Synthesis of Silver Nanoparticles and Composites by Valorization of Spent Coffee Grounds via Artificial Silicification

On a global scale, coffee is the second most traded stock after petroleum. Billions of cups of this refreshing drink are consumed worldwide on a daily basis. As a consequence, enormous amounts of wet spent coffee grounds are discarded in the environment, which constitute a notable ecological problem. This article presents an experimental evaluation of a proposed approach for the synthesis of silver nanoparticles by exploiting the capabilities of low-molecular-weight compounds, which remain in the spent coffee grounds, to reduce Ag+ ions. Moreover, the effectiveness of a method for the valorization of the cited bio-waste has also been assessed. The method mimics a naturally occurring petrification process, which is carried out with the additional simultaneous synthesis of silver nanoparticles. The spent coffee grounds are first treated with ethanol and then delignified with NaOH, Na2SO3 and H2O2. Bleached cellulose is obtained, which is then subjected to biomimetic petrification with the simultaneous synthesis of silver nanoparticles. Tetraethyl orthosilicate and AgNO3 are used for this purpose. The obtained mineralized powder is then used to produce ceramic-based nanocomposites, along with the additional synthesis of nanoparticles. More silver nanoparticles are synthesized from the initially obtained ethanol extract. TEM, SAED, SEM, EDS and DTA/TG are used to analyze the synthesized nanoparticles.