Industrial wastewater containing dyes like Congo red poses serious environmental and health risks due to its high toxicity, resistance to conventional treatments, and stability under environmental conditions. Adsorption has emerged as a promising alternative for dye removal due to its simplicity, cost-effectiveness, and sustainability. In this study, hydrochar (HC) and nano-hydrochar (nano-HC) were synthesized from Areca catechu (betel nut husk) and evaluated for their ability to adsorb Congo red. High-energy milling was applied to reduce the hydrochar to nanoscale, significantly enhancing its surface area, active site availability, and adsorption efficiency. Nano-HC demonstrated a maximum adsorption capacity of 596.617 mg/g, surpassing HC (356.132 mg/g) and raw Areca husk (128.654 mg/g). The adsorption process followed pseudo-second-order kinetics and Langmuir isotherm models, indicating chemisorption and monolayer adsorption behavior. The findings highlight the potential of Areca catechu-derived nano-HC as an eco-friendly, cost-effective adsorbent for dye-contaminated wastewater treatment. This study emphasizes the importance of sustainable biomass utilization and advances in particle engineering for environmental remediation.