Poster Presentation Royal Australian Chemical Institute National Congress 2026

Metastable photoacids for direct air capture (#228)

Todd M Hartshorn 1 , Deanna M D'Alessandro 1
  1. The University of Sydney, The University Of Sydney, ACT, Australia

Direct Air Capture (DAC) is an emerging approach to atmospheric carbon dioxide removal that addresses two critical challenges: the need for a sustainable, non‑fossil source of carbon, and the durable removal of CO₂ from the atmosphere to mitigate global warming.1 To date, much DAC research has focused on aqueous amine-based systems, however, these approaches are limited by high regeneration energy requirements and the use of volatile and caustic chemicals.2

Our group has previously reported electrochemical DAC strategies, including redox‑active Metal-Organic Frameworks and aqueous systems.3–5 While effective, electrochemical approaches still require significant energy input to drive cycling between reduced and oxidised CO₂‑binding states.

In this presentation, we describe our preliminary investigations into photochemical DAC, which offers a pathway to reduced energy consumption by directly utilising sunlight as the driving force. We have characterised the metastable states of spiropyran‑based photoacids that undergo reversible isomerisation upon photoirradiation, producing controllable and reversible pH changes. This light‑driven pH swing can be coupled with a sorbent molecule that binds and releases CO₂ in a pH‑dependent manner.

To enhance performance, we have functionalised the photoacid with a photosensitiser to improve charge transfer, broaden the absorption wavelength range, and increase quantum yield. Our latest results on reaction mechanisms and kinetics, including insights gained through custom spectroelectrochemical techniques will be presented.6

 

  1. (1) Climate Change 2022 - Mitigation of Climate Change: Technical Summary. In Climate Change 2022 - Mitigation of Climate Change; Intergovernmental Panel On Climate Change (Ipcc), Ed.; Cambridge University Press, 2023; pp 51–148. https://doi.org/10.1017/9781009157926.002.
  2. (2) D’Alessandro, D. M.; Smit, B.; Long, J. R. Carbon Dioxide Capture: Prospects for New Materials. Angew. Chem. Int. Ed. 2010, 49 (35), 6058–6082. https://doi.org/10.1002/anie.201000431.
  3. (3) Wenger, S. R.; Hall, L. A.; D’Alessandro, D. M. Mechanochemical Impregnation of a Redox-Active Guest into a Metal–Organic Framework for Electrochemical Capture of CO2. ACS Sustain. Chem. Eng. 2023, 11 (23), 8442–8449. https://doi.org/10.1021/acssuschemeng.3c00133.
  4. (4) Wenger, S. R.; D’Alessandro, D. M. Improving the Sustainability of Electrochemical Direct Air Capture in a 3D Printed Redox Flow Cell. ACS Sustain. Chem. Eng. 2024, 12 (12), 4789–4794. https://doi.org/10.1021/acssuschemeng.3c07866.
  5. (5) Wenger, S. R.; D’Alessandro, D. M. Aqueous Electrochemical Direct Air Capture Using Alizarin Red S. ChemSusChem 2025, 18 (3), e202401315. https://doi.org/10.1002/cssc.202401315.
  6. (6) D’Alessandro, D. M.; Usov, P. M. Spectroelectrochemistry: A Powerful Tool for Studying Fundamental Properties and Emerging Applications of Solid-State Materials Including Metal–Organic Frameworks. Aust. J. Chem. 2021, 74 (2), 77–93. https://doi.org/10.1071/CH20301.