Novel experimental and theoretical study on the synthesis and use of microalgae-derived silver nanomaterials for water purification

A green procedure involving metabolites of the microalga Haematococcus pluvialis is proposed to synthesize silver nanoparticles (Ag NPs) capable of removing the polluting dye brilliant blue R (BBR) from water. The X-ray diffraction (XRD) analysis revealed the crystalline nature of the product with Ag 2 O and Ag phases with a crystallite size of 14.27 nm. Fourier Transform Infrared Spectroscopy (FTIR) showed abundant functional groups from the extract on Ag NPs. Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) and Thermogravimetric (TGA) analyses further corroborated the involvement of microalgal metabolites from the extract. Experiments were performed to assess BBR removal under different conditions, including varying light intensities, concentration of Ag NPs and BBR, and pH levels. Removal efficiency close to 70 % was achieved under visible light and using specific operating conditions. A novel mathematical model considering both BBR adsorption on the Ag NPs surface and its photocatalytic reaction dynamics was also developed. Simulation results were successfully compared with experimental data, thus demonstrating the reliability of the proposed model. Model results also suggest that, under the investigated conditions, the main mechanism underlying the BBR removal is adsorption rather than photocatalysis. Based on the model and experimental data, it was found that enhancing photocatalytic degradation would likely require more energetic light, prompting further research into optimizing light sources for better efficiency and sustainability. • Ag NPs were synthesized using Haematococcus pluvialis extract for the first time. • Ag NPs were then successfully used for BBR removal from water solutions. • The effects of several operating conditions on BBR removal were investigated. • A mathematical model is proposed to describe BBR adsorption and photodegradation. • The model can accurately explain the experimental BBR degradation dynamics.