Water-methanol mixture under confinement

Treballs Finals de Màster en Física dels Sistemes Complexos i Biofísica, Facultat de Física, Universitat de Barcelona. Curs: 2021-2022. Tutor: Giancarlo FranzeseWater pollution and renewable energy sources are a matter of broad concern, both environmental challenges for our society. For its applications in the chemical and pharmaceutical industry, production of synthetic fibers and plastic, and as a fuel additive, methanol attracts interest for how to model its properties when mixed with water. Here, we consider a minimalistic model for a water-methanol mixture confined between two parallel graphene nanosheets and analyze the diffusion coefficient of each component as the slit-pore’s width δ increases. We find that layering in the hydrophobic pore induces segregation between the two components. The methanol apolar moiety accumulates near the pore walls, while water populates more in the central layer away from the hydrophobic walls. Furthermore, both liquids have a diffusion coefficient that changes non-monotonically with δ, with water always diffusing faster than methanol. Changes in the pore widths affect the two mixture components in different amounts, suggesting the possibility of an efficient method for methanol-water separation based on a physical procedure

Water-methanol mixture confined in a graphene slit-pore

Efficient and sustainable techniques for separating water-methanol mixtures are in high demand in the industry. Recent studies have revealed that membranes and 2D materials could achieve such separation. In our research, we explore the impact of a nanoconfining graphene slit-pore on the dynamics and structure of water-methanol mixtures. By Molecular Dynamics simulations of a coarse-grained model for water mixtures containing up to 25% methanol, we show that, for appropriate pore sizes, water tends to occupy the center of the pore. In contrast, methanol's apolar moiety accumulates near the hydrophobic walls. Additionally, modifying the pore's width leads to a non-monotonic change in the diffusivity of each component. However, water always diffuses faster than methanol, implying that it should be possible to identify an optimal configuration for water-methanol separation based on physical mechanisms. Our calculations indicate that one of the more effective pore sizes, 12.5{\AA}, is also mechanically stable, minimizing the energy cost of a possible filtering membrane

Size-Pore-Dependent Methanol Sequestration from Water-Methanol Mixtures by an Embedded Graphene Slit

The separation of liquid mixture components is relevant to many applications¿ranging from water purification to biofuel production¿and is a growing concern related to the UN Sustain- able Development Goals (SDGs), such as 'Clean water and Sanitation' and 'Affordable and clean energy'. One promising technique is using graphene slit-pores as filters, or sponges, because the confinement potentially affects the properties of the mixture components in different ways, favoring their separation. However, no systematic study has shown how the size of a pore changes the ther- modynamics of the surrounding mixture. Here, we focus on water-methanol mixtures and explore, using Molecular Dynamics simulations, the effects of a graphene pore, with size ranging from 6.5 to 13 Å, for three compositions: pure water, 90%-10%, and 75%-25% water-methanol. We show that tuning the pore size can change the mixture pressure, density and composition in bulk due to the size-dependent methanol sequestration within the pore. Our results can help in optimizing the graphene pore size for filtering applications

Exploring optimal graphene slit-pore width for the physical separation of water-methanol mixture

Efficient and sustainable techniques for separating water- alcohol mixtures are in high demand in the industry. Recent research has revealed that nanotechnology could be the optimal solution. In this study, we investigate how the width of a nano-confining graphene slit-pore affects the filtration and purification of water-methanol mixtures. Using Molecular Dynamics simulations of a coarse-grained model for mixtures containing up to 25 percent methanol, we found that specific pore sizes segregate the two components, with water being preferred in the center and methanol accumulating near the hydrophobic walls. Altering the pore width also affects non-monotonically the diffusivity of each component, with water diffusing faster than methanol. Hence, optimal pore size, leveraging segregation and diffusion differences, can enable the successful extraction of both components. However, the system requires external forces and work to maintain mechanical stability at specific pore widths. Our research indicates that Å pore size maximizes physical separation, ensuring that the energy cost of a filtering graphene membrane is minimized