Laser-Induced Graphene from Waste Almond Shells

Abstract

Laser-induced graphene (LIG) is a 3D conductive carbon material typically produced from petroleum-based polymers via a one-step laser-induced pyrolysis in air, without chemicals. Recently, the focus has shifted toward bioderived and biodegradable precursors as potentially sustainable alternatives. Here, this approach is advanced by repurposing almond shells–an abundant raw agricultural by-product–blended with chitosan to form almond shell composites (ASC). ASC exhibits over 60% weight loss after 90 days under soil burial. It serves both as a bioderived substrate for electronics and as a precursor for LIG. ASC is converted into LIG through UV and IR laser scribing, and its structure is thoroughly investigated. ASC-LIG achieves sheet resistance values as low as 114.3 ± 0.9 Ω sq−1 (UV), and an electrochemical impedance modulus |Z| ≈ 1 kΩ at 10⁶ Hz (1 cm2 electrodes). It is implemented in proof-of-concept electronic devices, including circuits with resistive and capacitive elements, and humidity sensors, which show sensitivities of 2.25 ± 0.13 pf%RH−1 (30%–55% RH) and 19.8 ± 2.69 pf%RH−1 (55%–80% RH). These results highlight the potential of upcycling agricultural by-products into functional materials, demonstrating the suitability of ASC-LIG for transient electronic applications such as environmental sensors.