Contamination of water by heavy metals, especially Cu(II), presents considerable environmental and health hazards owing to their toxicity and endurance. This research examines the eco-friendly extraction of divalent copper ions from water using a biochar-based geopolymer produced from rice husks and fly ash. Rice husks were converted into biochar via pyrolysis at 300 °C for 1 hours, while fly ash served as the precursor for geopolymerization using 12 M NaOH as an alkaline activator. Biochar was partially substituted into the geopolymer matrix at ratios of 50–90% to produce adsorbents labeled BCG50–BCG90. The structural, functional, morphological, and textural properties of the materials were assessed using FTIR, SEM-EDS, BET, and atomic absorption spectroscopy. The effects of pH (4–9), contact time (10–60 min), and initial Cu(II) concentration (10–1000 mg/L) were investigated through adsorption experiments. The results indicated that BCG80 possessed the most favorable characteristics, including a high surface area (744.30 m²/g), sufficient hydroxyl groups, and robust silicate structures. The equilibrium was achieved within 10 minutes at pH 6, where the maximal adsorption efficiency was observed. The Langmuir model was followed by Cu(II) adsorption, as indicated by isotherm analysis, with a maximum adsorption capacity (q_max) of 68.97 mg/g (R² = 0.9647). This confirms monolayer adsorption on a comparatively homogeneous surface. The results indicate that the incorporation of rice husk biochar into a fly ash-based geopolymer matrix results in an environmentally benign, sustainable, and effective adsorbent for the removal of copper ions from contaminated water.