Transformation of glass fiber reinforced epoxy from waste printed circuit boards to adsorbents for effective CO2 storage in abandoned mines

Abstract

Waste printed circuit boards (PCBs) pose environmental challenges due to their toxic and varied composition. Current recycling methods prioritize metal recovery, leaving non-metallic fractions (NMFs) underutilized. These NMFs can be converted into nitrogen-doped porous carbons with good CO₂ adsorption capacity. However, waste PCBs are dominated by the FR-4 type in which fibers comprise a large mass fraction and intrinsically limit carbon yield and accessible porosity. We report a targeted valorization route for FR-4 NMFs that couples one-step KOH/urea activation with post-treatments aimed at the glass-fiber/polymer composite: (i) aqueous ultrasonication to increase the surface area by enhancing surface roughness and fragmenting particles to smaller sizes, and (ii) amine functionalization with polyethylenimine (PEI) to improve CO₂ affinity. Ultrasonication significantly increased BET surface area (from 444 to 928 m² g⁻¹) and CO₂ uptake (from 1.34 to 1.90 mmol g⁻¹), primarily through particle size reduction. PEI functionalization increased isosteric heat of adsorption (indicative of stronger CO₂ affinity) but concurrently caused pore blockage, lowering net adsorption capacity. Quantitative analysis across all samples shows that CO₂ uptake correlates strongly with microporosity and total BET area, weakly with external surface area. We discuss mechanistic roles of cavitation-driven fragmentation and glass-fiber/carbon interplay. Our findings suggest ultrasonication is a promising method for enhancing PCB-derived porous carbons in carbon capture applications, while PEI functionalization needs further optimization to balance affinity and accessibility.