Zahra Solati

Background: This study focuses on the synthesis of zinc oxide nanoparticles using the red algae Gracilaria extract and the hydrothermal method. In this process, the algae extract is converted into a colloidal mixture of carbon quantum dots and hydrochar, which can form a carbon coating on the nanoparticles. Due to their carbon coating and photocatalytic properties, these nanoparticles exhibit high activity under sunlight and can be useful in environmental applications and renewable energy technologies... Aim: The aim of this study is to use hydrothermal conditions to synthesize ZnO nanoparticles with a carbon coating and to investigate their photocatalytic activity under sunlight exposure. In this study, the extract of *Gracilaria* algae is used as a carbon source for the production of carbonized materials via a hydrothermal method. Four different methods are applied to synthesize ZnO nanoparticles from this carbonized colloidal mixture, and after characterization with various techniques, their photocatalytic activity is comparedMethodology: write a paragraph describing the research methodology, including population, sampling and the size, techniques and methods being used. Conclusions: The results of the study showed that *Gracilaria* algae extract is a good source for synthesizing a carbonized colloidal mixture, and by utilizing this colloidal mixture, nanoparticles with strong photocatalytic activity were synthesized. The prepared zinc oxide nanoparticles demonstrated a high potential for adsorbing dye.