Waste hemp-stalk derived nutrient encapsulated aerogels for slow release of fertilizers: A step towards sustainable agriculture

Abstract

With a renewed focus towards circular economy, a novel eco-friendly aerogel was prepared from waste hemp stalk derived cellulose for sustained release of fertilizers. The approach encompasses replenishment the bio-waste back to the soil with addition of fortifying nutrients. Cellulose was converted to carboxymethyl cellulose (HCMC), which was further cross-linked using a green moiety, citric acid (CA) to a yield a three-dimensional aerogel (HCMC-CA-aero). Chemical, physical and thermal properties of the aerogel were evaluated using FTIR, XRD, TEM, EDS, FESEM and TGA. The HCMC-CA-aero was assessed for its swelling behavior, pH response and fertilizer release mechanism, both in water and soil. The aerogel absorbed 80 g/g water after 27 h at neutral pH exhibiting super-absorbent behavior owing to its highly porous structure, large free volume available amid polymeric chains, occurrence of large number of hydrophilic groups and high flexibility. It also exhibited a sustained release of encapsulated nutrients, urea and ammonium dihydrogen phosphate (ADP). The percentage release of nutrients in water after 40 h was 48.4 % and 44.46 % for HCMC-CA-aero@urea and HCMC-CA-aero@ADP, respectively, while in soil it was 62.28 % and 56.62 % after 120 h, unveiling its excellent potential for soil conditioning. The release kinetics for both the fertilizers followed Higuchi model and Fickian diffusion, demonstrating a controlled release of fertilizers governed by dissolution and diffusion. The results indicated that this is an effective approach for agriculture waste management and has great potential in sustained agriculture applications.