Direct Air Capture of CO2 using Amine-Functionalised Nanofibrous Silica

Edwards, Jake (2024) Direct Air Capture of CO2 using Amine-Functionalised Nanofibrous Silica. Doctoral thesis, University of East Anglia.

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Abstract

Limiting global warming to 1.5°C by 2100 necessitates both decarbonisation of the global economy and also the deployment of carbon dioxide removal technologies like direct air capture (DAC) at scale. Amine-functionalised solid adsorbents are one of the most widely studied family of materials for DAC, however, most are powders, which are impractical for industrial scale application. This thesis focuses on developing scalable amine-functionalised nanofibrous silicas for DAC.

Porous silica nanofibrous supports were prepared via electrospinning of colloidal silica and poly(vinyl alcohol), followed by heat treatment to remove the organic template. The optimal silica-to-polymer weight ratio was 2:1, with a calcination temperature of 700°C, yielding mesoporous nanofibres with a specific surface area of 130 m2/g.

The nanofibres were functionalised with amine groups via hydrous silane grafting. The grafting conditions, such as the amount of silane added and choice of grafting agent, significantly affected the resulting silane loading and grafting efficiency. The nanofibres were characterised at various stages of synthesis using TGA, FTIR, and 13C and 29Si solid-state NMR techniques.

Testing of amine-functionalised nanofibres under simulated DAC conditions revealed that amine loading, temperature, flow rate and humidity impacted the pseudo-equilibrium capacity and uptake kinetics of the amine-modified nanofibres. 13C NMR experiments indicated that the dominant product of adsorption was ammonium carbamate. The Avrami kinetic model best described the CO2 uptake behaviour of functionalised nanofibres. This study introduces a new interpretation of the Avrami exponent to understand mechanistic changes to the uptake process when the adsorption conditions were altered.

When factoring in both adsorption capacity and half-time, triamine-grafted nanofibrous silica (4.7 mmolN/gsample) had comparable performance to other similarly-loaded amine adsorbents from the literature, with an average uptake rate of 0.42 and 0.34 mmol·g-1·h-1 under dry and humid conditions, respectively. The presented findings indicate that amine-functionalised nanofibrous silicas have promising application for DAC.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Engineering, Mathematics and Physics
Depositing User:	Chris White
Date Deposited:	02 Apr 2025 13:30
Last Modified:	02 Apr 2025 13:30
URI:	https://ueaeprints.uea.ac.uk/id/eprint/98923
DOI:

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