Growing Crystal Sponges on a Chip With Sound MOFs From a Single Droplet

This application covers a way of making metal organic frameworks, the porous crystalline materials often compared to molecular sponges, by shaking a droplet of precursor liquid with sound waves on a piezoelectric chip. Claim 1 is a method: put a liquid containing a metal ion and an organic ligand on a piezoelectric substrate, apply acoustic irradiation so the liquid swirls in an azimuthal loop, and isolate the framework that forms. It was filed by the Royal Melbourne Institute of Technology and names four inventors. The application is a divisional of Australian application 2020259906.

The Problem

Metal organic frameworks (MOFs) are crystals in which metal nodes are joined by organic linker molecules into a rigid, open lattice. The specification notes their very large surface area and porosity, up to 90 per cent of their volume being free space, and lists uses in catalysis, gas separation, sensing, charge storage and drug delivery. Changing the metal or the linker changes the pore size and chemistry, which is why there are so many of them.

Making them is slower and messier than using them. The specification lists hydrothermal, solvothermal, microwave, sonochemical and electrochemical routes and says they share problems: they are hard to scale, the crystals come out randomly oriented and full of defects, and the pores usually have to be “activated” afterwards. Activation means removing the solvent trapped inside, by heating under vacuum, solvent exchange, supercritical carbon dioxide, freeze-drying or chemical treatment. These steps use energy or generate waste solvent, and solvent exchange, the specification says, often fails to deliver the expected internal surface area.

Methods that grow oriented films layer by layer, such as liquid phase epitaxy, do control orientation but are described as taking several days even when automated, and defects build up as layers are added. Freestanding films then need a delamination step that is itself prone to failure.

What This Invention Does

The claimed method deposits a liquid holding MOF precursors on a piezoelectric substrate, applies acoustic irradiation that induces azimuthal liquid recirculation, which causes the MOF to form within the liquid, and then isolates it. The specification explains the mechanism as asymmetric: an interdigitated transducer (IDT) placed off-centre sends surface acoustic waves into a droplet, which makes the droplet spin like a tiny centrifuge. Solute is swept to the contact line at the droplet edge and deposited there as the liquid recedes, building oriented stacks of crystal.

The control experiment shows the contrast. Without sound, a drying droplet leaves the familiar coffee ring, a weak convection cell that carries crystals to the edge and gives them no long-range order. With sound, the specification says, the oscillation smears out the ring and the crystals stack in a highly ordered way. X-ray diffraction shows strong orientation parallel to the {222} plane, especially at higher input voltages, in contrast to the slow-evaporation control.

The worked examples use HKUST-1, a copper and trimesic acid framework. The device is a lithium niobate chip (lithium tantalate for the shear-horizontal wave tests) with an off-centre pair of IDTs, each with 25 finger pairs, a 12 mm aperture and a 110 micron gap and width. A 10 microlitre droplet holds 5 microlitres of copper precursor and 5 microlitres of trimesic acid solution. Input voltages of 1.5, 4.5, 7.5 and 9 Vrms were tried, capped at 9 Vrms to stop the liquid being blown off the device as a mist.

The headline figures are the surface areas from nitrogen sorption, shown in Figure 4. Bulk HKUST-1 made conventionally measured 698 m2/g, against 849 m2/g for crystals made at 1.5 Vrms, 1300 at 4.5 Vrms, 1434 at 7.5 Vrms and 1682 at 9 Vrms. Higher power gave higher surface area, which the specification attributes to the sound squeezing solvent out of the pores so that the framework is activated as it forms. Example 5 repeats the approach with an iron framework, Fe-MIL-88B, at 9 Vrms.

A caution on the text: parts of the dumped specification are missing, including some dependent claims and result passages, so figures here are limited to what is legible.

Key Features

• Off-centre acoustic drive. The method relies on an IDT positioned off-centre so that the waves are asymmetric and the liquid recirculates in a loop. Claim 23 covers the device itself, with at least one off-centre IDT on a piezoelectric substrate, and a dependent claim adds two opposing off-centre IDTs.
• Synthesis and activation in one step. The specification says the frameworks come out at least partly activated, with no separate solvent-removal stage. Claims 2 and 3 cover partially activated and activated MOFs.
• Orientation as a claimed result. Claim 4 recites a high degree of orientation, with crystals aligned along the same crystallographic plane.
• Several wave types. Claims cover surface, bulk or hybrid acoustic waves, including Rayleigh and shear-horizontal surface waves, and travelling or standing waves.
• Low temperature and low voltage. The specification says the method can run at room temperature, below about 50 degrees C or lower, with input voltage under 40 Vrms and preferably far lower, down to under 1.5 Vrms.
• A choice of products. Claims cover surface anchored MOFs (SURMOFs), free-standing oriented films and free-flowing powder, with HKUST-1 named in claim 21 and a MOF made by the method in claim 22.

Who Is Behind It

The applicant is the Royal Melbourne Institute of Technology, which trades as RMIT University. The work comes from its Micro/Nanophysics Research Laboratory. Inventor Leslie Yeo is a Distinguished Professor in the School of Engineering at RMIT, and his RMIT profile describes research on how megahertz-frequency sound waves interact with fluids and crystals, with applications including sonochemical materials synthesis. RMIT’s 2019 news release names Heba Ahmed as lead author and Amgad Rezk as co-author on the related paper in Nature Communications, and says the method produces customised MOFs “within a few minutes” that are already activated, tested on copper-based and iron-based frameworks.

This application is a divisional of Australian application 2020259906, as the title page and the first line of the description state. The specification itself contains no priority claim. Its page headers carry the international publication WO 2020/210868 and PCT/AU2020/050372. From the published family record, not from this specification, that PCT application was filed on 15 April 2020 and claims priority from Australian provisional application 2019901294 of 15 April 2019, with parallel European and US entries. That makes the priority country Australia.

Why It Matters

Porous materials of this kind could be useful for capturing gases, storing energy and delivering drugs, but a material that takes days to grow and then needs a harsh clean-out step is hard to turn into a product. The attraction of this approach is speed and simplicity: a droplet, a chip and a few volts, with the framework ending up open and ready to use.

The specification also claims scalability, from nanogram to multi-kilogram quantities, but its worked examples are single microlitre droplets, so that claim is stated rather than demonstrated here. The surface area results are the real evidence: conventional HKUST-1 at 698 m2/g against 1682 m2/g for the 9 Vrms crystals is a large gap, if it holds beyond a laboratory device.

Related Concepts

• Metal organic framework – the porous crystalline material class the method produces.
• Surface acoustic wave – the high-frequency wave travelling along the chip surface that drives the droplet.
• Interdigital transducer – the comb-like electrode pattern that turns an electrical signal into the acoustic wave.
• Piezoelectricity – the property of the lithium niobate substrate that links electric fields to mechanical vibration.
• Coffee ring effect – the edge deposition pattern of a drying droplet that the acoustic swirling overcomes.
• Microfluidics – the field of handling tiny liquid volumes on chips, in which this platform sits.

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AU 2026202269 was published in the Australian Official Journal of Patents on 9 April 2026 and is open for public inspection. Patent applications represent inventions that are sought to be protected and do not necessarily reflect commercially available products.