Direct air capture has an energy problem. The fans that pull air through the system? Those are cheap. The real cost is regeneration — heating or pressurizing the sorbent material to release the captured CO₂ so it can be collected and stored. That step accounts for roughly 70–80% of a DAC system’s energy consumption.
A new research paper offers a genuinely clever workaround: a sorbent made from upcycled wood waste that uses sunlight to release its captured CO₂. No external energy required for regeneration.
How It Works
The sorbent is built from cellulose-based materials derived from wood waste — specifically, it retains the lignin that’s normally stripped out during industrial processing. That lignin is the key innovation.
Lignin is dark-colored and naturally absorbs solar radiation efficiently. When exposed to sunlight, it converts light energy into heat through a process called photothermal heating. The sorbent captures CO₂ from ambient air at normal temperatures, then when you expose it to sunlight, the lignin heats the material enough to release the stored CO₂ — without needing any electricity, natural gas, or steam.
In lab conditions, the material showed a CO₂ capture capacity of roughly 6.5 mmol/g at 25°C, and effective regeneration at photothermal temperatures around 60°C. Those numbers are competitive with commercial amine-based sorbents, but with dramatically lower energy requirements for the release step.
Why This Matters
DAC’s biggest challenge isn’t whether it works — it’s whether it can ever be cheap enough to matter. Current costs range from $400 to $1,000+ per ton of CO₂, depending on the technology and energy source. Most of that cost traces back to the thermal energy needed for sorbent regeneration.
A sorbent that regenerates with sunlight eliminates the largest variable cost in the system. No natural gas boilers. No electrical heating elements. No competing with the grid for clean energy. Just sunlight — which is free, abundant, and getting more accessible every year.
The feedstock economics are equally interesting. Wood waste and lignin are abundant industrial byproducts. Paper mills, sawmills, and timber operations generate millions of tons of lignin-rich residues annually. Turning them into DAC sorbents would upcycle waste into climate infrastructure.
The Reality Check
This is early-stage research, not a commercial product. Lab-demonstrated capture capacity doesn’t automatically translate to field performance. Real-world conditions — humidity, temperature swings, dust, variable sunlight — will test the material in ways a controlled lab environment doesn’t.
Scaling photothermal regeneration also raises design questions. Solar heating works great in Riyadh. Less so in Glasgow in November. DAC systems need to operate year-round, and seasonal sunlight variation would either limit throughput or require hybrid regeneration approaches.
There’s also the durability question. Sorbents degrade over thousands of capture-release cycles. How well a wood-derived material holds up over years of continuous operation in outdoor conditions is unknown.
The Bigger Picture
Even with those caveats, the direction is encouraging. The DAC field is systematically attacking its cost drivers — cheaper sorbents, lower regeneration energy, modular designs, waste-derived materials. No single paper will make DAC competitive with biochar at $100/ton. But each advance that chips away at the energy penalty makes the pathway more plausible at scale.
If you could combine cheap feedstock (wood waste), free regeneration energy (sunlight), and reasonable capture capacity — even if the numbers are 20% worse than the lab suggests — you’d have something that could fundamentally reshape DAC economics for sunny, warm regions.
And there are a lot of sunny, warm regions that could use the jobs.
Source: Research paper via @geoengineering1, referencing work on cellulose-lignin photothermal adsorbents. See also: ScienceDirect