Weekly Publication Highlights
This week: a materials breakthrough for direct air capture sorbents, a mesocosm study mapping which minerals work for ocean alkalinity enhancement, a membrane fix for water loss in liquid-based DAC, and a global comparative analysis of how soil properties shape the agronomic payoff of rock dust.
1. In Situ Azetidine Polymerization Elevates the Performance of Commercial Polymer Resin Sorbents in Carbon Dioxide Capture
Authors: Arkaprabha Giri, UnJin Ryu, Jiaqi Zhang, Opeyemi Ojelade, Wenyang Zhao, Jacob Hoffman, Mark Robertson, Jordi Espín, Madison Nichols, Surya Parker, Omid Ghaffari Nik, Christopher W. Jones
Introduction
Direct air capture (DAC) needs to scale from today’s thousands of tons of CO₂ removed per year to roughly 10 billion tons annually by 2050 if the world is to stay below 2°C, and to around 20 billion tons by 2100. Most of the commercial amine-functionalized sorbents used in solid DAC systems today, however, were never purpose-built for that job; they’re adapted from existing industrial resins. This study comes from Christopher W. Jones’s group at Georgia Tech’s School of Chemical and Biomolecular Engineering, working with Omid Ghaffari Nik, VP of materials science and process at CarbonCapture Inc., bringing an industry partner’s deployment perspective directly into the materials design process.
Main analysis
The team took Lewatit VP OC 1065, a commercial amine resin already considered a benchmark sorbent for DAC, and modified it by growing branched poly(propyleneimine) (bPPI) chains directly from the resin’s existing amine sites. The process is straightforward: soak the resin in azetidine with a small amount of acid, then heat for two days. This in situ polymerization step densifies the amine content on the resin without requiring a new base material. Tested against the unmodified resin, the branched version captured roughly 75% more CO₂ from dry air (~400 ppm, i.e., ambient conditions) and more than 50% more from simulated industrial flue gas. The modified resin also held its advantage across a range of humidity levels and temperatures from 25°C down to -20°C — though that edge disappeared in very cold, dry air. On durability, the branching roughly halved oxidative degradation and held up markedly better than the untreated resin over 150 simulated capture-and-release cycles on industrial exhaust. Critically, the same grafting method worked on a second, different commercial resin (Purolite A110), suggesting the approach generalizes rather than being a one-material trick.
Key insights
- Practical innovation: rather than inventing an exotic new sorbent from scratch, the team upgraded an already-commercial, already-scaled material, which could shorten the path from lab result to deployed DAC hardware.
- The combination of higher capacity and roughly halved oxidative degradation addresses two of DAC’s most persistent cost drivers at once: capture efficiency and sorbent replacement frequency.
- Working across two different base resins is a meaningful signal of generalizability, though it’s still unclear how the benefit holds up at full industrial scale and over longer-than-150-cycle lifetimes.
- The team has filed a provisional patent and plans to extend the grafting technique to other amine-based sorbent materials and scale it toward industrial quantities.
Takeaways
- Grew branched poly(propyleneimine) (bPPI) directly onto a commercial DAC resin (Lewatit VP OC 1065) via a simple two-day azetidine-grafting process.
- Captured ~75% more CO₂ from dry ambient air and >50% more from simulated flue gas versus the unmodified resin.
- Oxidative degradation roughly halved; performance held up better over 150 capture/release cycles.
- Advantage held across most humidity and temperature conditions (25°C to -20°C), except very cold, dry air.
- Method also worked on a second commercial resin (Purolite A110), suggesting broader applicability.
- Provisional patent filed; next steps are extending to other amine sorbents and scaling up.
Read the full paper here: In Situ Azetidine Polymerization Elevates the Performance of Commercial Polymer Resin Sorbents in Carbon Dioxide Capture
2. Biogeochemical and Carbonate Chemistry Response to Natural and Anthropogenic Mineral-Based Ocean Alkalinity Enhancement
Authors: Shreya Mehta, Jitender Kumar, Sipai Nazirahmed, Himanshu Saxena, Jyotiranjan S. Ray, Sanjeev Kumar, Indrani Karunasagar, Arvind Singh
Introduction
Ocean alkalinity enhancement (OAE) is being explored as a scalable marine CDR pathway, but not all alkaline feedstocks behave the same way once added to real seawater. Some dissolve too slowly to matter on practical timescales, while others risk triggering secondary carbonate precipitation that can claw back the alkalinity gain (and the CO₂ storage benefit) the addition was meant to create. This study comes from a team centered at the Physical Research Laboratory (PRL) in Ahmedabad, India, working with Jyotiranjan Ray and Arvind Singh, alongside collaborators at IIT Gandhinagar and NITTE University in Mangalore, bringing the OAE mineral-screening question to a region, the southeastern Arabian Sea, that has had little direct experimental attention to date.
Main analysis
The team ran a controlled mesocosm experiment using coastal seawater collected near Mangalore, India, filling nine 300-liter tanks and tracking them for nine days. They tested three natural minerals (olivine, kaolinite, dolomite) and two industrial materials (periclase and two hydrated lime formulations), at two target alkalinity-addition levels, while monitoring total alkalinity, pH, dissolved inorganic carbon (DIC), and the carbon isotope signature of that DIC. The results split sharply by feedstock type: the natural minerals produced no meaningful change in alkalinity, pH, or DIC over the nine-day window, pointing to very limited dissolution rates under these conditions. The industrial materials, by contrast, acted fast and strong: periclase and hydrated lime raised total alkalinity by as much as roughly 16% (about 80% of the alkalinity physically added) and raised pH by up to 0.6 units within hours, with carbonate saturation states rising sharply before gradually settling over the following days. Using the DIC concentration together with its isotopic signature, the authors were able to flag where secondary carbonate precipitation would start eating into the alkalinity gain, and found no evidence of that happening at alkalinity additions up to roughly 500 µmol/kg in this system, letting them propose that level as a provisional safe operating threshold for the region.
Key insights
- The finding that natural silicate/clay minerals (olivine, kaolinite, dolomite) showed essentially no detectable effect over nine days is an important caution against assuming all “enhanced weathering” feedstocks behave similarly; dissolution kinetics matter enormously.
- The use of DIC and its carbon isotope signature as a joint indicator for secondary precipitation risk is a useful, transferable monitoring approach for other OAE field trials trying to verify that alkalinity additions are being retained rather than reprecipitated.
- As with any mesocosm study, the nine-day timescale and 300 L volume are useful for screening but don’t by themselves establish how these dynamics play out at open-ocean scale or over longer exposure.
Takeaways
- Tested three natural minerals (olivine, kaolinite, dolomite) and two industrial materials (periclase, hydrated lime) in 300 L coastal seawater mesocosms off Mangalore, India.
- Natural minerals showed no significant change in alkalinity, pH, or DIC over nine days: limited short-term dissolution.
- Periclase and hydrated lime raised alkalinity by up to ~16% (~80% efficiency relative to material added) and pH by up to 0.6 units.
- DIC concentration plus its carbon isotope (δ¹³C) signature served as a useful indicator of secondary carbonate precipitation risk.
- No secondary precipitation detected at alkalinity additions up to ~500 µmol/kg, proposed as a provisional safe threshold for this region.
Read the full paper here: Biogeochemical and Carbonate Chemistry Response to Natural and Anthropogenic Mineral-Based Ocean Alkalinity Enhancement
3. Mitigating Water Evaporation in Aqueous Liquid-Based Direct Air Capture Using Supported Ionic Liquid Membranes
Authors: Nobuhide Yasuda, Toshiyuki Nonaka, Kota Yoshida, Hajime Ohno, Yasuhiro Fukushima, Koki Yagihara
Introduction
Liquid-absorbent DAC systems — typically using aqueous potassium hydroxide (KOH) to chemically bind atmospheric CO₂ — are energy-efficient and technologically mature compared to many alternatives, but they have a persistent operational weakness: continuous contact with a huge volume of ambient air causes significant water evaporation from the absorbent, concentrating the solution and forcing frequent, costly make-up water additions. This study comes from a team at Tohoku University’s Department of Frontier Sciences for Advanced Environment, who propose placing a membrane barrier between the air stream and the KOH absorbent to control water loss without blocking CO₂ transport.
Main analysis
The team built supported ionic liquid membranes (SILMs) by impregnating a porous PTFE filter support with one of three ionic liquids (ILs) spanning a range of water affinities: two hydrophobic phosphonium-based ILs ([ThtdP][DCA] and [ThtdP][NTf₂]) and one hydrophilic imidazolium-based IL ([Emim][Gly]). These were tested in a semi-batch membrane contactor against a 1 M aqueous KOH absorbent, compared to a bare (“blank”) membrane with no IL. In a 7-day ambient-air exposure test, the most hydrophobic membrane, [ThtdP][NTf₂], cut the absorbent’s net weight loss to about 10% (13.4 g lost) versus roughly 40% for both the hydrophilic [Emim][Gly] membrane (49.8 g) and the blank membrane (51.7 g), effectively suppressing water evaporation to about a quarter of the uncontrolled rate. In short, 2-hour CO₂ absorption tests using real ambient air (120 L/min inflow, 426–591 ppm CO₂), all SILMs showed roughly 10–15% lower CO₂ recovery and permeance than the blank membrane, reflecting the added mass-transfer resistance of the IL layer, but critically, relative humidity had little to no effect on CO₂ recovery for any of the SILMs, and the specific IL type used didn’t significantly change CO₂ transport performance either. After a further 7-day thermal exposure at 40°C, the hydrophobic SILMs retained their IL loading and CO₂ absorption performance essentially unchanged, while the hydrophilic [Emim][Gly] membrane showed a larger performance drop.
Key insights
- Directly tackles an under-addressed practical bottleneck in liquid DAC: water management, which drives both operating cost and, in arid or hot regions, outright water availability constraints.
- The core trade-off is quantified cleanly: accepting roughly a 10% CO₂ recovery penalty buys roughly a 75% reduction in water loss, the authors estimate this cuts water loss per ton of CO₂ captured to about 30% of the uncontrolled case, a favorable trade for water-stressed deployment sites.
- The robustness of CO₂ recovery to relative humidity when using SILMs is a notable operational benefit, since it suggests more consistent performance across variable climate conditions than an unprotected absorbent.
- Honest about scale-up limitations: the authors note that this is laboratory-scale work, and that IL cost, long-term IL retention/leaching, membrane durability, and module design (e.g., hollow-fiber contactors) all remain open questions before practical deployment.
Takeaways
- Tested supported ionic liquid membranes (SILMs) as a water-vapor barrier between ambient air and KOH absorbent in liquid-based DAC.
- The hydrophobic [ThtdP][NTf₂] membrane cut 7-day water loss to ~10% of the absorbent’s weight, versus ~40% for a blank membrane or hydrophilic IL membrane — roughly a 75% reduction in evaporation.
- SILMs reduced CO₂ recovery and permeance by roughly 10–15% compared to a blank membrane, due to added mass-transfer resistance.
- Relative humidity had little effect on CO₂ recovery when SILMs were used, improving operational consistency.
- Hydrophobic SILMs retained CO₂ absorption performance after a further 7-day exposure at 40°C; the hydrophilic IL membrane degraded more.
- A patent application related to this membrane-based DAC approach has been filed with the Japan Patent Office.
Read the full paper here: Mitigating Water Evaporation in Aqueous Liquid-Based Direct Air Capture Using Supported Ionic Liquid Membranes
4. The Influence of Soil Properties on the Agronomic Efficacy of Rock Dust: A Comparative Analysis of a Semiarid Ultisol and Global Soil Types
Authors: Dennis O. Galdino, William De Paiva
Introduction
Enhanced rock weathering (ERW) — spreading finely ground silicate rock dust on agricultural land — is a dual-purpose strategy: it can remineralize depleted soils with essential nutrients while removing atmospheric CO₂ as the rock dissolves. But the technique’s agronomic payoff varies widely between studies, and much of that variation may come down to the receiving soil itself rather than the rock material. This study comes from Dennis O. Galdino (Instituto Federal de Educação Ciência e Tecnologia da Paraíba) and William De Paiva (Universidade Estadual da Paraíba) in Brazil, building on the authors’ own prior work modeling nutrient-release kinetics from silicate remineralizers applied to a semiarid Ultisol.
Main analysis
The authors compiled a comparative dataset: soil properties and crop-yield responses from 19 recent (2020–2025) global ERW studies, spanning Brazil, the US, the UK, Belgium, and Morocco, and soil orders including Oxisols, Mollisols, Alfisols, Entisols, and Aridisols, combined with their own prior experimental data on a semiarid Ultisol, for 20 total observations. Using ANOVA, Pearson correlation, and principal component analysis (PCA), they found that cation exchange capacity (CEC) varied enormously across soil orders (F = 104.6, p < 0.0001), with Oxisols characterized by low pH (4.95), low CEC (8.81 cmol꜀/kg) but high clay content (61.9%), while the study’s own Ultisol had a notably higher CEC (15.2 cmol꜀/kg, 72.5% higher than Oxisols, p < 0.001) and moderate clay content (35%). Clay content was significantly, positively correlated with crop yield increase (r = 0.510, p = 0.0304), suggesting finer-textured soils retain and supply rock-dust-released nutrients more effectively. The most striking result: despite the Ultisol’s much higher CEC, Oxisols showed a substantially larger average yield increase (83.2% vs. 0% for the Ultisol in its early experimental stage), though this difference wasn’t statistically significant due to high variance in the Oxisol data. PCA explained 85.9% of total variance, with a “fertility gradient” component (driven by CEC and pH) separating the low-fertility Oxisols from more fertile temperate soils, and positioned the Ultisol in an intermediate zone.
Key insights
- Proposes a “fertility threshold” explanation for the counterintuitive Oxisol result: the most heavily weathered, nutrient-depleted soils may respond most dramatically to rock dust precisely because they have so little native fertility to begin with — meaning high CEC alone doesn’t guarantee agronomic benefit.
- Reframes ERW effectiveness as fundamentally soil-dependent rather than purely a function of rock type or application rate, arguing against one-size-fits-all deployment recommendations.
- A meaningful methodological limitation: this is a meta-analytic synthesis of other studies’ data (plus the authors’ own prior experiment) rather than a new controlled field trial, so differences in original study design, duration, and measurement protocols across the 19 source studies add noise the statistics can’t fully account for.
- Positions the semiarid Ultisol as a useful “intermediate case” model for the large global footprint of moderately weathered soils, which have received less ERW research attention than heavily studied Oxisols.
Takeaways
- Compiled soil-property and crop-yield data from 19 global ERW studies (2020–2025) plus the authors’ own Ultisol experiment, covering six soil orders across five countries.
- CEC varied most dramatically across soil orders (F = 104.6, p < 0.0001); Oxisols: low pH/CEC but high clay; the study’s Ultisol: higher CEC, moderate clay.
- Clay content was significantly positively correlated with crop yield increase from rock dust (r = 0.510, p = 0.0304).
- Oxisols showed much larger average yield gains (83.2%) than the higher-CEC Ultisol (0% at early stage), despite the Ultisol’s significantly higher CEC — pointing to a “fertility threshold” effect in depleted soils.
- PCA (85.9% variance explained) mapped a fertility gradient placing the Ultisol between highly weathered Oxisols and more fertile temperate soils.
- Authors call for site-specific ERW recommendations based on soil texture, pH, and initial fertility rather than a universal application approach.
Read the full paper here: The Influence of Soil Properties on the Agronomic Efficacy of Rock Dust: A Comparative Analysis of a Semiarid Ultisol and Global Soil Types
As always, feel free to add comments below with your own takes on these papers, or flag anything you’d like to see covered in next week’s highlights.