Kinetic and thermodynamic investigation of removing some pollutants from water by hydrochar and activated carbon produced from the kızılbacak (sirken) plant (chenopodium botrys)

In this study, the adsorption performances of activated carbons obtained directly (CB-AK) and after hydrothermal carbonization (CB-HK-AK) from the Chenopodium botrys plant were investigated for the removal of heavy metal ions (Cu(II)) and organic dye (methylene blue). Activation parameters (activating agent type, ratio, temperature, and duration) for activated carbon production were optimized based on iodine adsorption capacity. The synthesized adsorbents were characterized using FT-IR, SEM-EDX, TGA-DTG, and BET analyses. Characterization results revealed that the CB-HK-AK adsorbent had a higher surface functionality, while the CB-AK adsorbent exhibited a larger surface area. Adsorption experiments were conducted by examining the effects of various parameters such as adsorbent dosage, contact time, solution pH, and initial concentration. Moreover, adsorption kinetics, isotherms, and thermodynamic parameters were systematically evaluated. Kinetic studies indicated that the adsorption processes generally followed the pseudo-second-order kinetic model, suggesting that chemical adsorption mechanisms were predominant. Isotherm analyses showed that the Freundlich model fitted better at lower temperatures, while the Langmuir model provided a better fit at higher temperatures. Thermodynamic studies confirmed that the adsorption processes were exothermic and spontaneous in nature. Overall, the CB-HK-AK adsorbent demonstrated superior adsorption capacity and efficiency compared to CB-AK for the removal of both Cu(II) ions and methylene blue. The findings of this study suggest that the Chenopodium botrys plant can serve as a low-cost, eco-friendly, and sustainable source for adsorbent production.