Sunlight-activated photocatalysts derived from Pandanus leaf extract: performance limitations and kinetic analysis of ZnO, MgO, and ZnO–MgO nanostructures

Abstract This study successfully produced ZnO, MgO, and ZnO–MgO nanoparticles (NPs) via a green precipitation method using Pandanus amaryllifolius leaf extract as a natural reducing and stabilising agent. XRD analysis revealed hexagonal ZnO, cubic MgO, and a mixed-phase ZnO–MgO, whereas SEM and TEM images showed nanoscale particles with several morphologies. The FTIR spectra confirmed the presence of metal oxygen bonds, including organic functional groups originating from the extract. ZnO exhibited the best optical absorption properties, while MgO and the ZnO–MgO blend showed broader bandgaps. Based on the photocatalytic results from natural sunlight, ZnO had the highest methylene blue degradation efficiency (96.8%), followed by MgO (39.4%) and ZnO–MgO, about 32.5%. All samples followed a pseudo-first order model, with ZnO exhibiting the highest rate constant and the best correlation across all kinetic models. The reduced photocatalytic performance of the ZnO–MgO composite is attributed to phase segregation, wider bandgap, and reduced light absorption. The results demonstrate the limitations of high Mg incorporation in ZnO–MgO systems produced with plant-based extracts and highlight the significant photocatalytic potential of ZnO NPs derived from Pandanus amaryllifolius leaf.