Remazol yellow is a synthetic dye that pollutes the environment and causes disease because it is carcinogenic and mutagenic. Photocatalyst is one of the technologies to remove the dye concentration, and tin oxide (SnO₂) with cobalt (Co) dopant has the potential to be a good semiconductor in the process. Therefore, this study aims to synthesize SnO₂/Co composites as a photocatalyst to degrade Remazol yellow dye. The photodegradation process was carried out with several variables, including the effect of time and the initial concentration of the dye and conditions under pHpzc. Furthermore, the composites were made with SnO to Co mass ratios of (2:1), (2:2), (2:3), and were characterized using X-Ray Diffraction (XRD), Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX), and Ultraviolet-Visible Diffuse Reflectance Spectroscopy (UV-Vis DRS) instruments. Based on the results, the SnO2/Co (2:3) composite was selected as a photocatalyst to degrade the dye as the XRD characterization showed the formation of a typical peak of 2θ at 33o. The energy bandgap of SnO₂ is 3.05 eV, while the (2:3) composite had a value of 2.8eV. Moreover, the SEM characterization showed a non-uniform surface with pores and elements composition of Sn, O, and Co with the values 61.24, 24.67, and 14.09 wt%, respectively. The optimum condition for photodegradation was obtained at a contact time and concentration of 180 minutes and 10 ppm, respectively, while the removal of the dye reached 65-80%.

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