Sustainable Liquid-Phase Production of Cellulose-Derived Graphene for Printable Agricultural Monitoring Devices

Highly conductive graphene is becoming an integral device component for printed electronics toward applications such as smart agricultural monitoring. However, top-down approaches for scalable manufacturing of graphene traditionally use non-sustainable source materials (e.g., n-methyl-2-pyrrolidone, mined graphite, and surfactants) that utilize critical resources or cause long-term environmental harm. In this work, cellulosic source materials were employed in liquid phase exfoliation (LPE) to manufacture highly conductive graphene nanoplatelets. Specifically, hardwood-derived biochar was harvested as a co-product from biodiesel production and pyrolyzed with iron powder to create a highly crystalline and renewable source of bulk graphitic material. Functionalized cellulose nanocrystals (CNCs) derived from the perennial grass species Miscanthus X. Giganteus (MxG) were employed in place of incumbent polymers or surfactants to exfoliate the cellulosic graphite in an eco-friendly aqueous system. Exfoliated graphene nanoplatelets were then formulated into an aerosol jet printing ink with cellulose-based ink additives to create fully biodegradable device components.

Humidity sensors are fabricated onto coated paper substrates (derived from miscanthus and hemp agricultural residues) as a demonstration of a fully plant-based device. The printed graphene-CNC composite enables a resistance-based humidity detection mechanism, where the swelling of the CNCs upon water absorption decreases the electronic percolation through the graphene network. The printed humidity sensors show excellent cyclability and sensitivity, with relative resistance change of 2.6 over a humidity range of 35 – 85% RH. By utilizing biomass for all sourced materials, the sensor fabrication is sustainable, cost-effective, and easily processable while minimizing supply chain risks. As such, this eco-manufacturing scheme will tackle environmental challenges ranging from material sourcing to the end-of-life behavior of printable electronics. Continued development of cellulosic materials for LPE and downstream Internet of Things device applications can thus create new avenues for biomass to revolutionize the fabrication of printable electronics.