Evaluating nitrogen-doping and elimination effect in peanut shell-derived composites for improving microwave absorption using PMMA as a matrix

Abstract

Humans are surrounded by harmful non-visible electromagnetic (EM) waves. Application and production of microwaves have become integral to technology, but it is essential to mitigate their adverse effects while maintaining accessibility to devices. In this study, engineered nitrogen-doping and etching were employed using urea, ball milling, KOH, and reflux treatments to develop optimized microwave-absorbing and shielding composites. Peanut shells were selected as a sustainable carbon source, and nitrogen-doping was enhanced by urea as a dopant, while nitrogen elimination was conducted using HCl and NaNO₂. Additionally, polymethyl methacrylate (PMMA) was utilized as a polymeric matrix, fabricated via in situ polymerization to create microwave-absorbing composites. The total shielding performance (SE_T = SE_A + SE_R), absorption shielding value (SE_A), and reflection shielding parameter (SER) were evaluated. The pyrolized, KOH-refluxed, and nitrogen-doped PMMA composite achieved a reflection loss (RL) of −81.34 dB at 25.61 GHz, with an efficient bandwidth (EBW) of 8.50 GHz (RL ≤ −20 dB) at a thickness of 0.55 mm. Nitrogen elimination led to a maximum RL of −92.38 dB at 23.32 GHz, covering the entire K-band (RL ≤ −20 dB) with a narrow thickness of 0.60 mm. Both samples camouflaged the K-band (RL ≤ −10 dB) at thicknesses between 0.40 and 0.85 mm. Our innovative nitrogen-doping and defect engineering resulted in exceptional microwave absorption and moderate shielding of EM waves, paving the way for practical applications in affordable and sustainable materials.