for the developed approach.

Molecular Dynamics Simulation on the Diffusion of Flavor, O2 and H2O Molecules in LDPE Film

The diffusion of five flavor organic molecules, including D-limonene, myrcene, ethyl hexanoate, 2-nonanone, and linalool in low density polyethylene (LDPE) film were investigated by combined experimental and molecular dynamics (MD) simulation studies. The diffusion coefficients derived from the prediction model, experimental determination, and MD simulation were compared, and the related microscopic diffusion mechanism was investigated. The effects of the presence of the flavor organic molecules on the diffusion of O₂ and H₂O in polyethylene (PE) were also studied by MD simulation. Results show that: The diffusion of five flavor molecules in LDPE is well followed to Fick’s second law by the immersion experiment; MD simulation indicates the dual mode diffusion mechanism of the flavor molecules is in LDPE; the diffusion coefficients from MD simulation are close to those from the experimental determination, but are slightly larger than those values; the presence of the flavor organic molecules hinders the diffusion of O₂ and H₂O, which can be well explained from the fraction of free volume (FFV) and interaction energy calculation results derived from MD simulation.