Inorganic 2D Materials for Selective Separation Membranes

拟议的项目旨在研究使用各种2D材料来形成膜，这些膜可以作为各种分子和离子物种的选择性和可调分离器。这类膜的潜在应用非常广泛，包括：水过滤(例如海水淡化和去除环境修复中的重金属、有毒有机污染物和放射性元素)、非水过滤(例如催化剂回收、溶剂回收、离子液体等)，甚至能源生产(例如氧化还原液流电池和渗透电力)。这些膜将由以无机为主的广泛资料库构建，包括过渡金属二卤化物(例如MoS2、WS2、MoSe2、WSe2等)、六方氮化硼(HBN)和层状金属氧化物(例如V2O5、MoO3、WO3)。这些2D材料中的每一种都可以从大片状剥落到分散的个别或少数几层厚的薄片。然后，这些分散体可以用来制造由所需2D材料的堆叠层组成的类似于纸的膜。除了单组分膜，还将形成由多种不同的不同层2D材料组成的复合膜，使我们能够调整所需的过滤性能。目前的过滤技术需要使用能源效率极低的膜，这需要大量的能量才能达到所需的溶剂通量，并可接受地拒绝不需要的物种。在用于海水淡化或净化的水反渗透的情况下，通常使用聚合物基膜。为了获得所需的过滤水通量，必须施加很大的压力以迫使水通过，同时拒绝溶解的离子(如Na+，Cl-)。这需要非常大量的电力，而且效率极低。由于由2D材料组成的膜的固有特性，它们可以克服这一缺点，并允许极大地提高水过滤的效率，以及同时通过产生的化学势梯度产生能量。这是通过在2D晶体的相邻层之间形成溶剂分子的纳米毛细管来实现的。这使得溶剂分子的传输非常高效，但对不需要的水合离子的截留率非常高，因为水合离子不能进入毛细管通道。2D材料基膜的定义特征是剥离晶层之间的间距，因为这决定了允许的物种的大小。目前，人们对使用石墨烯和氧化石墨烯(GO)非常感兴趣，石墨烯和氧化石墨烯作为分离膜使用，特别是用于水过滤。结果表明，GO基膜表现出极高的水传输率，同时拒绝较大的分子物种，这使它们成为可能的过滤应用的理想选择。然而，尽管这些GO膜前景看好，但到目前为止仍有几个关键问题阻碍了进一步的进展。这包括使用实际过滤所固有的高压时的长期稳定性和机械强度问题。令人惊讶的是，大量结构相似的无机2D材料的使用几乎没有涉及，只有少数现有的研究表明，这些其他材料显示出巨大的前景，高溶剂通量以及优异的拒绝性能。使用一系列无机2D材料和石墨烯的复合材料将使它们相互补充，选择性地从给定的溶剂中去除所需的物种。

The proposed project aims to investigate the use of a variety of 2D materials for the formation of membranes that can function as selective and tuneable separators for a wide variety of molecular and ionic species. The potential applications of such membranes are vast and include; water filtration (e.g. sea water desalination and the removal of heavy metals, toxic organic contaminants, radioactive elements in environmental remediation), non-aqueous filtration (e.g. catalyst recovery, solvent recycling, ionic liquids etc.), and even energy generation (e.g. redox flow batteries and osmotic power). These membranes will be constructed from a wide library of predominantly inorganic materials; including transition metal dichalcogenides (e.g. MoS2, WS2, MoSe2, WSe2, etc.), hexagonal boron nitride (hBN), and layered metal oxides (e.g. V2O5, MoO3, WO3). Each of these 2D materials can be exfoliated from a bulk form down to a dispersion of individual or few layered thick flakes. These dispersions can then be used to create 'paper' like membranes consisting of stacked layers of the desired 2D material. As well as single component membranes the formation of composite membranes will be performed which consist of a plurality of various different layered 2D materials, allowing us to tune the desired filtration properties. Current filtration technology requires the use of extremely energy inefficient membranes which require enormous amounts of energy to achieve the desired solvent flux combined with acceptable rejection of the unwanted species. In the case of water reverse osmosis for desalination or purification a polymer based membranes is typically used. To achieve the desired flux of filtered water very large applied pressures must be applied to force the water through while rejecting the dissolved ions (e.g. Na+, Cl-). This requires very large amounts of electricity and is highly inefficient. Due to the intrinsic properties of membranes consisting of 2D materials they can overcome this drawback and allow for vastly increased efficiency of water filtration, as well as simultaneously generating energy through the created chemical potential gradient. This is achieved through the formation of nanocapillaries of solvent molecules which are formed in between the neighbouring layers of 2D crystal. This allows for extremely efficient transport of solvent molecules but very high rejection of undesired hydrated ions which cannot fit into the capillary channels. The defining feature of 2D material based membranes in the spacing between the layers of exfoliated crystal as this determines what the size of allowed species is.There is currently a great deal of interest in the use of graphene, and graphene oxide (GO), based materials for use as separation membranes, particularly for water filtration. This is fuelled by results which show that GO-based membranes exhibit extremely high water transport while rejecting larger molecular species making them ideal for possible filtration applications. However, despite the promise of these GO membranes there are several key issues which have so far prevented further progress. This includes issues with long term stability and mechanical strength when high pressures inherent to practical filtration are used. Surprisingly, the use of the vast number of similarly structured inorganic 2D materials remains barely touched with only a handful of existing studies that indicate that these other materials show immense promise with high solvent flux as well as excellent rejection properties. The use of composites of both a selection of inorganic 2D materials as well as graphene would allow them to complement one another to selectively remove desired species from a given solvent.