This investigation focuses on examining the adsorption behavior of crystal violet dye on cellulose (CS) and its modified forms, including cellulose loaded with nicotinic acid (CSN) and cellulose loaded with thiourea (CST). Batch experiments were performed to analyze the adsorption process, while various characterization techniques, such as Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), were utilized to assess the structural and morphological changes in the cellulose materials. The findings reveal that the adsorption process follows a pseudo-second-order kinetic model, indicating a chemical adsorption mechanism. Additionally, the Langmuir isotherm model suggests monolayer adsorption on cellulose surfaces. Thermodynamic analysis demonstrates that the adsorption process is spontaneous and exothermic for CS and CSN, whereas it is endothermic for CST. The characterization techniques employed provide valuable insights into the structural modifications and porous properties of cellulose materials. Overall, this study underscores the potential of modified cellulose materials to effectively remove dyes in wastewater treatment applications. Notably, thiourea-loaded cellulose CST exhibits superior adsorption capacity with removal percentages of 78.2% compared to CS and CSN, whose removal percentages were 76.45% and 76.72%, respectively, suggesting the promising role of CST in dye removal. These findings contribute to a comprehensive understanding of crystal violet dye adsorption on cellulose and its modified forms, thereby paving the way for future research on the application of modified cellulose materials in wastewater treatment processes.