Algae constitute a diverse group that is useful in many biotechnological areas. In this paper, the usefulness of Caulerpa sertularioides methanol extract in the synthesis of ZnO and Zn(OH)2 nanoparticles was explored. This work had two main objectives: (1) to use the extract in the synthesis as an organic harmless complexing agent, and (2) to enhance a photocatalytic effect over AZO dyes in wastewater from fabric industries without adding nanomaterial to the environment due to its toxicity. Caulerpa extract performed the expected complexing action, and nanoparticles were formed in a size range from 45 to 69 nm. X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) and UV-Vis spectroscopy were used to characterize the system. It was demonstrated that the nanoparticles were useful to photocatalyst AZO dyes in the water, while contained in tetraethylorthosilicate composites. These could be used in industrial wastewater and are expected to have no environmental consequences because the composites do not add nanoparticles to the water.