Layer-by-layer assembly of metal-organic framework films

背景：由金属有机框架（mof）组成的薄多孔薄膜的创建是一项具有挑战性的任务，但具有显著的潜在回报。多孔MOF膜作为一种具有高渗透性和选择性的纳滤膜，在水净化等领域具有很大的应用潜力。然而，在没有固体支撑或衬底的情况下制造MOF薄膜的策略是有限的，这反过来又限制了这些潜在的应用。控制薄膜的厚度也是极具挑战性的，因为MOF合成通常遵循不受控制的生长模式。该建议建立在Bloch等人最近实现的基本原理的基础上，即“MOF”，一种多孔盐，通过离散的、带相反电荷的金属有机笼（moc）聚集而成1，以及Nitschke等人最近报道的将带电荷的moc沉积在氧化铝表面并使用pH刺激去除它们2的方法我们将结合这些原理来实现厚度可控的MOF薄膜的合成；带正电荷和负电荷的moc交替层沉积在氧化铝上（图1）将产生层状材料，共价交联将用于在通过pH控制去除模板之前赋予稳定性。我们将使用实验和计算相结合的方法来阐明和预测关键的实验参数，并匹配合适尺寸的moc，以创建具有定制孔隙度的薄膜。目标：(i)使用计算筛选和高通量方法来确定可形成稳定、有序、分层结构的mof的潜在共混合物；（ii）合成目标MOCs，并建立其在氧化铝表面的逐层沉积和去除；（iii）开发新的有机配体，使我们能够化学交联膜中的不同层，以提高材料的坚固性；（iv）表征我们的moc薄膜，重点研究薄膜的孔隙度、尺寸（厚度）和坚固性。新颖的方法：这将是第一次对moc在表面上逐层沉积的研究，我们将利用计算和实验工具来建立这个新概念。对于计算工作，我们希望能够使用MOF-UFF或QuickFF等已建立的力场来进行这些筛选计算，并使用GFN-xtb或密度泛函理论等紧密结合方案进行更精细的筛选，这两种方案都在CP2K代码中实现。实验工作将是探索性的，并将利用吸附等温线来确定MOCs可以从溶液中吸附到我们表面的条件。我们的计算和实验相结合的方法将有助于简化所进行的物理实验，并可以输入到自动化的材料发现过程中。与EPSRC的研究主题保持一致：(i)该项目的核心目标与EPSRC的未来制造和物理科学主题保持一致，特别是在合成超分子化学、计算与理论化学、合成配位化学、材料工程-复合材料的组合中；（ii）这项工作进入自动化发现管道的潜力与EPSRC人工智能和机器人主题一致；（iii） moc薄膜在水净化、化学分离和纳米过滤方面的潜在应用与EPSRC的“制造未来”主题一致，并适合制造技术组合。

Background: The creation of thin, porous films comprised of metal organic frameworks (MOFs) is a challenging task yet one with significant potential reward. Porous MOF films have great potential as nanofiltration membranes with high permeability and selectivity for applications such as water purification. However, strategies to create thin MOF films in the absence of a solid support or substrate are limited, which in turn limits these potential applications. Controlling the thickness of the films is also extremely challenging, as MOF syntheses normally follow uncontrolled growth patterns.This proposal builds upon the recently realised rationale of Bloch et al., whereby a "MOF", a porous salt, is constructed through aggregation of discrete, oppositely charged metal organic cages (MOCs),1 and the recent methodology reported by Nitschke et al. to deposit charged MOCs onto an alumina surface and remove them using a pH stimulus.2 We will combine these principles to realise the synthesis of MOF films of controllable thickness; the deposition of alternate layers of positively and negatively charged MOCs onto alumina (Figure 1) will yield layered materials, and covalent cross-linking will be used to confer stability before template removal through pH control. We will use a combined experimental and computational approach to elucidate and predict key experimental parameters and match MOCs of suitable dimensions to create films with tailored porosity.Objectives: (i) Use computational screening and high-throughput approaches to identify potential co-mixtures of MOFs that lead to stable, well-ordered, layered structures; (ii) synthesise target MOCs and establish their layer-by-layer deposition onto and removal from alumina surfaces; (iii) develop new organic ligands which will enable us to chemically cross-link the distinct layers in the films to improve the robustness of the materials; (iv) characterise our MOC-films, with a focus on investigating the porosity, dimensions (thickness) and robustness of the films.Novel methodology: this will be the first study of the layer-by-layer deposition of MOCs onto a surface, and we will utilise both computational and experimental tools in establishing this new concept. For the computational work, we expect to be able to use established forcefields such as MOF-UFF or QuickFF to undertake these screening calculations, supplemented with finer level sifting using either tightbinding schemes such as GFN-xtb or density functional theory, both of which are implemented in the CP2K code. Experimental work will be exploratory and will utilise adsorption isotherms to identify conditions under which MOCs can be adsorbed from solution onto our surfaces. Our combined computational and experimental methodology will serve to streamline the physical experiments undertaken and can feed in to automated materials discovery processes.Alignment to EPSRC's research themes: (i) the core aims of this project align with EPSRC's Manufacturing the future and Physical Sciences themes, specifically within the portfolios of Synthetic Supramolecular Chemistry, Computational & Theoretical Chemistry, Synthetic Coordination Chemistry, Materials Engineering - composites; (ii) the potential for this work to feed into an automated discovery pipeline aligns with the EPSRC Artificial intelligence and robotics theme; (iii) the potential application of thin MOC-films in water purification, chemical separations and nanofiltrations align with EPSRC's Manufacturing the Future theme, and fits within the Manufacturing Technologies portfolio.