Omar Yaghi Wins 2020 Sustainable Water Prize from Royal Society of Chemistry
News Article written for BENG0027 Tech Journalism, aimed at Chemistry world readers. Most have chemistry undergraduate knowledge but articles are suitable for chemists not working directly in the area of research.
Figure 1: Pictured above, Professor Yaghi in the celebratory graphic from the Royal Society of Chemistry website. [RSC copyright]
Omar Yaghi Wins 2020 Sustainable Water Prize from Royal Society of Chemistry
The Royal Society of Chemistry Sustainable Water 2020 prize has been awarded to Professor Omar Yaghi for “the impactful development of water harvesting from desert air using metal–organic frameworks”. Recognised ‘as the father of reticular chemistry’, Yaghi defined reticular chemistry as “linking molecular building blocks by strong bonds to make extended crystalline structures”. This definition now encompasses the millions of structures falling under the categories of zeolites, metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs).
Despite 70% of our planet’s surface being covered by water, only 3% of this is potable. World Wildlife Fund state 1.1 billion people lack access to water, 2.7 billion face frequent water scarcity. By 2025, two thirds of the world’s population may face water shortages – currently, underground reserves are being consumed faster than they are replenished. Climate change will impact potable water scarcity. Yaghi states this technology is “making water independent of the [local] grid” and his research aims “to give citizens of the world water independence”.
Figure 2: Infographic illustrating the current MOF-based water harvesting research position.
Yaghi’s recent research proves scalability for his metal-organic framework (MOF) water-harvesting devices. Hanikel et al’s nature nanotechnology review presents a roadmap for future testing, upscaling, and optimisation of their technology. In particular their MOF framework is at an advanced stage (as illustrated in figure 2), and the device is at an exciting turning point.
Yaghi’s foray into water harvesting technology proved serendipitous. In 2014, whilst researching MOF-801’s potential as a water separator in carbon capture, Yaghi noted that this material achieved remarkable uptake of water at low humidity. Examining MOF-801’s isotherm, clearly this material had potential, achieving water uptake of 42% with respect to weight. Additionally, it adsorbs and desorbs at reasonably low temperatures (25° C for adsorption, 45° C for desorption).
Desalination provides large-scale freshwater but is unsustainable due to its high energy costs and environmental impact. Fog harvesting is sustainable and on an industrial scale, is appealing for its energy-passivity but requires a consistently high humidity environment for efficiency. Direct air cooling, cannot function in arid climates – the very locations with the greatest water harvesting requirement.
Effective desiccants, salt and zeolite-based materials have been tested as potential water harvesting candidates. Though both function at low humidity, neither has the level of capacity or kinetics for viability. The quick kinetics of MOF-801 in low humidity conditions, indicated that MOF materials might hold the solution; MOFs have high capacities and can be modified for property optimisation. MOF-801 produced good cycling performance, but showed an initial drop in capacity after the first cycle. Investigations showed cycle water binding in tetrahedral or cubic arrangements to the MOF within the initial cycle, then continuing to act as seeds for water uptake within the pores. This water remains in place and affects the kinetics, as subsequent water molecules bind to the water seed structures rather, than directly to the MOF.
In situ passive MOF water harvesting was initially demonstrated in 2017 (the device only used 2 g of zirconium-based MOF-801, but proved the concept). In 2018, a similar larger device was tested in Berkeley. This first-generation of harvester was energy passive, low-tech and cheap and in lab conditions, it produced up to 0.3 L kgMOF-1. The water produced was pure, requiring only mineralisation to achieve potability. Zirconium is expensive, so lower cost alternatives were investigated. Aluminium is cheap and abundant, but vulnerable to water corrosion, yet when aluminium is deployed in a rod structure, it is water resistant. Using this principle MOF-303 was developed, which achieved 0.33 L kgMOF-1.
The group’s first energy-active water harvester was developed in 2018. This second-generation harvester was rapid cycling, and harvested day and night at humidity as low as 7%. Rapid cycling produced up to 1 L per kg of MOF. The device was further optimised to produce a third generation harvester; this latest assembly uses 100 g of MOF-303, and cycles 200-250 times per day producing in the most arid conditions, a minimum of 5 L kgMOF-1 daily, to a maximum of 100 L kgMOF-1 daily in more humid conditions. MOF-303 has run over 50,000 cycles, without any degradation. The MOF is expected to last (or even outlast) the water harvesting unit itself.
Figure 3: Pictured above the third (and latest) generation of MOF based water harvester and a video of the device working (53:53 timestamp). [Copyright Omar Yaghi]
Yaghi envisages “the next generation device will be a nice tabletop device that delivers around five litres per day, based on 100 grams [of MOF], of water”. He dismisses concerns that atmospheric water harvesting could affect the environment, pointing out the statistic – “If we served 50L [of water] to all 6.7 billion people on the planet, we would use just 0.002% of the water in the atmosphere on any given day.”
Spanning his work in reticular chemistry, to his current device testing, clearly Yaghi’s contribution to sustainable potable water technology has been pivotal. Yaghi has maintained his research interest in this area, alongside other reticular chemistry interests, most recently examining xenon separation.
References
https://www.rsc.org/awards-funding/awards/2020-winners/professor-omar-yaghi/#undefined
https://orcid.org/0000-0002-5611-3325
Hanikel, N., Prévot, M. S. & Yaghi, O. M. MOF water harvesters. Nat. Nanotechnol. 15, 348–355 (2020).
Xu, W. & Yaghi, O. M. Metal-Organic Frameworks for Water Harvesting from Air, Anywhere, Anytime. ACS Cent. Sci. 6, 1348–1354 (2020).
Hanikel, N. et al. Rapid Cycling and Exceptional Yield in a Metal-Organic Framework Water Harvester. ACS Cent. Sci. 5, 1699–1706 (2019).