This paper evaluates the use of acorn-synthesized hydrochar as an adsorptive agent to adsorb the cationic dye of malachite green in aqueous media. In addition to being cost-effective, the synthesized adsorbent can be regenerated and recovered, it is environmentally friendly, and it also has high efficiency and adsorption compared to similar compounds. Different analyzes were investigated to determine the specific surface area, C/O ratio, structure, and characterization of the synthesized adsorbent. Adsorption of malachite green dye using hydrochar in different dye concentrations (5–50 mg/L), solution pH (5–9), reaction temperature (25–40 °C), adsorbent dose (0.25–2 g/L), and the contact time (5–240 min) was investigated. The highest MG removal rate was 98.12% under optimal operating conditions. Langmuir, Freundlich, and Temkin isotherm models were used to investigate the adsorption data. The Freundlich isotherm had the best agreement with equilibrium data. The adsorption capacity of hydrochar toward MG was maximized to 39.84 mg/g. Pseudo-first-order and pseudo-second-order kinetic models were employed to assess experimental kinetic data. The kinetic analysis revealed that the adsorption data agreed more with the pseudo-second-order kinetic model. The analysis of thermodynamic variables, i.e., ΔH°, ΔS°, and ΔG°, suggested a spontaneous, endothermic adsorption mechanism for MG.
