In the field of micro- and nano-scale membranes, useful for separation, and purification, catalysis, energy storage, and other applications, conventional structures follow a paradigm in which the membrane structure is formed as a thin film or ultra-thin film. While these conventional film-based structures are capable of considerable separation of target materials from other materials (e.g. solute from solvent, mixtures of gases, etc.) the separation capacity is a function of the surface area of the film-based structure. Since the film-based structure has no appreciable thickness (i.e. nanometer scale thickness, e.g. approximately 30 nm), a substantially two-dimensional structure has a surface area which is essentially the area of the membrane. This structural configuration is thus limiting on the desirable characteristics of a membrane, particularly permeability and selectivity.
It would be highly beneficial to provide techniques for synthesizing novel structures offering superior permeability and selectivity to existing thin-film based porous membrane structures.
Conventional membranes tend to be two dimensional and with relatively large thickness, which limit the achievable permeability. The ultimate goal in membrane technologies is to combine high permeability and high selectivity. LLNL has developed a transformational 3D nm-thick membrane structure using ALD (atomic layer deposition) template approach. Our membrane structure has two independent bicontinuous pore systems separated by a nm-thick membrane. It dramatically increases the number of exchange sites and shortens the exchange pathway.
These material can be used as a sacrificial template to realize a 3D membrane by applying a suitable surface coating technique, which needs to meet the following requirements: (1) capable of coating high aspect ratio structures with (2) ultra-thin, uniform and conformal coatings that are (3) pinhole-free. Among available coating techniques, atomic layer deposition (ALD) is ideally suited due to its self-limiting character that warrants uniform and conformal coatings with atom-scale thickness control.
The unique feature of these materials is that it has two independent, interwoven pore systems separated by a 3D nanometer-thick membrane.
This structural design possesses two novel advantages:
- the ultrathin membrane shortens the exchange pathway.
- the high surface area dramatically increases the number of exchange sites.
The invention will be potentially useful in gas separation, water purification, energy storage, chemical sensing, photocatalysis, etc. It will have great impact on membrane-based separation and a variety of clean energy technologies.
LLNL also successfully generated nanotubular metal oxide foams with excellent mechanical properties.
LLNL has demonstrated in proof-of-principle experiments that this 3D membrane material can effectively filter dye from water, with 100% rejection of dye (direct blue 71) and high permeance of water.
LLNL has filed for patent protection on this invention.