Hyperloop-like diffusion of long-chain molecules under confinement

Pore engineering of Porous Materials: Effects and Applications

Porous materials, characterized by their controllable pore size, high specific surface area, and controlled space functionality, have become cross-scale structures with microenvironment effects and multiple functions and have gained tremendous attention in the fields of catalysis, energy storage, and biomedicine. They have evolved from initial nanopores to multiscale pore-cavity designs with yolk-shell, multishells, or asymmetric structures, such as bottle-shaped, multichambered, and branching architectures. Various synthesis strategies have been developed for the interfacial engineering of porous structures, including bottom-up approaches by using liquid-liquid or liquid-solid interfaces "templating" and top-down approaches toward chemical tailoring of polymers with different cross-linking degrees, as well as interface transformation using the Oswald ripening, Kirkendall effect, or atomic diffusion and rearrangement methods. These techniques permit the design of functional porous materials with diverse microenvironment effects, such as the pore size effect, pore enrichment effect, pore isolation and synergistic effect, and pore local field enhancement effect, for enhanced applications. In this review, we delve into the bottom-up and top-down interfacial-oriented synthesis approaches of porous structures with advanced structures and microenvironment effects. We also discuss the recent progress in the applications of these collaborative effects and structure-activity relationships in the areas of catalysis, energy storage, electrochemical conversion, and biomedicine. Finally, we outline the persisting obstacles and prospective avenues in terms of controlled synthesis and functionalization of porous engineering. The perspectives proposed in this paper may contribute to promote wider applications in various interdisciplinary fields within the confined dimensions of porous structures.

Nanorod Diffusion near the Solid-Liquid Interface with Varied Wall Nonuniformity

The complex diffusion behaviors of rod-shaped nanoparticles near the solid-liquid interface are closely related to various biological processes and technological applications. Despite recent advancements in understanding the diffusion dynamics of nanoparticles near some specific solid-liquid interfaces, systematical studies to tune the interfacial interaction or fabricating nonuniform wall to see their effects on the nanorod (NR) diffusion are still lacking. This work utilized molecular dynamics simulations to investigate the rotational and translational diffusion dynamics of a single NR near the solid-liquid interface. We constructed a patterned wall featuring adjustable nonuniformity, which was accomplished by modifying the interaction between NR and the wall, noting that the resulting nonuniformity limits both the translational and rotational diffusion of NR, evident from decreases in diffusion coefficients and exponents. By trajectory analysis, we categorized the diffusion modes of NRs near the patterned wall with varied nonuniformities into three types: Fickian diffusion, desorption-mediated flight, and in-plane diffusion. Furthermore, energy analysis based on the adsorption-desorption mechanism has demonstrated that the three diffusion states are driven by interactions between the NR and the wall, which are primarily influenced by rotational diffusion. These results could significantly deepen the understanding of anisotropic nanoparticle interfacial diffusion and would provide new insights into the transport mechanisms of nanoparticles within confined environments.

Unveiling the mechanisms of carboxylic acid esterification on acid zeolites for biomass-to-energy: A review of the catalytic process through experimental and computational studies

In recent years, there has been significant interest from industrial and academic areas in the esterification of carboxylic acids catalyzed by acidic zeolites, as it represents a sustainable and economically viable approach to producing a wide range of high-value-added products. However, there is a lack of comprehensive reviews that address the intricate reaction mechanisms occurring at the catalyst interface at both the experimental and atomistic levels. Therefore, in this review, we provide an overview of the esterification reaction on acidic zeolites based on experimental and theoretical studies. The combination of infrared spectroscopy with atomistic calculations and experimental strategies using modulation excitation spectroscopy techniques combined with phase-sensitive detection is presented as an approach to detecting short-lived intermediates at the interface of zeolitic frameworks under realistic reaction conditions. To achieve this goal, this review has been divided into four sections: The first is a brief introduction highlighting the distinctive features of this review. The second addresses questions about the topology and activity of different zeolitic systems, since these properties are closely correlated in the esterification process. The third section deals with the mechanisms proposed in the literature. The fourth section presents advances in IR techniques and theoretical calculations that can be applied to gain new insights into reaction mechanisms. Finally, this review concludes with a subtle approach, highlighting the main aspects and perspectives of combining experimental and theoretical techniques to elucidate different reaction mechanisms in zeolitic systems.

Dynamics of polymer chains confined to a periodic cylinder: molecular dynamics simulation vs. Lifson-Jackson formula

The dynamics of polymer chains confined to a periodic cylinder is explored using molecular dynamics simulation and theoretical analysis. The cylinder is divided into two cavities in one periodicity: one cavity consists of a channel of length L1 and diameter D1 and another cavity is a channel of length L2 and diameter D2. For L1 = L2 = L/2, the diffusion coefficient D of a single confined polymer chain decreases rapidly with increase in periodicities L. For a fixed periodicity with L = L1 + L2 = constant, the diffusion coefficient D of a single confined polymer chain shows strong dependence on L1 (or L2). Moreover, for a multi-chain system with L1 = L2, the diffusion coefficient D shows strong non-monotonic dependence on the chain monomer density ρ, and the confined polymer chains diffuse fastest for ρ = 0.068, in which there are three polymer chains in two periodicities as well as two opposing effects: one is that the excluded volume effect between polymer chains can reduce the free energy barrier, and another is that when the chain monomer density ρ increases further, the entanglement effect increases, which leads to that the diffusion coefficient D decreases as ρ increases. Finally, we found that the diffusion coefficient D has a similar oscillation relationship with the ratio of R/L for different chain lengths N and different periodicity L, and the oscillation amplitude decreases gradually as R/L increases; here R is the mean end-to-end distance of a single confined polymer chain, i.e., . From the view of free energy potential, both the width of the free energy potential well and the height of the free energy potential barrier govern simultaneously the diffusion behavior of confined polymer chains. According to the mean force potential (PMF) based on the weighted histogram analysis method (WHAM), we found that our results agree very well with the theoretical analysis using the Lifson-Jackson formula. Our investigation may help us understand the dynamics of particles in a periodic medium, which is one of the interesting problems in many different fields of science, such as physics, chemistry and biology.