Rapid biosynthesis of highly active gold nanoparticles for colorimetric detection of p-phenylenediamine and p-nitrophenol reduction in wastewater

Green synthesis of multifunctional nanocatalysts has been a focal point in scientific research. In this work, we investigated the eco-friendly synthesis of gold nanoparticles (AuNPs) using Gracilaria lemaneiformis biomolecule extract (Gbe) and explored their application potential in colorimetric sensing and catalysis. Gbe contains a significant number of oxygen-functional groups with reducing properties, enabling the reduction of Au3+ to Au0, leading to the formation of uniform nanoparticles. Simultaneously, Gbe can establish hydrogen-bond interactions with p-phenylenediamine (p-PD), allowing Gbe-modified AuNPs to detect p-PD using a colorimetric approach (the detection limit was 0.039 μM). Furthermore, quantitative analysis of p-PD can be performed by measuring Red-Green-Blue (RGB) values with a smartphone equipped with the Color Picker app, offering a reliable and straightforward real-time analytical method. Additionally, the synthesized small-sized AuNPs demonstrate superior catalytic activity in the conversion of p-nitrophenol (p-NP) to p-aminophenol (p-AP) (k = 0.6 min−1). Theoretical calculations were conducted to elucidate the reduction mechanism of p-NP. This study highlights the intrinsic potential of algae as a bioresource for synthesizing multifunctional AuNPs in an eco-friendly manner, providing a potentially economical solution for achieving efficient pollutant detection and environmental remediation.