Water pollution requires sustainable materials to develop green treatment solutions. Nanocellulose with outstanding properties is a sustainable building block of adsorbent for wastewater treatment. However, nanocellulose extraction from plants remains an energy and chemical-intensive process. This study aims to produce nanocellulose from microalgae via facile extraction for the synthesis of hydrogel adsorbents. Without TEMPO-mediated oxidation, nanocellulose was successfully extracted from Chlorella vulgaris through alkaline treatment, bleaching, and hydrolysis only in a high-speed blender in this study. The effects of acid concentration on nanocellulose properties were studied. The maximum yield (58.5%) was achieved using sulphuric acid with a concentration of 60%(v/v). Scanning electron microscopy and transmission electron microscopy images showed the fibrillated structure at the nanoscale. Fourier-transform infrared spectroscopy results confirmed the elimination of lignin and hemicellulose through alkaline treatment, while X-ray diffraction patterns proved that microalgae nanocellulose were typical cellulose I. The microalgae nanocellulose was further incorporated into carboxymethyl cellulose/sodium alginate beads. Methylene blue adsorption capacity raised from 28.46 mg/g to 109.03 mg/g. Dye removal percentage as high as 93.7% could be achieved due to the hydrogen bonding and electrostatic interaction with carboxylate groups.