Passive Moisture-Swing Direct Air Capture and Carbon-Mineralizing Planter Device
An Urban Structure Powered by Rain, Snowmelt, and Sunlight, Beginning with the Physics of French Fries
1. Standing Before the Physics of French Fries
I was looking into the physics of French fries because I wanted to understand how they work. As a potato cooks, the starch inside absorbs water and swells under heat, while moisture escapes from the surface, leaving behind a firm, crisp layer. It was a familiar food revealing a movement of water and heat within it.
At that moment, I thought of beads that could capture carbon.
Beads that continually change their volume in response to natural conditions such as temperature and moisture. When dry, they take in carbon dioxide from the air. When water reaches them, they swell and release the carbon they had been holding. As they dry again, they shrink and begin capturing the next round of carbon. The structure I imagined was not one in which the entire device moves, but one in which the beads inside operate repeatedly, almost as though they were breathing.
This paper records the full path of thought that began with those beads: where the carbon could go, what roles rain and snow might play, how captured carbon could remain as a planter that ordinary people can take home, and how summer cooling and winter hand warming might be placed within a single passive urban structure. I disclose the device configuration, operating sequence, and alternative forms together, so that anyone can examine and pursue the same concept.
2. The First Turn: Where Does the Captured Carbon Go?
Once the idea of the beads appeared, the next problem followed immediately. If a bead captures carbon on dry days and releases it when it becomes wet, there must be somewhere for the released carbon to go.
Why does carbon not simply disappear? How do companies deal with the carbon they emit? Following these questions made one point clear: handling carbon means moving carbon dioxide dispersed in the air into another state and another location. It can be separated and stored, or it can be reacted with mineral materials so that it remains in a solid form. The IPCC describes mineral carbonation as the process by which calcium- or magnesium-containing materials react with carbon dioxide to form stable carbonates.[1]
The first use that came to mind was rainwater treatment. I thought that if captured carbon could be used to treat rainwater, the carbon collected by the beads would acquire an actual function within the city. In summer, the same water might even help cool overheated surroundings.
Once I decided not to use it as drinking water, a different role for water became visible. Rainwater could wet the beads, draw out the captured carbon, and serve as a transport route carrying that carbon toward a fixing material. On dry days, the beads collect carbon from the air. When rain falls or snow melts, the wet beads release it. The water then carries that carbon toward a material in which it can remain as a solid.
After this turn, one question remained: what would the carbon finally become?
Could carbon captured from the air remain as an object that a person could actually take home?
3. How the Beads Breathe
To determine whether beads that capture carbon when dry and release it when wet could exist as an actual material, I looked for relevant research. There I found moisture-swing direct air capture.
In 2011, Wang, Lackner, and Wright reported that an anion-exchange-resin-based sorbent captured carbon dioxide from ambient air in a dry state and released it when exposed to water, demonstrating the principle of moisture-swing capture.[2] A follow-up study in 2013 analyzed thermodynamically how changes in moisture, rather than heat or vacuum, can drive the capture-and-release cycle.[3] Methods for manufacturing related sorbents and releasing captured carbon through moisture exposure have also been disclosed in a U.S. patent held by Columbia University.[4]
This research shows exactly the operation the beads would need to perform: capture during dry periods, release when water enters, and begin the next capture cycle once they dry again. If the sorbent is arranged as swelling and shrinking beads, or as porous composite granules, the internal movement of carbon can be expressed outwardly as a visible form of breathing. Recent research comparing and modeling water uptake and CO₂ adsorption characteristics of ion-exchange resins for moisture-swing operation also provides foundational data for such bead-based design.[5]
What is needed next is a structure that receives the carbon released by the beads. The beads repeatedly gather carbon and pass it onward; below them must be a place where that carbon remains as a solid.
4. Rain and Snowmelt Carry Carbon into a Planter
The central component is the transfer section that sends the carbon released by the beads into the planter without losing it along the way.
On dry days, natural airflow passes through a ventilated capture layer. The beads capture carbon dioxide from that air. When rain falls, or when accumulated snow melts under sunlight, water enters the bead layer from an upper collection section. The wetted beads release the carbon dioxide they have held. To reduce loss of the released carbon to the open air, a short enclosed or semi-enclosed carbon-transfer section is placed beneath the beads.
This transfer section is configured as a short downward path through which water passes from the bead layer directly through the mineralization layer of a planter cartridge and then drains out below. In winter, stored water can freeze and expand, so drainage matters more than storage. A complete-drainage channel immediately discharges residual water after snowmelt has passed through.
The research closest to this structure is an outdoor pilot disclosed by Flory and colleagues in 2025. The researchers filled elongated mesh-tube packets with commercial anion-exchange resin beads, exposed them to natural airflow, and demonstrated a system in which moisture transfers captured carbon into an alkaline aqueous solution. Their 4.2 m² outdoor pilot was operated to deliver approximately 100 g of CO₂ per day into solution, and elongated tube packets shortened drying and recapture time by approximately fourfold compared with large mesh bags.[6]
This demonstration, published as a 2025 preprint, presents an outdoor route by which carbon captured by beads is delivered into an aqueous medium. The present structure connects that transfer route to rain, snowmelt, gravity drainage, and planter cartridges, forming a passive urban structure.
Its operation is as follows.
Dry day
Natural airflow → moisture-swing bead layer → capture of atmospheric CO₂
Rainy day
Rainwater inflow → wetting of beads and CO₂ release
→ short carbon-transfer channel → passage through planter mineralization layer
→ gravity drainage of residual water
Winter day when snow melts
Snowmelt inflow → wetting of beads and CO₂ release
→ passage through planter mineralization layer → complete drainage of residual internal water
Day of drying again
Beads dry and shrink → recontact with natural airflow → next CO₂ capture cycleWind, rain and snow, gravity, and sunlight provide the motive forces. Natural airflow moves air through the device; rain and snowmelt transport carbon; gravity drains water; and sunlight and wind dry the beads again.
5. Captured Carbon Becomes a Takeaway Object, and That Object Becomes a Planter
Once the direction of rainwater purification had been set aside, only one question remained: what should the captured carbon become in the end?
The first idea that emerged was a takeaway object. I wanted the fact that carbon had been captured not to end as an invisible record, but to remain in a form people could physically take with them. The structure would mold a carbon-fixed final product and make it available to ordinary people.
The planter was the result chosen next.
A key ring or small ornament could also be made. A paperweight or tile would be possible as well. Among these options, a planter most clearly holds the image of carbon returning to everyday life. A person takes it home, fills it with soil, plants a seed or a small plant, waters it, and keeps it nearby for a long time. An act associated with the environment becomes the practical act of taking home an object and growing something in it.
The planter is completed as it receives carbon inside a replaceable cartridge. Within its wall is a thin mineralization layer that accepts carbon. As captured carbon is carried by rain and snowmelt repeatedly through this layer, carbon accumulates in the planter in the form of carbonates.
A completed planter is placed in a distribution section separated from the reaction area. People may freely take it. Inside the device, cartridge reactions continue; on a free shelf or in a lower dispensing bin, only completed products are made available. Carbon capture and seasonal operation occur automatically within the structure, leaving replenishment of semi-finished planter units and safety inspection and placement of finished products as maintenance tasks. In an alternative configuration, verified planters may be moved to an automatic gravity-release outlet or a rotating display section for completed products.
A planter needs a record more than it needs a decorative phrase.
This planter contains CO₂ captured from the air and retained in solid form.
Please take one freely and plant something in it.
If the actual fixed amount can be analyzed, the statement becomes more precise.
This planter contains ○ g of CO₂ fixed from the air.
6. The Planter's Mineralization Layer: Silicates
A candidate material for the planter's mineralization layer is a mineral feedstock based on calcium silicates such as wollastonite, or on magnesium silicates. In the presence of water, wollastonite can react with carbon dioxide to leave calcium carbonate and silica-related products.
CaSiO₃ + CO₂ + H₂O → CaCO₃ + SiO₂·H₂ODi Lorenzo and colleagues analyzed wollastonite carbonation in 2018 as a model reaction for carbon dioxide fixation, confirming the sequence in which wollastonite dissolves and carbonates precipitate.[7] In this process, the dissolution rate of wollastonite and the accumulation of surface products govern the rate of carbonation.
The planter is designed with multiple distributed layers of thin, porous mineralization material through which carbon passes. The basic planter body provides shape and durability, while the carbon-receiving region is formed as a thin reactive layer that can be replaced or analyzed.
The possibility of placing wollastonite in proximity to plants also connects with separate research. Haque and colleagues applied wollastonite to agricultural soil and investigated both CO₂ fixation through mineral weathering and effects on plant growth.[8] A planter intended for distribution and planting would have an inner-wall structure separating the mineralization layer from plant roots, and would move to the distribution section only after checks for dust, pH, leaching characteristics, and durability. The reaction cartridge and the freely distributed planter occupy separate areas within the device.
In 2026, Wu and colleagues reported a process in which an ion-exchange material that had captured atmospheric CO₂ is regenerated with waste brine containing calcium ions, mineralizing the captured carbon as solid calcium carbonate at ambient temperature.[9] This connection—from carbon captured in air to a solid mineral at room temperature—forms a design basis for the planter cartridge.
What this device discloses is the next step: leaving the captured carbon not as powder inside a factory, but inside the body of a planter that people can take away one by one.
7. In Summer, Rainwater Lowers Urban Heat
This device also acts on the human thermal environment through the seasons.
In summer, rain falls. The upper part of the device receives rainwater, and a cooling reservoir separated from the carbon-transfer channel slowly supplies that water to an external porous ceramic surface. Capillary action wets the surface; on hot days, the water evaporates and carries heat away.
There is already outdoor experimental support for this direction. In 2010, He and Hoyano built a passive evaporative cooling wall from highly absorbent porous ceramic material and tested its ability to draw water upward without a pump, reducing both surface temperature and the temperature of air passing through an outdoor space. They considered such a structure applicable to outdoor or semi-outdoor spaces such as parks, pedestrian areas, and residential courtyards.[10]
The important point is to separate the water route used for cooling from the water route used for carbon transfer. The external cooling surface is a section close to human contact, so it performs only the function of evaporating rainwater. The internal carbon-transfer channel performs only the function of sending carbon released by the beads to the planter's mineralization layer and draining it immediately afterward. Keeping these two routes separate reduces the risk that fine particles or salts from the mineralization layer will clog the cooling skin.
In summer, after rain has passed and hot weather returns, the device sends stored water to its surface and cools itself. At the same time, the beads inside dry again and prepare to capture the next round of carbon.
8. In Winter, Snowmelt Carries Carbon and Sunlight Warms Hands
Water must be handled differently in winter than in summer. If water is stored for long periods inside the device, it can freeze and damage channels and outer surfaces. Water entering in winter is therefore passed through and drained immediately. Snow accumulates on top of the device; only when sunlight or daytime temperature melts part of it does the water pass through the bead layer and planter cartridge, after which it is discharged downward without remaining inside.
Throughout dry winter periods, the beads capture carbon from the air. At the moment snow melts, the water wets the beads and causes them to release that carbon. The carbon-bearing water travels through a short transfer channel, reaches the planter's mineralization layer, and exits without pooling within the structure. When conditions dry again, capture begins anew.
Snow becomes a natural input that moves carbon captured during winter into the planter.
Winter hand warming is provided by a black hand-contact surface exposed to sunlight.
In 2025, Jung and colleagues reported in Joule a study that used laser-induced pyrolysis to implement both a radiative-cooling surface and a solar-heating surface in a single PDMS-based material. In their disclosed outdoor test, the white surface remained an average of 5.89°C below ambient air temperature, while the black surface heated to 58.1°C under sunlight.[11] In this device, that heating surface is arranged as a south-facing winter handle, a vertical hand-contact panel, a bench armrest, or a contact ring around the planter exterior.
On a sunny winter day, a passerby can briefly warm their hands on the device's black contact surface. At the same time, on days when snow melts, carbon is transferred internally into the planter.
9. A Planter Anyone Can Take Home
The final stage of this device is its distribution section.
Completed planters are placed beside the device, and anyone may take one, fill it with soil, and plant something in it. Carbon capture is thereby connected directly to personal daily life.
Completed planters can be distributed as follows.
1. Semi-finished planter cartridges undergoing mineralization are installed inside the device. 2. After a defined reaction period, the planters are separated from the reaction section. 3. Where dust, residual pH, durability, and fixed-carbon quantity can be verified, the results are displayed. 4. Completed planters are placed on a free distribution shelf, in a rotating display bin, or in an automatic dispensing bin at the lower part of the structure. 5. Citizens freely take one and plant something in it.
Fixed carbon remains within the planter, and the user receives that object and creates a new place where a plant can grow. An act that helps the environment does not occur only in distant factories or underground storage sites; it continues in a small planter that one person carries home.
10. Disclosed Technical Structure: Device and Method
The following describes the basic configuration and operating method disclosed in this paper. This structure combines a moisture-swing sorbent, natural-airflow contact, passive desorption driven by rain and snowmelt, a carbon-mineralizing planter cartridge, a separated rainwater cooling skin, a solar-absorbing hand-contact surface, and a finished-planter distribution section within a single passive urban structure.
10.1 Basic Configuration
[Upper collection and heat-absorbing section]
- Sloped collection canopy receiving rain and snow
- Black hand-contact surface or handle receiving winter sunlight
- Inlet directing snowmelt only into the internal pathway
[Air-contact capture section]
- Moisture-swing direct air capture bead cartridge
- Beads, mesh tubes, sheets, fiber layers, or porous composite forms
- Captures CO₂ through contact with natural airflow when dry
- Releases CO₂ when wet
[Carbon-transfer section]
- Enclosed or semi-enclosed channel connecting the bead release area to the planter cartridge
- Rain or snowmelt carries the captured carbon
- Short downward pathway suppressing water pooling
- Complete-drainage structure leaving no residual water under subfreezing conditions
[Planter mineralization section]
- Replaceable or movable semi-finished planter cartridge
- Wollastonite, calcium silicate, magnesium silicate, or composite mineralization layer thereof
- Thin multilayer or porous reactive layer
- Separated structure between the plant-contact inner wall and the mineralization layer
[Summer cooling section]
- Rainwater reservoir separated from the carbon-transfer channel
- Porous ceramic, porous mineral panel, capillary fiber, or composite evaporative-cooling skin
- Outer skin wetted by gravity and capillary action without a pump
[Finished-product distribution section]
- Free shelf for completed planters
- Rotating display bin
- Gravity-fed or mechanically actuated passive dispensing bin
- Engraving or QR area indicating fixed CO₂ quantity or device origin10.2 Operating Method
1. Dry capture stage
Natural airflow passes through the capture section.
The moisture-swing beads absorb atmospheric CO₂.
2. Rain or snowmelt release stage
Rainwater or snowmelt passes through the collection section and wets the capture section.
In response to moisture, the beads release CO₂.
3. Carbon-transfer stage
Before it is lost to the exterior, the released CO₂ travels through water
or a wet transfer zone into the planter mineralization layer.
4. Mineralization stage
A silicate-based reactive layer within the semi-finished planter
fixes part of the transferred carbon in carbonate form.
5. Drainage and regeneration stage
Residual water is immediately discharged below the device.
Once the weather dries, the beads dry again and begin the next capture cycle.
6. Summer cooling stage
Separately stored rainwater moves into the porous exterior and evaporates.
It serves to reduce the perceived thermal load in the area surrounding the device.
7. Winter hand-warming stage
A black contact surface exposed to sunlight absorbs solar radiant heat.
It provides a surface on which passersby may briefly warm their hands.
8. Distribution stage
A completed planter containing captured carbon is separated from the reaction area
and placed in a distribution section from which anyone may take it.10.3 Disclosed Variations
Variants of the capture section may include ion-exchange resin beads, composite gel beads, membrane-type sorbents, fibrous capture layers, mesh-tube packed beds, and porous granulates that absorb and release atmospheric CO₂ in response to changes in moisture.
Variants of the carbon-containing final product may include small personal planters, wall-mounted planters, seed-germination pots, street-landscaping planters, landscaping blocks, bench side panels, tiles, paperweights, marker stones, or objects displaying their fixed-carbon quantity. The central end product of this disclosure is a planter that anyone can take home and use for growing a plant.
Variants of moisture input may include dew, condensate, gravity-fed stored water requiring no external power, or structures operated by changes in ambient humidity.
The summer cooling section may be implemented not only as a porous ceramic skin, but also as a porous mineral panel, a capillary fiber panel, an evaporative plate beneath a shade structure, a bench-side cooling panel, or the outer wall of a planter.
The winter hand-warming section may be implemented as a handle, a vertical contact panel, a bench armrest, a contact ring on a planter rim, or a south-facing solar-absorbing panel. This function is intended for localized contact warming during hours of sunlight.
Methods of providing completed products may include placement by an operator on a distribution shelf, movement of cartridges into a completed-product zone by rotation, release of products through a gravity-fed dispensing bin, direct placement in a communal planting area, or a combination of free personal distribution and street planting.
11. The Critical Sections to Be Tested Experimentally
Each principle composing this device has already been demonstrated in separate areas of research.
Research and patents exist for moisture-swing capture, in which carbon dioxide is captured under dry conditions and released under wet conditions. An outdoor pilot has also been disclosed in which granular resin captures carbon in natural airflow and transfers it into water. Silicates are known to fix carbon in carbonate form. Porous ceramic cooling using rainwater and passive heating surfaces using sunlight have likewise been experimentally tested separately.
The first experimental target for this structure is the transfer section connecting the beads to the planter. How much of the carbon released from the beads can rain or snowmelt deliver to the planter's thin mineralization layer without loss? At what rate does a wollastonite-based layer carbonate under outdoor, low-concentration carbon dioxide conditions? How much time and surface area are required to leave a recordable amount of carbon within a single planter?
The next target is four-season durability. Can the summer evaporative-cooling skin remain unclogged while separated from the mineralization section? Can the winter snowmelt pathway discharge water without leaving liquid inside, thereby preventing freeze damage? Will a planter distributed free to the public have sufficient strength and safety for planting?
The reason for disclosing this structure is to enable someone to actually build and test the beads, transfer channel, planter cartridge, cooling skin, and hand-contact surface.
12. The Distance from Carbon in the Air to a Planter
A conversation that began by asking how French fries work eventually arrived at the question of what carbon could be used for.
Carbon is already dispersed throughout the air. Technologies exist to capture it. Technologies also exist to turn it into minerals. There are structures that cool surfaces with rainwater, and surfaces that briefly warm hands using sunlight.
What I propose is to gather those separate elements into a single object.
On dry days, the beads capture carbon dioxide from the air. When it rains, the beads receive water and pass the carbon into a planter. In winter, snowmelt does the same. In summer, the outer skin evaporates stored rainwater and cools one heated point in the city. In winter, the black contact surface briefly warms the hand of a passerby when sunlight is present.
As time passes, planters appear beside the device.
Anyone can take one. Someone may fill it with soil and plant something in it. It may be placed on a balcony, in front of a shop, or on the windowsill of a small room.
Carbon once dispersed in the air is carried in a person's hands. And inside it, a plant grows again.
That is the final scene this device is intended to create.
References
- IPCC. (2005). IPCC Special Report on Carbon Dioxide Capture and Storage: Chapter 7. Mineral Carbonation and Industrial Uses of Carbon Dioxide. Cambridge University Press. In particular, the report defines mineral carbonation as the fixation of CO₂ into inorganic carbonates through reaction with materials containing metal oxides. ↩
- Wang, T., Lackner, K. S., & Wright, A. (2011). Moisture-swing sorbent for carbon dioxide capture from ambient air. Environmental Science & Technology, 45(15), 6670–6675. DOI: 10.1021/es201180v. ↩
- Wang, T., Lackner, K. S., & Wright, A. B. (2013). Moisture-swing sorption for carbon dioxide capture from ambient air: A thermodynamic analysis. Physical Chemistry Chemical Physics, 15, 504–514. DOI: 10.1039/C2CP43124F. ↩
- The Trustees of Columbia University in the City of New York. (2016). Method for producing a moisture swing sorbent for carbon dioxide capture from air. U.S. Patent No. 9,283,510 B2. Publication date: 2016-03-15. ↩
- Lopez-Marques, H., et al. (2026). CO₂ Sorption in Moisture Swing Anion Exchange Resins for Direct Air Capture: Experimental Isotherm Determination and Modeling. Environmental Science & Technology. DOI: 10.1021/acs.est.5c11862. ↩
- Flory, J., Taylor, S., Li, S., et al. (2025). Design and demonstration of a direct air capture system with moisture-driven CO₂ delivery into aqueous medium. arXiv preprint, arXiv:2508.02650. DOI: 10.48550/arXiv.2508.02650. The outdoor pilot findings cited in the text are drawn from a publicly available preprint rather than a peer-reviewed paper. ↩
- Di Lorenzo, F., Ruiz-Agudo, C., Ibañez-Velasco, A., Gil-San Millán, R., Navarro, J. A. R., Ruiz-Agudo, E., & Rodriguez-Navarro, C. (2018). The carbonation of wollastonite: A model reaction to test natural and biomimetic catalysts for enhanced CO₂ sequestration. Minerals, 8(5), 209. DOI: 10.3390/min8050209. ↩
- Haque, F., Santos, R. M., Dutta, A., Thimmanagari, M., & Chiang, Y. W. (2019). Co-benefits of wollastonite weathering in agriculture: CO₂ sequestration and promoted plant growth. ACS Omega, 4(1), 1425–1433. DOI: 10.1021/acsomega.8b02477. ↩
- Wu, X., Chen, H., Liu, H., & SenGupta, A. K. (2026). Direct Air Capture (DAC) and CO₂ Sequestration with Waste Brine Using a Novel Sorbent at Ambient Temperature. Carbon Capture Science & Technology, 100584. DOI: 10.1016/j.ccst.2026.100584. ↩
- He, J., & Hoyano, A. (2010). Experimental study of cooling effects of a passive evaporative cooling wall constructed of porous ceramics with high water soaking-up ability. Building and Environment, 45(2), 461–472. DOI: 10.1016/j.buildenv.2009.07.002. ↩
- Jung, Y., Jeong, S.-M., Heo, G., et al. (2025). Monolithic integration of radiative cooling and solar heating functionalities by laser-induced pyrolysis. Joule, 9(8), 102007. DOI: 10.1016/j.joule.2025.102007. ↩
An Seungwon / Wonbrand / https://wonbrand.co.kr