Analysis by response surface methodology of gold nanoparticles obtained by green chemical reduction using aqueous coffee pulp extract (Coffea arabica)

Green synthesis of gold nanoparticles using an aqueous coffee (<i>Coffea arabica</i>) pulp extract as a reducing agent was achieved and analyzed by response surface methodology, given the diverse applicability of these nanoparticles containing a wide range of phenolic compounds from the coffee pulp extract. Three factors (precursor concentration, reducing agent concentration, and reaction time) were considered and their combined effects on the maximum intensity (<i>MA</i>), particle size (<i>d</i>), and particle density (<i>N</i>) were analyzed. An opposing effect between the precursor and reducing agent was observed during synthesis because while the precursor increased <i>d</i> and diminished <i>N</i>, the reducing agent diminished <i>d</i> and increased <i>N</i>. These effects were observed simultaneously through the response surfaces of <i>d</i> and <i>N</i>. This methodology allowed the synthesis of nanoparticles with an average particle size between 5–22 nm and <i>N</i> around 2.9x10¹¹−3.7x10¹³ (part/mL), depending on the response surface methodology, Box-Behnken design. The R² value determined for all cases was 0.98 (<i>MA</i>), 0.99 (<i>d</i>), and 0.97 (<i>N</i>), clearly indicating that the model can be used to predict or design the response variables in the design space. Finally, Fourier transform infrared measurements showed that the organic compounds present in the aqueous coffee pulp extract were coating the surface of the gold nanoparticles. The proposed methodology could contribute to the design of new alternatives for the synthesis of specific nanostructures with potential applications in the therapeutic area.