Synthesis of eco-friendly ZnO-based heterophotocatalysts with enhanced properties under visible light

Heterogeneous photocatalysts have been widely used for the removal of various organic pollutants from wastewater. The main challenge so far resides in the sustainability of the process, with regard to the synthesis and the application under visible light. In this study the precipitated materials from the moringa oleifera seed (MO), groundnut shells (GS) and apatite (A) agrowastes were functionalized with zinc oxide (ZnO) and silver (Ag) solution, to produce novel bioheterophotocatalysts. Various analytical techniques such as scanning electron microscope (SEM), energy-dispersive x-ray spectroscopy (EDS), photoluminescence (PL) and x-ray diffraction (XRD) analyses were used for the characterization of the novel photocatalysts. It was proven that, besides the addition of metals into a semiconductor, agrowastes were also proven to be even better to enhance the photocatalytic activity of a ZnO-based photocatalyst. The combination of MO/GS/A/ZnO/Ag in a 1:1:1 ratio, resulted in a lower band gap of 1.59 eV, as compared to the larger band gap of 2.96 eV for ZnO/ Ag. These photocatalysts' efficiency was also tested on the photodegradation of PAHs derived from coal leaching in various water sources such as acidic mine drainage, alkaline mine drainage and sewage wastewater. From MO/GS/A/ZnO/Ag, the removal efficiency was obtained to be 69.59%, 62.19% and 61.68% while 52.62%, 37.96 and 44.30% using ZnO/Ag in acidic mine drainage, alkaline mine drainage and sewage wastewater in 60 min under solar irradiation. Which happens to highly influence the destabilization of PAHs in the water sources.