Carbon Nanoassembly-Enhanced Sand-Clay Substrates as a Proof of Concept for Living Building Envelopes

The integration of living vegetation into building envelopes offers demonstrable ther-mal, ecological, and well-being benefits; however, conventional vertical greening sys-tems rely on synthetic, resource-intensive growing media requiring continuous fertiga-tion, limiting their regenerative credentials. This study presents a proof of concept for sustaining plant growth in engineered sand-clay substrates which are low-embodied-energy materials suited to building surface application using carbon nanoassemblies (CNAs) synthesised from citric acid and urea as a growth-sustaining additive. CNAs were characterised by FTIR spectroscopy, dynamic light scattering, zeta potential analysis, and fluorescence spectroscopy, confirming an amphiphilic sur-face chemistry and blue-range photoluminescence at 458 nm consistent with dual nu-tritional and optical plant growth promotion mechanisms. Five sand-to-clay substrate formulations were evaluated in a 25-day greenhouse cultivation trial using Raphanus sativus, with and without a weekly 200 mg/L CNA root drench. Unamended control plants ceased foliar growth upon depletion of endogenous seed reserves, whilst CNA-treated plants sustained continued vegetative growth across all substrate compo-sitions, achieving dry biomass increases of up to 695% relative to controls. These find-ings establish a functional basis for ecologically active soil systems capable of support-ing living building envelopes in both the regenerative retrofitting of existing buildings and the integration of biological components into new building design.