<p>The lack of clean water due to water pollution is a significant issue, particularly in developed and low-income nations. This work investigates an economic approach to removing the carcinogenic heavy metal cadmium (Cd) from wastewater using activated carbon derived from coconut biomass (C-AC) and acid-modified coconut biochar (HC-AC). The characterization results demonstrate that both C-AC and HC-AC had porous structures with high surface areas of 572.6 and 664.4 m²&#xa0;g⁻¹, respectively. They also contained oxygen- related functional f groups such as C–O, C=O, O–H, and –COOH, which help enhance the adsorption of Cd²⁺ through complexation and ion exchange. Experimental results indicated that the adsorption performance of Cd²⁺ ions strongly depends on solution pH, with the highest removal efficiency observed at pH 6.0. First-order and second-order kinetic models were applied to investigate the time-dependent and removal rate of Cd²⁺ ions. Moreover, the removal efficiency of Cd²⁺ decreases from 84.9 to 55.3% for C-AC and from 96.7 to 67.5% for HC-AC as the initial concentration increases from 10 to 200&#xa0;mg L⁻¹. After 180&#xa0;min of contact time, HC-AC completely removed Cd²⁺ ions from the wastewater sample, and C-AC also displayed a high removal rate of around 95%. After three reuse cycles, both adsorbents retained effective removal efficiencies for Cd²⁺ ions, with 75.3% for C-AC and 87.8% for HC-AC. Compared with other adsorbents, HC-AC not only exhibits a high adsorption capacity for Cd²⁺ (140.3&#xa0;mg&#xa0;g⁻¹) but also offers several benefits, including low cost, waste-to-resource conversion, and scalability. This work presents an effective approach to converting waste biomass into value-added materials.</p>