PM-DAC: Passive Modular Direct Air Capture System

To develop an effective sorbent for CO₂ capture, I sourced, assessed, and combined a range of materials into a multi-stage fabrication process. All chemical selections were based on a thorough review of technical datasheets to ensure safe handling, compatibility, and appropriate laboratory storage.

The core materials included silica, cellulose acetate (CA), polyvinylpyrrolidone (PVP), polyethyleneimine (PEI), carbon fibre threads (CF), and a selection of solvents. Each served a specific role in delivering structural strength, surface area enhancement, and targeted CO₂ reactivity.

Cellulose acetate formed the main matrix, binding silica particles together to create a mechanically stable and porous coating. The silica contributed a high microscopic surface area, improving the likelihood of CO₂ contact. PVP improved adhesion between the coating and the carbon fibre substrate, ensuring mechanical stability during operation.

Polyethyleneimine, rich in amine groups (-NH₂), provided the active CO₂ capture functionality. The chemical adsorption mechanism followed the carbamate formation reaction:

A carefully selected solvent system of acetone, methanol, deionized water, and hexane supported the manufacturing process. Each solvent was chosen for its polarity characteristics, enabling controlled dissolution, impregnation of PEI into silica pores, and efficient removal of unreacted material.

The fabrication process began with drying hygroscopic materials under vacuum to remove any residual humidity. [see image] A polymer–silica slurry was then prepared with controlled viscosity to ensure even coverage when applied to carbon fibres. This application was achieved using a custom-built roll-to-roll system, allowing precise feed control during dip-coating.

To lock the porous structure in place, the coated fibres underwent phase inversion, in which a solvent exchange with a non-solvent triggered polymer solidification. Following this, PEI was introduced into the silica pores to impart chemical CO₂ capture capability. The coated fibres were then rinsed with a non-polar solvent to remove unbound PEI and dried in both ambient and vacuum conditions to complete fabrication.

Custom-built laboratory apparatus was used to characterise the sorbent. Adsorption capacity was measured by tracking changes in mass over time when exposed to controlled CO₂ concentrations. Adsorption rate was determined by monitoring the reduction in CO₂ concentration within a sealed chamber.

The optimal desorption temperature was identified by gradually heating the carbon fibre core under controlled conditions while logging CO₂ release. Cyclic stability was tested through repeated adsorption and regeneration cycles to assess long-term performance.

The final sorbent coating combined mechanical stability, high surface area, and strong adhesion to the carbon fibre substrate. Testing confirmed the intended CO₂ uptake and release profiles, pinpointed optimal regeneration conditions, and demonstrated consistent performance across multiple cycles.