Dual‑purpose 3D printed monoliths for NO3 absorption and desorption from spent coffee ground/biobased polyurethane blends

Nitrate is one of the most damaging pollutants derived from agricultural use as it easily leaches into fresh water. The result is eutrophication and damage to the ecosystem. Despite this, it is of fundamental importance to maintain both the current and future global population. Many avenues have been explored to mitigate this problem, whereby bioabsorbents and slow-release fertilisers are the most favoured and widely studied solutions. In this paper, we explore the use of spent coffee grounds (SCGs) blended with biobased thermoplastic polyurethane (TPU) as a potential absorbent and platform for controlled release of fertiliser. SCGs are blended with TPU up to concentrations of 50 wt% and are 3D printed using the FDM process. Each composition has been evaluated based on their thermal, mechanical, morphological and NO3 absorption characteristics. Printed samples containing SCGs were able to absorb up to 51, 41 and 34% of NO3 at 5, 15 and 25 mg/L, respectively, in water, before releasing after a period of eight hours in a controlled manner, acting as a dual-purpose hybrid sustainable platform capable of absorption/controlled release of fertiliser.